Fig. 2. Absence of somatic motor nuclei and reduced sizes of branchiomotor nuclei in Nkx6.1 mutant embryos at E18.5. In situ hybridization with a peripherin probe on coronal sections through the hindbrain of wild type (left column) and Nkx6.1 mutant (right column) embryos. In Nkx6.1 mutant embryos, the somatic motor nuclei of the abducens (nVI) (arrow in A,B) and hypoglossal (nXII) (arrow in C,D) nerve are absent. The branchiomotor nuclei of the trigeminal (nV) (E,F) and facial (nVII) (G,H) nerve and the nucleus ambiguous (nA) (I,J) are present in Nkx6.1 mutants, but reduced in size. By contrast, the dorsal motor nucleus of the vagal nerve (dmnX) (arrowhead in C,D) appears normal in size.