Functional properties of the neuronal nicotinic acetylcholine receptor beta3 promoter in the developing central...

Within the chick central nervous system, expression of the beta3 nicotinic acetylcholine receptor gene is restricted to a subset of retinal neurons, the majority of which are ganglion cells. Transient transfection in retinal neurons and in neural and non-neural cells from other regions of the chick embryo allowed the identification of the cis-regulatory domain of the beta3 gene. Within this domain, a 75-base pair fragment located immediately upstream of the transcription start site suffices to reproduce the neuron-specific expression pattern of beta3. This fragment encompasses an E-box and a CAAT box, both of which are shown to be key positive regulatory elements of the beta3 promoter. Co-transfection experiments into retinal, telencephalic, and tectal neurons with plasmid reporters of beta3 promoter activity and a number of vectors expressing different neuronal (ASH-1, NeuroM, NeuroD, CTF-4) and non-neuronal (MyoD) basic helix-loop-helix transcription factors indicate that the cis-regulatory domain of beta3 has the remarkable property of discriminating accurately between related members of the basic helix-loop-helix protein family. The sequence located immediately 3' of the E-box participates in this selection, and the E-box acts in concert with the nearby CAAT box.