Protein kinase C isoforms undergo quantitative variations during rat spermatogenesis and are selectively retained at...

Signal transduction elements, including protein kinase C, have been identified in mammalian spermatozoa. In order to evaluate the pattern of expression and the subcellular localization of nine different protein kinase C isoforms in the course of spermatogenesis, we utilized quantitative electron microscopy immunocytochemistry on thin sections of rat seminiferous tubules. The results indicate a progressive reduction of the protein kinase C isoforms present in the early stages of spermatogenesis, so that in late spermatids none of them is present in the nucleus, while the isoforms alpha, gamma and beta II are specifically retained in the acrosome, the isoforms beta I and zeta in the neck, and the isoform epsilon in the tail. These isoforms, except for beta II, are maintained at the same sites in spermatozoa. Western blotting analysis indicates the presence of alpha and gamma isoforms in the head subfraction, and of beta I, zeta and epsilon isoforms in the tail subfraction of spermatozoa. These findings suggest that specific protein kinase C isoforms may be functionally involved in some events of spermatozoa differentiation and, eventually, in the fertilization process.