Loss of galectin-3 impairs membrane polarisation of mouse enterocytes in vivo

Epithelial cells are characterised by distinct apical and basolateral membrane domains that are separated by tight junctions. Establishment and maintenance of this polarity depend on specific gene expression and protein targeting to their correct location. Our former studies, performed with renal epithelial MDCK cells, revealed a new function for galectin-3, a member of a conserved family of lectins. There, galectin-3 is required for intracellular sorting and correct targeting of non-raft-associated glycoproteins to the apical plasma membrane. In the present study, we found transport defects of the intestinal brush border hydrolases lactase-phlorizin hydrolase (LPH) and dipeptidylpeptidase IV (DPPIV) in galectin-3-null mutant mice. We could show that, in enterocytes of wild-type mice, both glycoproteins directly interact with galectin-3 and transit through non-raft-dependent apical transport platforms. Therefore, this genetic analysis provides definitive evidence for the involvement of galectin-3 in protein intracellular trafficking in vivo. Further investigations revealed that gal3-null enterocytes also exhibit striking cytoarchitecture defects, with the presence of numerous and regular protrusions located along basolateral membranes. Moreover, -actin and villin, two characteristic markers of brush borders, become abnormally distributed along these atypical basolateral membranes in gal3^-/- mice. Taken together, our results demonstrate that, in addition to a pivotal role in apical trafficking, galectin-3 also participates in epithelial morphogenesis in mouse enterocytes.