Required for organization of septate junctions and paracellular barrier functions. Septate junctions, which are the equivalent of vertebrates tight junctions, are characterized by regular arrays of transverse structures that span the intermembrane space and form a physical barrier to diffusion. Forms a complex with Nrg and Nrx. Component of epithelial septate junctions. Nrx is required for its cell surface localization. Expressed in ectodermally derived epithelial cells from stage 12. All these tissues, such as epidermis, hindgut, foregut, salivary glands and trachea, which contain pleated septate junctions. Expressed by ectodermally derived epithelial cells and along peripheral nerves. Not present in midline glial cells. Expressed in epithelial cells and glial cells of peripheral nerves. N-glycosylated. Belongs to the immunoglobulin superfamily. Contactin family.