title: Rescue of high expression beta-tropomyosin transgenic mice by 5-propyl-2-thiouracil. Regulating the alpha-myosin heavy chain promoter.
abstract: Tropomyosin is an essential component of the sarcomeric thin filament in striated muscle that participates in the regulation of muscle contraction through Ca(2+)-mediated activation. The two predominant tropomyosin isoforms expressed in striated muscle are alpha- and beta-tropomyosin, which exhibit an 86% amino acid identity between themselves. Previous studies by our laboratory utilized a transgenic mouse system to overexpress beta-tropomyosin in the heart to address the functional differences between these two tropomyosin isoforms. Interestingly, when a high percentage of beta-tropomyosin replaces alpha-tropomyosin in the hearts of transgenic mice, the mice die due to severe cardiac abnormalities. In this study, we have rescued these high expression beta-tropomyosin mice by turning off the alpha-myosin heavy chain promoter, which is driving the beta-tropomyosin transgene. This down-regulation of the alpha-myosin heavy chain promoter was accomplished by the administration of 5-propyl-2-thiouracil, which disrupts thyroid hormone synthesis and inhibits promoter activity through thyroid regulatory elements located in the 5'-flanking region of the promoter. Results show that as beta-tropomyosin expression is down-regulated, alpha-tropomyosin expression is increased. Also, alpha- and beta-myosin heavy chain expression is modified in response to the changes in thyroid hormone expression. Morphological analysis of these rescued mice show a moderate pathological phenotype, characterized by atrial myocytolysis; echocardiographic analyses demonstrate altered ventricular functions, such as peak filling rates and left ventricular fractional shortening. This is the first report demonstrating that transcriptional regulatory elements located within the alpha-myosin heavy chain promoter can be manipulated to rescue potentially lethal phenotypes, such as high expression beta-tropomyosin transgenic mice.
authors.affiliation: Department of Molecular Genetics, Division of Cardiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524, USA.
authors.forename: R
authors.initials: R
authors.lastname: Prabhakar
authors.forename: G P
authors.initials: GP
authors.lastname: Boivin
authors.forename: B
authors.initials: B
authors.lastname: Hoit
authors.forename: D F
authors.initials: DF
authors.lastname: Wieczorek
mesh_terms: D000818:Animals; D015536:Down-Regulation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects*; D006325:Heart Atria / Q000473:pathology; D006330:Heart Defects, Congenital / Q000235:genetics; D006334:Heart Function Tests; D051379:Mice; D008822:Mice, Transgenic; D018995:Myosin Heavy Chains / Q000235:genetics; D009218:Myosins / Q000235:genetics; D009929:Organ Size; D010641:Phenotype; D011401:Promoter Regions, Genetic; D011441:Propylthiouracil / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D014335:Tropomyosin / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D014335:Tropomyosin; D011441:Propylthiouracil; D018995:Myosin Heavy Chains; D009218:Myosins