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Artigos de revistas sobre o assunto "Meiosis transition"
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Soygur, B., R. G. Jaszczak, A. Fries, D. H. Nguyen, S. Malki, G. Hu, N. Demir, R. Arora e D. J. Laird. "Intercellular bridges coordinate the transition from pluripotency to meiosis in mouse fetal oocytes". Science Advances 7, n.º 15 (abril de 2021): eabc6747. http://dx.doi.org/10.1126/sciadv.abc6747.
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Meiosis is critical to generating oocytes and ensuring female fertility; however, the mechanisms regulating the switch from mitotic primordial germ cells to meiotic germ cells are poorly understood. Here, we implicate intercellular bridges (ICBs) in this state transition. We used three-dimensional in toto imaging to map meiotic initiation in the mouse fetal ovary and revealed a radial geometry of this transition that precedes the established anterior-posterior wave. Our studies reveal that appropriate timing of meiotic entry across the ovary and coordination of mitotic-meiotic transition within a cyst depend on the ICB componentTex14, which we show is required for functional cytoplasmic sharing. We find thatTex14mutants more rapidly attenuate the pluripotency transcriptDppa3upon meiotic initiation, andDppa3mutants undergo premature meiosis similar toTex14. Together, these results lead to a model that ICBs coordinate and buffer the transition from pluripotency to meiosis through dilution of regulatory factors.
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Cairo, Albert, Anna Vargova, Neha Shukla, Claudio Capitao, Pavlina Mikulkova, Sona Valuchova, Jana Pecinkova, Petra Bulankova e Karel Riha. "Meiotic exit in Arabidopsis is driven by P-body–mediated inhibition of translation". Science 377, n.º 6606 (5 de agosto de 2022): 629–34. http://dx.doi.org/10.1126/science.abo0904.
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Meiosis, at the transition between diploid and haploid life cycle phases, is accompanied by reprograming of cell division machinery and followed by a transition back to mitosis. We show that, in Arabidopsis , this transition is driven by inhibition of translation, achieved by a mechanism that involves processing bodies (P-bodies). During the second meiotic division, the meiosis-specific protein THREE-DIVISION MUTANT 1 (TDM1) is incorporated into P-bodies through interaction with SUPPRESSOR WITH MORPHOGENETIC EFFECTS ON GENITALIA 7 (SMG7). TDM1 attracts eIF4F, the main translation initiation complex, temporarily sequestering it in P-bodies and inhibiting translation. The failure of tdm1 mutants to terminate meiosis can be overcome by chemical inhibition of translation. We propose that TDM1-containing P-bodies down-regulate expression of meiotic transcripts to facilitate transition of cell fates to postmeiotic gametophyte differentiation.
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Hayashi, Aki, Haruhiko Asakawa, Tokuko Haraguchi e Yasushi Hiraoka. "Reconstruction of the Kinetochore during Meiosis in Fission Yeast Schizosaccharomyces pombe". Molecular Biology of the Cell 17, n.º 12 (dezembro de 2006): 5173–84. http://dx.doi.org/10.1091/mbc.e06-05-0388.
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During the transition from mitosis to meiosis, the kinetochore undergoes significant reorganization, switching from a bipolar to a monopolar orientation. To examine the centromere proteins that are involved in fundamental reorganization in meiosis, we observed the localization of 22 mitotic and 2 meiotic protein components of the kinetochore during meiosis in living cells of the fission yeast. We found that the 22 mitotic proteins can be classified into three groups: the Mis6-like group, the NMS (Ndc80-Mis12-Spc7) group, and the DASH group, based on their meiotic behavior. Mis6-like group proteins remain at the centromere throughout meiosis. NMS group proteins disappear from the centromere at the onset of meiosis and reappear at the centromere in two steps in late prophase. DASH group proteins appear shortly before metaphase of meiosis I. These observations suggest that Mis6-like group proteins constitute the structural basis of the centromere and that the NMS and DASH group proteins reassemble to establish the functional metaphase kinetochore. On the other hand, the meiosis-specific protein Moa1, which plays an important role in forming the meiotic monopolar kinetochore, is loaded onto the centromere significantly earlier than the NMS group, whereas another meiosis-specific protein, Sgo1, is loaded at times similar to the NMS group.
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Zhang, Xingxia, Ming Li, Xiaohua Jiang, Hui Ma, Suixing Fan, Yang Li, Changping Yu et al. "Nuclear translocation of MTL5 from cytoplasm requires its direct interaction with LIN9 and is essential for male meiosis and fertility". PLOS Genetics 17, n.º 8 (13 de agosto de 2021): e1009753. http://dx.doi.org/10.1371/journal.pgen.1009753.
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Meiosis is essential for the generation of gametes and sexual reproduction, yet the factors and underlying mechanisms regulating meiotic progression remain largely unknown. Here, we showed that MTL5 translocates into nuclei of spermatocytes during zygotene-pachytene transition and ensures meiosis advances beyond pachytene stage. MTL5 shows strong interactions with MuvB core complex components, a well-known transcriptional complex regulating mitotic progression, and the zygotene-pachytene transition of MTL5 is mediated by its direct interaction with the component LIN9, through MTL5 C-terminal 443–475 residues. Male Mtl5c-mu/c-mu mice expressing the truncated MTL5 (p.Ser445Arg fs*3) that lacks the interaction with LIN9 and is detained in cytoplasm showed male infertility and spermatogenic arrest at pachytene stage, same as that of Mtl5 knockout mice, indicating that the interaction with LIN9 is essential for the nuclear translocation and function of MTL5 during meiosis. Our data demonstrated MTL5 translocates into nuclei during the zygotene-pachytene transition to initiate its function along with the MuvB core complex in pachytene spermatocytes, highlighting a new mechanism regulating the progression of male meiosis.
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Bogdanov, Yuri. "Why is meiosis different from mitosis". Priroda, n.º 11 (2024): 18. https://doi.org/10.7868/s0032874x24110021.
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Meiosis was existing already in the last eukaryotic common ancestor (LECA). During evolution and transition from the first eukaryotic ancestor to LECA, a whole complex of genes was formed in the genome of the latter (about 300 genes), which provided the process of meiotic division. This is only a few percent of the genome, but these genes significantly changed the course of cell division, and meiosis arose. The paper describes the features of meiosis and possible ways of its formation.
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LeMaire-Adkins, Renée, Kristi Radke e Patricia A. Hunt. "Lack of Checkpoint Control at the Metaphase/Anaphase Transition: A Mechanism of Meiotic Nondisjunction in Mammalian Females". Journal of Cell Biology 139, n.º 7 (29 de dezembro de 1997): 1611–19. http://dx.doi.org/10.1083/jcb.139.7.1611.
