Romano S J, Pugh P C, McIntosh J M, Berg D K
Department of Biology, University of California, San Diego, La Jolla 92093-0357, USA.
J Neurobiol. 1997 Jan;32(1):69-80.
Several neuronal nicotinic acetylcholine receptor (AChR) genes are expressed in chick skeletal muscle during development. One of the most abundantly expressed is alpha 7, which produces a protein capable of binding alpha-bungarotoxin and is physically distinct from muscle AChRs containing the alpha 1 gene product. We show here that the alpha 7-containing species in muscle is indistinguishable pharmacologically from alpha 7-containing AChRs in neurons. In addition, immunologic analysis with subunit-specific muscle antibodies shows that the alpha 7-containing species in muscle lacks the beta 1 and delta muscle AChR gene products as it does the alpha 1. RNase protection experiments measuring alpha 7 mRNA levels indicate that the alpha 1 and alpha 7 genes may, in part, be subject to similar kinds of regulation in the tissue. Surgical denervation of leg muscle in newly hatched chicks caused a small and transient increase in alpha 7 mRNA after 8 days, while alpha 1 transcripts underwent a large and sustained increase in number. Similarly, treating myotube cultures with tetrodotoxin caused a modest increase in alpha 7 transcript levels and a large increase in alpha 1. Calcitonin gene-related peptide (CGRP) increased both kinds of transcripts in myotube cultures equally as did treatment with 8-bromo-cyclic AMP; CGRP is thought to work via a cyclic AMP-dependent pathway in muscle. In at least one respect, however, alpha 7 expression in muscle differs qualitatively from that of alpha 1: AChR-inducing activity (ARIA) increased alpha 1 mRNA levels in culture while slightly depressing alpha 7 mRNA levels. The regulatory pattern of alpha 7 expression in muscle may combine features of both alpha 7 expression in neurons and alpha 1 expression in muscle.
在发育过程中，几种神经元烟碱型乙酰胆碱受体（AChR）基因在鸡骨骼肌中表达。其中表达量最为丰富的一种是α7，它产生的一种蛋白质能够结合α-银环蛇毒素，并且在物理性质上与含有α1基因产物的肌肉AChR不同。我们在此表明，肌肉中含α7的受体在药理学上与神经元中含α7的AChR无法区分。此外，用亚基特异性肌肉抗体进行的免疫分析表明，肌肉中含α7的受体缺乏β1和δ肌肉AChR基因产物，就像它缺乏α1一样。测量α7 mRNA水平的核糖核酸酶保护实验表明，α1和α7基因在该组织中可能部分受到相似类型的调控。对刚孵出的小鸡腿部肌肉进行手术去神经支配，8天后α7 mRNA出现了小幅度的短暂增加，而α1转录本的数量则出现了大幅度的持续增加。同样，用河豚毒素处理肌管培养物导致α7转录本水平适度增加，而α1则大幅增加。降钙素基因相关肽（CGRP）与用8-溴环磷酸腺苷处理一样，使肌管培养物中的两种转录本均等量增加；人们认为CGRP在肌肉中通过环磷酸腺苷依赖性途径发挥作用。然而，在至少一个方面，肌肉中α7的表达在性质上与α1不同：AChR诱导活性（ARIA）增加了培养物中α1 mRNA的水平，同时略微降低了α7 mRNA的水平。肌肉中α7表达的调控模式可能兼具神经元中α7表达和肌肉中α1表达的特征。
