T-CELL-SPECIFIC DELETION OF A POLYPEPTIDE N-ACETYLGALACTOSAMINYLTRANSFERASE GENE BY SITE-DIRECTED RECOMBINATION

UDP-N-acetylgalactosamine (GalNAc): polypeptide N-acetylgalactosaminyl transferase (polypeptide GalNAc-T) catalyzes transfer of the monosacch aride GalNAc to serine and threonine residues, thereby initiating O-li nked oligosaccharide biosynthesis, Previous studies have suggested the possibility of multiple polypeptide GalNAc-Ts, although attachment of saccharide units to polypeptide or lipid in generating oligosaccharid e structures in vertebrates has been dependent upon the activity of si ngle gene products. To address this issue and to determine the relevan ce of O-glycosylation variation in T-cell ontogeny; we have directed C re/loxP mutagenic recombination to the polypeptide GalNAc-T locus in g ene-targeted mice, Resulting deletion in the catalytic region of polyp eptide GalNAc-T occurred to completion on both alleles in thymocytes a nd was found in peripheral T cells, but not among other cell types. Th ymocyte O-linked oligosaccharide formation persisted in the absence of a functional targeted polypeptide GalNAc-T allele as determined by O- glycan-specific lectin binding, T-cell development and colonization of secondary lymphoid organs were also normal, These results indicate a complexity in vertebrate O-glycan biosynthesis that involves multiple polypeptide GalNAc-Ts, We infer the potential for protein-specific O-g lycan formation governed by distinct polypeptide GalNAc-Ts.