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A checkpoint mechanism operates at the metaphase/anaphase transition to ensure that a bipolar spindle is formed and that all the chromosomes are aligned at the spindle equator before anaphase is initiated. Since mistakes in the segregation of chromosomes during meiosis have particularly disastrous consequences, it seems likely that the meiotic cell division would be characterized by a stringent metaphase/ anaphase checkpoint. To determine if the presence of an unaligned chromosome activates the checkpoint and delays anaphase onset during mammalian female meiosis, we investigated meiotic cell cycle progression in murine oocytes from XO females and control siblings. Despite the fact that the X chromosome failed to align at metaphase in a significant proportion of cells, we were unable to detect a delay in anaphase onset. Based on studies of cell cycle kinetics, the behavior and segregation of the X chromosome, and the aberrant behavior and segregation of autosomal chromosomes in oocytes from XO females, we conclude that mammalian female meiosis lacks chromosome-mediated checkpoint control. The lack of this control mechanism provides a biological explanation for the high incidence of meiotic nondisjunction in the human female. Furthermore, since available evidence suggests that a stringent checkpoint mechanism operates during male meiosis, the lack of a comparable checkpoint in females provides a reason for the difference in the error rate between oogenesis and spermatogenesis.
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Lin, T. Y., S. Viswanathan, C. Wood, P. G. Wilson, N. Wolf e M. T. Fuller. "Coordinate developmental control of the meiotic cell cycle and spermatid differentiation in Drosophila males". Development 122, n.º 4 (1 de abril de 1996): 1331–41. http://dx.doi.org/10.1242/dev.122.4.1331.
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Wild-type function of four Drosophila genes, spermatocyte arrest, cannonball, always early and meiosis I arrest, is required both for cell-cycle progression through the G2/M transition of meiosis I in males and for onset of spermatid differentiation. In males mutant for any one of these meiotic arrest genes, mature primary spermatocytes with partially condensed chromosomes accumulate and postmeiotic cells are lacking. The arrest in cell-cycle progression occurs prior to degradation of cyclin A protein. The block in spermatogenesis in these mutants is not simply a secondary consequence of meiotic cell-cycle arrest, as spermatid differentiation proceeds in males mutant for the cell cycle activating phosphatase twine. Instead, the arrest of both meiosis and spermiogenesis suggests a control point that may serve to coordinate the male meiotic cell cycle with the spermatid differentiation program. The phenotype of the Drosophila meiotic arrest mutants is strikingly similar to the histopathological features of meiosis I maturation arrest infertility in human males, suggesting that the control point may be conserved from flies to man.
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Guan, Yongjuan, N. Adrian Leu, Jun Ma, Lukáš Chmátal, Gordon Ruthel, Jordana C. Bloom, Michael A. Lampson, John C. Schimenti, Mengcheng Luo e P. Jeremy Wang. "SKP1 drives the prophase I to metaphase I transition during male meiosis". Science Advances 6, n.º 13 (março de 2020): eaaz2129. http://dx.doi.org/10.1126/sciadv.aaz2129.
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The meiotic prophase I to metaphase I (PI/MI) transition requires chromosome desynapsis and metaphase competence acquisition. However, control of these major meiotic events is poorly understood. Here, we identify an essential role for SKP1, a core subunit of the SKP1–Cullin–F-box (SCF) ubiquitin E3 ligase, in the PI/MI transition. SKP1 localizes to synapsed chromosome axes and evicts HORMAD proteins from these regions in meiotic spermatocytes. SKP1-deficient spermatocytes display premature desynapsis, precocious pachytene exit, loss of PLK1 and BUB1 at centromeres, but persistence of HORMAD, γH2AX, RPA2, and MLH1 in diplonema. Strikingly, SKP1-deficient spermatocytes show sharply reduced MPF activity and fail to enter MI despite treatment with okadaic acid. SKP1-deficient oocytes exhibit desynapsis, chromosome misalignment, and progressive postnatal loss. Therefore, SKP1 maintains synapsis in meiosis of both sexes. Furthermore, our results support a model where SKP1 functions as the long-sought intrinsic metaphase competence factor to orchestrate MI entry during male meiosis.
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Farini, Donatella, e Massimo De Felici. "The Beginning of Meiosis in Mammalian Female Germ Cells: A Never-Ending Story of Intrinsic and Extrinsic Factors". International Journal of Molecular Sciences 23, n.º 20 (20 de outubro de 2022): 12571. http://dx.doi.org/10.3390/ijms232012571.
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Meiosis is the unique division of germ cells resulting in the recombination of the maternal and paternal genomes and the production of haploid gametes. In mammals, it begins during the fetal life in females and during puberty in males. In both cases, entering meiosis requires a timely switch from the mitotic to the meiotic cell cycle and the transition from a potential pluripotent status to meiotic differentiation. Revealing the molecular mechanisms underlying these interrelated processes represents the essence in understanding the beginning of meiosis. Meiosis facilitates diversity across individuals and acts as a fundamental driver of evolution. Major differences between sexes and among species complicate the understanding of how meiosis begins. Basic meiotic research is further hindered by a current lack of meiotic cell lines. This has been recently partly overcome with the use of primordial-germ-cell-like cells (PGCLCs) generated from pluripotent stem cells. Much of what we know about this process depends on data from model organisms, namely, the mouse; in mice, the process, however, appears to differ in many aspects from that in humans. Identifying the mechanisms and molecules controlling germ cells to enter meiosis has represented and still represents a major challenge for reproductive medicine. In fact, the proper execution of meiosis is essential for fertility, for maintaining the integrity of the genome, and for ensuring the normal development of the offspring. The main clinical consequences of meiotic defects are infertility and, probably, increased susceptibility to some types of germ-cell tumors. In the present work, we report and discuss data mainly concerning the beginning of meiosis in mammalian female germ cells, referring to such process in males only when pertinent. After a brief account of this process in mice and humans and an historical chronicle of the major hypotheses and progress in this topic, the most recent results are reviewed and discussed.
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Hiraoka, Daisaku, Enako Hosoda, Kazuyoshi Chiba e Takeo Kishimoto. "SGK phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation at the meiotic G2/M transition". Journal of Cell Biology 218, n.º 11 (19 de setembro de 2019): 3597–611. http://dx.doi.org/10.1083/jcb.201812122.
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The kinase cyclin B–Cdk1 complex is a master regulator of M-phase in both mitosis and meiosis. At the G2/M transition, cyclin B–Cdk1 activation is initiated by a trigger that reverses the balance of activities between Cdc25 and Wee1/Myt1 and is further accelerated by autoregulatory loops. In somatic cell mitosis, this trigger was recently proposed to be the cyclin A–Cdk1/Plk1 axis. However, in the oocyte meiotic G2/M transition, in which hormonal stimuli induce cyclin B–Cdk1 activation, cyclin A–Cdk1 is nonessential and hence the trigger remains elusive. Here, we show that SGK directly phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation in starfish oocytes. Upon hormonal stimulation of the meiotic G2/M transition, SGK is activated by cooperation between the Gβγ-PI3K pathway and an unidentified pathway downstream of Gβγ, called the atypical Gβγ pathway. These findings identify the trigger in oocyte meiosis and provide insights into the role and activation of SGK.
Teses / dissertações sobre o assunto "Meiosis transition"
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Connor, Colette. "Investigating the role of Cdc14 in the regulation of the meiosis I to meiosis II transition". Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/21086.
