SULFATED GLYCOLIPID THAT REGULATES DEVELOPMENT OF MALE GERM CELLS

硫化糖脂，即半脂类，在睾丸中占总糖脂的90%以上，并且在睾丸中特异表达。在精子发生过程中，半脂是在精母细胞高尔基膜中生物合成的。首先，被称为神经酰胺半乳糖转移酶(CGT)的半乳糖基转移酶作用于前体甘油脂，并合成中间产物半乳糖基烷基甘油(GaIEAG)。然后，一种名为脑苷磺基转移酶(CST)的磺基转移酶催化GaIEAG的硫化反应，合成最终产物半脂。我们发现CST缺陷小鼠的睾丸完全缺乏精脂，精子发生在第一次减数分裂中期受阻。这些发现表明，精脂是精子发生所必需的(Proc.Natl.Academy.Science，USA 99,4227-4232,2002)。接下来，我们一直在研究精脂是如何参与精子发生的。首先，我们研究了精母细胞质膜上的脂筏中是否存在精脂的问题。为此，我们建立了用密度梯度离心法从小鼠睾丸中分离精母细胞的方法。结果，我们证实了脂筏中含有半脂类物质。类似地，我们发现另一种硫化糖脂硫脂也包括在脑髓鞘的脂筏中。其次，我们开发了一种光敏碳水化合物探针来识别与精母细胞细胞表面的半脂类相互作用的分子。我们计划将这种探针引入到培养的精母细胞中，并在活细胞中检测这种分子。第三，我们一直在尝试向生精小管注射半脂类物质，使睾丸恢复生精。

The sulfated glycolipid, seminolipid occupies more than 90% of total glycolipids in the testis and is specifically expressed in the testis. Seminolipid is biosynthesized in the Golgi membranes of spermatocytes during spermatogenesis. First, a galactosyltransferase called ceramide galactosyltransferase (CGT) acts on the precursor glycerolipid, and synthesizes an intermediate product, galactosylalkylacylglycerol (GaIEAG). Then, a sulfotransferase called cerebroside sulfotransferase (CST) catalyzes the sulfation of GaIEAG, synthesizing the terminal product, seminolipid. We have found that the testes of CST-deficient mice completely lack seminolipid and spermatogenesis is arrested at the metaphase of the first meiosis. These findings indicate that seminolipid is essential for spermatogenesis (Proc.Natl.Acad.Sci.USA 99, 4227-4232, 2002). Next, we have been studying how seminolipid is involved in spermatogenesis. First, we examined the issue whether seminolipid exists in the lipid raft on the plasma membranes of spermatocytes. To this end, we had established the procedure to isolate spermatocytes from mouse testis using a density-gradient centrifugation. As a result, we confirmed that seminolipid is included in the lipid raft. Similarly, we found that another sulfated glycolipid, sulfatide is also included in the lipid raft of brain myelin sheath. Secondly, we have developed a photo-sensitive carbohydrate probe to identify the molecules that interact with seminolipid on the cell-suface of spermatocytes. We are planning to introduce this probe into cultured spermatocytes and detect such molecules in living cells. Thirdly, we have been trying to inject seminolipid into the seminiferous tubules and make the testis to resume spermatogenesis