Horton M J, Brandon C A, Morris T J, Braun T W, Yaw K M, Sciote J J
Department of Orthodontics, School of Dental Medicine, University of Pittsburgh, 3501 Terrace Street, Pittsburgh, PA 15261, USA.
Arch Oral Biol. 2001 Nov;46(11):1039-50. doi: 10.1016/s0003-9969(01)00066-8.
Type IIB fast fibres are typically demonstrated in human skeletal muscle by histochemical staining for the ATPase activity of myosin heavy-chain (MyHC) isoforms. However, the monoclonal antibody specific for the mammalian IIB isoform does not detect MyHC IIB protein in man and MyHC IIX RNA is found in histochemically identified IIB fibres, suggesting that the IIB protein isoform may not be present in man; if this is not so, jaw-closing muscles, which express a diversity of isoforms, are likely candidates for their presence. ATPase histochemistry, immunohistochemistry polyacrylamide gel electrophoresis and in situ hybridization, which included a MyHC IIB-specific mRNA riboprobe, were used to compare the composition and RNA expression of MyHC isoforms in a human jaw-closing muscle, the masseter, an upper limb muscle, the triceps, an abdominal muscle, the external oblique, and a lower limb muscle, the gastrocnemius. The external oblique contained a mixture of histochemically defined type I, IIA and IIB fibres distributed in a mosaic pattern, while the triceps and gastrocnemius contained only type I and IIA fibres. Typical of limb muscle fibres, the MyHC I-specific mRNA probes hybridized with histochemically defined type I fibres, the IIA-specific probes with type IIA fibres and the IIX-specific probes with type IIB fibres. The MyHC IIB mRNA probe hybridized only with a few histochemically defined type I fibres in the sample from the external oblique; in addition to this IIB message, these fibres also expressed RNAs for MyHC I, IIA and IIX. MyHC IIB RNA was abundantly expressed in histochemical and immunohistochemical type IIA fibres of the masseter, together with transcripts for IIA and in some cases IIX. No MyHC IIB protein was detected in fibres and extracts of either the external oblique or masseter by immunohistochemistry, immunoblotting and electrophoresis. Thus, IIB RNA, but not protein, was found in the fibres of two different human skeletal muscles. It is believed this is the first report of the substantial expression of IIB mRNA in man as demonstrated in a subset of masseter fibres, but rarely in limb muscle, and in only a few fibres of the external oblique. These findings provide further evidence for the complexity of myosin gene expression, especially in jaw-closing muscles.
通过对肌球蛋白重链（MyHC）同工型的ATP酶活性进行组织化学染色，通常可在人类骨骼肌中显示出IIB型快肌纤维。然而，针对哺乳动物IIB同工型的单克隆抗体在人类中无法检测到MyHC IIB蛋白，并且在组织化学鉴定的IIB纤维中发现了MyHC IIX RNA，这表明IIB蛋白同工型可能在人类中不存在；如果并非如此，那么表达多种同工型的咬肌很可能存在这种同工型。采用ATP酶组织化学、免疫组织化学、聚丙烯酰胺凝胶电泳和原位杂交（其中包括MyHC IIB特异性mRNA核糖探针）来比较人类咬肌（咀嚼肌）、上肢肌肉肱三头肌、腹部肌肉腹外斜肌和下肢肌肉腓肠肌中MyHC同工型的组成和RNA表达。腹外斜肌包含组织化学定义的I型、IIA型和IIB型纤维的混合物，呈镶嵌状分布，而肱三头肌和腓肠肌仅包含I型和IIA型纤维。典型的肢体肌纤维中，MyHC I特异性mRNA探针与组织化学定义的I型纤维杂交，IIA特异性探针与IIA型纤维杂交，IIX特异性探针与IIB型纤维杂交。MyHC IIB mRNA探针仅与腹外斜肌样本中少数组织化学定义的I型纤维杂交；除了这种IIB信息外，这些纤维还表达MyHC I、IIA和IIX的RNA。MyHC IIB RNA在咬肌的组织化学和免疫组织化学IIA型纤维中大量表达，同时还有IIA的转录本，在某些情况下还有IIX的转录本。通过免疫组织化学、免疫印迹和电泳，在腹外斜肌或咬肌的纤维和提取物中均未检测到MyHC IIB蛋白。因此，在两种不同的人类骨骼肌纤维中发现了IIB RNA，但未发现蛋白。据信，这是首次报道IIB mRNA在人类中的大量表达，如在咬肌纤维的一个亚群中所示，但在肢体肌肉中很少见，仅在腹外斜肌的少数纤维中出现。这些发现为肌球蛋白基因表达的复杂性提供了进一步的证据，尤其是在咀嚼肌中。
