Artykuły w czasopismach na temat „Nucleolus”
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Ukil, Leena, Colin P. De Souza, Hui-Lin Liu i Stephen A. Osmani. "Nucleolar Separation from Chromosomes during Aspergillus nidulans Mitosis Can Occur Without Spindle Forces". Molecular Biology of the Cell 20, nr 8 (15.04.2009): 2132–45. http://dx.doi.org/10.1091/mbc.e08-10-1046.
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How the nucleolus is segregated during mitosis is poorly understood and occurs by very different mechanisms during closed and open mitosis. Here we report a new mechanism of nucleolar segregation involving removal of the nucleolar-organizing regions (NORs) from nucleoli during Aspergillus nidulans mitosis. This involves a double nuclear envelope (NE) restriction which generates three NE-associated structures, two daughter nuclei (containing the NORs), and the nucleolus. Therefore, a remnant nucleolar structure can exist in the cytoplasm without NORs. In G1, this parental cytoplasmic nucleolus undergoes sequential disassembly releasing nucleolar proteins to the cytoplasm as nucleoli concomitantly reform in daughter nuclei. By depolymerizing microtubules and mutating spindle assembly checkpoint function, we demonstrate that a cycle of nucleolar “segregation” can occur without a spindle in a process termed spindle-independent mitosis (SIM). During SIM physical separation of the NOR from the nucleolus occurs, and NE modifications promote expulsion of the nucleolus to the cytoplasm. Subsequently, the cytoplasmic nucleolus is disassembled and rebuilt at a new site around the nuclear NOR. The data demonstrate the existence of a mitotic machinery for nucleolar segregation that is normally integrated with mitotic spindle formation but that can function without it.
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Chen, Hongying, Torsten Wurm, Paul Britton, Gavin Brooks i Julian A. Hiscox. "Interaction of the Coronavirus Nucleoprotein with Nucleolar Antigens and the Host Cell". Journal of Virology 76, nr 10 (15.05.2002): 5233–50. http://dx.doi.org/10.1128/jvi.76.10.5233-5250.2002.
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ABSTRACT Coronavirus nucleoproteins (N proteins) localize to the cytoplasm and the nucleolus, a subnuclear structure, in both virus-infected primary cells and in cells transfected with plasmids that express N protein. The nucleolus is the site of ribosome biogenesis and sequesters cell cycle regulatory complexes. Two of the major components of the nucleolus are fibrillarin and nucleolin. These proteins are involved in nucleolar assembly and ribosome biogenesis and act as chaperones for the import of proteins into the nucleolus. We have found that fibrillarin is reorganized in primary cells infected with the avian coronavirus infectious bronchitis virus (IBV) and in continuous cell lines that express either IBV or mouse hepatitis virus N protein. Both N protein and a fibrillarin-green fluorescent protein fusion protein colocalized to the perinuclear region and the nucleolus. Pull-down assays demonstrated that IBV N protein interacted with nucleolin and therefore provided a possible explanation as to how coronavirus N proteins localize to the nucleolus. Nucleoli, and proteins that localize to the nucleolus, have been implicated in cell growth-cell cycle regulation. Comparison of cells expressing IBV N protein with controls indicated that cells expressing N protein had delayed cellular growth. This result could not to be attributed to apoptosis. Morphological analysis of these cells indicated that cytokinesis was disrupted, an observation subsequently found in primary cells infected with IBV. Coronaviruses might therefore delay the cell cycle in interphase, where maximum translation of viral mRNAs can occur.
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Maddox-Hyttel, Poul, Bolette Bjerregaard i Jozef Laurincik. "Meiosis and embryo technology: renaissance of the nucleolus". Reproduction, Fertility and Development 17, nr 2 (2005): 3. http://dx.doi.org/10.1071/rd04108.
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The nucleolus is the site of rRNA and ribosome production. This organelle presents an active fibrillogranular ultrastructure in the oocyte during the growth of the gamete but, at the end of the growth phase, the nucleolus is transformed into an inactive remnant that is dissolved when meiosis is resumed at germinal vesicle breakdown. Upon meiosis, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities harbour the development of fibrillogranular nucleoli and re-establishment of nucleolar function in conjunction with the major activation of the embryonic genome. This so-called nucleologenesis occurs at a species-specific time of development and can be classified into two different models: one where nucleolus development occurs inside the NPBs (e.g. cattle) and one where the nucleolus is formed on the surface of the NPBs (e.g. pigs). A panel of nucleolar proteins with functions during rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) are localised to specific compartments of the oocyte nucleolus and those engaged in late processing are, to some degree, re-used for nucleologenesis in the embryo, whereas the others require de novo embryonic transcription in order to be allocated to the developing nucleolus. In the oocyte, inactivation of the nucleolus coincides with the acquisition of full meiotic competence, a parameter that may be of importance in relation to in vitro oocyte maturation. In embryo, nucleologenesis may be affected by technological manipulations: in vitro embryo production apparently has no impact on this process in cattle, whereas in the pig this technology results in impaired nucleologenesis. In cattle, reconstruction of embryos by nuclear transfer results in profound disturbances in nucleologenesis. In conclusion, the nucleolus is an organelle of great importance for the developmental competence of oocytes and embryos and may serve as a morphological marker for the completion of oocyte growth and normality of activation of the embryonic genome.
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Chen, Hung-Kai, Chi-Yun Pai, Jing-Yi Huang i Ning-Hsing Yeh. "Human Nopp140, Which Interacts with RNA Polymerase I: Implications for rRNA Gene Transcription and Nucleolar Structural Organization". Molecular and Cellular Biology 19, nr 12 (1.12.1999): 8536–46. http://dx.doi.org/10.1128/mcb.19.12.8536.
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ABSTRACT Nopp140 is thought to shuttle between nucleolus and cytoplasm. However, the predominant nucleolar localization of Nopp140 homologues from different species suggests that Nopp140 is also involved in events occurring within the nucleolus. In this study, we demonstrated that the largest subunit of RNA polymerase I, RPA194, was coimmunoprecipitated with the human Nopp140 (hNopp140). Such an interaction is mediated through amino acids 204 to 382 of hNopp140. By double immunofluorescence, hNopp140 was colocalized with RNA polymerase I at the rDNA (rRNA genes) transcription active foci in the nucleolus. These results suggest that Nopp140 can interact with RNA polymerase I in vivo. Transfected cells expressing the amino-terminal half of hNopp140, hNopp140N382 (amino acids 1 to 382), displayed altered nucleoli with crescent-shaped structures. This phenotype is reminiscent of the segregated nucleoli induced by actinomycin D treatment, which is known to inhibit rRNA synthesis. Consistently, the hNopp140N382 protein mislocalized the endogenous RNA polymerase I and shut off cellular rRNA gene transcription as revealed by an in situ run-on assay. These dominant negative effects of the mutant hNopp140N382 suggest that Nopp140 plays an essential role in rDNA transcription. Interestingly, ectopic expression of hNopp140 to a very high level caused the formation of a transcriptionally inactive spherical structure occupying the entire nucleolar area which trapped the RNA polymerase I, fibrillarin, and hNopp140 but excluded the nucleolin. The mislocalizations of these nucleolar proteins after hNopp140 overexpression imply that Nopp140 may also play roles in maintenance of nucleolar integrity.
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Wang, Jianyue, i Feixiong Zhang. "Nucleolus disassembly and distribution of segregated nucleolar material in prophase of root-tip meristematic cells in Triticum aestivum L." Archives of Biological Sciences 67, nr 2 (2015): 405–10. http://dx.doi.org/10.2298/abs140810007w.
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This paper presents details of the process of nucleolar disassembly, studied by conventional transmission electron microscopy (TEM) in wheat root cells. In early prophase, chromatin condensation and irregular nucleolar morphology are observed, with many small particles appearing around the nucleolus. In middle prophase, the nucleolus radiates outwards; in late prophase, the fine structure of the nucleolus disappears and nucleolar material diffuses away. Using ?en bloc? silver-staining to distinguish between nucleoli and chromatin, we observed that the dispersed nucleolar material aggregates around the chromatin, forming a sheath-like perichromosomal structure that coats the chromosomes in late prophase.
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Dundr, M., G. H. Leno, N. Lewis, D. Rekosh, M. L. Hammarskjoid i M. O. Olson. "Location of the HIV-1 Rev protein during mitosis: inactivation of the nuclear export signal alters the pathway for postmitotic reentry into nucleoli". Journal of Cell Science 109, nr 9 (1.09.1996): 2239–51. http://dx.doi.org/10.1242/jcs.109.9.2239.
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The HIV-1 Rev protein localizes predominantly to the nucleolus of HIV-1-infected or Rev-expressing cells. The subcellular location of Rev during mitotic nucleolar disintegration was examined at various stages of mitosis in synchronized Rev-expressing CMT3 cells. During early prophase Rev was predominantly located in disintegrating nucleoli and began to accumulate at the peripheral regions of chromosomes in late prophase, eventually distributing uniformly on all chromosomes in prometaphase. In anaphase Rev remained associated with the perichromosomal regions, but significant amounts of Rev were also seen in numerous nucleolus-derived foci. The movement of Rev from disintegrating nucleoli to perichromosomal regions and foci was similar to that of nonribosomal nucleolar proteins, including fibrillarin, nucleolin, protein B23 and p52 of the granular component. During telophase Rev remained associated with perichromosomal regions and mitotic foci until the nuclear envelope started to reform. When nuclear envelope formation was complete in late telophase, nonribosomal nucleolar proteins were present in prenucleolar bodies (PNBs) which were eventually incorporated into nucleoli; at the same time, Rev was excluded from nuclei. In contrast, a trans-dominant negative Rev protein containing an inactive nuclear export signal reentered nuclei by the nonribosomal nucleolar protein pathway in late telophase, associating with PNBs and reformed nucleoli. Rev protein reentry into postmitotic nuclei was delayed until early G1 phase, but before the arrival of ribosomal protein S6. Thus, Rev behaves like a nonribosomal nucleolar protein through mitosis until early telophase; however, its nuclear reentry seems to require reestablishment of both a nuclear import system and active nucleoli.
