Regulation of transcription in the neuronal nicotinic receptor subunit gene cluster by a neuron-selective enhancer and ETS domain factors

Expression of neurotransmitter receptors encoded by the nicotinic acetylcholine receptor (nAchR) subunit gene cluster depends on coexpression of the β4, α3, and α5 subunits in certain kinds of neurons. One way in which coexpression might be achieved is through the regulation of promoters in the cluster by neuron-selective enhancers. The β43' enhancer is located between the β4 and α3 promoters and it directs cell type-specific expression in cell lines. It is not known, however, whether β43' is active in neurons. Therefore, we assayed β43' in dissociated rat sympathetic ganglia cultures, which contain nAchR-positive neurons as well as nAchR-negative non-neuronal cells. Reporters controlled by the α3 promoter and β43' were expressed in a neuron-selective manner; greater than 90% and up to 100% of luciferase expression was detected in neurons. Neuron selectivity was maintained when β43' was placed next to ubiquitously active viral promoters. In contrast, replacing β43' with the SV40 enhancer eliminated neuron selectivity. The enhancer is composed of at least two separate but functionally interdependent elements, each of which interacts with a different type of ETS domain factor. These findings support a model in which β43' controls neuronal expression of one or more genes in the cluster through interactions with a combination of ETS factors.