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The gamete fusion process is defective in eggs of Cd9-deficient mice

Abstract

The cell-surface molecule Cd9, a member of the transmembrane-4 superfamily1, interacts with the integrin family2 and other membrane proteins3,4,5, and is postulated to participate in cell migration and adhesion6,7,8. Expression of Cd9 enhances membrane fusion between muscle cells9 and promotes viral infection in some cells10,11. Fertilization also involves membrane fusion, between gametes. In mammals, the sperm binds to microvilli on the egg surface, and sperm-egg membrane fusion first occurs around the equatorial region of the sperm head12. The fused membrane is then disrupted, and the sperm nucleus as well as the cytoplasm is incorporated into the egg. Cd9 is expressed on the plasma membrane of the mouse egg, and an anti-Cd9 monoclonal antibody inhibits sperm-egg surface interactions13. We generated Cd9−/− mice and found that homozygous mutant females were infertile. Sperm-egg binding was normal, but sperm-egg fusion was almost entirely inhibited in eggs from Cd9−/− females. Intracellular Ca2+ oscillations, which signal fertilization, were absent in almost all mutant eggs; in rare cases, a response occurred after a long time period. In normal animals, Cd9 molecules were expressed on the egg microvilli and became densely concentrated at the sperm attachment site. Thus, our results show that Cd9 is important in the gamete fusion process at fertilization.

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Figure 1: Generation of mice carrying a mutation in Cd9.
Figure 2: Defective gamete fusion in eggs from Cd9−/− mice.
Figure 3: Ca2+ oscillations in eggs of wild-type and Cd9−/− mice after insemination.
Figure 4: Localization of Cd9 on fertilizing eggs.

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Acknowledgements

We thank M. Tazaki, S. Takeshita and T. Watanabe for their help in the early stage of these experiments, and L. Jaffe for critical reading of the manuscript. This work was supported by a Grant-in-Aid for scientific research from the Japan Ministry of Education, Science, Sports and Culture to A.K. and S.M.

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Correspondence to Akira Kudo.

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Kaji, K., Oda, S., Shikano, T. et al. The gamete fusion process is defective in eggs of Cd9-deficient mice. Nat Genet 24, 279–282 (2000). https://doi.org/10.1038/73502

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