A 43 kD c-mos protein is only expressed before meiosis during rat spermatogenesis.

We have investigated the RNA and protein expression pattern of the rat c-mos proto-oncogene during spermatogenesis. In mouse testis a 43kD c-mos protein is expressed throughout spermatogenesis, which is in agreement with one report detecting a 1.7 kb c-mos RNA in pachytene spermatocytes and in early spermatids. However, several other reports show that the mouse 1.7 kb c-mos RNA is exclusively expressed in post-meiotic male germ cells. We report that in rat male germ cells three c-mos RNA species of 5, 3.6 and 1.7 kb are detectable by Northern blotting analysis both before and after meiosis, with highest levels in early spermatids. However, western immuno-blot analysis reveals the presence of a 43 kD c-mos protein in total testis and pachytene spermatocytes, but not in post-meiotic cells. These findings combined with those made in the mouse system strongly suggest that c-mos protein may be a regulator of meiosis during spermatogenesis.