ESPE Yearbook of Paediatric Endocrinology

Front Cell Dev Biol. 2021 Jun 11;9:669354. doi: 10.3389/fcell.2021.669354. eCollection 2021. PMID: 34249923

Brief Summary: This in vitro study analyzed the transcriptome of the developing thyroid gland in human embryonic thyroids compared to non-thyroidal human embryonic tissues and adult thyroid and adult non-thyroidal tissues. They identified four differently regulated sets of genes co-regulated during thyroid development belonging to different gene ontology groups.

This study covers the key developmental window of thyroid structural and functional differentiation characterized by folliculogenesis and onset of thyroid hormone synthesis [1,2]. The methodological approach to compare embryonic thyroid tissues not only to adult thyroid tissues but to pools of non-thyroidal tissues of the embryo and the adult as control provide a unique insight into dynamics of gene expression changes during thyroid development. The authors identified four major groups of gene expression patterns when comparing the four tissue samples: 1) functional genes upregulated during thyroid differentiation and further increased expression until the adult stage (e.g. thyroglobulin, thyroperoxidase), 2) regulatory genes upregulated during embryonic stages and maintained expression in the adult thyroid (e.g. known transcription factors like FOXE1, HHEX), 3) possible transient thyroid regulators with highest expression level in the embryonic tissue (e.g. IGF1, FGF10), and genes of thyroid maturation with low expression in embryonic thyroid but high expression in adult thyroid tissues (e.g. DIO1, CLIC6). These sets of genes belonged to different gene ontology groups, providing evidence that structural and functional differentiation of the thyroid is a complex process combining angiogenesis, cell polarization and adhesion and cellular maturation as a basis for onset of thyroid hormone synthesis.

This exhaustive data set is an important basis for further research on normal and pathologic thyroid development in the context of congenital hypothyroidism.

References: 1. Sodium/iodide symporter (NIS) gene expression is the limiting step for the onset of thyroid function in the human fetus. Szinnai G, Lacroix L, Carré A, Guimiot F, Talbot M, Martinovic J, Delezoide AL, Vekemans M, Michiels S, Caillou B, Schlumberger M, Bidart JM, Polak M. J Clin Endocrinol Metab. 2007 Jan;92(1):70-6. doi: 10.1210/jc.2006-1450. Epub 2006 Oct 31. PMID: 17077129. 2. The thyrotropin receptor and the regulation of thyrocyte function and growth. Vassart G, Dumont JE. Endocr Rev. 1992 Aug;13(3):596-611. doi: 10.1210/edrv-13-3-596. PMID: 1425489.