Karasu, M. E. | bioRxiv Science

bioRxiv2018

REC114 partner ANKRD31 controls number, timing and location of meiotic DNA breaks

Double-strand breaks (DSBs) initiate the homologous recombination that is crucial for meiotic chromosome pairing and segregation. Here we unveil mouse ANKRD31 as a lynchpin governing multiple aspects of DSB formation. Spermatocytes lacking ANKRD31 have altered DSB locations and fail to target DSBs to sex chromosomes pseudoautosomal regions (PAR). They also have delayed/fewer recombination sites but, paradoxically, more DSBs, suggesting DSB dysregulation. Unrepaired DSBs and pairing failures--stochastic on autosomes, nearly absolute on X and Y--cause meiotic arrest and sterility in males. Ankrd31-deficient females have reduced oocyte reserves. A crystal structure defines direct ANKRD31- REC114 molecular contacts and reveals a surprising pleckstrin homology domain in REC114. In vivo, ANKRD31 stabilizes REC114 association with the PAR and elsewhere. Our findings inform a model that ANKRD31 is a scaffold anchoring REC114 and other factors to specific genomic locations, promoting efficient and timely DSB formation but possibly also suppressing formation of clustered DSBs.

genetics↗

bioRxiv2018

Cyclin B3 promotes APC/C activation and anaphase I onset in oocyte meiosis

As obligate kinase partners, cyclins control the switch-like cell cycle transitions that orchestrate orderly duplication and segregation of genomes. Meiosis, the cell division that generates gametes for sexual reproduction, poses unique challenges because two rounds of chromosome segregation must be executed without intervening DNA replication. Mammalian cells express numerous, temporally regulated cyclins, but how these proteins collaborate to control meiosis remains poorly understood. Here, we delineate an essential function for mouse cyclin B3 in the first meiotic division of oocytes. Females genetically ablated for cyclin B3 are viable, indicating the protein is dispensable for mitotic divisions, but are sterile. Mutant oocytes appear normal until metaphase I but then display a highly penetrant failure to transition to anaphase I. They arrest with hallmarks of defective APC/C activation, including no separase activity and high MPF, cyclin B1, and securin levels. Partial APC/C activation occurs, however, as exogenously expressed APC/C substrates can be degraded and arrest can be suppressed by inhibiting MPF kinase. Cyclin B3 is itself targeted for degradation by the APC/C. Cyclin B3 forms active kinase complexes with CDK1, and meiotic progression requires cyclin B3-associated kinase activity. Collectively, our findings indicate that cyclin B3 is essential for oocyte meiosis because it fine-tunes APC/C activity as a kinase-activating CDK partner. Cyclin B3 homologs from frog, zebrafish, and fruitfly rescue meiotic progression in cyclin B3-deficient mouse oocytes, indicating conservation of the biochemical properties and possibly cellular functions of this germline-critical cyclin.

cell biology↗