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1
Wang, S. W., F. J. Griffin und W. H. Clark. „Cell-cell association directed mitotic spindle orientation in the early development of the marine shrimp Sicyonia ingentis“. Development 124, Nr. 4 (15.02.1997): 773–80. http://dx.doi.org/10.1242/dev.124.4.773.
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During early cleavages of Sicyonia ingentis embryos, mitotic spindle orientations differ between blastomeres and change in a predictable manner with each successive mitosis. From 2nd through 7th cleavages, spindles orient at a 90 degrees angle with respect to the spindle of the parent blastomere. Thus, spindle orientation is parallel to the cleavage plane that formed the blastomere. To determine if specific spindle orientations were intrinsic properties of individual blastomeres, we altered blastomere associations and asked how mitotic spindle orientation was affected in successive cleavages using laser scanning confocal microscopy. Linear embryos were constructed by dissociating 4-cell embryos and recombining the blastomeres in a linear array. The ensuing cleavage (3rd embryonic cleavage) of these linear embryos was parallel to the long axis of the embryo, resulting in four parallel pairs of blastomeres which lay in a common plane that was parallel to the substratum. The 4th cleavage produced a linear embryo with the 16 blastomeres arranged in four parallel quartets. Then, in preparation for 5th cleavage, spindles oriented at a 45 degrees angle (not parallel as in normal development) with respect to the previous cleavage plane. When 8-cell linear embryos were separated into linear half-embryos, subsequent spindle orientations were not like those observed for intact 8-cell linear embryos, but rather regressed to the orientation seen in 4-cell linear embryos. We suggest that the reorientation of mitotic spindles during early cleavage of S. ingentis is neither an intrinsic property nor age dependent, but rather is cell contact related. Further, these results in conjunction with observations of non-manipulated embryos suggest that spindle poles (centrosomes) avoid cytoplasmic regions adjacent to where there is cell-cell contact during early development.
2
Juschke, C., Y. Xie, M. P. Postiglione und J. A. Knoblich. „Analysis and modeling of mitotic spindle orientations in three dimensions“. Proceedings of the National Academy of Sciences 111, Nr. 3 (31.12.2013): 1014–19. http://dx.doi.org/10.1073/pnas.1314984111.
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3
Chan, Derek C. H., Joshua Xu, Ana Vujovic, Nicholas Wong, Victor Gordon, Laura P. M. H. de Rooij, Steven Moreira et al. „Arhgef2 regulates mitotic spindle orientation in hematopoietic stem cells and is essential for productive hematopoiesis“. Blood Advances 5, Nr. 16 (18.08.2021): 3120–33. http://dx.doi.org/10.1182/bloodadvances.2020002539.
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Abstract How hematopoietic stem cells (HSCs) coordinate their divisional axis and whether this orientation is important for stem cell–driven hematopoiesis is poorly understood. Single-cell RNA sequencing data from patients with Shwachman-Diamond syndrome (SDS), an inherited bone marrow failure syndrome, show that ARHGEF2, a RhoA-specific guanine nucleotide exchange factor and determinant of mitotic spindle orientation, is specifically downregulated in SDS hematopoietic stem and progenitor cells (HSPCs). We demonstrate that transplanted Arhgef2−/− fetal liver and bone marrow cells yield impaired hematopoietic recovery and a production deficit from long-term HSCs, phenotypes that are not the result of differences in numbers of transplanted HSCs, their cell cycle status, level of apoptosis, progenitor output, or homing ability. Notably, these defects are functionally restored in vivo by overexpression of ARHGEF2 or its downstream activated RHOA GTPase. By using live imaging of dividing HSPCs, we show an increased frequency of misoriented divisions in the absence of Arhgef2. ARHGEF2 knockdown in human HSCs also impairs their ability to regenerate hematopoiesis, culminating in significantly smaller xenografts. Together, these data demonstrate a conserved role for Arhgef2 in orienting HSPC division and suggest that HSCs may divide in certain orientations to establish hematopoiesis, the loss of which could contribute to HSC dysfunction in bone marrow failure.
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Sei, Yoshitatsu, Jianying Feng, Carson C. Chow und Stephen A. Wank. „Asymmetric cell division-dominant neutral drift model for normal intestinal stem cell homeostasis“. American Journal of Physiology-Gastrointestinal and Liver Physiology 316, Nr. 1 (01.01.2019): G64—G74. http://dx.doi.org/10.1152/ajpgi.00242.2018.
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The normal intestinal epithelium is continuously regenerated at a rapid rate from actively cycling Lgr5-expressing intestinal stem cells (ISCs) that reside at the crypt base. Recent mathematical modeling based on several lineage-tracing studies in mice shows that the symmetric cell division-dominant neutral drift model fits well with the observed in vivo growth of ISC clones and suggests that symmetric divisions are central to ISC homeostasis. However, other studies suggest a critical role for asymmetric cell division in the maintenance of ISC homeostasis in vivo. Here, we show that the stochastic branching and Moran process models with both a symmetric and asymmetric division mode not only simulate the stochastic growth of the ISC clone in silico but also closely fit the in vivo stem cell dynamics observed in lineage-tracing studies. In addition, the proposed model with highest probability for asymmetric division is more consistent with in vivo observations reported here and by others. Our in vivo studies of mitotic spindle orientations and lineage-traced progeny pairs indicate that asymmetric cell division is a dominant mode used by ISCs under normal homeostasis. Therefore, we propose the asymmetric cell division-dominant neutral drift model for normal ISC homeostasis. NEW & NOTEWORTHY The prevailing mathematical model suggests that intestinal stem cells (ISCs) divide symmetrically. The present study provides evidence that asymmetric cell division is the major contributor to ISC maintenance and thus proposes an asymmetric cell division-dominant neutral drift model. Consistent with this model, in vivo studies of mitotic spindle orientation and lineage-traced progeny pairs indicate that asymmetric cell division is the dominant mode used by ISCs under normal homeostasis.
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Copp, A. J., F. A. Brook und H. J. Roberts. „A cell-type-specific abnormality of cell proliferation in mutant (curly tail) mouse embryos developing spinal neural tube defects“. Development 104, Nr. 2 (01.10.1988): 285–95. http://dx.doi.org/10.1242/dev.104.2.285.
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The mouse mutant curly tail (ct) provides a model system for studies of neurulation mechanisms. 60% of ct/ct embryos develop spinal neural tube defects (NTD) as a result of delayed neurulation at the posterior neuropore whereas the remaining 40% of embryos develop normally. In order to investigate the role of cell proliferation during mouse neurulation, cell cycle parameters were studied in curly tail embryos developing spinal NTD and in their normally developing litter-mates. Measurements were made of mitotic index, median length of S-phase and percent reduction of labelling index during a [3H]thymidine pulse-chase experiment. These independent measures of cell proliferation rate indicate a reduced rate of proliferation of gut endoderm and notochord cells in the neuropore region of embryos developing spinal NTD compared with normally developing controls. The incidence of cell death and the relative frequency of mitotic spindle orientations does not differ consistently between normal and abnormal embryos. These results suggest a mechanism of spinal NTD pathogenesis in curly tail embryos based on failure of normal cell proliferation in gut endoderm and notochord.
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Li, Jie, Hiroki Shima, Hironari Nishizawa, Masatoshi Ikeda, Andrey Brydun, Mitsuyo Matsumoto, Hiroki Kato et al. „Phosphorylation of BACH1 switches its function from transcription factor to mitotic chromosome regulator and promotes its interaction with HMMR“. Biochemical Journal 475, Nr. 5 (15.03.2018): 981–1002. http://dx.doi.org/10.1042/bcj20170520.
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The transcription repressor BACH1 performs mutually independent dual roles in transcription regulation and chromosome alignment during mitosis by supporting polar ejection force of mitotic spindle. We now found that the mitotic spindles became oblique relative to the adhesion surface following endogenous BACH1 depletion in HeLa cells. This spindle orientation rearrangement was rescued by re-expression of BACH1 depending on its interactions with HMMR and CRM1, both of which are required for the positioning of mitotic spindle, but independently of its DNA-binding activity. A mass spectrometry analysis of BACH1 complexes in interphase and M phase revealed that BACH1 lost during mitosis interactions with proteins involved in chromatin and gene expression but retained interactions with HMMR and its known partners including CHICA. By analyzing BACH1 modification using stable isotope labeling with amino acids in cell culture, mitosis-specific phosphorylations of BACH1 were observed, and mutations of these residues abolished the activity of BACH1 to restore mitotic spindle orientation in knockdown cells and to interact with HMMR. Detailed histological analysis of Bach1-deficient mice revealed lengthening of the epithelial fold structures of the intestine. These observations suggest that BACH1 performs stabilization of mitotic spindle orientation together with HMMR and CRM1 in mitosis, and that the cell cycle-specific phosphorylation switches the transcriptional and mitotic functions of BACH1.
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Kapoor, Tarun M., Thomas U. Mayer, Margaret L. Coughlin und Timothy J. Mitchison. „Probing Spindle Assembly Mechanisms with Monastrol, a Small Molecule Inhibitor of the Mitotic Kinesin, Eg5“. Journal of Cell Biology 150, Nr. 5 (04.09.2000): 975–88. http://dx.doi.org/10.1083/jcb.150.5.975.
