scholarly journals Multiple motors cooperate to establish and maintain acentrosomal spindle bipolarity in C. elegans oocyte meiosis

2021 ◽  
Author(s):  
Gabriel Cavin-Meza ◽  
Michelle M. Kwan ◽  
Sarah M. Wignall
Keyword(s):  
Chromosome Segregation ◽  
Meiotic Spindle ◽  
Complete Dissolution ◽  
C Elegans ◽  
Spindle Poles ◽  
Oocyte Meiosis ◽  
Monopolar Spindle ◽  
Spindle Stability ◽  
Bipolar Spindles ◽  
Spindle Structure

ABSTRACTWhile centrosomes organize spindle poles during mitosis, oocyte meiosis can occur in their absence. Spindles in human oocytes frequently fail to maintain bipolarity and consequently undergo chromosome segregation errors, making it important to understand mechanisms that promote acentrosomal spindle stability. To this end, we have optimized the auxin-inducible degron system in C. elegans to remove factors from pre-formed oocyte spindles within minutes and assess effects on spindle structure. This approach revealed that dynein is required to maintain the integrity of acentrosomal poles; removal of dynein from bipolar spindles caused pole splaying, and when coupled with a monopolar spindle induced by depletion of kinesin-12 motor KLP-18, dynein depletion led to a complete dissolution of the monopole. Surprisingly, we went on to discover that following monopole disruption, individual chromosomes were able to reorganize local microtubules and re-establish a miniature bipolar spindle that mediated chromosome segregation. This revealed the existence of redundant microtubule sorting forces that are undetectable when KLP-18 and dynein are active. We found that the kinesin-5 family motor BMK-1 provides this force, uncovering the first evidence that kinesin-5 contributes to C. elegans meiotic spindle organization. Altogether, our studies have revealed how multiple motors are working synchronously to establish and maintain bipolarity in the absence of centrosomes.

scholarly journals KLP-7 acts through the Ndc80 complex to limit pole number in C. elegans oocyte meiotic spindle assembly

2015 ◽  
Vol 210 (6) ◽  
pp. 917-932 ◽  
Author(s):  
Amy A. Connolly ◽  
Kenji Sugioka ◽  
Chien-Hui Chuang ◽  
Joshua B. Lowry ◽  
Bruce Bowerman
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Meiotic Spindle ◽  
Meiotic Cell ◽  
Bipolar Structure ◽  
C Elegans ◽  
Spindle Poles ◽  
Ndc80 Complex ◽  
Bipolar Spindles

During oocyte meiotic cell division in many animals, bipolar spindles assemble in the absence of centrosomes, but the mechanisms that restrict pole assembly to a bipolar state are unknown. We show that KLP-7, the single mitotic centromere–associated kinesin (MCAK)/kinesin-13 in Caenorhabditis elegans, is required for bipolar oocyte meiotic spindle assembly. In klp-7(−) mutants, extra microtubules accumulated, extra functional spindle poles assembled, and chromosomes frequently segregated as three distinct masses during meiosis I anaphase. Moreover, reducing KLP-7 function in monopolar klp-18(−) mutants often restored spindle bipolarity and chromosome segregation. MCAKs act at kinetochores to correct improper kinetochore–microtubule (k–MT) attachments, and depletion of the Ndc-80 kinetochore complex, which binds microtubules to mediate kinetochore attachment, restored bipolarity in klp-7(−) mutant oocytes. We propose a model in which KLP-7/MCAK regulates k–MT attachment and spindle tension to promote the coalescence of early spindle pole foci that produces a bipolar structure during the acentrosomal process of oocyte meiotic spindle assembly.

scholarly journals Katanin controls mitotic and meiotic spindle length

2006 ◽  
Vol 175 (6) ◽  
pp. 881-891 ◽  
Author(s):  
Karen McNally ◽  
Anjon Audhya ◽  
Karen Oegema ◽  
Francis J. McNally
Keyword(s):  
Chromosome Segregation ◽  
Eukaryotic Cell ◽  
Meiotic Spindle ◽  
Mitotic Spindles ◽  
Wild Type ◽  
Female Meiosis ◽  
C Elegans ◽  
Microtubule Severing ◽  
Spindle Poles ◽  
Type C

Accurate control of spindle length is a conserved feature of eukaryotic cell division. Lengthening of mitotic spindles contributes to chromosome segregation and cytokinesis during mitosis in animals and fungi. In contrast, spindle shortening may contribute to conservation of egg cytoplasm during female meiosis. Katanin is a microtubule-severing enzyme that is concentrated at mitotic and meiotic spindle poles in animals. We show that inhibition of katanin slows the rate of spindle shortening in nocodazole-treated mammalian fibroblasts and in untreated Caenorhabditis elegans meiotic embryos. Wild-type C. elegans meiotic spindle shortening proceeds through an early katanin-independent phase marked by increasing microtubule density and a second, katanin-dependent phase that occurs after microtubule density stops increasing. In addition, double-mutant analysis indicated that γ-tubulin–dependent nucleation and microtubule severing may provide redundant mechanisms for increasing microtubule number during the early stages of meiotic spindle assembly.

