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Soygur, B., R. G. Jaszczak, A. Fries, D. H. Nguyen, S. Malki, G. Hu, N. Demir, R. Arora et D. J. Laird. « Intercellular bridges coordinate the transition from pluripotency to meiosis in mouse fetal oocytes ». Science Advances 7, no 15 (avril 2021) : eabc6747. http://dx.doi.org/10.1126/sciadv.abc6747.
Texte intégralRésumé :
Meiosis is critical to generating oocytes and ensuring female fertility; however, the mechanisms regulating the switch from mitotic primordial germ cells to meiotic germ cells are poorly understood. Here, we implicate intercellular bridges (ICBs) in this state transition. We used three-dimensional in toto imaging to map meiotic initiation in the mouse fetal ovary and revealed a radial geometry of this transition that precedes the established anterior-posterior wave. Our studies reveal that appropriate timing of meiotic entry across the ovary and coordination of mitotic-meiotic transition within a cyst depend on the ICB componentTex14, which we show is required for functional cytoplasmic sharing. We find thatTex14mutants more rapidly attenuate the pluripotency transcriptDppa3upon meiotic initiation, andDppa3mutants undergo premature meiosis similar toTex14. Together, these results lead to a model that ICBs coordinate and buffer the transition from pluripotency to meiosis through dilution of regulatory factors.
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Cairo, Albert, Anna Vargova, Neha Shukla, Claudio Capitao, Pavlina Mikulkova, Sona Valuchova, Jana Pecinkova, Petra Bulankova et Karel Riha. « Meiotic exit in Arabidopsis is driven by P-body–mediated inhibition of translation ». Science 377, no 6606 (5 août 2022) : 629–34. http://dx.doi.org/10.1126/science.abo0904.
Texte intégralRésumé :
Meiosis, at the transition between diploid and haploid life cycle phases, is accompanied by reprograming of cell division machinery and followed by a transition back to mitosis. We show that, in Arabidopsis , this transition is driven by inhibition of translation, achieved by a mechanism that involves processing bodies (P-bodies). During the second meiotic division, the meiosis-specific protein THREE-DIVISION MUTANT 1 (TDM1) is incorporated into P-bodies through interaction with SUPPRESSOR WITH MORPHOGENETIC EFFECTS ON GENITALIA 7 (SMG7). TDM1 attracts eIF4F, the main translation initiation complex, temporarily sequestering it in P-bodies and inhibiting translation. The failure of tdm1 mutants to terminate meiosis can be overcome by chemical inhibition of translation. We propose that TDM1-containing P-bodies down-regulate expression of meiotic transcripts to facilitate transition of cell fates to postmeiotic gametophyte differentiation.
3
Hayashi, Aki, Haruhiko Asakawa, Tokuko Haraguchi et Yasushi Hiraoka. « Reconstruction of the Kinetochore during Meiosis in Fission Yeast Schizosaccharomyces pombe ». Molecular Biology of the Cell 17, no 12 (décembre 2006) : 5173–84. http://dx.doi.org/10.1091/mbc.e06-05-0388.
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During the transition from mitosis to meiosis, the kinetochore undergoes significant reorganization, switching from a bipolar to a monopolar orientation. To examine the centromere proteins that are involved in fundamental reorganization in meiosis, we observed the localization of 22 mitotic and 2 meiotic protein components of the kinetochore during meiosis in living cells of the fission yeast. We found that the 22 mitotic proteins can be classified into three groups: the Mis6-like group, the NMS (Ndc80-Mis12-Spc7) group, and the DASH group, based on their meiotic behavior. Mis6-like group proteins remain at the centromere throughout meiosis. NMS group proteins disappear from the centromere at the onset of meiosis and reappear at the centromere in two steps in late prophase. DASH group proteins appear shortly before metaphase of meiosis I. These observations suggest that Mis6-like group proteins constitute the structural basis of the centromere and that the NMS and DASH group proteins reassemble to establish the functional metaphase kinetochore. On the other hand, the meiosis-specific protein Moa1, which plays an important role in forming the meiotic monopolar kinetochore, is loaded onto the centromere significantly earlier than the NMS group, whereas another meiosis-specific protein, Sgo1, is loaded at times similar to the NMS group.
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Zhang, Xingxia, Ming Li, Xiaohua Jiang, Hui Ma, Suixing Fan, Yang Li, Changping Yu et al. « Nuclear translocation of MTL5 from cytoplasm requires its direct interaction with LIN9 and is essential for male meiosis and fertility ». PLOS Genetics 17, no 8 (13 août 2021) : e1009753. http://dx.doi.org/10.1371/journal.pgen.1009753.
Texte intégralRésumé :
Meiosis is essential for the generation of gametes and sexual reproduction, yet the factors and underlying mechanisms regulating meiotic progression remain largely unknown. Here, we showed that MTL5 translocates into nuclei of spermatocytes during zygotene-pachytene transition and ensures meiosis advances beyond pachytene stage. MTL5 shows strong interactions with MuvB core complex components, a well-known transcriptional complex regulating mitotic progression, and the zygotene-pachytene transition of MTL5 is mediated by its direct interaction with the component LIN9, through MTL5 C-terminal 443–475 residues. Male Mtl5c-mu/c-mu mice expressing the truncated MTL5 (p.Ser445Arg fs*3) that lacks the interaction with LIN9 and is detained in cytoplasm showed male infertility and spermatogenic arrest at pachytene stage, same as that of Mtl5 knockout mice, indicating that the interaction with LIN9 is essential for the nuclear translocation and function of MTL5 during meiosis. Our data demonstrated MTL5 translocates into nuclei during the zygotene-pachytene transition to initiate its function along with the MuvB core complex in pachytene spermatocytes, highlighting a new mechanism regulating the progression of male meiosis.
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Bogdanov, Yuri. « Why is meiosis different from mitosis ». Priroda, no 11 (2024) : 18. https://doi.org/10.7868/s0032874x24110021.
Texte intégralRésumé :
Meiosis was existing already in the last eukaryotic common ancestor (LECA). During evolution and transition from the first eukaryotic ancestor to LECA, a whole complex of genes was formed in the genome of the latter (about 300 genes), which provided the process of meiotic division. This is only a few percent of the genome, but these genes significantly changed the course of cell division, and meiosis arose. The paper describes the features of meiosis and possible ways of its formation.
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LeMaire-Adkins, Renée, Kristi Radke et Patricia A. Hunt. « Lack of Checkpoint Control at the Metaphase/Anaphase Transition : A Mechanism of Meiotic Nondisjunction in Mammalian Females ». Journal of Cell Biology 139, no 7 (29 décembre 1997) : 1611–19. http://dx.doi.org/10.1083/jcb.139.7.1611.
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A checkpoint mechanism operates at the metaphase/anaphase transition to ensure that a bipolar spindle is formed and that all the chromosomes are aligned at the spindle equator before anaphase is initiated. Since mistakes in the segregation of chromosomes during meiosis have particularly disastrous consequences, it seems likely that the meiotic cell division would be characterized by a stringent metaphase/ anaphase checkpoint. To determine if the presence of an unaligned chromosome activates the checkpoint and delays anaphase onset during mammalian female meiosis, we investigated meiotic cell cycle progression in murine oocytes from XO females and control siblings. Despite the fact that the X chromosome failed to align at metaphase in a significant proportion of cells, we were unable to detect a delay in anaphase onset. Based on studies of cell cycle kinetics, the behavior and segregation of the X chromosome, and the aberrant behavior and segregation of autosomal chromosomes in oocytes from XO females, we conclude that mammalian female meiosis lacks chromosome-mediated checkpoint control. The lack of this control mechanism provides a biological explanation for the high incidence of meiotic nondisjunction in the human female. Furthermore, since available evidence suggests that a stringent checkpoint mechanism operates during male meiosis, the lack of a comparable checkpoint in females provides a reason for the difference in the error rate between oogenesis and spermatogenesis.
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Lin, T. Y., S. Viswanathan, C. Wood, P. G. Wilson, N. Wolf et M. T. Fuller. « Coordinate developmental control of the meiotic cell cycle and spermatid differentiation in Drosophila males ». Development 122, no 4 (1 avril 1996) : 1331–41. http://dx.doi.org/10.1242/dev.122.4.1331.
Texte intégralRésumé :
Wild-type function of four Drosophila genes, spermatocyte arrest, cannonball, always early and meiosis I arrest, is required both for cell-cycle progression through the G2/M transition of meiosis I in males and for onset of spermatid differentiation. In males mutant for any one of these meiotic arrest genes, mature primary spermatocytes with partially condensed chromosomes accumulate and postmeiotic cells are lacking. The arrest in cell-cycle progression occurs prior to degradation of cyclin A protein. The block in spermatogenesis in these mutants is not simply a secondary consequence of meiotic cell-cycle arrest, as spermatid differentiation proceeds in males mutant for the cell cycle activating phosphatase twine. Instead, the arrest of both meiosis and spermiogenesis suggests a control point that may serve to coordinate the male meiotic cell cycle with the spermatid differentiation program. The phenotype of the Drosophila meiotic arrest mutants is strikingly similar to the histopathological features of meiosis I maturation arrest infertility in human males, suggesting that the control point may be conserved from flies to man.
