The Ly6/uPAR protein Bouncer is necessary and sufficient for species-specific fertilization

Bouncer keeps fertilization specific Fertilization needs to be highly efficient while remaining species-specific. However, despite decades of research, it is still unclear how these two requirements are met. Herberg et al. report the discovery of the Ly6/uPAR-type protein Bouncer as a species-specific fertilization factor in zebrafish (see the Perspective by Lehmann). Bouncer localizes to the egg membrane and is required for sperm entry. Remarkably, expression of Bouncer from another fish species (medaka) in zebrafish allowed for cross-species fertilization. Science , this issue p. 1029 ; see also p. 974