Function of cyclins in regulating the mitotic and meiotic cell cycles in male germ cells

Abstract

The specialized cell cycles that characterize various aspects of the differentiation of germ cells provide a unique opportunity to understand heretofore elusive aspects of the in vivo function of cell cycle regulators. Key components of the cell cycle machinery are the regulatory sub-units, the cyclins, and their catalytic partners, the cyclin-dependent kinases. Some of the cyclins exhibit unique patterns of expression in germ cells that suggest possible concomitant distinct functions, predictions that are being explored by targeted mutagenesis in mouse models. A novel, meiosis-specific function has been shown for one of the A-type cyclins, cyclin A1. Embryonic lethality has obviated understanding of the germline functions of cyclin A2 and cyclin B1, while yet other cyclins, although expressed at specific stages of germ cell development, may have less essential function in the male germline.

Figure 1

Cartoon summarizing the meiotic stages of spermatogenesis in which cyclin expression has been documented. The bars are color-coded to depict expression of specific cyclins, as indicated, that have been detected at the mRNA and/or protein level. No attempt is made to convey relative levels since the methods used for detection were not quantitative.