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Dundr, Miroslav, Tom Misteli i Mark O. J. Olson. "The Dynamics of Postmitotic Reassembly of the Nucleolus". Journal of Cell Biology 150, nr 3 (7.08.2000): 433–46. http://dx.doi.org/10.1083/jcb.150.3.433.
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Mammalian cell nucleoli disassemble at the onset of M-phase and reassemble during telophase. Recent studies showed that partially processed preribosomal RNA (pre-rRNA) is preserved in association with processing components in the perichromosomal regions (PRs) and in particles called nucleolus-derived foci (NDF) during mitosis. Here, the dynamics of nucleolar reassembly were examined for the first time in living cells expressing fusions of the processing-related proteins fibrillarin, nucleolin, or B23 with green fluorescent protein (GFP). During telophase the NDF disappeared with a concomitant appearance of material in the reforming nuclei. Prenucleolar bodies (PNBs) appeared in nuclei in early telophase and gradually disappeared as nucleoli formed, strongly suggesting the transfer of PNB components to newly forming nucleoli. Fluorescence recovery after photobleaching (FRAP) showed that fibrillarin-GFP reassociates with the NDF and PNBs at rapid and similar rates. The reentry of processing complexes into telophase nuclei is suggested by the presence of pre-rRNA sequences in PNBs. Entry of specific proteins into the nucleolus approximately correlated with the timing of processing events. The mitotically preserved processing complexes may be essential for regulating the distribution of components to reassembling daughter cell nucleoli.
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Intine, Robert V., Miroslav Dundr, Alex Vassilev, Elena Schwartz, Yingmin Zhao, Yingxin Zhao, Melvin L. DePamphilis i Richard J. Maraia. "Nonphosphorylated Human La Antigen Interacts with Nucleolin at Nucleolar Sites Involved in rRNA Biogenesis". Molecular and Cellular Biology 24, nr 24 (15.12.2004): 10894–904. http://dx.doi.org/10.1128/mcb.24.24.10894-10904.2004.
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ABSTRACT La is a RNA-binding protein implicated in multiple pathways related to the production of tRNAs, ribosomal proteins, and other components of the translational machinery (D. J. Kenan and J. D. Keene, Nat. Struct. Mol. Biol. 11 :303-305, 2004). While most La is phosphorylated and resides in the nucleoplasm, a fraction is in the nucleolus, the site of ribosome production, although the determinants of this localization are incompletely known. In addition to its conserved N-terminal domain, human La harbors a C-terminal domain that contains an atypical RNA recognition motif and a short basic motif (SBM) adjacent to phosphoserine-366. We report that nonphosphorylated La (npLa) is concentrated in nucleolar sites that correspond to the dense fibrillar component that harbors nascent pol I transcripts as well as fibrillarin and nucleolin, which function in early phases of rRNA maturation. Affinity purification and native immunoprecipitation of La and fluorescence resonance energy transfer in the nucleolus reveal close association with nucleolin. Moreover, La lacking the SBM does not localize to nucleoli. Lastly, La exhibits SBM-dependent, phosphorylation-sensitive interaction with nucleolin in a yeast two-hybrid assay. The data suggest that interaction with nucleolin is, at least in part, responsible for nucleolar accumulation of La and that npLa may be involved in ribosome biogenesis.
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Kill, I. R. "Localisation of the Ki-67 antigen within the nucleolus. Evidence for a fibrillarin-deficient region of the dense fibrillar component". Journal of Cell Science 109, nr 6 (1.06.1996): 1253–63. http://dx.doi.org/10.1242/jcs.109.6.1253.
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The Ki-67 antigen is detected in proliferating cells in all phases of the cell division cycle. Throughout most of interphase, the Ki-67 antigen is localised within the nucleous. To learn more about the relationship between the Ki-67 antigen and the nucleolus, we have compared the distribution of Ki-67 antibodies with that of a panel of antibodies reacting with nucleolar components by confocal laser scanning microscopy of normal human dermal fibroblasts in interphase stained in a double indirect immunofluorescence assay. During early G1, the Ki-67 antigen is detected at a large number of discrete foci throughout the nucleoplasm, extending to the nuclear envelope. During S-phase and G2, the antigen is located in the nucleolus. Double indirect immunofluorescence studies have revealed that during early to mid G1 the Ki-67 antigen is associated with reforming nucleoli within discrete domains which are distinct from domains containing two of the major nucleolar antigens fibrillarin and RNA polymerase I. Within mature nucleoli the Ki-67 antigen is absent from regions containing RNA polymerase I and displays only partial co-localisation within domains containing either fibrillarin or B23/nucleophosmin. Following disruption of nucleolar structure, induced by treatment of cells with the drug 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole or with actinomycin D, the Ki-67 antigen translocates to nucleoplasmic foci which are associated with neither fibrillarin nor RNA polymerase I. However, in treated cells the Ki-67 Ag remains associated with, but not co-localised to, regions containing B23/nucleophosmin. Our observations suggest that the Ki-67 antigen associates with a fibrillarin-deficient region of the dense fibrillar component of the nucleolus. Integrity of this region is lost following either nucleolar dispersal or nucleolar segregation.
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Pontvianne, Frederic, Isabel Matía, Julien Douet, Sylvette Tourmente, Francisco J. Medina, Manuel Echeverria i Julio Sáez-Vásquez. "Characterization of AtNUC-L1 Reveals a Central Role of Nucleolin in Nucleolus Organization and Silencing of AtNUC-L2 Gene in Arabidopsis". Molecular Biology of the Cell 18, nr 2 (luty 2007): 369–79. http://dx.doi.org/10.1091/mbc.e06-08-0751.
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Nucleolin is one of the most abundant protein in the nucleolus and is a multifunctional protein involved in different steps of ribosome biogenesis. In contrast to animals and yeast, the genome of the model plant Arabidopsis thaliana encodes two nucleolin-like proteins, AtNUC-L1 and AtNUC-L2. However, only the AtNUC-L1 gene is ubiquitously expressed in normal growth conditions. Disruption of this AtNUC-L1 gene leads to severe plant growth and development defects. AtNUC-L1 is localized in the nucleolus, mainly in the dense fibrillar component. Absence of this protein in Atnuc-L1 plants induces nucleolar disorganization, nucleolus organizer region decondensation, and affects the accumulation levels of pre-rRNA precursors. Remarkably, in Atnuc-L1 plants the AtNUC-L2 gene is activated, suggesting that AtNUC-L2 might rescue, at least partially, the loss of AtNUC-L1. This work is the first description of a higher eukaryotic organism with a disrupted nucleolin-like gene and defines a new role for nucleolin in nucleolus structure and rDNA chromatin organization.
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Lavrentyeva, Elena, Kseniya Shishova, German Kagarlitsky i Olga Zatsepina. "Localisation of RNAs and proteins in nucleolar precursor bodies of early mouse embryos". Reproduction, Fertility and Development 29, nr 3 (2017): 509. http://dx.doi.org/10.1071/rd15200.
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Early embryos of all mammalian species contain morphologically distinct but transcriptionally silent nucleoli called the nucleolar precursor bodies (NPBs), which, unlike normal nucleoli, have been poorly studied at the biochemical level. To bridge this gap, here we examined the occurrence of RNA and proteins in early mouse embryos with two fluorochromes – an RNA-binding dye pyronin Y (PY) and the protein-binding dye fluorescein-5′-isothiocyanate (FITC). The staining patterns of zygotic NPBs were then compared with those of nucleolus-like bodies (NLBs) in fully grown surrounded nucleolus (SN)-type oocytes, which are morphologically similar to NPBs. We show that both entities contain proteins, but unlike NLBs, NPBs are significantly impoverished for RNA. Detectable amounts of RNA appear on the NPB surface only after resumption of rDNA transcription and includes pre-rRNAs and 28S rRNA as evidenced by fluorescence in situ hybridisation with specific oligonucleotide probes. Immunocytochemical assays demonstrate that zygotic NPBs contain rRNA processing factors fibrillarin, nucleophosmin and nucleolin, while UBF (the RNA polymerase I transcription factor) and ribosomal proteins RPL26 and RPS10 are not detectable. Based on the results obtained and data in the contemporary literature, we suggest a scheme of NPB assembly and maturation to normal nucleoli that assumes utilisation of maternally derived nucleolar proteins but of nascent rRNAs.
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Terzaghi, Laura, Alberto Maria Luciano, Priscila C. Dall’Acqua, Silvia C. Modina, John J. Peluso i Valentina Lodde. "PGRMC1 localization and putative function in the nucleolus of bovine granulosa cells and oocytes". Reproduction 155, nr 3 (marzec 2018): 273–82. http://dx.doi.org/10.1530/rep-17-0534.
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Progesterone receptor membrane component-1 (PGRMC1) is a highly conserved multifunctional protein that is found in numerous systems, including reproductive system. Interestingly, PGRMC1 is expressed at several intracellular locations, including the nucleolus. The aim of this study is to investigate the functional relationship between PGRMC1 and nucleolus. Immunofluorescence experiments confirmed PGRMC1’s nucleolar localization in cultured bovine granulosa cells (bGC) and oocytes. Additional experiments conducted on bGC revealed that PGRMC1 co-localizes with nucleolin (NCL), a major nucleolar protein. Furthermore, small interfering RNA (RNAi)-mediated gene silencing experiments showed that when PGRMC1 expression was depleted, NCL translocated from the nucleolus to the nucleoplasm. Similarly, oxidative stress induced by hydrogen peroxide (H2O2) treatment, reduced PGRMC1 immunofluorescent signal in the nucleolus and increased NCL nucleoplasmic signal, when compared to non-treated cells. Although PGRMC1 influenced NCL localization, a direct interaction between these two proteins was not detected using in situ proximity ligation assay. This suggests the involvement of additional molecules in mediating the co-localization of PGRMC1 and nucleolin. Since nucleolin translocates into the nucleoplasm in response to various cellular stressors, PGRMC1’s ability to regulate its localization within the nucleolus is likely an important component of mechanism by which cells response to stress. This concept is consistent with PGRMC1’s well-described ability to promote ovarian cell survival and provides a rationale for future studies on PGRMC1, NCL and the molecular mechanism by which these two proteins protect against the adverse effect of cellular stressors, including oxidative stress.
