Fig. 1. Expression of Lmx1b in the developing embryo and its localization in the MHB. (A-C) Lmx1b expression revealed by whole-mount in situ hybridization. Expression of Lmx1b was first detected at E7.5 in the anterior embryo (A, arrow), appeared at the prospective MHB at E8.5 (B, arrow) and in the isthmus at E9.5 (C, arrow). (D-F) Expression of Wnt1 (D), Fgf8 (E) and Lmx1b (F) in the MHB at the 4-somite stage. Expression of Wnt1 and Fgf8 showed anteroposterior non-overlapping patterns (arrowheads), whereas the Lmx1b expression domain covered the majority of these two domains. (G,H) Lmx1b expression (G,H, red arrows) overlapped with Wnt1 expression (H, blue arrows) in the isthmus, as shown for the same embryo processed sequentially for the detection of Lmx1b and Wnt1 RNAs. Note that there was a Lmx1b⁺ domain located posterior to the Wnt1⁺ domain in the MHB. (I) Double in situ hybridization for Lmx1b and Fgf8. Note that the Lmx1b⁺ domain (red arrow) overlaps with the anterior portion of the Fgf8⁺ domain (blue arrow) in the isthmus.