The motor innervation of Hb9cre/+, BmprIaflox/-hindlimbs is normal. Retrograde labeling was used to determine the columnar origin of axons innervating Hb9cre/+, BmprIaflox/-hindlimbs. (a) Dorsal nerves originate from Isl1- Lim1+ lateral LMC neurons in normal and Hb9cre/+, BmprIaflox/-mutant embryos. (b) Schematic of the experiment in (a). (c) Ventral nerves originate from Isl1+ Lim1- medial LMC neurons in normal and Hb9cre/+, BmprIaflox/-mutant embryos. (d) Schematic of the experiment in (c). (e,f) Quantification of dorsal (e) and ventral (f) retrograde labeling data. Lateral LMC cells were Lim1+ Isl1- HRP+; medial LMC cells were Lim1- Isl1+ HRP+. The percentage of labeled lateral or medial LMC cells marked by either dorsal or ventral limb HRP injection does not differ significantly between normal and mutant. Dorsal: lateral LMC 93% ± 0.9%, n = 8 embryos, N > 750 HRP+ neurons; mutant lateral LMC 93% ± 0.5%, n = 3 embryos, N > 450 HRP+ neurons; P = 0.79. Ventral: medial LMC 95% ± 1.5%, n = 5 embryos, N > 350 HRP+ neurons; mutant medial LMC 96% ± 0.9%, n = 3 embryos, N > 240 HRP+ neurons; P = 0.60.