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Monastrol, a cell-permeable small molecule inhibitor of the mitotic kinesin, Eg5, arrests cells in mitosis with monoastral spindles. Here, we use monastrol to probe mitotic mechanisms. We find that monastrol does not inhibit progression through S and G2 phases of the cell cycle or centrosome duplication. The mitotic arrest due to monastrol is also rapidly reversible. Chromosomes in monastrol-treated cells frequently have both sister kinetochores attached to microtubules extending to the center of the monoaster (syntelic orientation). Mitotic arrest–deficient protein 2 (Mad2) localizes to a subset of kinetochores, suggesting the activation of the spindle assembly checkpoint in these cells. Mad2 localizes to some kinetochores that have attached microtubules in monastrol-treated cells, indicating that kinetochore microtubule attachment alone may not satisfy the spindle assembly checkpoint. Monastrol also inhibits bipolar spindle formation in Xenopus egg extracts. However, it does not prevent the targeting of Eg5 to the monoastral spindles that form. Imaging bipolar spindles disassembling in the presence of monastrol allowed direct observations of outward directed forces in the spindle, orthogonal to the pole-to-pole axis. Monastrol is thus a useful tool to study mitotic processes, detection and correction of chromosome malorientation, and contributions of Eg5 to spindle assembly and maintenance.
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Woodard, Geoffrey E., Ning-Na Huang, Hyeseon Cho, Toru Miki, Gregory G. Tall und John H. Kehrl. „Ric-8A and Giα Recruit LGN, NuMA, and Dynein to the Cell Cortex To Help Orient the Mitotic Spindle“. Molecular and Cellular Biology 30, Nr. 14 (17.05.2010): 3519–30. http://dx.doi.org/10.1128/mcb.00394-10.
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ABSTRACT In model organisms, resistance to inhibitors of cholinesterase 8 (Ric-8), a G protein α (Gα) subunit guanine nucleotide exchange factor (GEF), functions to orient mitotic spindles during asymmetric cell divisions; however, whether Ric-8A has any role in mammalian cell division is unknown. We show here that Ric-8A and Gαi function to orient the metaphase mitotic spindle of mammalian adherent cells. During mitosis, Ric-8A localized at the cell cortex, spindle poles, centromeres, central spindle, and midbody. Pertussis toxin proved to be a useful tool in these studies since it blocked the binding of Ric-8A to Gαi, thus preventing its GEF activity for Gαi. Linking Ric-8A signaling to mammalian cell division, treatment of cells with pertussis toxin, reduction of Ric-8A expression, or decreased Gαi expression similarly affected metaphase cells. Each treatment impaired the localization of LGN (GSPM2), NuMA (microtubule binding nuclear mitotic apparatus protein), and dynein at the metaphase cell cortex and disturbed integrin-dependent mitotic spindle orientation. Live cell imaging of HeLa cells expressing green fluorescent protein-tubulin also revealed that reduced Ric-8A expression prolonged mitosis, caused occasional mitotic arrest, and decreased mitotic spindle movements. These data indicate that Ric-8A signaling leads to assembly of a cortical signaling complex that functions to orient the mitotic spindle.
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Siletti, Kimberly, Basile Tarchini und A. J. Hudspeth. „Daple coordinates organ-wide and cell-intrinsic polarity to pattern inner-ear hair bundles“. Proceedings of the National Academy of Sciences 114, Nr. 52 (11.12.2017): E11170—E11179. http://dx.doi.org/10.1073/pnas.1716522115.
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The establishment of planar polarization by mammalian cells necessitates the integration of diverse signaling pathways. In the inner ear, at least two systems regulate the planar polarity of sensory hair bundles. The core planar cell polarity (PCP) proteins coordinate the orientations of hair cells across the epithelial plane. The cell-intrinsic patterning of hair bundles is implemented independently by the G protein complex classically known for orienting the mitotic spindle. Although the primary cilium also participates in each of these pathways, its role and the integration of the two systems are poorly understood. We show that Dishevelled-associating protein with a high frequency of leucine residues (Daple) interacts with PCP and cell-intrinsic signals. Regulated by the cell-intrinsic pathway, Daple is required to maintain the polarized distribution of the core PCP protein Dishevelled and to position the primary cilium at the abneural edge of the apical surface. Our results suggest that the primary cilium or an associated structure influences the domain of cell-intrinsic signals that shape the hair bundle. Daple is therefore essential to orient and pattern sensory hair bundles.
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Giansanti, M. G., M. Gatti und S. Bonaccorsi. „The role of centrosomes and astral microtubules during asymmetric division of Drosophila neuroblasts“. Development 128, Nr. 7 (01.04.2001): 1137–45. http://dx.doi.org/10.1242/dev.128.7.1137.
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Drosophila neuroblasts are stem cells that divide asymmetrically to produce another large neuroblast and a smaller ganglion mother cell (GMC). During neuroblast division, several cell fate determinants, such as Miranda, Prospero and Numb, are preferentially segregated into the GMC, ensuring its correct developmental fate. The accurate segregation of these determinants relies on proper orientation of the mitotic spindle within the dividing neuroblast, and on the correct positioning of the cleavage plane. In this study we have analyzed the role of centrosomes and astral microtubules in neuroblast spindle orientation and cytokinesis. We examined neuroblast division in asterless (asl) mutants, which, although devoid of functional centrosomes and astral microtubules, form well-focused anastral spindles that undergo anaphase and telophase. We show that asl neuroblasts assemble a normal cytokinetic ring around the central spindle midzone and undergo unequal cytokinesis. Thus, astral microtubules are not required for either signaling or positioning cytokinesis in Drosophila neuroblasts. Our results indicate that the cleavage plane is dictated by the positioning of the central spindle midzone within the cell, and suggest a model on how the central spindle attains an asymmetric position during neuroblast mitosis. We have also analyzed the localization of Miranda during mitotic division of asl neuroblasts. This protein accumulates in morphologically regular cortical crescents but these crescents are mislocalized with respect to the spindle orientation. This suggests that astral microtubules mediate proper spindle rotation during neuroblast division.
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Li, Jingchen, Longcan Cheng und Hongyuan Jiang. „Cell shape and intercellular adhesion regulate mitotic spindle orientation“. Molecular Biology of the Cell 30, Nr. 19 (01.09.2019): 2458–68. http://dx.doi.org/10.1091/mbc.e19-04-0227.
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Cell division orientation plays an essential role in tissue morphogenesis and cell fate decision. Recent studies showed that either cell shape or adhesion geometry can regulate the orientation of mitotic spindles and thereby the cell division orientation. However, how they together regulate the spindle orientation remains largely unclear. In this work, we use a general computational model to investigate the competitive mechanism of determining the spindle orientation between cell shape and intercellular adhesion in epithelial cells. We find the spindle orientation is dominated by the intercellular adhesion when the cell shape anisotropy is small, but dominated by the cell shape when the shape anisotropy is large. A strong adhesion and moderate adhesive size can ensure the planar division of epithelial cells with large apico-basal elongation. We also find the spindle orientation could be perpendicular to the adhesive region when only one side of the cell is adhered to an E-cadherin–coated matrix. But after the cell is compressed, the spindle orientation is governed by the cell shape and the spindle will be parallel to the adhesive region when the cell shape anisotropy is large. Finally, we demonstrate the competition between cell shape and tricellular junctions can also effectively regulate the spindle orientation.
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Gassmann, Reto, Ana Carvalho, Alexander J. Henzing, Sandrine Ruchaud, Damien F. Hudson, Reiko Honda, Erich A. Nigg, Dietlind L. Gerloff und William C. Earnshaw. „Borealin“. Journal of Cell Biology 166, Nr. 2 (12.07.2004): 179–91. http://dx.doi.org/10.1083/jcb.200404001.
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The chromosomal passenger complex of Aurora B kinase, INCENP, and Survivin has essential regulatory roles at centromeres and the central spindle in mitosis. Here, we describe Borealin, a novel member of the complex. Approximately half of Aurora B in mitotic cells is complexed with INCENP, Borealin, and Survivin; and Borealin binds Survivin and INCENP in vitro. A second complex contains Aurora B and INCENP, but no Borealin or Survivin. Depletion of Borealin by RNA interference delays mitotic progression and results in kinetochore–spindle misattachments and an increase in bipolar spindles associated with ectopic asters. The extra poles, which apparently form after chromosomes achieve a bipolar orientation, severely disrupt the partitioning of chromosomes in anaphase. Borealin depletion has little effect on histone H3 serine10 phosphorylation. These results implicate the chromosomal passenger holocomplex in the maintenance of spindle integrity and suggest that histone H3 serine10 phosphorylation is performed by an Aurora B–INCENP subcomplex.
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Chan, Ying Wai, Luca L. Fava, Andreas Uldschmid, Michael H. A. Schmitz, Daniel W. Gerlich, Erich A. Nigg und Anna Santamaria. „Mitotic control of kinetochore-associated dynein and spindle orientation by human Spindly“. Journal of Cell Biology 185, Nr. 5 (25.05.2009): 859–74. http://dx.doi.org/10.1083/jcb.200812167.
