Tissue-specific thyroid hormone regulation of gene transcripts encoding iodothyronine deiodinases and thyroid hormone receptors in striped parrotfish (Scarus iseri)

Abstract

In fish as in other vertebrates, the diverse functions of thyroid hormones are mediated at the peripheral tissue level through iodothyronine deiodinase (dio) enzymes and thyroid hormone receptor (tr) proteins. In this study, we examined thyroid hormone regulation of mRNAs encoding the three deiodinases dio1, dio2 and dio3 - as well as three thyroid hormone receptors trαA, trαB and trβ - in initial phase striped parrotfish (Scarus iseri). Parrotfish were treated with dissolved phase T(3) (20 nM) or methimazole (3 mM) for 3 days. Treatment with exogenous T(3) elevated circulating T(3), while the methimazole treatment depressed plasma T(4). Experimentally-induced hyperthyroidism increased the relative abundance of transcripts encoding trαA and trβ in the liver and brain, but did not affect trαB mRNA levels in either tissue. In both sexes, methimazole-treated fish exhibited elevated dio2 transcripts in the liver and brain, suggesting enhanced outer-ring deiodination activity in these tissues. Accordingly, systemic hyperthyroidism elevated relative dio3 transcript levels in these same tissues. In the gonad, however, patterns of transcript regulation were distinctly different with elevated T(3) increasing mRNAs encoding dio2 in testicular and ovarian tissues and dio3, trαA and trαB in the testes only. Thyroid hormone status did not affect dio1 transcript abundance in the liver, brain or gonads. Taken as a whole, these results demonstrate that thyroidal status influences relative transcript abundance for dio2 and dio3 in the liver, provide new evidence for similar patterns of dio2 and dio3 mRNA regulation in the brain, and make evident that fish exhibit tr subtype-specific transcript abundance changes to altered thyroid status.

Bioconcentration and metabolism of decabromodiphenyl ether (BDE-209) result in thyroid endocrine disruption in zebrafish larvae

“…In addition, we measured gene transcriptions on pools of whole larvae. Taking into consideration the tissue specific gene expressions in fish larvae and adults (Johnson and Lema, 2011), the results of the present study on larvae may have limitations to establish how individuals and specific tissues respond to THs. However, fish larval stages are believed to be more sensitive to toxic chemicals than adults.…”

Deiodinases and thyroid metabolism disruption in teleost fish

“…hypothyroidism, induce the opposite effect. However, specific regulations may also occur at local level (Johnson and Lema, 2011). ID1 usually shows a lower degree of response as its action seems to be restricted in teleosts, and, opposite to mammals, it seems to be down-and up-regulated under hyper-and hypothyroidism conditions, respectively (Van der Geyten et al, 2001).…”

Discovery of latitudinal gradient of triidothyronine concentrations in ectotherms as revealed from a cyprinid fish, the common roach Rutilus rutilus

“…Thyroid hormones regulate the transcriptional activity of many genes through binding with nuclear receptors of THs (Hulbert, 2000;Johnson and Lema, 2011;Grimaldi et al, 2013). They can both up-regulate, and downregulate gene expression in target tissues or cells (Flamant et al, 2007).…”