Distinct cytoskeletal tracks direct individual vesicle populations to the apical membrane of epithelial cells.

A key aspect in the structure of epithelial and neuronal cells is the maintenance of a polarized organization based on highly specific sorting machinery at the exit site of the trans Golgi network (TGN). Epithelial cells sort protein and lipid components into different sets of carriers for the apical or basolateral plasma membrane. The two intestinal proteins lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are delivered to the apical plasma membrane of epithelial cells with high fidelity but differ in their affinity to detergent-insoluble, glycolipid-enriched complexes (DIGs). Using a two-color labeling technique, we have recently characterized two post-Golgi vesicle populations that direct LPH and SI separately to the apical cell surface. Here, we investigated the structure and identification of protein components in these vesicle populations and assessed the role of cytoskeletal post-Golgi transport routes for apical cargo. Apart from the central role of microtubules in vesicle transport, we demonstrate that the transport of SI-carrying apical vesicles (SAVs) occurs along actin tracks in the cellular periphery, whereas LPH-carrying apical vesicles (LAVs) are transferred in an actin-independent fashion to the apical membrane. Our data further indicate that myosin 1A is the actin-associated motor protein that drives SAVs along actin filaments to the apical cell surface.