CHARACTERIZATION OF THE NICOTINIC ACETYLCHOLINE-RECEPTOR BETA-3 GENE - ITS REGULATION WITHIN THE AVIAN NERVOUS-SYSTEM IS EFFECTED BY A PROMOTER 143 BASE-PAIRS IN LENGTH

Genomic and cDNA clones encoding the chicken neuronal nicotinic acetyl choline receptor beta 3 subunit were isolated and sequenced. The beta 3 gene consists of six protein encoding exons and the deduced protein has the structural features found in all other members of the neuronal nicotinic acetylcholine receptor subunit family. Although they are un detectable in most brain compartments, beta 3 mRNAs are relatively abu ndant in the developing retina and in the trigeminal ganglion. In situ hybridization and immunohistochemical analysis demonstrated that in r etina, beta 3 transcripts and protein are confined to subpopulations o f cells in the inner nuclear and ganglion cell. layers. beta 3 is expr essed in the proximal and distal regions of the developing trigeminal ganglion, i.e. in both placode and neural crest-derived neurons. Trans ient transfection assays in cells freshly dissociated from selected re gions of the central nervous system at different developmental stages allowed the identification of genetic elements involved in the neurona l-selective expression of the beta 3 gene. A promoter fragment 143 bas e pairs in length and containing TATA, CAAT, and other consensus seque nces is sufficient to restrict reporter gene expression to a subpopula tion of retinal neurons. This promoter is totally inactive upon transf ection into neuronal and non-neuronal cells from other regions of the central nervous system.