Localization of two mammalian cyclin dependent kinases during mammalian meiosis

Mammalian meiotic progression, like mitotic cell cycle progression, is regu lated by cyclins and cyclin dependent kinases (CDKs). However, the unique r equirements of meiosis (homologous synapsis, reciprocal recombination and t he dual divisions that segregate first homologues, then sister chromatids) have led to different patterns of CDK expression. Here we show that Cdk4 co localizes with replication protein A (RPA) on the synaptonemal complexes (S Cs) of newly synapsed axes of homologously pairing bivalents, but disappear s from these axes by mid-pachynema. The switch from the mitotic pattern of expression occurs during the la:st two spermatogonial divisions. Cdk2 coloc alizes with MLH1, a mismatch repair protein at sites of reciprocal recombin ation in mid-late pachynema, In addition Cdk2 localizes to the telomeres of chromosomal bivalents throughout meiotic prophase. The mitotic pattern of expression of Cdk2 remains unchanged throughout the spermatogonial division s, but is altered in meiosis of the spermatocytes.