Tanigawa Maya, Miyamoto Kiyoko, Kobayashi Satoshi, Sato Masahiro, Akutsu Hidenori, Okabe Masaru, Mekada Eisuke, Sakakibara Keiichi, Miyado Mami, Umezawa Akihiro, Miyado Kenji
Department of Reproductive Biology and Pathology, National Center for Child Health and Development, Tokyo, Japan.
Mol Reprod Dev. 2008 Jan;75(1):150-5. doi: 10.1002/mrd.20709.
Tetraspanin CD81 is closely homologous in amino acid sequence with CD9. CD9 is well known to be involved in sperm-egg fusion, and CD81 has also been reported to be involved in membrane fusion events. However, the function of CD81 as well as that of CD9 in membrane fusion remains unclear. Here, we report that disruption of the mouse CD81 gene led to a reduction in the fecundity of female mice, and CD81-/- eggs had impaired ability to fuse with sperm. Furthermore, we demonstrated that when CD81-/- eggs were incubated with sperm, some of the sperm that penetrated into the perivitelline space of CD81-/- eggs had not yet undergone the acrosome reaction, indicating that the impaired fusibility of CD81-/- eggs may be in part caused by failure of the acrosome reaction of sperm. In addition, we showed that CD81 was highly expressed in granulosa cells, somatic cells that surround oocytes. Our observations suggest that there is an interaction between sperm and CD81 on somatic cells surrounding eggs before the direct interaction of sperm and eggs. Our results may provide new clues for clarifying the cellular mechanism of the acrosome reaction, which is required for sperm-egg fusion.
四跨膜蛋白CD81在氨基酸序列上与CD9高度同源。众所周知，CD9参与精卵融合，并且也有报道称CD81参与膜融合事件。然而，CD81以及CD9在膜融合中的功能仍不清楚。在此，我们报道小鼠CD81基因的缺失导致雌性小鼠生育力下降，且CD81基因敲除的卵子与精子融合的能力受损。此外，我们证明，当将CD81基因敲除的卵子与精子一起孵育时，一些进入CD81基因敲除卵子卵周隙的精子尚未发生顶体反应，这表明CD81基因敲除卵子融合能力受损可能部分是由精子顶体反应失败所致。另外，我们发现CD81在颗粒细胞（围绕卵母细胞的体细胞）中高表达。我们的观察结果表明，在精子与卵子直接相互作用之前，精子与卵子周围体细胞上的CD81之间存在相互作用。我们的结果可能为阐明顶体反应的细胞机制提供新线索，而顶体反应是精卵融合所必需的。
