Thyroid hormone and mammalian tissue regeneration.

Recent articles show that thyroid hormone is a key determinant of regeneration. The regeneration capacity in adults of two cell types, cerebellum neurons and cardiomyocytes, disappeared during mammalian evolution. However, it persists at early stages of development. Data indicate that thyroid hormone, bound to its TRα1 nuclear receptor, defines the timing of the developmental transition which results in a loss of regenerative capacity. The identification of hormone-activated genes that are responsible for this transition is a new challenge for regenerative medicine.