ELEMENTS BETWEEN THE PROTEIN-CODING REGIONS OF THE ADJACENT BETA-4 AND ALPHA-3 ACETYLCHOLINE-RECEPTOR GENES DIRECT NEURON-SPECIFIC EXPRESSION IN THE CENTRAL-NERVOUS-SYSTEM

The expression patterns of three clustered neuronal nicotinic acetylch oline receptor (nAchR) subunit genes ordered beta 4, alpha 3, and alph a 5 overlap extensively in the peripheral nervous system (PNS) but onl y partially in the central nervous system (CNS). We have begun to inve stigate cell type-specific cis elements regulating these genes by anal yzing in both cell culture and transgenic mice, a 2.8-kb fragment (-27 32/+47) containing the alpha 3 promoter region, the beta 4/alpha 3 int ergenic region, and a portion of the beta 4 3'-untranslated exon. The -2732/+47 fragment is preferentially active in PC12 cells relative to nonneural cell lines. Deletion analysis revealed a cell type-specific positive transcriptional element positioned in the beta 4 3'-untransla ted exon. The positive element is likely to be an enhancer and not a s econd alpha 3 promoter, because no alpha 3 exons are present in this r egion. Having shown in cell culture that cell-type specific cis elemen ts are positioned between the beta 4 and alpha 3 coding regions, we in vestigated the activity of -2732/+47 in vivo. Transgenic mice were gen erated, which carry the lacZ gene fused downstream of -2732/+47. Expre ssion of the lacZ transgene is restricted to neurons of the CNS; no ex pression was detected in the PNS or in nonneural tissues. LacZ-positiv e cells mere detected virtually exclusively in a subset of CNS nuclei that transcribe the endogenous alpha 3 gene, Some overlap was seen wit h the beta 4 gene, but nearly none with the alpha 5 gene. Our results demonstrate that cis elements positioned between the alpha 3 and beta 4 coding regions are important for establishing part of the restricted CNS patterns of beta 4, alpha 3, and alpha 5 gene transcription. (C) 1997 John Wiley & Sons, Inc.