scholarly journals Male meiotic spindle features that efficiently segregate paired and lagging chromosomes

2019 ◽  
Author(s):  
Gunar Fabig ◽  
Robert Kiewisz ◽  
Norbert Lindow ◽  
James A. Powers ◽  
Vanessa Cota ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Chromosome Pairing ◽  
Electron Tomography ◽  
Male Meiosis ◽  
Meiotic Spindle ◽  
Sperm Production ◽  
C Elegans ◽  
Anaphase Onset ◽  
Unpaired Chromosome ◽  
Anaphase B

AbstractChromosome segregation during male meiosis is tailored to rapidly generate multitudes of sperm. Little, however, is known about the mechanisms that efficiently segregate chromosomes to produce sperm. Using live imaging in Caenorhabditis elegans, we find that spermatocytes exhibit simultaneous pole-to-chromosome shortening (anaphase A) and pole-to-pole elongation (anaphase B). Electron tomography unexpectedly revealed that spermatocyte anaphase A does not stem from kinetochore microtubule shortening. Instead, movement is driven by changes in distance between chromosomes, microtubules, and centrosomes upon tension release at anaphase onset. We also find that the lagging X chromosome, a distinctive feature of anaphase I in C. elegans males, is due to lack of chromosome pairing. The unpaired chromosome remains tethered to centrosomes by continuously lengthening kinetochore microtubules which are under tension, suggesting a ‘tug of war’ that can reliably resolve chromosome lagging. Overall, we define features that partition both paired and lagging chromosomes for optimal sperm production.

A highly conserved centrosomal kinase, AIR-1, is required for accurate cell cycle progression and segregation of developmental factors in Caenorhabditis elegans embryos

Development ◽  
1998 ◽  
Vol 125 (22) ◽  
pp. 4391-4402 ◽  
Author(s):  
J.M. Schumacher ◽  
N. Ashcroft ◽  
P.J. Donovan ◽  
A. Golden
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Cell Cycle Progression ◽  
Cycle Progression ◽  
Centrosomal Protein ◽  
C Elegans ◽  
Developmental Factors ◽  
Centrosome Separation ◽  
Spindle Dynamics ◽  
Bipolar Spindles

S. cerevisiae Ipl1, Drosophila Aurora, and the mammalian centrosomal protein IAK-1 define a new subfamily of serine/threonine kinases that regulate chromosome segregation and mitotic spindle dynamics. Mutations in ipl1 and aurora result in the generation of severely aneuploid cells and, in the case of aurora, monopolar spindles arising from a failure in centrosome separation. Here we show that a related, essential protein from C. elegans, AIR-1 (Aurora/Ipl1 related), is localized to mitotic centrosomes. Disruption of AIR-1 protein expression in C. elegans embryos results in severe aneuploidy and embryonic lethality. Unlike aurora mutants, this aneuploidy does not arise from a failure in centrosome separation. Bipolar spindles are formed in the absence of AIR-1, but they appear to be disorganized and are nucleated by abnormal-looking centrosomes. In addition to its requirement during mitosis, AIR-1 may regulate microtubule-based developmental processes as well. Our data suggests AIR-1 plays a role in P-granule segregation and the association of the germline factor PIE-1 with centrosomes.

scholarly journals Revised and Improved Procedure for Immunolocalization of Male Meiotic Chromosomal Proteins and Spindle in Plants without the Use of Enzymes

Plants ◽  
2018 ◽  
Vol 7 (4) ◽  
pp. 93
Author(s):  
Kuntal De ◽  
Li Yuan ◽  
Christopher Makaroff
Keyword(s):  
Arabidopsis Thaliana ◽  
Chromosome Segregation ◽  
Sister Chromatid ◽  
Model Organism ◽  
Meiotic Spindle ◽  
Chromosomal Proteins ◽  
Meiotic Chromosomes ◽  
Wide Range ◽  
Chromatid Cohesion ◽  
Spindle Structure

Immunolocalization studies to visualize the distribution of proteins on meiotic chromosomes have become an integral part of studies on meiosis in the model organism Arabidopsis thaliana. These techniques have been used to visualize a wide range of meiotic proteins involved in different aspects of meiosis, including sister chromatid cohesion, recombination, synapsis, and chromosome segregation. However, the analysis of meiotic spindle structure by immunofluorescence is of outstanding importance in plant reproductive biology and is very challenging. In the following report, we describe the complete and easy protocol for the localization of proteins to the male meiotic spindle and male meiotic chromosomes. The protocol is fast, improved, and robust without the use of any harsh enzymes.

scholarly journals CDK-1 inhibits meiotic spindle shortening and dynein-dependent spindle rotation in C. elegans

2011 ◽  
Vol 193 (7) ◽  
pp. 1229-1244 ◽  
Author(s):  
Marina L. Ellefson ◽  
Francis J. McNally
Keyword(s):  
Polar Body ◽  
Spindle Pole ◽  
Cyclin B ◽  
Meiotic Spindle ◽  
Anaphase Promoting Complex ◽  
C Elegans ◽  
Perpendicular Orientation ◽  
Spindle Poles ◽  
Spindle Rotation ◽  
Chromosome Separation

