He Zhi-Yong, Gupta Surabhi, Myles Diana, Primakoff Paul
Department of Molecular and Cellular Biology, College of Biological Sciences, University of California Davis, Davis, California 95616, USA.
Mol Reprod Dev. 2009 Jul;76(7):629-36. doi: 10.1002/mrd.20991.
CD9, a member of the tetraspanin family, associates with a variety of other proteins to form the tetraspanin web. CD9 forms direct and relatively stable associations with the immunoglobulin superfamily proteins EWI-2 and EWI-F. Deletion of the Cd9 gene results in female infertility since Cd9 null mice produce oocytes that fail to fuse. It is thought that the absence of CD9 causes the inability of the oocytes to fuse. In this study, we report that the expression level of EWI-2 on the Cd9(-/-) oocyte surface is <10% of the wild-type level. Hence, the severe reduction in EWI-2 activity may be responsible for the loss of fusion ability. An entirely different mutant of CD9, not a deletion but a depalmitoylated construct, does not affect in vivo female fertility suggesting that the palmitate modification of CD9 is not essential for its putative fusion function. Additionally, the level of EWI-2 on the surface of the oocytes from these females was comparable to the EWI-2 level on wild-type oocytes. We also found that soluble, recombinant EWI-2 binds preferentially to acrosome-reacted sperm but the bound EWI-2 does not inhibit sperm-oocyte fusion. Overall, the results indicate that deletion of CD9, which is known to have multiple associations, may have pleiotropic effects on function that will require further dissection.
CD9是四跨膜蛋白家族的成员之一，它与多种其他蛋白质相互作用形成四跨膜蛋白网络。CD9与免疫球蛋白超家族蛋白EWI-2和EWI-F形成直接且相对稳定的结合。Cd9基因的缺失会导致雌性不育，因为Cd9基因敲除小鼠产生的卵母细胞无法融合。据认为，CD9的缺失导致卵母细胞无法融合。在本研究中，我们报道Cd9(-/-)卵母细胞表面EWI-2的表达水平不到野生型水平的10%。因此，EWI-2活性的严重降低可能是融合能力丧失的原因。CD9的一个完全不同的突变体，不是缺失而是去棕榈酰化构建体，并不影响体内雌性生育能力，这表明CD9的棕榈酸修饰对于其假定的融合功能并非必不可少。此外，这些雌性小鼠卵母细胞表面的EWI-2水平与野生型卵母细胞上的EWI-2水平相当。我们还发现可溶性重组EWI-2优先结合顶体反应的精子，但结合的EWI-2并不抑制精卵融合。总体而言，结果表明已知具有多种相互作用的CD9的缺失可能对功能产生多效性影响，这需要进一步剖析。
