Practice question

Human zona pellucida contains four glycoproteins ZP1 to ZP4 forming elastic matrix surrounding oocyte. Gene-knockout humanized mouse assays demonstrate essential binding determinant resides in N-terminal region of ZP2 rather than ZP3 as in mouse model. Intact ZP2 supports tight adhesion of acrosome-reacted sperm; after fertilization ovastacin protease cleaves ZP2 abolishing binding, contributing to block to polyspermy. Thus human gamete recognition depends dominantly on supramolecular presentation of ZP2, whose cleavage status regulates post-fertilization incompatibility and ensures monospermic fertilization and diploidy maintenance for embryogenesis.