Native and recombinant DM-GRASP selectively support neurite extension from neurons that express GRASP.

DM-GRASP (GRASP) is an integral membrane glycoprotein expressed on a restricted set of axons in the developing chick nervous system. We demonstrate that purified GRASP supports neurite extension from the subpopulation of neurons that express GRASP. Sensory, sympathetic, and ciliary neurons express GRASP and extend neurites on a GRASP substrate. In contrast, tectal, diencephalic, and retinal cells express GRASP at a very low level, if at all, and do not extend neurites on a GRASP substrate. Moreover, as GRASP is downregulated on sensory neurons during development, they lose the capacity to extend neurites on a GRASP substrate. Recombinant GRASP produced in a baculovirus expression system is biochemically and functionally identical to GRASP purified from embryonic chick brain. The finding that GRASP selectively supports neurite extension supports the hypothesis that it mediates selective fasciculation via a homophilic binding mechanism.