Molecular mechanisms mediating synapse-specific gene expression during development of the neuromuscular junction.

Adult skeletal muscle locally expresses nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction by selective induction of their subunit-encoding genes (alpha beta epsilon delta) in endplate-associated myonuclei. Neuregulin/ARIA is a nerve-derived factor that is thought to be largely responsible for this local gene induction. Neuregulin/ARIA activates a Ras/MAP kinase signalling cascade, which ultimately induces nAChR epsilon-subunit gene expression via a 15 bp sequence that harbors a core Ets transcription factor binding site (GGA). Interestingly, this same sequence also appears to participate in extrajunctional repression of the epsilon-subunit gene. Muscle Ets 2 overexpression induces nAChR epsilon-subunit gene promoter activity, whereas a dominant/negative Ets blocks neuregulin-dependent induction. These results suggest that Ets transcription factors play a role in mediating synapse-specific and neuregulin-mediated motor neuron control of nAChR gene expression.