Ninjurin2, a novel homophilic adhesion molecule, is expressed in mature sensory and enteric neurons and promotes neurite outgrowth

A large number of cell adhesion molecules mediate cell-to-cell and cell-to- extracellular matrix interaction during development, differentiation and re generation of the peripheral nervous system. Here, we report the identifica tion of a novel cell surface adhesion molecule, ninjurin2 (for nerve injury induced protein 2). Ninjurin2 is a homolog of a homophilic cellular adhesi on molecule, ninjurin1, that was previously isolated as a gene induced in S chwann cells after nerve injury. Ninjurin1 and 2 share conserved hydrophobi c regions for their transmembrane domains; however, they do not contain com parable adhesion motifs nor do they interact with each other. In the periph eral nervous system, ninjurin2 is expressed constitutively in mature sensor y and enteric neurons but not in glial cells or in auto-nomic ganglia. Ninj urin2 is upregulated in Schwann cells surrounding the distal segment of inj ured nerve with a time course similar to that of ninjurin1, neural CAM, and L1. Ninjurin2 promotes neurite outgrowth from primary cultured dorsal root ganglion neurons, presumably via homophilic cellular interactions. Ninjuri n2 is also highly expressed in hematopoietic and lymphatic tissues. Finally , the ninjurin2 gene is located on human chromosome 12p13 in which several disorders of unknown etiology have been mapped, including inflammatory bowe l disease and acrocallosal syndrome.