The development of the nervous system is dominated by the central consideration that its ability to function properly depends on the accuracy of its spatial organization. The neuronal precursors must attain the correct position within the organism to insure that future axons are able to make synaptic contact with their designated targets. Several mechanisms operate to achieve this goal: the embryonic environment influences both the pattern of cellular migration and neuronal differentiation; diffusible factors and recognition molecules on cell surfaces guide axons to their appropriate targets; and signals are released from target cells that allow neuronal degeneration to occur in response to incongruous neuron-target interactions. Studies of the peripheral nervous system have been invaluable in elucidating many of these developmental processes. The discovery of the well-characterized trophic agent, nerve growth factor (NGF), is one example. NGF is a polypeptide hormone that is crucial for the survival and differentiation of sympathetic neuroblasts and mature sympathetic neurons. Recently, a cell line (PC12) that responds to NGF has been used extensively to study the mechanism of action of this hormone. Experiments with inhibitors of RNA transcription have demonstrated that many NGF-stimulated responses require alterations in the pattern of gene expression. In this proposal, experiments designed to identify, isolate, and characterize the gene products whose synthesis is induced by the actions of NGF will be outlined. (1) cDNA libraries of NGF-treated PC12 cells will be constructed and subsequently screened with probes enriched for NGF-regulated mRNA species. (2) The identity, structure, and function of these gene products will be investigated by determining the nucleotide sequence of the NGF-activated genes. Antibodies directed against the peptides encoded by the NGF-regulated cDNAs will be produced. (3) The temporal and spatial patterns of expression of these gene products in the developing embryo and adult animal will be determined. From these studies, new insight will be gained with regard to the role of NGF in neuronal development. Knowledge in this area may lead to an increased understanding of the defects manifested in familial dysautonomia hereditary sensory neuropathies, and other neurological defects in the newborn.
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