Research Institute for Microbial Diseases, Osaka University, Suita, 565-0871 Osaka, Japan.
Center for Drug Discovery and Department of Pathology & Immunology, Baylor College of Medicine, Houston, TX 77030.
Proc Natl Acad Sci U S A. 2020 Apr 28;117(17):9393-9400. doi: 10.1073/pnas.1917060117. Epub 2020 Apr 15.
Sperm-oocyte fusion is a critical event in mammalian fertilization, categorized by three indispensable proteins. Sperm membrane protein IZUMO1 and its counterpart oocyte membrane protein JUNO make a protein complex allowing sperm to interact with the oocyte, and subsequent sperm-oocyte fusion. Oocyte tetraspanin protein CD9 also contributes to sperm-oocyte fusion. However, the fusion process cannot be explained solely by these three essential factors. In this study, we focused on analyzing a testis-specific gene and generated mutant mice using the CRISPR/Cas9 system. Although IZUMO1 remained in knockout (KO) spermatozoa, the KO spermatozoa were unable to fuse with oocytes and the KO males were severely subfertile. 4930451I11Rik encodes two isoforms: a transmembrane (TM) form and a secreted form. Both CRISPR/Cas9-mediated TM deletion and transgenic (Tg) rescue with the TM form revealed that only the TM form plays a critical role in sperm-oocyte fusion. Thus, we renamed this TM form Fertilization Influencing Membrane Protein (FIMP). The mCherry-tagged FIMP TM form was localized to the sperm equatorial segment where the sperm-oocyte fusion event occurs. Thus, FIMP is a sperm-specific transmembrane protein that is necessary for the sperm-oocyte fusion process.
精卵融合是哺乳动物受精过程中的一个关键事件，由三种不可或缺的蛋白来分类。精子膜蛋白 IZUMO1 及其对应的卵母细胞膜蛋白 JUNO 形成一个蛋白复合物，使精子能够与卵母细胞相互作用，并随后发生精卵融合。卵母细胞四跨膜蛋白 CD9 也有助于精卵融合。然而，融合过程并不仅仅由这三个必需因素来解释。在这项研究中，我们专注于分析一个睾丸特异性基因，并使用 CRISPR/Cas9 系统生成突变小鼠。尽管 IZUMO1 在 KO 精子中仍然存在，但 KO 精子无法与卵母细胞融合，KO 雄性的生育能力严重受损。4930451I11Rik 编码两种异构体：一种跨膜（TM）形式和一种分泌形式。两种 CRISPR/Cas9 介导的 TM 缺失和 TM 形式的转基因（Tg）拯救都表明，只有 TM 形式在精卵融合中发挥关键作用。因此，我们将这种 TM 形式重新命名为受精影响膜蛋白（FIMP）。mCherry 标记的 FIMP TM 形式定位于精子赤道段，该区域发生精卵融合事件。因此，FIMP 是一种精子特异性跨膜蛋白，对于精卵融合过程是必需的。
