Fig. 5. Branchial motoneurons of the spinal accessory nerve are reduced in Nkx2.9-deficient mouse embryos. Transversal serial sections through the neural tube at C4-C3 level of E 10.5 wild-type (A,C) and homozygous mutant (B,D) embryos were stained with Isl1-specific antibody (green) together with Nkx2.2 antibody (red in A,B) or Lim3 antibody (red in C,D). Note the drastic reduction of dorsolaterally migrating Isl1-positive cells (compare arrows in A and B) and the markedly increased number of Isl1/Lim3-positive somatic motoneurons (yellow cells indicated by arrows in C,D) in the mutant. Quantification of migrating Isl1-positive and Isl1/Lim3 double-positive cells was obtained by computer-aided determination of total pixel area with color information for the respective cell types. (C',D') A typical example of at least five independent determinations on level-matched sections of embryos of both genotypes. Changes in cell numbers of approximately 60% were consistently found.