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Meiosis is a specialized cell division that produces haploid gametes from a diploid progenitor cell. It consists of one round of DNA replication followed by two consecutive rounds of chromosome segregation. Homologous chromosomes segregate in meiosis I and sister chromatids segregate in meiosis II. Failure to correctly regulate meiosis can result in aneuploidy, where daughter cells inherit an incorrect number of chromosomes. Aneuploidy is usually poorly tolerated in eukaryotes, and is associated with infertility, miscarriages and birth defects. At the meiosis I to meiosis II transition, DNA replication does not occur between chromosome segregation steps despite the need for Spindle Pole Bodies (SPBs) to be re-licensed in order to build meiosis II spindles. The mechanisms that make this distinction are not yet known. In budding yeast, the protein phosphatase Cdc14 is essential for the progression of cells into meiosis II. Cdc14 is sequestered for the majority of the cell cycle in the nucleolus by the inhibitor Cfi1/Net, and is only released in anaphase. We have observed Cdc14 localizing to and interacting with SPB components when nucleolar sequestration is inhibited. Through fluorescence microscopy and EM analysis, we have determined that Cdc14 is required for the re-duplication of SPBs after meiosis I. Our data implies a role for Cdc14 in the phospho-regulation of SPB half-bridge component Sfi1. Cdc14 is therefore essential for the relicensing of SPB duplication, a crucial step necessary to ensure accurate chromosome segregation in meiosis.
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Maier, Nolan Kenji Kwaisun. "Separase cleaves the kinetochore protein Meikin to direct the meiosis I/II transition". Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/130663.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, February, 2021Cataloged from the official PDF of thesis. "February 2021."
Includes bibliographical references.
To generate haploid gametes, meiotic cells must undergo two consecutive rounds of chromosome segregation without an intervening gap phase. Importantly, because homologous chromosomes are segregated in meiosis I, but sister chromatids are segregated in meiosis II, this requires a dramatic rewiring of the cell division machinery between the two divisions. How meiotic cells coordinate this rapid and substantial change to the cell division machinery is a central mystery at the heart of proper fertility and reproduction. Our work reveals a new paradigm that rewires key cell division processes at the meiosis I/II transition through the action of the protease Separase, which we demonstrate acts by cleaving the meiosis-specific kinetochore protein Meikin. Cleavage of Separase substrates such as cohesin results in their potent and complete inactivation.
In contrast, we find that Separase cleavage of Meikin acts as a molecular "scalpel," providing an elegant mechanism to precisely and irreversibly modulate Meikin activity between the two meiotic divisions without inactivating Meikin function. Our results demonstrate that the C-terminal Meikin cleavage product generated by Separase proteolysis retains substantial activity such that it localizes to kinetochores, binds to Plk1 kinase, and promotes downstream activities such as the cleavage of the meiosis-specific cohesin subunit Rec8, similar to full length Meikin. Importantly, we demonstrate that both the failure to cleave Meikin or the complete inactivation of Meikin at the meiosis I/II transition each result in dramatic defects in the proper execution of meiosis II. Our functional analysis in mouse oocytes demonstrates that precise Meikin cleavage is critical to differentially control meiosis I and II.
Thus, in contrast to previous models, Meikin is not just a regulator of meiosis I-specific activities, but differentially coordinates chromosome segregation across both meiotic divisions. Our discovery of Meikin as a new substrate for Separase cleavage represents a novel mechanism for the regulatory control of the meiosis I/II transition.
by Nolan Kenji Kwaisun Maier.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Biology
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Whitfield, Zachary James. "A meiosis-specific form of the Anaphase Promoting Complex/Cyclosome regulates the oocyte-to-embryo transition in Drosophila". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83781.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references.
Cell cycle transitions during mitosis and meiosis must proceed in an irreversible manner. At the heart of this is the Anaphase Promoting Complex/Cyclosome (APC/C), an E3 ubiquitin ligase. The APC/C targets its substrates for degradation, and thus progresses the cell cycle irreversibly forward. Many substrates of the APC/C have been identified in mitosis, but how the APC/C regulates meiosis is less well understood. The Drosophila gene cortex encodes a female, meiosis-specific activator of the APC/C. We set out to identify specific substrates of APCCort both genetically and biochemically. A genetic screen identified five deficiencies that suppress an arrest caused by low APCCort activity. In some cases, these deficiencies could be narrowed to regions containing only a few genes. IP/mass-spectrometry was also performed to identify interactors of Cortex. One hit was Matrimony, a potent inhibitor of Polo kinase during prophase 1. Cort and Mtrm can interact directly in vitro, while a mitotic APC/C activator, fzy/cdc20, cannot. Mtrm proteins levels are drastically reduced upon completion of meiosis, and this reduction is dependent on cort. When expressed in cell culture, Cort causes a proteasome dependent decrease in Matrimony protein levels. Cort and Mtrm also interact genetically, and overexpression of Mtrm in the early embryo causes developmental defects in a subset of embryos. This work contributes to our understanding of the meiotic cell cycle and the specific regulation that distinguishes it from mitosis.
by Zachary James Whitfield.
Ph.D.
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Hazra, Ditipriya. "Insights into the control of mRNA decay by YTH proteins during the transition from meiosis to mitosis in yeasts". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX041.
