Protein Transport Processes at the Apical Membrane: Applications for TIRF Microscopy

摘要

Due to their special role in organ function and the exchange of biological components some body cells developed certain polarization characteristics. These are reflected in differences of their plasma membrane composition. The essential and fascinating task of polarized protein transport in epithelial cells is to get the right protein into the right membrane. In this article we show several protein transport and sorting events occurring in polarized epithelial cells. By applying TIRF microscopy (TIRFM) we were able to identify the apical membrane protein P75-GFP together with its sorting receptor Galectin-3 in close proximity or inside the apical plasma membrane. Furthermore we were able to show microvilli and even endosomal structures at the subapical surface of MDCK cells. Live cell imaging at this cell pole revealed videos of moving vesicles gliding along the primary cilium. Apical TIRFM did not only show secretory protein trafficking events but also endocytosis of the apical sorting receptor Galectin-3. All these facts demonstrate the potential of TIRFM for the visual decipherment of protein sorting in polarized epithelial cells.