Fig. 2. Sox10-dependent survival of undifferentiated postmigratory neural crest cells. (A-C) Apoptotic cell death of undifferentiated postmigratory Sox10^–/– neural crest cells. Transverse cryosections through DRG from E11 embryos were triple labeled for p75 (FITC fluorescence), NF (Cy5 fluorescence) and TUNEL (Cy3 fluorescence), and analyzed by confocal microscopy. A single confocal plane is shown. Apoptosis as assayed by TUNEL labeling was frequent in undifferentiated p75-positive DRG cells of Sox10 homozygous (–/–) mouse mutants (arrow in B) but not of wild-type (+/+) littermates. The association of nuclear TUNEL staining with p75 labeling (on the cell surface) was particularly apparent when various confocal planes were analyzed (not shown). Note that NF-positive differentiated neurons were usually not associated with apoptotic figures at this stage (arrowhead in B). Scale bar: 10 µm. (C) Quantification of apoptotic figures in DRG of wild-type (+/+) and Sox10^–/– (–/–) embryos. Each bar represents the number (mean±s.d.) of apoptotic nuclei in DRG per section. Two independent experiments using non-sibling embryos were performed, scoring 13 consecutive thoracic sections per experiment. (D) NRG1 is a Sox10-dependent survival factor of undifferentiated postmigratory neural crest cells. Postmigratory neural crest cells prepared from wild-type (+/+) or Sox10^–/– (–/–) DRG were plated at clonal density, the position of single neural crest cells was mapped, and clones were allowed to develop in differentiation medium (‘no NRG1’) or in differentiation medium supplemented with NRG1 (‘NRG1’). The numbers indicate the percentage of clones lost owing to cell death of the founder neural crest cell. The data were obtained from four independent experiments counting 60 clones each. Note that cell death of wild-type cells but not of Sox10^–/– mutant cells was significantly reduced in the presence of NRG1.