Specialized cranial muscles: How different are they from limb and abdominal muscles?
Specialized cranial muscles: How different are they from limb and abdominal muscles?
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DOI：
10.1159/000070576
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发表时间：
2003-01-01
影响因子：
2.7
通讯作者：
Link, J
中科院分区：
文献类型：
--
作者：
Sciote, JJ;Horton, MJ;Link, J
哺乳动物骨骼肌纤维可根据其所含肌球蛋白（主要运动蛋白）的重链（MyHC）和轻链（MyLC）同种型分为功能类型。大多数人类骨骼肌含有纤维类型和肌球蛋白亚型I、IIA和IIX。人类眼外肌和下颌闭合肌中的一些高度特化的肌纤维表达新的肌球蛋白或功能意义未知的亚型的不寻常组合。喉外肌可表达眼外肌型肌球蛋白（MyHC）亚型，用于快速收缩，表达强直肌型肌球蛋白（MyHC）亚型，用于缓慢强直收缩。在下颌闭合肌中，纤维表型和肌球蛋白表达的特点是非常不寻常的。大多数食肉动物和灵长类动物的下颌闭合肌肉具有IIM型或“II型咀嚼肌”MyHC的组织特异性表达。然而，人类的下颌闭合肌不含IN肌球蛋白。相反，除了I型、IIA型和IN型肌球蛋白外，它们还表达发育中心肌的典型肌球蛋白，并且它们的许多纤维是杂交体，表达两种或更多种同种型。纤维形态也是不寻常的，因为II型纤维的直径大多小于I型。通过结合生理学和生物化学技术，可以确定单个骨骼肌纤维的无负荷缩短的最大速度（V-o），并随后确定肌球蛋白同种型的类型和量。当分析时，一些喉纤维缩短的速度比肢体和腹肌的II型纤维快得多。然而咬肌中的一些I型纤维显示出相反的趋势，其速度比肢体肌肉的I型纤维慢10倍。这些不寻常的缩短速度最有可能调节喉纤维中的MyHC亚型和咬肌中的MyLC亚型。对于下颌闭合肌肉，这一发现代表了轻链对人体肌肉动力学进行生理调节的首例。总之，这些结果表明，与其他骨骼肌相比，颅肌具有更广泛的收缩蛋白表达和功能。mRNA逆转录和聚合酶链反应扩增的分子技术已被应用于从肢体肌肉中分离的单纤维的分型，成功地鉴定了纯I型、IIA型和IIX型以及混合型I/IIA和IIA/IIX型纤维。这表明了未来研究下颌闭合和喉肌基因表达调控的潜力，这些肌肉具有多种复杂的纤维类型，适合它们在体内的作用。版权所有（C）2003 S. Karger AG，巴塞尔。
Mammalian skeletal muscle fibers can be classified into functional types by the heavy chain (MyHC) and light chain (MyLC) isoforms of myosin (the primary motor protein) that they contain. Most human skeletal muscle contains fiber types and myosin isoforms I, IIA and IIX Some highly specialized muscle fibers in human extraocular and jaw-closing muscles express either novel myosins or unusual combinations of isoforms of unknown functional significance. Extrinsic laryngeal muscles may express the extraocular MyHC isoform for rapid contraction and a tonic MyHC isoform for slow tonic contractions. In jaw-closing muscles, fiber phenotypes and myosin expression have been characterized as highly unusual. The jaw-closing muscles of most carnivores and primates have tissue-specific expression of the type IIM or 'type II masticatory' MyHC. Human jaw-closing muscles, however, do not contain IN myosin. Rather, they express myosins typical of developing or cardiac muscle in addition to type I, IIA and IN myosins, and many of their fibers are hybrids, expressing two or more isoforms. Fiber morphology is also unusual in that the type II fibers are mostly of smaller diameter than type I. By combining physiological and biochemical techniques it is possible to determine the maximum velocity of unloaded shortening (V-o) of an individual skeletal muscle fiber and subsequently determine the type and amount of myosin isoform. When analyzed, some laryngeal fibers shorten at much faster rates than type II fibers from limb and abdominal muscle. Yet some type I fibers in masseter show an opposite trend towards speeds 10-fold slower than type I fibers of limb muscle. These unusual shortening velocities are most probably regulated by MyHC isoforms in laryngeal fibers and by MyLC isoforms in masseter. For the jaw-closing muscles, this finding represents the first case in human muscle of physiological regulation of kinetics by light chains. Together, these results demonstrate that, compared to other skeletal muscles, cranial muscles have a wider repertoire of contractile protein expression and function. Molecular techniques for reverse transcription of mRNA and amplification by polymerase chain reaction have been applied to typing of single fibers isolated from limb muscles, successfully identifying pure type I, IIA and IIX and hybrid type I/IIA and IIA/IIX fibers. This demonstrates the potential for future studies of the regulation of gene expression in jaw-closing and laryngeal muscles, which have such a variety of complex fiber types fitting them for their roles in vivo. Copyright (C) 2003 S. Karger AG, Basel.