Kitamura Kouichi, Tanaka Hiromitsu, Nishimune Yoshitake
Department of Science for Laboratory Animal Experimentation, Research Institute for Microbial Disease, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Biol Chem. 2003 Nov 7;278(45):44417-23. doi: 10.1074/jbc.M304306200. Epub 2003 Aug 13.
The acrosome reaction (i.e. the exocytosis of the sperm vesicle) is a prerequisite for fertilization, but its molecular mechanism is largely unknown. We have identified a cDNA clone for a gene named haprin, which encodes a haploid germ cell-specific RING finger protein. This protein is a novel member of the RBCC (RING finger, B-box type zinc finger, and coiled-coil domain) motif family that has roles in several cellular processes, such as exocytosis. It is transcribed exclusively in testicular germ cells after meiotic division. Western blot and immunohistochemical analyses showed the molecular weight of Haprin protein to be Mr approximately 82,000. It was localized in the acrosomal region of elongated spermatids and mature sperm and was not present in acrosome-reacted sperm. The specific antibody against the RING finger domain of Haprin inhibited the acrosome reaction in permeabilized sperm. These results indicated that the novel RBCC protein Haprin plays a key role in the acrosome reaction and fertilization.
顶体反应（即精子泡的胞吐作用）是受精的先决条件，但其分子机制在很大程度上尚不清楚。我们鉴定出一个名为haprin基因的cDNA克隆，该基因编码一种单倍体生殖细胞特异性的环指蛋白。这种蛋白质是RBCC（环指、B盒型锌指和卷曲螺旋结构域）基序家族的一个新成员，在诸如胞吐作用等多种细胞过程中发挥作用。它在减数分裂后的睾丸生殖细胞中特异性转录。蛋白质印迹法和免疫组织化学分析表明，Haprin蛋白的分子量约为82,000道尔顿。它定位于延长型精子细胞和成熟精子的顶体区域，而不存在于发生顶体反应的精子中。针对Haprin环指结构域的特异性抗体抑制了通透精子中的顶体反应。这些结果表明，新型RBCC蛋白Haprin在顶体反应和受精过程中起关键作用。
