EMB30: An APC4 homologue required for metaphase-to-anaphase transitions during meiosis and mitosis in Caenorhabditis elegans

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 anaphas e I. As a result, polar bodies are not produced, pronuclei fail to form, an d cytokinesis does not occur. Severe-reduction-of-function emb-30 alleles ( class I alleles) result in zygotic sterility and lead to germline and somat ic defects that are consistent with an essential role in promoting the meta phase-to-anaphase transition during mitosis. Analysis of the vulval cell li neages in these emb-30(class I) mutant animals suggests that mitosis is len gthened 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-ana phase transition in many, if not all, cells. Metaphase arrest in emb-30 mut ants is not due to activation of the spindle assembly checkpoint but rather reflects an essential emb-30 requirement for M-phase progression. A reduct ion in emb-30 activity can suppress the lethality and sterility caused by a null mutation in mdf-l, a component of the spindle assembly checkpoint mac hinery. This result suggests that delaying anaphase onset can bypass the sp indle checkpoint requirement for normal development. Positional cloning est ablished 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/cycl osome is likely to be required for all metaphase-to-anaphase transitions in a multicellular organism.