The Experts below are selected from a list of 2292 Experts worldwide ranked by ideXlab platform
Francis J Mcnally - One of the best experts on this subject based on the ideXlab platform.
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kinesin 1 and cytoplasmic dynein act sequentially to move the meiotic spindle to the Oocyte Cortex in caenorhabditis elegans
Molecular Biology of the Cell, 2009Co-Authors: Marina L Ellefson, Francis J McnallyAbstract:During female meiosis in animals, the meiotic spindle is attached to the egg Cortex by one pole during anaphase to allow selective disposal of half the chromosomes in a polar body. In Caenorhabditis elegans, this anaphase spindle position is achieved sequentially through kinesin-1–dependent early translocation followed by anaphase-promoting complex (APC)-dependent spindle rotation. Partial depletion of cytoplasmic dynein heavy chain by RNA interference blocked spindle rotation without affecting early translocation. Dynein depletion also blocked the APC-dependent late translocation that occurs in kinesin-1–depleted embryos. Time-lapse imaging of green fluorescent protein-tagged dynein heavy chain as well as immunofluorescence with dynein-specific antibodies revealed that dynein starts to accumulate at spindle poles just before the initiation of rotation or late translocation. Accumulation of dynein at poles was kinesin-1 independent and APC dependent, just like dynein driven spindle movements. This represents a case of kinesin-1/dynein coordination in which these two motors of opposite polarity act sequentially and independently on a cargo to move it in the same direction.
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kinesin 1 mediates translocation of the meiotic spindle to the Oocyte Cortex through kca 1 a novel cargo adapter
Journal of Cell Biology, 2005Co-Authors: Hsin Ya Yang, Paul E Mains, Francis J McnallyAbstract:In animals, female meiotic spindles are attached to the egg Cortex in a perpendicular orientation at anaphase to allow the selective disposal of three haploid chromosome sets into polar bodies. We have identified a complex of interacting Caenorhabditis elegans proteins that are involved in the earliest step in asymmetric positioning of anastral meiotic spindles, translocation to the Cortex. This complex is composed of the kinesin-1 heavy chain orthologue, UNC-116, the kinesin light chain orthologues, KLC-1 and -2, and a novel cargo adaptor, KCA-1. Depletion of any of these subunits by RNA interference resulted in meiosis I metaphase spindles that remained stationary at a position several micrometers from the cell Cortex during the time when wild-type spindles translocated to the Cortex. After this prolonged stationary period, unc-116(RNAi) spindles moved to the Cortex through a partially redundant mechanism that is dependent on the anaphase-promoting complex. This study thus reveals two sequential mechanisms for translocating anastral spindles to the Oocyte Cortex.
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mei 1 katanin is required for translocation of the meiosis i spindle to the Oocyte Cortex in c elegans
Developmental Biology, 2003Co-Authors: Hsin Ya Yang, Karen Mcnally, Francis J McnallyAbstract:In most animals, successful segregation of female meiotic chromosomes involves sequential associations of the meiosis I and meiosis II spindles with the cell Cortex so that extra chromosomes can be deposited in polar bodies. The resulting reduction in chromosome number is essential to prevent the generation of polyploid embryos after fertilization. Using time-lapse imaging of living Caenorhabditis elegans Oocytes containing fluorescently labeled chromosomes or microtubules, we have characterized the movements of meiotic spindles relative to the cell Cortex. Spindle assembly initiated several microns from the Cortex. After formation of a bipolar structure, the meiosis I spindle translocated to the Cortex. When microtubules were partially depleted, translocation of the bivalent chromosomes to the Cortex was blocked without affecting cell cycle timing. In Oocytes depleted of the microtubule-severing enzyme, MEI-1, spindles moved to the Cortex, but association with the Cortex was unstable. Unlike translocation of wild-type spindles, movement of MEI-1-depleted spindles was dependent on FZY-1/CDC20, a regulator of the metaphase/anaphase transition. We observed a microtubule and FZY-1/CDC20-dependent circular cytoplasmic streaming in wild-type and mei-1 mutant embryos during meiosis. We propose that, in mei-1 mutant Oocytes, this cytoplasmic streaming is sufficient to drive the spindle into the Cortex. Cytoplasmic streaming is not the normal spindle translocation mechanism because translocation occurred in the absence of cytoplasmic streaming in embryos depleted of either the orbit/CLASP homolog, CLS-2, or FZY-1. These results indicate a direct role of microtubule severing in translocation of the meiotic spindle to the Cortex.
David F Albertini - One of the best experts on this subject based on the ideXlab platform.
