Conservation and divergence of the molecular regulators of the vertebrate fertilization synapse

Fertilization - the process during which sperm and egg find each other, bind and eventually fuse - marks the beginning of a new individual. Research over the past years in vertebrates has shed new light on conserved and divergent molecular regulators that mediate the formation of the fertilization synapse, the close apposition of the two plasma membranes before fusion. Here, we review the known proteins that are required for sperm-egg interaction in mammals and fish from a phylogenetic perspective. While some sperm factors are only conserved in vertebrates and share phylogenetic and structural features, others have a longer evolutionary history. In contrast, the egg factors have changed even within vertebrates despite recognizing the preserved sperm machinery. Future functional work on these factors will be essential to understand the fusion mechanism of vertebrate sperm and egg.