The Yeast APC/C Subunit Mnd2 Prevents Premature Sister Chromatid Separation Triggered by the Meiosis-Specific APC/C-Ama1

Abstract

Cohesion established between sister chromatids during pre-meiotic DNA replication mediates two rounds of chromosome segregation. The first division is preceded by an extended prophase wherein homologous chromosomes undergo recombination. The persistence of cohesion during prophase is essential for recombination and both meiotic divisions. Here we show that Mnd2, a subunit of the anaphase-promoting complex (APC/C) from budding yeast, is essential to prevent premature destruction of cohesion in meiosis. During S- and prophase, Mnd2 prevents activation of the APC/C by a meiosis-specific activator called Ama1. In cells lacking Mnd2 the APC/C-Ama1 enzyme triggers degradation of Pds1, which causes premature sister chromatid separation due to unrestrained separase activity. In vitro, Mnd2 inhibits ubiquitination of Pds1 by APC/C-Ama1 but not by other APC/C holo-enzymes. We conclude that chromosome segregation in meiosis depends on the selective inhibition of a meiosis-specific form of the APC/C.

Sporulation in the Budding Yeast Saccharomyces cerevisiae

“…If this regulation is disrupted (e.g., in mnd2D mutants), premature activation of APC-Ama1 leads to defects in chromosome segregation (Oelschlaegel et al 2005;Penkner et al 2005). Though there is some evidence for an Ama1 function during meiosis, the combined action of Mnd2 and CDK likely limits the primary functions of APCAma1 to the end of meiosis II (Cooper et al 2000;Oelschlaegel et al 2005;Tan et al 2010).…”

“…AMA1 encodes a sporulation-specific member of the Cdc20 family (Cooper et al 2000). Though expressed as an early-middle gene, its activity is repressed early in meiosis by CDK phosphorylation and by another APC subunit, Mnd2, which leaves the APC during meiosis II (Oelschlaegel et al 2005;Penkner et al 2005). If this regulation is disrupted (e.g., in mnd2D mutants), premature activation of APC-Ama1 leads to defects in chromosome segregation (Oelschlaegel et al 2005;Penkner et al 2005).…”

“…Though expressed as an early-middle gene, its activity is repressed early in meiosis by CDK phosphorylation and by another APC subunit, Mnd2, which leaves the APC during meiosis II (Oelschlaegel et al 2005;Penkner et al 2005). If this regulation is disrupted (e.g., in mnd2D mutants), premature activation of APC-Ama1 leads to defects in chromosome segregation (Oelschlaegel et al 2005;Penkner et al 2005). Though there is some evidence for an Ama1 function during meiosis, the combined action of Mnd2 and CDK likely limits the primary functions of APCAma1 to the end of meiosis II (Cooper et al 2000;Oelschlaegel et al 2005;Tan et al 2010).…”

“…Though AMA1 is induced as a pre-middle gene, the activity of APC-Ama1 is restricted by the action of the APC subunit Mnd2 and by Clb-CDK phosphorylation, so that it does not become fully active until late in meiosis II (Oelschlaegel et al 2005;Penkner et al 2005). As described earlier, once APC-Ama1 is active, it leads to degradation of the leading edge protein Ssp1 (though direct Ama1-dependent ubiquitylation of Ssp1 has not been demonstrated) and this serves to link membrane closure to the end of meiosis (Diamond et al 2008).…”

The Ras/cAMP Pathway and the CDK-Like Kinase Ime2 Regulate the MAPK Smk1 and Spore Morphogenesis in Saccharomyces cerevisiae

“…Positive regulators of Smk1 activation include Ama1 (McDonald et al 2005), a meiosis-specific Cdc20-family member that links substrates to the APC (Cooper et al 2000). It has been proposed that the APC Ama1 plays a role in coupling completion of the meiotic divisions to gamete formation (Oelschlaegel et al 2005;Penkner et al 2005). Ssp2, a middle meiosis-specific protein that regulates spore formation (Sarkar et al 2002;Coluccio et al 2004;Li et al 2007) is also required for efficient phosphorylation of Smk1's activation loop (McDonald et al 2005).…”