Divergent microtubule-organizing center strategies in mammalian gametogenesis

Meiotic chromosome segregation relies on the spindle microtubules, which are assembled by microtubule-organizing centers (MTOCs). Mammalian gametogenesis reveals starkly divergent strategies between the sexes. Spermatocytes harbor canonical centrosomes that undergo biogenesis events unique to the meiotic cycle. However, recent findings reviewed here show that these centrosomes are dispensable for chromosome segregation and that a noncentrosomal MTOC pathway can accomplish this segregation. By contrast, oocytes eliminate centrioles and assemble microtubule spindles by coalescing pericentriolar material components to form bipolar MTOCs, a process assisted by a chromosome-driven spindle assembly pathway. This review discusses the species-specific differences in MTOC regulation between mouse and human oocytes and examines how defects in these MTOC pathways are a primary cause of aneuploidy and infertility.