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Aperçu du contrôle de la dégradation des ARNm par les protéines YTHpendant la transition de la méiose à la mitose chez les levures.Le cycle cellulaire est contrôlé par des processus complexes et interconnectés. Un gène est transcrit en ARNm qui est traduit en protéines mais de nombreux processus de régulation travaillent pour contrôler chaque étape de ce processus apparemment simple. Parmi ces points de contrôle, la régulation post-transcriptionnelle est importante, et la formation d'un complexe protéine-ARN peut diriger le destin cellulaire. Parmi ces protéines de liaison à l'ARN, les protéines contenant des domaines YTH n’ont été découvertes qu’à la fin des années 90. Les protéines contenant des domaines YTH sont abondantes chez les eucaryotes et absentes chez les procaryotes. Elles constituent la majorité des protéines « readers » capables de reconnaître spécifiquement la modification m6A. L’Homme possède cinq protéines YTH, YTHDF1-3, YTHDC1,2 (Hazra, D., C. Chapat, et Graille, M. (2019). Destin de l'ARNm de m6A : enchaînés au rythme par les protéines contenant de la YTH. , 10 (1), 49.). Bien qu'il soit évident que ces protéines contrôlent le destin cellulaire, la fonction de chaque protéine et son réseau d’interaction restent à élucider. Chez les levures, une seule protéine YTH est présente: Pho92 chez Saccharomyces cerevisiae et Mmi1 chez Schizosaccharomyces pombe. Hormis le domaine YTH, il n'y a pas d'homologie de séquence entre ces deux protéines mais leur fonction cellulaire est similaire.Il est bien établi que Mmi1 est responsable de la dégradation des transcrits spécifiques de la méiose au cours de la croissance végétative des cellules chez la levure S. pombe. Mmi1 forme un complexe stable avec une petite protéine, Erh1 (complexe Erh1-Mmi1 ou EMC). Le complexe EMC peut physiquement interagir avec la sous-unité Not1 du complexe CCR4-Not et la recruter pour la dégradation des ARNm contenant des motifs DSR (déterminant de l'élimination sélective). L'action de Mmi1 est à son tour régulée par une protéine possédant un domaine RRM, Mei2. Au cours de la méiose, Mei2, avec l’aide d’un lncRNA meiRNA, séquestre Mmi1 dans un point nucléaire, le rendant inactif et assurant la continuité de la méiose. Ces trois protéines, Mmi1-Erh1-Mei2, jouent un rôle clé dans la transition de la mitose vers la méiose.Chez S. cerevisiae, Pho92 est impliquée dans la dégradation des transcrits de PHO4, contribuant à la voie du métabolisme du phosphate, pendant la privation en phosphate et participe également à la dégradation des ARNm contenant les marques épitranscriptomiques de N6-méthyladénosine (m6A). Comme pour S. pombe Mmi1, Pho92 recrute le complexe CCR4-Not via une interaction physique avec Not1.Au cours de ma thèse, j'ai tenté d'élucider le rôle de ces deux protéines du domaine YTH de deux organismes modèles, S. cerevisiae et S. pombe, dans la dégradation de l'ARNm et la régulation du cycle cellulaire par des approches biochimiques et structurales.Pho92 de S. cerevisiae interagit physiquement avec Not1 du complexe CCR4-Not, nous avons pu déterminer les limites des domaines impliqués dans cette interaction. L’interaction entre ces deux protéines a été étudiée par anisotropie de fluorescence. Le complexe protéique a été purifié avec succès et des essais de cristallisation sont en cours.Chez S. pombe, la structure de Mei2-RRM3 a été résolue avec et sans ARN. Les propriétés de liaison à l'ARN de Mei2-RRM3 ont été étudiées par ITC. La structure de Erh1 a également été résolue révélant une organisation en homodimere. Nous avons montré que la formation de cet homodimere est important pour la fonction biologique de Mmi1. Des essais de co-cristallisation ont été réalisés avec de l'ARN et les protéines Mmi1 et Mei2, mais sans succès et nous avons obtenu des cristaux de Mmi1Insights into the control of mRNA decay by YTH proteinsduring the transition from meiosis to mitosis in yeasts.Keywords: Epitranscriptomics, mRNA decay, meiosis, multi-protein complexes, YTH domainCell cycle is controlled by multi-layered processes. A gene is transcribed in mRNA which is translated in proteins but innumerable regulation processes are working to control every step of this apparently simple process. Among these regulatory check points, post-transcriptional regulation is an important one, where formation of a protein-RNA complex may direct the cellular fate. Among these RNA binding proteins, YTH domain proteins are most novel, discovered in late 90s. YTH domain proteins are abundant in eukaryotes and absent in prokaryotes. YTH domain proteins constitute the majority of reader proteins that can specifically identify m6A modification. Human beings have five YTH domain proteins YTHDF1-3, YTHDC1-2 (Hazra, D., Chapat, C., & Graille, M. (2019). m6A mRNA Destiny: Chained to the rhYTHm by the YTH-Containing Proteins. Genes, 10(1), 49.). Although it is evident that these proteins are controlling cellular fate, the function of each protein and their network is yet to be elucidated. In yeast, there is only one YTH domain protein present: Pho92 in Saccharomyces cerevisiae and Mmi1 in Schizosaccharomyces pombe. Apart from the YTH domain there is no sequence homology between these two proteins but their cellular function is similar.It is well established that Mmi1 is responsible for degradation of meiosis specific transcripts during vegetative growth of the cell. Mmi1 forms a tight complex with a small protein, Erh1 (Erh1-Mmi1 complex or EMC). EMC can physically interact with Not1 of CCR4-Not complex and recruit it for degradation of DSR (determinant of selective removal) containing RNAs. The action of Mmi1 is in turn regulated by an RRM domain protein, Mei2. During meiosis, Mei2, along with a lncRNA meiRNA sequesters Mmi1 in a nuclear dot, rendering it inactive and ensuring smooth continuance of meiosis. These three proteins, Mmi1-Erh1-Mei2 play a key role in mitosis to meiosis switch.In S. cerevisiae, Pho92 is involved in the degradation of PHO4 transcripts contributing to phosphate metabolism pathway, during phosphate starvation and also participates in the degradation of mRNAs containing the N6-methyladenosine (m6A) epitranscriptomics marks. Similarly, to S. pombe Mmi1, Pho92 recruits CCR4-Not complex by physical interaction with Not1.During my PhD, I have tried to elucidate the role of these two YTH domain proteins from two model organisms, S. cerevisiae and S. pombe, in mRNA degradation and cell cycle regulation using biochemical and structural approaches.Pho92 of S. cerevisiae physically interacts with Not1 of CCR4-Not complex, we were able to determine the boundaries of this interaction. The interaction between these two proteins was studied by Fluorescence anisotropy. The protein complex was successfully purified and crystallization trials are ongoing.From S. pombe, structure of Mei2-RRM3 was solved with and without an RNA. RNA binding properties of Mei2-RRM3 was studied by ITC. The structure of Erh1 was also solved and we tried to elucidate its importance for biological function of Mmi1. A co-crystallization trial was performed with Mmi1-Mei2-RNA but it was unsuccessful and we ended up with Mmi1 crystals
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Detti, Mélanie. "Méthylation des adénosines (m6A) des ARN dans les cellules germinales et infertilité". Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ6044.
