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

• Published in: Mechanisms of development 2014-11, Vol.134, p.80-95
• Main Authors: Iwao, Yasuhiro, Shiga, Keiko, Shiroshita, Ayumi, Yoshikawa, Tomoyasu, Sakiie, Maho, Ueno, Tomoyo, Ueno, Shuichi, Ijiri, Takashi W., Sato, Ken-ichi
• Format: Article
• Language: English
• Subjects: Animals; Anura; Calcium - metabolism; Cell Membrane - metabolism; Egg activation; Fertilization; Fertilization - physiology; Hemopexin - metabolism; Male; Matrix Metalloproteinase 2 - metabolism; Membrane binding/fusion; Membrane Potentials - physiology; Ovum; Polyspermy block; Spermatozoa - metabolism; Xenopus laevis
• ISSN: 0925-4773; 1872-6356
• DOI: 10.1016/j.mod.2014.09.005

•We examine the role of MMP-2 on the sperm membrane upon frog fertilization.•Enzymatic activity of MMP-2 is necessary for fertilization of jellied eggs.•A positively-charged hemopexin domain is involved in voltage-dependent fertilization.•The hemopexin domain interacts with a negatively charged GM1 on the egg membrane.•We propose a novel model for a fast and electrical block to polypsermy. 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 [Ca2+]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.