The developmentally restricted pattern of expression in the male germ line of a murine cyclin A, cyclin A2, suggests roles in both mitotic and meiotic cell cycles.

We have isolated cDNAs encoding a murine cyclin A, designated cyclinA2, and have examined its in vivo expression at the level of both mRNA and protein, with particular focus on the male germ line. Cyclin A2 is expressed in embryos and in a variety of adult tissues, including the testis. In the testis, however, a striking cellular specificity of expression was observed. At both the DNA and protein levels, the predominant sites of cyclin A2 expression were in the germ line stem cells, the spermatogonia, and in highest levels in preleptotene spermatocytes, cells in which premeiotic DNA synthesis occurs. The concurrent localization of cyclin A2 mRNA and protein further suggested that cyclin A2 is regulated at the level of transcription in these cells. The observed cellular specificity of cyclin A2 expression is consistent with its function during mitosis in the stem cell stage of this lineage, while the restricted meiotic stage localization suggests function in G1/S or S but not in the meiotic divisions per se.