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allocation of gamma tubulin between Oocyte Cortex and meiotic spindle influences asymmetric cytokinesis in the mouse Oocyte
Biology of Reproduction, 2007Co-Authors: Susan L Barrett, David F AlbertiniAbstract:In Oocytes, asymmetric cytokinesis represents a conserved strategy for karyokinesis during meiosis to retain ooplasmic maternal factors needed after fertilization. Given the role of gamma-tubulin in cell cycle progression and microtubule dynamics, this study focused on gamma-tubulin as a key regulator of asymmetric cytokinesis in mouse Oocytes. Gamma-tubulin properties were studied using multiple-label digital imaging, Western blots, quantitative RT-PCR, and microinjection strategies in mouse Oocytes matured in vivo (IVO) or in vitro (IVM). Quantitative image analysis established that IVO Oocytes extrude smaller first polar bodies (PBs), contain smaller spindles, and have more cytoplasmic microtubule organizing centers (MTOCs) relative to IVM Oocytes. Maturation in culture was shown to alter gamma-tubulin distribution, as evidenced by incorporation throughout the meiotic spindle and within the first PB. Western blot analysis confirmed that total gamma-tubulin content remained elevated in IVM Oocytes compared with IVO Oocytes. Analysis of gamma-tubulin mRNA during maturation revealed fluctuations in IVO Oocytes, whereas IVM Oocytes maintained relatively stable at lower levels for the time points examined (0-16 h). Selective reduction of gamma-tubulin mRNA by injection of siRNA diminished both spindle and PB size, whereas overexpression of enhanced green fluorescent protein gamma-tubulin had the opposite effect. Together, these studies reinforce the notion that limiting gamma-tubulin availability during meiotic maturation ensures coordination of karyokinesis and cytokinesis and conservation of gamma-tubulin as an embryonic reserve.
Bruce Bowerman - One of the best experts on this subject based on the ideXlab platform.
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c elegans clasp cls 2 negatively regulates membrane ingression throughout the Oocyte Cortex and is required for polar body extrusion
PLOS Genetics, 2020Co-Authors: Aleesa J Schlientz, Bruce BowermanAbstract:The requirements for Oocyte meiotic cytokinesis during polar body extrusion are not well understood. In particular, the relationship between the Oocyte meiotic spindle and polar body contractile ring dynamics remains largely unknown. We have used live cell imaging and spindle assembly defective mutants lacking the function of CLASP/CLS-2, kinesin-12/KLP-18, or katanin/MEI-1 to investigate the relationship between meiotic spindle structure and polar body extrusion in C. elegans Oocytes. We show that spindle bipolarity and chromosome segregation are not required for polar body contractile ring formation and chromosome extrusion in klp-18 mutants. In contrast, Oocytes with similarly severe spindle assembly defects due to loss of CLS-2 or MEI-1 have penetrant and distinct polar body extrusion defects: CLS-2 is required early for contractile ring assembly or stability, while MEI-1 is required later for contractile ring constriction. We also show that CLS-2 both negatively regulates membrane ingression throughout the Oocyte Cortex during meiosis I, and influences the dynamics of the central spindle-associated proteins Aurora B/AIR-2 and MgcRacGAP/CYK-4. We suggest that proper regulation by CLS-2 of both Oocyte cortical stiffness and central spindle protein dynamics may influence contractile ring assembly during polar body extrusion in C. elegans Oocytes.
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c elegans clasp cls 2 negatively regulates membrane ingression throughout the Oocyte Cortex and is required for polar body extrusion
bioRxiv, 2020Co-Authors: Aleesa J Schlientz, Bruce BowermanAbstract:The requirements for Oocyte meiotic cytokinesis during polar body extrusion are not well understood. In particular, the relationship between the Oocyte meiotic spindle and polar body contractile ring dynamics remains largely unknown. We have used live cell imaging and spindle assembly defective mutants lacking the function of CLASP/CLS-2, kinesin-12/KLP-18, or katanin/MEI-1 to investigate the relationship between meiotic spindle structure and polar body extrusion in C. elegans Oocytes. We show that spindle bipolarity and chromosome segregation are not required for polar body contractile ring formation and chromosome extrusion in klp-18 mutants, but Oocytes with severe spindle assembly defects due to loss of CLS-2 or MEI-1 have penetrant and distinct polar body extrusion defects: CLS-2 is required early for contractile ring assembly or stability, while MEI-1 is required later for contractile ring constriction. We also show that CLS-2 negatively regulates membrane ingression throughout the Oocyte Cortex during meiosis I, and we explore the relationship between global cortical dynamics and Oocyte meiotic cytokinesis.
John Carroll - One of the best experts on this subject based on the ideXlab platform.
