Functional significance of a truncated thyroid receptor subtype lacking a hormone-binding domain in goldfish.
Thyroid hormones are important mediators of growth and development in vertebrates and act by binding to a specific family of thyroid receptors (TRs). The TRs belong to the nuclear receptor superfamily, with two conserved regions, a DNA binding domain and a ligand binding domain (LBD). We recently demonstrated the presence of four TR subtypes in goldfish, two with complete DNA binding domains and LBDs (TRalpha-1 and TRbeta) and two novel forms including a transcript resembling TRalpha with variation in the LBD as well as a TRalpha-truncated (TRalpha-t) form lacking a LBD. To study the functional significance of TR subtypes, we first investigated the regulation of hepatic goldfish deiodinase type 3 (D3) by T3 and validated a bioassay in which D3 gene expression is up-regulated significantly in vivo and in vitro. Using short interfering RNA, TRalpha-1, TRbeta, or TRalpha-t was specifically knocked down and thyroid hormone-induced D3 gene expression was measured. Short interfering RNA against TRalpha-1 or TRbeta reduced the T3 induction of deiodinase gene expression to 50% or less than 25% of control (T3 treated) cells, respectively. Knocking down TRalpha-t alone, however, increased D3 expression 500-fold supporting the hypothesis that TRalpha-t plays a modulatory role in thyroid hormone-induced gene expression. Our results provide important insight into thyroid receptor biology in goldfish and a framework for the better understanding of thyroid receptor function in all vertebrates.
Nelson
Erik R
ER
Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
Habibi
Hamid R
HR
D000818:Animals; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018389:Codon, Nonsense / Q000235:genetics; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006054:Goldfish / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D006655:Histone Deacetylases / Q000502:physiology; D007453:Iodide Peroxidase / Q000235:genetics; D008297:Male; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D011988:Receptors, Thyroid Hormone / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014284:Triiodothyronine / Q000378:metabolism* / Q000494:pharmacology
D018389:Codon, Nonsense; D020033:Protein Isoforms; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D007453:Iodide Peroxidase; D006655:Histone Deacetylases