Specific expression of nuclear proto-oncogenes before entry into meiotic prophase of spermatogenesis.

The expression of proto-oncogenes representative of several functional categories has been investigated during development of mouse male germ cells. The c-raf proto-oncogene and three members of the c-ras gene family were expressed in mitotically active stem cells, throughout the prophase of meiosis and to varying extents in post-meiotic cell types. In contrast, the nuclear proto-oncogenes c-fos, c-jun, and c-myc were specifically expressed at high levels in type B spermatogonia. High levels of c-myc and c-jun RNAs were also detected in spermatocytes early in the prophase of meiosis. The type B spermatogonia represent the last mitotic cell division before entry into meiotic prophase; therefore, these nuclear proto-oncogenes may be involved in altering programs of gene expression at this developmental transition.