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Boyd, Mark T., Nikolina Vlatković i Carlos P. Rubbi. "The nucleolus directly regulates p53 export and degradation". Journal of Cell Biology 194, nr 5 (5.09.2011): 689–703. http://dx.doi.org/10.1083/jcb.201105143.
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The correlation between stress-induced nucleolar disruption and abrogation of p53 degradation is evident after a wide variety of cellular stresses. This link may be caused by steps in p53 regulation occurring in nucleoli, as suggested by some biochemical evidence. Alternatively, nucleolar disruption also causes redistribution of nucleolar proteins, potentially altering their interactions with p53 and/or MDM2. This raises the fundamental question of whether the nucleolus controls p53 directly, i.e., as a site where p53 regulatory processes occur, or indirectly, i.e., by determining the cellular localization of p53/MDM2-interacting factors. In this work, transport experiments based on heterokaryons, photobleaching, and micronucleation demonstrate that p53 regulatory events are directly regulated by nucleoli and are dependent on intact nucleolar structure and function. Subcellular fractionation and nucleolar isolation revealed a distribution of ubiquitylated p53 that supports these findings. In addition, our results indicate that p53 is exported by two pathways: one stress sensitive and one stress insensitive, the latter being regulated by activities present in the nucleolus.
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Johnson, Jarrod S., i R. Jude Samulski. "Enhancement of Adeno-Associated Virus Infection by Mobilizing Capsids into and Out of the Nucleolus". Journal of Virology 83, nr 6 (24.12.2008): 2632–44. http://dx.doi.org/10.1128/jvi.02309-08.
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ABSTRACT Adeno-associated virus (AAV) serotypes are being tailored for numerous therapeutic applications, but the parameters governing the subcellular fate of even the most highly characterized serotype, AAV2, remain unclear. To understand how cellular conditions control capsid trafficking, we have tracked the subcellular fate of recombinant AAV2 (rAAV2) vectors using confocal immunofluorescence, three-dimensional infection analysis, and subcellular fractionation. Here we report that a population of rAAV2 virions enters the nucleus and accumulates in the nucleolus after infection, whereas empty capsids are excluded from nuclear entry. Remarkably, after subcellular fractionation, virions accumulating in nucleoli were found to retain infectivity in secondary infections. Proteasome inhibitors known to enhance transduction were found to potentiate nucleolar accumulation. In contrast, hydroxyurea, which also increases transduction, mobilized virions into the nucleoplasm, suggesting that two separate pathways influence vector delivery in the nucleus. Using a small interfering RNA (siRNA) approach, we then evaluated whether nucleolar proteins B23/nucleophosmin and nucleolin, previously shown to interact with AAV2 capsids, affect trafficking and transduction efficiency. Similar to effects observed with proteasome inhibition, siRNA-mediated knockdown of nucleophosmin potentiated nucleolar accumulation and increased transduction 5- to 15-fold. Parallel to effects from hydroxyurea, knockdown of nucleolin mobilized capsids to the nucleoplasm and increased transduction 10- to 30-fold. Moreover, affecting both pathways simultaneously using drug and siRNA combinations was synergistic and increased transduction over 50-fold. Taken together, these results support the hypothesis that rAAV2 virions enter the nucleus intact and can be sequestered in the nucleolus in stable form. Mobilization from the nucleolus to nucleoplasmic sites likely permits uncoating and subsequent gene expression or genome degradation. In summary, with these studies we have refined our understanding of AAV2 trafficking dynamics and have identified cellular parameters that mobilize virions in the nucleus and significantly influence AAV infection.
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LEUNG, Anthony K. L., Jens S. ANDERSEN, Matthias MANN i Angus I. LAMOND. "Bioinformatic analysis of the nucleolus". Biochemical Journal 376, nr 3 (15.12.2003): 553–69. http://dx.doi.org/10.1042/bj20031169.
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The nucleolus is a plurifunctional, nuclear organelle, which is responsible for ribosome biogenesis and many other functions in eukaryotes, including RNA processing, viral replication and tumour suppression. Our knowledge of the human nucleolar proteome has been expanded dramatically by the two recent MS studies on isolated nucleoli from HeLa cells [Andersen, Lyon, Fox, Leung, Lam, Steen, Mann and Lamond (2002) Curr. Biol. 12, 1–11; Scherl, Coute, Deon, Calle, Kindbeiter, Sanchez, Greco, Hochstrasser and Diaz (2002) Mol. Biol. Cell 13, 4100–4109]. Nearly 400 proteins were identified within the nucleolar proteome so far in humans. Approx. 12% of the identified proteins were previously shown to be nucleolar in human cells and, as expected, nearly all of the known housekeeping proteins required for ribosome biogenesis were identified in these analyses. Surprisingly, approx. 30% represented either novel or uncharacterized proteins. This review focuses on how to apply the derived knowledge of this newly recognized nucleolar proteome, such as their amino acid/peptide composition and their homologies across species, to explore the function and dynamics of the nucleolus, and suggests ways to identify, in silico, possible functions of the novel/uncharacterized proteins and potential interaction networks within the human nucleolus, or between the nucleolus and other nuclear organelles, by drawing resources from the public domain.
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Savino, Tulia Maria, Jeannine Gébrane-Younès, Jan De Mey, Jean-Baptiste Sibarita i Danièle Hernandez-Verdun. "Nucleolar Assembly of the Rrna Processing Machinery in Living Cells". Journal of Cell Biology 153, nr 5 (28.05.2001): 1097–110. http://dx.doi.org/10.1083/jcb.153.5.1097.
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To understand how nuclear machineries are targeted to accurate locations during nuclear assembly, we investigated the pathway of the ribosomal RNA (rRNA) processing machinery towards ribosomal genes (nucleolar organizer regions [NORs]) at exit of mitosis. To follow in living cells two permanently transfected green fluorescence protein–tagged nucleolar proteins, fibrillarin and Nop52, from metaphase to G1, 4-D time-lapse microscopy was used. In early telophase, fibrillarin is concentrated simultaneously in prenucleolar bodies (PNBs) and NORs, whereas PNB-containing Nop52 forms later. These distinct PNBs assemble at the chromosome surface. Analysis of PNB movement does not reveal the migration of PNBs towards the nucleolus, but rather a directional flow between PNBs and between PNBs and the nucleolus, ensuring progressive delivery of proteins into nucleoli. This delivery appeared organized in morphologically distinct structures visible by electron microscopy, suggesting transfer of large complexes. We propose that the temporal order of PNB assembly and disassembly controls nucleolar delivery of these proteins, and that accumulation of processing complexes in the nucleolus is driven by pre-rRNA concentration. Initial nucleolar formation around competent NORs appears to be followed by regroupment of the NORs into a single nucleolus 1 h later to complete the nucleolar assembly. This demonstrates the formation of one functional domain by cooperative interactions between different chromosome territories.
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Schmidt-Zachmann, M. S., i E. A. Nigg. "Protein localization to the nucleolus: a search for targeting domains in nucleolin". Journal of Cell Science 105, nr 3 (1.07.1993): 799–806. http://dx.doi.org/10.1242/jcs.105.3.799.
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Nucleolin, a major nucleolar phosphoprotein, is presumed to function in rDNA transcription, rRNA packaging and ribosome assembly. Its primary sequence was highly conserved during evolution and suggests a multi-domain structure. To identify structural elements required for nuclear uptake and nucleolar accumulation of nucleolin, we used site-directed mutagenesis to introduce point- and deletion-mutations into a chicken nucleolin cDNA. Following transient expression in mammalian cells, the intracellular distribution of the corresponding wild-type and mutant proteins was determined by indirect immunofluorescence microscopy. We found that nucleolin contains a functional nuclear localization signal (KRKKEMANKSAPEAKKKK) that conforms exactly to the consensus proposed recently for a bipartite signal (Robbins, J., Dilworth, S.M., Laskey, R.A. and Dingwall, C. (1991) Cell 64, 615–623). Concerning nucleolar localization, we found that the N-terminal 250 amino acids of nucleolin are dispensible, but deletion of either the centrally located RNA-binding motifs (the RNP domain) or the glycine/arginine-rich C terminus (the GR domain) resulted in an exclusively nucleoplasmic distribution. Although both of these latter domains were required for correct subcellular localization of nucleolin, they were not sufficient to target non-nucleolar proteins to the nucleolus. From these results we conclude that nucleolin does not contain a single, linear nucleolar targeting signal. Instead, we propose that the protein uses a bipartite NLS to enter the nucleus and then accumulates within the nucleolus by virtue of binding to other nucleolar components (probably rRNA) via its RNP and GR domains.
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Créancier, L., H. Prats, C. Zanibellato, F. Amalric i B. Bugler. "Determination of the functional domains involved in nucleolar targeting of nucleolin." Molecular Biology of the Cell 4, nr 12 (grudzień 1993): 1239–50. http://dx.doi.org/10.1091/mbc.4.12.1239.
