Postnatal development of rat colon epithelial cells is associated with changes in the expression of the β1,4-N-acetylgalactosaminyltransferase involved in the synthesis of Sda antigen of α2,6-sialyltransferase activity towards N-acetyl-lactosamine

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Abstract
.beta.1,4-N-acetylgalactosaminyltransferase (.beta.1,4GalNAc-transferase) and .alpha.2,3-sialytransferase 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 .alpha.2,6-sialytransferase activity towards N-acetyl-lactosamine was investigated in rat intestinal cells and correlated with both cell differentiation and extent of postnatal maturation. The .beta.1,4Ga1NAc-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 .beta.1,4Ga1NAc-transferase and .alpha.2,3-sialytransferase 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-lactosomine as an acceptor, the predominant sialytransferase in the colon cells was that capable of adding sialic acid in the .alpha.2,3-linkage, whereas in the ileum cells the major enzyme was that forming the .alpha.2,6-isomer. There were dramatic changes in the expression of colonic .beta.1,4Ga1Nac-transferase and of .alpha.2,6-sialytransferase 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 .alpha.2,3-sialytransferase activity towards N-acetyl-lactosamine did not change during the postnatal period, the ratio between the .alpha.2,6- and .alpha.2,3-sialytransferase activities was reversed after weaning.

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