There is a paucity of information regarding the anatomy and muscle fiber phenotype of the masseter. The objective of this study was to characterize the distribution of each myosin heavychain (MyHC) isoform within different anatomical regions of male and female mouse masseters. Masseters from male and female CD-1 mice (2-4 months old) were examined for description of the anatomical partitioning of muscle fibers and endplate distribution. The spatial distribution of MyHC isoforms—embryonic, neonatal, slow, α cardiac, IIa, and IIb—was determined within the defined masseter partitions by means of Western blot analysis and immunofluorescent localization. Types IIa, IIx, and lIb were the predominant MyHC isoforms observed. Distinct differences in the spatial distribution of these MyHC isoforms were found between muscle regions and varied between sexes. The regionalization of muscle fiber types in the mouse masseter is consistent with the functional compartmentalization of the masseter observed in other species.
Acakpo-SatchiviL.J., EdelmannW., SartoriusC., LuB.D., WahrP.A., WatkinsS.C.. (1997). Growth and muscle defects in mice lacking adult myosin heavy chain genes.J Cell Biol139: 1219–1229.
2.
AndersenJ.L., Gruschy-KnudsenT., SandriC., LarssonL., SchiaffinoS. (1999). Bed rest increases the amount of mismatched fibers in human skeletal muscle.J Appl Physiol86: 455–460.
3.
AusoniS., GorzaL., SchiaffinoS., GundersenK., LomoT. (1990). Expression of myosin heavy chain isoforms in stimulated fast and slow rat muscles.J Neurosci10: 153–160.
4.
BredmanJ.J., WesselsA., WeijsW.A., KorfageJ.A., SoffersC.A., MoormanA.F. (1991). Demonstration of ‘cardiac-specific’ myosin heavy chain in masticatory muscles of human and rabbit.Histochem J23: 160–170.
5.
BredmanJ.J., WeijsW.A., KorfageJ.A., BrugmanP., MoormanA.F. (1992). Myosin heavy chain expression in rabbit masseter muscle during postnatal development.J Anat180: 263–274.
6.
d'AlbisA., JanmotC., BechetJ.J. (1986). Comparison of myosins from the masseter muscle of adult rat, mouse and guinea pig. Persistance of neonatal-type isoforms in the murine muscle.Eur J Biochem156: 291–296.
7.
EasonJ.M., SchwartzG.A., PavlathG.K., EnglishA.W. (2000). Sexually dimorphic expression of myosin heavy chains in the adult mouse masseter.J Appl Physiol89: 251–258.
8.
EnglishA.W., LetbetterW.D. (1982). A histochemical analysis of identified compartments of cat lateral gastrocnemius muscle.Anat Rec204: 123–130.
9.
EnglishA.W., CarrascoD.I., WidmerC.G. (1999a). Torques produced by different compartments of the rabbit masseter muscle.J Appl Biomech15: 348–360.
10.
EnglishA.W., EasonJ., SchwartzG., ShirleyA., CarrascoDI (1999b). Sexual dimorphism in the rabbit masseter muscle: myosin heavy chain composition of neuromuscular compartments.Cells Tissue Org164: 179–191.
11.
LuB.D., AllenD.L., LeinwandL.A., LyonsG.E. (1999). Spatial and temporal changes in myosin heavy chain gene expression in skeletal muscle development.Dev Biol216: 312–326.
12.
LyonsG.E., KellyA.M., RubinsteinN.A. (1986). Testosterone-induced changes in contractile protein isoforms in the sexually dimorphic temporalis muscle of the guinea pig.J Biol Chem261: 13278–13284.
13.
LyonsG.E., OntellM., CoxR., SassoonD., BuckinghamM. (1990). The expression of myosin genes in developing skeletal muscle in the mouse embryo.J Cell Biol111: 1465–1476.
14.
MonemiM., ErikssonP.O., DubailI., Butler-BrowneG.S., ThornellL.E. (1996). Fetal myosin heavy chain increases in human masseter muscle during aging.FEBS Lett386: 87–90.
PeukerH., ConjardA., PetteD. (1998). Alpha-cardiac-like myosin heavy chain as an intermediate between MHCIIa and MHCI beta in transforming rabbit muscle.Am J Physiol274: C595–C602.
17.
PrevostM.C., NelsonA.G., KellyK.P., HanD.H., ConleeR.K. (1995). Cocaine alters myosin isoform expression in the rat soleus.J Appl Physiol79: 514–517.
18.
ReiserP.J., MossR.L., GiulianG.G., GreaserM.L. (1985). Shortening velocity in single fibers from adult rabbit soleus muscles is correlated with myosin heavy chain composition.J Biol Chem260: 9077–9080.
19.
SartoriusC.A., LuB.D., Acakpo-SatchiviL., JacobsenR.P., ByrnesW.C., LeinwandL.A. (1998). Myosin heavy chains IIa and IId are functionally distinct in the mouse.J Cell Biol141: 943–953.
20.
SchiaffinoS. (1974). Histochemical enzyme profile of the masseter muscle in different mammalian species.Anat Rec180: 53–61.
21.
SchiaffinoS., GorzaL., SartoreS., SagginL., CarliM. (1986). Embryonic myosin heavy chain as a differentiation marker of developing human skeletal muscle and rhabdomyosarcoma.Exp Cell Res163: 211–220.
22.
SchiaffinoS., GorzaL., PittonG., SagginL., AusoniS., SartoreS.. (1988). Embryonic and neonatal myosin heavy chain in denervated and paralyzed rat skeletal muscle.Dev Biol127: 1–11.
23.
SchiaffinoS., GorzaL., SartoreS., SagginL., AusoniS., VianelloM.. (1989). Three myosin heavy chain isoforms in type 2 skeletal muscle fibres.J Muscle Res Cell Motil10: 197–205.
24.
SchumacherG.H., RehmerH. (1960). Morphologische und funktionelle untersuchungen an der kaumuskulatur von Oryctolagus und Lepus.Morph JP100: 678–705.
25.
Soussi-YanicostasN., BarbetJ.P., Laurent-WinterC., BartonP., Butler-BrowneG.S. (1990). Transition of myosin isozymes during development of human masseter muscle. Persistence of developmental isoforms during postnatal stage.Development108: 239–249.
26.
StevensL., GohlschB., MounierY., PetteD. (1999). Changes in myosin heavy chain mRNA and protein isoforms in single fibers of unloaded rat soleus muscle.FEBS Lett463: 15–18.
27.
TalmadgeR.J., RoyR.R. (1993). Electrophoretic separation of rat skeletal muscle myosin heavy-chain isoforms.J Appl Physiol75: 2337–2340.
