A few axonal proteins distinguish ventral spinal cord neurons from dorsal root ganglion neurons.

A series of proteins putatively involved in the generation of axonal diversity was identified. Neurons from ventral spinal cord and dorsal root ganglia were grown in a compartmented cell-culture system which offers separate access to cell somas and axons. The proteins synthesized in the neuronal cell somas and subsequently transported into the axons were selectively analyzed by 2-dimensional gel electrophoresis. The patterns of axonal proteins were substantially less complex than those derived from the proteins of neuronal cell bodies. The structural and functional similarity of axons from different neurons was reflected in a high degree of similarity of the gel pattern of the axonal proteins from sensory ganglia and spinal cord neurons. Each axonal type, however, had several proteins that were markedly less abundant or absent in the other. These neuron-population enriched proteins may be involved in the implementation of neuronal diversity. One of the proteins enriched in dorsal root ganglia axons had previously been found to be expressed with decreased abundance when dorsal root ganglia axons were co-cultured with ventral spinal cord cells under conditions in which synapse formation occurs (P. Sonderegger, M. C. Fishman, M. Bokoum, H. C. Bauer, and P.G. Nelson, 1983, Science [Wash. DC], 221:1294-1297). This protein may be a candidate for a role in growth cone functions, specific for neuronal subsets, such as pathfinding and selective axon fasciculation or the initiation of specific synapses. The methodology presented is thus capable of demonstrating patterns of protein synthesis that distinguish different neuronal subsets. The accessibility of these proteins for structural and functional studies may contribute to the elucidation of neuron-specific functions at the molecular level.