Differential toxicity of RCAII (ricin) on rabbit intestinal epithelium in relation to postnatal maturation

Regulation of the intestinal glycoprotein glycosylation during postnatal development: role of hormonal and nutritional factors

This review focuses on the regulation of the glycoprotein glycosylation process in small intestine and colon during postnatal development. Glycoproteins play a prominent part in intestine as mucins secreted by the goblet cells and as molecules of biological interest largely present in the microvillus membrane of the enterocytes (digestive enzymes, transporters). The age-related changes in the intestinal glycosylation control the quality of glycan chains of glycoproteins. Postnatal maturation is observed at all stages of the glycoprotein glycosylation. But it is essentially characterised in the external glycosylation by a shift from sialylation to fucosylation depending on the transcriptional regulation of the corresponding glycosyltransferases, but also on coordinate changes in the activities of glycosyltransferases and of their regulatory proteins, in nucleotide-sugar bioavailability and in product degradation by oxidases. Many factors have been evoked to trigger these changes, among which are hormonal (glucocorticoids, insulin) and dietary factors. Changes in the structure of the glycoprotein glycans might be important for the transport, the barrier function, the implantation of the immune defences and of the microflora and even probably for the biological activity of some digestive enzymes.

Lectin binding patterns in developing rat colon

To evaluate qualitative changes in brush-border and goblet cell glycoconjugates during colonic development, rhodamine-conjugated lectins were applied to tissue from fetal (18-22 day), suckling (1-20 day), and weanling (22-26 day) rats. Tissue from the proximal and distal colon of each animal was incubated with Triticum vulgaris, Arachis hypogaea, Glycine max, or Ulex europeus agglutinin I. Formalin-fixed paraffin sections and unfixed frozen sections were coded, read blindly, and graded from negative (-) or weak (+) to intensely positive (4+). The results showed a unique developmental pattern for each lectin, although in all cases the adult binding pattern was established by weaning. Alterations in the binding pattern between paraffin and frozen sections were noted only for Arachis hypogaea and Glycine max. Minimal Glycine max binding was seen at any age in paraffin sections, although in frozen sections a weak but consistent supranuclear binding was seen in goblet cells of postnatal animals. In contrast, both the brush-border and goblet cells were intensely fluorescent after exposure to Triticum vulgaris. This fluorescence was present in both regions at all ages studied. Ulex europeus agglutinin I also labeled goblet cells in the fetal and neonatal colon, but late in the suckling period regional differences appeared. This resulted in a significant loss of labeled goblet cells distally and a restriction of Ulex europeus agglutinin I-positive cells to the base of the crypts proximally. Finally, Arachis hypogaea showed a transient brush-border binding in paraffin sections of the proximal colon before weaning, whereas frozen sections revealed a supranuclear localization in goblet cells in both regions after birth. These studies indicate significant changes in membrane-associated and goblet cell secretory glycoconjugates in the developing rat colon.