Molecular basis of egg coat cross-linking sheds light on ZP1-associated female infertility

Kaoru Nishimura,Luca Jovine,Ling Han,Alessandra Villa,Shunsuke Nishio,Elisa Dioguardi,Tsukasa Matsuda

doi:10.1038/s41467-019-10931-5

Kaoru Nishimura, Luca Jovine + Show 5 more

Open Access

https://doi.org/10.1038/s41467-019-10931-5

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Journal: Nature Communications	Publication Date: Jul 12, 2019
Citations: 46	License type: open-access

Affiliation: Karolinska Institutet, Nagoya University

Abstract

Mammalian fertilisation begins when sperm interacts with the egg zona pellucida (ZP), whose ZP1 subunit is important for fertility by covalently cross-linking ZP filaments into a three-dimensional matrix. Like ZP4, a structurally-related component absent in the mouse, ZP1 is predicted to contain an N-terminal ZP-N domain of unknown function. Here we report a characterisation of ZP1 proteins carrying mutations from infertile patients, which suggests that, in human, filament cross-linking by ZP1 is crucial to form a stable ZP. We map the function of ZP1 to its ZP-N1 domain and determine crystal structures of ZP-N1 homodimers from a chicken homolog of ZP1. These reveal that ZP filament cross-linking is highly plastic and can be modulated by ZP1 fucosylation and, potentially, zinc sparks. Moreover, we show that ZP4 ZP-N1 forms non-covalent homodimers in chicken but not in human. Together, these data identify human ZP1 cross-links as a promising target for non-hormonal contraception.

Highlights

Mammalian fertilisation begins when sperm interacts with the egg zona pellucida (ZP), whose ZP1 subunit is important for fertility by covalently cross-linking ZP filaments into a three-dimensional matrix
We used human embryonic kidney (HEK) 293T cells to compare the expression of the mutant protein, which is truncated shortly after the ZP-N domain, to that of wild-type hZP1 (Fig. 1a)
Even if mutated hZP1 could cause intracellular retention of hZP3 or other ZP subunits, this would only affect a small fraction of the latter. This is because hZP2-4 are expressed in significantly higher amounts than hZP121,49,50 and—in agreement with observations in the mouse51—can be secreted by mammalian cells independently from each other

Summary

Introduction

Mammalian fertilisation begins when sperm interacts with the egg zona pellucida (ZP), whose ZP1 subunit is important for fertility by covalently cross-linking ZP filaments into a three-dimensional matrix. 1234567890():,; Vertebrate oocytes are surrounded by a specialised extracellular coat that is referred to as zona pellucida in mammals (ZP) and vitelline envelope in non-mammals (VE) This matrix plays essential roles in oogenesis and provides a physical barrier that protects the developing embryo; in tetrapods, it mediates the initial interaction between gametes at fertilization and, in mammals, contributes to the block to polyspermy[1,2]. Their fine morphological appearance differs between classes, all vertebrate egg coats consist of filaments made up of a variable number of glycoprotein components that polymerise using a common ZP module[3,4]. ZP-N domains at the N-terminus of ZP2 as well as mollusk vitelline envelope receptor for lysin (VERL) have been shown to regulate sperm binding[28,29]

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