Anaphase onset requires CKS-1-mediated destruction of securin in meiosis I and cyclin B1 in meiosis II.

The cyclin-dependent kinase subunit CKS remains poorly understood. We found that Caenorhabditis elegans CKS-1 and its partner CDK-1 co-localized to the cytosol, chromosomes, and spindle structures throughout cell division. Nevertheless, CKS-1 was required well after CDK-1, during oocyte meiosis I metaphase, which was prolonged in cks-1 mutants. Anaphase A precedes anaphase B in C. elegans oocytes, and while delayed in onset, chromosomes in cks-1 mutants separated normally during meiosis I anaphase A but failed to separate further and instead rapidly transitioned into meiosis II prometaphase, skipping anaphase B. The anaphase A to B transition also was defective during meiosis II. Furthermore, meiosis I anaphase B required that CKS-1 be bound to CDK-1 and have a functional anion pocket. Finally, our results suggest that CKS-1 promotes anaphase onset during meiosis I through securin destruction and during meiosis II through cyclin B1 destruction, and that both securin and cyclin B3 have positive roles independent of their destruction during meiosis II.