Tight junctions are structures that serve as barriers on epithelial cells—separating fluids from either side of the epithelial sheet and preventing the diffusion of membrane proteins to different domains of the cell’s plasma membrane. Image is of epithelial cells (Caco-2, a human colon adenocarcinoma cell line) immunostained for MarvelD3 and occludin, colocalizing at tight junctions. MarvelD3 is a novel member of the occludin family of tight junction transmembrane proteins. Although MarvelD3 is not necessary for the formation of tight junctions, its function is important in regulating ion permeability of the cell.
Reference: Emily Steed, Nelio TL Rodrigues, Maria S Balda and Karl Matter. Identification of MarvelD3 as a tight junction-associated transmembrane protein of the occludin family. BMC Cell Biology 2009, 10:95