The chapter reviews the emerging functions of neurexins and identifies additional members of the neurexin superfamily. The neurexins is a polymorphic family of neuronal-specific, type-I cell surface-membrane proteins that are involved in specifying synaptic specificity and synaptic vesicle docking at the synaptic active zone. In addition, neurexins have been found to interact with a number of unrelated proteins that include synaptotagmin, neurexophilins, neuroligins, and CASK to suggest a role in synaptic function. Some of the conclusions on the functions of the neurexins remain an area of immense interest because of their proposed synaptic functions and their presence in invertebrates. Application of genetic and molecular techniques, particularly gene ablation mutagenesis and homologous recombination in embryonic stem cells, has clearly demonstrated the critical role of some of the neurexin family members in neuronal function. The chapter also discusses the genomic structure of neurexin genes and role of NCP1 at paranodal junctions and domain organization at the node of Ranvier.
