Molecular mechanism of male infertility caused by arrest of spermatogenesis

哺乳动物睾丸中90%以上的糖脂是由一种独特的硫酸化甘油糖脂--胆固醇脂组成。精脂是由神经酰胺半乳糖基转移酶（CGT）和半乳糖苷磺基转移酶（CST）两种酶依次作用合成的。小鼠中Cgt和/或Cst基因的破坏导致雄性不育，这是由于在第一次减数分裂的中期之前精子发生的停滞。这一观察结果提供了第一个实验证据，表明胆固醇是正常精子发生所必需的。阐明了在无脂条件下生殖细胞变性的过程和机制，用双向电泳分离睾丸蛋白。在7、10、13和16天的年龄，在野生型和CGT缺陷小鼠之间比较所得的凝胶图像，在这些年龄附近，野生型睾丸中开始生物合成胆固醇。CGT缺陷小鼠在10、13和16日龄时睾丸中的蛋白质点增加。通过凝胶内蛋白水解，然后通过MALDI-TOFMS，斑点被鉴定为波形蛋白。此外，通过对磷蛋白的特异性检测，在CGT缺陷小鼠的睾丸中，几个斑点增加或减少。研究表明，生殖细胞与支持细胞之间通过细胞连接的表面相互作用可能介导生殖细胞的分化，而细胞连接的重组受多种信号分子的调控。波形蛋白是桥粒的一种蛋白质组分，桥粒是生殖细胞和支持细胞之间的一种细胞连接。由于维生素E脂质在初级精母细胞的细胞表面上表达，因此表明维生素E脂质的缺乏可能通过细胞连接功能障碍导致支持细胞-生殖细胞相互作用的破坏。

More than 90% of the glycolipid in mammalian testis consists of a unique sulfated glyceroglycolipid, seminolipid. Seminolipid is synthesizedby sequential action of the two enzymes, ceramide galactosyltransferase (CGT) and GalCer sulfotransferase (CST). Disruption of the Cgt and/or Cst gene in mice results in male infertility due to the an est of spermatogenesis prior to the metaphase of the first meiosis. This observation provided the first experimental evidence that seminolipid is essential for normal spermatogenesis. Lb clarify the process and mechanism of germ cell degeneration in the absence of seminolipid, testicular proteins were separated by two-dimensional electrophoresis. The resulting gel images were compared between the wild-type and CGT-deficient mice at the age of 7, 10, 13 and 16 days, around which biosynthesis of seminolipid begins in the wild-type testis. A protein spot was increased in the testis of CGT-deficient mice at the age of 10, 13 and 16 days. By in-gel proteolysis followed by MALDI-TOFMS, the spot was identified as vimentin In addition, by specific detection for phosphoproteins, several spots were increased or decreased in the testis of CGT-deficient mice. It was reported that germ cell differentiation may be mediated by surface interactions between germ cells and Sertoli cells through cell junctions and the junction restructuring is regulated by various signaling molecules. It was also known that vimentin is a protein component of desmosome, which is a type of cell junctions between germ cells and Sertoli cells. Because seminolipid is expressed on the cell surface of primary spermatocytes, it was suggested that the lack of seminolipid may result in disruption of Sertoli-germ cell interactions via dysfunction of the cell junction.