prdm1 MO injection reduces neural crest and eliminates Rohon–Beard sensory neurons, reproducing the nrd phenotype. (A–C, G–I) 11 hpf dorsal views, anterior is to the left. (D–F) Twenty-four hpf dorsal views, anterior to the left. (J–L) Eighteen hpf lateral views, anterior is to the left. (A–C) In situ hybridization with HuC showing the three lateral stripes of primary neurons: lateral (L), intermediate (I) and medial (M). The neurons in the lateral stripe form RB sensory neurons (arrow in A) and are completely absent in nrd (B). Following prdm1 MO injection (C), there is a loss of RB sensory neurons, reproducing the nrd phenotype (B). (D–F) HNK-1 immunohistochemistry at 24 hpf, showing the characteristically large RB sensory neurons in a wildtype embryo (arrow in D). Both nrd (E) and prdm1 MO-injected embryos (F) lack RB sensory neurons. Consistent with a loss of RB sensory neurons, both nrd embryos (H) and prdm1 MO embryos (I) display a reduction in foxd3 expression at 11 hpf as compared to wildtype (G). This early reduction of neural crest remains in older embryos shown with crestin (J–L). Abbreviations: wt, wildtype; nrd, narrowminded mutant embryos; MO, prdm1 MO; DLF, dorsal lateral fasciculas; Scale bar is 50 μm.