Thyroid hormone receptor gene knockouts

The thyroid hormone receptor genes, TR alpha and TR beta, differ in developmental expression and tissue distribution. TR beta knockout mice have goiter, elevated thyroid hormone and TSH levels, and a functional auditory defect. In contrast, mice with TR alpha 1/alpha 2 inactivation have thyroid hypoplasia, low serum thyroid hormone levels, growth arrest and delayed small intensive maturation. Mice with selective TR alpha 1 inactivation have apparent normal growth and development, but have bradycardia and reduced body temperature. The dramatic differences between these mice with TR beta and TR alpha gene inactivations indicate the differential functional of these genes. The influence of these gene inactivations on thyroid-stimulating hormone regulation is central to the resulting phenotypes.