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© The Rockefeller University Press,
0021-9525/2000//1289 $5.00
The Journal of Cell Biology, Volume 149, Number 6,
, 2000 1289-1296
Original Article |
Normal Fertilization Occurs with Eggs Lacking the Integrin
6β1 and Is Cd9-Dependent
dgmyles{at}ucdavis.edu
Previous results, based on inhibition of fertilization by an anti–
6 integrin mAb (GoH3), suggest that the
6β1 integrin on mouse eggs functions as the receptor for sperm (Almeida, E.A., A.P. Huovila, A.E. Sutherland, L.E. Stephens, P.G. Calarco, L.M. Shaw, A.M. Mercurio, A. Sonnenberg, P. Primakoff, D.G. Myles, and J.M. White. 1995. Cell. 81:1095–1104). Because the egg surface tetraspanin CD9 is essential for gamete fusion (Kaji, K., S. Oda, T. Shikano, T. Ohnuki, Y. Uematsu, J. Sakagami, N. Tada, S. Miyazaki, and A. Kudo. 2000. Nat. Genet. 24:279–282; Le Naour, F., E. Rubinstein, C. Jasmin, M. Prenant, and C. Boucheix. 2000. Science. 287:319–321; Miyado, K., G. Yamada, S. Yamada, H. Hasuwa, Y. Nakamura, F. Ryu, K. Suzuki, K. Kosai, K. Inoue, A. Ogura, M. Okabe, and E. Mekada. 2000. Science. 287:321–324) and CD9 is known to associate with integrins, recent models of gamete fusion have posited that egg CD9 acts in association with
6β1 in fusion (Chen, M.S., K.S. Tung, S.A. Coonrod, Y. Takahashi, D. Bigler, A. Chang, Y. Yamashita, P.W. Kincade, J.C. Herr, and J.M. White. 1999. Proc. Natl. Acad. Sci. USA. 96:11830–11835; Kaji, K., S. Oda, T. Shikano, T. Ohnuki, Y. Uematsu, J. Sakagami, N. Tada, S. Miyazaki, and A. Kudo. 2000. Nat. Genet. 24:279–282; Le Naour, F., E. Rubinstein, C. Jasmin, M. Prenant, and C. Boucheix. 2000. Science. 287:319–321; Miyado, K., G. Yamada, S. Yamada, H. Hasuwa, Y. Nakamura, F. Ryu, K. Su- zuki, K. Kosai, K. Inoue, A. Ogura, M. Okabe, and E. Mekada. 2000. Science. 287:321–324). Using eggs from cultured ovaries of mice lacking the
6 integrin subunit, we found that the fertilization rate, fertilization index, and sperm binding were not impaired compared with wild-type or heterozygous controls. Furthermore, a reexamination of antibody inhibition, using an assay that better simulates in vivo fertilization conditions, revealed no inhibition of fusion by the GoH3 mAb. We also found that an anti-CD9 mAb completely blocks sperm fusion with either wild-type eggs or eggs lacking
6β1. Based on these results, we conclude that the
6β1 integrin is not essential for sperm–egg fusion, and we suggest a new model in which CD9 acts by itself, or interacts with egg protein(s) other than
6β1, to function in sperm–egg fusion.
Key Words: sperm–egg fusion tetraspanin membrane adhesion oocyte ovarian cultare
© 2000 The Rockefeller University Press
Abbreviations used in this paper: DAPI, 4',6'-diamidino-2-phenylindole dihydrochloride; FI, fertilization index; FR, fertilization rate.
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