Title

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

Author Info

Kaitlin M. Johnson, University of North Carolina
Sean C. Lema, University of North CarolinaFollow

Recommended Citation

Postprint version. Published in General and Comparative Endocrinology, Volume 172, Issue 3, July 1, 2011, pages 505-517.

NOTE: At the time of publication, the author Sean C. Lema was not yet affiliated with Cal Poly.

The definitive version is available at https://doi.org/10.1016/j.ygcen.2011.04.022.

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 T₃ (20 nM) or methimazole (3 mM) for 3 days. Treatment with exogenous T₃ elevated circulating T₃, while the methimazole treatment depressed plasma T₄. 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 T₃ 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.

Disciplines

Biology

Copyright

2011 Elsevier.