Fig. 1. Cellular populations in dorsal rhombomere 1 at E10.5. (A) Dorsal view schematic of r1. Anterior (a) and posterior (p) domains of r1 are indicated. 4v, 4th ventricle, IsO, isthmus, RRL, rostral rhombic lip. (B-D) Whole-mount in situ staining of E10.5 r1 demonstrating anterior (a) and posterior (p) roof plate domains. Arrowhead indicates reduced expression of Lmx1a and Gdf7 and no Wnt1 expression in the anterior domain. (E-I) In situ and immunostained paramedial sagittal sections through r1 in wild-type (E,G-I) and Gdf7-Cre;ROSA (F) E10.5 mice. Markers are indicated. Arrowheads in e'-e''' point to the medial single cell layer. Arrows point to dorsal neuroepithelium, which expresses Lmx1a, Gdf7 and Wnt1.(F) Arrowheads and arrow point to the medial single cell layer and dorsal neuroepithelium, respectively. (H) Arrows point to BrdU⁺/Lmx1a⁺ double-labeled cells. Arrowheads point to the medial single cell layer. (I) Arrowhead indicates Lmx1a⁺/Msx1/2⁺ region and the arrow indicates the Msx1/2⁺ region outside of this domain (J,K) Summary diagrams of gene expression domains, with provided key. Roof plate is defined as the Lmx1a⁺/Gdf7⁺ region in both anterior and posterior r1.