The thyroid hormones, T4 (3,5,3′,5′tetraiodo-L-thyronine) and T3 (3,5,3′tri-iodo-L-thyronine; also known as tri-iodothyronine) are iodinated amino acids produced and secreted by the thyroid gland. These hormones regulate many developmental and metabolic processes.
The nuclear T3 receptors are ligand-modulated transcription factors encoded by two genes, THRA and THRB. These genes encode several receptor proteins, of which three (thyroid hormone receptor α1, thyroid hormone receptor β1 and thyroid hormone receptor β2) interact with T3, which results in tissue-specific and developmentally-dependent transcriptomic changes.
In the developing cerebral cortex, 500–1,000 genes are directly or indirectly affected by thyroid hormones. In addition, both T4 and T3 perform nongenomic, extranuclear actions. For example, T3 might interact with a plasma-membrane-associated thyroid hormone receptor α variant, and with cytoplasmic thyroid hormone receptor β, while T4 interacts with integrin αvβ3 and activates diverse signalling pathways such as the phosphoinositide 3-kinase pathway and mitogen-activated protein kinase pathways.
Source: NatureReviewsEndocrinology
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