Analysis of Membrane Traffic in Polarized Epithelial Cells

Spatial asymmetry is fundamental to the structure and function of most eukaryotic cells. A basic aspect of this polarity is that the cell's plasma membrane is divided into discrete domains. The best studied and simplest example of this occurs in epithelial cells, which line exposed body surfaces. Epithelial cells use two pathways to send proteins to the cell surface. Newly made proteins can travel directly from the trans-Golgi network (TGN) to either the apical or basolateral surface. Alternatively, proteins can be sent to the basolateral surface and then endocytosed and transcytosed to the apical surface. Epithelial cells grown on porous filters adopt a typical polarized morphology; transfected epithelial cells can be used to biosynthetically characterize the trafficking patterns of a given protein. These cells can also be used to study delivery to a particular surface and to localize the protein by immunofluorescence.