DISTINCT PATTERNS OF EXPRESSION OF THE D-TYPE CYCLINS DURING TESTICULAR DEVELOPMENT IN THE MOUSE

The three D-type cyclins have been shown to be differentially expresse d in a number of isolated cell types and cell lines, suggesting distin ct roles in cell cycle regulation in particular cell lineages. The tes tis provides unique opportunities to study genes involved in cell cycl e regulation, since it contains cells in both mitosis and meiosis as w ell as differentiated cells with little proliferation activity. Major transcripts of 4.2 kb, 6.8 kb, and 2.3 kb were detected in the adult m ouse testis by Northern hybridization analyses for cyclin D1, cyclin D 2, and cyclin D3, respectively. Additional transcripts of 1.8 and 2.7 kb were detected by Northern hybridization for cyclin D3 in the testis , but not in other tissues, and these transcripts were limited to germ cells. Northern and in situ hybridization analyses of normal and germ cell-deficient testes showed the surprising result that cyclin D1 was expressed in a pattern consistent with expression in the non-dividing Sertoli cells. Cyclin D2 levels appeared slightly enriched in germ ce ll-deficient testes as compared to intact testis, but in situ hybridiz ation analysis did not reveal any distinct cellular localization. Also surprising was the observation that cyclin D3 expression was highest in the non-dividing, haploid, round spermatids. The possible roles of these cyclins in the events of spermatogenesis are discussed. (C) 1995 Wiley-Liss, Inc.