EVIDENCE FOR REGION-SPECIFIC REGULATION AND CORTISONE INDUCTION OF SIALYLTRANSFERASE mRNA EXPRESSION IN THE DEVELOPING INTESTINE

Abstract

The immature intestinal epithelium is characterized by increased sialyltransferase (ST) activity that controls the sialylation of glycoproteins and glycolipids. Cell-surface sialic acid with specific glycosidic linkages may serve as a receptor determinant for certain viruses, bacteria and their toxins, and thereby may increase the host susceptibility in neonates. Further study of the rat small intestine reveals that developmental changes in ST activity occurred primarily in the distal (ileal), but not in the proximal (jejunal) region. Furthermore, the Galβl, 4GlcNAc α2, 6-ST activity, but not the Galβl, 4GlcNAc α2, 3-ST activity, was the major ST activity under developmental regulation. Northern blots of total RNA prepared from the proximal and distal small intestine of neonatal and adult rats were probed with a cDNA clone encoding the rat liver α2, 5-ST (a gift of Dr. James C. Paulson, UCLA). The data show that α2, 6-ST mRNA expression was age-dependent and regionally specific, with the highest level of mRNA expressed in the immature distal gut. Cortisone, a known transciption modulator, when injected into suckling rats, induced expression of ST mRNA only In the distal intestine. A parallel induction of distal ST activity by cortisone was also noted. This study indicates that the levels of ST activity are well correlated with the levels of ST mRNA and suggests that developmental variation in the intestinal ST activity is mainly caused by the control of the steady state levels of ST mRNA.