Neurexins function in the vertebrate nervous system as cell adhesion molecules and receptors. Two neurexin genes are among the largest known in human (NRXN1 and NRXN3). By using alternate promoters, splice sites and exons, predictions of hundreds or even thousands of distinct mRNAs have been made. Most transcripts use the upstream promoter and encode alpha-neurexin isoforms; fewer transcripts are produced from the downstream promoter and encode beta-neurexin isoforms. Alpha-neurexins contain epidermal growth factor-like (EGF-like) sequences and laminin G domains, and they interact with neurexophilins. Beta-neurexins lack EGF-like sequences and contain fewer laminin G domains than alpha-neurexins.