Evidence for transcriptional regulation of the urea transporter in the gill of the Gulf toadfish, Opsanus beta

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology Vol. 160; no. 2; pp. 72 - 80
• Main Authors: Rodela, Tamara M., Esbaugh, Andrew J., McDonald, M. Danielle, Gilmour, Kathleen M., Walsh, Patrick J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.10.2011
• Subjects: Animals; Antimetabolites - pharmacology; Base Sequence; Batrachoidiformes - physiology; Cortisol; excretion; gene expression; gene expression regulation; Gene Expression Regulation - drug effects; genes; gills; Gills - metabolism; Glucocorticoid receptor; glucocorticoid receptors; Glucocorticoid response element (GRE); Hormone Antagonists - pharmacology; Hydrocortisone - blood; luciferase; Marine; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; messenger RNA; Metyrapone; Metyrapone - pharmacology; Mifepristone - pharmacology; Mineralocorticoid receptor; Molecular Sequence Data; Opsanus beta; Phylogeny; promoter regions; Promoter Regions, Genetic; Receptors, Glucocorticoid - classification; Receptors, Glucocorticoid - genetics; Receptors, Glucocorticoid - metabolism; Spironolactone - pharmacology; Tissue Distribution; Toadfish urea transporter (tUT); transcription (genetics); Transcription, Genetic; transporters; urea; Urea - metabolism; Urea Transporters; Cortisol; Mineralocorticoid receptor; Glucocorticoid response element (GRE); Glucocorticoid receptor; Metyrapone; Toadfish urea transporter (tUT)
• ISSN: 1096-4959; 1879-1107
• DOI: 10.1016/j.cbpb.2011.06.004

Ureotelic Gulf toadfish ( Opsanus beta) do not excrete urea continuously; instead, urea is accumulated internally until a branchial urea transport mechanism is activated to facilitate the excretion of urea in distinct pulses. This unusual pulsatile urea excretion pattern is regulated, in part, by permissive declines in circulating cortisol concentrations. The current study examined toadfish urea transporter (tUT) and glucocorticoid receptor (GR) transcript levels in toadfish gill following chronic (days) and acute (hours) changes in corticosteroid activity. Experimentally lowering circulating cortisol did not significantly alter tUT mRNA abundance but increased GR mRNA. On an acute timescale, a 6.2-fold upregulation of tUT mRNA occurred 12 to 18 h following a urea pulse event with no change in GR mRNA. In silico analysis of an isolated 1.2 kb fragment, upstream promoter region of the tUT gene, revealed 6 putative glucocorticoid response element (GRE) half sites. In vivo reporter assays of the tUT promoter fragment demonstrated relative luciferase activity was enhanced 3.4- and 9.8-fold following exposure to moderate ( via a 48 h crowding stress) and high ( via infusion for 48 h) cortisol. We conclude that a GRE-mediated upregulation of mRNA may be required to maintain tUT activity by offsetting post-transcriptional and/or post-translational changes that may be associated with chronically elevated plasma cortisol.