Craniofacial Muscles

220 A. Sokoloff and T. Burkholder
Fig. 12.5 Myosin heavy chain (MyHC) mRNA pro fi les for anterior tongue body muscles in
human, rhesus macaque, and rat determined by quantitative PCR (Rahnert et al. 2010 ; S. Karger
AG, Basel; used with permission). ( a ) Conventional and prominently expressed isoforms.
( b ) Developmental and unconventional isoforms, eo: extraocular muscle speci fi c; beta: beta cardiac;
alpha: alpha cardiac; emb: embryonic; neo: neonatal; st: slow tonic
cranial mesoderm and undergo differentiation via a Tbx1 or Pitx2 pathway (Kelly et al.
2004 ; see Chap. 2 ). Expression of unconventional MyHC isoforms (MyHCalphacardiac,
MyHCextraocular, MyHCmasticatory and MyHCslow tonic) is largely
restricted to these branchial arch muscles and the extraocular muscles, and the Tbx1
and Pitx2 pathway may be less effective in silencing their expression .
12.5.2 MyHC Composition of Tongue Muscles
Quantitative PCR, separation SDS-polyacrylamide gel electrophoresis (SDS-PAGE),
western blot, and immunohistochemistry (IHC) demonstrate that adult tongue muscles
of the mouse, rat, macaque, and human consist almost entirely of MyHCI,
MyHCIIA, MyHCIIX, and MyHCIIB. By PCR, only limited mRNA (0.1–0.8% total
mRNA) of MyHCembryonic and MyHCneo is detected in anterior tongue body
muscles of the rat, macaque, and human with the exception of MyHCalpha-cardiac
in the human (5%) and MyHCeom in the macaque (3.7%) (Rahnert et al. 2010 )
(Fig. 12.5 ). The developmental and additional MyHC proteins are not visualized in
tongue muscles of the adult mouse, rat, and human by SDS-PAGE (d’Albis et al.
1990 ; Agbulut et al. 2003 ; Granberg et al. 2010 ; Daugherty et al. 2012 ) .
MyHC phenotype prevalence by IHC has been studied most extensively in
humans. In human extrinsic muscles, phenotype prevalence is generally ordered
MyHCIIA > MyHCI > MyHCI-IIX with limited MyHCI-IIA and minimal MyHCIIX
(Sokoloff et al. 2010 ) . Predominance of MyHCIIA and MyHCI with minimal
MyHCIIX has also been reported in human intrinsic tongue muscles (Granberg
et al. 2010 ) . These studies however, suggest differences between extrinsic and
intrinsic muscles with respect to the presence of phenotype MyHCI-IIX (in human
extrinsic but not intrinsic muscles) and phenotype MyHCIIA-IIX (in human intrinsic
muscles but not GG (Daugherty et al. 2012 ) . MyHC expression is related to the
pattern of nerve activation (Ausoni et al. 1990 ; Pette 2001 ; Schiaf fi no et al. 2007 ),