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Guan, Yongjuan, N. Adrian Leu, Jun Ma, Lukáš Chmátal, Gordon Ruthel, Jordana C. Bloom, Michael A. Lampson, John C. Schimenti, Mengcheng Luo et P. Jeremy Wang. « SKP1 drives the prophase I to metaphase I transition during male meiosis ». Science Advances 6, no 13 (mars 2020) : eaaz2129. http://dx.doi.org/10.1126/sciadv.aaz2129.
Texte intégralRésumé :
The meiotic prophase I to metaphase I (PI/MI) transition requires chromosome desynapsis and metaphase competence acquisition. However, control of these major meiotic events is poorly understood. Here, we identify an essential role for SKP1, a core subunit of the SKP1–Cullin–F-box (SCF) ubiquitin E3 ligase, in the PI/MI transition. SKP1 localizes to synapsed chromosome axes and evicts HORMAD proteins from these regions in meiotic spermatocytes. SKP1-deficient spermatocytes display premature desynapsis, precocious pachytene exit, loss of PLK1 and BUB1 at centromeres, but persistence of HORMAD, γH2AX, RPA2, and MLH1 in diplonema. Strikingly, SKP1-deficient spermatocytes show sharply reduced MPF activity and fail to enter MI despite treatment with okadaic acid. SKP1-deficient oocytes exhibit desynapsis, chromosome misalignment, and progressive postnatal loss. Therefore, SKP1 maintains synapsis in meiosis of both sexes. Furthermore, our results support a model where SKP1 functions as the long-sought intrinsic metaphase competence factor to orchestrate MI entry during male meiosis.
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Farini, Donatella, et Massimo De Felici. « The Beginning of Meiosis in Mammalian Female Germ Cells : A Never-Ending Story of Intrinsic and Extrinsic Factors ». International Journal of Molecular Sciences 23, no 20 (20 octobre 2022) : 12571. http://dx.doi.org/10.3390/ijms232012571.
Texte intégralRésumé :
Meiosis is the unique division of germ cells resulting in the recombination of the maternal and paternal genomes and the production of haploid gametes. In mammals, it begins during the fetal life in females and during puberty in males. In both cases, entering meiosis requires a timely switch from the mitotic to the meiotic cell cycle and the transition from a potential pluripotent status to meiotic differentiation. Revealing the molecular mechanisms underlying these interrelated processes represents the essence in understanding the beginning of meiosis. Meiosis facilitates diversity across individuals and acts as a fundamental driver of evolution. Major differences between sexes and among species complicate the understanding of how meiosis begins. Basic meiotic research is further hindered by a current lack of meiotic cell lines. This has been recently partly overcome with the use of primordial-germ-cell-like cells (PGCLCs) generated from pluripotent stem cells. Much of what we know about this process depends on data from model organisms, namely, the mouse; in mice, the process, however, appears to differ in many aspects from that in humans. Identifying the mechanisms and molecules controlling germ cells to enter meiosis has represented and still represents a major challenge for reproductive medicine. In fact, the proper execution of meiosis is essential for fertility, for maintaining the integrity of the genome, and for ensuring the normal development of the offspring. The main clinical consequences of meiotic defects are infertility and, probably, increased susceptibility to some types of germ-cell tumors. In the present work, we report and discuss data mainly concerning the beginning of meiosis in mammalian female germ cells, referring to such process in males only when pertinent. After a brief account of this process in mice and humans and an historical chronicle of the major hypotheses and progress in this topic, the most recent results are reviewed and discussed.
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Hiraoka, Daisaku, Enako Hosoda, Kazuyoshi Chiba et Takeo Kishimoto. « SGK phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation at the meiotic G2/M transition ». Journal of Cell Biology 218, no 11 (19 septembre 2019) : 3597–611. http://dx.doi.org/10.1083/jcb.201812122.
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The kinase cyclin B–Cdk1 complex is a master regulator of M-phase in both mitosis and meiosis. At the G2/M transition, cyclin B–Cdk1 activation is initiated by a trigger that reverses the balance of activities between Cdc25 and Wee1/Myt1 and is further accelerated by autoregulatory loops. In somatic cell mitosis, this trigger was recently proposed to be the cyclin A–Cdk1/Plk1 axis. However, in the oocyte meiotic G2/M transition, in which hormonal stimuli induce cyclin B–Cdk1 activation, cyclin A–Cdk1 is nonessential and hence the trigger remains elusive. Here, we show that SGK directly phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation in starfish oocytes. Upon hormonal stimulation of the meiotic G2/M transition, SGK is activated by cooperation between the Gβγ-PI3K pathway and an unidentified pathway downstream of Gβγ, called the atypical Gβγ pathway. These findings identify the trigger in oocyte meiosis and provide insights into the role and activation of SGK.
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Clandinin, T. R., et P. E. Mains. « Genetic studies of mei-1 gene activity during the transition from meiosis to mitosis in Caenorhabditis elegans. » Genetics 134, no 1 (1 mai 1993) : 199–210. http://dx.doi.org/10.1093/genetics/134.1.199.
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Abstract Genetic evidence suggests that the mei-1 locus of Caenorhabditis elegans encodes a maternal product required for female meiosis. However, a dominant gain-of-function allele, mei-1(ct46), can support normal meiosis but causes defects in subsequent mitotic spindles. Previously identified intragenic suppressors of ct46 lack functional mei-1 activity; null alleles suppress only in cis but other alleles arise frequently and suppress both in cis and in trans. Using a different screen for suppressors of the dominant ct46 defect, the present study describes another type of intragenic mutation that also arises at high frequency. These latter alleles appear to have reduced meiotic activity and retain a weakened dominant effect. Characterization of these alleles in trans-heterozygous combinations with previously identified mei-1 alleles has enabled us to define more clearly the role of the mei-1 gene product during normal embryogenesis. We propose that a certain level of mei-1 activity is required for meiosis but must be eliminated prior to mitosis. The dominant mutation causes mei-1 activity to function at mitosis; intragenic trans-suppressors act in an antimorphic manner to inactivate multimeric mei-1 complexes. We propose that inactivation of meiosis-specific functions may be an essential precondition of mitosis; failure to eliminate such functions may allow ectopic meiotic activity during mitosis and cause embryonic lethality.
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Zickler, D., et N. Kleckner. « THE LEPTOTENE-ZYGOTENE TRANSITION OF MEIOSIS ». Annual Review of Genetics 32, no 1 (décembre 1998) : 619–97. http://dx.doi.org/10.1146/annurev.genet.32.1.619.
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Keating, Leonor, Sandra A. Touati et Katja Wassmann. « A PP2A-B56—Centered View on Metaphase-to-Anaphase Transition in Mouse Oocyte Meiosis I ». Cells 9, no 2 (7 février 2020) : 390. http://dx.doi.org/10.3390/cells9020390.
Texte intégralRésumé :
Meiosis is required to reduce to haploid the diploid genome content of a cell, generating gametes—oocytes and sperm—with the correct number of chromosomes. To achieve this goal, two specialized cell divisions without intermediate S-phase are executed in a time-controlled manner. In mammalian female meiosis, these divisions are error-prone. Human oocytes have an exceptionally high error rate that further increases with age, with significant consequences for human fertility. To understand why errors in chromosome segregation occur at such high rates in oocytes, it is essential to understand the molecular players at work controlling these divisions. In this review, we look at the interplay of kinase and phosphatase activities at the transition from metaphase-to-anaphase for correct segregation of chromosomes. We focus on the activity of PP2A-B56, a key phosphatase for anaphase onset in both mitosis and meiosis. We start by introducing multiple roles PP2A-B56 occupies for progression through mitosis, before laying out whether or not the same principles may apply to the first meiotic division in oocytes, and describing the known meiosis-specific roles of PP2A-B56 and discrepancies with mitotic cell cycle regulation.
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Gomes, José-Eduardo, Nicolas Tavernier, Bénédicte Richaudeau, Etienne Formstecher, Thomas Boulin, Paul E. Mains, Julien Dumont et Lionel Pintard. « Microtubule severing by the katanin complex is activated by PPFR-1–dependent MEI-1 dephosphorylation ». Journal of Cell Biology 202, no 3 (5 août 2013) : 431–39. http://dx.doi.org/10.1083/jcb.201304174.
