Kaji K, Oda S, Shikano T, Ohnuki T, Uematsu Y, Sakagami J, Tada N, Miyazaki S, Kudo A
Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
Nat Genet. 2000 Mar;24(3):279-82. doi: 10.1038/73502.
The cell-surface molecule Cd9, a member of the transmembrane-4 superfamily, interacts with the integrin family and other membrane proteins. and is postulated to participate in cell migration and adhesion. Expression of Cd9 enhances membrane fusion between muscle cells and promotes viral infection in some cells. Fertilization also involves membrane fusion, between gametes. In mammals, the sperm binds to microvilli on the egg surface, and sperm-egg membrane fusion first occurs around the equatorial region of the sperm head12. The fused membrane is then disrupted, and the sperm nucleus as well as the cytoplasm is incorporated into the egg. Cd9 is expressed on the plasma membrane of the mouse egg, and an anti-Cd9 monoclonal antibody inhibits sperm-egg surface interactions. We generated Cd9 mice and found that homozygous mutant females were infertile. Sperm-egg binding was normal, but sperm-egg fusion was almost entirely inhibited in eggs from Cd9 females. Intracellular Ca2 oscillations, which signal fertilization, were absent in almost all mutant eggs; in rare cases, a response occurred after a long time period. In normal animals, Cd9 molecules were expressed on the egg microvilli and became densely concentrated at the sperm attachment site. Thus, our results show that Cd9 is important in the gamete fusion process at fertilization.
细胞表面分子Cd9是跨膜4超家族的成员，它与整合素家族及其他膜蛋白相互作用，据推测参与细胞迁移和黏附。Cd9的表达增强肌肉细胞间的膜融合，并促进某些细胞中的病毒感染。受精过程也涉及配子间的膜融合。在哺乳动物中，精子与卵子表面的微绒毛结合，精卵膜融合首先发生在精子头部的赤道区域附近。然后融合的膜被破坏，精子细胞核和细胞质被纳入卵子。Cd9在小鼠卵子的质膜上表达，抗Cd9单克隆抗体可抑制精卵表面相互作用。我们培育了Cd9基因敲除小鼠，发现纯合突变雌性小鼠不育。精卵结合正常，但Cd9基因敲除雌性小鼠的卵子中精卵融合几乎完全受到抑制。几乎所有突变卵子中都没有作为受精信号的细胞内钙离子振荡；在极少数情况下，经过很长一段时间才会出现反应。在正常动物中，Cd9分子在卵子微绒毛上表达，并在精子附着部位密集聚集。因此，我们的结果表明，Cd9在受精时的配子融合过程中起重要作用。
