Cell adhesion molecule involved in the establishment and/or maintenance of cell integrity. Involved in the formation and regulation of the tight junction (TJ) paracellular permeability barrier in epithelial cells. Induces primordial adhesive contact and aggregation of epithelial cells in a Ca(2+)-independent manner. Involved in epithelial movement during corneal sheet formation and regeneration. May play a role in VAMP3-mediated vesicular transport and recycling of receptor molecules. May play a role in the regulation of cell shape and movement by modulating the Rho-GTPase activity. May be involved in skeletal muscle and heart development as well as in the maintenance of heart function (By similarity). May also be involved in striated muscle regeneration and in the regulation of cell spreading. Homodimer. Homodimerization requires the C-terminus cytoplasmic region. Detected at points of cell-cell contact in confluent epithelial sheets. Colocalizes with components of the adherens and tight junctions. Expressed in the heart and skeletal muscle (at protein level). Isoform 1 and isoform 4: expressed in heart, muscle, brain, stomach, kidney, lung and spleen. Expressed during heart development in the proepicardial organ, migrating proepicardial strands, delaminated mesenchymal cells and vascular smooth muscle. Expressed in epithelial precursors of the cornea, lens and retina of the developing eye (at protein level). Expressed in the left ventricular segment of the tubular heart at stage 11. Expressed in the myotome, notochord and ventral half of the neuronal tube. Incomplete sequence. Belongs to the popeye family. Extended N-terminus.