Immunoelectron microscopic localization of testicular and somatic cytochromes c in the seminiferous epithelium of the rat

Somatic and testis-specific cytochromes c were localized ultrastructurally in the seminiferous epithelium by immunocytochemistry using monospecific antibodies. Cytochrome c(S) was lost from the mitochondria as spermatogenesis advanced, while there was a relative increase in cytochrome c(T) during the zygotene-to-pachytene transition; this was in agreement with other studies that have suggested activation of the cytochrome c(T) gene during prophase of the first meiotic division. Cytochrome c(T) was highly concentrated in mitochondria that were being degraded within cytoplasmic lobes of spermatids and in residual bodies that were phagocytized by Sertoli cells. The two isoforms were found to coexist within the same mitochondrion during the transitional period from cytochrome c(S) to cytochrome c(T) predominance. In addition, both cytochromes c were present in the chromatoid bodies of spermatocytes and round spermatids; this suggests that the chromatoid body may be involved in the storage of these isozymes and possibly in their differential expression within germ cell mitochondria. Apocytochrome c was concentrated in mitochondria and chromatoid bodies of the germ cells and also scattered in the cytoplasm. The presence of the holoprotein and apoprotein immunoprobes within the chromatoid bodies of spermatocytes and spermatids was an interesting observation that raises questions regarding the precise location of the synthesis of cytochromes c in spermatogenic cells.