Cell specificity of a rat neuronal nicotinic acetylcholine receptor α7 subunit gene promoter

An interaction between α7 nicotinic receptors and a G-protein pathway complex regulates neurite growth in neural cells

The α7 acetylcholine nicotinic receptor (α7) is an important mediator of cholinergic transmission during brain development. Here we present an intracellular signaling mechanism for the α7 receptor. Proteomic analysis of immunoprecipitated α7 subunits reveals an interaction with a G protein pathway complex (GPC) comprising Gα(i/o), GAP-43 and G protein regulated inducer of neurite outgrowth 1 (Gprin1) in differentiating cells. Morphological studies indicate that α7 receptors regulate neurite length and complexity via a Gprin1-dependent mechanism that directs the expression of α7 to the cell surface. α7-GPC interactions were confirmed in embryonic cortical neurons and were found to modulate the growth of axons. Taken together, these findings reveal a novel intracellular pathway of signaling for α7 within neurons, and suggest a role for its interactions with the GPC in brain development.

alpha7 nicotinic receptor gene promoter polymorphisms in inbred mice affect expression in a cell type-specific fashion

Inbred mouse strains display significant differences in their levels of brain alpha7 nicotinic acetylcholine receptor (alpha7 nAChR) expression, as measured by binding of the alpha7-selective antagonist alpha-bungarotoxin. Variations in alpha-bungarotoxin binding have been shown to correlate with an animal's sensitivity to nicotine-induced seizures and sensory gating. In two inbred mouse strains, C3H/2Ibg (C3H) and DBA/2Ibg (DBA/2), the inter-strain binding differences are linked to a restriction length polymorphism in the alpha7 nAChR gene, Chrna7. Despite this finding, the molecular mechanism(s) through which genetic variability in Chrna7 may contribute to alpha7 nAChR expression differences remains unknown. However, studies of the human alpha7 nAChR gene (CHRNA7) previously have demonstrated that CHRNA7 promoter polymorphisms are associated with differences in promoter activity as well as differences in sensory processing. In the present study, a 947-base pair region of the Chrna7 promoter was cloned from both the C3H and DBA/2 inbred mouse strains in an attempt to identify polymorphisms that may underlie alpha7 nAChR differential expression. Sequence analysis of these fragments identified 14 single nucleotide polymorphisms (SNPs). A combination of two of these SNPs affects promoter activity in an in vitro luciferase reporter assay. These results suggest a mechanism through which the Chrna7 promoter genotype may influence interstrain variations in alpha7 nAChR expression.