Seems to play a role in the formation and function of septate junctions. 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. Required for the blood-brain barrier formation. The C-terminal region interacts with coracle. Interacts with Patj in cis form. Forms a complex with Nrg and Cont. Found in septate junctions of epithelial and glial cells. Belongs to the neurexin family.