REGULATION OF NEURONAL NICOTINIC ACETYLCHOLINE RECEPTOR

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Molecular cloning studies have identified gene families encoding functionally distinct heteromeric ligand-gated ion-channels. One such family of genes encodes subunits that are assembled into several functionally-distinct heteromeric neuronal nicotinic acetylcholine receptors. The nicotinic receptor subunit gene family is abundantly expressed in the vertebrate brain and peripheral nervous system. Each member has a unique pattern of expression, although these patterns overlap partially. Thus, this gene family is likely to encode multiple heteromeric receptors to subserve synaptic functions in numerous cholinergic pathways of the brain and periphery. This proposal is concerned with identifying the mechanisms that control vertebrate receptor subunit gene expression so that functionally distinct heteromeric nicotinic receptors can be assembled in different subsets of phenotypically distinct neurons. The experiments described are designed to: 1) identify the cis-acting elements that control neuronal nicotinic receptor subunit gene transcription in a neural-specific manner, 2) determine whether the influence of NGF on nicotinic receptor subunit RNAs is exerted at the level of transcription or RNA stability, 3) determine the influence of activity on receptor subunit gene expression, and 4) determine if changes in receptor subunit gene expression occur during periods of rapid synaptogenesis. The gene family encoding neuronal nicotinic receptor subunits are particularly amenable to the proposed investigation because its members are expressed in a wellcharacterized clonal cell line, PC12 and in the accessible and experimentally manipulatable sympathetic nervous system. The PC12 line provides a convenient cell culture system in which to begin characterizing transcription regulatory elements controlling ligand-gated ion-channel genes. Sympathetic ganglia provide an accessible experimental system of primary neurons for complementary in vivo and in vitro approaches to address the influence of cell-cell interactions on receptor subunit gene expression. Neuronal nicotinic receptor subunit genes and other ligand-gated ion-channel genes are co-expressed in numerous nuclei and cell layers of the brain. Common neuronal environments raise the possibility that the genes encoding different ligand-gated ion-channels share similar mechanisms of regulation. Thus, this investigation is likely to serve as a model for the regulation of other ligand-gated ion-channel genes, for which well-characterized and accessible experimental models systems are not as well developed. The investigation of nicotinic receptor gene expression will ultimately lead to an understanding of the importance of receptor gene regulatory mechanisms to the development of the nervous system and perhaps insight into the molecular mechanisms of neurological disorders which result from aberrant development.