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Katanin is an evolutionarily conserved microtubule (MT)-severing complex implicated in multiple aspects of MT dynamics. In Caenorhabditis elegans, the katanin homologue MEI-1 is required for meiosis, but must be inactivated before mitosis. Here we show that PPFR-1, a regulatory subunit of a trimeric protein phosphatase 4 complex, enhanced katanin MT-severing activity during C. elegans meiosis. Loss of ppfr-1, similarly to the inactivation of MT severing, caused a specific defect in meiosis II spindle disassembly. We show that a fraction of PPFR-1 was degraded after meiosis, contributing to katanin inactivation. PPFR-1 interacted with MEL-26, the substrate recognition subunit of the CUL-3 RING E3 ligase (CRL3MEL-26), which also targeted MEI-1 for post-meiotic degradation. Reversible protein phosphorylation of MEI-1 may ensure temporal activation of the katanin complex during meiosis, whereas CRL3MEL-26-mediated degradation of both MEI-1 and its activator PPFR-1 ensure efficient katanin inactivation in the transition to mitosis.
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Borgers, Mareike, Martin Wolter, Anna Hentrich, Martin Bergmann, Angelika Stammler et Lutz Konrad. « Role of compensatory meiosis mechanisms in human spermatogenesis ». REPRODUCTION 148, no 3 (septembre 2014) : 315–20. http://dx.doi.org/10.1530/rep-14-0279.
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Disturbances of checkpoints in distinct stages of spermatogenesis (mitosis, meiosis, and spermiogenesis) contribute to impaired spermatogenesis; however, the efficiency of meiotic entry has not been investigated in more detail. In this study, we analyzed azoospermic patients with defined spermatogenic defects by the use of octamer-binding protein 2 for type A spermatogonia, sarcoma antigen 1 for mitosis–meiosis transition and SMAD3 for pachytene spermatocytes. Especially patients with maturation arrest (MA) at the level of primary spermatocytes showed significantly reduced numbers of spermatogonia compared with patients with histologically intact spermatogenesis or patients with hypospermatogenesis (Hyp). For a detailed individual classification of the patients, we distinguished between ‘high efficiency of meiotic entry’ (high numbers of pachytene spermatocytes) and ‘low efficiency of meiotic entry’ (low numbers of pachytene spermatocytes). Only patients with histologically normal spermatogenesis (Nsp) and patients with Hyp showed normal numbers of spermatogonia and a high efficiency of meiotic entry. Of note, only patients with histologically Nsp or patients with Hyp could compensate low numbers of spermatogonia with a high efficiency of meiotic entry. In contrast, patients with MA always showed a low efficiency of meiotic entry. This is the first report on patients with impaired spermatogenesis, showing that half of the patients with Hyp but all patients with MA cannot compensate reduced numbers in spermatogonia with a highly efficient meiosis. Thus, we suggest that compensatory meiosis mechanisms in human spermatogenesis exist.
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Susor, Andrej, Zdenka Ellederova, Lucie Jelinkova, Petr Halada, Daniel Kavan, Michal Kubelka et Hana Kovarova. « Proteomic analysis of porcine oocytes during in vitro maturation reveals essential role for the ubiquitin C-terminal hydrolase-L1 ». Reproduction 134, no 4 (octobre 2007) : 559–68. http://dx.doi.org/10.1530/rep-07-0079.
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In this study, we performed proteomic analysis of porcine oocytes during in vitro maturation. Comparison of oocytes at the initial and final stages of meiotic division characterized candidate proteins that were differentially synthesized during in vitro maturation. While the biosynthesis of many of these proteins was significantly decreased, we found four proteins with increased biosynthetic rate, which are supposed to play an essential role in meiosis. Among them, the ubiquitin C-terminal hydrolase-L1 (UCH-L1) was identified by mass spectrometry. To study the regulatory role of UCH-L1 in the process of meiosis in pig model, we used a specific inhibitor of this enzyme, marked C30, belonging to the class of isatin O-acyl oximes. When germinal vesicle (GV) stage cumulus-enclosed oocytes were treated with C30, GV breakdown was inhibited after 28 h of culture, and most of the oocytes were arrested at the first meiosis after 44 h. The block of metaphase I–anaphase transition was not completely reversible. In addition, the inhibition of UCH-L1 resulted in elevated histone H1 kinase activity, corresponding to cyclin–dependent kinase(CDK1)–cyclin B1 complex, and a low level of monoubiquitin. These results supported the hypothesis that UCH-L1 might play a role in metaphase I–anaphase transition by regulating ubiquitin-dependent proteasome mechanisms. In summary, a proteomic approach coupled with protein verification study revealed an essential role of UCH-L1 in the completion of the first meiosis and its transition to anaphase.
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Moore, Daniel P., Andrea W. Page, Tracy Tzu-Ling Tang, Anne W. Kerrebrock et Terry L. Orr-Weaver. « The Cohesion Protein MEI-S332 Localizes to Condensed Meiotic and Mitotic Centromeres until Sister Chromatids Separate ». Journal of Cell Biology 140, no 5 (9 mars 1998) : 1003–12. http://dx.doi.org/10.1083/jcb.140.5.1003.
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The Drosophila MEI-S332 protein has been shown to be required for the maintenance of sister-chromatid cohesion in male and female meiosis. The protein localizes to the centromeres during male meiosis when the sister chromatids are attached, and it is no longer detectable after they separate. Drosophila melanogaster male meiosis is atypical in several respects, making it important to define MEI-S332 behavior during female meiosis, which better typifies meiosis in eukaryotes. We find that MEI-S332 localizes to the centromeres of prometaphase I chromosomes in oocytes, remaining there until it is delocalized at anaphase II. By using oocytes we were able to obtain sufficient material to investigate the fate of MEI-S332 after the metaphase II–anaphase II transition. The levels of MEI-S332 protein are unchanged after the completion of meiosis, even when translation is blocked, suggesting that the protein dissociates from the centromeres but is not degraded at the onset of anaphase II. Unexpectedly, MEI-S332 is present during embryogenesis, localizes onto the centromeres of mitotic chromosomes, and is delocalized from anaphase chromosomes. Thus, MEI-S332 associates with the centromeres of both meiotic and mitotic chromosomes and dissociates from them at anaphase.
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Kadyk, L. C., et J. Kimble. « Genetic regulation of entry into meiosis in Caenorhabditis elegans ». Development 125, no 10 (15 mai 1998) : 1803–13. http://dx.doi.org/10.1242/dev.125.10.1803.
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The Caenorhabditis elegans germline is composed of mitotically dividing cells at the distal end that give rise to meiotic cells more proximally. Specification of the distal region as mitotic relies on induction by the somatic distal tip cell and the glp-1 signal transduction pathway. However, the genetic control over the transition from mitosis to meiosis is not understood. In this paper, we report the identification of a gene, gld-2, that has at least two functions in germline development. First, gld-2 is required for normal progression through meiotic prophase. Second, gld-2 promotes entry into meiosis from the mitotic cell cycle. With respect to this second function, gld-2 appears to be functionally redundant with a previously described gene, gld-1 (Francis, R., Barton, M. K., Kimble, J. and Schedl, T. (1995) Genetics 139, 579–606). Germ cells in gld-1(o) and gld-2 single mutants enter meiosis at the normal time, but germ cells in gld-2 gld-1(o) double mutants do not enter meiosis. Instead, the double mutant germline is mitotic throughout and forms a large tumor. We suggest that gld-1 and gld-2 define two independent regulatory pathways, each of which can be sufficient for entry into meiosis. Epistasis analyses show that gld-1 and gld-2 work downstream of the glp-1 signal transduction pathway. Therefore, we hypothesize that glp-1 promotes proliferation by inhibiting the meiosis-promoting functions of gld-1 and gld-2.
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Fox, Colette, Juan Zou, Juri Rappsilber et Adele L. Marston. « Cdc14 phosphatase directs centrosome re-duplication at the meiosis I to meiosis II transition in budding yeast ». Wellcome Open Research 2 (5 janvier 2017) : 2. http://dx.doi.org/10.12688/wellcomeopenres.10507.1.
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Background Gametes are generated through a specialized cell division called meiosis, in which ploidy is reduced by half because two consecutive rounds of chromosome segregation, meiosis I and meiosis II, occur without intervening DNA replication. This contrasts with the mitotic cell cycle where DNA replication and chromosome segregation alternate to maintain the same ploidy. At the end of mitosis, CDKs are inactivated. This low CDK state in late mitosis/G1 allows for critical preparatory events for DNA replication and centrosome/spindle pole body (SPB) duplication. However, their execution is inhibited until S phase, where further preparatory events are also prevented. This “licensing” ensures that both the chromosomes and the centrosomes/SPBs replicate exactly once per cell cycle, thereby maintaining constant ploidy. Crucially, between meiosis I and meiosis II, centrosomes/SPBs must be re-licensed, but DNA re-replication must be avoided. In budding yeast, the Cdc14 protein phosphatase triggers CDK down regulation to promote exit from mitosis. Cdc14 also regulates the meiosis I to meiosis II transition, though its mode of action has remained unclear. Methods Fluorescence and electron microscopy was combined with proteomics to probe SPB duplication in cells with inactive or hyperactive Cdc14. Results We demonstrate that Cdc14 ensures two successive nuclear divisions by re-licensing SPBs at the meiosis I to meiosis II transition. We show that Cdc14 is asymmetrically enriched on a single SPB during anaphase I and provide evidence that this enrichment promotes SPB re-duplication. Cells with impaired Cdc14 activity fail to promote extension of the SPB half-bridge, the initial step in morphogenesis of a new SPB. Conversely, cells with hyper-active Cdc14 duplicate SPBs, but fail to induce their separation. Conclusion Our findings implicate reversal of key CDK-dependent phosphorylations in the differential licensing of cyclical events at the meiosis I to meiosis I transition.
