CELLULAR-LOCALIZATION OF THE MESSENGER-RNAS OF THE SOMATIC AND TESTIS-SPECIFIC CYTOCHROMES-C DURING SPERMATOGENESIS IN THE RAT

During mammalian spermatogenesis, two forms of cytochrome c, cytochromes c(s) and c(t), are present in male germ cells. During meiosis, cytochrome c(t) begins to replace cytochrome c(s). At least four size classes of cytochrome c(s) mRNA are expressed in all somatic cells and in early stages of male germ cells. In addition, a cytochrome c(s) transcript of 1.7 kB has been detected in rodent testes and is abundant in post meiotic male germ cells. Here we utilize ''in situ'' hybridization to define the cellular sites where the four ubiquitous cytochrome c(s) transcripts, the 1.7 kB cytochrome c(s) transcripts, and the testis-specific cytochrome c(t) transcripts are expressed in the rat. Low levels of cytochrome c(s) mRNAs are detected in Leydig cells, myoepithelial cells, Sertoli cells, all types of spermatogonia, and during meiotic prophase. The 1.7 kB cytochrome c(s) mRNA is first detected in late stages of meiotic prophase and reaches its highest levels in steps 1 to 9 spermatids. No cytochrome c(s) mRNAs are detected in spermatids between steps 10 to 19. Low levels of cytochrome c(t) mRNAs, initially detected in zygotene spermatocytes, reach maximal levels in round spermatids. For all three probes the majority of the silver grains are localized randomly throughout the cytoplasm, suggesting that neither the translating nor non-translating (the 1.7 kB mRNA) forms of cytochrome c(s) mRNA nor the cytochrome c(t) mRNAs are sequestered during spermatogenesis. The absence of cytochrome c(s) or c(t) mRNAs in steps 10-19 spermatids suggest that the cytochrome c(t) protein does not turn over rapidly in late stage male germ cells.