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Mitotic spindle formation and chromosome segregation depend critically on kinetochore–microtubule (KT–MT) interactions. A new protein, termed Spindly in Drosophila and SPDL-1 in C. elegans, was recently shown to regulate KT localization of dynein, but depletion phenotypes revealed striking differences, suggesting evolutionarily diverse roles of mitotic dynein. By characterizing the function of Spindly in human cells, we identify specific functions for KT dynein. We show that localization of human Spindly (hSpindly) to KTs is controlled by the Rod/Zw10/Zwilch (RZZ) complex and Aurora B. hSpindly depletion results in reduced inter-KT tension, unstable KT fibers, an extensive prometaphase delay, and severe chromosome misalignment. Moreover, depletion of hSpindly induces a striking spindle rotation, which can be rescued by co-depletion of dynein. However, in contrast to Drosophila, hSpindly depletion does not abolish the removal of MAD2 and ZW10 from KTs. Collectively, our data reveal hSpindly-mediated dynein functions and highlight a critical role of KT dynein in spindle orientation.
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Larson, Matthew E., und William M. Bement. „Automated mitotic spindle tracking suggests a link between spindle dynamics, spindle orientation, and anaphase onset in epithelial cells“. Molecular Biology of the Cell 28, Nr. 6 (15.03.2017): 746–59. http://dx.doi.org/10.1091/mbc.e16-06-0355.
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Proper spindle positioning at anaphase onset is essential for normal tissue organization and function. Here we develop automated spindle-tracking software and apply it to characterize mitotic spindle dynamics in the Xenopus laevis embryonic epithelium. We find that metaphase spindles first undergo a sustained rotation that brings them on-axis with their final orientation. This sustained rotation is followed by a set of striking stereotyped rotational oscillations that bring the spindle into near contact with the cortex and then move it rapidly away from the cortex. These oscillations begin to subside soon before anaphase onset. Metrics extracted from the automatically tracked spindles indicate that final spindle position is determined largely by cell morphology and that spindles consistently center themselves in the XY-plane before anaphase onset. Finally, analysis of the relationship between spindle oscillations and spindle position relative to the cortex reveals an association between cortical contact and anaphase onset. We conclude that metaphase spindles in epithelia engage in a stereotyped “dance,” that this dance culminates in proper spindle positioning and orientation, and that completion of the dance is linked to anaphase onset.
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Buttrick, Graham J., Luke M. A. Beaumont, Jessica Leitch, Christopher Yau, Julian R. Hughes und James G. Wakefield. „Akt regulates centrosome migration and spindle orientation in the early Drosophila melanogaster embryo“. Journal of Cell Biology 180, Nr. 3 (11.02.2008): 537–48. http://dx.doi.org/10.1083/jcb.200705085.
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Correct positioning and morphology of the mitotic spindle is achieved through regulating the interaction between microtubules (MTs) and cortical actin. Here we find that, in the Drosophila melanogaster early embryo, reduced levels of the protein kinase Akt result in incomplete centrosome migration around cortical nuclei, bent mitotic spindles, and loss of nuclei into the interior of the embryo. We show that Akt is enriched at the embryonic cortex and is required for phosphorylation of the glycogen synthase kinase-3β homologue Zeste-white 3 kinase (Zw3) and for the cortical localizations of the adenomatosis polyposis coli (APC)–related protein APC2/E-APC and the MT + Tip protein EB1. We also show that reduced levels of Akt result in mislocalization of APC2 in postcellularized embryonic mitoses and misorientation of epithelial mitotic spindles. Together, our results suggest that Akt regulates a complex containing Zw3, Armadillo, APC2, and EB1 and that this complex has a role in stabilizing MT–cortex interactions, facilitating both centrosome separation and mitotic spindle orientation.
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Sana, Shrividya, Riya Keshri, Ashwathi Rajeevan, Sukriti Kapoor und Sachin Kotak. „Plk1 regulates spindle orientation by phosphorylating NuMA in human cells“. Life Science Alliance 1, Nr. 6 (16.11.2018): e201800223. http://dx.doi.org/10.26508/lsa.201800223.
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Proper orientation of the mitotic spindle defines the correct division plane and is essential for accurate cell division and development. In metazoans, an evolutionarily conserved complex comprising of NuMA/LGN/Gαi regulates proper orientation of the mitotic spindle by orchestrating cortical dynein levels during metaphase. However, the molecular mechanisms that modulate the spatiotemporal dynamics of this complex during mitosis remain elusive. Here, we report that acute inactivation of Polo-like kinase 1 (Plk1) during metaphase enriches cortical levels of dynein/NuMA/LGN and thus influences spindle orientation. We establish that this impact of Plk1 on cortical levels of dynein/NuMA/LGN is through NuMA, but not via dynein/LGN. Moreover, we reveal that Plk1 inhibition alters the dynamic behavior of NuMA at the cell cortex. We further show that Plk1 directly interacts and phosphorylates NuMA. Notably, NuMA-phosphorylation by Plk1 impacts its cortical localization, and this is needed for precise spindle orientation during metaphase. Overall, our finding connects spindle-pole pool of Plk1 with cortical NuMA and answers a long-standing puzzle about how spindle-pole Plk1 gradient dictates proper spindle orientation for error-free mitosis.
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Nakajima, Yu-ichiro, Zachary T. Lee, Sean A. McKinney, Selene K. Swanson, Laurence Florens und Matthew C. Gibson. „Junctional tumor suppressors interact with 14-3-3 proteins to control planar spindle alignment“. Journal of Cell Biology 218, Nr. 6 (14.05.2019): 1824–38. http://dx.doi.org/10.1083/jcb.201803116.
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Proper orientation of the mitotic spindle is essential for cell fate determination, tissue morphogenesis, and homeostasis. During epithelial proliferation, planar spindle alignment ensures the maintenance of polarized tissue architecture, and aberrant spindle orientation can disrupt epithelial integrity. Nevertheless, in vivo mechanisms that restrict the mitotic spindle to the plane of the epithelium remain poorly understood. Here we show that the junction-localized tumor suppressors Scribbled (Scrib) and Discs large (Dlg) control planar spindle orientation via Mud and 14-3-3 proteins in the Drosophila wing disc epithelium. During mitosis, Scrib is required for the junctional localization of Dlg, and both affect mitotic spindle movements. Using coimmunoprecipitation and mass spectrometry, we identify 14-3-3 proteins as Dlg-interacting partners and further report that loss of 14-3-3s causes both abnormal spindle orientation and disruption of epithelial architecture as a consequence of basal cell delamination and apoptosis. Combined, these biochemical and genetic analyses indicate that 14-3-3s function together with Scrib, Dlg, and Mud during planar cell division.
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Bergstralh, Dan T., Timm Haack und Daniel St Johnston. „Epithelial polarity and spindle orientation: intersecting pathways“. Philosophical Transactions of the Royal Society B: Biological Sciences 368, Nr. 1629 (05.11.2013): 20130291. http://dx.doi.org/10.1098/rstb.2013.0291.
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During asymmetric stem cell divisions, the mitotic spindle must be correctly oriented and positioned with respect to the axis of cell polarity to ensure that cell fate determinants are appropriately segregated into only one daughter cell. By contrast, epithelial cells divide symmetrically and orient their mitotic spindles perpendicular to the main apical–basal polarity axis, so that both daughter cells remain within the epithelium. Work in the past 20 years has defined a core ternary complex consisting of Pins, Mud and Gαi that participates in spindle orientation in both asymmetric and symmetric divisions. As additional factors that interact with this complex continue to be identified, a theme has emerged: there is substantial overlap between the mechanisms that orient the spindle and those that establish and maintain apical–basal polarity in epithelial cells. In this review, we examine several factors implicated in both processes, namely Canoe, Bazooka, aPKC and Discs large, and consider the implications of this work on how the spindle is oriented during epithelial cell divisions.
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den Elzen, Nicole, Carmen V. Buttery, Madhavi P. Maddugoda, Gang Ren und Alpha S. Yap. „Cadherin Adhesion Receptors Orient the Mitotic Spindle during Symmetric Cell Division in Mammalian Epithelia“. Molecular Biology of the Cell 20, Nr. 16 (15.08.2009): 3740–50. http://dx.doi.org/10.1091/mbc.e09-01-0023.
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Oriented cell division is a fundamental determinant of tissue organization. Simple epithelia divide symmetrically in the plane of the monolayer to preserve organ structure during epithelial morphogenesis and tissue turnover. For this to occur, mitotic spindles must be stringently oriented in the Z-axis, thereby establishing the perpendicular division plane between daughter cells. Spatial cues are thought to play important roles in spindle orientation, notably during asymmetric cell division. The molecular nature of the cortical cues that guide the spindle during symmetric cell division, however, is poorly understood. Here we show directly for the first time that cadherin adhesion receptors are required for planar spindle orientation in mammalian epithelia. Importantly, spindle orientation was disrupted without affecting tissue cohesion or epithelial polarity. This suggests that cadherin receptors can serve as cues for spindle orientation during symmetric cell division. We further show that disrupting cadherin function perturbed the cortical localization of APC, a microtubule-interacting protein that was required for planar spindle orientation. Together, these findings establish a novel morphogenetic function for cadherin adhesion receptors to guide spindle orientation during symmetric cell division.
