Taxon-specific sperm recognition of the N terminus of chimeric ZP2. (A) Ectodomains of huZP2, chimeric hu/moZP2, and chimeric mo/huZP2 proteins. Red and green, human and mouse protein, respectively. Yellow, conserved cysteine residues. Postfertilization cleavage site (arrowhead) and zona domains are indicated above. (B) Ovarian histology of hu/moZp2^Rescue and mo/huZP2^Rescue as in Fig. 1 C. (C) huZP2^Rescue, hu/moZp2^Rescue, and mo/huZP2^Rescue eggs stained with domain-specific monoclonal antibodies as in Fig. 2 C. (D) Human sperm binding to huZP2^Rescue, hu/moZp2^Rescue, and mo/huZP2^Rescue eggs as in Fig. 3 C. (E) Schematic of human (red) and mouse (green) recombinant peptides in which mouse ZP2^52–83, ZP2^85–101, or ZP2^103–133 replace the corresponding human sequence. The green bar under the huZP2 protein was deleted in the mouse ZP2^Trunc. Cysteine residues, yellow bars. Predicted N-glycosylation sites, blue bars with asterisks. Arrowhead, di-acidic residues and potential ovastacin cleavage sites. (F) Capacitated human sperm binding to chimeric ZP2 peptide beads. huZP2^39–154 and moZP2^35–149 peptides were positive and negative controls, respectively. DIC (top) and confocal z projection (bottom) images after staining with Hoechst. (G) Box plots reflect the median (vertical line) number of human sperm binding to peptide beads (left) and data points within the 10th and 90th percentiles (error bars). Boxes include the middle two quartiles and outliers are indicated by dots.