Neuronal Guidance Molecules: Inhibitory and Soluble Factors

Abstract

Axonal guidance factors play a central role in neural development and regeneration. The ability of cell surface adhesive proteins and extracellular matrix components to promote axonal outgrowth has been documented for some time. Recently, the existence and the importance of molecules that repulse axons and of soluble factors that attract axons have been appreciated. By virtue of their long-range diffusible action, the netrins are now well- defined, soluble axonal guidance molecules. The physiological role of repulsive mecha nisms has been best documented in the development of the retinotectal map and in the ability of CNS myelin to inhibit axonal regeneration. The collapsin/semaphorin family of axonal growth inhibitors has been characterized at the molecular level. It is now clear that an understanding of axonal guidance mechanisms must include soluble cell-surface and matrix-bound factors, which are both attractive and repulsive for axonal growth cones. The Neuroscientist 1:255-258, 1995