Novel gene families involved in neural pathfinding.

Recent studies have uncovered a bifunctional role of the diffusible axon guidance molecules netrin-1 and UNC-6 in that they attract some axons and steer others away simultaneously. Homology screens have extended the semaphorin and collapsin family to include at least 20 members, in both secreted and membrane-bound forms. Eph-related receptors and their membrane-bound ligands, the function of which have only been characterized poorly to date, have been added to the growing number of molecules involved in axon guidance and fasciculation.