Thyroid hormone regulates abrupt skin morphogenesis during zebrafish postembryonic development

ABSTRACT Thyroid hormone is a key regulator of post-embryonic vertebrate development. Skin is a biomedically important thyroid hormone target organ, but the cellular and molecular mechanisms underlying skin pathologies associated with thyroid dysfunction remain obscure. The transparent skin of zebrafish is an accessible model system for studying vertebrate skin development. During post-embryonic development of the zebrafish, scales emerge in the skin from a hexagonally patterned array of dermal papillae, like other vertebrate skin appendages such as feathers and hair follicles. We show here that thyroid hormone regulates the rate of post-embryonic dermal development through interaction with nuclear hormone receptors. This couples skin development with body growth to generate a well ordered array of correctly proportioned scales. This work extends our knowledge of thyroid hormone actions on skin by providing in-vivo evidence that thyroid hormone regulates multiple aspects of dermal development. Highlights Thyroid hormone (TH) is necessary for normal squamation patterning in zebrafish. Stratified dermis develops by migration of primary hypodermal cells. Dermis stratifies in an invariant wave. TH regulates the rates of multiple aspects of dermis development. Scale size and density are sensitive to skin size at onset of squamation.