Thyroid Hormone Action During Brain Development: More Questions Than Answers

Thyroid hormoneis essential for proper brain development since it acts on processes such as neuronal migrationand differentiation, myelination and synaptogenesis. In this review, we summarize the consequences of thyroid hormonedeficiency for brain development with special focus on the cerebellum, an important target of thyroidaction. In addition, we discuss the role of iodothyronine deiodinasesand thyroid hormonetransporters in regulating local thyroid hormoneconcentrations as well as current knowledge about the function of thyroid hormone receptorsand their target genes during brain maturation. Despite considerable progress in recent years in deciphering thyroid hormonesignaling pathways we still know very little on the molecular level by which mode of action thyroid hormoneexerts its cell-specific effects. Hence, we will particularly address the open questions that remain to be addressed in order to better understand the role of thyroid hormonein brain development.