Severely reduced female fertility in CD9-deficient mice

CD9 is a widely expressed cell surface molecule that belongs to the tetraspanin superfamily of proteins. The tetraspanins CD9, KAI-1/CD82, and CD63 are involved in metastasis suppression, an effect that may be related to their association with beta 1 integrins. Knockout mice lacking CD9 were created to evaluate the physiological importance of CD9. CD9(-/-) females displayed a severe reduction of fertility. Oocytes were ovulated but were not successfully fertilized because sperm did not fuse with the oocytes from CD9(-/-) females. Thus, CD9 appears to be essential for sperm-egg fusion, a process involving the CD9-associated integrin alpha 6 beta 1.