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Fox, Colette, Juan Zou, Juri Rappsilber et Adele L. Marston. « Cdc14 phosphatase directs centrosome re-duplication at the meiosis I to meiosis II transition in budding yeast ». Wellcome Open Research 2 (21 février 2017) : 2. http://dx.doi.org/10.12688/wellcomeopenres.10507.2.
Texte intégralRésumé :
Background: Gametes are generated through a specialized cell division called meiosis, in which ploidy is reduced by half because two consecutive rounds of chromosome segregation, meiosis I and meiosis II, occur without intervening DNA replication. This contrasts with the mitotic cell cycle where DNA replication and chromosome segregation alternate to maintain the same ploidy. At the end of mitosis, cyclin-dependent kinases (CDKs) are inactivated. This low CDK state in late mitosis/G1 allows for critical preparatory events for DNA replication and centrosome/spindle pole body (SPB) duplication. However, their execution is inhibited until S phase, where further preparatory events are also prevented. This “licensing” ensures that both the chromosomes and the centrosomes/SPBs replicate exactly once per cell cycle, thereby maintaining constant ploidy. Crucially, between meiosis I and meiosis II, centrosomes/SPBs must be re-licensed, but DNA re-replication must be avoided. In budding yeast, the Cdc14 protein phosphatase triggers CDK down regulation to promote exit from mitosis. Cdc14 also regulates the meiosis I to meiosis II transition, though its mode of action has remained unclear. Methods: Fluorescence and electron microscopy was combined with proteomics to probe SPB duplication in cells with inactive or hyperactive Cdc14. Results: We demonstrate that Cdc14 ensures two successive nuclear divisions by re-licensing SPBs at the meiosis I to meiosis II transition. We show that Cdc14 is asymmetrically enriched on a single SPB during anaphase I and provide evidence that this enrichment promotes SPB re-duplication. Cells with impaired Cdc14 activity fail to promote extension of the SPB half-bridge, the initial step in morphogenesis of a new SPB. Conversely, cells with hyper-active Cdc14 duplicate SPBs, but fail to induce their separation. Conclusion: Our findings implicate reversal of key CDK-dependent phosphorylations in the differential licensing of cyclical events at the meiosis I to meiosis II transition.
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Endo, Tsutomu, Maria M. Mikedis, Peter K. Nicholls, David C. Page et Dirk G. de Rooij. « Retinoic Acid and Germ Cell Development in the Ovary and Testis ». Biomolecules 9, no 12 (24 novembre 2019) : 775. http://dx.doi.org/10.3390/biom9120775.
Texte intégralRésumé :
Retinoic acid (RA), a derivative of vitamin A, is critical for the production of oocytes and sperm in mammals. These gametes derive from primordial germ cells, which colonize the nascent gonad, and later undertake sexual differentiation to produce oocytes or sperm. During fetal development, germ cells in the ovary initiate meiosis in response to RA, whereas those in the testis do not yet initiate meiosis, as they are insulated from RA, and undergo cell cycle arrest. After birth, male germ cells resume proliferation and undergo a transition to spermatogonia, which are destined to develop into haploid spermatozoa via spermatogenesis. Recent findings indicate that RA levels change periodically in adult testes to direct not only meiotic initiation, but also other key developmental transitions to ensure that spermatogenesis is precisely organized for the prodigious output of sperm. This review focuses on how female and male germ cells develop in the ovary and testis, respectively, and the role of RA in this process.
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Li, Yufei, Leyun Wang, Linlin Zhang, Zhengquan He, Guihai Feng, Hao Sun, Jiaqiang Wang et al. « Cyclin B3 is required for metaphase to anaphase transition in oocyte meiosis I ». Journal of Cell Biology 218, no 5 (15 février 2019) : 1553–63. http://dx.doi.org/10.1083/jcb.201808088.
Texte intégralRésumé :
Meiosis with a single round of DNA replication and two successive rounds of chromosome segregation requires specific cyclins associated with cyclin-dependent kinases (CDKs) to ensure its fidelity. But how cyclins control the distinctive meiosis is still largely unknown. In this study, we explored the role of cyclin B3 in female meiosis by generating Ccnb3 mutant mice via CRISPR/Cas9. Ccnb3 mutant oocytes characteristically arrested at metaphase I (MetI) with normal spindle assembly and lacked enough anaphase-promoting complex/cyclosome (APC/C) activity, which is spindle assembly checkpoint (SAC) independent, to initiate anaphase I (AnaI). Securin siRNA or CDK1 inhibitor supplements rescued the MetI arrest. Furthermore, CCNB3 directly interacts with CDK1 to exert kinase function. Besides, the MetI arrest oocytes had normal development after intracytoplasmic sperm injection (ICSI) or parthenogenetic activation (PA), along with releasing the sister chromatids, which implies that Ccnb3 exclusively functioned in meiosis I, rather than meiosis II. Our study sheds light on the specific cell cycle control of cyclins in meiosis.
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Terret, M. Emilie, Katja Wassmann, Irene Waizenegger, Bernard Maro, Jan-Michael Peters et Marie-Hélène Verlhac. « The Meiosis I-to-Meiosis II Transition in Mouse Oocytes Requires Separase Activity ». Current Biology 13, no 20 (octobre 2003) : 1797–802. http://dx.doi.org/10.1016/j.cub.2003.09.032.
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Capitao, Claudio, Sorin Tanasa, Jaroslav Fulnecek, Vivek K. Raxwal, Svetlana Akimcheva, Petra Bulankova, Pavlina Mikulkova et al. « A CENH3 mutation promotes meiotic exit and restores fertility in SMG7-deficient Arabidopsis ». PLOS Genetics 17, no 9 (30 septembre 2021) : e1009779. http://dx.doi.org/10.1371/journal.pgen.1009779.
Texte intégralRésumé :
Meiosis in angiosperm plants is followed by mitotic divisions to form multicellular haploid gametophytes. Termination of meiosis and transition to gametophytic development is, in Arabidopsis, governed by a dedicated mechanism that involves SMG7 and TDM1 proteins. Mutants carrying the smg7-6 allele are semi-fertile due to reduced pollen production. We found that instead of forming tetrads, smg7-6 pollen mother cells undergo multiple rounds of chromosome condensation and spindle assembly at the end of meiosis, resembling aberrant attempts to undergo additional meiotic divisions. A suppressor screen uncovered a mutation in centromeric histone H3 (CENH3) that increased fertility and promoted meiotic exit in smg7-6 plants. The mutation led to inefficient splicing of the CENH3 mRNA and a substantial decrease of CENH3, resulting in smaller centromeres. The reduced level of CENH3 delayed formation of the mitotic spindle but did not have an apparent effect on plant growth and development. We suggest that impaired spindle re-assembly at the end of meiosis limits aberrant divisions in smg7-6 plants and promotes formation of tetrads and viable pollen. Furthermore, the mutant with reduced level of CENH3 was very inefficient haploid inducer indicating that differences in centromere size is not the key determinant of centromere-mediated genome elimination.
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Courtois, Aurélien, Melina Schuh, Jan Ellenberg et Takashi Hiiragi. « The transition from meiotic to mitotic spindle assembly is gradual during early mammalian development ». Journal of Cell Biology 198, no 3 (30 juillet 2012) : 357–70. http://dx.doi.org/10.1083/jcb.201202135.
Texte intégralRésumé :
The transition from meiosis to mitosis, classically defined by fertilization, is a fundamental process in development. However, its mechanism remains largely unexplored. In this paper, we report a surprising gradual transition from meiosis to mitosis over the first eight divisions of the mouse embryo. The first cleavages still largely share the mechanism of spindle formation with meiosis, during which the spindle is self-assembled from randomly distributed microtubule-organizing centers (MTOCs) without centrioles, because of the concerted activity of dynein and kinesin-5. During preimplantation development, the number of cellular MTOCs progressively decreased, the spindle pole gradually became more focused, and spindle length progressively scaled down with cell size. The typical mitotic spindle with centrin-, odf2-, kinesin-12–, and CP110-positive centrosomes was established only in the blastocyst. Overall, the transition from meiosis to mitosis progresses gradually throughout the preimplantation stage in the mouse embryo, thus providing a unique system to study the mechanism of centrosome biogenesis in vivo.
