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. 2020 Apr 30;21(9):3185. doi: 10.3390/ijms21093185

Figure 1.

Figure 1

TR isoforms and structure distribution. Thyroid hormone receptors (TR) contain several domains, specifically, the amino terminal A/B that may function as a gene enhancer, the DNA-binding domain (DBD), the hinge region containing the nuclear localization signal and the carboxy-terminal ligand-binding domain that binds T3. The four major TR isoforms are TRα1, TRα2, TRβ1, and TRβ2. TH binding is widely distributed in a tissue-specific manner such as TRα1 and TRα2 expressed in the kidney, skeletal muscle, lungs, heart, and testes, with particularly high levels detected in the brain. TRβ1 expression is significant in the brain, thyroid, liver, and kidney while the TRβ2 isoform is specifically expressed in the anterior pituitary, hypothalamus, and developing brain.