POSTNATAL-DEVELOPMENT OF RAT COLON EPITHELIAL-CELLS IS ASSOCIATED WITH CHANGES IN THE EXPRESSION OF THE BETA-1,4-N-ACETYLGALACTOSAMINYLTRANSFERASE INVOLVED IN THE SYNTHESIS OF SDA ANTIGEN AND OF ALPHA-2,6-SIALYLTRANSFERASE ACTIVITY TOWARDS N-ACETYL-LACTOSAMINE

β1,4-N-Acetylgalactosaminyltransferase (β1,4GalNAc-transferase) and α2,3-sialyltransferase are both involved in the biosynthesis of the Sda blood group antigen, which is also present in cells of large intestine. The expression of these enzymes and of α2,6-sialyltransferase activity towards N-acetyl-lactosamine was investigated in rat intestinal cells and correlated with both cell differentiation and extent of postnatal maturation. The β1,4GalNAc-transferase activity was exclusively found in epithelial cells of the large intestine, preferentially in the proximal segments suggesting a proximal-distal gradient of expression. The β1,4GalNAc-transferase and α2,3-sialyltransferase activity towards N-acetyl-lactosamine were expressed in all cell fractions of the colonic crypt, with a maximum activity in the deeply located cells; therefore Sda antigen biosynthesis appears to occur preferentially at a specific stage of cell differentiation. By using N-acetyl-lactosamine as an acceptor, the predominant sialyltransferase in the colon cells was that capable of adding sialic acid in the α2,3- linkage, whereas in the ileum cells the major enzyme was that forming the α2,6-isomer. There were dramatic changes in the expression of colonic β1,4GalNAc-transferase and of α2,6-sialyltransferase activity towards N-acetyl-lactosamine during postnatal maturation. The former enzyme, practically absent at birth, increased slowly in the first days of life and then rapidly after weaning; by contrast, the latter enzyme was largely expressed only in newborn animals. As the colonic α2,3-sialyltransferase activity towards N-acetyl-lactosamine did not change during the postnatal period, the ratio between the α2,6- and α2,3-sialyltransferase activities was reversed after weaning.