Neuronal cell surface protein that may be involved in cell recognition and cell adhesion. A number of isoforms, alpha-type and beta-type are produced by alternative promoter usage. Beta-type isoforms differ from alpha-type isoforms in their N-terminus. After the very early developmental stages, the expression levels decrease and remain relatively constant until around 24 h, with the onset of an increase of expression that continues till the larval stages. Belongs to the neurexin family.