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O'Connell, Christopher B., und Yu-li Wang. „Mammalian Spindle Orientation and Position Respond to Changes in Cell Shape in a Dynein-dependent Fashion“. Molecular Biology of the Cell 11, Nr. 5 (Mai 2000): 1765–74. http://dx.doi.org/10.1091/mbc.11.5.1765.
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In animal cells, positioning of the mitotic spindle is crucial for defining the plane of cytokinesis and the size ratio of daughter cells. We have characterized this phenomenon in a rat epithelial cell line using microscopy, micromanipulation, and microinjection. Unmanipulated cells position the mitotic spindle near their geometric center, with the spindle axis lying roughly parallel to the long axis of the cell. Spindles that were initially misoriented underwent directed rotation and caused a delay in anaphase onset. To gain further insight into this process, we gently deformed cells with a blunted glass needle to change the spatial relationship between the cortex and spindle. This manipulation induced spindle movement or rotation in metaphase and/or anaphase, until the spindle reached a proper position relative to the deformed shape. Spindle positioning was inhibited by either treatment with low doses of nocodazole or microinjection of antibodies against dynein, apparently due to the disruption of the organization of dynein and/or astral microtubules. Our results suggest that mitotic cells continuously monitor and maintain the position of the spindle relative to the cortex. This process is likely driven by interactions among astral microtubules, the motor protein dynein, and the cell cortex and may constitute part of a mitotic checkpoint mechanism.
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Lázaro-Diéguez, Francisco, Iaroslav Ispolatov und Anne Müsch. „Cell shape impacts on the positioning of the mitotic spindle with respect to the substratum“. Molecular Biology of the Cell 26, Nr. 7 (April 2015): 1286–95. http://dx.doi.org/10.1091/mbc.e14-08-1330.
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All known mechanisms of mitotic spindle orientation rely on astral microtubules. We report that even in the absence of astral microtubules, metaphase spindles in MDCK and HeLa cells are not randomly positioned along their x-z dimension, but preferentially adopt shallow β angles between spindle pole axis and substratum. The nonrandom spindle positioning is due to constraints imposed by the cell cortex in flat cells that drive spindles that are longer and/or wider than the cell's height into a tilted, quasidiagonal x-z position. In rounder cells, which are taller, fewer cortical constraints make the x-z spindle position more random. Reestablishment of astral microtubule–mediated forces align the spindle poles with cortical cues parallel to the substratum in all cells. However, in flat cells, they frequently cause spindle deformations. Similar deformations are apparent when confined spindles rotate from tilted to parallel positions while MDCK cells progress from prometaphase to metaphase. The spindle disruptions cause the engagement of the spindle assembly checkpoint. We propose that cell rounding serves to maintain spindle integrity during its positioning.
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Wang, Mengqiao, und Ruth N. Collins. „A lysine deacetylase Hos3 is targeted to the bud neck and involved in the spindle position checkpoint“. Molecular Biology of the Cell 25, Nr. 18 (15.09.2014): 2720–34. http://dx.doi.org/10.1091/mbc.e13-10-0619.
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An increasing number of cellular activities can be regulated by reversible lysine acetylation. Targeting the enzymes responsible for such posttranslational modifications is instrumental in defining their substrates and functions in vivo. Here we show that a Saccharomyces cerevisiae lysine deacetylase, Hos3, is asymmetrically targeted to the daughter side of the bud neck and to the daughter spindle pole body (SPB). The morphogenesis checkpoint member Hsl7 recruits Hos3 to the neck region. Cells with a defect in spindle orientation trigger Hos3 to load onto both SPBs. When associated symmetrically with both SPBs, Hos3 functions as a spindle position checkpoint (SPOC) component to inhibit mitotic exit. Neck localization of Hos3 is essential for its symmetric association with SPBs in cells with misaligned spindles. Our data suggest that Hos3 facilitates cross-talk between the morphogenesis checkpoint and the SPOC as a component of the intricate monitoring of spindle orientation after mitotic entry and before commitment to mitotic exit.
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Lázaro-Diéguez, Francisco, und Anne Müsch. „Cell–cell adhesion accounts for the different orientation of columnar and hepatocytic cell divisions“. Journal of Cell Biology 216, Nr. 11 (08.09.2017): 3847–59. http://dx.doi.org/10.1083/jcb.201608065.
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Mitotic spindle alignment with the basal or substrate-contacting domain ensures that dividing epithelial cells remain in the plane of the monolayer. Spindle orientation with respect to the substratum is established in metaphase coincident with maximal cell rounding, which enables unobstructed spindle rotation. Misaligned metaphase spindles are believed to result in divisions in which one daughter loses contact with the basal lamina. Here we describe a rescue mechanism that drives substrate-parallel spindle alignment of quasi-diagonal metaphase spindles in anaphase. It requires a Rho- and E-cadherin adhesion–dependent, substrate-parallel contractile actin belt at the apex that governs anaphase cell flattening. In contrast to monolayered Madin–Darby canine kidney cells, hepatocytic epithelial cells, which typically feature tilted metaphase spindles, lack this anaphase flattening mechanism and as a consequence maintain their spindle tilt through cytokinesis. This results in out-of-monolayer divisions, which we propose contribute to the stratified organization of hepatocyte cords in vivo.
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Takeda, Yutaka, Kaho Yamazaki, Kaho Hashimoto, Koki Watanabe, Takumi Chinen und Daiju Kitagawa. „The centriole protein CEP76 negatively regulates PLK1 activity in the cytoplasm for proper mitotic progression“. Journal of Cell Science 133, Nr. 19 (02.09.2020): jcs241281. http://dx.doi.org/10.1242/jcs.241281.
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ABSTRACTPolo-like kinase 1 (PLK1) dynamically changes its localization and plays important roles in proper mitotic progression. In particular, strict control of cytoplasmic PLK1 is needed to prevent mitotic defects. However, the regulation of cytoplasmic PLK1 is not fully understood. In this study, we show that CEP76, a centriolar protein, physically interacts with PLK1 and tightly controls the activation of cytoplasmic PLK1 during mitosis in human cells. We found that removal of centrosomes induced ectopic aggregation of PLK1, which is highly phosphorylated, in the cytoplasm during mitosis. Importantly, a targeted RNAi screen revealed that depletion of CEP76 resulted in a similar phenotype. In addition, depletion of CEP76 caused defective spindle orientation and mitotic delay. Moreover, the formation of ectopic PLK1 aggregates and defective spindle orientation were significantly suppressed by the inhibition of PLK1 kinase activity. Overall, these results demonstrate that CEP76 suppresses the aberrant activation of cytoplasmic PLK1 for proper mitotic progression.This article has an associated First Person interview with the first author of the paper.
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Saadaoui, Mehdi, Mickaël Machicoane, Florencia di Pietro, Fred Etoc, Arnaud Echard und Xavier Morin. „Dlg1 controls planar spindle orientation in the neuroepithelium through direct interaction with LGN“. Journal of Cell Biology 206, Nr. 6 (08.09.2014): 707–17. http://dx.doi.org/10.1083/jcb.201405060.
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Oriented cell divisions are necessary for the development of epithelial structures. Mitotic spindle orientation requires the precise localization of force generators at the cell cortex via the evolutionarily conserved LGN complex. However, polarity cues acting upstream of this complex in vivo in the vertebrate epithelia remain unknown. In this paper, we show that Dlg1 is localized at the basolateral cell cortex during mitosis and is necessary for planar spindle orientation in the chick neuroepithelium. Live imaging revealed that Dlg1 is required for directed spindle movements during metaphase. Mechanistically, we show that direct interaction between Dlg1 and LGN promotes cortical localization of the LGN complex. Furthermore, in human cells dividing on adhesive micropatterns, homogenously localized Dlg1 recruited LGN to the mitotic cortex and was also necessary for proper spindle orientation. We propose that Dlg1 acts primarily to recruit LGN to the cortex and that Dlg1 localization may additionally provide instructive cues for spindle orientation.
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Penisson, Maxime, Mingyue Jin, Shengming Wang, Shinji Hirotsune, Fiona Francis und Richard Belvindrah. „Lis1 mutation prevents basal radial glia-like cell production in the mouse“. Human Molecular Genetics 31, Nr. 6 (12.10.2021): 942–57. http://dx.doi.org/10.1093/hmg/ddab295.
