scholarly journals The Kinesinlike Protein Subito Contributes to Central Spindle Assembly and Organization of the Meiotic Spindle in Drosophila Oocytes

2005 ◽  
Vol 16 (10) ◽  
pp. 4684-4694 ◽  
Author(s):  
J. K. Jang ◽  
T. Rahman ◽  
K. S. McKim
Keyword(s):  
Meiotic Spindle ◽  
Spindle Formation ◽  
Present Evidence ◽  
Homologous Chromosomes ◽  
Central Spindle ◽  
Bipolar Spindle ◽  
Passenger Proteins ◽  
Bipolar Spindles ◽  
Meiosis I

In the oocytes of many species, bipolar spindles form in the absence of centrosomes. Drosophila melanogaster oocyte chromosomes have a major role in nucleating microtubules, which precedes the bundling and assembly of these microtubules into a bipolar spindle. Here we present evidence that a region similar to the anaphase central spindle functions to organize acentrosomal spindles. Subito mutants are characterized by the formation of tripolar or monopolar spindles and nondisjunction of homologous chromosomes at meiosis I. Subito encodes a kinesinlike protein and associates with the meiotic central spindle, consistent with its classification in the Kinesin 6/MKLP1 family. This class of proteins is known to be required for cytokinesis, but our results suggest a new function in spindle formation. The meiotic central spindle appears during prometaphase and includes passenger complex proteins such as AurB and Incenp. Unlike mitotic cells, the passenger proteins do not associate with centromeres before anaphase. In the absence of Subito, central spindle formation is defective and AurB and Incenp fail to properly localize. We propose that Subito is required for establishing and/or maintaining the central spindle in Drosophila oocytes, and this substitutes for the role of centrosomes in organizing the bipolar spindle.

scholarly journals Telomeres and centromeres have interchangeable roles in promoting meiotic spindle formation

2015 ◽  
Vol 208 (4) ◽  
pp. 415-428 ◽  
Author(s):  
Alex Fennell ◽  
Alfonso Fernández-Álvarez ◽  
Kazunori Tomita ◽  
Julia Promisel Cooper
Keyword(s):  
Fission Yeast ◽  
Nuclear Membrane ◽  
Meiotic Prophase ◽  
Meiotic Spindle ◽  
The Sun ◽  
Spindle Formation ◽  
Domain Protein ◽  
Bipolar Spindles ◽  
Sun Domain ◽  
Meiosis I

Telomeres and centromeres have traditionally been considered to perform distinct roles. During meiotic prophase, in a conserved chromosomal configuration called the bouquet, telomeres gather to the nuclear membrane (NM), often near centrosomes. We found previously that upon disruption of the fission yeast bouquet, centrosomes failed to insert into the NM at meiosis I and nucleate bipolar spindles. Hence, the trans-NM association of telomeres with centrosomes during prophase is crucial for efficient spindle formation. Nonetheless, in approximately half of bouquet-deficient meiocytes, spindles form properly. Here, we show that bouquet-deficient cells can successfully undergo meiosis using centromere–centrosome contact instead of telomere–centrosome contact to generate spindle formation. Accordingly, forced association between centromeres and centrosomes fully rescued the spindle defects incurred by bouquet disruption. Telomeres and centromeres both stimulate focal accumulation of the SUN domain protein Sad1 beneath the centrosome, suggesting a molecular underpinning for their shared spindle-generating ability. Our observations demonstrate an unanticipated level of interchangeability between the two most prominent chromosomal landmarks.

scholarly journals Shugoshin protects centromere pairing and promotes segregation of non-exchange partner chromosomes in meiosis

2018 ◽  
Author(s):  
Luciana Previato de Almeida ◽  
Jared M. Evatt ◽  
Hoa H. Chuong ◽  
Emily L. Kurdzo ◽  
Craig A. Eyster ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Segregation ◽  
Meiotic Prophase ◽  
Single Unit ◽  
Meiotic Chromosome ◽  
Model Systems ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Meiosis I

