Roles of Src family kinase signaling during fertilization and the first cell cycle in the marine protostome worm Cerebratulus.

For eggs to generate a calcium response during fertilization, the sperm of many deuterostome animals must first activate a group of egg kinases, called Src family kinases (SFKs). However, whether SFK activation is also required for fertilization-induced calcium signals in eggs of protostomes remains unknown. Thus, in this study, unfertilized oocytes of the marine protostome worm Cerebratulus were treated with either PP2 to inhibit SFKs or with U73122 to block phospholipase C activity downstream of SFK. Compared with control fertilizations, the inhibitors significantly reduced post-insemination levels of polar body formation and cleavage, but apparently did so via different mechanisms, based on the variable effects of these drugs on sperm incorporations and pronuclear differentiation. Moreover, confocal calcium imaging revealed that repetitive calcium waves (=oscillations) were blocked by U73122, but not by PP2, even though immunoblots indicated SFK activity was inhibited by PP2. Such findings fail to support the view that SFKs are required for initiating fertilization-induced calcium oscillations in Cerebratulus, and alternative mechanisms for the observed inhibition of polar body formation and cleavage in drug-treated specimens are discussed.