The Role of the Immunoglobulin/Fibronectin Axonal Glycoprotein Subfamily in Axonal Fasciculation and Guidance

A major class of glycoproteins found on the surfaces of growing axons are members of the immunoglobulin (Ig) super-family of proteins that contain both Ig-like domains and fibronectin type III-like domains. The pattern of expression of these proteins during development combined with in vitro studies of their function, suggest that these proteins have a role in regulating axonal growth patterns and guidance by modulating cell surface adhesivity. Recent in vivo studies suggest that at least one mechanism used to modulate axonal adhesivity involves regulation of the polysialic acid content of one member of this family, NCAM. The increasing diversity of this family and the discovery of multiple isoforms of these proteins suggest that other mechanisms may also exist for regulating axonal growth and guidance.