The plasma membrane of intestinal epithelial cells (enterocytes) is divided into distinct domains. The apical domain – which is rich in digestive enzymes – is the site of nutrient uptake from the intestinal lumen, whereas the basolateral domain mediates cell-cell and cell-matrix interactions. The distribution of key proteins within the plasma membrane is highly polarised, but the machinery that directs proteins to the apical domain remains obscure. Now Ralf Jacob and colleagues (p. 458) describe the role of the carbohydrate-binding protein galectin-3 in apical trafficking in vivo. The authors show that galectin-3 binds directly to the apical enzymes lactase-phlorizin hydrolase and dipeptidylpeptidase IV, and that both enzymes are mislocalised in the enterocytes of mice that lack galectin-3. Moreover, knocking out galectin-3 alters the subcellular distribution of β-actin, villin and ezrin, all of which localise to the apical domain in wild-type enterocytes in vivo. Strikingly, the authors report, the absence of galectin-3 also leads to morphological changes in the basolateral membrane, which acquires microvillus-like projections that are typical of the apical domain. Galectin-3, therefore, plays an important role in apical protein sorting and in epithelial morphogenesis.
- © The Company of Biologists Limited 2008