Fig. 8. lLMC neurons are generated normally, but fail to migrate laterally, and are scattered throughout ventral horn in Hoxc10^-/-/Hoxd10^-/- double-mutant embryos. (A) Cross-sections of the ventral spinal cord of Hoxc10^+/-/Hoxd10^+/- and Hoxc10^-/-/Hoxd10^-/- embryos processed with an hrGFP in situ probe. In control embryos, hrGFP expression closely resembles Hoxd10 expression (see Fig. 1E). In Hoxc10^-/-/Hoxd10^-/- mutant embryos, however, hrGFP⁺ cells are scattered throughout the ventral horn. Dashed white lines outline the LMC; dashed red lines outline the region of the LMC that contains hrGFP⁺ cells. (B) To examine the fate of late-born motoneurons, timed pregnant animals were injected with BrdU at E10.5 and analyzed at E12.0. Cross-sections of the ventral spinal cord were labeled with anti-BrdU and either anti-Isl1 (top panels) or anti-Lim1 (bottom panels). In control embryos, most late-born BrdU⁺ motoneurons are laterally migrating Lim1⁺ lLMC neurons (arrows indicate double-labeled cells), whereas in Hoxc10^-/-/Hoxd10^-/- double-mutant embryos, most late-born BrdU⁺ motoneurons expressed neither Isl1 nor Lim1 and were scattered in ventral horn, intermixed with earlier-born Isl1⁺ motoneurons. Scale bars: 100 µm.