Novel guidance cues during neuronal pathfinding in the early scaffold of axon tracts in the rostral brain

A scaffold of axons consisting of a pair of longitudinal tracts and several commissures is established during early development of the vertebrate brai n. We report here that NOC-2, a cell surface carbohydrate, is selectively e xpressed by a subpopulation of growing axons in this scaffold in Xenopus. N OC-2 is present on two glycoproteins, one of which is a novel glycoform of the neural cell adhesion molecule N-CAM. When the function of NOC-2 was per turbed using either soluble carbohydrates or anti-NOC-2 antibodies, axons e xpressing NOC-2 exhibited aberrant growth at specific points in their pathw ay. NOC-2 is the first-identified axon guidance molecule essential for deve lopment of the axon scaffold in the embryonic vertebrate brain.