Neuronal cell surface protein that may be involved in cell recognition and cell adhesion by forming intracellular junctions through binding to neuroligins. May play a role in formation or maintenance of synaptic junctions. May mediate intracellular signaling (By similarity). Plays a role in angiogenesis. A number of isoforms, beta-type and alpha-type are produced by alternative promoter usage. Beta-type isoforms differ from alpha-type isoforms in their N-terminus. Additional isoforms seem to exist. There are probably more than 60 isoforms. There is a combination of five alternatively spliced domains at sites 1 to 5, each consisting of modular sequences that seem to be used independently. Experimental confirmation may be lacking for some isoforms. Brain and arteries (at protein level). Belongs to the neurexin family.