Hes1 Is Required for Appropriate Morphogenesis and Differentiation during Mouse Thyroid Gland Development Aurore Carre1, Latif Rachdi1, Elodie Tron1, Be´ ne´ dicte Richard1, Mireille Castanet1, Martin Schlumberger2, Jean-Michel Bidart3, Gabor Szinnai4,5., Michel Polak1,6*. 1 INSERM U845, Universite´ Paris-Descartes, Paris, France, 2 Department of Nuclear Medicine, Institut Gustave-Roussy, Villejuif, France, 3 Department of Clinical Biology, Institut Gustave-Roussy, Villejuif, France, 4 Paediatric Endocrinology, University Children’s Hospital Basel, Basel, Switzerland, 5 Department of Biomedicine, University of Basel, Basel, Switzerland, 6 Paediatric Endocrine Unit, Necker Enfants-Malades Hospital, and Centre des Maladies Endocriniennes Rares de la Croissance, AP-HP, Paris, France Abstract Notch signalling plays an important role in endocrine development, through its target gene Hes1. Hes1, a bHLH transcriptional repressor, influences progenitor cell proliferation and differentiation. Recently, Hes1 was shown to be expressed in the thyroid and regulate expression of the sodium iodide symporter (Nis). To investigate the role of Hes1 for thyroid development, we studied thyroid morphology and function in mice lacking Hes1. During normal mouse thyroid development, Hes1 was detected from E9.5 onwards in the median anlage, and at E11.5 in the ultimobranchial bodies. Hes12/2 mouse embryos had a significantly lower number of Nkx2-1-positive progenitor cells (p,0.05) at E9.5 and at E11.5. Moreover, Hes12/2 mouse embryos showed a significantly smaller total thyroid surface area (240 to 260%) compared to wild type mice at all study time points (E9.52E16.5). In both Hes12/2 and wild type mouse embryos, most Nkx2-1-positive thyroid cells expressed the cell cycle inhibitor p57 at E9.5 in correlation with low proliferation index. In Hes12/2 mouse embryos, fusion of the median anlage with the ultimobranchial bodies was delayed by 3 days (E16.5 vs. E13.5 in wild type mice). After fusion of thyroid anlages, hypoplastic Hes12/2 thyroids revealed a significantly decreased labelling area for T4 (278%) and calcitonin (265%) normalized to Nkx2-1 positive cells. Decreased T4-synthesis might be due to reduced Nis labelling area (269%). These findings suggest a dual role of Hes1 during thyroid development: first, control of the number of both thyrocyte and C-cell progenitors, via a p57-independent mechanism; second, adequate differentiation and endocrine function of thyrocytes and C-cells. Citation: Carre A, Rachdi L, Tron E, Richard B, Castanet M, et al. (2011) Hes1 Is Required for Appropriate Morphogenesis and Differentiation during Mouse Thyroid Gland Development. PLoS ONE 6(2): e16752. doi:10.1371/journal.pone.0016752 Editor: Hang Nguyen, Emory University, United States of America Received September 22, 2010; Accepted January 10, 2011; Published February 25, 2011 Copyright: 2011 Carre et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: AC was supported by CIFRE in collaboration with HRA Pharma and by the Ministe`re de l’Education Nationale et de la Recherche. GS and MP received the Collaborative Research Unit Grant from the European Society for Paediatric Endocrinology (ESPE). GS received a Research Grant from the University Children’s Hospital Basel, Basel, Switzerland. This study was supported in part by a grant from Electricite´ de France (RB 200605), by Sandoz France and by the Fondation Princesse Grace de la Principaute´ de Monaco. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. We declare commercial funders: HRA Pharma and Electricite´ de France do not alter the adherence to all the PLoS ONE policies on sharing data and materials. * E-mail: michel.polak@nck.aphp.fr . These authors contributed equally to this work. Introduction The thyroid gland contains two types of hormone-producing cells: thyroid follicular cells or thyrocytes, which produce thyroxin (T4) and originate mainly in the median anlage; and C-cells (parafollicular cells), which produce calcitonin (CT) and originate only in the ultimobranchial bodies. In mice, the median anlage invaginates from the floor of the foregut starting at E8.5 and expresses Nkx2-1, Pax8, and Foxe1, three transcription factors whose simultaneous expression is specific of the thyroid gland [1]. From E11.5 onwards, the ultimobranchial bodies develop from the fourth pharyngeal pouch on each side [2] and express transcription factors such as Mash1 and Nkx2-1. The median and lateral anlagen migrate and then fuse, at E13.5 at the definitive pretracheal position. The cells differentiate into thyrocytes expressing thyroglobulin (from E14.5) and producing T4 (from E16.5) or into C-cells expressing calcitonin (from E15.5) [3]. One factor essential for the onset of T4 synthesis is the active iodide uptake by the thyrocytes through the sodium iodide symporter (Nis) [4]. Several genes involved in thyroid development (most of which encode homeodomain proteins) have been identified, the molecular mechanisms that regulate the development and differentiation of each type of thyroid cells remains unknown. Hes1 (hairy/enhancer of split 1) is a basic Helix-Loop-Helix (bHLH) transcriptional repressor regulated by the Notch pathway and expressed in various tissues [5]. In general, Hes1 maintains cells in the undifferentiated progenitor state by negatively regulating bHLH transcription factors such as Ngn3 in the pancreas and Mash1 in the nervous system [6]. Sound evidence PLoS ONE | www.plosone.org 1 February 2011 | Volume 6 | Issue 2 | e16752