Thyroid hormone plays a major role in brain development. For instance, low level of thyroid hormone during pregnancy can lead to microcephaly, or very small brain size. This condition, known as cretinism, leads to lifelong severe behavioral deficits and is the number one cause of preventable brain damage in the world. Yet little is known about exactly where and when thyroid hormone acts on the developing brain. It is especially difficult to determine the function of thyroid hormone in early brain development in mammals because of the inaccessibility of the fetal brain in the uterine environment and the challenge of disambiguating maternal versus fetal contributions of thyroid hormone. In this study, Chris Thompson used African clawed frog (Xenopus laevis) tadpoles because their external development allows for manipulation and direct observation of the molecular and cellular mechanisms underlying thyroid hormone's effects on brain development in ways not possible in mammals. He and his colleague, Prof. Holly Cline at The Scripps Research Institute found that endogenous thyroid hormone locally regulates neurogenesis at developmental stages relevant to circuit assembly by affecting neural progenitor cell proliferation and differentiation and by acting on directly neurons to enhance dendritic arbor elaboration. These results will serve as useful endpoints for analysis of environmental compounds that impact thyroid hormone signaling (better known as endocrine disruptors) for their effects on brain development.

See the publication: Thompson CK, Cline HT. 2016. Thyroid Hormone Acts Locally to Increase Neurogenesis, Neuronal Differentiation, and Dendritic Arbor Elaboration in the Tadpole Visual System.