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Nucleolin (713 aa), a major nucleolar protein, presents two structural domains: a N-terminus implicated in interaction with chromatin and a C-terminus containing four RNA-binding domains (RRMs) and a glycine/arginine-rich domain mainly involved in pre-rRNA packaging. Furthermore, nucleolin was shown to shuttle between cytoplasm and nucleolus. To get an insight on the nature of nuclear and nucleolar localization signals, a set of nucleolin deletion mutants in fusion with the prokaryotic chloramphenicol acetyltransferase (CAT) were constructed, and the resulting chimeric proteins were recognized by anti-CAT antibodies. First, a nuclear location signal bipartite and composed of two short basic stretches separated by eleven residues was characterized. Deletion of either motifs renders the protein cytoplasmic. Second, by deleting one or more domains implicated in nucleolin association either with DNA, RNA, or proteins, we demonstrated that nucleolar accumulation requires, in addition to the nuclear localization sequence, at least two of the five RRMs in presence or absence of N-terminus. However, in presence of only one RRM the N-terminus allowed a partial targeting of the chimeric protein to the nucleolus.
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Sutter, Sereina O., Anouk Lkharrazi, Elisabeth M. Schraner, Kevin Michaelsen, Anita Felicitas Meier, Jennifer Marx, Bernd Vogt, Hildegard Büning i Cornel Fraefel. "Adeno-associated virus type 2 (AAV2) uncoating is a stepwise process and is linked to structural reorganization of the nucleolus". PLOS Pathogens 18, nr 7 (11.07.2022): e1010187. http://dx.doi.org/10.1371/journal.ppat.1010187.
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Nucleoli are membrane-less structures located within the nucleus and are known to be involved in many cellular functions, including stress response and cell cycle regulation. Besides, many viruses can employ the nucleolus or nucleolar proteins to promote different steps of their life cycle such as replication, transcription and assembly. While adeno-associated virus type 2 (AAV2) capsids have previously been reported to enter the host cell nucleus and accumulate in the nucleolus, both the role of the nucleolus in AAV2 infection, and the viral uncoating mechanism remain elusive. In all prior studies on AAV uncoating, viral capsids and viral genomes were not directly correlated on the single cell level, at least not in absence of a helper virus. To elucidate the properties of the nucleolus during AAV2 infection and to assess viral uncoating on a single cell level, we combined immunofluorescence analysis for detection of intact AAV2 capsids and capsid proteins with fluorescence in situ hybridization for detection of AAV2 genomes. The results of our experiments provide evidence that uncoating of AAV2 particles occurs in a stepwise process that is completed in the nucleolus and supported by alteration of the nucleolar structure.
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Mladineo, Ivona, i Jerko Hrabar. "Leukocyte Nucleolus and Anisakis pegreffii—When Falling Apart Means Falling in Place". Genes 11, nr 6 (23.06.2020): 688. http://dx.doi.org/10.3390/genes11060688.
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The view of the nucleolus as a mere ribosomal factory has been recently expanded, highlighting its essential role in immune and stress-related signalling and orchestrating. It has been shown that the nucleolus structure, formed around nucleolus organiser regions (NORs) and attributed Cajal bodies, is prone to disassembly and reassembly correlated to various physiological and pathological stimuli. To evaluate the effect of parasite stimulus on the structure of the leukocyte nucleolus, we exposed rat peripheral blood mononuclear cells (PBMC) to the crude extract of the nematode A. pegreffii (Anisakidae), and compared the observed changes to the effect of control (RPMI-1640 media), immunosuppressive (MPA) and immunostimulant treatment (bacterial lipopolysaccharide (LPS) and viral analogue polyinosinic:polycytidylic acid (poly I:C)) by confocal microscopy. Poly I:C triggered the most accentuated changes such as nucleolar fragmentation and structural unravelling, LPS induced nucleolus thickening reminiscent of cell activation, while MPA induced disassembly of dense fibrillar and granular components. A. pegreffii crude extract triggered nucleolar segregation, expectedly more enhanced in treatment with a higher dose. This is the first evidence that leukocyte nucleoli already undergo structural changes 12 h post-parasitic stimuli, although these are likely to subside after successful cell activation.
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Zhu, Lian, Tiffany M. Richardson, Ludivine Wacheul, Ming-Tzo Wei, Marina Feric, Gena Whitney, Denis L. J. Lafontaine i Clifford P. Brangwynne. "Controlling the material properties and rRNA processing function of the nucleolus using light". Proceedings of the National Academy of Sciences 116, nr 35 (9.08.2019): 17330–35. http://dx.doi.org/10.1073/pnas.1903870116.
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The nucleolus is a prominent nuclear condensate that plays a central role in ribosome biogenesis by facilitating the transcription and processing of nascent ribosomal RNA (rRNA). A number of studies have highlighted the active viscoelastic nature of the nucleolus, whose material properties and phase behavior are a consequence of underlying molecular interactions. However, the ways in which the material properties of the nucleolus impact its function in rRNA biogenesis are not understood. Here we utilize the Cry2olig optogenetic system to modulate the viscoelastic properties of the nucleolus. We show that above a threshold concentration of Cry2olig protein, the nucleolus can be gelled into a tightly linked, low mobility meshwork. Gelled nucleoli no longer coalesce and relax into spheres but nonetheless permit continued internal molecular mobility of small proteins. These changes in nucleolar material properties manifest in specific alterations in rRNA processing steps, including a buildup of larger rRNA precursors and a depletion of smaller rRNA precursors. We propose that the flux of processed rRNA may be actively tuned by the cell through modulating nucleolar material properties, which suggests the potential of materials-based approaches for therapeutic intervention in ribosomopathies.
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Leitch, A. R., W. Mosgoller, M. Shi i J. S. Heslop-Harrison. "Different patterns of rDNA organization at interphase in nuclei of wheat and rye". Journal of Cell Science 101, nr 4 (1.04.1992): 751–57. http://dx.doi.org/10.1242/jcs.101.4.751.
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The physical location of the rDNA repeating units (25 S, 18 S and 5.8 S rRNA genes and the intergenic spacer sequences) was investigated in rye (Secale cereale L.) and wheat (Triticum aestivum L.) root tip meristematic cells by in situ hybridization using light and electron microscopy. The rDNA sequences are organized differently in the two related and intercrossable species. In rye (2n = 14, one pair of chromosomes with nucleolar organizing regions, NORs), two condensed blocks of rDNA-containing chromatin occurred in each interphase nucleus. The blocks were associated with the periphery of nucleoli and a single-labelled, decondensed rDNA fibre extended into the nucleolus from the block. We term this expression pattern terminal decondensation. In wheat (2n = 6x = 42, five pairs of chromosomes with NORs), inactive condensed labelled chromatin was found unassociated with nucleoli. Active NORs had some condensed rDNA associated with the nucleolar periphery, but, in contrast to rye, condensed rDNA was also found within the nucleolus. The condensed labelled rDNA in wheat nucleoli was visible as fluorescent foci in the light microscope and labelled condensed chromatin in the electron microscope. Its absence in rye shows that condensed rDNA need not be present in active plant nucleoli. Diffuse labelled sites of rDNA, likely to represent actively transcribed rDNA, were found in both rye and wheat. Active rDNA loci in wheat have many expressed segments separated by unexpressed, condensed, rDNA-fragmented decondensation-while each locus in rye has a single, unexpressed perinucleolar condensed block of rRNA genes. Thus the positions of actively transcribed genes within the tandem arrays of rDNA at each locus are fundamentally different in the two cereals. The NOR chromosome appeared to extend through the nucleolus, and active rDNA sequences did not loop out from chromatin into the nucleolus as is frequently described in nucleolar models.
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Lange, Thilo Sascha, i Susan A. Gerbi. "Transient Nucleolar Localization Of U6 Small Nuclear RNA InXenopus Laevis Oocytes". Molecular Biology of the Cell 11, nr 7 (lipiec 2000): 2419–28. http://dx.doi.org/10.1091/mbc.11.7.2419.
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Recent studies on the 2′-O-methylation and pseudouridylation of U6 small nuclear RNA (snRNA) hypothesize that these posttranscriptional modifications might occur in the nucleolus. In this report, we present direct evidence for the nucleolar localization of U6 snRNA and analyze the kinetics of U6 nucleolar localization after injection of in vitro transcribed fluorescein-labeled transcripts into Xenopus laevis oocytes. In contrast to U3 small nucleolar RNA (snoRNA) which developed strong nucleolar labeling over 4 h and maintained strong nucleolar signals through 24 h, U6 snRNA localized to nucleoli immediately after injection, but nucleolar staining decreased after 4 h. By 24 h after injection of U6 snRNA, only weak nucleolar signals were observed. Unlike the time-dependent profile of strong nucleolar localization of U6 snRNA or U3 snoRNA, injection of fluorescein-labeled U2 snRNA gave weak nucleolar staining at all times throughout a 24-h period; U2 snRNA modifications are believed to occur outside of the nucleolus. The notion that the decrease of U6 signals over time was due to its trafficking out of nucleoli and not to transcript degradation was supported by the demonstration of U6 snRNA stability over time. Therefore, in contrast to snoRNAs like U3, U6 snRNA transiently passes through nucleoli.
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Stochaj, Ursula, i Stephanie C. Weber. "Nucleolar Organization and Functions in Health and Disease". Cells 9, nr 3 (25.02.2020): 526. http://dx.doi.org/10.3390/cells9030526.
