Myosin isoform expression and MAFbx mRNA levels in hibernating golden-mantled ground squirrels (Spermophilus lateralis)

Physiol Biochem Zool. Jul-Aug 2004;77(4):582-93. doi: 10.1086/421753.


Hibernating mammals present many unexplored opportunities for the study of muscle biology. The hindlimb muscles of a small rodent hibernator (Spermophilus lateralis) atrophy slightly during months of torpor, representing a reduction in the disuse atrophy commonly seen in other mammalian models. How torpor affects contractile protein expression is unclear; therefore, we examined the myosin heavy-chain (MHC) isoform profile of ground squirrel skeletal muscle before and after hibernation. Immunoblotting was performed first to identify the MHC isoforms expressed in this species. Relative percentages of MHC isoforms in individual muscles were then measured using SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). The soleus and diaphragm did not display differences in isoforms following hibernation, but we found minor fast-to-slow isoform shifts in MHC protein in the gastrocnemius and plantaris. These subtle changes are contrary to those predicted by other models of inactivity but may reflect the requirement for shivering thermogenesis during arousals from torpor. We also measured mRNA expression of the Muscle Atrophy F-box (MAFbx), a ubiquitin ligase important in proteasome-mediated proteolysis. Expression was elevated in the hibernating gastrocnemius and the plantaris but was not associated with atrophy. Skeletal muscle from hibernators displays unusual plasticity, which may be a combined result of the intense activity during arousals and the reduction of metabolism during torpor.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • DNA Primers
  • Electrophoresis, Polyacrylamide Gel
  • Hibernation / physiology*
  • Hindlimb / metabolism
  • Immunoblotting
  • Muscle Proteins / metabolism*
  • Myosin Heavy Chains / metabolism*
  • Protein Isoforms / metabolism
  • RNA, Messenger / metabolism*
  • SKP Cullin F-Box Protein Ligases / metabolism*
  • Sciuridae / metabolism*
  • Sciuridae / physiology


  • DNA Primers
  • Muscle Proteins
  • Protein Isoforms
  • RNA, Messenger
  • SKP Cullin F-Box Protein Ligases
  • Myosin Heavy Chains