title: Abundant expression of myosin heavy-chain IIB RNA in a subset of human masseter muscle fibres.
abstract: 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.
authors.affiliation: Department of Orthodontics, School of Dental Medicine, University of Pittsburgh, 3501 Terrace Street, Pittsburgh, PA 15261, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Horton
authors.forename: C A
authors.initials: CA
authors.lastname: Brandon
authors.forename: T J
authors.initials: TJ
authors.lastname: Morris
authors.forename: T W
authors.initials: TW
authors.lastname: Braun
authors.forename: K M
authors.initials: KM
authors.lastname: Yaw
authors.forename: J J
authors.initials: JJ
authors.lastname: Sciote
mesh_terms: D000009:Abdominal Muscles / Q000378:metabolism / Q000648:ultrastructure; D000251:Adenosine Triphosphatases; D000293:Adolescent; D000328:Adult; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D015870:Gene Expression; D006801:Humans; D015151:Immunoblotting; D017403:In Situ Hybridization; D008297:Male; D008406:Masseter Muscle / Q000378:metabolism* / Q000648:ultrastructure; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000648:ultrastructure; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000378:metabolism / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000032:analysis* / Q000235:genetics; D024461:Myosin Type I / Q000032:analysis / Q000235:genetics; D024462:Myosin Type II / Q000032:analysis / Q000235:genetics; D024507:Nonmuscle Myosin Type IIA / Q000032:analysis / Q000235:genetics; D024501:Nonmuscle Myosin Type IIB / Q000032:analysis* / Q000235:genetics; D010641:Phenotype; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics; D015347:RNA Probes; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics
chemical_list: D020033:Protein Isoforms; D015347:RNA Probes; D012333:RNA, Messenger; D000251:Adenosine Triphosphatases; D024461:Myosin Type I; D024462:Myosin Type II; D024507:Nonmuscle Myosin Type IIA; D024501:Nonmuscle Myosin Type IIB; C103815:nonmuscle myosin type IIB heavy chain; D018995:Myosin Heavy Chains