Junctional Adhesion Molecule 1 (JAM1) seems to play a role in epithelial tight junction formation. It appears early in primordial forms of cell junctions and recruits PARD3. The association of the PARD6-PARD3 complex may prevent the interaction of PARD3 with JAM1, thereby preventing tight junction assembly. JAM1 plays a role in regulating monocyte transmigration involved in integrity of the epithelial barrier. JAM1 is also involved in platelet activation.