Molecular Basis of Cell and Developmental Biology
Mouse Sperm Lacking ADAM1b/ADAM2 Fertilin Can Fuse with the Egg Plasma Membrane and Effect Fertilization*

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Fertilin, a heterodimeric protein complex composed of α (ADAM1) and β (ADAM2) subunits on the sperm surface, is believed to mediate adhesion and fusion between the sperm and egg plasma membranes. Here we have shown that mutant male mice lacking ADAM1b are fertile and that the loss of ADAM1b results in no significant defect in sperm functions such as migration from the uterus into oviduct, binding to egg zona pellucida, and fusion with zona pellucida-free eggs. ADAM1b-deficient epididymal sperm showed a severe reduction of ADAM2 on the cell surface, despite the normal presence of ADAM2 in testicular germ cells. The appearance of ADAM1b and ADAM2 on the sperm surface depended on formation and abundance of ADAM1b/ADAM2 fertilin in testicular germ cells. These results suggest that mouse ADAM1b/ADAM2 fertilin may play a crucial role not in the sperm/egg fusion but in the appearance of these two ADAMs on the sperm surface.

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This work was supported in part by grants-in-aid for Scientific Research on Priority Area, Scientific Researches (A) and (B), Young Scientists, and Exploratory Research from Japan Society for the Promotion of Science (JSPS) and Ministry of Education, Culture, Sports, Science, and Technology (MEXT) in Japan, and by the 21st Century COE Program from MEXT. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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Supported by the JSPS Postdoctoral Fellowship Program for Foreign Researchers.