Regulation of polysialic acid expressed on NCAM in neuromuscular junction

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Polysialic acid (PSA) and HNK-1 carbohydrate epitope expressed on NCAM are spatially and temporally regulated during the development of the nervous system. It has been reported that PSA on NCAM is expressed on chick motoneurons during their growth, and then decreases at about the time that synaptogenesis is completed. In order to investigate the molecular mechanism of the regulation of PSA expression, present study focus on the biosynthesis of PSA on NCAM.It is known that PSA is expressed on the fifth Ig domain of NCAM, In the present study, we purified NCAM and determined the position of HNK-1 epitope on NCAM, The result indicated that HNK-I epitope is also expressed on the fifth Ig domain of NCAM, suggesting that glucuronyltransferase, which is one of the key enzyme in the biosynthesis of the LINK-I epitope could be considered as one of potential regulator of PSA synthesis. Because, the glucuronyltransferase can catalyze the transfer of glucuronic acid to galactose residue of NCAM, substituting the first sialic acid residue of PSA by glucuronic acid residue and thus blocking polysialylation. To demonstrate the possibility described above, we cloned the glucuronyltransferase cDNA from chick embryo and the distribution of the glucuronyltransferase are comparing with that of polysialyltransferase by in situ hybridization.