Desmosomes and hemidesmosomes both form plaques on the cytoplasmic side of cell membranes and link keratin intermediate filaments. Desmosomes directly link adjacent cell membranes through homophilic interactions between transmembrane proteins, while hemidesmosomes link the cell membrane to the basal lamina using integrin proteins. Tight junctions form a barrier near the apical surfaces of epithelial cells and regulate the diffusion of molecules between cells. They are composed of claudin and occludin transmembrane proteins that interact homophilically. Gap junctions link the cytoplasms of adjacent cells and allow small molecules to pass through, and are composed of connexin proteins that oligomerize into connexons.