Regulation of acrosome reaction of fowl spermatozoa: evidence for the involvement of protein kinase C and protein phosphatase-type 1 and/or -type 2A

Abstract

The signal transduction pathways involved in the regulation of the acrosome reaction and motility of fowl spermatozoa were investigated. The motility and acrosomal integrity of fowl spermatozoa in TES/NaCl buffer, with or without homogenised inner perivitelline layers (IPVL), prepared from laid fowl eggs, was almost negligible at 40 °C. In the presence of 2 mmol CaCl2/l at 40 °C, motility became vigorous and the acrosome reaction was stimulated when IPVL was added. In the absence of Ca2+, motility was stimulated by the addition of calyculin A and okadaic acid, both specific inhibitors of protein phosphatase-type 1 (PP1) and -type 2A (PP2A), but Okadaic acid, which is a weaker inhibitor of PP1, did not completely restore motility at 40 °C. However, the acrosome reaction was significantly and equally stimulated in a dose-dependent manner by both inhibitors in the range of 10–1000 nmol/l, when spermatozoa were incubated with IPVL but without Ca2+. These inhibitors did not stimulate the acrosome reaction in the absence of IPVL. The vigorous motility of spermatozoa, stimulated by the addition of Ca2+, was reduced gradually as the concentrations of SC-9, a selective activator of protein kinase C (PKC), were increased and a similar SC-9-induced inhibition was observed in the acrosome reaction in the presence of Ca2+ and IPVL. These results confirm that IPVL is necessary for the activation of the acrosome reaction in fowl spermatozoa and that Ca2+ plays an important role in the stimulation of motility and acrosomal exocytosis. Furthermore, it appears that the intracellular molecular mechanisms for the regulation of acrosome reaction of fowl spermatozoa are different from those for the restoration of motility, i.e., protein dephosporylation involving PP1 and/or PP2A in the former, and PP1 alone in the latter case. In addition, the activation of PKC may contribute to a decrease in the flagellar movement and acrosome reaction of fowl spermatozoa.