ABSTRACTFaithful chromosome segregation during meiosis I depends upon the formation of connections between homologous chromosomes. Crossovers between homologs connect the partners allowing them to attach to the meiotic spindle as a unit, such that they migrate away from one another at anaphase I. Homologous partners also become connected by pairing of their centromeres in meiotic prophase. This centromere pairing can promote proper segregation at anaphase I of partners that have failed to become joined by a crossover. Centromere pairing is mediated by synaptonemal complex (SC) proteins that persist at the centromere when the SC disassembles. Here, using mouse spermatocyte and yeast model systems, we tested the role of shugoshin in promoting meiotic centromere pairing by protecting centromeric synaptonemal components from disassembly. The results show that shugoshin protects centromeric SC in meiotic prophase and, in anaphase, promotes the proper segregation of partner chromosomes that are not linked by a crossover.SIGNIFICANCEMeiotic crossovers form a connection between homologous chromosomes that allows them to attach to the spindle as a single unit in meiosis I. In humans, failures in this process are a leading cause of aneuploidy. A recently described process, called centromere pairing, can also help connect meiotic chromosome partners in meiosis. Homologous chromosomes become tightly joined by a structure called the synaptonemal complex (SC) in meiotic prophase. After the SC disassembles, persisting SC proteins at the centromeres mediate their pairing. Here, studies in mouse spermatocytes and yeast are used to show that the shugoshin protein helps SC components persist at centromeres and helps centromere pairing promote the proper segregation of yeast chromosomes that fail to become tethered by crossovers.

scholarly journals Shugoshin protects centromere pairing and promotes segregation of nonexchange partner chromosomes in meiosis

2019 ◽  
Vol 116 (19) ◽  
pp. 9417-9422 ◽  
Author(s):  
Luciana Previato de Almeida ◽  
Jared M. Evatt ◽  
Hoa H. Chuong ◽  
Emily L. Kurdzo ◽  
Craig A. Eyster ◽  
...  
Keyword(s):  
Synaptonemal Complex ◽  
Chromosome Segregation ◽  
Meiotic Prophase ◽  
Model Systems ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Meiosis I ◽  
Yeast Model

Faithful chromosome segregation during meiosis I depends upon the formation of connections between homologous chromosomes. Crossovers between homologs connect the partners, allowing them to attach to the meiotic spindle as a unit, such that they migrate away from one another at anaphase I. Homologous partners also become connected by pairing of their centromeres in meiotic prophase. This centromere pairing can promote proper segregation at anaphase I of partners that have failed to become joined by a crossover. Centromere pairing is mediated by synaptonemal complex (SC) proteins that persist at the centromere when the SC disassembles. Here, using mouse spermatocyte and yeast model systems, we tested the role of shugoshin in promoting meiotic centromere pairing by protecting centromeric synaptonemal components from disassembly. The results show that shugoshin protects the centromeric SC in meiotic prophase and, in anaphase, promotes the proper segregation of partner chromosomes that are not linked by a crossover.

scholarly journals Bimodal Interaction of Mammalian Polo-Like Kinase 1 and a Centrosomal Scaffold, Cep192, in the Regulation of Bipolar Spindle Formation

2015 ◽  
Vol 35 (15) ◽  
pp. 2626-2640 ◽  
Author(s):  
Lingjun Meng ◽  
Jung-Eun Park ◽  
Tae-Sung Kim ◽  
Eun Hye Lee ◽  
Suk-Youl Park ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Spindle Assembly ◽  
Human Cells ◽  
Mitotic Progression ◽  
Spindle Formation ◽  
Content Type ◽  
Bipolar Spindle ◽  
Egg Extracts ◽  
Cultured Human Cells ◽  
Bipolar Spindles

Serving as microtubule-organizing centers, centrosomes play a key role in forming bipolar spindles. The mechanism of how centrosomes promote bipolar spindle assembly in various organisms remains largely unknown. A recent study withXenopus laevisegg extracts suggested that the Plk1 ortholog Plx1 interacts with the phospho-T46 (p-T46) motif ofXenopusCep192 (xCep192) to form an xCep192-mediated xAurA-Plx1 cascade that is critical for bipolar spindle formation. Here, we demonstrated that in cultured human cells, Cep192 recruits AurA and Plk1 in a cooperative manner, and this event is important for the reciprocal activation of AurA and Plk1. Strikingly, Plk1 interacted with Cep192 through either the p-T44 (analogous toXenopusp-T46) or the newly identified p-S995 motif via its C-terminal noncatalytic polo-box domain. The interaction between Plk1 and the p-T44 motif was prevalent in the presence of Cep192-bound AurA, whereas the interaction of Plk1 with the p-T995 motif was preferred in the absence of AurA binding. Notably, the loss of p-T44- and p-S995-dependent Cep192-Plk1 interactions induced an additive defect in recruiting Plk1 and γ-tubulin to centrosomes, which ultimately led to a failure in proper bipolar spindle formation and mitotic progression. Thus, we propose that Plk1 promotes centrosome-based bipolar spindle formation by forming two functionally nonredundant complexes with Cep192.

scholarly journals Klp2 and Ase1 synergize to maintain meiotic spindle stability during metaphase I