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La différenciation sexuelle est un mécanisme complexe, où une gonade indifférenciée, va se développer en testicule chez les mâles ou en ovaire chez les femelles. Le sexe chromosomique est à l'origine de la détermination sexuelle, en activant des voies de signalisation sexe-spécifique. Découvert en 1990, le gène SRY, présent sur le chromosome Y des mâles, est un gène qui a longtemps été décrit comme le régisseur de toute la différenciation sexuelle. En sa présence, les embryons XY se différencient en mâles, mais son absence est suffisante pour induire la différenciation femelle, « par défaut ». Or, la détermination du sexe est bien plus complexe, impliquant l'expression de nombreux gènes, dont les niveaux d'expression équilibrés activent la voie ovarienne et répriment simultanément la voie testiculaire ou vice versa. Le développement d'un ovaire ou d'un testicule repose sur la présence des cellules somatiques ainsi que des cellules germinales, les seules cellules capables de réaliser la méiose.La méiose, découvert en 1883, est également un événement dépendant de la détermination du sexe, étant donné qu'elle se produit pendant le développement embryonnaire chez la femelle, et en post-natal chez les mâles. Encore une fois, de nombreux gènes doivent être finement régulés pour l'initiation et le déroulement correct de la méiose. En effet, les cellules germinales prolifèrent activement, puis doivent perdre leur pluripotence et entrer en méiose chez les femelles, tandis qu'elles restent pluripotentes et rentrent en quiescence chez les mâles. Cette transition s'opère par un changement de programme génétique, qui n'est pas encore totalement compris.L'étude des différents acteurs régulant la différenciation sexuelle, autant au niveau somatique que germinale, est alors une priorité de mon équipe, spécialiste du développement gonadique embryonnaire.La méthylation en position 6 de l'adénine des molécules d'adénosine de l'ARN (m6A) est un mécanisme émergent et encore peu compris de la régulation de l'expression des gènes. Pourtant elle est la modification de l'ARN la plus courante et la plus conservée chez les eucaryotes, et son importance est soulignée par différentes pathologies résultant des dysfonctionnements de cette méthylation. A l'heure actuelle, elle est connue pour réguler des processus très variés comme des processus de métaboliques, de développement, de différenciation cellulaire ou de réponse au stress.C'est alors que nous avons décidé d'étudier le rôle de Wtap, un acteur du complexe de méthylation m6A, dans la détermination du sexe et la méiose. Mes recherches ont permis de comprendre dans un premier temps que Wtap est bien exprimé dans les différents types cellulaire de la gonade, et ce, pendant la fenêtre critique de la différenciation sexuelle. Dans un second temps, grâce à un modèle murin perte de fonction pour Wtap spécifiquement dans les cellules somatiques, nous avons pu montrer que ce gène est crucial pour la différenciation des cellules somatiques mâles et femelles. En effet, les cellules de Sertoli et de la granulosa semblent pour la majeure partie, bloquées dans un stade pré-cellules de soutient. Enfin, dans un dernier temps, cette fois ci avec un modèle murin permettant l'inactivation de Wtap dans les cellules germinales uniquement, nous avons également analysé une diminution de leur différenciation. Les cellules germinales ne sont plus totalement en capacité d'induire la méiose chez les femelles, et de rentrer en quiescence chez les mâles.Ces résultats indiquent que Wtap, est un acteur clé pour la régulation de la différenciation des cellules somatiques et germinales, autant chez le mâle que chez la femelleSexual differentiation is a complex mechanism where an undifferentiated gonad develops into a testis in males or an ovary in females. Chromosomal sex is at the origin of sexual determination, by activating sex-specific signaling pathways. Discovered in 1990, the Sry gene, found on the Y chromosome of males, has long been described as the regulator of all sexual differentiation. In its presence, XY embryos differentiate into males, but its absence is sufficient to induce female differentiation, “by default”. However, sex determination is far more complex, involving the expression of numerous genes, whose balanced expression levels activate the ovarian pathway and simultaneously repress the testicular pathway, or vice versa. The development of an ovary or testis relies on the presence of somatic cells as well as germ cells, the only cells capable of meiosis.Meiosis, discovered in 1883, is also a sex-determining event, as it occurs during embryonic development in females, and post-natal in males. Once again, many genes must be finely regulated for meiosis for correct initiation and progressing. Germ cells proliferate actively, then lose their pluripotency and enter meiosis in females, while they remain pluripotent and enter quiescence in males. This transition takes place by a change in the genetic program, which is not yet fully understood.The study of the various actors regulating sexual differentiation, at both somatic and germline levels, is therefore a priority for my team, which specializes in embryonic gonadal development.N6-methyladenosine (m6A) is an emerging and still poorly understood mechanism of gene expression regulation. Yet it is the most common and most conserved RNA modification in eukaryotes, and its importance is underlined by various pathologies resulting from dysfunctions of this methylation. It is currently known to regulate a wide variety of processes, including metabolism, development, cell differentiation and stress response.We therefore decided to investigate the role of Wtap, an actor in the m6A methylation complex, in sex determination and meiosis. Firstly, my research showed that Wtap is well expressed in different gonadal cell types during the critical window of sexual differentiation. Secondly, using a loss-of-function mouse model for Wtap specifically in somatic cells, we were able to show that this gene is crucial for the differentiation of male and female somatic cells. Indeed, most Sertoli and granulosa cells appear to be blocked in a pre-supporting state. Finally, using a mouse model in which Wtap is inactivated in germ cells only, we also analyzed a decrease in germ cell differentiation. Germ cells are no longer fully able to induce meiosis in females, and enter quiescence in males.These results indicate that Wtap is a key player in the regulation of somatic and germ cell differentiation in both males and females
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Terret, Marie-Emilie. "controle de la transition meiose I/meiose II et role de DOC1R au cours de l'arret CSF lors de la maturation meiotique chez la souris". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2004. http://tel.archives-ouvertes.fr/tel-00009435.
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La maturation méiotique des vertébrés diffère de la mitose par plusieurs aspects. J'ai étudié deux de ces particularités. 1) En méiose I, les chromosomes homologues sont ségrégés, en mitose, les chromatides sœurs sont séparées. En mitose, un mécanisme de contrôle bloque la cellule en métaphase en inhibant l'APC/C tant que tous les chromosomes ne sont pas correctement alignés sur le fuseau. En méiose I, des résultats contradictoires existent selon les espèces quant à l'existence d'un mécanisme de contrôle de ce type. J'ai montré que l'activité séparase (activité indirectement régulée par l'APC/C) est requise pour effectuer la transition métaphase/anaphase en méiose I, suggérant qu'un mécanisme de contrôle de ce type est requis chez la souris, organisme proche de l'homme. 2) A l'issue de la maturation méiotique, l'ovocyte reste bloqué en métaphase de méiose II en attendant la fécondation, alors que la mitose s'achève toujours. Ce blocage est dû à l'activité CSF et requiert la voie Mos/.../MAPK. J'ai montré que DOC1R, un nouveau substrat des MAPK, contrôle l'organisation des microtubules au cours de l'arrêt CSF. Ces résultats font évoluer la vision de l'arrêt CSF qui était considéré comme une voie linéaire aboutissant à la stabilisation du MPF. L'arrêt CSF est une voie non linéaire contrôlant aussi la morphologie de l'ovocyte.
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Morais, Pablo Abreu de. "Correlações e interações de longo alcance em meios desordenados: linhas costeiras e transição de Anderson". reponame:Repositório Institucional da UFC, 2012. http://www.repositorio.ufc.br/handle/riufc/12378.
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MORAIS, Pablo Abreu de. Correlações e interações de longo alcance em meios desordenados: linhas costeiras e transição de Anderson. 2012. 117 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012.Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-19T18:48:02Z No. of bitstreams: 1 2012_tese_pamorais.pdf: 35280964 bytes, checksum: f36822e135c7b0c6f6a09cfca085d2e4 (MD5)
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Many physical phenomena have strong dependence on the disorder of the medium in which they occur. The {it Anderson} theory localization, for example, states that the introduction of disorder in electronic systems can promote the metal-insulator transition, also known as {it Anderson} transition. However, for low dimensional systems, according to the same theory, any finite degree of uncorrelated disorder is able to promote the exponential localization of all electronic functions. The general {it Anderson} theory localization is violated when long-range correlations and long-range interactions are used. In this scenario, the metal-insulator transition also occurs for low dimensional systems. In network problems, the long-range connections are responsible for the short average distance between individuals belonging to the same social network. This phenomenon is popularly known as six degrees of separation. Furthermore, {it Kleinberg} showed that the introduction of a power-law distribution of long-range links in a network produces a minimum in the transmission time information from a source site to a target site network . In this thesis, we investigate how the long-range disorder changes the universality class of two mathematical models that represent the following physical problems: the erosion process in correlated landscapes and the delocalization-localization transition of the normal modes of a harmonic chain with long range connections restricted by a cost function. In the first model, we show that long-range spatial correlations in the geological properties of the coast, in the critical regime of our model, generates a spectrum of fractals shorelines whose fractal dimensions vary between {it D} = 1.33 and 1.00 when we vary the {it Hurst} exponent in the range $0< H <1$. Furthermore, when we use uncorrelated surfaces, the shoreline, for very intense sea erosion, are self-affine and belong to the same universality class of the interfaces described by the equation of {it Kardar-Parisi-Zhang} ({it KPZ}). In the second model, we show that long-range links in a chain harmonic inserted with a probability with decreasing size of the bond, $p sim r^{-alpha}$, restricted by a cost function proportional to chain length, promotes a delocalization-localization transition of the normal modes for the exponent $ alpha simeq 1.25$.