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The nucleolus is a prominent, membraneless compartment found within the nucleus of eukaryotic cells. It forms around ribosomal RNA (rRNA) genes, where it coordinates the transcription, processing, and packaging of rRNA to produce ribosomal subunits. Recent efforts to characterize the biophysical properties of the nucleolus have transformed our understanding of the assembly and organization of this dynamic compartment. Indeed, soluble macromolecules condense from the nucleoplasm to form nucleoli through a process called liquid–liquid phase separation. Individual nucleolar components rapidly exchange with the nucleoplasm and separate within the nucleolus itself to form distinct subcompartments. In addition to its essential role in ribosome biogenesis, the nucleolus regulates many aspects of cell physiology, including genome organization, stress responses, senescence and lifespan. Consequently, the nucleolus is implicated in several human diseases, such as Hutchinson–Gilford progeria syndrome, Diamond–Blackfan anemia, and various forms of cancer. This Special Issue highlights new insights into the physical and molecular mechanisms that control the architecture and diverse functions of the nucleolus, and how they break down in disease.
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Westendorf, Joanne M., Konstantin N. Konstantinov, Steven Wormsley, Mei-Di Shu, Naoko Matsumoto-Taniura, Fabienne Pirollet, F. George Klier, Larry Gerace i Susan J. Baserga. "M Phase Phosphoprotein 10 Is a Human U3 Small Nucleolar Ribonucleoprotein Component". Molecular Biology of the Cell 9, nr 2 (luty 1998): 437–49. http://dx.doi.org/10.1091/mbc.9.2.437.
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We have previously developed a novel technique for isolation of cDNAs encoding M phase phosphoproteins (MPPs). In the work described herein, we further characterize MPP10, one of 10 novel proteins that we identified, with regard to its potential nucleolar function. We show that by cell fractionation, almost all MPP10 was found in isolated nucleoli. By immunofluorescence, MPP10 colocalized with nucleolar fibrillarin and other known nucleolar proteins in interphase cells but was not detected in the coiled bodies stained for either fibrillarin or p80 coilin, a protein found only in the coiled body. When nucleoli were separated into fibrillar and granular domains by treatment with actinomycin D, almost all the MPP10 was found in the fibrillar caps, which contain proteins involved in rRNA processing. In early to middle M phase of the cell cycle, MPP10 colocalized with fibrillarin to chromosome surfaces. At telophase, MPP10 was found in cellular structures that resembled nucleolus-derived bodies and prenucleolar bodies. Some of these bodies lacked fibrillarin, a previously described component of nucleolus-derived bodies and prenucleolar bodies, however, and the bulk of MPP10 arrived at the nucleolus later than fibrillarin. To further examine the properties of MPP10, we immunoprecipitated it from cell sonicates. The resulting precipitates contained U3 small nucleolar RNA (snoRNA) but no significant amounts of other box C/D snoRNAs. This association of MPP10 with U3 snoRNA was stable to 400 mM salt and suggested that MPP10 is a component of the human U3 small nucleolar ribonucleoprotein.
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Diez, M., i M. J. Puertas. "Quantitative analysis of the formation of nucleoli in Locusta migratoria". Canadian Journal of Genetics and Cytology 28, nr 2 (1.04.1986): 207–18. http://dx.doi.org/10.1139/g86-029.
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At meiosis of Locusta migratoria, zero, one, or two nucleoli per long (L), medium (M), or short (S) nucleolar organizer region (NOR) bivalent can be clearly seen using an Ag-NOR technique. Diplotene cells with zero to six nucleoli were observed, whose distribution fitted a normal one. However, the distribution of nucleoli in the particular bivalents was not at random. A mathematical model was developed in an attempt to explain this differential activation of nucleoli. The model is based on the assumption that the activation of nucleoli is sequential following successive rounds, in such a way that the probability of a particular L, M, or S nucleolus being activated depends on the type of nucleoli previously activated. The nucleoli activated per cell tend to be distributed among bivalents, and the activation of a second nucleolus in a bivalent has a lower probability than the first one of any bivalent, generating interference. The model was developed for wild-type individuals and it was also applied to mutants that showed a distribution of nucleoli different from wild types, i.e., individuals carrying a translocation between two NOR chromosomes and asynaptic mutants. In both cases the model fits with the observed results. This suggests its general validity.Key words: nucleolus, Locusta, translocation, asynapsis.
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Lu, Jinhua, Yitian Cai, Boon Heng Dennis Teo, Joo Guan Yeo i Junjie Chen. "Apoptotic nucleolus is recognized by complement C1q and degraded by C1 proteases". Journal of Immunology 196, nr 1_Supplement (1.05.2016): 48.6. http://dx.doi.org/10.4049/jimmunol.196.supp.48.6.
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Abstract In infections, complement C1q recognizes pathogen-congregated antibodies and elicits complement activation. Among endogenous ligands, C1q binds to DNA and apoptotic cells but whether C1q binds to nuclear DNA in apoptotic cells remains to be investigated. With UV-induced apoptosis, C1q initially bound to peripheral cellular regions in early apoptotic cells. By 6 hr, binding concentrated in the nuclei to the nucleolus but not the chromatins. When nucleoli were isolated from non-apoptotic cells, C1q also bound to these structures. By affinity chromatography, a number of nuclear proteins were found to bind to C1q including nucleophosmin 1 and nucleolin. In vivo, C1q exists as C1 complex (C1qC1r2C1s2) and C1q binding to ligands activates the C1r/C1s proteases. Incubation of nucleoli with C1 caused degradation of nucleolar proteins neucleolin and nucleophosmin 1. Cleavage of purified nucleophosin 1 by C1 is studied in details revealing three defined fragments of 11, 17 and 18 kDa, respectively. This was inhibited by C1 inhibitor. The nucleoli are abundant with autoantigens. C1q binding and C1r/C1s degradation of nucleolar antigens during cell apoptosis potentially reduce autoimmunity. These findings suggest broader substrate spectrum of C1 proteases and help understand why genetic C1q and C1r/C1s deficiencies cause systemic lupus erythematosus.
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Matsumori, Haruka, Kenji Watanabe, Hiroaki Tachiwana, Tomoko Fujita, Yuma Ito, Makio Tokunaga, Kumiko Sakata-Sogawa i in. "Ribosomal protein L5 facilitates rDNA-bundled condensate and nucleolar assembly". Life Science Alliance 5, nr 7 (23.03.2022): e202101045. http://dx.doi.org/10.26508/lsa.202101045.
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The nucleolus is the site of ribosome assembly and formed through liquid–liquid phase separation. Multiple ribosomal DNA (rDNA) arrays are bundled in the nucleolus, but the underlying mechanism and significance are unknown. In the present study, we performed high-content screening followed by image profiling with the wndchrm machine learning algorithm. We revealed that cells lacking a specific 60S ribosomal protein set exhibited common nucleolar disintegration. The depletion of RPL5 (also known as uL18), the liquid–liquid phase separation facilitator, was most effective, and resulted in an enlarged and un-separated sub-nucleolar compartment. Single-molecule tracking analysis revealed less-constrained mobility of its components. rDNA arrays were also unbundled. These results were recapitulated by a coarse-grained molecular dynamics model. Transcription and processing of ribosomal RNA were repressed in these aberrant nucleoli. Consistently, the nucleoli were disordered in peripheral blood cells from a Diamond–Blackfan anemia patient harboring a heterozygous, large deletion in RPL5. Our combinatorial analyses newly define the role of RPL5 in rDNA array bundling and the biophysical properties of the nucleolus, which may contribute to the etiology of ribosomopathy.
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Ma, Hanhui, i Thoru Pederson. "Nucleophosmin Is a Binding Partner of Nucleostemin in Human Osteosarcoma Cells". Molecular Biology of the Cell 19, nr 7 (lipiec 2008): 2870–75. http://dx.doi.org/10.1091/mbc.e08-02-0128.
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Nucleostemin (NS) is expressed in the nucleoli of adult and embryonic stem cells and in many tumors and tumor-derived cell lines. In coimmunoprecipitation experiments, nucleostemin is recovered with the tumor suppressor p53, and more recently we have demonstrated that nucleostemin exerts its role in cell cycle progression via a p53-dependent pathway. Here, we report that in human osteosarcoma cells, nucleostemin interacts with nucleophosmin, a nucleolar protein believed to possess oncogenic potential. Nucleostemin (NS) and nucleophosmin (NPM) displayed an extremely high degree of colocalization in the granular component of the nucleolus during interphase, and both proteins associated with prenucleolar bodies in late mitosis before the reformation of nucleoli. Coimmunoprecipitation experiments revealed that NS and NPM co-reside in complexes, and yeast two-hybrid experiments confirmed that they are interactive proteins, revealing the NPM-interactive region to be the 46-amino acid N-terminal domain of NS. In bimolecular fluorescence complementation studies, bright nucleolar signals were observed, indicating that these two proteins directly interact in the nucleolus in vivo. These results support the notion that cell cycle regulatory proteins congress and interact in the nucleolus, adding to the emerging concept that this nuclear domain has functions beyond ribosome production.
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Belagal, Praveen, Christophe Normand, Ashutosh Shukla, Renjie Wang, Isabelle Léger-Silvestre, Christophe Dez, Purnima Bhargava i Olivier Gadal. "Decoding the principles underlying the frequency of association with nucleoli for RNA polymerase III–transcribed genes in budding yeast". Molecular Biology of the Cell 27, nr 20 (15.10.2016): 3164–77. http://dx.doi.org/10.1091/mbc.e16-03-0145.
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The association of RNA polymerase III (Pol III)–transcribed genes with nucleoli seems to be an evolutionarily conserved property of the spatial organization of eukaryotic genomes. However, recent studies of global chromosome architecture in budding yeast have challenged this view. We used live-cell imaging to determine the intranuclear positions of 13 Pol III–transcribed genes. The frequency of association with nucleolus and nuclear periphery depends on linear genomic distance from the tethering elements—centromeres or telomeres. Releasing the hold of the tethering elements by inactivating centromere attachment to the spindle pole body or changing the position of ribosomal DNA arrays resulted in the association of Pol III–transcribed genes with nucleoli. Conversely, ectopic insertion of a Pol III–transcribed gene in the vicinity of a centromere prevented its association with nucleolus. Pol III–dependent transcription was independent of the intranuclear position of the gene, but the nucleolar recruitment of Pol III–transcribed genes required active transcription. We conclude that the association of Pol III–transcribed genes with the nucleolus, when permitted by global chromosome architecture, provides nucleolar and/or nuclear peripheral anchoring points contributing locally to intranuclear chromosome organization.