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Xu, L., M. Ajimura, R. Padmore, C. Klein et N. Kleckner. « NDT80, a meiosis-specific gene required for exit from pachytene in Saccharomyces cerevisiae. » Molecular and Cellular Biology 15, no 12 (décembre 1995) : 6572–81. http://dx.doi.org/10.1128/mcb.15.12.6572.
Texte intégralRésumé :
We describe the identification of a new meiosis-specific gene of Saccharomyces cerevisiae, NDT80. The ndt80 null and point mutants arrest at the pachytene stage of meiosis, with homologs connected by full-length synaptonemal complexes and spindle pole bodies duplicated but unseparated. Meiotic recombination in an ndt80 delta mutant is relatively normal, although commitment to heteroallelic recombination is elevated two- to threefold and crossing over is decreased twofold compared with those of the wild type. ndt80 arrest is not alleviated by mutations in early recombination genes, e.g., SPO11 or RAD50, and thus cannot be attributed to an intermediate block in prophase chromosome metabolism like that observed in several other mutants. The ndt80 mutant phenotype during meiosis most closely resembles that of a cdc28 mutant, which contains a thermolabile p34, the catalytic subunit of maturation-promoting factor. Cloning and molecular analysis reveal that the NDT80 gene maps on the right arm of chromosome VIII between EPT1 and a Phe-tRNA gene, encodes a 627-amino-acid protein which exhibits no significant homology to other known proteins, and is transcribed specifically during middle meiotic prophase. The NDT80 gene product could be a component of the cell cycle regulatory machinery involved in the transition out of pachytene, a participant in an unknown aspect of meiosis sensed by a pachytene checkpoint, or a SPO11- and RAD50-independent component of meiotic chromosomes that is the target of cell cycle signaling.
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González-Arranz, Sara, Isabel Acosta, Jesús A. Carballo, Beatriz Santos et Pedro A. San-Segundo. « The N-Terminal Region of the Polo Kinase Cdc5 Is Required for Downregulation of the Meiotic Recombination Checkpoint ». Cells 10, no 10 (27 septembre 2021) : 2561. http://dx.doi.org/10.3390/cells10102561.
Texte intégralRésumé :
During meiosis, the budding yeast polo-like kinase Cdc5 is a crucial driver of the prophase I to meiosis I (G2/M) transition. The meiotic recombination checkpoint restrains cell cycle progression in response to defective recombination to ensure proper distribution of intact chromosomes to the gametes. This checkpoint detects unrepaired DSBs and initiates a signaling cascade that ultimately inhibits Ndt80, a transcription factor required for CDC5 gene expression. Previous work revealed that overexpression of CDC5 partially alleviates the checkpoint-imposed meiotic delay in the synaptonemal complex-defective zip1Δ mutant. Here, we show that overproduction of a Cdc5 version (Cdc5-ΔN70), lacking the N-terminal region required for targeted degradation of the protein by the APC/C complex, fails to relieve the zip1Δ-induced meiotic delay, despite being more stable and reaching increased protein levels. However, precise mutation of the consensus motifs for APC/C recognition (D-boxes and KEN) has no effect on Cdc5 stability or function during meiosis. Compared to the zip1Δ single mutant, the zip1Δ cdc5-ΔN70 double mutant exhibits an exacerbated meiotic block and reduced levels of Ndt80 consistent with persistent checkpoint activity. Finally, using a CDC5-inducible system, we demonstrate that the N-terminal region of Cdc5 is essential for its checkpoint erasing function. Thus, our results unveil an additional layer of regulation of polo-like kinase function in meiotic cell cycle control.
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Tung, Jeffrey J., et Peter K. Jackson. « Emi1 Class of Proteins Regulate Entry into Meiosis and the Meiosis I to Meiosis II Transition in Xenopus Oocytes ». Cell Cycle 4, no 3 (février 2005) : 478–82. http://dx.doi.org/10.4161/cc.4.3.1532.
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Meneau, Ferdinand, Aude Dupré, Catherine Jessus et Enrico Maria Daldello. « Translational Control of Xenopus Oocyte Meiosis : Toward the Genomic Era ». Cells 9, no 6 (19 juin 2020) : 1502. http://dx.doi.org/10.3390/cells9061502.
Texte intégralRésumé :
The study of oocytes has made enormous contributions to the understanding of the G2/M transition. The complementarity of investigations carried out on various model organisms has led to the identification of the M-phase promoting factor (MPF) and to unravel the basis of cell cycle regulation. Thanks to the power of biochemical approaches offered by frog oocytes, this model has allowed to identify the core signaling components involved in the regulation of M-phase. A central emerging layer of regulation of cell division regards protein translation. Oocytes are a unique model to tackle this question as they accumulate large quantities of dormant mRNAs to be used during meiosis resumption and progression, as well as the cell divisions during early embryogenesis. Since these events occur in the absence of transcription, they require cascades of successive unmasking, translation, and discarding of these mRNAs, implying a fine regulation of the timing of specific translation. In the last years, the Xenopus genome has been sequenced and annotated, enabling the development of omics techniques in this model and starting its transition into the genomic era. This review has critically described how the different phases of meiosis are orchestrated by changes in gene expression. The physiological states of the oocyte have been described together with the molecular mechanisms that control the critical transitions during meiosis progression, highlighting the connection between translation control and meiosis dynamics.
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Tang, Wanli, Judy Qiju Wu, Yanxiang Guo, David V. Hansen, Jennifer A. Perry, Christopher D. Freel, Leta Nutt, Peter K. Jackson et Sally Kornbluth. « Cdc2 and Mos Regulate Emi2 Stability to Promote the Meiosis I–Meiosis II Transition ». Molecular Biology of the Cell 19, no 8 (août 2008) : 3536–43. http://dx.doi.org/10.1091/mbc.e08-04-0417.
Texte intégralRésumé :
The transition of oocytes from meiosis I (MI) to meiosis II (MII) requires partial cyclin B degradation to allow MI exit without S phase entry. Rapid reaccumulation of cyclin B allows direct progression into MII, producing a cytostatic factor (CSF)-arrested egg. It has been reported that dampened translation of the anaphase-promoting complex (APC) inhibitor Emi2 at MI allows partial APC activation and MI exit. We have detected active Emi2 translation at MI and show that Emi2 levels in MI are mainly controlled by regulated degradation. Emi2 degradation in MI depends not on Ca2+/calmodulin-dependent protein kinase II (CaMKII), but on Cdc2-mediated phosphorylation of multiple sites within Emi2. As in MII, this phosphorylation is antagonized by Mos-mediated recruitment of PP2A to Emi2. Higher Cdc2 kinase activity in MI than MII allows sufficient Emi2 phosphorylation to destabilize Emi2 in MI. At MI anaphase, APC-mediated degradation of cyclin B decreases Cdc2 activity, enabling Cdc2-mediated Emi2 phosphorylation to be successfully antagonized by Mos-mediated PP2A recruitment. These data suggest a model of APC autoinhibition mediated by stabilization of Emi2; Emi2 proteins accumulate at MI exit and inhibit APC activity sufficiently to prevent complete degradation of cyclin B, allowing MI exit while preventing interphase before MII entry.
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Lee, Jibak, Takashi Miyano et Robert M. Moor. « Localisation of phosphorylated MAP kinase during the transition from meiosis I to meiosis II in pig oocytes ». Zygote 8, no 2 (mai 2000) : 119–25. http://dx.doi.org/10.1017/s0967199400000897.
Texte intégralRésumé :
Mitogen-activated protein kinase (MAPK) has been reported to be involved in oocyte maturation in all animals so far examined. In the present study we investigate the expression and localisation of active phosphorylated MAPKs (p44ERK1/p42ERK2) during maturation of pig oocytes. In immunoblot analysis using anti-p44ERK1 antibody which recognised both active and inactive forms of p44ERK1 and p42ERK2, we confirmed that MAPKs were phosphorylatred around the time of germinal vesicle breakdown (GVBD) and the active phosphorylated MAPKs (pMAKs) were maintained until metaphase II, as has been reported. On immunofluorescent confocal microscopy using anti-pMAPK antibody which recognised only phosphorylated forms of MAPKs, pMAPK was localised at the spindle poles in pig mitotic cells. On the other hand, in pig oocytes, no signal was detected during GV stage. After GVBD, the area around condensed chromosomes was preferentially stained at metaphase I although whole cytoplasm was faintly stained. At early anaphase I, the polar regions of the meiotic spindle were prominently stained. However, during the progression of anaphase I and telophase I pMAPK was detected at the mid-zone of the elongated spindle, gradually becoming concentrated at the centre. Finally, at the time of emission of the first polar body, pMAPK was detected as a ring-like structure between the condensed chromosomes and the first polar body, and the staining was maintained even after the metaphase II spindle was formed. The inhibition of MAPK activity with the MAPK kinase inhibitor U0126 during the meiosis I/meiosis II transition suppressed chromosome separation, first polar body emission and formation of the metaphase II spindle. From these results, we propose that the spindle-associated pMAPKs play an important role in the events occurring during the meiosis I/meiosis II transition, such as chromosome separation, spindle elongation and cleavage furrow formation in pig oocytes.
