Myosin isoform fiber type and fiber size in the tail of the Virginia opossum (Didelphis virginiana)

Anat Rec (Hoboken). 2013 Jan;296(1):96-107. doi: 10.1002/ar.22614. Epub 2012 Nov 14.


Muscle fiber type is a well studied property in limb muscles, however, much less is understood about myosin heavy chain (MHC) isoform expression in caudal muscles of mammalian tails. Didelphid marsupials are an interesting lineage in this context as all species have prehensile tails, but show a range of tail-function depending on either their arboreal or terrestrial locomotor habits. Differences in prehensility suggest that MHC isoform fiber types may also be different, in that terrestrial opossums may have a large distribution of oxidative fibers for object carrying tasks instead of faster, glycolytic fiber types expected in mammals with long tails. To test this hypothesis, MHC isoform fiber type and their regional distribution (proximal/transitional/distal) were determined in the tail of the Virginia opossum (Didelphis virginiana). Fiber types were determined by a combination of myosin-ATPase histochemistry, immunohistochemistry, and SDS-PAGE. Results indicate a predominance of the fast MHC-2A and -2X isoforms in each region of the tail. The presence of two fast isoforms, in addition to the slow MHC-1 isoform, was confirmed by SDS-PAGE analysis. The overall MHC isoform fiber type distribution for the tail was: 25% MHC-1, 71% MHC-2A/X hybrid, and 4% MHC-1/2A hybrid. Oxidative MHC-2A/X isoform fibers were found to be relatively large in cross-section compared to slow, oxidative MHC-1 and MHC-1/2A hybrid fibers. A large percentage of fast MHC-2A/X hybrids fibers may be suggestive of an evolutionary transition in MHC isoform distribution (fast-to-slow fiber type) in the tail musculature of an opossum with primarily a terrestrial locomotor habit and adaptive tail-function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Didelphis / anatomy & histology*
  • Didelphis / metabolism*
  • Female
  • Locomotion
  • Male
  • Muscle Fibers, Skeletal / chemistry
  • Muscle Fibers, Skeletal / metabolism
  • Muscle Fibers, Skeletal / ultrastructure
  • Myosin Heavy Chains / analysis
  • Myosin Heavy Chains / metabolism*
  • Myosin Heavy Chains / ultrastructure
  • Protein Isoforms / analysis
  • Protein Isoforms / metabolism
  • Protein Isoforms / ultrastructure
  • Tail / anatomy & histology*
  • Tail / metabolism*


  • Protein Isoforms
  • Myosin Heavy Chains