Hes1 in Thyroid Development Figure 3. Thyroid morphology and expression of thyrocyte and C-cell markers at late embryonic stages. Staining for Nkx2-1 (A, B, F, G, K, L, P, Q), Pax8 and TG (C, H, M, R), CT and T4 (D, I, N, S), and Mash1 (E, J, O, T) at E16.5 (A–J) and E15.5 (K–T) in transverse sections from wild type and Hes12/2 mice. Boxed areas were enlarged (B–E, G–J, L–O, Q–T). Thyroid fusion was delayed by 3 days in Hes12/2 thyroids compared to wild type thyroids. tr: trachea; thy: thyroid; ma: median anlage; pt: parathyroid; UB: ultimobranchial body. doi:10.1371/journal.pone.0016752.g003 Nkx2-1 positive surface area in Hes12/2 vs. wild type mice. The ratio of Nis-positive to Nkx2-1 positive surface area at E16.5 was 69% lower in Hes12/2 mice than in wild type mice (p,0.05) (Figure 5A–G) reflecting a reduced iodide uptake capacity. Thyroid hypoplasia in Hes12/2 mutants due to decreased progenitor number We investigated four possible hypotheses for thyroid hypoplasia in Hes12/2 thyroids: 1) decreased proportion of proliferating cells in the Table 1. Morphological abnormalities in Hes12/2 mutant thyroid. Embryonic stage E9.5 E11.5 E13.5 E15.5 E16.5 Thyroid anlages MA UB total MA, median anlage; UB, ultimobranchial bodies; WT, wild type. doi:10.1371/journal.pone.0016752.t001 Structural features of the thyroid gland in Hes2/2 mice Elliptical, close to aortic sac, as in WT 1out of 3 median anlage separated laterally 1 out of 3 embryos: UB lacking on one side 1 out of 3 thyroids: no isthmus 3 out of 3 thyroids: UB not fused with MA 2 out of 3 thyroids: enlarged isthmus 3 out of 3 thyroids: UB not fused with MA 2 out of 3 thyroids: enlarged isthmus UB fused with MA, but C-cells not disseminated in thyroid gland Decrease in surface area (%) vs WT 36% 65% 36% 83% 65% 34% 50% PLoS ONE | www.plosone.org 5 February 2011 | Volume 6 | Issue 2 | e16752