Fig. 5: Impaired axon growth of sympathetic neurons in Isl1 hypomorphic mutants.

a–d Wholemount TH immunostaining of hypomorphic (hypo, Isl1^f-neo/f-neo) and wildtype control (ctrl, Isl1^+/+) embryos at E14.5 and E17.5 showing sympathetic ganglia and axons (arrowhead) extending toward, and neural plexus (arrow) around the dorsal aorta (da, red dashed line). Scale bar, 500 µm. e Quantitative analysis showing that the number of sympathetic neurons in Isl1 hypomorphic embryos was comparable with control littermates at E13.5 and E14.5, but significantly reduced at E17.5. Error bars represent the s.d., n = 4, E13.5 (p = 0.854), E14.5 (p = 0.525), E17.5 (p = 0.014), two-tailed t-test. f–m Markedly reduced sympathetic innervations to the salivary gland (f, g), heart (h–k), and stomach (l, m) in Isl1 hypomorphic embryos at E14.5 and E17.5 compared with control littermates revealed by TH immunostaining. Scale bar, 200 µm (f, g), 1 mm (h–m). n–p Increased proliferation in E14.5 Isl1 hypomorphic sympathetic ganglia compared with controls revealed by co-immunostaining for BrdU and Phox2b. Error bars represent the s.d., n = 4, p = 0.011, two-tailed t-test. Scale bar, 100 µm. q–s Increased neuronal death revealed by co-immunostaining for activated caspase-3 and neurofilament (NF) in E14.5 Isl1 hypomorphic sympathetic ganglia compared with controls. Error bars represent the s.d., n = 4, p = 0.024, two-tailed t-test. Scale bar, 100 µm. * p < 0.05, or ** p < 0.01