The motoneuronal domain is ventrally expanded in hedgehog mutants. (A–F) Expression of nkx2.2b (blue) and olig2 (red) in lateral view of trunk regions (A–C) and transverse sections (D–F). In wt embryos, nkx2.2b is expressed in LFP and p3 neuronal progenitor cells, olig2 is expressed in the motoneuronal domain (A, D). Olig2 expression is ventrally expanded in regions with no nkx2.2b in dtr+/− (E; n = 35 out of a clutch of 71 embryos obtained from mutant carriers, 49%) or along the entire axis in dtr−/− embryos (n = 17/71, 24%). The section shown in panel (E) was made in a region between remaining nkx2.2b expression. (G, H) Differentiated motoneurons expressing isl2 (in blue) are formed within the lateral motoneuronal domain in wt and yot+/− embryos (n = 16/22, 73%; G). The same position of isl2 is observed in yot−/− (n = 6/22, 27%). Most notably, no expression in cells neighboring the MFP expressing col2A1 (in red) are found (H). Homozygous yot embryos were identified by loss of eng2 (in blue) in muscle pioneer cells (MPC). Panels A–C are lateral views of trunk, anterior to the left. Panels D–H are transverse sections of middle trunk. MPC, muscle pioneer cells. Scale bars: C, F, 10 μM.
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