Molecular mechanism of male infertility caused by arrest of spermatogenesis

哺乳动物睾丸中90%以上的糖脂由一种独特的硫酸甘油糖脂组成，即半脂。半脂是由神经酰胺半乳糖转移酶（CGT）和半乳糖转移酶（CST）两种酶的顺序作用合成的。小鼠Cgt和/或Cst基因的破坏导致雄性不育，这是由于精子发生在第一次减数分裂中期之前的测试。这一观察提供了第一个实验证据，证明半脂是正常精子发生所必需的。为了阐明半脂缺失情况下生殖细胞变性的过程和机制，采用双向电泳法分离了睾丸蛋白。将野生型和cgt缺陷小鼠在7、10、13和16天时的凝胶图像进行比较，在这段时间左右，半脂生物合成开始在野生型睾丸中进行。cgt缺陷小鼠在10、13和16日龄时睾丸中的蛋白斑点增加。通过凝胶内蛋白水解和MALDI-TOFMS鉴定，该斑点为vimentin。此外，通过特异性检测磷酸化蛋白，cgt缺陷小鼠睾丸中多个斑点增加或减少。据报道，生殖细胞的分化可能是通过生殖细胞和支持细胞之间的表面相互作用通过细胞连接介导的，并且这种连接的重组受多种信号分子的调控。我们还知道，波形蛋白是桥粒的一种蛋白质成分，桥粒是生殖细胞和支持细胞之间的一种细胞连接。由于半脂在原代精母细胞的细胞表面表达，这表明半脂的缺乏可能通过细胞连接功能障碍导致支持细胞与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.