title: Tissue-specific regulation of thyroid hormone receptor mRNA isoforms and target gene proteins in domestic ducks.
abstract: Skeletal muscles are important target tissues for thyroid hormone action. The present study examines the influence of thyroid status on muscle growth and tissue-specific expression of thyroid receptor (TR) mRNA isoforms in a commercial strain of the domestic duck (Anas platyrhynchos). Four groups (n=5) of 1-week-old ducklings were rendered either hypothyroid by treatment with methimazole (6 mg 100 g(-1) body mass or 12 mg 100 g(-1) body mass), or hyperthyroid by treatment with methimazole (6 mg 100 g(-1) body mass) in combination with thyroid hormones (5 microg thyroxine (T(4)) and tri-iodothyronine (T(3)) 100 g(-1) body mass or 10 microg T(4) and T(3) 100 g(-1) body mass). Serum and tissue samples (cardiac, pectoralis and semimembranosus leg muscle, liver, pituitary and cerebral cortex) were collected from these four groups, and from a group of untreated controls, at 8 weeks of age. Development of duckling morphology was retarded in methimazole-treated birds compared with that in euthyroid controls, as evidenced by differences in skeletal dimensions, primary feather length, and body and muscle masses. Body mass was lower by 18%, and relative masses of cardiac and pectoralis muscles were lower by 28% and 32% respectively. Heterologous oligonucleotides for TR alpha, TR beta 0, TR beta2 and the housekeeping gene beta-actin were derived from chicken sequences. RT-PCR showed that TR alpha mRNA was expressed in all tissues but was not significantly affected by any of the experimental treatments. TR beta 0 mRNA expression was significantly lower in the leg muscles of ducklings treated with 12 mg methimazole 100 g(-1) body mass (0.109+/-0.047 TR:beta-actin ratio, P<0.05) compared with that in euthyroid controls (0.380+/-0.202), but was unaltered in the pectoralis and cardiac muscles. Expression of TR beta 0 mRNA was significantly higher in pectoralis (by 3.5-fold, P<0. 05), cardiac (by 4.2-fold, P=0.003) and leg (by 4.0-fold, P<0.001) muscles of ducklings treated with thyroid hormones compared with those in euthyroid controls (0.098+/-0.019, 0.822+/-0.297 and 0. 38+/-0.202 TR:beta-actin respectively). Only the pituitary gland expressed significant levels of TR beta 2 mRNA.
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. c.bishop@bangor.ac.uk
authors.forename: C M
authors.initials: CM
authors.lastname: Bishop
authors.forename: C J
authors.initials: CJ
authors.lastname: McCabe
authors.forename: N J
authors.initials: NJ
authors.lastname: Gittoes
authors.forename: P J
authors.initials: PJ
authors.lastname: Butler
authors.forename: J A
authors.initials: JA
authors.lastname: Franklyn
mesh_terms: D000818:Animals; D001483:Base Sequence; D002645:Chickens / Q000235:genetics; D004372:Ducks / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006980:Hyperthyroidism / Q000378:metabolism / Q000473:pathology; D007037:Hypothyroidism / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000473:pathology; D009206:Myocardium / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D011988:Receptors, Thyroid Hormone / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D013974:Thyroxine