Gilmour B P, Goldman D, Chahine K G, Gardner P D
Center for Molecular Medicine, University of Texas Health Science Center, San Antonio 78245-3207, USA.
Dev Biol. 1995 Apr;168(2):416-28. doi: 10.1006/dbio.1995.1091.
Nicotinic acetylcholine receptors are pentameric, transmembrane, ligand-gated ion channels critical for neuromuscular signal transmission. Prior to innervation, the genes encoding these receptors are expressed in nuclei throughout the muscle fiber. Muscle innervation leads to a dramatic decrease in expression of these genes in extrasynaptic nuclei. This reduction in gene expression can be reversed by muscle denervation. The effects of denervation on receptor gene expression can be blocked by electrical stimulation of muscle using extracellular electrodes. The molecular mechanisms by which muscle electrical activity leads to altered patterns of nicotinic acetylcholine receptor gene expression are not well understood. Using an in vitro electrical stimulation paradigm to induce muscle activity, we have been able to mimic the effect of innervation on extrasynaptic acetylcholine receptor gene expression. We have found that a 93-bp region of 5'-flanking DNA, spanning nucleotides -150 to -57 relative to the transcription start site of the gamma subunit gene, is required for the suppression of gene expression in response to muscle activity. Sequences downstream of this region are transcriptionally active but are not responsive to muscle activity. However, these downstream sequences become responsive to muscle activity when placed under the control of the gamma subunit muscle-specific enhancer.
烟碱型乙酰胆碱受体是五聚体跨膜配体门控离子通道，对神经肌肉信号传递至关重要。在神经支配之前，编码这些受体的基因在整个肌纤维的细胞核中表达。肌肉神经支配导致这些基因在突触外细胞核中的表达显著下降。这种基因表达的降低可通过肌肉去神经支配来逆转。使用细胞外电极对肌肉进行电刺激可阻断去神经支配对受体基因表达的影响。肌肉电活动导致烟碱型乙酰胆碱受体基因表达模式改变的分子机制尚不清楚。利用体外电刺激模式诱导肌肉活动，我们能够模拟神经支配对突触外乙酰胆碱受体基因表达的影响。我们发现，相对于γ亚基基因转录起始位点，5'-侧翼DNA的一个93-bp区域（跨越核苷酸-150至-57）是响应肌肉活动抑制基因表达所必需的。该区域下游的序列具有转录活性，但对肌肉活动无反应。然而，当置于γ亚基肌肉特异性增强子的控制下时，这些下游序列对肌肉活动变得有反应。
