Subcellular localization of the regulatory subunits of cyclic adenosine 3',5'-monophosphate-dependent protein kinase in bovine spermatozoa

Cyclic AMP (cAMP) is a regulator of sperm flagellar activity. The action of this cyclic nucleotide is presumably mediated by cAMP-dependent protein kinase (PKA). PKA is localized or targeted to specific subcellular sites through the interaction of PKA regulatory subunits with A-kinase anchoring proteins (AKAPs). We have recently shown that the addition of PKA anchoring inhibitor peptides to spermatozoa leads to the complete arrest of motility. A knowledge of the subcellular localization of PKA and AKAPs is essential for an understanding of how cAMP acts in spermatozoa. In this report, monospecific, affinity-purified, antipeptide antibodies were used to determine the distribution of the regulatory (R) subunit isoforms. Immunocytochemistry staining revealed that RIα and RIβ subunits are both localized predominantly in the acrosomal segment of the head, although they have distinct staining patterns within this region. In addition to the head, RIβ was observed in the midpiece of the tail while RIβ was detected in the connecting piece. RIIβ is prominent in the axonemal region of the flagellum but was not observed in the head region. These data suggest distinct roles for each of these isoforms in sperm functions such as motility and the acrosome reaction.