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Abstract Human cerebral cortical malformations are associated with progenitor proliferation and neuronal migration abnormalities. Progenitor cells include apical radial glia, intermediate progenitors and basal (or outer) radial glia (bRGs or oRGs). bRGs are few in number in lissencephalic species (e.g. the mouse) but abundant in gyrencephalic brains. The LIS1 gene coding for a dynein regulator, is mutated in human lissencephaly, associated also in some cases with microcephaly. LIS1 was shown to be important during cell division and neuronal migration. Here, we generated bRG-like cells in the mouse embryonic brain, investigating the role of Lis1 in their formation. This was achieved by in utero electroporation of a hominoid-specific gene TBC1D3 (coding for a RAB-GAP protein) at mouse embryonic day (E) 14.5. We first confirmed that TBC1D3 expression in wild-type (WT) brain generates numerous Pax6+ bRG-like cells that are basally localized. Second, using the same approach, we assessed the formation of these cells in heterozygote Lis1 mutant brains. Our novel results show that Lis1 depletion in the forebrain from E9.5 prevented subsequent TBC1D3-induced bRG-like cell amplification. Indeed, we observe perturbation of the ventricular zone (VZ) in the mutant. Lis1 depletion altered adhesion proteins and mitotic spindle orientations at the ventricular surface and increased the proportion of abventricular mitoses. Progenitor outcome could not be further altered by TBC1D3. We conclude that disruption of Lis1/LIS1 dosage is likely to be detrimental for appropriate progenitor number and position, contributing to lissencephaly pathogenesis.
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Carminati, Janet L., und Tim Stearns. „Microtubules Orient the Mitotic Spindle in Yeast through Dynein-dependent Interactions with the Cell Cortex“. Journal of Cell Biology 138, Nr. 3 (11.08.1997): 629–41. http://dx.doi.org/10.1083/jcb.138.3.629.
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Proper orientation of the mitotic spindle is critical for successful cell division in budding yeast. To investigate the mechanism of spindle orientation, we used a green fluorescent protein (GFP)–tubulin fusion protein to observe microtubules in living yeast cells. GFP–tubulin is incorporated into microtubules, allowing visualization of both cytoplasmic and spindle microtubules, and does not interfere with normal microtubule function. Microtubules in yeast cells exhibit dynamic instability, although they grow and shrink more slowly than microtubules in animal cells. The dynamic properties of yeast microtubules are modulated during the cell cycle. The behavior of cytoplasmic microtubules revealed distinct interactions with the cell cortex that result in associated spindle movement and orientation. Dynein-mutant cells had defects in these cortical interactions, resulting in misoriented spindles. In addition, microtubule dynamics were altered in the absence of dynein. These results indicate that microtubules and dynein interact to produce dynamic cortical interactions, and that these interactions result in the force driving spindle orientation.
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Dewey, Evan B., und Christopher A. Johnston. „Diverse mitotic functions of the cytoskeletal cross-linking protein Shortstop suggest a role in Dynein/Dynactin activity“. Molecular Biology of the Cell 28, Nr. 19 (15.09.2017): 2555–68. http://dx.doi.org/10.1091/mbc.e17-04-0219.
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Proper assembly and orientation of the bipolar mitotic spindle is critical to the fidelity of cell division. Mitotic precision fundamentally contributes to cell fate specification, tissue development and homeostasis, and chromosome distribution within daughter cells. Defects in these events are thought to contribute to several human diseases. The underlying mechanisms that function in spindle morphogenesis and positioning remain incompletely defined, however. Here we describe diverse roles for the actin-microtubule cross-linker Shortstop (Shot) in mitotic spindle function in Drosophila. Shot localizes to mitotic spindle poles, and its knockdown results in an unfocused spindle pole morphology and a disruption of proper spindle orientation. Loss of Shot also leads to chromosome congression defects, cell cycle progression delay, and defective chromosome segregation during anaphase. These mitotic errors trigger apoptosis in Drosophila epithelial tissue, and blocking this apoptotic response results in a marked induction of the epithelial–mesenchymal transition marker MMP-1. The actin-binding domain of Shot directly interacts with Actin-related protein-1 (Arp-1), a key component of the Dynein/Dynactin complex. Knockdown of Arp-1 phenocopies Shot loss universally, whereas chemical disruption of F-actin does so selectively. Our work highlights novel roles for Shot in mitosis and suggests a mechanism involving Dynein/Dynactin activation.
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Loginova, Dina B., Anastasia A. Zhuravleva und Olga G. Silkova. „Random chromosome distribution in the first meiosis of F1 disomic substitution line 2R(2D) x rye hybrids (ABDR, 4× = 28) occurs without bipolar spindle assembly“. Comparative Cytogenetics 14, Nr. 4 (09.10.2020): 453–82. http://dx.doi.org/10.3897/compcytogen.v14.i4.55827.
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The assembly of the microtubule-based spindle structure in plant meiosis remains poorly understood compared with our knowledge of mitotic spindle formation. One of the approaches in our understanding of microtubule dynamics is to study spindle assembly in meiosis of amphyhaploids. Using immunostaining with phH3Ser10, CENH3 and α-tubulin-specific antibodies, we studied the chromosome distribution and spindle organisation in meiosis of F1 2R(2D)xR wheat-rye hybrids (genome structure ABDR, 4× = 28), as well as in wheat and rye mitosis and meiosis. At the prometaphase of mitosis, spindle assembly was asymmetric; one half of the spindle assembled before the other, with simultaneous chromosome alignment in the spindle mid-zone. At diakinesis in wheat and rye, microtubules formed a pro-spindle which was subsequently disassembled followed by a bipolar spindle assembly. In the first meiosis of hybrids 2R(2D)xR, a bipolar spindle was not found and the kinetochore microtubules distributed the chromosomes. Univalent chromosomes are characterised by a monopolar orientation and maintenance of sister chromatid and centromere cohesion. Presence of bivalents did not affect the formation of a bipolar spindle. Since the central spindle was absent, phragmoplast originates from “interpolar” microtubules generated by kinetochores. Cell plate development occurred with a delay. However, meiocytes in meiosis II contained apparently normal bipolar spindles. Thus, we can conclude that: (1) cohesion maintenance in centromeres and between arms of sister chromatids may negatively affect bipolar spindle formation in the first meiosis; (2) 2R/2D rye/wheat chromosome substitution affects the regulation of the random chromosome distribution in the absence of a bipolar spindle.
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Lee, Laifong, Saskia K. Klee, Marie Evangelista, Charles Boone und David Pellman. „Control of Mitotic Spindle Position by the Saccharomyces cerevisiae Formin Bni1p“. Journal of Cell Biology 144, Nr. 5 (08.03.1999): 947–61. http://dx.doi.org/10.1083/jcb.144.5.947.
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Alignment of the mitotic spindle with the axis of cell division is an essential process in Saccharomyces cerevisiae that is mediated by interactions between cytoplasmic microtubules and the cell cortex. We found that a cortical protein, the yeast formin Bni1p, was required for spindle orientation. Two striking abnormalities were observed in bni1Δ cells. First, the initial movement of the spindle pole body (SPB) toward the emerging bud was defective. This phenotype is similar to that previously observed in cells lacking the kinesin Kip3p and, in fact, BNI1 and KIP3 were found to be in the same genetic pathway. Second, abnormal pulling interactions between microtubules and the cortex appeared to cause preanaphase spindles in bni1Δ cells to transit back and forth between the mother and the bud. We therefore propose that Bni1p may localize or alter the function of cortical microtubule-binding sites in the bud. Additionally, we present evidence that other bipolar bud site determinants together with cortical actin are also required for spindle orientation.
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Chippalkatti, Rohan, Boris Egger und Beat Suter. „Mms19 promotes spindle microtubule assembly in Drosophila neural stem cells“. PLOS Genetics 16, Nr. 11 (19.11.2020): e1008913. http://dx.doi.org/10.1371/journal.pgen.1008913.
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Mitotic divisions depend on the timely assembly and proper orientation of the mitotic spindle. Malfunctioning of these processes can considerably delay mitosis, thereby compromising tissue growth and homeostasis, and leading to chromosomal instability. Loss of functional Mms19 drastically affects the growth and development of mitotic tissues in Drosophila larvae and we now demonstrate that Mms19 is an important factor that promotes spindle and astral microtubule (MT) growth, and MT stability and bundling. Mms19 function is needed for the coordination of mitotic events and for the rapid progression through mitosis that is characteristic of neural stem cells. Surprisingly, Mms19 performs its mitotic activities through two different pathways. By stimulating the mitotic kinase cascade, it triggers the localization of the MT regulatory complex TACC/Msps (Transforming Acidic Coiled Coil/Minispindles, the homolog of human ch-TOG) to the centrosome. This activity of Mms19 can be rescued by stimulating the mitotic kinase cascade. However, other aspects of the Mms19 phenotypes cannot be rescued in this way, pointing to an additional mechanism of Mms19 action. We provide evidence that Mms19 binds directly to MTs and that this stimulates MT stability and bundling.
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Sandquist, Joshua C., Matthew E. Larson, Sarah Woolner, Zhiwei Ding und William M. Bement. „An interaction between myosin-10 and the cell cycle regulator Wee1 links spindle dynamics to mitotic progression in epithelia“. Journal of Cell Biology 217, Nr. 3 (10.01.2018): 849–59. http://dx.doi.org/10.1083/jcb.201708072.