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Zhang, Qing-Hua, Wai Shan Yuen, Deepak Adhikari, Jennifer A. Flegg, Greg FitzHarris, Marco Conti, Piotr Sicinski, Ibtissem Nabti, Petros Marangos et John Carroll. « Cyclin A2 modulates kinetochore–microtubule attachment in meiosis II ». Journal of Cell Biology 216, no 10 (17 août 2017) : 3133–43. http://dx.doi.org/10.1083/jcb.201607111.
Texte intégralRésumé :
Cyclin A2 is a crucial mitotic Cdk regulatory partner that coordinates entry into mitosis and is then destroyed in prometaphase within minutes of nuclear envelope breakdown. The role of cyclin A2 in female meiosis and its dynamics during the transition from meiosis I (MI) to meiosis II (MII) remain unclear. We found that cyclin A2 decreases in prometaphase I but recovers after the first meiotic division and persists, uniquely for metaphase, in MII-arrested oocytes. Conditional deletion of cyclin A2 from mouse oocytes has no discernible effect on MI but leads to disrupted MII spindles and increased merotelic attachments. On stimulation of exit from MII, there is a dramatic increase in lagging chromosomes and an inhibition of cytokinesis. These defects are associated with an increase in microtubule stability in MII spindles, suggesting that cyclin A2 mediates the fidelity of MII by maintaining microtubule dynamics during the rapid formation of the MII spindle.
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d'Erfurth, Isabelle, Laurence Cromer, Sylvie Jolivet, Chloé Girard, Christine Horlow, Yujin Sun, Jennifer P. C. To, Luke E. Berchowitz, Gregory P. Copenhaver et Raphael Mercier. « The CYCLIN-A CYCA1;2/TAM Is Required for the Meiosis I to Meiosis II Transition and Cooperates with OSD1 for the Prophase to First Meiotic Division Transition ». PLoS Genetics 6, no 6 (17 juin 2010) : e1000989. http://dx.doi.org/10.1371/journal.pgen.1000989.
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Golubovskaya, Inna N., Lisa C. Harper, Wojciech P. Pawlowski, Denise Schichnes et W. Zacheus Cande. « Thepam1Gene Is Required for Meiotic Bouquet Formation and Efficient Homologous Synapsis in Maize (Zea maysL.) ». Genetics 162, no 4 (1 décembre 2002) : 1979–93. http://dx.doi.org/10.1093/genetics/162.4.1979.
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AbstractThe clustering of telomeres on the nuclear envelope (NE) during meiotic prophase to form the bouquet arrangement of chromosomes may facilitate homologous chromosome synapsis. The pam1 (plural abnormalities of meiosis 1) gene is the first maize gene that appears to be required for telomere clustering, and homologous synapsis is impaired in pam1. Telomere clustering on the NE is arrested or delayed at an intermediate stage in pam1. Telomeres associate with the NE during the leptotene-zygotene transition but cluster slowly if at all as meiosis proceeds. Intermediate stages in telomere clustering including miniclusters are observed in pam1 but not in wild-type meiocytes. The tight bouquet normally seen at zygotene is a rare event. In contrast, the polarization of centromeres vs. telomeres in the nucleus at the leptotene-zygotene transition is the same in mutant and wild-type cells. Defects in homologous chromosome synapsis include incomplete synapsis, nonhomologous synapsis, and unresolved interlocks. However, the number of RAD51 foci on chromosomes in pam1 is similar to that of wild type. We suggest that the defects in homologous synapsis and the retardation of prophase I arise from the irregularity of telomere clustering and propose that pam1 is involved in the control of bouquet formation and downstream meiotic prophase I events.
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Turner, J. E., C. G. Minkoff, K. H. Martin, R. Misra et K. I. Swenson. « Oocyte activation and passage through the metaphase/anaphase transition of the meiotic cell cycle is blocked in clams by inhibitors of HMG-CoA reductase activity. » Journal of Cell Biology 128, no 6 (15 mars 1995) : 1145–62. http://dx.doi.org/10.1083/jcb.128.6.1145.
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Cell cycle progression for postembryonic cells requires the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R), the enzyme which catalyzes the production of the isoprenoid precursor, mevalonate. In this study, we examine the requirements of HMG-R activity for cell cycle progression during the meiotic and early mitotic divisions using oocytes and dividing embryos from the surf clam, Spisula solidissima. Using two different inhibitors of HMG-R, we find that the activity of this enzyme appears to be required at three distinct points of the cell cycle during meiosis. Depending on the stage at which these inhibitors are added to synchronous clam cultures, a reversible cell cycle block is triggered at the time of activation or at metaphase of either meiosis I or II, whereas there is not block to the mitotic cell cycle. Inhibition of HMG-R activity in activated oocytes does not affect the transient activation of p42MAPK but results in a block at metaphase of meiosis I that is accompanied by the stabilization of cyclins A and B and p34cdc2 kinase activity. Our results suggest that metabolites from the mevalonate biosynthetic pathway can act to influence the process of activation, as well as the events later in the cell cycle that lead to cyclin proteolysis and the exit from M phase during clam meiosis.
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Ohe, Munemichi, Daigo Inoue, Yoshinori Kanemori et Noriyuki Sagata. « Erp1/Emi2 is essential for the meiosis I to meiosis II transition in Xenopus oocytes ». Developmental Biology 303, no 1 (mars 2007) : 157–64. http://dx.doi.org/10.1016/j.ydbio.2006.10.044.
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Alonso-Ramos, Paula, et Jesús A. Carballo. « Decoding the Nucleolar Role in Meiotic Recombination and Cell Cycle Control : Insights into Cdc14 Function ». International Journal of Molecular Sciences 25, no 23 (29 novembre 2024) : 12861. http://dx.doi.org/10.3390/ijms252312861.
Texte intégralRésumé :
The cell cycle, essential for growth, reproduction, and genetic stability, is regulated by a complex network of cyclins, Cyclin-Dependent Kinases (CDKs), phosphatases, and checkpoints that ensure accurate cell division. CDKs and phosphatases are crucial for controlling cell cycle progression, with CDKs promoting it and phosphatases counteracting their activity to maintain balance. The nucleolus, as a biomolecular condensate, plays a key regulatory role by serving as a hub for ribosome biogenesis and the sequestration and release of various cell cycle regulators. This phase separation characteristic of the nucleolus is vital for the specific and timely release of Cdc14, required for most essential functions of phosphatase in the cell cycle. While mitosis distributes chromosomes to daughter cells, meiosis is a specialized division process that produces gametes and introduces genetic diversity. Central to meiosis is meiotic recombination, which enhances genetic diversity by generating crossover and non-crossover products. This process begins with the introduction of double-strand breaks, which are then processed by numerous repair enzymes. Meiotic recombination and progression are regulated by proteins and feedback mechanisms. CDKs and polo-like kinase Cdc5 drive recombination through positive feedback, while phosphatases like Cdc14 are crucial for activating Yen1, a Holliday junction resolvase involved in repairing unresolved recombination intermediates in both mitosis and meiosis. Cdc14 is released from the nucleolus in a regulated manner, especially during the transition between meiosis I and II, where it helps inactivate CDK activity and promote proper chromosome segregation. This review integrates current knowledge, providing a synthesis of these interconnected processes and an overview of the mechanisms governing cell cycle regulation and meiotic recombination.
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Kolarov, A. « Prostaglandin F2A Disturbs Oogenesis by Causing Meiotic Spindle Damage ». Acta Medica Bulgarica 51, no 4 (23 novembre 2024) : 47–51. http://dx.doi.org/10.2478/amb-2024-0077.
Texte intégralRésumé :
Abstract According to recent data, prostaglandin F2 alpha can have a negative influence on meiosis during oogenesis. Previously, we have found that this prostaglandin may accelerate in a dosage-dependent way the postovulatory aging in ovulated mature oocytes, compromising the integrity of their meiotic spindles. Aim. The study aimed to investigate the effects of prostaglandin F2α on the course and outcome of oocyte meiosis in a mouse model. Materials and Methods. Mouse oocytes were matured in vitro in the presence of prostaglandin F2α in a concentration of 100 ng/ml. Their meiotic stage, spindle morphology and chromosome arrangement were assessed by immunofluorescent labeling of tubulin and fluorescent staining of DNA. Results. We obtained a higher percentage of immature oocytes in metaphase I after the treatment than in untreated control oocytes. In addition, there were specific morphological changes in the meiotic spindles of oocytes exposed to prostaglandin F2α associated with a reduced number of fibers. Conclusion. It is probable that prostaglandin F2α has an impact on the microtubule dynamics of the meiotic spindle that can prevent the transition of maturing oocytes to the second meiotic division, most likely by triggering the spindle assembly checkpoint.
