Crossregulation of the Thyroid Hormone and Corticosteroids in Amphibians and Fish: The Effects of Endocrine Disruption

Thyroid hormones are involved in many physiological processes, during growth, develop‐ ment, behaviour, stress. Their actions are mediated by TH receptors (TR-alpha and TR-beta), which are members of the nuclear receptor (NR) superfamily and function as ligand-activat‐ ed transcription factors. In amphibians, TR-alpha is expressed shortly after hatching and is maintained at a relatively constant level throughout tadpole life and metamorphosis. Then amphibian metamorphosis is dependent on thyroid hormone (TH) changes, which induces the suite of molecular and cellular changes that cause a tadpole to transform into a frog.