MOLECULAR BASES OF NEURONAL CONNECTIVITY

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In order for damaged pathways to regenerate after injury, nerve cells must begin to express gene products required for the reconstruction of their axons; this in turn is influenced by the extracellular milieu provided by non-neuronal support cells. Lower vertebrates are able to regenerate their optic nerve after injury and recover vision fully, a phenomenon that may enable us to understand the molecular and cellular changes that underlie growth and plasticity in the vertebrate central nervous system. We will utilize biochemistry and gene cloning methods to identify neuronal and non-neuronal molecules that are critical for the regeneration of the goldfish optic nerve. Aim 1 will identify portions of the molecular cascade involved in the expression of the best characterized growth-associated protein, GAP-43. Our preliminary evidence indicates that the expression of GAP-43 is controlled largely at the post-transcriptional level, and involves the binding of specific proteins to sequences in the 3'untranslated end of the messenger RNA that may serve to protect it from degradation by nucleases. We will isolate these proteins and identify the nucleotide sequences to which they bind. Aim 2 will isolate and sequence a less well-characterized growth-associated protein of the optic pathway, GAP-24. We will compare the mechanisms that regulate its expression with those found in Aim 1 to gain a broader understanding of the cascade of events occurring within the neuron as it regenerates its axon. Aim 3 focuses on a protein secreted from the non-neuronal sheath cells of the nerve that may serve as a trigger for the molecular changes studied in the other two sections. We will combine classical protein purification methods, monoclonal antibody technology partial amino acid sequencing, cDNA library screening, antibodies and probes to identified growth factors, and several bioassay systems to isolate and sequence this trophic factor. Together, these studies represent an integrated approach to understanding the cellular and molecular biology underlying regeneration in the visual system, knowledge that may eventually be applied for inducing visual recovery in man.