Metamorphosis has fascinated scientists and artists since Aristotle and Ovid. Perhaps the first experimental study of the endogenous control of metamorphosis was carried out by Gudernatsch, an American academic visitor in Prague in the early twentieth century. He was interested in the most classic example of vertebrate metamorphosis: the transformation of a tadpole to a frog. By feeding tadpoles with small pieces of various organs taken from a horse, Gudernatsch found that the thyroid gland contains a substance that triggered the change from tadpole to frog. This was the first hint that metamorphosis is controlled by a hormonal signal.

Metamorphosis, classically defined as a spectacular post-embryonic transition, is well exemplified by the transformation of a tadpole into a frog. It implies the appearance of new body parts (such as the limbs), the resorption of larval features (such as the tail) and the remodelling of many organs (such as the skin or the intestine). In vertebrates, metamorphosis has been well characterized in anuran amphibians, where thyroid hormones orchestrate the intricate and seemingly contradictory changes observed at the cellular and tissue levels. Thyroid hormones control a complex hierarchical cascade of target genes via binding to specific receptors, TRα and TRβ, ligand-activated transcription factors belonging to the nuclear receptor superfamily.

To change completely the nature or appearance of; “In Kafka’s story, a person metamorphoses into a bug”; “The treatment and diet transfigured her into a beautiful young woman”; “Jesus was transfigured after his resurrection”