Limb muscles of eutherian (placental) mammals express a slow and three fast isoforms of myosin heavy chain (MyHC), but little is known about marsupial MyHCs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of limb MyHCs from seven marsupial species, spanning two orders, revealed four components, each of which specifically cross-reacted in Western blots with a monoclonal antibody (mAb) against a corresponding eutherian MyHC. For all seven species, the relative mobility of the band identified by each mAb matched that in the rat, suggesting that the four are homologous to eutherian slow, 2B, 2X and 2A MyHCs, respectively, in the order of decreasing mobility. Immunohistochemical analysis of fast marsupial limb muscles identified four different fiber populations whose relative fiber size spectra IIIA

Keywords:fiber type;muscle;marsupial;myosin heavy chain;sodium dodecyl sulfate-polyacrylamide gel electrophoresis