Epicardial formation involves the attachment of proepicardial (PE) cells to the heart and the superficial migration of mesothelial cells over the surface of the heart. Superficial migration has long been known to involve the interaction of integrins expressed by the epicardium and their ligands expressed by the myocardium; however, little is understood about signals that maintain the mesothelium as it migrates. One signaling pathway known to regulate junctional contacts in epithelia is the

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... Akt signaling pathway and this pathway can be modified by integrins. Here, we tested the hypothesis that the myocardially expressed, integrin ligand VCAM-1 modulates the activity of the PI3K/Akt signaling pathway by activating the lipid phosphatase activity of PTEN. We found that epicardial cells stimulated with a soluble form of VCAM-1 (sVCAM-1) lipid phosphatase activity. Chick embryonic epicardial mesothelial cells (EMCs) expressing a shRNA to PTEN increased invasion in collagen gels, but only after stimulation OPEN ACCESS J. Dev. Biol. 2013, 1 Expression of an activated form of PTEN was capable of blocking degradation of mesothelial state of epicardium and not in EMT. We tested if altering PTEN activity could affect coronary vessel development and observed that embryonic chick hearts infected with a virus expressing activated human PTEN had fewer coronary vessels. Our data support a role for VCAM-1 in mediating critical steps in epicardial development through PTEN in epicardial cells.