Alteration in sialyltransferase and sialic acid expression accompanies cell differentiation in rat intestine

The subcellular distribution of sialyltransferase and its product of action, sialic acid, was investigated in the undifferentiated cells of the rat intestinal crypts and compared with the pattern observed in the differentiated cells present in the surface epithelium. Sialyltransferase was immunocytochemically detected with an antibody, affinity-purified on a beta-galactosidase/sialyltransferase fusion protein, which recognizes only protein epitopes of the enzyme. A similar pattern and intensity of immunolabeling were observed in the Golgi apparatus, apical and basolateral plasma membranes of both undifferentiated and differentiated absorptive cells. However, in the goblet cells, the mucus was only weakly labeled in cells present in the basal portion of the crypts but increased in intensity through the zone of migration to the surface epithelium. Sialic acid as detected with the Limax flavus lectin was observed in the Golgi apparatus and post-Golgi apparatus structures of both absorptive and goblet cells regardless of their position along the crypt-to-surface epithelium axis. However, a striking difference in the plasma membrane distribution of sialic acid existed between undifferentiated cells of the lower half of the crypts and those of the upper half and the surface epithelium: in the former, label was present in both the apical and basolateral domain, whereas in the latter it became restricted to the apical domain. These results suggest that the presence of sialyltransferase immunoreactivity in the goblet cell mucus and the polarization of sialic acid to the apical plasma membrane of both goblet and absorptive cells may be markers for the differentiated state.