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Anaphase in epithelia typically does not ensue until after spindles have achieved a characteristic position and orientation, but how or even if cells link spindle position to anaphase onset is unknown. Here, we show that myosin-10 (Myo10), a motor protein involved in epithelial spindle dynamics, binds to Wee1, a conserved regulator of cyclin-dependent kinase 1 (Cdk1). Wee1 inhibition accelerates progression through metaphase and disrupts normal spindle dynamics, whereas perturbing Myo10 function delays anaphase onset in a Wee1-dependent manner. Moreover, Myo10 perturbation increases Wee1-mediated inhibitory phosphorylation on Cdk1, which, unexpectedly, concentrates at cell–cell junctions. Based on these and other results, we propose a model in which the Myo10–Wee1 interaction coordinates attainment of spindle position and orientation with anaphase onset.
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Keshri, Riya, Ashwathi Rajeevan und Sachin Kotak. „PP2A-B55γ counteracts Cdk1 and regulates proper spindle orientation through the cortical dynein adaptor NuMA“. Journal of Cell Science 133, Nr. 14 (26.06.2020): jcs243857. http://dx.doi.org/10.1242/jcs.243857.
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ABSTRACTProper orientation of the mitotic spindle is critical for accurate development and morphogenesis. In human cells, spindle orientation is regulated by the evolutionarily conserved protein NuMA, which interacts with dynein and enriches it at the cell cortex. Pulling forces generated by cortical dynein orient the mitotic spindle. Cdk1-mediated phosphorylation of NuMA at threonine 2055 (T2055) negatively regulates its cortical localization. Thus, only NuMA not phosphorylated at T2055 localizes at the cell cortex. However, the identity and the mechanism of action of the phosphatase complex involved in T2055 dephosphorylation remains elusive. Here, we characterized the PPP2CA-B55γ (PPP2R2C)–PPP2R1B complex that counteracts Cdk1 to orchestrate cortical NuMA for proper spindle orientation. In vitro reconstitution experiments revealed that this complex is sufficient for T2055 dephosphorylation. Importantly, we identified polybasic residues in NuMA that are critical for T2055 dephosphorylation, and for maintaining appropriate cortical NuMA levels for accurate spindle elongation. Furthermore, we found that Cdk1-mediated phosphorylation and PP2A-B55γ-mediated dephosphorylation at T2055 are reversible events. Altogether, this study uncovers a novel mechanism by which Cdk1 and its counteracting PP2A-B55γ complex orchestrate spatiotemporal levels of cortical force generators for flawless mitosis.
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Zheng, Zhen, Huabin Zhu, Qingwen Wan, Jing Liu, Zhuoni Xiao, David P. Siderovski und Quansheng Du. „LGN regulates mitotic spindle orientation during epithelial morphogenesis“. Journal of Cell Biology 189, Nr. 2 (12.04.2010): 275–88. http://dx.doi.org/10.1083/jcb.200910021.
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Coordinated cell polarization and mitotic spindle orientation are thought to be important for epithelial morphogenesis. Whether spindle orientation is indeed linked to epithelial morphogenesis and how it is controlled at the molecular level is still unknown. Here, we show that the NuMA- and Gα-binding protein LGN is required for directing spindle orientation during cystogenesis of MDCK cells. LGN localizes to the lateral cell cortex, and is excluded from the apical cell cortex of dividing cells. Depleting LGN, preventing its cortical localization, or disrupting its interaction with endogenous NuMA or Gα proteins all lead to spindle misorientation and abnormal cystogenesis. Moreover, artificial mistargeting of endogenous LGN to the apical membrane results in a near 90° rotation of the spindle axis and profound cystogenesis defects that are dependent on cell division. The normal apical exclusion of LGN during mitosis appears to be mediated by atypical PKC. Thus, cell polarization–mediated spatial restriction of spindle orientation determinants is critical for epithelial morphogenesis.
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Machicoane, Mickael, Cristina A. de Frutos, Jenny Fink, Murielle Rocancourt, Yannis Lombardi, Sonia Garel, Matthieu Piel und Arnaud Echard. „SLK-dependent activation of ERMs controls LGN–NuMA localization and spindle orientation“. Journal of Cell Biology 205, Nr. 6 (23.06.2014): 791–99. http://dx.doi.org/10.1083/jcb.201401049.
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Mitotic spindle orientation relies on a complex dialog between the spindle microtubules and the cell cortex, in which F-actin has been recently implicated. Here, we report that the membrane–actin linkers ezrin/radixin/moesin (ERMs) are strongly and directly activated by the Ste20-like kinase at mitotic entry in mammalian cells. Using microfabricated adhesive substrates to control the axis of cell division, we found that the activation of ERMs plays a key role in guiding the orientation of the mitotic spindle. Accordingly, impairing ERM activation in apical progenitors of the mouse embryonic neocortex severely disturbed spindle orientation in vivo. At the molecular level, ERM activation promotes the polarized association at the mitotic cortex of leucine-glycine-asparagine repeat protein (LGN) and nuclear mitotic apparatus (NuMA) protein, two essential factors for spindle orientation. We propose that activated ERMs, together with Gαi, are critical for the correct localization of LGN–NuMA force generator complexes and hence for proper spindle orientation.
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Fraschini, Roberta, Denis Bilotta, Giovanna Lucchini und Simonetta Piatti. „Functional Characterization of Dma1 and Dma2, the Budding Yeast Homologues of Schizosaccharomyces pombe Dma1 and Human Chfr“. Molecular Biology of the Cell 15, Nr. 8 (August 2004): 3796–810. http://dx.doi.org/10.1091/mbc.e04-02-0094.
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Proper transmission of genetic information requires correct assembly and positioning of the mitotic spindle, responsible for driving each set of sister chromatids to the two daughter cells, followed by cytokinesis. In case of altered spindle orientation, the spindle position checkpoint inhibits Tem1-dependent activation of the mitotic exit network (MEN), thus delaying mitotic exit and cytokinesis until errors are corrected. We report a functional analysis of two previously uncharacterized budding yeast proteins, Dma1 and Dma2, 58% identical to each other and homologous to human Chfr and Schizosaccharomyces pombe Dma1, both of which have been previously implicated in mitotic checkpoints. We show that Dma1 and Dma2 are involved in proper spindle positioning, likely regulating septin ring deposition at the bud neck. DMA2 overexpression causes defects in septin ring disassembly at the end of mitosis and in cytokinesis. The latter defects can be rescued by either eliminating the spindle position checkpoint protein Bub2 or overproducing its target, Tem1, both leading to MEN hyperactivation. In addition, dma1Δ dma2Δ cells fail to activate the spindle position checkpoint in response to the lack of dynein, whereas ectopic expression of DMA2 prevents unscheduled mitotic exit of spindle checkpoint mutants treated with microtubule-depolymerizing drugs. Although their primary functions remain to be defined, our data suggest that Dma1 and Dma2 might be required to ensure timely MEN activation in telophase.
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McHugh, Toni, Agata A. Gluszek und Julie P. I. Welburn. „Microtubule end tethering of a processive kinesin-8 motor Kif18b is required for spindle positioning“. Journal of Cell Biology 217, Nr. 7 (16.04.2018): 2403–16. http://dx.doi.org/10.1083/jcb.201705209.
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Mitotic spindle positioning specifies the plane of cell division during anaphase. Spindle orientation and positioning are therefore critical to ensure symmetric division in mitosis and asymmetric division during development. The control of astral microtubule length plays an essential role in positioning the spindle. In this study, using gene knockout, we show that the kinesin-8 Kif18b controls microtubule length to center the mitotic spindle at metaphase. Using in vitro reconstitution, we reveal that Kif18b is a highly processive plus end–directed motor that uses a C-terminal nonmotor microtubule-binding region to accumulate at growing microtubule plus ends. This region is regulated by phosphorylation to spatially control Kif18b accumulation at plus ends and is essential for Kif18b-dependent spindle positioning and regulation of microtubule length. Finally, we demonstrate that Kif18b shortens microtubules by increasing the catastrophe rate of dynamic microtubules. Overall, our work reveals that Kif18b uses its motile properties to reach microtubule ends, where it regulates astral microtubule length to ensure spindle centering.
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Zellag, Réda M., Yifan Zhao, Vincent Poupart, Ramya Singh, Jean-Claude Labbé und Abigail R. Gerhold. „CentTracker: a trainable, machine-learning–based tool for large-scale analyses of Caenorhabditis elegans germline stem cell mitosis“. Molecular Biology of the Cell 32, Nr. 9 (19.04.2021): 915–30. http://dx.doi.org/10.1091/mbc.e20-11-0716.
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We provide technical and analytical tools to facilitate large-scale intravital imaging studies of Caenorhabditis elegans germline stem cell (GSC) mitosis, which are expandable to other model systems. We assess multiple GSC mitotic features and find evidence for spatial clustering of divisions and a spindle orientation bias within the stem cell pool.
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Kosetsu, Ken, Takashi Murata, Moé Yamada, Momoko Nishina, Joanna Boruc, Mitsuyasu Hasebe, Daniël Van Damme und Gohta Goshima. „Cytoplasmic MTOCs control spindle orientation for asymmetric cell division in plants“. Proceedings of the National Academy of Sciences 114, Nr. 42 (02.10.2017): E8847—E8854. http://dx.doi.org/10.1073/pnas.1713925114.
