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Phospholipase C causes Ca²⁺ oscillations and parthenogenetic activation of human oocytes

¹ Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, ² Assisted Conception Unit and GKT Department of Women’s Health, Guy’s and St Thomas’s NHS Trust, Guy’s Hospital, London SE1 9RT, ³ Wales Heart Research Institute, Wales College of Medicine, Heath Park, Cardiff University, Cardiff CF14 4XN and ⁴ Department of Obstetrics and Gynaecology, Wales College of Medicine, Heath Park, Cardiff University, Cardiff CF14 4XN, UK

Correspondence should be addressed to K Swann; Email: SwannK1{at}cf.ac.uk

At fertilization in mammals the sperm activates development of the oocyte by inducing a prolonged series of oscillations in the cytosolic free Ca²⁺ concentration. One theory of signal transduction at fertilization suggests that the sperm cause the Ca²⁺ oscillations by introducing a protein factor into the oocyte after gamete membrane fusion. We recently identified this sperm-specific protein as phospholipase C (PLC), and we showed that PLC triggers Ca²⁺ oscillations in unfertilized mouse oocytes. Here we report that microinjection of the complementary RNA for human PLC causes prolonged Ca²⁺ oscillations in aged human oocytes that had failed to fertilize during in vitro fertilization or intracytoplasmic sperm injection. The frequency of Ca²⁺ oscillations was related to the concentration of complementary RNA injected. At low concentrations, PLC stimulated parthenogenetic activation of oocytes. These embryos underwent cleavage divisions and some formed blastocysts. These data show that PLC is a novel parthenogenetic stimulus for human oocytes and that it is unique in its ability to mimic the repetitive nature of the Ca²⁺ stimulus provided by the sperm during human fertilization.