Sperm activation for fertilization requires robust activity of the TAT-5 lipid flippase.

During fertilization, sperm and egg membranes signal and fuse to form a zygote and begin embryonic development. Here, we investigated the role of lipid asymmetry in gametogenesis, fertilization, and embryogenesis. We find that phosphatidylethanolamine asymmetry is lost during meiosis prior to phosphatidylserine exposure. We show that TAT-5, the P4-ATPase that maintains phosphatidylethanolamine asymmetry, is required for both oocyte formation and sperm activation, albeit at different levels of flippase activity. Loss of TAT-5 significantly decreases fertility in both males and hermaphrodites and decreases sperm activation. TAT-5 localizes to the plasma membrane of primary spermatocytes but is sorted away from maturing spermatids during meiosis. Our findings demonstrate that phosphatidylethanolamine asymmetry plays key roles during gametogenesis and sperm activation, expanding the roles of lipid dynamics in developmental cell fusion.