Muitos fenômenos físicos têm forte dependência da desordem do meio no qual ocorrem. A teoria de localização de Anderson, por exemplo, estabelece que a introdução de desordem em sistemas eletrônicos pode promover a transição metal-isolante, também conhecida como transição de Anderson. Contudo, para sistemas de baixa dimensionalidade, segundo essa mesma teoria, qualquer grau finito de desordem pode promover a localização exponencial de todas as funções eletrônicas. No entanto, foi mostrado que a teoria geral de localização de Anderson é violada quando correlações e interações de longo alcance são utilizadas. Nesse cenário, a transição metal-isolante ocorre também para sistemas de baixa dimensionalidade. Nos problemas relacionados com redes, as ligações de longo alcance são responsáveis pela pequena distância média entre indivíduos pertencentes à mesma rede social. Esse fenômeno é popularmente conhecido como os seis graus de separação. Além disso, Kleinberg mostrou que a introdução de uma distribuição em lei de potência de ligações de longo alcance em uma rede substrato gera um mínimo no tempo de envio de uma informação de um sítio fonte a um sítio alvo da rede. Nesta tese, investigamos como a desordem de longo alcance altera a classe de universalidade de dois modelos matemáticos que representam os seguintes problemas físicos: o processo de erosão na costa de paisagens correlacionadas e a transição deslocalização-localização dos modos normais de vibração de uma cadeia harmônica com ligações de longo alcance restritas por uma função custo. No primeiro modelo, mostramos que correlações espaciais de longo alcance nas propriedades geológicas da costa, no regime crítico do nosso modelo, gera um espectro de linhas costeiras fractais cujas dimensões fractais variam entre D=1.33 e 1.00 quando variamos o expoente de Hurst no intervalo 0< H < 1. Além disso, quando utilizamos superfícies não correlacionadas, as linha costeiras, para erosões marítimas muito intensas, são auto-afins e pertencem a mesma classe de universalidade das interfaces descritas pela equação de Kardar-Parisi-Zhang (KPZ). No segundo modelo, mostramos que ligações de longo alcance inseridas em uma cadeia harmônica com uma probabilidade decaindo com o tamanho da ligação, p ∼ r−α, restritas por uma função custo proporcional ao tamanho da cadeia, promovem uma transição deslocalização localização dos modos normais de vibração para o expoente α ≅ 1.25.
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Morais, Pablo Abreu de. "CorrelaÃÃes e interaÃÃes de longo alcance em meios desordenados: linhas costeiras e transiÃÃo de Anderson". Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=8649.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoMuitos fenÃmenos fÃsicos tÃm forte dependÃncia da desordem do meio no qual ocorrem. A teoria de localizaÃÃo de Anderson, por exemplo, estabelece que a introduÃÃo de desordem em sistemas eletrÃnicos pode promover a transiÃÃo metal-isolante, tambÃm conhecida como transiÃÃo de Anderson. Contudo, para sistemas de baixa dimensionalidade, segundo essa mesma teoria, qualquer grau finito de desordem pode promover a localizaÃÃo exponencial de todas as funÃÃes eletrÃnicas. No entanto, foi mostrado que a teoria geral de localizaÃÃo de Anderson à violada quando correlaÃÃes e interaÃÃes de longo alcance sÃo utilizadas. Nesse cenÃrio, a transiÃÃo metal-isolante ocorre tambÃm para sistemas de baixa dimensionalidade. Nos problemas relacionados com redes, as ligaÃÃes de longo alcance sÃo responsÃveis pela pequena distÃncia mÃdia entre indivÃduos pertencentes à mesma rede social. Esse fenÃmeno à popularmente conhecido como os seis graus de separaÃÃo. AlÃm disso, Kleinberg mostrou que a introduÃÃo de uma distribuiÃÃo em lei de potÃncia de ligaÃÃes de longo alcance em uma rede substrato gera um mÃnimo no tempo de envio de uma informaÃÃo de um sÃtio fonte a um sÃtio alvo da rede. Nesta tese, investigamos como a desordem de longo alcance altera a classe de universalidade de dois modelos matemÃticos que representam os seguintes problemas fÃsicos: o processo de erosÃo na costa de paisagens correlacionadas e a transiÃÃo deslocalizaÃÃo-localizaÃÃo dos modos normais de vibraÃÃo de uma cadeia harmÃnica com ligaÃÃes de longo alcance restritas por uma funÃÃo custo. No primeiro modelo, mostramos que correlaÃÃes espaciais de longo alcance nas propriedades geolÃgicas da costa, no regime crÃtico do nosso modelo, gera um espectro de linhas costeiras fractais cujas dimensÃes fractais variam entre D=1.33 e 1.00 quando variamos o expoente de Hurst no intervalo 0
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Carvalho, Rafael Aleixo de. "Tempo de transito em meios com isotropia transversal vertical (VTI) : aproximações e inversão dos parametros". [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/307310.
