Practice question

Species-specific sperm binding to human zona pellucida relies predominantly on recognition of intact ZP2 N-terminal domain within matrix context composed of ZP1-4 heteropolymers. Transgenic mouse models expressing human ZP genes show human sperm adhere only to zona containing human ZP2, sufficient alone to support binding, while human ZP3 insufficient. This contrasts mouse where ZP3 induces acrosome reaction. Following fertilization ovastacin cleaves ZP2 destroying binding epitope providing block. ZP1 crosslinks filaments structurally. Thus ZP2 provides primary ligand for human gamete attachment, monospermy regulation, species-restricted fertilization, recognition and post-fertilization polyspermy block.