The Unique Catalytic Subunit of Sperm cAMP-dependent Protein Kinase Is the Product of an Alternative Cα mRNA Expressed Specifically in Spermatogenic Cells

Abstract

cAMP-dependent protein kinase has a central role in the control of mammalian sperm capacitation and motility. Previous protein biochemical studies indicated that the only cAMP-dependent protein kinase catalytic subunit (C) in ovine sperm is an unusual isoform, termed Cs, whose amino terminus differs from those of published C isoforms of other species. Isolation and sequencing of cDNA clones encoding ovine Cs and Cα1 (the predominant somatic isoform) now reveal that Cs is the product of an alternative transcript of the Cα gene. Cs cDNA clones from murine and human testes also were isolated and sequenced, indicating that Cs is of ancient origin and widespread in mammals. In the mouse, Cs transcripts were detected only in testis and not in any other tissue examined, including ciliated tissues and ovaries. Finally, immunohistochemistry of the testis shows that Cs first appears in pachytene spermatocytes. This is the first demonstration of a cell type–specific expression for any C isoform. The conservation of Cs throughout mammalian evolution suggests that the unique structure of Cs is important in the subunit's localization or function within the sperm.