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Journal of Thyroid Research
Volume 2011, Article ID 402320, 8 pages
http://dx.doi.org/10.4061/2011/402320
Review Article

Thyroid Hormone Receptors in Two Model Species for Vertebrate Embryonic Development: Chicken and Zebrafish

1Division Animal Physiology and Neurobiology, Biology Department, Laboratory of Comparative Endocrinology, K.U.Leuven, 3000 Leuven, Belgium
2Department of Agricultural Sciences, Centre for Agribiosciences, La Trobe University, Bundoora, VIC 3086, Australia

Received 24 February 2011; Accepted 1 April 2011

Academic Editor: Michelina Plateroti

Copyright © 2011 Veerle M. Darras et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Chicken and zebrafish are two model species regularly used to study the role of thyroid hormones in vertebrate development. Similar to mammals, chickens have one thyroid hormone receptor α (TRα) and one TRβ gene, giving rise to three TR isoforms: TRα, TRβ2, and TRβ0, the latter with a very short amino-terminal domain. Zebrafish also have one TRβ gene, providing two TRβ1 variants. The zebrafish TRα gene has been duplicated, and at least three TRα isoforms are expressed: TRαA1-2 and TRαB are very similar, while TRαA1 has a longer carboxy-terminal ligand-binding domain. All these TR isoforms appear to be functional, ligand-binding receptors. As in other vertebrates, the different chicken and zebrafish TR isoforms have a divergent spatiotemporal expression pattern, suggesting that they also have distinct functions. Several isoforms are expressed from the very first stages of embryonic development and early chicken and zebrafish embryos respond to thyroid hormone treatment with changes in gene expression. Future studies in knockdown and mutant animals should allow us to link the different TR isoforms to specific processes in embryonic development.