Regulation of M-phase promoting factor activity during development of mouse male germ cells.

While the role of M-phase promoting factor (MPF) in controlling meiosis in oocytes has been well documented, very little is known about its function in male germ cells. Previous studies have localized transcripts for cyclin B1, the regulatory subunit of MPF, in male germ cells, with highest levels in postmeiotic, early round spermatids and much reduced levels in the meiotically dividing pachytene spermatocytes. The present study describes the localization of the regulatory and the catalytic subunits of MPF, CycB1 and Cdc2, respectively, to specific cell types within the testis. Immunoblotting revealed that both CycB1 and Cdc2 were present at highest levels in pachytene spermatocytes, with lower levels observed in the postmeiotic compartment. To assay for MPF activity, kinase complexes were isolated from lysates of testicular cells using p13suc1 agarose and antibodies directed against Cdc2 and CycB1. Activity of these kinase complexes was analyzed using histone H1 as an exogenous substrate. Cdc2 and CycB1-associated kinase activities were localized to the meiotically dividing pachytene spermatocytes, but not to postmeiotic spermatids.