Differential Expression of the Cs and Ca1 Isoforms of the Catalytic Subunit of Cyclic 39,59-Adenosine Monophosphate-Dependent Protein Kinase in Testicular Cells1

The amino terminus of the sperm cAMP-dependent protein kinase catalytic subunit (termed Cs) differs from that of the Ca1 isoform expressed in most tissues due to the use of alternative transcripts of the Ca gene. Both Ca1 and Cs transcripts are present in testis; Cs is expressed specifically in spermatogenic cells and is the only C isoform detected in mature sperm. Immunohistochemistry of mouse testis using antibodies specific for Cs and Ca1 now shows that Ca1 is present in somatic testicular cells, spermatogonia, and preleptotene spermatocytes but not in cells that are in later stages of spermatogenesis. In contrast, Cs is expressed only in midpachytene and later stage spermatocytes and in spermatids. Therefore, Cs and Ca1 expression do not overlap. Immunofluorescence microscopic localization of Cs in murine and ovine sperm reveals that Cs is located primarily in sperm tail components, including the midpiece mitochondria and the axoneme. Quantitative analysis of Western blots indicates that individual ovine sperm contain ;4 3 105 molecules of Cs, a seemingly large number for a protein that acts catalytically. cyclic adenosine monophosphate, kinases, sperm, spermatogenesis, testis