(A–P) Motor neurons labeled with Hb9 are present in the neural tube and the periphery (arrowheads, B, D, F–H, J–L, N–P) Control, Isl1 hypo, Isl2 KO and Isl1 hypo; Isl2 KO mice (n >10 sections in 5 embryos). (Q, R) The number of ectopic Hb9+ cells in the periphery (Q) and Hb9+ motor neurons in the column (R). Error bars represent SEM. **p < 0.01, ***p < 0.001 vs. control; #p < 0.05, ###p < 0.001 vs. Isl1 hypo; Kruskal-Wallis test. Scale bar: 50 μm.