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Tadros, Wael, Simon A. Houston, Arash Bashirullah, Ramona L. Cooperstock, Jennifer L. Semotok, Bruce H. Reed et Howard D. Lipshitz. « Regulation of Maternal Transcript Destabilization During Egg Activation in Drosophila ». Genetics 164, no 3 (1 juillet 2003) : 989–1001. http://dx.doi.org/10.1093/genetics/164.3.989.
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AbstractIn animals, the transfer of developmental control from maternal RNAs and proteins to zygotically derived products occurs at the midblastula transition. This is accompanied by the destabilization of a subset of maternal transcripts. In Drosophila, maternal transcript destabilization occurs in the absence of fertilization and requires specific cis-acting instability elements. We show here that egg activation is necessary and sufficient to trigger transcript destabilization. We have identified 13 maternal-effect lethal loci that, when mutated, result in failure of maternal transcript degradation. All mutants identified are defective in one or more additional processes associated with egg activation. These include vitelline membrane reorganization, cortical microtubule depolymerization, translation of maternal mRNA, completion of meiosis, and chromosome condensation (the S-to-M transition) after meiosis. The least pleiotropic class of transcript destabilization mutants consists of three genes: pan gu, plutonium, and giant nuclei. These three genes regulate the S-to-M transition at the end of meiosis and are thought to be required for the maintenance of cyclin-dependent kinase (CDK) activity during this cell cycle transition. Consistent with a possible functional connection between this S-to-M transition and transcript destabilization, we show that in vitro-activated eggs, which exhibit aberrant postmeiotic chromosome condensation, fail to initiate transcript degradation. Several genetic tests exclude the possibility that reduction of CDK/cyclin complex activity per se is responsible for the failure to trigger transcript destabilization in these mutants. We propose that the trigger for transcript destabilization occurs coincidently with the S-to-M transition at the end of meiosis and that pan gu, plutonium, and giant nuclei regulate maternal transcript destabilization independent of their role in cell cycle regulation.
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Bickel, Sharon E., Dudley W. Wyman et Terry L. Orr-Weaver. « Mutational Analysis of the Drosophila Sister-Chromatid Cohesion Protein ORD and Its Role in the Maintenance of Centromeric Cohesion ». Genetics 146, no 4 (1 août 1997) : 1319–31. http://dx.doi.org/10.1093/genetics/146.4.1319.
Texte intégralRésumé :
The ord gene is required for proper segregation of all chromosomes in both male and female Drosophila meiosis. Here we describe the isolation of a null ord allele and examine the consequences of ablating ord function. Cytologically, meiotic sister-chromatid cohesion is severely disrupted in flies lacking ORD protein. Moreover, the frequency of missegregation in genetic tests is consistent with random segregation of chromosomes through both meiotic divisions, suggesting that sister cohesion may be completely abolished. However, only a slight decrease in viability is observed for ord null flies, indicating that ORD function is not essential for cohesion during somatic mitosis. In addition, we do not observe perturbation of germ-line mitotic divisions in flies lacking ORD activity. Our analysis of weaker ord alleles suggests that ORD is required for proper centromeric cohesion after arm cohesion is released at the metaphase I/anaphase I transition. Finally, although meiotic cohesion is abolished in the ord null fly, chromosome loss is not appreciable. Therefore, ORD activity appears to promote centromeric cohesion during meiosis II but is not essential for kinetochore function during anaphase.
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Li, Ping, Hui Jin et Hong-Guo Yu. « Condensin suppresses recombination and regulates double-strand break processing at the repetitive ribosomal DNA array to ensure proper chromosome segregation during meiosis in budding yeast ». Molecular Biology of the Cell 25, no 19 (octobre 2014) : 2934–47. http://dx.doi.org/10.1091/mbc.e14-05-0957.
Texte intégralRésumé :
During meiosis, homologues are linked by crossover, which is required for bipolar chromosome orientation before chromosome segregation at anaphase I. The repetitive ribosomal DNA (rDNA) array, however, undergoes little or no meiotic recombination. Hyperrecombination can cause chromosome missegregation and rDNA copy number instability. We report here that condensin, a conserved protein complex required for chromosome organization, regulates double-strand break (DSB) formation and repair at the rDNA gene cluster during meiosis in budding yeast. Condensin is highly enriched at the rDNA region during prophase I, released at the prophase I/metaphase I transition, and reassociates with rDNA before anaphase I onset. We show that condensin plays a dual role in maintaining rDNA stability: it suppresses the formation of Spo11-mediated rDNA breaks, and it promotes DSB processing to ensure proper chromosome segregation. Condensin is unnecessary for the export of rDNA breaks outside the nucleolus but required for timely repair of meiotic DSBs. Our work reveals that condensin coordinates meiotic recombination with chromosome segregation at the repetitive rDNA sequence, thereby maintaining genome integrity.
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Tarsounas, M., R. E. Pearlman et P. B. Moens. « Meiotic activation of rat pachytene spermatocytes with okadaic acid : the behaviour of synaptonemal complex components SYN1/SCP1 and COR1/SCP3 ». Journal of Cell Science 112, no 4 (15 février 1999) : 423–34. http://dx.doi.org/10.1242/jcs.112.4.423.
Texte intégralRésumé :
The phosphatase inhibitor okadaic acid accelerates meiotic events in rodent germ cells in culture. Isolated pachytene spermatocytes treated with okadaic acid proceed to a metaphase I arrest in a few hours as opposed to the similar process in vivo, which requires several days. Leptotene/zygotene spermatocytes cannot be activated in this way, suggesting that okadaic acid enables cells to bypass a sensor of the meiotic progression, which is pachytene specific. We monitored the chromosome behaviour accompanying the transition to metaphase I in rat spermatocytes with antibodies against COR1/SCP3, a component of the meiotic chromosome cores, and against the synaptic protein, SYN1/SCP1. Okadaic acid induced a rapid synaptonemal complex dissolution and bivalent separation, followed by chromosome condensation and chiasmata formation, similar to the succession of events in untreated cells. The similarity between meiosis I induced with okadaic acid and the meiosis I events in vivo extends to the dissolution of the nuclear membrane and the disappearance of the microtubule network at the onset of metaphase I. This cell culture system provides a model for the in vivo transition from pachytene to metaphase I and therefore can be used in the study of this transition at the molecular level. The effect of okadaic acid is most likely mediated by the activation of tyrosine kinases, as addition of genistein, a general tyrosine kinase inhibitor, completely abolishes the observed effect of okadaic acid on chromosome metabolism. The okadaic acid-induced progression to the metaphase I arrest is not affected by the inhibition of protein synthesis. However, pachytene spermatocytes incubated in the presence of protein synthesis inhibitors for 6 hours show loss of synapsis which is abnormal in that it is not accompanied by chiasmata formation. The two meiosis-specific proteins, SYN1/SCP1 and COR1/SCP3, are efficiently phosphorylated in vitro by extracts from isolated pachytene cells. Extracts from cells that have reached metaphase I upon okadaic acid treatment, with concomitant displacement of SYN1/SCP1 and COR1/SCP3 from their chromosomes, do not have this capability. These data support the hypothesis that phosphorylation of SYN1/SCP1 and COR1/SCP3 targets their removal from the chromosomes and that activity of the kinases involved correlates with the presence of these two proteins on the chromosomes.
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Golden, Andy, Penny L. Sadler, Matthew R. Wallenfang, Jill M. Schumacher, Danielle R. Hamill, Gayle Bates, Bruce Bowerman, Geraldine Seydoux et Diane C. Shakes. « Metaphase to Anaphase (mat) Transition–Defective Mutants inCaenorhabditis elegans ». Journal of Cell Biology 151, no 7 (25 décembre 2000) : 1469–82. http://dx.doi.org/10.1083/jcb.151.7.1469.
Texte intégralRésumé :
The metaphase to anaphase transition is a critical stage of the eukaryotic cell cycle, and, thus, it is highly regulated. Errors during this transition can lead to chromosome segregation defects and death of the organism. In genetic screens for temperature-sensitive maternal effect embryonic lethal (Mel) mutants, we have identified 32 mutants in the nematode Caenorhabditis elegans in which fertilized embryos arrest as one-cell embryos. In these mutant embryos, the oocyte chromosomes arrest in metaphase of meiosis I without transitioning to anaphase or producing polar bodies. An additional block in M phase exit is evidenced by the failure to form pronuclei and the persistence of phosphohistone H3 and MPM-2 antibody staining. Spermatocyte meiosis is also perturbed; primary spermatocytes arrest in metaphase of meiosis I and fail to produce secondary spermatocytes. Analogous mitotic defects cause M phase delays in mitotic germline proliferation. We have named this class of mutants “mat” for metaphase to anaphase transition defective. These mutants, representing six different complementation groups, all map near genes that encode subunits of the anaphase promoting complex or cyclosome, and, here, we show that one of the genes, emb-27, encodes the C. elegans CDC16 ortholog.
