Stimulation of acetylcholine receptor transcription by neuregulin-2 requires an N-box response element and is regulated by alternative splicing.
The neuregulin (Nrg) family of growth/differentiation factors is encoded by at least four genes in the mammalian genome: nrg-1, nrg-2, nrg-3 and nrg-4. Nrg-1 and Nrg-2 share the highest homology within the family, and the primary RNA transcripts from their encoding genes are subjected to extensive alternative splicing. Although little is known about the biological function of Nrg-2-4, their structural similarity with Nrg-1 suggests that they could account for some of the activities presently attributed to Nrg-1. Thus, at the neuromuscular junction Nrg-1 has been a favored candidate for the signal that activates selective acetylcholine receptor (AChR) transcription in synaptic myonuclei. However, we have recently shown that like Nrg-1, Nrg-2 can also activate AChR transcription in cultured myotubes and accumulates at the synaptic site. Synapse-specific and Nrg-1-induced AChR transcription require an enhancer sequence, the N-box, which is also mutated in some patients with congenital myasthenia gravis. Here, we show that Nrg-2-induced AChR transcription requires an N-box motif and is regulated by alternative splicing. We also show that unique Nrg-2 isoforms are differentially distributed between spinal cord and skeletal muscle, the tissues that harbor the cellular components of the neuromuscular synapse.