A refined map of early gene expression in the dorsal rhombomere 1 of mouse embryos

Rhombomere 1 (r1), a temporary structure in the early developing brain, is bounded rostrally by the isthmus organizer and caudally by the r2 domain. Many genes involved in r1 induction and patterning have been identified. However, our knowledge of a comprehensive map of r1 regionalization defined by these genes at early embryonic stages remains fragmentary. In the present study, we examined the expression of a variety of genes in the dorsal r1 of E9.0–E10.5 mouse embryos. The expression domains within ventricular zone of these genes examined allowed us to define four distinct regions along the anterior–posterior (A–P) axis of the dorsal r1: the Wnt1/Lmx1a/Gdf7/Msx1/Msx2-positive roof plate, Math1/Olig3/Msx1/Msx2-positive, upper rhombic lip, Mash1/Ngn1/Ngn2-positive intermediate domain, and Mash1/Ngn1/Ngn2-positive rostral domain. Moreover, we defined the distribution of several genes expressed in the mantle zone of the dorsal r1, including Lmx1b, Lhx2, Lhx9, Phox2a and Phox2b. Taken together, our gene expression data identify a refined subdivision of the dorsal r1 with four distinct domains along the A–P axis and a mantle zone at early embryonic stages.