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Vieira, Rita, Álvaro Queiroz, Leonor Morais, Augusta Barão, T. Mello-Sampayo i Wanda S. Viegas. "1R chromosome nucleolus organizer region activation by 5-azacytidine in wheat × rye hybrids". Genome 33, nr 5 (1.10.1990): 707–12. http://dx.doi.org/10.1139/g90-106.
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Nucleolar activity was studied in several lines of Triticum aestivum cv. Chinese Spring, Triticum turgidum cv. Durum, and F1 hybrids from euploid and aneuploid lines of T. aestivum and Secale cereale cv. Centeio do Alto, in cells from root tips of seeds germinated in water or in 5-azacytidine. 5-Azacytidine, an analog of cytidine modified in the 5 position of the pyrimidine ring, inhibits DNA methylation. By using silver staining to determine the number of nucleolus organizer regions and the average number of nucleoli per root-tip cell from seeds germinated in both situations, it became apparent that the presence of 5-azacytidine during germination allowed for the expression of the nucleolus organizer region locus belonging to the rye genome, in contrast to the usual observed cytological absence of the rye nucleolus organizer region in wheat–rye hybrids. It is suggested that wheat nucleolar dominance in wheat–rye hybrids is mainly a consequence of methylation of rRNA genes or its regulators located on the 1R chromosome of rye.Key words: 1R nucleolar organizer, wheat–rye hybrids, methylation, Ag-NOR.
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Lee, Li-Wei, Chi-Chang Lee, Chi-Ruei Huang i Szecheng J. Lo. "The Nucleolus ofCaenorhabditis elegans". Journal of Biomedicine and Biotechnology 2012 (2012): 1–11. http://dx.doi.org/10.1155/2012/601274.
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Nucleolar size and appearance correlate with ribosome biogenesis and cellular activity. The mechanisms underlying changes in nucleolar appearance and regulation of nucleolar size that occur during differentiation and cell cycle progression are not well understood.Caenorhabditis elegansprovides a good model for studying these processes because of its small size and transparent body, well-characterized cell types and lineages, and because its cells display various sizes of nucleoli. This paper details the advantages of usingC. elegansto investigate features of the nucleolus during the organism's development by following dynamic changes in fibrillarin (FIB-1) in the cells of early embryos and aged worms. This paper also illustrates the involvement of thencl-1gene and other possible candidate genes in nucleolar-size control. Lastly, we summarize the ribosomal proteins involved in life span and innate immunity, and those homologous genes that correspond to human disorders of ribosomopathy.
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Kim, S. H., E. V. Ryabov, J. W. S. Brown i M. Taliansky. "Involvement of the nucleolus in plant virus systemic infection". Biochemical Society Transactions 32, nr 4 (1.08.2004): 557–60. http://dx.doi.org/10.1042/bst0320557.
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The nucleolus is a prominent subnuclear domain and is classically regarded as the site of transcription of rRNA, processing of the precursor rRNAs and biogenesis of pre-ribosomal particles. In addition to these traditionally recognized activities, the nucleolus also participates in many other aspects of cell function. The umbravirus-encoded ORF3 protein is a multifunctional RNA-binding protein involved in long-distance RNA movement, and protection of viral RNA from RNase attack, including possibly small interfering RNA-guided RNA silencing. In addition to its presence in cytoplasmic ribonucleoprotein particles containing viral RNA, the umbraviral ORF3 protein accumulates in nuclei, preferentially targeting nucleoli. The ORF3 protein domains involved in the localization of the protein to the nucleolus were identified. Functional analysis of the mutants revealed the correlation between the ORF3 protein nucleolar localization and its ability to form the cytoplasmic ribonucleoprotein particles and transport viral RNA long distances via the phloem. Possible mechanisms of the nucleolar involvement in systemic virus infection are discussed.
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BratuliĆ, M., Ž. GrabareviĆ, B. ArtukoviĆ i D. Capak. "Number of Nucleoli and Nucleolar Organizer Regions per Nucleus and Nucleolus — Prognostic Value in Canine Mammary Tumors". Veterinary Pathology 33, nr 5 (wrzesień 1996): 527–32. http://dx.doi.org/10.1177/030098589603300507.
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Twenty-eight canine mammary tumors were evaluated for histopathologic classification as recommended by the World Health Organization and silver-binding nucleolar organizer region (AgNOR) and nucleolus counts. Samples of surgically excised tumors and tumors taken at necropsy were fixed in neutral formalin, embedded in paraffin, and cut into 1-3-μm-thick sections. Two sections were taken from each tumor: one was stained with hematoxylin and eosin and the other was treated with the silver staining technique for the demonstration of AgNORs. After histopathologic classification, the number of nucleoli and the number of AgNORs/nucleus and AgNORs/nucleolus were determined. Statistical analysis (Student's t-test) showed a significant difference in the mean number of nucleoli ( P < 0.005), mean number of AgNORs/nucleolus ( P < 0.001), and mean number of AgNORs/nucleus ( P < 0.005) between benign and malignant canine mammary tumors. There was no significant differences between metastatic and nonmetastatic malignant tumors.
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Coleman, Jack, Hilary Cox, Zaiguo Li, Praveen Pande, Dee Shen, Divina Gatica i Wayne F. Patton. "Red/green Dual Fluorescence Detection of Both the Nucleus and Nucleolus in Living Cells". Microscopy Today 17, nr 4 (26.06.2009): 18–21. http://dx.doi.org/10.1017/s1551929509000066.
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The nucleolus represents a highly dynamic nuclear domain arising from an equilibrium between the level of ribosomal RNA synthesis and the efficiency of ribosomal RNA processing [1, 2]. Although the nucleolus is primarily associated with ribosome biogenesis, several lines of evidence now demonstrate that it has additional functions, such as regulation of mitosis, cell-cycle progression and proliferation, many forms of stress response, and biogenesis of multiple ribonucleoprotein particles. Ribosome biogenesis is regulated throughout interphase and ceases during mitosis (Figure 1). Thus, there is a direct relationship between cell growth and nucleolar activities. Nucleoli are well known to be dramatically modified in cancer cells. Additionally, a large number of key proteins from both DNA- and RNA-containing viruses are localized in the nucleolus, including the human immunodeficiency virus (HIV)-1 Rev and Tat proteins. Targeting of viral proteins to the nucleolus not only facilitates virus replication, but may also be required for pathogenic processes. The nucleolus can also be considered a sensor of stress due to the redistribution of the ribosomal proteins in the nucleoplasm through its disruption.
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Deltour, R., i T. de Barsy. "Nucleolar activation and vacuolation in embryo radicle cells during early germination". Journal of Cell Science 76, nr 1 (1.06.1985): 67–83. http://dx.doi.org/10.1242/jcs.76.1.67.
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The activation of the nucleolus of primary root cells of Sinapis alba embryos during the first 72 h of germination was monitored by autoradiographic, ultrastructural and microstereological methods. Autoradiographs showed that within 48 h, the nucleolus progressively resumed the capacity to synthesize pre-rRNA molecules at a high rate. In quiescent embryos the nucleolus was small, compact and composed of mixed granular and fibrillar components. Within the first 6 h of germination a strong nucleolar vacuolation occurred, accompanied by a decrease in the volume of the nucleolus and a concomitant high loss of its ribonucleoproteins (RNPs). From 6 to 24 h, nucleolar vacuolation decreased to reach a stable level. During this last period the volume of the nucleolus increased by the accumulation of the fibrillar component resulting from a slow pre-rRNA processing. At 24 h the nucleolus presented a predominantly fibrillar texture. After 24 h, nucleolus growth continued but was due to the accumulation of the granular component, indicating that pre-rRNA processing occurred at a higher rate than during the first day of germination. From 48 h the nucleolus was composed of well-delineated granular and fibrillar areas. Dense nucleolus-associated chromatin as well as fibrillar centres were always observed during the whole period of observation. In addition, previous studies on the nucleolus of radicle cells of Zea mays embryo during early germination were completed by studying changes in the nucleolar volume and in the density of pre-ribosomal subunits of the granular component. On the basis of the data obtained with both species we suggest that a possible function for the nucleolar vacuoles is the increase in the nucleolus-nucleoplasm exchange interface in response to a rapid increase in the output of nucleolar RNPs. The nucleolar growth pattern during early germination is also discussed.
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Pendle, Alison F., Gillian P. Clark, Reinier Boon, Dominika Lewandowska, Yun Wah Lam, Jens Andersen, Matthias Mann, Angus I. Lamond, John W. S. Brown i Peter J. Shaw. "Proteomic Analysis of the Arabidopsis Nucleolus Suggests Novel Nucleolar Functions". Molecular Biology of the Cell 16, nr 1 (styczeń 2005): 260–69. http://dx.doi.org/10.1091/mbc.e04-09-0791.
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The eukaryotic nucleolus is involved in ribosome biogenesis and a wide range of other RNA metabolism and cellular functions. An important step in the functional analysis of the nucleolus is to determine the complement of proteins of this nuclear compartment. Here, we describe the first proteomic analysis of plant (Arabidopsis thaliana) nucleoli, in which we have identified 217 proteins. This allows a direct comparison of the proteomes of an important nuclear structure between two widely divergent species: human and Arabidopsis. The comparison identified many common proteins, plant-specific proteins, proteins of unknown function found in both proteomes, and proteins that were nucleolar in plants but nonnucleolar in human. Seventy-two proteins were expressed as GFP fusions and 87% showed nucleolar or nucleolar-associated localization. In a striking and unexpected finding, we have identified six components of the postsplicing exon-junction complex (EJC) involved in mRNA export and nonsense-mediated decay (NMD)/mRNA surveillance. This association was confirmed by GFP-fusion protein localization. These results raise the possibility that in plants, nucleoli may have additional functions in mRNA export or surveillance.
