Open AccessA Unique Egg Cortical Granule Localization Motif Is Required for Ovastacin Sequestration to Prevent Premature ZP2 Cleavage and Ensure Female Fertility in Mice
Author(s) -
Bo Xiong,
Yangu Zhao,
Stephanie Beall,
Anna Burkart Sadusky,
Jurrien Dean
Publication year - 2017
Publication title -
plos genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.587
H-Index - 233
eISSN - 1553-7404
pISSN - 1553-7390
DOI - 10.1371/journal.pgen.1006580
Subject(s) - polyspermy , zona pellucida , cortical granule , biology , microbiology and biotechnology , endomembrane system , sperm , oocyte , genetics , embryo , endoplasmic reticulum , golgi apparatus
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. Astl Null mice lack the post-fertilization block to sperm binding and the ability to rescue this phenotype with Astl mCherry transgenic 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 ovastacin mCherry expressed in growing oocytes define a unique 7 amino acid motif near its N-terminus that is necessary and sufficient for cortical granule localization. Deletion of the 7 amino acids by CRISPR/Cas9 at the endogenous locus ( Astl Δ ) 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 Astl Δ/Δ mice with partially cleaved ZP2 and female mice are sub-fertile.