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Proper orientation of the cell division axis is critical for asymmetric cell divisions that underpin cell differentiation. In animals, centrosomes are the dominant microtubule organizing centers (MTOC) and play a pivotal role in axis determination by orienting the mitotic spindle. In land plants that lack centrosomes, a critical role of a microtubular ring structure, the preprophase band (PPB), has been observed in this process; the PPB is required for orienting (before prophase) and guiding (in telophase) the mitotic apparatus. However, plants must possess additional mechanisms to control the division axis, as certain cell types or mutants do not form PPBs. Here, using live imaging of the gametophore of the moss Physcomitrella patens, we identified acentrosomal MTOCs, which we termed “gametosomes,” appearing de novo and transiently in the prophase cytoplasm independent of PPB formation. We show that gametosomes are dispensable for spindle formation but required for metaphase spindle orientation. In some cells, gametosomes appeared reminiscent of the bipolar MT “polar cap” structure that forms transiently around the prophase nucleus in angiosperms. Specific disruption of the polar caps in tobacco cells misoriented the metaphase spindles and frequently altered the final division plane, indicating that they are functionally analogous to the gametosomes. These results suggest a broad use of transient MTOC structures as the spindle orientation machinery in plants, compensating for the evolutionary loss of centrosomes, to secure the initial orientation of the spindle in a spatial window that allows subsequent fine-tuning of the division plane axis by the guidance machinery.
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Hwang, Hyung-Seo, und Kiwon Song. „IBD2 Encodes a Novel Component of the Bub2p-Dependent Spindle Checkpoint in the Budding Yeast Saccharomyces cerevisiae“. Genetics 161, Nr. 2 (01.06.2002): 595–609. http://dx.doi.org/10.1093/genetics/161.2.595.
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Abstract During mitosis, genomic integrity is maintained by the proper coordination of mitotic events through the spindle checkpoint. The bifurcated spindle checkpoint blocks cell cycle progression at metaphase by monitoring unattached kinetochores and inhibits mitotic exit in response to the incorrect orientation of the mitotic spindle. Bfa1p is a spindle checkpoint regulator of budding yeast in the Bub2p checkpoint pathway for proper mitotic exit. We have isolated a novel Bfa1p interacting protein named Ibd2p in the budding yeast Saccharomyces cerevisiae. We found that IBD2 (Inhibition of Bud Division 2) is not an essential gene but its deletion mutant proceeded through the cell cycle in the presence of microtubule-destabilizing drugs, thereby inducing a sharp decrease in viability. In addition, overexpression of Mps1p caused partial mitotic arrest in ibd2Δ as well as in bub2Δ, suggesting that IBD2 encodes a novel component of the spindle checkpoint downstream of MPS1. Overexpression of Ibd2p induced mitotic arrest with increased levels of Clb2p in wild type and mad2Δ, but not in deletion mutants of BUB2 and BFA1. Pds1p was also stabilized by the overexpression of Ibd2p in wild-type cells. The mitotic arrest defects observed in ibd2Δ in the presence of nocodazole were restored by additional copies of BUB2, BFA1, and CDC5, whereas an extra copy of IBD2 could not rescue the mitotic arrest defects of bub2Δ and bfa1Δ. The mitotic arrest defects of ibd2Δ were not recovered by MAD2, or vice versa. Analysis of the double mutant combinations ibd2Δmad2Δ, ibd2Δbub2Δ, and ibd2Δdyn1Δ showed that IBD2 belongs to the BUB2 epistasis group. Taken together, these data demonstrate that IBD2 encodes a novel component of the BUB2-dependent spindle checkpoint pathway that functions upstream of BUB2 and BFA1.
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Molla, Annie. „Aurora kinases orchestrate mitosis; who are the players?“ BioMolecular Concepts 1, Nr. 2 (01.08.2010): 147–55. http://dx.doi.org/10.1515/bmc.2010.014.
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AbstractThe Aurora are a conserved family of serine/threonine kinases with essential functions in cell division. In mitosis, Aurora kinases are required for chromosome segregation, condensation and orientation in the metaphase plate, spindle assembly, and the completion of cytokinesis. This review presents the Aurora kinases, their partners and how their interactions impact on the different mitotic functions.
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Varma, Dileep, Pascale Monzo, Stephanie A. Stehman und Richard B. Vallee. „Direct role of dynein motor in stable kinetochore-microtubule attachment, orientation, and alignment“. Journal of Cell Biology 182, Nr. 6 (22.09.2008): 1045–54. http://dx.doi.org/10.1083/jcb.200710106.
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Cytoplasmic dynein has been implicated in diverse mitotic functions, several involving its association with kinetochores. Much of the supporting evidence comes from inhibition of dynein regulatory factors. To obtain direct insight into kinetochore dynein function, we expressed a series of dynein tail fragments, which we find displace motor-containing dynein heavy chain (HC) from kinetochores without affecting other subunits, regulatory factors, or microtubule binding proteins. Cells with bipolar mitotic spindles progress to late prometaphase-metaphase at normal rates. However, the dynein tail, dynactin, Mad1, and BubR1 persist at the aligned kinetochores, which is consistent with a role for dynein in self-removal and spindle assembly checkpoint inactivation. Kinetochore pairs also show evidence of misorientation relative to the spindle equator and abnormal oscillatory behavior. Further, kinetochore microtubule bundles are severely destabilized at reduced temperatures. Dynein HC RNAi and injection of anti-dynein antibody in MG132-arrested metaphase cells produced similar effects. These results identify a novel function for the dynein motor in stable microtubule attachment and maintenance of kinetochore orientation during metaphase chromosome alignment.
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Schoborg, Todd, Allison L. Zajac, Carey J. Fagerstrom, Rodrigo X. Guillen und Nasser M. Rusan. „An Asp–CaM complex is required for centrosome–pole cohesion and centrosome inheritance in neural stem cells“. Journal of Cell Biology 211, Nr. 5 (30.11.2015): 987–98. http://dx.doi.org/10.1083/jcb.201509054.
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The interaction between centrosomes and mitotic spindle poles is important for efficient spindle formation, orientation, and cell polarity. However, our understanding of the dynamics of this relationship and implications for tissue homeostasis remains poorly understood. Here we report that Drosophila melanogaster calmodulin (CaM) regulates the ability of the microcephaly-associated protein, abnormal spindle (Asp), to cross-link spindle microtubules. Both proteins colocalize on spindles and move toward spindle poles, suggesting that they form a complex. Our binding and structure–function analysis support this hypothesis. Disruption of the Asp–CaM interaction alone leads to unfocused spindle poles and centrosome detachment. This behavior leads to randomly inherited centrosomes after neuroblast division. We further show that spindle polarity is maintained in neuroblasts despite centrosome detachment, with the poles remaining stably associated with the cell cortex. Finally, we provide evidence that CaM is required for Asp’s spindle function; however, it is completely dispensable for Asp’s role in microcephaly suppression.
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Heald, Rebecca, Régis Tournebize, Anja Habermann, Eric Karsenti und Anthony Hyman. „Spindle Assembly in Xenopus Egg Extracts: Respective Roles of Centrosomes and Microtubule Self-Organization“. Journal of Cell Biology 138, Nr. 3 (11.08.1997): 615–28. http://dx.doi.org/10.1083/jcb.138.3.615.
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In Xenopus egg extracts, spindles assembled around sperm nuclei contain a centrosome at each pole, while those assembled around chromatin beads do not. Poles can also form in the absence of chromatin, after addition of a microtubule stabilizing agent to extracts. Using this system, we have asked (a) how are spindle poles formed, and (b) how does the nucleation and organization of microtubules by centrosomes influence spindle assembly? We have found that poles are morphologically similar regardless of their origin. In all cases, microtubule organization into poles requires minus end–directed translocation of microtubules by cytoplasmic dynein, which tethers centrosomes to spindle poles. However, in the absence of pole formation, microtubules are still sorted into an antiparallel array around mitotic chromatin. Therefore, other activities in addition to dynein must contribute to the polarized orientation of microtubules in spindles. When centrosomes are present, they provide dominant sites for pole formation. Thus, in Xenopus egg extracts, centrosomes are not necessarily required for spindle assembly but can regulate the organization of microtubules into a bipolar array.
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Yang, Zhenye, Jing Guo, Qi Chen, Chong Ding, Juan Du und Xueliang Zhu. „Silencing Mitosin Induces Misaligned Chromosomes, Premature Chromosome Decondensation before Anaphase Onset, and Mitotic Cell Death“. Molecular and Cellular Biology 25, Nr. 10 (15.05.2005): 4062–74. http://dx.doi.org/10.1128/mcb.25.10.4062-4074.2005.
