Cell type‐ and differentiation‐dependent expression from the mouse acetylcholine receptor ϵ‐subunit promoter

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Abstract
The nicotinic acetylcholine receptor (AChR) in adult skeletal muscle is composed of α-, β-, ϵ-, and δ-sub-units and is localized at the neuromuscular junction; in contrast, the more diffusely distributed fetal form is composed of α-, β-, γ-, and δ-subunits. To define sequences necessary for the transcriptional regulation of the mouse ϵ-subunit gene, we sequenced and analyzed 1036 bp upstream of the transcription start site. Using deletion analysis of the 5′-flanking region linked to the bacterial chloramphenicol acetyltransferase (CAT) gene and transfection of the resulting constructs into established cell lines, we demonstrate that a 151 bp fragment exhibits cell type- and differentiation-specific promoter activity. This activity was independent of a myogenic factor putative binding site (E-box). However, transactivation experiments with recombinant myoD, myogenin, or MRF4 showed that the E-box was functional and that MRF4 preferentially transactivates the ϵ-promoter. Thus, like other AChR promoters, the proximal region of the ϵ-promoter contains information for cell type-specific and developmental regulation of CAT and can be transactivated by myogenci factors in cultured cell lines. Unlike the other AChR promoters characterized to date, ϵ-promoter function can be partially independent of myogenic factors of the helix-loop-helix class.