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.

Muscle contractile properties as an explanation of the higher mean power output in marmosets than humans during jumping

“…An intriguing question is why type IIB MHC is abundantly expressed in leg muscles of marmosets but not in adult human leg muscles (Smerdu et al, 1994;Ennion et al, 1995;Pereira Sant'Ana et al, 1997;Wu et al, 2000;Horton et al, 2001). Type IIB MHC mRNA expression in human skeletal muscle occurs only at very low levels; IIB MHC mRNA expression is upregulated only in cases of severe muscle degeneration/regeneration, but protein levels remain undetectable (Harrison et al, 2011).…”

A Novel Intronic Single Nucleotide Polymorphism in the Myosin heavy polypeptide 4 Gene Is Responsible for the Mini-Muscle Phenotype Characterized by Major Reduction in Hind-Limb Muscle Mass in Mice

“…Although Myh4 (MyHC IIb) is an essential motor protein in rats and mice, in humans the messenger RNA has been found only in masseter muscles (e.g., Horton et al 2001). However, functional equivalents have been identified in humans (Myh1), and a patient with a mutation in Myh7 had a phenotypically similar myopathy to the Myh4 arl / Myh4 arl mouse (Tasca et al 2012).…”

Differential Expression of Equine Myosin Heavy-chain mRNA and Protein Isoforms in a Limb Muscle

“…After several rinses in 1 ϫ PBS and refixation for 2 min in 4% paraformaldehyde followed by several washes in 1 ϫ PBS, the sections were completely dehydrated before hybridization. Procedures for hybridization with digoxigenin-labeled riboprobes were adapted from Horton et al (2001), with some modifications.…”