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Nabti, Ibtissem, Petros Marangos, Jenny Bormann, Nobuaki R. Kudo et John Carroll. « Dual-mode regulation of the APC/C by CDK1 and MAPK controls meiosis I progression and fidelity ». Journal of Cell Biology 204, no 6 (17 mars 2014) : 891–900. http://dx.doi.org/10.1083/jcb.201305049.
Texte intégralRésumé :
Female meiosis is driven by the activities of two major kinases, cyclin-dependent kinase 1 (Cdk1) and mitogen-activated protein kinase (MAPK). To date, the role of MAPK in control of meiosis is thought to be restricted to maintaining metaphase II arrest through stabilizing Cdk1 activity. In this paper, we find that MAPK and Cdk1 play compensatory roles to suppress the anaphase-promoting complex/cyclosome (APC/C) activity early in prometaphase, thereby allowing accumulation of APC/C substrates essential for meiosis I. Furthermore, inhibition of MAPK around the onset of APC/C activity at the transition from meiosis I to meiosis II led to accelerated completion of meiosis I and an increase in aneuploidy at metaphase II. These effects appear to be mediated via a Cdk1/MAPK-dependent stabilization of the spindle assembly checkpoint, which when inhibited leads to increased APC/C activity. These findings demonstrate new roles for MAPK in the regulation of meiosis in mammalian oocytes.
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Karasu, Mehmet E., Nora Bouftas, Scott Keeney et Katja Wassmann. « Cyclin B3 promotes anaphase I onset in oocyte meiosis ». Journal of Cell Biology 218, no 4 (5 février 2019) : 1265–81. http://dx.doi.org/10.1083/jcb.201808091.
Texte intégralRésumé :
Meiosis poses unique challenges because two rounds of chromosome segregation must be executed without intervening DNA replication. Mammalian cells express numerous temporally regulated cyclins, but how these proteins collaborate to control meiosis remains poorly understood. Here, we show that female mice genetically ablated for cyclin B3 are viable—indicating that the protein is dispensable for mitotic divisions—but are sterile. Mutant oocytes appear normal until metaphase I but then display a highly penetrant failure to transition to anaphase I. They arrest with hallmarks of defective anaphase-promoting complex/cyclosome (APC/C) activation, including no separase activity, high CDK1 activity, and high cyclin B1 and securin levels. Partial APC/C activation occurs, however, as exogenously expressed APC/C substrates can be degraded. Cyclin B3 forms active kinase complexes with CDK1, and meiotic progression requires cyclin B3–associated kinase activity. Cyclin B3 homologues from frog, zebrafish, and fruit fly rescue meiotic progression in cyclin B3–deficient mouse oocytes, indicating conservation of the biochemical properties and possibly cellular functions of this germline-critical cyclin.
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Shao, Hua, Ruizhen Li, Chunqi Ma, Eric Chen et X. Johné Liu. « Xenopus oocyte meiosis lacks spindle assembly checkpoint control ». Journal of Cell Biology 201, no 2 (8 avril 2013) : 191–200. http://dx.doi.org/10.1083/jcb.201211041.
Texte intégralRésumé :
The spindle assembly checkpoint (SAC) functions as a surveillance mechanism to detect chromosome misalignment and to delay anaphase until the errors are corrected. The SAC is thought to control mitosis and meiosis, including meiosis in mammalian eggs. However, it remains unknown if meiosis in the eggs of nonmammalian vertebrate species is also regulated by SAC. Using a novel karyotyping technique, we demonstrate that complete disruption of spindle microtubules in Xenopus laevis oocytes did not affect the bivalent-to-dyad transition at the time oocytes are undergoing anaphase I. These oocytes also acquired the ability to respond to parthenogenetic activation, which indicates proper metaphase II arrest. Similarly, oocytes exhibiting monopolar spindles, via inhibition of aurora B or Eg5 kinesin, underwent monopolar anaphase on time and without additional intervention. Therefore, the metaphase-to-anaphase transition in frog oocytes is not regulated by SAC.
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Ma, Chunqi, Cathy Cummings et X. Johné Liu. « Biphasic Activation of Aurora-A Kinase during the Meiosis I- Meiosis II Transition in Xenopus Oocytes ». Molecular and Cellular Biology 23, no 5 (1 mars 2003) : 1703–16. http://dx.doi.org/10.1128/mcb.23.5.1703-1716.2003.
Texte intégralRésumé :
ABSTRACT Xenopus Aurora-A (also known as Eg2) is a member of the Aurora family of mitotic serine/threonine kinases. In Xenopus oocytes, Aurora-A phosphorylates and activates a cytoplasmic mRNA polyadenylation factor (CPEB) and therefore plays a pivotal role in MOS translation. However, hyperphosphorylation and activation of Aurora-A appear to be dependent on maturation-promoting factor (MPF) activation. To resolve this apparent paradox, we generated a constitutively activated Aurora-A by engineering a myristylation signal at its N terminus. Injection of Myr-Aurora-A mRNA induced germinal vesicle breakdown (GVBD) with the concomitant activation of MOS, mitogen-activated protein kinase, and MPF. Myr-Aurora-A-injected oocytes, however, appeared to arrest in meiosis I with high MPF activity and highly condensed, metaphase-like chromosomes but no organized microtubule spindles. No degradation of CPEB or cyclin B2 was observed following GVBD in Myr-Aurora-A-injected oocytes. In the presence of progesterone, the endogenous Aurora-A became hyperphosphorylated and activated at the time of MPF activation. Following GVBD, Aurora-A was gradually dephosphorylated and inactivated before it was hyperphosphorylated and activated again. This biphasic pattern of Aurora-A activation mirrored that of MPF activation and hence may explain meiosis I arrest by the constitutively activated Myr-Aurora-A.
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Perez, Laurent H., Celia Antonio, Stéphane Flament, Isabelle Vernos et Angel R. Nebreda. « Xkid chromokinesin is required for the meiosis I to meiosis II transition in Xenopus laevis oocytes ». Nature Cell Biology 4, no 10 (23 septembre 2002) : 737–42. http://dx.doi.org/10.1038/ncb850.
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Lee, Jibak, Takashi Miyano, Yanfeng Dai, Peter Wooding, Tim J. Yen et Robert M. Moor. « Specific regulation of CENP-E and kinetochores during meiosis I/meiosis II transition in pig oocytes ». Molecular Reproduction and Development 56, no 1 (mai 2000) : 51–62. http://dx.doi.org/10.1002/(sici)1098-2795(200005)56:1<51 ::aid-mrd7>3.0.co;2-n.
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Furuta, Tokiko, Simon Tuck, Jay Kirchner, Bryan Koch, Roy Auty, Risa Kitagawa, Ann M. Rose et David Greenstein. « EMB-30 : An APC4 Homologue Required for Metaphase-to-Anaphase Transitions during Meiosis and Mitosis in Caenorhabditis elegans ». Molecular Biology of the Cell 11, no 4 (avril 2000) : 1401–19. http://dx.doi.org/10.1091/mbc.11.4.1401.
Texte intégralRésumé :
Here we show that emb-30 is required for metaphase-to-anaphase transitions during meiosis and mitosis inCaenorhabditis elegans. Germline-specificemb-30 mutant alleles block the meiotic divisions. Mutant oocytes, fertilized by wild-type sperm, set up a meiotic spindle but do not progress to anaphase I. As a result, polar bodies are not produced, pronuclei fail to form, and cytokinesis does not occur. Severe-reduction-of-function emb-30 alleles (class I alleles) result in zygotic sterility and lead to germline and somatic defects that are consistent with an essential role in promoting the metaphase-to-anaphase transition during mitosis. Analysis of the vulval cell lineages in these emb-30(class I) mutant animals suggests that mitosis is lengthened and eventually arrested when maternally contributed emb-30 becomes limiting. By further reducing maternal emb-30 function contributed to class I mutant animals, we show that emb-30 is required for the metaphase-to-anaphase transition in many, if not all, cells. Metaphase arrest in emb-30 mutants is not due to activation of the spindle assembly checkpoint but rather reflects an essential emb-30 requirement for M-phase progression. A reduction in emb-30 activity can suppress the lethality and sterility caused by a null mutation in mdf-1, a component of the spindle assembly checkpoint machinery. This result suggests that delaying anaphase onset can bypass the spindle checkpoint requirement for normal development. Positional cloning established thatemb-30 encodes the likely C. elegansorthologue of APC4/Lid1, a component of the anaphase-promoting complex/cyclosome, required for the metaphase-to-anaphase transition. Thus, the anaphase-promoting complex/cyclosome is likely to be required for all metaphase-to-anaphase transitions in a multicellular organism.