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ABSTRACT Mitosin (also named CENP-F) is a large human nuclear protein transiently associated with the outer kinetochore plate in M phase. Using RNA interference and fluorescence microscopy, we showed that mitosin depletion attenuated chromosome congression and led to metaphase arrest with misaligned polar chromosomes whose kinetochores showed few cold-stable microtubules. Kinetochores of fully aligned chromosomes often failed to show orientation in the direction of the spindle long axis. Moreover, tension across their sister kinetochores was decreased by 53% on average. These phenotypes collectively imply defects in motor functions in mitosin-depleted cells and are similar to those of CENP-E depletion. Consistently, the intensities of CENP-E and cytoplasmic dynein and dynactin, which are motors controlling microtubule attachment and chromosome movement, were reduced at the kinetochore in a microtubule-dependent manner. In addition, after being arrested in pseudometaphase for approximately 2 h, mitosin-depleted cells died before anaphase initiation through apoptosis. The dying cells exhibited progressive chromosome arm decondensation, while the centromeres were still associated with spindles. Mitosin is therefore essential for full chromosome alignment, possibly by promoting proper kinetochore attachments through modulating CENP-E and dynein functions. Its depletion also prematurely triggers chromosome decondensation, a process that normally occurs from telophase for the nucleus reassembly, thus resulting in apoptosis.
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Meadows, John C. „Interplay between mitotic kinesins and the Aurora kinase–PP1 (protein phosphatase 1) axis“. Biochemical Society Transactions 41, Nr. 6 (20.11.2013): 1761–65. http://dx.doi.org/10.1042/bst20130191.
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Correct transmission of genetic information from mother to daughter cells is necessary for development and survival. Accurate segregation is achieved by bipolar attachment of sister kinetochores in each chromatid pair to spindle microtubules emanating from opposite spindle poles, a process known as chromosome bi-orientation. Achieving this requires dynamic interplay between kinetochore proteins, kinesin motor proteins and cell cycle regulators. Chromosome bi-orientation is monitored by a surveillance mechanism known as the SAC (spindle assembly checkpoint). The Aurora B kinase, which is bound to the inner centromere during early mitosis, plays a central role in both chromosome bi-orientation and the spindle checkpoint. The application of tension across centromeres establishes a spatial gradient of high phosphorylation activity at the inner centromere and low phosphorylation activity at the outer kinetochore. This gradient is further refined by the association of PP1 (protein phosphatase 1) to the outer kinetochore, which stabilizes kinetochore–microtubule interactions and silences the spindle checkpoint by dephosphorylating Aurora B kinase targets when chromosome bi-orientation is achieved. In the present review, I discuss emerging evidence that bidirectional cross-talk between mitotic kinesins and the Aurora kinase–PP1 axis is crucial for co-ordinating chromosome bi-orientation and spindle checkpoint signalling in eukaryotes.
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Levesque, Aime A., und Duane A. Compton. „The chromokinesin Kid is necessary for chromosome arm orientation and oscillation, but not congression, on mitotic spindles“. Journal of Cell Biology 154, Nr. 6 (17.09.2001): 1135–46. http://dx.doi.org/10.1083/jcb.200106093.
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Chromokinesins have been postulated to provide the polar ejection force needed for chromosome congression during mitosis. We have evaluated that possibility by monitoring chromosome movement in vertebrate-cultured cells using time-lapse differential interference contrast microscopy after microinjection with antibodies specific for the chromokinesin Kid. 17.5% of cells injected with Kid-specific antibodies have one or more chromosomes that remain closely opposed to a spindle pole and fail to enter anaphase. In contrast, 82.5% of injected cells align chromosomes in metaphase, progress to anaphase, and display chromosome velocities not significantly different from control cells. However, injected cells lack chromosome oscillations, and chromosome orientation is atypical because chromosome arms extend toward spindle poles during both congression and metaphase. Furthermore, chromosomes cluster into a mass and fail to oscillate when Kid is perturbed in cells containing monopolar spindles. These data indicate that Kid generates the polar ejection force that pushes chromosome arms away from spindle poles in vertebrate-cultured cells. This force increases the efficiency with which chromosomes make bipolar spindle attachments and regulates kinetochore activities necessary for chromosome oscillation, but is not essential for chromosome congression.
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Efimov, Vladimir P., und N. Ronald Morris. „A Screen for Dynein Synthetic Lethals in Aspergillus nidulans Identifies Spindle Assembly Checkpoint Genes and Other Genes Involved in Mitosis“. Genetics 149, Nr. 1 (01.05.1998): 101–16. http://dx.doi.org/10.1093/genetics/149.1.101.
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Abstract Cytoplasmic dynein is a ubiquitously expressed microtubule motor involved in vesicle transport, mitosis, nuclear migration, and spindle orientation. In the filamentous fungus Aspergillus nidulans, inactivation of cytoplasmic dynein, although not lethal, severely impairs nuclear migration. The role of dynein in mitosis and vesicle transport in this organism is unclear. To investigate the complete range of dynein function in A. nidulans, we searched for synthetic lethal mutations that significantly reduced growth in the absence of dynein but had little effect on their own. We isolated 19 sld (synthetic lethality without dynein) mutations in nine different genes. Mutations in two genes exacerbate the nuclear migration defect seen in the absence of dynein. Mutations in six other genes, including sldA and sldB, show a strong synthetic lethal interaction with a mutation in the mitotic kinesin bimC and, thus, are likely to play a role in mitosis. Mutations in sldA and sldB also confer hypersensitivity to the microtubule-destabilizing drug benomyl. sldA and sldB were cloned by complementation of their mutant phenotypes using an A. nidulans autonomously replicating vector. Sequencing revealed homology to the spindle assembly checkpoint genes BUB1 and BUB3 from Saccharomyces cerevisiae. Genetic interaction between dynein and spindle assembly checkpoint genes, as well as other mitotic genes, indicates that A. nidulans dynein plays a role in mitosis. We suggest a model for dynein motor action in A. nidulans that can explain dynein involvement in both mitosis and nuclear distribution.
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Kuo, Wei-Ting, Li Zuo und Jerrold Turner. „THE TIGHT JUNCTION PROTEIN ZO-1 REGULATES MITOTIC SPINDLE ORIENTATION TO ENABLE EFFICIENT MUCOSAL REPAIR“. Inflammatory Bowel Diseases 27, Supplement_1 (01.01.2021): S28. http://dx.doi.org/10.1093/ibd/izaa347.064.
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Abstract The intestinal damage can be caused by physical, infectious, and immune-mediated injury. Rapid repair, which is essential for a return to mucosal homeostasis, depends on rapid epithelial migration, i.e., restitution, as well as epithelial proliferation and differentiation. Barrier restoration is a critical component of this repair process, but the contributions of structural proteins that form the barrier to mucosal repair have not been defined. Aim: To determine the contributions of the intestinal epithelial tight junction protein zonula occludens-1 (ZO-1) to mucosal repair. Results: Intestinal epithelial ZO-1 transcript and protein expression are reduced in biopsies from inflammatory bowel disease (IBD) patients relative to healthy controls. To determine if this ZO-1 loss contributes to disease pathogenesis, we created intestinal epithelial ZO-1-deficient Tjp1f/f x villin-Cre+ mice. When stressed, for example, with 2% DSS, ZO-1-deficient mice displayed much greater mucosal damage and weight loss relative to ZO-1-sufficient mice and failed to recover fully, even 4 weeks after DSS discontinuation. To better define the defect, mice were injected with nucleoside analogs (BrdU and EdU) to label proliferating cells 1 and 3 days after DSS discontinuation. When assessed 2 hours after labeling, numbers of labeled nuclei were significantly reduced in ZO-1-deficient mice relative to ZO-1-sufficient mice. More striking, however, was the nuclear fragmentation and staining for cleaved caspase-3 at 24 hours after labeling. In vitro studies of colonoids were used to better define the mechanisms of epithelial loss. Colonoids from ZO-1-deficient mice were smaller, had reduced numbers of buds (crypt domains) and Lgr5+ stem cells, and were nonresponsive to enhanced Wnt signaling induced by the GSK3 inhibitor CHIR99021, relative to ZO-1-sufficient colonoids. Live imaging of mitosis showed misoriented mitotic spindles in ZO-1-deficient colonoids that caused one daughter cell to lose contact with the extracellular matrix. Misoriented mitotic spindles were also present in tissues from DSS-treated ZO-1-deficient, not ZO-1-sufficient, mice. Live imaging of colonoids from mRFP1-ZO-1 transgenic mice detected transient accumulation of ZO-1 at the cleavage furrow, suggesting that ZO-1 interactions at this site required for accurate mitotic spindle orientation. Conclusion: ZO-1 has a previously unappreciated, noncanonical function in mitotic spindle orientation that is independent of barrier maintenance but central to epithelial proliferation and repair. We postulate that, in the absence of ZO-1, loss of contact with the basement membrane leads to anoikis, i.e., detachment-induced apoptosis, and an abortive proliferative response that compromises repair. We speculate that ZO-1 downregulation in IBD may similarly interfere with mucosal healing. Support: NIH (DK068271, DK061931)
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Nestor-Bergmann, Alexander, Georgina Goddard und Sarah Woolner. „Force and the spindle: Mechanical cues in mitotic spindle orientation“. Seminars in Cell & Developmental Biology 34 (Oktober 2014): 133–39. http://dx.doi.org/10.1016/j.semcdb.2014.07.008.
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