2020 ◽  
Author(s):  
Fan Zheng ◽  
Fenfen Dong ◽  
Shuo Yu ◽  
Tianpeng Li ◽  
Yanze Jian ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Yeast Cells ◽  
Meiotic Spindle ◽  
Homologous Chromosomes ◽  
Spindle Dynamics ◽  
Live Cell Microscopy ◽  
Spindle Stability ◽  
Cell Microscopy ◽  
Mitosis And Meiosis ◽  
Meiosis I

ABSTRACTThe spindle apparatus segregates bi-oriented sister chromatids during mitosis but mono-oriented homologous chromosomes during meiosis I. It has remained unclear if similar molecular mechanisms operate to regulate spindle dynamics during mitosis and meiosis I. Here, we employed live-cell microscopy to compare the spindle dynamics of mitosis and meiosis I in fission yeast cells and demonstrated that the conserved kinesin-14 motor Klp2 plays a specific role in maintaining metaphase spindle length during meiosis I, but not during mitosis. Moreover, the maintenance of metaphase spindle stability during meiosis I requires the synergism between Klp2 and the conserved microtubule crosslinker Ase1 as the absence of both proteins causes exacerbated defects in metaphase spindle stability. The synergism is not necessary for regulating mitotic spindle dynamics. Hence, our work reveals a new molecular mechanism underlying meiotic spindle dynamics and provides insights into understanding differential regulation of meiotic and mitotic events.

Maize meiotic spindles assemble around chromatin and do not require paired chromosomes

1998 ◽  
Vol 111 (23) ◽  
pp. 3507-3515 ◽  
Author(s):  
A. Chan ◽  
W.Z. Cande
Keyword(s):  
Nuclear Envelope ◽  
Higher Plants ◽  
Metaphase Plate ◽  
Meiotic Spindle ◽  
Wild Type ◽  
Homologous Chromosomes ◽  
Nuclear Envelope Breakdown ◽  
Meiotic Spindles ◽  
Meiotic Mutations ◽  
Bipolar Spindles

To understand how the meiotic spindle is formed and maintained in higher plants, we studied the organization of microtubule arrays in wild-type maize meiocytes and three maize meiotic mutants, desynaptic1 (dsy1), desynaptic2 (dsy2), and absence of first division (afd). All three meiotic mutations have abnormal chromosome pairing and produce univalents by diakinesis. Using these three mutants, we investigated how the absence of paired homologous chromosomes affects the assembly and maintenance of the meiotic spindle. Before nuclear envelope breakdown, in wild-type meiocytes, there were no bipolar microtubule arrays. Instead, these structures formed after nuclear envelope breakdown and were associated with the chromosomes. The presence of univalent chromosomes in dsy1, dsy2, and afd meiocytes and of unpaired sister chromatids in the afd meiocytes did not affect the formation of bipolar spindles. However, alignment of chromosomes on the metaphase plate and subsequent anaphase chromosome segregation were perturbed. We propose a model for spindle formation in maize meiocytes in which microtubules initially appear around the chromosomes during prometaphase and then the microtubules self-organize. However, this process does not require paired kinetochores to establish spindle bipolarity.

Role of microtubules and microtubule organizing centers on meiotic chromosome elimination in Sciara ocellaris

1997 ◽  
Vol 110 (6) ◽  
pp. 721-730 ◽  
Author(s):  
M.R. Esteban ◽  
M.C. Campos ◽  
A.L. Perondini ◽  
C. Goday
Keyword(s):  
Meiotic Chromosome ◽  
Chromosome Elimination ◽  
Male Meiosis ◽  
Meiotic Spindle ◽  
Monopolar Spindle ◽  
Meiotic Spindles ◽  
Cytoplasmic Microtubules ◽  
Spindle Microtubules ◽  
Meiosis I

Spindle formation and chromosome elimination during male meiosis in Sciara ocellaris (Diptera, Sciaridae) has been studied by immunofluorescence techniques. During meiosis I a monopolar spindle is formed from a single polar complex (centrosome-like structure). This single centrosomal structure persists during meiosis II and is responsible for the non-disjunction of the maternal X chromatids. During meiosis I and II non-spindle microtubules are assembled in the cytoplasmic bud regions of the spermatocytes. The chromosomes undergoing elimination during both meiotic divisions are segregated to the bud region where they associate with bundles of microtubules. The presence and distribution of centrosomal antigens in S. ocellaris meiotic spindles and bud regions has been investigated using different antibodies. gamma-Tubulin and centrin are present in the bud as well as in the single polar complex of first meiotic spindle. The results suggest that spermatocyte bud regions contain microtubule-organizing centres (MTOCs) that nucleate cytoplasmic microtubules that are involved in capturing chromosomes in the bud regions. The distribution of actin and myosin in the spermatocytes during meiosis is also reported.