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biased inheritance of mitochondria during asymmetric cell division in the mouse Oocyte
Journal of Cell Science, 2013Co-Authors: Caroline Dalton, John CarrollAbstract:A fundamental rule of cell division is that daughter cells inherit half the DNA complement and an appropriate proportion of cellular organelles. The highly asymmetric cell divisions of female meiosis present a different challenge because one of the daughters, the polar body, is destined to degenerate, putting at risk essential maternally inherited organelles such as mitochondria. We have therefore investigated mitochondrial inheritance during the meiotic divisions of the mouse Oocyte. We find that mitochondria are aggregated around the spindle by a dynein-mediated mechanism during meiosis I, and migrate together with the spindle towards the Oocyte Cortex. However, at cell division they are not equally segregated and move instead towards the Oocyte-directed spindle pole and are excluded from the polar body. We show that this asymmetrical inheritance in favour of the Oocyte is not caused by bias in the spindle itself but is dependent on an intact actin cytoskeleton, spindle–Cortex proximity, and cell cycle progression. Thus, Oocyte-biased inheritance of mitochondria is a variation on rules that normally govern organelle segregation at cell division, and ensures that essential maternally inherited mitochondria are retained to provide ATP for early mammalian development.
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changes in endoplasmic reticulum structure during mouse Oocyte maturation are controlled by the cytoskeleton and cytoplasmic dynein
Developmental Biology, 2007Co-Authors: Gregory Fitzharris, Petros Marangos, John CarrollAbstract:Oocyte maturation in mouse is associated with a dramatic reorganisation of the endoplasmic reticulum (ER) from a network of cytoplasmic accumulations in the germinal vesicle-stage Oocyte (GV) to a network of distinctive cortical clusters in the metaphase II egg (MII). Multiple lines of evidence suggest that this redistribution of the ER is important to prepare the Oocyte for the generation of repetitive Ca 2+ transients which trigger egg activation at fertilisation. The aim of the current study was therefore to investigate the timecourse and mechanism of ER reorganisation during Oocyte maturation. The ER is first restructured at the time of GV-breakdown (GVBD) into a dense network of membranes which envelop and invade the developing meiotic spindle. GVBD is essential for the initiation of ER reorganisation, since ER structure does not change in GVarrested Oocytes. ER reorganisation is also prevented by the microtubule inhibitor nocodazole and by the inhibition of cytoplasmic dynein, a microtubule-associated motor protein. ER redistribution at GVBD is therefore dynein-driven and cell cycle-dependent. Following GVBD the dense network of ER surrounds the spindle during its migration to the Oocyte Cortex. Cortical clusters of ER are formed close to the time of, but independently of the metaphase I–metaphase II transition. Formation of the characteristic ER clusters is prevented by the depolymerisation of microfilaments, but not of microtubules. These experiments reveal that ER reorganisation during Oocyte maturation is a complex multi-step process involving distinct microtubule- and microfilament-dependent phases and indicate a role for dynein in the cytoplasmic changes which prepare the Oocyte for fertilisation.
J. Leblanc - One of the best experts on this subject based on the ideXlab platform.
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the small gtpase cdc42 promotes membrane protrusion during polar body emission via arp2 nucleated actin polymerization
Molecular Human Reproduction, 2011Co-Authors: J. Leblanc, D MckeeAbstract:Polar body emission is a specialized cell division throughout the animal kingdom, serving to reduce chromosome ploidy while preserving the egg cytoplasm. Critical to polar body emission are the asymmetric positioning of the meiotic spindle prior to anaphase, with one pole attached to the Oocyte Cortex, and the simultaneous membrane protrusion during subsequent cytokinesis. We have shown that, during Xenopus Oocyte maturation, the small GTPase Cdc42 promotes membrane protrusion while a classical RhoA contractile ring forms and constricts at the base of the protrusion. We report here that treating Oocytes with low concentrations of nocodazole diminished the size of metaphase I spindles and prevented polar body emission, and yet an active Cdc42 cap of correspondingly diminished size still developed, on time, atop of the spindle pole. Conversely, treating Oocytes with low concentrations of taxol resulted in a spindle with multiple poles attached to the Cortex, but still each of these poles were associated with activated cortical Cdc42 at the appropriate time. Therefore, the asymmetric positioning of the meiotic spindle with one pole anchored to the Cortex is a prerequisite for Cdc42 activation. Furthermore, we demonstrated that the Cdc42-regulated F-actin nucleator ARP2/3 complex was similarly localized at the Cortex of the protruding polar body membrane, suggesting that Cdc42 promotes membrane protrusion through an F-actin meshwork mechanism. Finally, we demonstrated that Cdc42 and RhoA formed similarly complementary activity zones during egg activation and that inhibition of Cdc42 prevented second polar body emission. Therefore, Cdc42 activation likely promotes membrane protrusion during polar body emission in widespread systems.
