Publication: Female fertility and the mammalian egg’s zona pellucida
Authors
Wassarman, Paul M. ; Litscher, Eveline S.
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Publisher
Universidad de Murcia. Departamento de Biología Celular e Histología
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DOI
https://doi.org/10.14670/HH-18-728
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info:eu-repo/semantics/article
Description
Abstract
All mammalian eggs are surrounded by a
relatively thick extracellular matrix (ECM) or zona
pellucida (ZP) to which free-swimming sperm bind in a
species-restricted manner during fertilization. The ZP
consists of either three (e.g., Mus musculus) or four (e.g.,
Homo sapiens) glycosylated proteins, called ZP1-4.
These proteins are unlike those found in somatic cell
ECM, are encoded by single-copy genes on different
chromosomes, and are well conserved among different
mammals. Mammalian ZP proteins are synthesized as
polypeptide precursors by growing oocytes that will
become ovulated, unfertilized eggs. These precursors are
processed to remove a signal-sequence and carboxyterminal propeptide and are secreted into the
extracellular space. Secreted ZP proteins assemble into
long, crosslinked fibrils that exhibit a structural repeat
due to the presence of ZP2-ZP3 dimers every 140 Å or
so along fibrils. Fibrils are crosslinked by ZP1 and are
oriented either perpendicular, parallel, or randomly to
the plasma membrane of eggs depending on their
position in the ZP. Free-swimming mouse sperm
recognize and bind to ZP2 or ZP3 that serve as sperm
receptors. Acrosome-intact sperm bind to ZP3
oligosaccharides and acrosome-reacted sperm bind to
ZP2 polypeptide. ZP fibrils fail to assemble in the
absence of either nascent ZP2 or ZP3 and results in
mouse eggs that lack a ZP and female infertility. Gene
sequence variations in genes encoding ZP1-4 result in
human eggs that lack a ZP or have an abnormal ZP and
female infertility. These and other features of the mouse
and human egg’s ZP are discussed here.
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