title: Heterogeneity of alpha-cardiac myosin heavy chains in a small marsupial, Antechinus flavipes, and the effect of hypothyroidism on its ventricular myosins.
abstract: The effect of drug-induced hypothyroidism on ventricular myosin gene expression was explored in a small marsupial, Antechinus flavipes. Pyrophosphate gel electrophoresis, SDS-PAGE and western blotting were used to analyse changes in native myosin isoforms and myosin heavy chains (MyHCs) in response to hypothyroidism. In some animals, five instead of the normal three native myosin components were found: V(1a), V(1b),V(1c), V(2) and V(3), in order of decreasing mobility. In western blots, V(1a), V(1b), and V(1c) reacted with anti-alpha-MyHC antibody, but not with anti-beta-MyHC, whereas V(2) and V(3) reacted with anti-beta-MyHC antibody. SDS-PAGE of the unusual ventricular myosins revealed three MyHC isoforms, two of which bound anti-alpha-MyHC antibody while the third bound anti-beta-MyHC antibody. We conclude that V(1a), V(1b), V(1c) are triplets arising from the dimerization of two distinct alpha-MyHC isoforms. Hypothyroidism, verified by metabolic studies, decreased alpha-MyHC content significantly (t-test, P < 0.001) from 91.6 +/- 5.9% (SEM, n = 4) in control animals to 67.2 +/- 5.7% (SEM, n = 4) in hypothyroid animals, with a concomitant increase in beta-MyHC content. We conclude that in adult marsupials, ventricular myosins are also responsive to changes in the thyroid state as found in eutherians, and suggest that evolution of the molecular mechanisms underlying this thyroid responsiveness predate the divergence of marsupials and eutherians.
authors.affiliation: Discipline of Physiology and the Bosch Institute, School of Medical Sciences, Faculty of Medicine, The University of Sydney, Bldg F13, Sydney, NSW, 2006, Australia. joeh@physiol.usyd.edu.au
authors.forename: Joseph F Y
authors.initials: JF
authors.lastname: Hoh
authors.forename: Kerry W
authors.initials: KW
authors.lastname: Withers
authors.forename: Wendy W H
authors.initials: WW
authors.lastname: Zhong
mesh_terms: D000818:Animals; D013956:Antithyroid Agents / Q000009:adverse effects; D001481:Basal Metabolism / Q000502:physiology; D024722:Cardiac Myosins / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism*; D007037:Hypothyroidism / Q000139:chemically induced / Q000378:metabolism* / Q000662:veterinary; D008394:Marsupialia / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism
chemical_list: D013956:Antithyroid Agents; D020033:Protein Isoforms; D024722:Cardiac Myosins; D018995:Myosin Heavy Chains