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Cellular diversity in the nervous system evolves from the concerted processes of cell proliferation, differentiation, migration, survival, and synapse formation. Neural adhesion and extracellular matrix molecules have been shown to play crucial roles in axonal migration, guidance, and growth cone targeting(Dodd and Jessell, 1988). Now the molecular components responsible for neuronal cell survival and differentiation are rapidly being defined with the discovery of new growth factors, their corresponding receptors, and signal transduction pathways. With multiple, structurally related molecules defining large gene families, this situation creates a problem in identifying the exact function for each individual family member and confronting the issue of redundancy that appears to be built into each biological process. Growthfactorsgenerallyinitiatesignaling byactivation of transmembrane receptors, which regulate the …