CDK FAMILY GENES ARE EXPRESSED NOT ONLY IN DIVIDING BUT ALSO IN TERMINALLY DIFFERENTIATED MOUSE GERM-CELLS, SUGGESTING THEIR POSSIBLE FUNCTION DURING BOTH CELL-DIVISION AND DIFFERENTIATION

The roles of the cyclin dependent kinase (Cdk) family in murine germ c ell development have been examined by studying the expression of five Cdk family genes (Cdc2, Cdk2, Cdk4, Pctaire-1, and Pctaire-3) in mouse reproductive organs. Northern blot and in situ hybridization analyses revealed distinctive expression patterns of these genes with striking cellular, lineage, and developmental stage specificity. We observed C dk expression in cell types with proliferative activity: Cdc2 and Cdk2 expression in premeiotic spermatocytes in the testis, and Cdc2, Cdk2, and Cdk4 expression in granulosa cells of ovarian follicles. Cdc2 tra nscripts were most abundant in late pachytene to diplotene spermatocyt es, soon to undergo meiosis. Surprisingly, we also observed expression of Cdk family genes in non-proliferating cell types. All five Cdk fam ily genes examined were expressed in Sertoli cells of the adult testis , which are no longer mitotically active. With regard to Pctaire-1 and Pctaire-3, the highest levels of expression were observed in postmeio tic spermatids. Immunoblot analysis also revealed the presence of high levels of Pctaire-1 in postmeiotic germ cells. These results suggest that Cdk family kinases may exhibit various functions in germinal and somatic cells during gametogenesis, not only in the cell cycle but als o in other regulatory processes, including differentiation. (C) 1995 W iley-Liss, Inc.