Lipid Modulation of Calcium Flux through CaV2.3 Regulates Acrosome Exocytosis and Fertilization

Summary Membrane lipid regulation of cell function is poorly understood. In early development, sterol efflux and the ganglioside G M1 regulate sperm acrosome exocytosis (AE) and fertilization competence through unknown mechanisms. Here, we show that sterol efflux and focal enrichment of G M1 trigger Ca 2+ influx necessary for AE through Ca V 2.3, whose activity has been highly controversial in sperm. Sperm lacking Ca V 2.3's pore-forming α 1E subunit showed altered Ca 2+ responses, reduced AE, and a strong subfertility phenotype. Surprisingly, AE depended on spatiotemporal information encoded by flux through Ca V 2.3, not merely the presence/amplitude of Ca 2+ waves. Using studies in both sperm and voltage clamp of Xenopus oocytes, we define a molecular mechanism for G M1 /Ca V 2.3 regulatory interaction, requiring G M1 's lipid and sugar components and Ca V 2.3's α 1E and α 2 δ subunits. Our results provide a mechanistic understanding of membrane lipid regulation of Ca 2+ flux and therefore Ca 2+ -dependent cellular and developmental processes such as exocytosis and fertilization.