Mad2 prevents aneuploidy and premature proteolysis of cyclin B and securin during meiosis I in mouse oocytes

Abstract

In mitosis, the spindle checkpoint protein Mad2 averts aneuploidy by delaying anaphase onset until chromosomes align. Here we show that depletion of Mad2 in meiosis I mouse oocytes induced an increased incidence of aneuploidy. Proteolysis of cyclin B and securin commenced earlier in Mad2-depleted oocytes, resulting in a shortened duration of meiosis I. Furthermore, overexpression of Mad2 inhibited homolog disjunction. We conclude that Mad2 delays the onset of cyclin B and securin degradation and averts aneuploidy during meiosis I in mammalian oocytes. The data suggest a link between trisomies such as Down syndrome and defective oocyte spindle checkpoint function.Supplemental material is available at http://www.genesdev.org.Received April 16, 2004; revised version accepted October 14, 2004. During meiosis, one round of DNA synthesis is followed by the sequential segregation of homologous chromosomes at meiosis I and sister chromatids at meiosis II. Although female meiosis I errors are the major genetic cause of miscarriage and mental retardation in humans, little is known about their molecular origins (Hassold and Hunt 2001). The spindle checkpoint is the principal mechanism for preventing chromosome missegregation during mitosis by delaying anaphase until completion of chromosome alignment (Mussachio and Hardwick 2002). Checkpoint proteins such as Mad2 prevent activation of a multi-subunit ubiquitin ligase called the anaphase-promoting complex or cyclosome (APC/C) by sequestering the APC/C activator protein, Cdc20 (Peters 2002). Once chromosomes establish a stable bipolar orientation on the mitotic spindle, the APC/C directs proteolysis of securin and cyclin B, thereby inducing anaphase and cytokinesis (Peters 2002). As in mitosis, securin and cyclin B destruction are required for homolog disjunction and exit from meiosis I in mouse oocytes (Herbert et al. 2003).In mammalian somatic cells, the Mad2-dependent spindle checkpoint is required for mitotic arrest in the presence of spindle poisons (Li and Benezra 1996) and to delay anaphase until proper chromosome alignment in the absence of spindle damage (Gorbsky et al. 1998). During meiosis I in budding yeast, Mad2 is also required to arrest cells following spindle disruption and to avert nondisjunction in unperturbed cells (Shonn et al. 2000(Shonn et al. , 2003. In mouse oocytes, a dominant-negative variant of human Mad2 (hMad2) destabilizes cyclin-dependent kinase 1 (Cdk1) activity in the presence of the spindle poison nocodazole, indicating that Mad2 is required for meiosis I arrest in the face of spindle damage (Wassmann et al. 2003). It is not known, however, whether Mad2 regulates progression through meiosis I in unperturbed oocytes.Conventional genetic approaches have not been informative regarding checkpoint function in female meiosis. For example, deletion of Mad2 and Bub3 causes mouse embryonic lethality (Dobles et al. 2000;Kalitsis et al. 2000). Furthermore, using such approaches, it would be difficult to distinguish between errors that occurred duri...

Cdc2 and Mos Regulate Emi2 Stability to Promote the Meiosis I–Meiosis II Transition

“…Early studies in Xenopus oocytes indicated that the APC was dispensable for this transition, as neither antibody neutralization of the APC nor overexpression of its natural inhibitor, Mad2, inhibited the first meiotic anaphase (Peter et al, 2001;Taieb et al, 2001). This idea was challenged more recently by the discovery that activation of the spindle assembly checkpoint (SAC), that targets the APC in MI, could lead to MI arrest (Homer et al, 2005). Moreover, in 2006, studies in both the Xenopus and murine oocyte systems demonstrated a requirement for Emi2 in the MI-MII transition and suggested that not only is the APC activated at MI anaphase, but also that its timely inhibition by Emi2 is required to promote entry into MII (Madgwick et al, 2006;Ohe et al, 2007).…”

Checkpoint kinase 1 is essential for meiotic cell cycle regulation in mouse oocytes

“…13 During meiotic maturation of mouse oocytes, SAC proteins such as mitotic arrest-deficient-1 (Mad1), Mad2, budding uninhibited by benzimidazole-1 (Bub1), Bub3, BubR1 and monopolar spindle 1 (Msp1) also play important roles. 1,[14][15][16][17][18][19][20][21][22][23] Chk1-depleted cells display metaphase block, chromosome misalignment in metaphase, chromosome lagging in anaphase and kinetochore defects, which are caused by negative regulation of Plk1 by Chk1. 24 Another study reports different results showing that Chk1 is required for the spindle assembly checkpoint by phosphorylating Aurora B and mediating phosphorylation and kinetochore localization of BubR1.…”

Origen parental, estado de no disyunción y recombinación meiótica del cromosoma 21 extra en el síndrome de Down: estudio en una muestra de población colombiana

“…The molecular correlates of non-disjunction in oocytes involve several mechanisms: chromosome condensation (29,30), pairing of homologous chromosomes (31,32), synaptonemal complex formation (33,34), recombination events (35,36), spindle formation (37,38) and meiotic checkpoints (39,40). Proteins actively functioning in these processes are essential for proper development, but their specific roles in oocyte maturation are difficult to unravel.…”