Developmental and cell lineage specificity of raf family gene expression in mouse testis.

The proto-oncogene c-raf-1 and the related genes A-raf and B-raf encode serine/threonine protein kinases thought to be involved in regulating gene expression by transducing extracellular signals into the cell. All three raf family genes have been shown previously to be expressed in mouse testis. Northern and in situ hybridization analyses with probes specific for each gene demonstrated that c-raf-1 mRNA is ubiquitously expressed in both somatic and germ cells as a 3.1-kb transcript. Additionally, the levels of c-raf-1 expression are developmentally regulated in the germ cells, exhibiting highest expression in early pachytene spermatocytes and decreasing progressively through later stages. A-raf is expressed predominantly in the somatic compartment as two transcripts of 2.6 and 4.3 kb. A-raf expression in Leydig cells appears to be elevated in testes undergoing spermatogenesis. In contrast, B-raf is expressed as two major transcripts of 4.0 and 2.6 kb, with the 4.0-kb transcript first expressed at low levels in pachytene spermatocytes and the more abundant 2.6-kb transcript restricted to post-meiotic spermatids. These studies indicate that each raf gene exhibits a characteristic, limited pattern of expression and suggests that the different forms may play a unique regulatory role in androgen production and/or spermatogenesis.