Cellular localization of the mRNAs of the somatic and testis‐specific cytochromes c during spermatogenesis in the rat

Abstract

During mammalian spermatogenesis, two forms of cytochrome c, cytochromes cs and ct, are present in male germ cells. During meiosis, cytochrome ct begins to replace cytochrome cs. At least four size classes of cytochrome cs mRNA are expressed in all somatic cells and in early stages of male germ cells. In addition, a cytochrome cs 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 cs transcripts, the 1.7 kB cytochrome cs transcripts, and the testis-specific cytochrome ct transcripts are expressed in the rat. Low levels of cytochrome cs mRNAs are detected in Leydig cells, myoepithelial cells, Sertoli cells, all types of spermatogonia, and during meiotic prophase. The 1.7 kB cytochrome cs mRNA is first detected in late stages of meiotic prophase and reaches its highest levels in steps 1 to 9 spermatids. No cytochrome cs mRNAs are detected in spermatids between steps 10 to 19. Low levels of cytochrome ct 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 cs mRNA nor the cytochrome ct mRNAs are sequestered during spermatogenesis. The absence of cytochrome cs or ct mRNAs in steps 10-19 spermatids suggest that the cytochrome ct protein does not turn over rapidly in late stage male germ cells.