Figure 3.

Mouse sperm bind to 2-cell embryos, if ZP2 remains uncleaved. Capacitated mouse sperm binding to 2-cell embryos in which ZP2 remains intact because ZP2 was mutated to prevent post-fertilization cleavage (Zp2^Mut, left panel) or because of the absence of ovastacin (Astl^Null, right panel). Astl^Null and Zp2^Mut eggs serve as positive controls and normal 2-cell embryos as negative controls. Modified from refs Gahlay et al. (2010) and Burkart et al. (2012).