THE UDP-GALACTOSE-CERAMIDE GALACTOSYLTRANSFERASE - EXPRESSION PATTERNIN OLIGODENDROCYTES AND SCHWANN-CELLS DURING MYELINATION AND SUBSTRATE PREFERENCE FOR HYDROXYCERAMIDE

Galactosylceramide (''galactocerebroside''; GalC) is a major glycolipi d in the myelin sheath of the CNS and the PNS, The enzyme UDP-galactos e:ceramide galactosyltransferase (CGalT) catalyzes the final step of t he synthesis of GalC: the transfer of galactose to ceramide. By a diff erential screening approach, we have isolated a cDNA, the sequence of which is identical to the recently isolated cDNA clones for CGalT. By northern analysis and in situ hybridization we demonstrated that CGalT mRNA is expressed at birth in oligodendrocytes and Schwann cells, an expression pattern corresponding to the onset of myelination. In addit ion to the high expression levels of CGalT in oligodendrocytes and Sch wann cells, in situ hybridization also showed expression in subtypes o f neurons in spinal cord, cerebellum, and brainstem in the adult CNS, but at a much lower level than in oligodendrocytes, Expression of CGal T in COS cells demonstrated that CGalT has a preference for hydroxycer amide as a substrate. CGalT-expressing COS cells synthesize and transp ort GalC to their cell surface as shown by immunofluorescence and by l ipid analysis of living cells. Our results suggested that the CGalT sp ecifically uses hydroxyceramide for the synthesis of GalC and that sep arate (co)enzymes are not needed.