CD81 and CD9 work independently as extracellular components upon fusion of sperm and oocyte

Naoko Ohnami, Akihiro Nakamura, Mami Miyado, Masahiro Sato, Natsuko Kawano, Keiichi Yoshida, Yuichirou Harada, Youki Takezawa, Seiya Kanai, Chihiro Ono, Yuji Takahashi, Ken Kimura, Toshio Shida, Kenji Miyado, Akihiro Umezawa

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)


When a sperm and oocyte unite into one cell upon fertilization, membranous fusion between the sperm and oocyte occurs. In mice, Izumo1 and a tetraspanin molecule CD9 are required for sperm-oocyte fusion as one of the oocyte factors, and another tetraspanin molecule CD81 is also thought to involve in this process. Since these two tetraspanins often forma complex upon cell-cell interaction, it is probable that such a complex is also formed in sperm-oocyte interaction; however, this possibility is still under debate among researchers. Here we assessed this problem using mouse oocytes. Immunocytochemical analysis demonstrated that both CD9 and CD81 were widely distributed outside the oocyte cell membrane, but these molecules were separate, forming bilayers, confirmed by immunobiochemical analysis. Electron-microscopic analysis revealed the presence of CD9- or CD81-incorporated extracellular structures in those bilayers. Finally, microinjection of in vitro-synthesized RNA showed that CD9 reversed a fusion defect in CD81-deficient oocytes in addition to CD9-deficient oocytes, but CD81 failed in both oocytes. These results suggest that both CD9 and CD81 independently work upon sperm-oocyte fusion as extracellular components.

Original languageEnglish
Pages (from-to)640-647
Number of pages8
JournalBiology Open
Issue number7
Publication statusPublished - 15 Jul 2012


  • CD81
  • CD9
  • Exosome
  • Membrane fusion


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