Cyclin B3 is dispensable for mouse spermatogenesis.

Cyclins, as regulatory partners of cyclin-dependent kinases (CDKs), control the switch-like cell cycle transitions that orchestrate orderly duplication and segregation of genomes. Compared to mitosis, relatively little is known about how cyclin-CDK complexes control meiosis, the specialized cell division that generates gametes for sexual production. Mouse cyclin B3 was previously shown to have expression restricted to the beginning of meiosis, making it a candidate to regulate meiotic events. Indeed, female mice lacking cyclin B3 are sterile because oocytes arrest at the metaphase-to-anaphase transition of meiosis I. However, whether cyclin B3 functions during spermatogenesis was untested. Here, we found that males lacking cyclin B3 are fertile and show no detectable defects in spermatogenesis based on histological analysis of seminiferous tubules. Cytological analysis further showed no detectable defects in homologous chromosome synapsis or meiotic progression, and suggested that recombination is initiated and completed efficiently. Moreover, absence of cyclin B3 did not exacerbate previously described meiotic defects in mutants deficient for cyclin E2, suggesting a lack of redundancy between these cyclins. Thus, unlike in females, cyclin B3 is not essential for meiosis in males despite its prominent meiosis-specific expression.