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Chromatin Spread Preparations for the Analysis of Mouse Oocyte Progression from Prophase to Metaphase II
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ZP2 cleavage blocks polyspermy by modulating the architecture of the egg coat

Shunsuke Nishio1, Chihiro Emori2, Benjamin Wiseman1

  • 1Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden.

Cell
|March 15, 2024
PubMed

Insights

After egg fertilization, the zona pellucida (ZP) hardens. Cleavage of ZP2 glycoprotein triggers its oligomerization, cross-linking ZP filaments and preventing further sperm entry.

Area of Science:

  • Reproductive Biology
  • Molecular Biology
  • Structural Biology

Background:

  • Fertilization triggers egg coat (zona pellucida, ZP) hardening to block polyspermy.
  • This hardening involves the cleavage of the N-terminal region (NTR) of ZP2 glycoprotein, a key ZP filament component.
  • The precise molecular mechanisms linking ZP2 cleavage to ZP hardening and sperm binding inactivation remain unclear.

Purpose of the Study:

  • To elucidate the molecular consequences of ZP2 cleavage.
  • To understand the structural basis of zona pellucida hardening and polyspermy block.

Main Methods:

  • Biochemical assays to study ZP2 processing and oligomerization.
  • Structural analysis of native egg coat filaments.
  • AlphaFold predictions for human ZP polymer structures.

Main Results:

  • ZP2 cleavage induces its oligomerization.
  • The native egg coat filament structure reveals interlocking type I (ZP3) and type II (ZP1/ZP2/ZP4) protofilaments forming a left-handed double helix.
  • Protruding ZP2 NTRs from cleaved ZP2 subunits extensively cross-link these ZP filaments.

Conclusions:

  • Oligomerization of cleaved ZP2 NTRs acts as a molecular glue, cross-linking ZP filaments.
  • This extensive cross-linking rigidifies the egg coat, rendering it physically impenetrable to sperm.
  • The findings provide a structural mechanism for polyspermy block during fertilization.
Keywords:
ZP protein filamentZP1ZP2 cleavageZP3block to polyspermyegg coat hardeningegg-sperm interactionfertilizationintegrative structural biologyzona pellucida

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