PKA activation in concert with ARIS and asterosap induces the acrosome reaction in starfish

Summary The acrosome reaction (AR) is a fundamental event for fertilization, which is induced in concert withacrosome reaction-inducing substance (ARIS) and asterosap, both of which are components of starfishegg jelly (EJ). During the AR, a spermatozoon undergoes a series of physiological changes, such as inintracellular cGMP concentration ([cGMP] i ), pH i and intracellular Ca 2+ concentration ([Ca 2+ ] i ). Affinitypurification of cGMP-binding protein resulted in the isolation of a regulatory subunit of the cAMP-dependent protein kinase A (PKA), suggesting the involvement of a cAMP-dependent pathway in theAR. By using a cAMP enzyme immunoassay, [cAMP] i was found to increase in starfish spermatozoawhen stimulated with ARIS and asterosap. ARIS could also increase the [cAMP] i in the presence of highpH seawater. Pretreatment of spermatozoa with two specific and cell-permeable PKA inhibitors, H89and KT5720, prevented the induction of the AR in a concentration-dependent manner. These resultssuggestthatPKAactivityparticipatesintheinductionoftheARwithARISandasterosap.Toinvestigatethis,wehaveclonedagenethatencodesaregulatory subunit ofPKAthathadbeenidentifiedinstarfishspermatozoa.Keywords: Acrosome reaction, Cyclic AMP, Egg jelly, PKA, Starfish