Role of CD9 in sperm-egg fusion and its general role in fusion phenomena

Natsuko Kawano, Yuichiro Harada, Keiichi Yoshida, Mami Miyado, Kenji Miyado

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

2 Citations (Scopus)


In fertilization, two types of sex cells or gametes - a sperm and an egg - unite in a stepwise manner to form a mother cell, which is capable of developing naturally into a new individual. Notably, the membrane fusion that occurs intercellularly between a sperm and an egg is essential for fertilization. A sperm factor that is delivered into the egg cytoplasm through fusion serves to activate a signaling pathway; this leads to the resumption of meiosis in the egg. In mammals, sperm-egg fusion is partly mediated by two integral membrane proteins, sperm Izumo (Inoue et al. 2005) and egg cluster of differentiation 9 (CD9) (Kaji et al. 2000, Le Naour et al. 2000, Miyado et al. 2000), and the roles played by both are critical but yet unknown. A recent study (Miyado et al. 2000) showed that CD9-containing vesicles are released from wild-type eggs, and that these exosome-like vesicles induce fusion between sperm and CD9-null eggs in vitro, even though CD9-null eggs are highly refractory to sperm-egg fusion. This result provides compelling evidence for the crucial involvement of CD9-containing, fusion-facilitating vesicles in sperm-egg fusion and offers new insight into both gamete fusion and other membrane fusion events.

Original languageEnglish
Title of host publicationCell Fusions
Subtitle of host publicationRegulation and Control
PublisherSpringer Netherlands
Number of pages14
ISBN (Print)9789048197712
Publication statusPublished - 1 Dec 2011


  • CD81
  • CD9
  • Izumo
  • cell-cell fusion
  • egg
  • exosomes
  • fertilization
  • membrane fusion
  • sperm
  • tetraspanins


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