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Chen, Danyang, i Sui Huang. "Nucleolar Components Involved in Ribosome Biogenesis Cycle between the Nucleolus and Nucleoplasm in Interphase Cells". Journal of Cell Biology 153, nr 1 (2.04.2001): 169–76. http://dx.doi.org/10.1083/jcb.153.1.169.
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We examined the mobilities of nucleolar components that act at various steps of the ribosome biogenesis pathway. Fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) analyses demonstrate that factors involved in rRNA transcription (upstream-binding factor [UBF]), processing (nucleolin, fibrillarin, and RNase MRP subunits, Rpp29), and ribosome assembly (B23) exchange rapidly between the nucleoplasm and nucleolus. In contrast, the mobilities of ribosomal subunit proteins (S5, L9) are much slower. Selective inhibition of RNA polymerase I transcription does not prevent the exchanges but influences the rates of exchange differentially for different nucleolar components. These findings suggest that the rapid exchange of nucleolar components between the nucleolus and nucleoplasm may represent a new level of regulation for rRNA synthesis. The different dynamic properties of proteins involved in different steps of ribosome biogenesis imply that the nucleolar association of these proteins is due to their specific functional roles rather than simply their specific nucleolar-targeting events.
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van Koningsbruggen, Silvana, Marek Gierliński, Pietá Schofield, David Martin, Geoffey J. Barton, Yavuz Ariyurek, Johan T. den Dunnen i Angus I. Lamond. "High-Resolution Whole-Genome Sequencing Reveals That Specific Chromatin Domains from Most Human Chromosomes Associate with Nucleoli". Molecular Biology of the Cell 21, nr 21 (listopad 2010): 3735–48. http://dx.doi.org/10.1091/mbc.e10-06-0508.
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The nuclear space is mostly occupied by chromosome territories and nuclear bodies. Although this organization of chromosomes affects gene function, relatively little is known about the role of nuclear bodies in the organization of chromosomal regions. The nucleolus is the best-studied subnuclear structure and forms around the rRNA repeat gene clusters on the acrocentric chromosomes. In addition to rDNA, other chromatin sequences also surround the nucleolar surface and may even loop into the nucleolus. These additional nucleolar-associated domains (NADs) have not been well characterized. We present here a whole-genome, high-resolution analysis of chromatin endogenously associated with nucleoli. We have used a combination of three complementary approaches, namely fluorescence comparative genome hybridization, high-throughput deep DNA sequencing and photoactivation combined with time-lapse fluorescence microscopy. The data show that specific sequences from most human chromosomes, in addition to the rDNA repeat units, associate with nucleoli in a reproducible and heritable manner. NADs have in common a high density of AT-rich sequence elements, low gene density and a statistically significant enrichment in transcriptionally repressed genes. Unexpectedly, both the direct DNA sequencing and fluorescence photoactivation data show that certain chromatin loci can specifically associate with either the nucleolus, or the nuclear envelope.
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Dousset, Thibaut, Chen Wang, Céline Verheggen, Danyang Chen, Danièle Hernandez-Verdun i Sui Huang. "Initiation of Nucleolar Assembly Is Independent of RNA Polymerase I Transcription". Molecular Biology of the Cell 11, nr 8 (sierpień 2000): 2705–17. http://dx.doi.org/10.1091/mbc.11.8.2705.
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This report examines the distribution of an RNA polymerase I transcription factor (upstream binding factor; UBF), pre-rRNA processing factors (nucleolin and fibrillarin), and pre-rRNAs throughout mitosis and postmitotic nucleologenesis in HeLa cells. The results demonstrate that nucleolin, fibrillarin, and pre-rRNAs synthesized at G2/M phase of the previous cell cycle are directly recruited to UBF-associated nucleolar organizer regions (NORs) early in telophase before chromosome decondensation. Unlike the fusion of prenucleolar bodies to the nucleoli, this early recruitment of processing factors and pre-rRNAs is independent of RNA polymerase I transcription. In the absence of polymerase I transcription, the initial localization of nucleolin, fibrillarin, and pre-rRNAs to UBF-associated NORs generates segregated mininucleoli that are similar to the larger ones observed in interphase cells grown under the same conditions. Pre-rRNAs are juxtaposed to UBF-nucleolin-fibrillarin caps that may represent the segregated nucleoli observed by electron microscopy. These findings lead to a revised model of nucleologenesis. We propose that nucleolar formation at the end of mitosis results from direct recruitment of processing factors and pre-rRNAs to UBF-associated NORs before or at the onset of rDNA transcription. This is followed by fusion of prepackaged prenucleolar bodies into the nucleolus. Pre-ribosomal ribonucleoproteins synthesized in the previous cell cycle may contribute to postmitotic nucleologenesis.
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Scherl, Alexander, Yohann Couté, Catherine Déon, Aleth Callé, Karine Kindbeiter, Jean-Charles Sanchez, Anna Greco, Denis Hochstrasser i Jean-Jacques Diaz. "Functional Proteomic Analysis of Human Nucleolus". Molecular Biology of the Cell 13, nr 11 (listopad 2002): 4100–4109. http://dx.doi.org/10.1091/mbc.e02-05-0271.
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The notion of a “plurifunctional” nucleolus is now well established. However, molecular mechanisms underlying the biological processes occurring within this nuclear domain remain only partially understood. As a first step in elucidating these mechanisms we have carried out a proteomic analysis to draw up a list of proteins present within nucleoli of HeLa cells. This analysis allowed the identification of 213 different nucleolar proteins. This catalog complements that of the 271 proteins obtained recently by others, giving a total of ∼350 different nucleolar proteins. Functional classification of these proteins allowed outlining several biological processes taking place within nucleoli. Bioinformatic analyses permitted the assignment of hypothetical functions for 43 proteins for which no functional information is available. Notably, a role in ribosome biogenesis was proposed for 31 proteins. More generally, this functional classification reinforces the plurifunctional nature of nucleoli and provides convincing evidence that nucleoli may play a central role in the control of gene expression. Finally, this analysis supports the recent demonstration of a coupling of transcription and translation in higher eukaryotes.
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Trumtel, Stéphanie, Isabelle Léger-Silvestre, Pierre-Emmanuel Gleizes, Frédéric Teulières i Nicole Gas. "Assembly and Functional Organization of the Nucleolus: Ultrastructural Analysis ofSaccharomyces cerevisiaeMutants". Molecular Biology of the Cell 11, nr 6 (czerwiec 2000): 2175–89. http://dx.doi.org/10.1091/mbc.11.6.2175.
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Using Saccharomyces cerevisiae strains with genetically modified nucleoli, we show here that changing parameters as critical as the tandem organization of the ribosomal genes and the polymerase transcribing rDNA, although profoundly modifying the position and the shape of the nucleolus, only partially alter its functional subcompartmentation. High-resolution morphology achieved by cryofixation, together with ultrastructural localization of nucleolar proteins and rRNA, reveals that the nucleolar structure, arising upon transcription of rDNA from plasmids by RNA polymerase I, is still divided in functional subcompartments like the wild-type nucleolus. rRNA maturation is restricted to a fibrillar component, reminiscent of the dense fibrillar component in wild-type cells; a granular component is also present, whereas no fibrillar center can be distinguished, which directly links this latter substructure to rDNA chromosomal organization. Although morphologically different, the mininucleoli observed in cells transcribing rDNA with RNA polymerase II also contain a fibrillar subregion of analogous function, in addition to a dense core of unknown nature. Upon repression of rDNA transcription in this strain or in an RNA polymerase I thermosensitive mutant, the nucleolar structure falls apart (in a reversible manner), and nucleolar constituents partially relocate to the nucleoplasm, indicating that rRNA is a primary determinant for the assembly of the nucleolus.
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Fulka, Helena, Jana Rychtarova i Pasqualino Loi. "The nucleolus-like and precursor bodies of mammalian oocytes and embryos and their possible role in post-fertilization centromere remodelling". Biochemical Society Transactions 48, nr 2 (22.04.2020): 581–93. http://dx.doi.org/10.1042/bst20190847.
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In nearly all somatic cells, the ribosome biosynthesis is a key activity. The same is true also for mammalian oocytes and early embryos. This activity is intimately linked to the most prominent nuclear organelles — the nucleoli. Interestingly, during a short period around fertilization, the nucleoli in oocytes and embryos transform into ribosome-biosynthesis-inactive structures termed nucleolus-like or nucleolus precursor bodies (NPBs). For decades, researchers considered these structures to be passive repositories of nucleolar proteins used by the developing embryo to rebuild fully functional, ribosome-synthesis competent nucleoli when required. Recent evidence, however, indicates that while these structures are unquestionably essential for development, the material is largely dispensable for the formation of active embryonic nucleoli. In this mini-review, we will describe some unique features of oocytes and embryos with respect to ribosome biogenesis and the changes in the structure of oocyte and embryonic nucleoli that reflect this. We will also describe some of the different approaches that can be used to study nucleoli and NPBs in embryos and discuss the different results that might be expected. Finally, we ask whether the main function of nucleolar precursor bodies might lie in the genome organization and remodelling and what the involved components might be.
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Panov, Konstantin I., Katherine Hannan, Ross D. Hannan i Nadine Hein. "The Ribosomal Gene Loci—The Power behind the Throne". Genes 12, nr 5 (18.05.2021): 763. http://dx.doi.org/10.3390/genes12050763.
