Ion channel function during oocyte maturation and fertilization

The proper maturation of both male and female gametes is essential for supporting fertilization and the early embryonic divisions. In the ovary, immature fully-grown oocytesthat are arrested in prophase Iof meiosisare not able to support fertilization. Acquiring fertilization competence requires resumption of meiosiswhich encompasses the remodeling of multiple signaling pathways and the reorganization of cellular organelles. Collectively, this differentiation endows the egg with the ability to activate at fertilization and to promote the egg-to-embryo transition. Oocytematuration is associated with changes in the electrical properties of the plasma membrane and alterations in the function and distribution of ion channels. Therefore, variations on the pattern of expression, distribution and function of ion channelsand transporters during oocytematuration are fundamental to reproductive success. Ion channelsand transporters are important in regulating membrane potential, but also in the case of calcium (Ca2+), they play a critical role in modulating intracellular signaling pathways. In the context of fertilization, Ca2+ has been shown to be the universal activator of development at fertilization, playing a central role in early events associated with egg activation and the egg-to-embryo transition. These early events include the block of polyspermy, the completion of meiosisand the transition to the embryonic mitotic divisions. In this review, we discuss the role of ion channelsduring oocytematuration, fertilization and early embryonic development. We will describe how ion channelstudies in Xenopus oocytes, an extensively studied model of oocytematuration, translate into a greater understanding of the role of ion channelsin mammalian oocytephysiology.