title: Regulation of myosin synthesis by thyroid hormone: relative change in the alpha- and beta-myosin heavy chain mRNA levels in rabbit heart.
abstract: The expression of mRNAs for two cardiac myosins has been examined in the ventricles of hypo- and hyperthyroid rabbits by means of cloned cDNA sequences corresponding to the mRNAs of the alpha- and beta-myosin heavy chains (HCs). The temporal change in the relative levels of the alpha- and beta-HC mRNAs after 3,5,3'-triiodothyronine (T3) treatment of hypothyroid rabbits was determined by nuclease S1 mapping. In the hypothyroid state, only HC beta-mRNA was expressed in the ventricles. The HC alpha-mRNA was first detectable 4 h after administration of T3 (200 micrograms/kg) to hypothyroid animals. By 12 h, HC alpha-mRNA represented 20% of total myosin mRNA, increasing to 50% by 24 h and to about 90% by 72 h. The relationship between the relative mRNA levels and relative synthesis rates of the myosin HCs was evaluated in 5-6-week-old normal and thyrotoxic rabbits. Myosin synthesis rates were determined by labeling of protein in vivo with [3H]leucine. The V1 (HC alpha) and V3 (HC beta) isomyosins were separated by affinity chromatography with monoclonal antibodies, and the HCs were isolated electrophoretically. In a normal euthyroid group of animals and in animals 12 and 24 h after administration of 200 micrograms of 3,5,3',5'-tetraiodothyronine/kg, the relative mRNA levels and relative synthesis rates of the alpha- and beta-HCs were not significantly different. Our results show that, first, thyroid hormone causes a rapid accumulation of HC alpha-mRNA and loss of HC beta-mRNA and, second, in normal and thyrotoxic rabbits, the relative synthesis rates of HC alpha and HC beta reflect the relative abundance of the alpha- and beta-HC mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000032:analysis; D004262:DNA Restriction Enzymes; D007037:Hypothyroidism / Q000378:metabolism; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009218:Myosins / Q000235:genetics*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D011817:Rabbits
chemical_list: D012333:RNA, Messenger; D004247:DNA; D004262:DNA Restriction Enzymes; D009218:Myosins