In animals, the female meiotic spindle is positioned at the egg cortex in a perpendicular orientation to facilitate the disposal of half of the chromosomes into a polar body. In Caenorhabditis elegans, the metaphase spindle lies parallel to the cortex, dynein is dispersed on the spindle, and the dynein activators ASPM-1 and LIN-5 are concentrated at spindle poles. Anaphase-promoting complex (APC) activation results in dynein accumulation at spindle poles and dynein-dependent rotation of one spindle pole to the cortex, resulting in perpendicular orientation. To test whether the APC initiates spindle rotation through cyclin B–CDK-1 inactivation, separase activation, or degradation of an unknown dynein inhibitor, CDK-1 was inhibited with purvalanol A in metaphase-I–arrested, APC-depleted embryos. CDK-1 inhibition resulted in the accumulation of dynein at spindle poles and dynein-dependent spindle rotation without chromosome separation. These results suggest that CDK-1 blocks rotation by inhibiting dynein association with microtubules and with LIN-5–ASPM-1 at meiotic spindle poles and that the APC promotes spindle rotation by inhibiting CDK-1.

scholarly journals RMD-1, a novel microtubule-associated protein, functions in chromosome segregation in Caenorhabditis elegans

2007 ◽  
Vol 179 (6) ◽  
pp. 1149-1162 ◽  
Author(s):  
Kumiko Oishi ◽  
Hideyuki Okano ◽  
Hitoshi Sawa
Keyword(s):  
Caenorhabditis Elegans ◽  
Chromosome Segregation ◽  
Growth Defect ◽  
Aurora B ◽  
C Elegans ◽  
Spindle Poles ◽  
Protein Functions ◽  
Microtubule Growth ◽  
Mild Defect

For proper chromosome segregation, the sister kinetochores must attach to microtubules extending from the opposite spindle poles. Any errors in microtubule attachment can induce aneuploidy. In this study, we identify a novel conserved Caenorhabditis elegans microtubule-associated protein, regulator of microtubule dynamics 1 (RMD-1), that localizes to spindle microtubules and spindle poles. Depletion of RMD-1 induces severe defects in chromosome segregation, probably through merotelic attachments between microtubules and chromosomes. Although rmd-1 embryos also have a mild defect in microtubule growth, we find that mutants of the microtubule growth regulator XMAP215/ZYG-9 show much weaker segregation defects. This suggests that the microtubule growth defect in rmd-1 embryos does not cause abnormal chromosome segregation. We also see that RMD-1 interacts with aurora B in vitro. Our results suggest that RMD-1 functions in chromosome segregation in C. elegans embryos, possibly through the aurora B–mediated pathway. Human homologues of RMD-1 could also bind microtubules, which would suggest a function for these proteins in chromosome segregation during mitosis in other organisms as well.

scholarly journals Translocation of phospho-protein kinase Cs implies their roles in meiotic-spindle organization, polar-body emission and nuclear activity in mouse eggs

Reproduction ◽  
2005 ◽  
Vol 129 (2) ◽  
pp. 229-234 ◽  
Author(s):  
Zhen-Yu Zheng ◽  
Qing-Zhang Li ◽  
Da-Yuan Chen ◽  
Heide Schatten ◽  
Qing-Yuan Sun
Keyword(s):  
Protein Kinase ◽  
Polar Body ◽  
Germinal Vesicle ◽  
Mouse Oocyte ◽  
Meiotic Spindle ◽  
Germinal Vesicle Breakdown ◽  
Nuclear Activity ◽  
Spindle Poles ◽  
Oocyte Meiosis ◽  
First Polar Body

The protein kinase Cs (PKCs) are a family of Ser/Thr protein kinases categorized into three subfamilies: classical, novel, and atypical. The phosphorylation of PKC in germ cells is not well defined. In this study, we described the subcellular localization of phopho-PKC in the process of mouse oocyte maturation, fertilization, and early embryonic mitosis. Confocal microscopy revealed that phospho-PKC (pan) was distributed abundantly in the nucleus at the germinal vesicle stage. After germinal vesicle breakdown, phospho-PKC was localized in the vicinity of the condensed chromosomes, distributed in the whole meiotic spindle, and concentrated at the spindle poles. After metaphase I, phospho-PKC was translocated gradually to the spindle mid-zone during emission of the first polar body. After sperm penetration and electrical activation, the distribution of phospho-PKC was moved from the spindle poles to the spindle mid-zone. After the extrusion of the second polar body (PB2) phospho-PKC was localized in the area between the oocyte and the PB2. In fertilized eggs, phospho-PKC was concentrated in the pronuclei except for the nucleolus. Phospho-PKC was dispersed after pronuclear envelope breakdown, but distributed on the entire spindle at mitotic metaphase. The results suggest that PKC activation may play important roles in regulating spindle organization and stabilization, polar-body extrusion, and nuclear activity during mouse oocyte meiosis, fertilization, and early embryonic mitosis.

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