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Orientador: Jorg Dietrich Wilhelm SchleicherTese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica
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Resumo: Como os alvos de exploração tornaram-se mais profundos, os comprimentos dos cabos têm aumentado em conformidade, fazendo a aproximação hiperbólica convencional produzir tempos de trânsito cada vez mais imprecisos. Em outras palavras, para as modernas geometrias de aquisição para grandes afastamentos, a aproximação hiperbólica já não é suficiente para horizontalizar a família CMP por causa da não homogeneidade ou anisotropia dos meios. Para resolver este problema, muitas fórmulas para o tempo de trânsito foram propostas na literatura que fornecem aproximações de qualidade diferente. Demonstrou-se que para meios com isotropia transversal vertical (meios VTI), apenas dois parâmetros do tempo de trânsito são suficientes para a realização de todo o processamento temporal, sendo a velocidade NMO e um parâmetro de anisotropia. Por isso, nesta tese, nos concentramos, na dedução de aproximações simples para o tempo de trânsito que dependem de um único parâmetro de anisotropia. Começamos por dar uma visão geral de uma coleção de tais aproximações para o tempo de trânsito encontradas na literatura e comparar suas qualidades. Em seguida, deduzimos um conjunto de novas aproximações para o tempo de trânsito que dependem de um parâmetro baseado em aproximações encontradas na literatura. A principal vantagem das nossas aproximações é que algumas delas são expressões analíticas bastante simples que as tornam fáceis de serem utilizadas, ao mesmo tempo que têm a mesma qualidade ou maior que as fórmulas já estabelecidas. Utilizamos estas aproximações para o tempo de trânsito para uma inversão dos parâmetros de anisotropia. Utilizando uma estimativa da velocidade NMO a partir da análise de velocidades hiperbólica, pode-se estimar o parâmetro anisotrópico a partir de uma aproximação para o tempo de trânsito mais geral. Estendemos o procedimento em dois passos utilizando um termo não hiperbólico mais preciso na aproximação para o tempo de trânsito. As aproximações para o tempo de trânsito deduzidas permitem predizer o viés na estimativa da velocidade NMO, proporcionando assim um meio de corrigir, tanto a estimativa a velocidade NMO, quanto o conseqüente valor do parâmetro de anisotropia. Por meio de um exemplo numérico, demonstramos que a estimativa dos parâmetros do tempo de trânsito, usando este processo iterativo, apresenta considerável melhora. Palavras-chave: Aproximação para tempos de trânsito, meios VTI, análise de velocidade e geofísica
Abstract: As exploration targets have become deeper, cable lengths have increased accordingly, making the conventional two term hyperbolic traveltime approximation produce increasingly erroneous traveltimes. In other words, for modern long-offset acquisition geometries, a hyperbolic traveltime approximation is no longer sufficient to flatten the CMP gather because of medium inhomogeneity or anisotropy. To overcome this problem, many traveltime formulas were proposed in the literature that provide approximations of different quality. It has been demonstrated that for transversly isotropic media with a vertical symmetry axis (VTI media), just two traveltime parameters are sufficient to perform all time-related processing, being the NMO velocity and one anisotropy parameter. Therefore, we concentrate in this thesis,on simple traveltime approximations that depend on a single anisotropy parameter. We start by giving an overview of a collection of such traveltime approximations found in the literature and compare their quality. Next, we derive a set of new single-parameter traveltime approximations based on the ones found in the literature. The main advantage of our approximations is that some of them are rather simple analytic expressions that make them easy to use, while achieving the same quality as the better of the established formulas. We then use these traveltime aproximations for an inversion of the anisotropy parameters. Using an estimate of the NMO velocity from a hyperbolic velocity analysis, one can estimate the anisotropic parameter from a more general traveltime approximation. We extend this two-step procedure using a more accurate nonhyperbolicity term in the traveltime approximation. The used traveltime approximations allow to predict the bias in the NMO velocity estimate, thus providing a means of correcting both the estimated NMO velocity and the resulting anisotropy parameter value. By means of a numerical example, we demonstrate that the estimation of the traveltime parameters, using this iterative procedure, is improved considerably. Keywords: Traveltime approximations, VTI media, velocity analysis and geophysics
Doutorado
Geofisica Computacional
Doutor em Matemática Aplicada
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JAGOSICH, FABIO H. "Estudos espectroscopicos para o desenvolvimento dos meios laser ativos de Ho sup [3+] e Er sup [3+] no YLF que operam na regiao de 3 microns". reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10805.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:97/10816-3
Livros sobre o assunto "Meiosis transition"
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Clarke, Hugh James. Cytoplasmic activities inducing the transition of chromosomes to metaphase and interphase in mouse oocytes during meiotic maturation. 1986.
Encontre o texto completo da fonteCapítulos de livros sobre o assunto "Meiosis transition"
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Courtois, Aurélien, e Takashi Hiiragi. "Gradual Meiosis-To-Mitosis Transition in the Early Mouse Embryo". In Results and Problems in Cell Differentiation, 107–14. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-30406-4_6.
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Terret, M. Emilie. "The Control of the Metaphase-to-Anaphase Transition in Meiosis I". In Oogenesis, 311–41. Chichester, UK: John Wiley & Sons, Ltd, 2010. http://dx.doi.org/10.1002/9780470687970.ch12.
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Ohsumi, Keita, Tomomi M. Yamamoto e Mari Iwabuchi. "Oocyte Extracts for the Study of Meiotic M-M Transition". In Xenopus Protocols, 445–58. Totowa, NJ: Humana Press, 2006. http://dx.doi.org/10.1007/978-1-59745-000-3_32.
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Arur, Swathi. "Signaling-Mediated Regulation of Meiotic Prophase I and Transition During Oogenesis". In Results and Problems in Cell Differentiation, 101–23. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-44820-6_4.
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Jaffe, Laurinda A., e Rachael P. Norris. "Initiation of the Meiotic Prophase-to-Metaphase Transition in Mammalian Oocytes". In Oogenesis, 179–97. Chichester, UK: John Wiley & Sons, Ltd, 2010. http://dx.doi.org/10.1002/9780470687970.ch7.
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Hey, Jody. "Recombination and Biological Species". In Genes, Categories, and Species, 88–104. Oxford University PressNew York, NY, 2001. http://dx.doi.org/10.1093/oso/9780195144772.003.0007.
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Abstract Most DNA molecules that are the genomes of organisms include genes that permit or encourage the breaking and joining of the DNA with other DNA molecules. In other words, most genomes include genes that cause recombination. This process of recombination is often highly choreographed and occurs regularly at specific stages of an organism’s life cycle. For many eukaryote genomes it occurs at the life cycle stage of transition from diploid cells (with two copies of every chromosome) to haploid cells (with just a single copy of each chromosome). This process is called meiosis, and when recombination occurs during meiosis it involves two similar genome copies that had previously come together earlier in the life cycle at the time of transition from haploid to diploid cells (i.e., syngamy or fertilization). Many genomes have also evolved multiple disjunct DNA molecules (chromosomes) among which there is effectively free recombination at the time of meiosis. For the genomes of prokaryotes there is no meiosis and syngamy, yet the breaking and joining of DNAs may still occur with high frequency (Lenski 1993). Whether or not the shuffiing of DNA segments occurs in the course of reproduction or at some other life stage and whether or not it proceeds by swapping portions of DNA molecules or by the incorporation of one DNA by another, recombination leads to a new genome that is an admixture of two.
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Teather, Kevin. "The Road to Sexual Reproduction". In The Evolution of Sex, 33–49. Oxford University PressOxford, 2024. http://dx.doi.org/10.1093/9780191994418.003.0003.
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Abstract Living organisms are divided into two superkingdoms: the prokaryotes and eukaryotes. Prokaryotes consist of eubacteria and archaebacteria, are single-celled, and breed asexually. All other organisms comprise eukaryotes. These are larger, more complex, often multicellular, and, with some exceptions, reproduce sexually. About two billion years ago, eukaryotes evolved from prokaryotes by incorporating oxygen-using eubacteria into anaerobic archaeans. This development was accompanied by increased oxidative metabolism using the newly acquired bacteria, or mitochondria. The mitochondrial genome interacts with the nuclear genome to provide the proteins necessary for energy production. While using oxygen is more efficient when producing energy for the cell, it also results in extensive DNA damage by releasing free oxygen radicals. Meiosis is an integral part of sexual reproduction and is present in nearly all organisms that reproduce sexually. It likely evolved during the transition between the prokaryotes and eukaryotes. Of significant importance, crossing-over during an early stage of meiosis provided the capacity to repair DNA and resulted in increased levels of variability in progeny. Both of these factors may be important in the evolution of sex.
