Developmentally regulated expression of cyclin D3 and its potential in vivo interacting proteins during murine gametogenesis

To begin to assess the function of the cell cycle regulator cyclin D3 durin g gametogenesis, the present study examined its expression, interacting par tners, and associated kinase activity in the murine testis and ovary. In th e early stages of postnatal testicular development, cyclin D3 protein was d etected in spermatogonia and Leydig cells. In the adult testis, cyclin D3 w as also expressed in terminally differentiating spermatids. In the embryoni c ovary, detection of cyclin D3 was limited to somatic cells. In the postna tal ovary, its localization was predominantly in the nuclei of oocytes in p rimordial and small follicles, a localization that diminished with oocyte g rowth. Cdk4 and p27 were expressed in a similar subset of testicular and ov arian cells, suggesting that they may regulate cyclin D3 function during te sticular and ovarian development in a cell type-specific manner. Cyclin D3- associated kinase activity was detected in immature, but not adult, testes and ovaries. These observations suggest unique roles for cyclin D3 in the c ontrol of cell division and differentiation in the germ line and the differ ential regulation of mitotic and meiotic cell cycles during male and female gametogenesis.