A Unique Egg Cortical Granule Localization Motif Is Required for Ovastacin Sequestration to Prevent Premature ZP2 Cleavage and Ensure Female Fertility in Mice

Monospermic fertilization is mediated by the extracellular zona pellucida composed of zp1,zp2 and zp3. sperm bind to the n-terminus of zp2 which is cleaved after fertilization by ovastacin (encoded by astl) exocytosed from egg cortical granules to prevent sperm binding. astlnullmice lack the post-fertilization block to sperm binding and the ability to rescue this phenotype with astlmcherrytransgenic mice confirms the role of ovastacin in providing a definitive block to polyspermy. during oogenesis,endogenous ovastacin traffics through the endomembrane system prior to storage in peripherally located cortical granules. deletion mutants of ovastacinmcherryexpressed in growing oocytes define a unique 13 amino acid motif near its n-terminus that is necessary and sufficient for cortical granule localization. deletion of the first 7 amino acids by crispr/cas9 at the endogenous locus (astlδ) prevents cortical granule localization of ovastacin. the misdirected enzyme is present within the endomembrane system and zp2 is prematurely cleaved. sperm bind poorly to the zona pellucida of astlδ/δmice with partially cleaved zp2 and female mice are sub-fertile. © 2017 public library of science. all rights reserved.