Epigenetic regulation of thyroid development

Abstract

Focusing on the molecular mechanisms of normal and abnormal thyroid development, this work had two main aims: 1) To establish a flow cytometry protocol for the developing and adult murine thyroid. 2) To analyze whether epigenetic mechanisms are regulating thyroid development. Project 1: A new tool for thyroid research: Flow cytometry of the thyroid gland The thyroid is composed of endocrine epithelial cells, blood vessels and mesenchyme. However, no data exist so far on absolute cell numbers, relative distribution, and proliferation of the different cell populations of the thyroid. First, we established a gating strategy for flow cytometry that is able to identify seven distinct cell populations in the embryonic and adult thyroid. Second, a detailed analysis of cell populations in vivo revealed unexpected frequencies and cell growth dynamics of the different cell populations at distinct embryonic stages and in adult tissues, extending our current knowledge on normal thyroid development. Finally, a yet unknown and uncharacterized cell population present in embryonic and adult thyroids at a frequency between 5-20% has been identified, that needs further detailed characterization. In summary, our approach provides a useful new tool for cell function analyses in murine thyroid disease models. Project 2: A new concept: Epigenetic regulation of thyroid development Abnormal thyroid development results in thyroid dysgenesis (TD). TD causes congenital hypothyroidism in neonates. Monozygotic twin are discordant for TD, suggesting epigenetic mechanisms. This epigenetic concept is further supported by disrupted histone acetylation in thyroid cancer and pathologic development of organs after inhibition of histone deacetylases (HDAC). To investigate the role of HDACs for normal and abnormal thyroid development, we first documented physiological dynamic changes of HDAC activity, HDAC expression and histone acetylation in the thyroid between E13.5-E17.5 in vivo. Second, we investigated the effect of HDAC inhibition on thyroid development in an ex vivo embryonic thyroid culture model. HDAC inhibition induced decreased HDAC activity and increased histone acetylation. HDAC inhibition resulted in profoundly disordered thyroid development compatible with all aspects of TD: reduced follicle formation, decreased endocrine cell mass, and disturbed angiogenesis. Hence, our data supports the concept of epigenetic regulation of thyroid development, and suggests a new molecular mechanism of TD.