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Mech Dev. 2014 Nov;134:80-95. doi: 10.1016/j.mod.2014.09.005. Epub 2014 Oct 5.

The need of MMP-2 on the sperm surface for Xenopus fertilization: its role in a fast electrical block to polyspermy.

Author information

1
Laboratory of Molecular Developmental Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8512, Japan. Electronic address: iwao@yamaguchi-u.ac.jp.
2
Laboratory of Molecular Developmental Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8512, Japan.
3
Laboratory of Cell Signaling and Development, Department of Molecular Biosciences, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan.

Abstract

Monospermic fertilization in the frog, Xenopus laevis, is ensured by a fast-rising, positive fertilization potential to prevent polyspermy on the fertilized egg, followed by a slow block with the formation of a fertilization envelope over the egg surface. In this paper, we found that not only the enzymatic activity of sperm matrix metalloproteinase-2 (MMP-2) was necessary for a sperm to bind and/or pass through the extracellular coat of vitelline envelope, but also the hemopexin (HPX) domain of MMP-2 on the sperm surface was involved in binding and membrane fusion between the sperm and eggs. A peptide with a partial amino acid sequence of the HPX domain caused egg activation accompanied by an increase in [Ca(2+)]i in a voltage-dependent manner, similar to that in fertilization. The membrane microdomain (MD) of unfertilized eggs bound the HPX peptide, and this was inhibited by ganglioside GM1 distributed in the MD. The treatment of sperm with GM1 or anti-MMP-2 HPX antibody allows the sperm to fertilize an egg clamped at 0 mV, which untreated sperm cannot achieve. We propose a model accounting for the mechanism of voltage-dependent fertilization based on an interaction between the positively charged HPX domain in the sperm membrane and negatively-charged GM1 in the egg plasma membrane.

KEYWORDS:

Egg activation; Fertilization; Membrane binding/fusion; Polyspermy block

PMID:
25296387
DOI:
10.1016/j.mod.2014.09.005
[Indexed for MEDLINE]
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