Factors regulating the expression of the neutral glycolipids in the mouse small intestinal mucosa

GDP-fucose:asialo GM1 alpha(1-2)fucosyltransferase (FT) is induced in the small intestinal mucosa after microbial contamination of germ-free mice (Umesaki, Y., Sakata, T. and Yajima, T. (1982) Biochem. Biophys. Res. Commun. 105, 439-443). As a result, asialo GM1 glycolipid, a major component of the epithelial cell membrane, drastically converted into fucosyl asialo GM1. There were many other examples in which FT was induced. One was the weaning period for conventional mice. Others included injuries of the small intestine by punctures or administration of cytosine arabinoside, and the injection of protein synthesis inhibitors, such as cycloheximide or emetine, or the soluble fraction of the small intestinal homogenate (SISF). The induction of FT was more rapid after injection of cycloheximide or SISF than after injury, mechanical puncturing or after administration of cytosine arabinoside. The changes in the neutral glycolipids of the small intestine by injection of cycloheximide or SISF were analyzed in detail. FT activity started to increase after approx. 5 h and reached the maximum 10-12 h after injection of cycloheximide or SISF, and rapidly declined thereafter. The conversion of asialo GM1 into fucosyl asialo GM1 started after about 10 h and reached the maximal value 24 h after the treatment. Fucosyl asialo GM1 persisted for a few days, although the FT activity fell to near the basal level. On the other hand, the amount of glucosyl ceramide was constant after these treatments. There was little difference in the time-courses of both the FT activity and the glycolipid conversion between these treatments. In the case of co-injection of cycloheximide and SISF, the effect of both materials on FT activity induction was synergistic. The distribution of FT activity and immunohistochemical staining using anti-fucosyl asialo GM1 antibody along the crypt-villus axis showed a stronger expression of fucosyl asialo GM1 in villus portion, the post-mitotic cell zone, than in the crypt portion. Asialo GM1 was converted into fucosyl asialo GM1 after the induction of FT by the various treatments mentioned above. Especially the effects of cycloheximide and/or SISF on FT induction suggest at least the presence of a regulatory protein(s) which controls the glycolipid expression in the small intestine.