Daily rhythms in male mice meiosis.

Various processes associated with mammalian reproduction exhibit circadian rhythms, yet no information is available concerning the presence of rhythmicity in meiosis-the crucial process of the production of sex cells. Following meiosis in cells derived from male mice exposed in vivo to daily light-dark cycles (LD), we were able to demonstrate the existence of a clear 24h rhythmic pattern in the overall meiotic process, as well as in the production of spermatids, the immediate products of male meiosis and the precursors of male sex cells. On the other hand, cells of free-running male mice exposed to constant external conditions (light-light, LL) revealed a 12h rhythmic pattern in the overall meiotic process, indicating the endogenous nature of this rhythm. The existence of a 24h rhythm component in a long-lasting (approximately 12 days) process like meiosis suggests a time-dependent gating mechanism that controls the dynamics of miocyte arrest and release. The 12h rhythms observed in LL may indicate the presence of either a 12h rhythm component or of two 24h endogenous components, phased 12h from each other, that are coupled in daily LD cycles and split up in the free-running condition (LL). The rhythmic pattern observed in the course of male meiosis might have significant implications for male reproduction.