JunD mRNA expression differs from c‐jun and junB mRNA expression during male germinal cell differentiation

The members of the jun family of protooncogenes (junB, c‐jun, and junD) share a high degree of sequence homology and function as transcriptional regulators. Here we compare the pattern of junD mRNA expression during spermatogenesis to that of junB and c‐jun (Alcivar et al.: J Biol Chem 265:20160–20165, 1990). junD transcripts are present at high levels in total RNA obtained from both prepuberal and adult intact testes, with the highest levels at stages containing predominantly premeiotic and postmeiotic germ cells. Analyses of cells isolated from testes of 8‐day‐old mice indicate that the level of the 1.8 kb junD mRNA is higher in type B spermatogonia than in type A spermatogonia. In testes of 17‐day‐old mice, the highest junD mRNA levels are detected in preleptotene spermatocytes compared to leptotene/zygotene and prepuberal pachytene spermatocytes. In cells from adult testes, the junD mRNA levels are higher in postmeiotic round spermatids and residual bodies/cytoplasts than in meiotic pachytene spermatocytes. An additional junD transcript of about 1.6 kb is detected in postmeiotic cells. Analyses of polysomal and nonpolysomal RNAs prepared from isolated testicular cells indicate that in early meiotic cell types the junD transcript is more efficiently loaded onto polysomes than in later cell types. In summary, the pattern of expression of junD differs from that of junB and c‐jun during spermatogenesis most notably in that 1) junD mRNA levels do not increase following dissociation of testicular cells and 2) in contrast to the nearly undetectable levels of junB and c‐jun mRNAs in adult postmeiotic testicular cells, high levels of junD mRNAs are seen. The differential expression of these three jun transcripts during development of the male gonad suggests a complex transcriptional regulatory role for the jun family of protooncogenes during spermatogenesis.