Expression of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase isoforms in murine tissues determined by real-time PCR: a new view of a large family.

The members of the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (ppGaNTase) family transfer GalNAc to serine and threonine sites and initiate mucin-type O-glycosylation. There are at least 13 functionally characterized family members in mammals. Explanations for the large size of this enzyme family have included functional redundancy, differences among isoforms in substrate specificity, and specific expression of individual isoforms in particular tissues or during certain developmental stages. To date no quantitative comparison of the levels of all ppGaNTase isoforms in any tissue of any species has been reported. We performed real-time polymerase chain reaction using the Taqman method to determine the expression of ppGaNTase isoforms in mouse tissues. Several tissues exhibited a common pattern in which isoforms T1 and T2 were the most strongly expressed, although the level of expression varied widely among tissues. In striking contrast to this general pattern, testis, sublingual gland, and colon exhibited distinctive profiles of isoform expression. Isoform T13 was expressed most strongly in brain, and one putative isoform was expressed only in testis. In mammary tissue the expression of several isoforms changed markedly during pregnancy and lactation. In summary these real-time PCR data indicate the contribution of each isoform to the overall ppGaNTase expression within each tissue and highlight the particular isoforms and tissues that will be the targets of future studies on the functions of the ppGaNTase family.