EMB-30: An APC4 Homologue Required for Metaphase-to-Anaphase Transitions during Meiosis and Mitosis inCaenorhabditis elegans

Abstract

Here we show that emb-30 is required for metaphase-to-anaphase transitions during meiosis and mitosis in Caenorhabditis elegans. Germline-specific emb-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-toanaphase 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 that emb-30 encodes the likely C. elegans orthologue 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.

The anaphase promoting complex/cyclosome is required during development for modified cell cycles

“…Mutations in APC͞C subunits in Caenorhabditis elegans have been demonstrated to block the metaphase I͞anaphase I transition and completion of meiosis (36)(37)(38). In contrast in Xenopus oocytes, inactivation of the APC by injection of antibodies to either the Cdc27 APC subunit or the Fzr activator or injection of inhibitory peptides does not affect the completion of meiosis I but causes a metaphase II block (39).…”

The anaphase-promoting complex: a key factor in the regulation of cell cycle

“…In this regard, the APC seems to be essential to induce metaphase II-exit, whereas this complex seems to be required for metaphase I -to anaphase I transition in some species like Caenorhabditis elegans (Furuta et al, 2000), mouse (Terret et al, 2003) or yeast (Salah and Nasmyth, 2000) and dispensable in others like in Xenopus (Peter et al, 2001;Taieb et al, 2001).…”

Loss of the anaphase-promoting complex in quiescent cells causes unscheduled hepatocyte proliferation

“…Mutations that affect the APC/C or its activator Cdc20 cause yeast (Irniger et al 1995), fly (Sigrist and Lehner 1997), and worm (Furuta et al 2000;Golden et al 2000) cells to arrest in a metaphase-like state with unseparated sister chromatids. Injection of antibodies specific for CDC16/APC6 and CDC27/APC3 produce a similar phenotype in mammalian tissue culture cells .…”

“…The APC/C at the same time triggers exit from mitosis by destroying mitotic cyclins, which are regulatory subunits of the cyclin-dependent kinase Cdk1. Inactivation of the APC/C causes cells from both yeast (Irniger et al 1995) and Caenorhabditis elegans to arrest in metaphase (Furuta et al 2000;Golden et al 2000). The APC/C's ubiquitination of securin and cyclins shortly before the onset of anaphase depends on an unstable regulatory ␤-propeller protein called Cdc20 (Visintin et al 1997), which is destroyed at the end of mitosis (Shirayama et al 1999).…”