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

• CaV2.3 mediates spatiotemporal regulation of acrosome exocytosis (AE)
• GM1 regulates Ca2+ influx, AE, and fertilization via CaV2.3’s α1E and α2δ1 subunits
• Mechanism of α1E regulation involves GM1’s lipid and sugar moieties and α2δ1

SummaryMembrane lipid regulation of cell function is poorly understood. In early development, sterol efflux and the ganglioside GM1 regulate sperm acrosome exocytosis (AE) and fertilization competence through unknown mechanisms. Here, we show that sterol efflux and focal enrichment of GM1 trigger Ca2+ influx necessary for AE through CaV2.3, whose activity has been highly controversial in sperm. Sperm lacking CaV2.3’s pore-forming α1E subunit showed altered Ca2+ responses, reduced AE, and a strong subfertility phenotype. Surprisingly, AE depended on spatiotemporal information encoded by flux through CaV2.3, not merely the presence/amplitude of Ca2+ waves. Using studies in both sperm and voltage clamp of Xenopus oocytes, we define a molecular mechanism for GM1/CaV2.3 regulatory interaction, requiring GM1’s lipid and sugar components and CaV2.3’s α1E and α2δ subunits. Our results provide a mechanistic understanding of membrane lipid regulation of Ca2+ flux and therefore Ca2+-dependent cellular and developmental processes such as exocytosis and fertilization.