Characterization of the calcium releasing activity of equine sperm extracts or equine sperm in murine and equine oocytes: Implications in the success of equine assisted reproductive technologies

At fertilization, the sperm induces a series of species-specific intracellular Ca2+ rises ([Ca2+]i) that are important for oocyte activation and embryonic development in all mammalian species studied to date. These have not been investigated in the horse, where in vitro assisted reproduction techniques generally provide suboptimal results. In this study, we characterize the activity of equine sperm extracts (sperm factor; eSF) in mouse oocytes, and demonstrate their ability to induce [Ca 2+]i transients and parthenogenetic activation in equine oocytes. However, sperm injected (ICSI) horse oocytes do not consistently mount [Ca2+]i responses, and this failure is not the result of inadequate sperm factor release into the oocyte. This research may explain suboptimal results reported for ICSI in the equine and suggests potential differences in fertilization induced-signaling mechanisms amongst different mammalian species.