scholarly journals Kinetochore-mediated outward force promotes spindle pole separation in fission yeast

2019 ◽  
Vol 30 (22) ◽  
pp. 2802-2813 ◽  
Author(s):  
Yutaka Shirasugi ◽  
Masamitsu Sato
Keyword(s):  
Fission Yeast ◽  
Motor Proteins ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Double Knockout ◽  
Bipolar Spindle ◽  
Spindle Poles ◽  
Bipolar Spindles ◽  
Meiosis I

Bipolar spindles are organized by motor proteins that generate microtubule-­dependent forces to separate the two spindle poles. The fission yeast Cut7 (kinesin-5) is a plus-end-directed motor that generates the outward force to separate the two spindle poles, whereas the minus-end-directed motor Pkl1 (kinesin-14) generates the inward force. Balanced forces by these antagonizing kinesins are essential for bipolar spindle organization in mitosis. Here, we demonstrate that chromosomes generate another outward force that contributes to the bipolar spindle assembly. First, it was noted that the cut7 pkl1 double knockout failed to separate spindle poles in meiosis I, although the mutant is known to succeed it in mitosis. It was assumed that this might be because meiotic kinetochores of bivalent chromosomes joined by cross-overs generate weaker tensions in meiosis I than the strong tensions in mitosis generated by tightly tethered sister kinetochores. In line with this idea, when meiotic mono-oriented kinetochores were artificially converted to a mitotic bioriented layout, the cut7 pkl1 mutant successfully separated spindle poles in meiosis I. Therefore, we propose that spindle pole separation is promoted by outward forces transmitted from kinetochores to spindle poles through microtubules.

scholarly journals Regulation of the meiotic divisions of mammalian oocytes and eggs

2018 ◽  
Vol 46 (4) ◽  
pp. 797-806 ◽  
Author(s):  
Jessica R. Sanders ◽  
Keith T. Jones
Keyword(s):  
Cell Division ◽  
Luteinizing Hormone ◽  
Spindle Assembly Checkpoint ◽  
Asymmetric Cell Division ◽  
Homologous Chromosomes ◽  
Mammalian Oocyte ◽  
Cellular Events ◽  
The Hours ◽  
Meiosis I

Initiated by luteinizing hormone and finalized by the fertilizing sperm, the mammalian oocyte completes its two meiotic divisions. The first division occurs in the mature Graafian follicle during the hours preceding ovulation and culminates in an extreme asymmetric cell division and the segregation of the two pairs of homologous chromosomes. The newly created mature egg rearrests at metaphase of the second meiotic division prior to ovulation and only completes meiosis following a Ca2+ signal initiated by the sperm at gamete fusion. Here, we review the cellular events that govern the passage of the oocyte through meiosis I with a focus on the role of the spindle assembly checkpoint in regulating its timing. In meiosis II, we examine how the egg achieves its arrest and how the fertilization Ca2+ signal allows the initiation of embryo development.

scholarly journals Ndj1, a Telomere-Associated Protein, Promotes Meiotic Recombination in Budding Yeast

2006 ◽  
Vol 26 (10) ◽  
pp. 3683-3694 ◽  
Author(s):  
Hsin-Yen Wu ◽  
Sean M. Burgess
Keyword(s):  
Meiotic Recombination ◽  
Double Strand Breaks ◽  
Homology Search ◽  
Strand Breaks ◽  
Homologous Chromosomes ◽  
Synaptonemal Complex Formation ◽  
Strand Invasion ◽  
Double Holliday Junction ◽  
Meiosis I

ABSTRACT Dynamic telomere repositioning is a prominent feature of meiosis. Deletion of a telomere-associated protein, Ndj1, results in the failure of both attachment and clustering of telomeres at the nuclear envelope and delays several landmarks of meiosis I, such as pairing, synaptonemal complex formation, and timing of the meiosis I division. We explored the role of Ndj1 in meiotic recombination, which occurs through the formation and repair of programmed double-strand breaks. The ndj1Δ mutation allows for the formation of the first detectable strand invasion intermediate (i.e., single-end invasion) with wild-type kinetics; however, it confers a delay in the formation of the double-Holliday junction intermediate and both crossover and noncrossover products. These results challenge the widely held notion that clustering of telomeres in meiosis promotes the ability of homologous chromosomes to find one another in budding Saccharomyces cerevisiae. We propose that an Ndj1-dependent function is critical for stabilizing analogous strand invasion intermediates that exist in two separate branches of the bifurcated pathway, leading to either noncrossover or crossover formation. These findings provide a link between telomere dynamics and a distinct mechanistic step of meiotic recombination that follows the homology search.

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