| Research Abstract |
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
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