Activation of protein kinase C after fertilization is required for remodeling the mouse egg into the zygote

Fertilization of the mammalian egg initiates numerous biochemical and structural changes which remodel the egg into a single-celled zygote. To date, the most extensively studied phenomenon of fertilization in virtually all species has been the relationship between sperm penetration and the induction of the initial rise in intracellular-free calcium ([Ca2+]i) concentration within the egg. In contrast, relatively few studies have focused on the biochemical events following this rise in calcium, and even fewer studies have directly linked the biochemical events to the structural changes which must ensue for proper development of the embryo. In this study, we exploited recently developed technologies to investigate the action of protein kinase C (PKC), a presumed downstream transducer of the initial rise in [Ca2+]i, during fertilization and artificial activation with calcium ionophore or phorbol 12-myristate 13-acetate (PMA). The newly developed myristoylated PKC pseudosubstrate (myrPKC psi) was used to specifically inhibit PKC, thereby averting the trauma of injecting the egg with nonmyristoylated PKC psi. Following fertilization, eggs which were pretreated with myr-PKC psi were not capable of forming a second polar body and pronuclear formation was significantly inhibited. Spatial and temporal localization of PKC using confocal microscopy to visualize the PKC reporter dye, Rim-1, demonstrated localization of PKC to the lateral aspects of the forming second polar body after fertilization, or after artificial activation with calcium ionophore or PMA. In vivo biochemical analysis of eggs which were fertilized or artificially activated demonstrated that PKC activity rose at the same time (40 min) as the second polar body formed and then subsided over the next 5 hr post activation. From these data, we conclude that PKC plays an integral role in directing the transformation from egg to embryo.