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Bernstein, Harris, e Carol Bernstein. "Origin of DNA Repair in the RNA World". In DNA Repair [Working Title]. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.93822.
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The early history of life on Earth likely included a stage in which life existed as self-replicating protocells with single-stranded RNA (ssRNA) genomes. In this RNA world, genome damage from a variety of sources (spontaneous hydrolysis, UV, etc.) would have been a problem for survival. Selection pressure for dealing with genome damage would have led to adaptive strategies for mitigating the damage. In today’s world, RNA viruses with ssRNA genomes are common, and these viruses similarly need to cope with genome damage. Thus ssRNA viruses can serve as models for understanding the early evolution of genome repair. As the ssRNA protocells in the early RNA world evolved, the RNA genome likely gave rise, through a series of evolutionary stages, to the double-stranded DNA (dsDNA) genome. In ssRNA to dsDNA evolution, genome repair processes also likely evolved to accommodate this transition. Some of the basic features of ssRNA genome repair appear to have been retained in descendants with dsDNA genomes. In particular, a type of strand-switching recombination occurs when ssRNA replication is blocked by a damage in the template strand. Elements of this process appear to have a central role in recombinational repair processes during meiosis and mitosis of descendant dsDNA organisms.
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Vemanna, Ramu S., Chanchal Kumari e Shobhna Yadav. "Influence of Abiotic Stress on Molecular Responses of Flowering in Rice". In Molecular and Physiological Insights into Plant Stress Tolerance and Applications in Agriculture, 1–14. BENTHAM SCIENCE PUBLISHERS, 2023. http://dx.doi.org/10.2174/9789815136562123010004.
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Rice is a short-day plant, and its heading date (Hd)/flowering time is one of the important agronomic traits for realizing the maximum yield with high nutrition. Theoretically, flowering initiates with the transition from the vegetative stage to shoot apical meristems (SAMs), and it is regulated by endogenous and environmental signals. Under favorable environmental conditions, flowering is triggered with the synthesis of mobile signal florigen in leaves and then translocated to the shoot for activation of cell differentiation-associated genes. In rice, the genetic pathway of flowering comprises OsGI–Hd1–Hd3a, which is an ortholog of the Arabidopsis GI–CO–FT pathway, and the Ehd1-Hd3a pathway. Climate change could affect photoperiod and temperature, which in turn influences heading date and crop yield. In low temperatures and long-day conditions, the expression of the HD3a gene analogous to FT in Arabidopsis deceased, which delays flowering. Similarly, during drought, expression of the Ehd1 gene is suppressed, resulting in a late-flowering phenotype in rice. Drought affects pollen fertility and reduction in grain yield by reducing male fertility, which affects male meiosis during reproduction, microspore development, and anther dehiscence. In this research field, substantial progress has been made to manipulate flowering-related genes to combat abiotic stresses. Here, we summarize the roles of a few genes in improving the flowering traits of rice.
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Maynard Smith, John, e Eors Szathmary. "The origin of sex and the nature of species". In The Major Transitions in Evolution. Oxford University Press, 1997. http://dx.doi.org/10.1093/oso/9780198502944.003.0013.
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By sex in eukaryotes, we understand a more-or-less regular succession of meiosis and syngamy. A natural consequence of this is the alternation of haploid and diploid phases in the life cycle. Eukaryotic sex significantly differs from prokaryotic sex in two crucial respects: the cellular mechanisms are quite different, and the transfer of genetic material in prokaryotes is less frequent and more localized (Maynard Smith et al., 1991). However, there seems to be significant continuity in the molecular mechanisms: sex in either case requires recombination enzymes, many of which are active in repair of damaged DNA as well. Thus, it seems plausible that recombinational repair was a preadaptation for sexual recombination. We mention in passing that there is a theory that selection for the recombinational repair of doublestrand DNA damage is responsible for the current maintenance of eukaryotic sex (Bernstein et al., 1981, 1988), but there are severe theoretical as well as factual problems with this theory; we will mention some factual difficulties later. Although an alternation of haploid and diploid phases follows from sex, a clue to the origin problem may lie in the idea that this alternation existed before the evolution of sexual recombination proper. The first hint that this may have been so comes from the classic paper by Cleveland (1947), where he proposed that the haploid-diploid cycle may have started with a spontaneous diploidization by endomitosis: that is, without syngamy. His suggestions were based on original observations on primitive flagellates (hypermastigotes and polymastigotes). Among them, Barbulanympha has a regular endomitosis-meiosis cycle. Margulis & Sagan (1986) called renewed attention to Cleveland’s ideas. In particular, they argued that the alternation of ploidy phases could have a primarily ecological explanation: if the environment alternates in some important factors, this may drive a haploid-diploid cycle, provided the phases are adaptations to different environments. For example, diploids have a smaller relative surface area than haploids, which may confer higher metabolic efficiency. We shall come back to such ideas soon. We focus first on the possible cellular mechanisms connecting the two phases. It is important that some protists have a one-step rather than a two-step meiosis: after syngamy, the two homologous chromosomes become disjunct without premeiotic doubling.
Trabalhos de conferências sobre o assunto "Meiosis transition"
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Rodrigues, Diego Oliveira, e Leandro Villas. "SMAFramework: Arcabouço para Integração de Dados Urbanos Cientes da Correlação Espaço-Temporal". In XXXVII Simpósio Brasileiro de Redes de Computadores e Sistemas Distribuídos. Sociedade Brasileira de Computação - SBC, 2019. http://dx.doi.org/10.5753/sbrc_estendido.2019.7777.
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Redes sociais, dispositivos móveis, redes veiculares e de sensores são utilizados como coletores de dados em centros urbanos; dados esses que podem ser utilizados para melhor compreender as dinâmicas das cidades. Muitos estudos tem focado em explorar essas fontes de dados, porém individualmente. A fim de reduzir o impacto na análise de dados urbanos causada por essa limitação foi desenvolvido o SMAFramework, para realizar a coleta e integração de dados de mobilidade urbana de fontes heterogêneas. Foi proposta uma metodologia para padronizar dados com anotações espaço-temporais provenientes de várias fontes de acordo com um modelo único de dados (i.e., Grafo Multi Aspecto). A ferramenta apresentada ainda permite que se realize diferentes tarefas de análise de dados. Para avaliar o arcabouço desenvolvido, experimentos foram realizados com dados reais. O primeiro experimento combinou dados de mídias sociais com dados de viagens de táxi a fim de avaliar a correlação espaço temporal entre essas fontes de dados. Em um segundo experimento dados de táxi foram combinados com informações de transito, rotas de transporte público e modelos de experiência de usuário a fim de avaliar como diferentes meios de transporte poderiam ser combinados a fim de melhorar a mobilidade urbana. Ferramentas e metodologias foram desenvolvidas para a execução de cada um desses experimentos, contribuindo com o avanço do estado da arte.