Differential expression of the Cs and Cα1 isoforms of the catalytic subunit of cyclic 3′,5′-adenosine monophosphate-dependent protein kinase in testicular cells

Abstract

The amino terminus of the sperm cAMP-dependent protein kinase catalytic subunit (termed Cs) differs from that of the Cα1 isoform expressed in most tissues due to the use of alternative transcripts of the Cα gene. Both Cα1 and Cs transcripts are present in testis; Cs is expressed specifically in spermatogenic cells and is the only C isoform detected in mature sperm. Immuno-histochemistry of mouse testis using antibodies specific for Cs and Cα1 now shows that Cα1 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 Cα1 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 × 105 molecules of Cs, a seemingly large number for a protein that acts catalytically.