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Nucleoli form around actively transcribed ribosomal RNA (rRNA) genes (rDNA), and the morphology and location of nucleolus-associated genomic domains (NADs) are linked to the RNA Polymerase I (Pol I) transcription status. The number of rDNA repeats (and the proportion of actively transcribed rRNA genes) is variable between cell types, individuals and disease state. Substantial changes in nucleolar morphology and size accompanied by concomitant changes in the Pol I transcription rate have long been documented during normal cell cycle progression, development and malignant transformation. This demonstrates how dynamic the nucleolar structure can be. Here, we will discuss how the structure of the rDNA loci, the nucleolus and the rate of Pol I transcription are important for dynamic regulation of global gene expression and genome stability, e.g., through the modulation of long-range genomic interactions with the suppressive NAD environment. These observations support an emerging paradigm whereby the rDNA repeats and the nucleolus play a key regulatory role in cellular homeostasis during normal development as well as disease, independent of their role in determining ribosome capacity and cellular growth rates.
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Waggoner, Shelly, i Peter Sarnow. "Viral Ribonucleoprotein Complex Formation and Nucleolar-Cytoplasmic Relocalization of Nucleolin in Poliovirus-Infected Cells". Journal of Virology 72, nr 8 (1.08.1998): 6699–709. http://dx.doi.org/10.1128/jvi.72.8.6699-6709.1998.
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ABSTRACT The poliovirus 3′ noncoding region (3′NCR) is involved in the efficient synthesis of viral negative-stranded RNA molecules. A strong interaction between a 105-kDa host protein and the wild-type 3′NCR, but not with a replication-defective mutant 3′NCR, was detected. This 105-kDa protein was identified as nucleolin which predominantly resides in the nucleolus and has been proposed to function in the folding of rRNA precursor molecules. A functional role for nucleolin in viral genome amplification was examined in a cell-free extract which has been shown to support the assembly of infectious virus from virion RNA. At early times of viral gene expression, extracts depleted of nucleolin produced less infectious virus than extracts depleted of fibrillarin, another resident of the nucleolus, indicating a functional role of nucleolin in the early stages of the viral life cycle in this in vitro system. Immunofluorescence analysis of uninfected and infected cells showed a nucleocytoplasmic relocalization of nucleolin, but not of fibrillarin, in poliovirus-infected cells. Relocalization of nucleolin was not simply a consequence of virally induced inhibition of translation or transcription, because inhibitors of translation or transcription did not induce nucleolar-cytoplasmic relocalization of nucleolin. These findings suggest a novel virus-induced mechanism by which certain nucleolar proteins are selectively redistributed in infected cells.
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Berry, Joel, Stephanie C. Weber, Nilesh Vaidya, Mikko Haataja i Clifford P. Brangwynne. "RNA transcription modulates phase transition-driven nuclear body assembly". Proceedings of the National Academy of Sciences 112, nr 38 (8.09.2015): E5237—E5245. http://dx.doi.org/10.1073/pnas.1509317112.
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Nuclear bodies are RNA and protein-rich, membraneless organelles that play important roles in gene regulation. The largest and most well-known nuclear body is the nucleolus, an organelle whose primary function in ribosome biogenesis makes it key for cell growth and size homeostasis. The nucleolus and other nuclear bodies behave like liquid-phase droplets and appear to condense from the nucleoplasm by concentration-dependent phase separation. However, nucleoli actively consume chemical energy, and it is unclear how such nonequilibrium activity might impact classical liquid–liquid phase separation. Here, we combine in vivo and in vitro experiments with theory and simulation to characterize the assembly and disassembly dynamics of nucleoli in early Caenorhabditis elegans embryos. In addition to classical nucleoli that assemble at the transcriptionally active nucleolar organizing regions, we observe dozens of “extranucleolar droplets” (ENDs) that condense in the nucleoplasm in a transcription-independent manner. We show that growth of nucleoli and ENDs is consistent with a first-order phase transition in which late-stage coarsening dynamics are mediated by Brownian coalescence and, to a lesser degree, Ostwald ripening. By manipulating C. elegans cell size, we change nucleolar component concentration and confirm several key model predictions. Our results show that rRNA transcription and other nonequilibrium biological activity can modulate the effective thermodynamic parameters governing nucleolar and END assembly, but do not appear to fundamentally alter the passive phase separation mechanism.
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Biggiogera, M., K. Burki, S. H. Kaufmann, J. H. Shaper, N. Gas, F. Amalric i S. Fakan. "Nucleolar distribution of proteins B23 and nucleolin in mouse preimplantation embryos as visualized by immunoelectron microscopy". Development 110, nr 4 (1.12.1990): 1263–70. http://dx.doi.org/10.1242/dev.110.4.1263.
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The ultrastructural distribution of proteins B23 and nucleolin in the nucleolus of mouse embryos from the zygote to the early blastocyst has been analyzed by means of specific antibodies and immunocytochemistry using colloidal gold complexes as markers. In parallel, silver staining of nucleoli was carried out on ultrathin sections. Our results show that the compact prenucleolar bodies at 1- and 2-cell stage as well as the compact residual fibrillar masses observed up to the morula stage, are labelled with the two antibodies. These masses, however, are not stained with silver up to the 4-cell stage. In well-developed nucleoli, the two antibodies co-localize in the dense fibrillar component (DFC) and the granular component (GC) while fibrillar centers (FCs) are devoid of label. On the contrary, silver staining occurs in the FCs and DFC but not in the GC. Our observations suggest that there is no direct relationship between the occurrence of silver staining and the distribution of protein B23 or nucleolin. Moreover, neither the localization of the two above proteins nor silver staining are unequivocally related to the nucleolar activity.
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Liu, Donghua, Wusheng Jiang, Wei Wang i Lin Zhai. "EVALUATION OF METAL ION TOXICITY ON ROOT TIP CELLS BY THE ALLIUM TEST". Israel Journal of Plant Sciences 43, nr 2 (13.05.1995): 125–33. http://dx.doi.org/10.1080/07929978.1995.10676598.
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The effects of different concentrations of eleven different metals (aluminum chloride, chromium nitrate and potassium dichromate, lead nitrate, copper sulfate, manganous sulfate, cobaltous nitrate, zinc sulfate, magnesium sulfate, nickel sulfate, cadmium chloride, and mercuric chloride) on cell division and nucleoli in root tip cells of Allium cepa were studied. The results showed that the metal ions could, in varying degrees, cause chromosome, nucleus, and nucleolus irregularities, including c-mitosis, chromosome bridges, chromosome stickiness, irregularly shaped nuclei, micronuclei, irregularly shaped nucleoli, some silver-stained material scattered in the nucleus, the weakening of silver-staining reaction at the periphery of the nucleolus, and the release of nucleolar material from the nucleus into the cytoplasm. The Allium test may be useful for the rapid screening of chemicals involved in environmental problems.
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Sakita-Suto, Shiho, Akifumi Kanda, Fumio Suzuki, Sunao Sato, Takashi Takata i Masaaki Tatsuka. "Aurora-B Regulates RNA Methyltransferase NSUN2". Molecular Biology of the Cell 18, nr 3 (marzec 2007): 1107–17. http://dx.doi.org/10.1091/mbc.e06-11-1021.
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Disassembly of the nucleolus during mitosis is driven by phosphorylation of nucleolar proteins. RNA processing stops until completion of nucleolar reformation in G1 phase. Here, we describe the RNA methyltransferase NSUN2, a novel substrate of Aurora-B that contains an NOL1/NOP2/sun domain. NSUN2 was concentrated in the nucleolus during interphase and was distributed in the perichromosome and cytoplasm during mitosis. Aurora-B phosphorylated NSUN2 at Ser139. Nucleolar proteins NPM1/nucleophosmin/B23 and nucleolin/C23 were associated with NSUN2 during interphase. In mitotic cells, association between NPM1 and NSUN2 was inhibited, but NSUN2-S139A was constitutively associated with NPM1. The Aurora inhibitor Hesperadin induced association of NSUN2 with NPM1 even in mitosis, despite the silver staining nucleolar organizer region disassembly. In vitro methylation experiments revealed that the Aurora-B-phosphorylation and the phosphorylation-mimic mutation (S139E) suppressed methyltransferase activities of NSUN2. These results indicate that Aurora-B participates to regulate the assembly of nucleolar RNA-processing machinery and the RNA methyltransferase activity of NSUN2 via phosphorylation at Ser139 during mitosis.
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Morimoto, Hiroyuki, Hirohiko Okamura i Tatsuji Haneji. "Interaction of Protein Phosphatase 1 Delta with Nucleolin in Human Osteoblastic Cells". Journal of Histochemistry & Cytochemistry 50, nr 9 (wrzesień 2002): 1187–93. http://dx.doi.org/10.1177/002215540205000905.
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We examined the expression and cytolocalization of the protein phosphatase type 1 delta (PP1δ) isoform and nucleolin in human osteoblastic MG63 and Saos-2 cells. Cellular fractionation of MG63 cells was done and protein was prepared from each fraction. Anti-nucleolin antibody interacted with the 100- and 95-kD proteins present in the whole-cell lysate. The 100-kD protein was detected in nuclear and nucleolar fractions. The 95-kD protein was detected in cytosolic and nucleoplasmic fractions. PP1δ and nucleolin were co-localized in the nucleolus in MG63 and Saos-2 cells revealed by an immunofluorescence method. PP1δ and nucleolin were also co-immunoprecipitated with anti-nucleolin and anti-PP1δ antibodies. In the actinomycin D-treated cells, the subcellular localization of PP1δ and nucleolin was changed. Expression of PP1δ was upregulated with actinomycin D treatment. The level of 100-kD protein did not change in the actinomycin D-treated cells. However, the level of the 95-kD band increased with actinomycin D treatment. These results indicate that PP1δ was associated with nucleolin in the nucleolus of MG63 and Saos-2 cells and that nucleolin is a possible candidate substrate for PP1δ.