Figure 1

Expression of bHLH genes in the chicken pancreas. (A-L) In situ hybridization on serial sections from HH st. 22 (A-D) and HH st. 31 (E-L) chick pancreas showing the expression patterns of Ngn3 (A, E, I), NeuroD (B, F; J), Hes1 (C, G, K), Hes6-1 (D, H, L). Dorsal (dp) and ventral pancreas (vp) and the bile duct (bd) are indicated in A-D. At HH st. 22, Ngn3 is expressed in a few cells scattered in the epithelium (A) whereas NeuroD expression is confined to endocrine cell clusters located at the most distal part of the dorsal pancreas (red dashed lines in B). Hes1 is expressed broadly in the dp and vp epithelium as well as in the bd epithelium (C). Hes6-1 is expressed in a pattern resembling Ngn3 (compare A to D). At HH st. 31, Ngn3 is expressed in scattered cells within the epithelium (E) where they co-localize with Nkx6.1 (I). Ngn3 is not expressed in glucagon positive cells adjacent to the Nkx6.1 positive epithelium (I). In contrast, NeuroD expressing cells are confined to endocrine cells and are excluded from the Nkx6.1 positive epithelium (F, J, area corresponding to boxed areas in E, H). Hairy-1 is still expressed broadly in the epithelium (G) and some of the forming amylase positive acini are also positive for Hes1 (black arrowhead in G, K) but amylase positive acini without Hes1 expression can also be found (red arrowhead in G, K). Hes6-1 is expressed in a pattern closely resembling Ngn3 (H) as it co-localizes with Nkx6.1 in the epithelium and is excluded from glucagon positive endocrine cells (L). * denotes Nkx6.1 positive β-cells