Neuregulin 1 is required for Schwann cell migration. (A-D′) nrg1 (A,B,B′) and nrg1 type III (C,D,D′) mRNA expression at 33 hpf, shown in dorsal (A,C) and lateral (B,D) views. (B′,D′) Higher magnification of the boxed regions in B,D. Arrowheads mark the PLLg and asterisks mark motoneurons. (E,F) Lateral views of control-injected (E) and nrg1 morpholino-injected (F) zebrafish embryos at 29 hpf. (G-H′) Lateral views of control-injected (G,G′) and morphant (H,H′) embryos carrying the Foxd3:GFP transgene (green) and stained with anti-acetylated tubulin (acTub, red) at 29 hpf. Schwann cells are marked by arrowheads and stellate-shaped pigment cells by asterisks. In lateral views, anterior is to the left and dorsal is up. In dorsal views, anterior is to the left. ALLg, anterior lateral line ganglion; PLLg, posterior lateral line ganglion. Scale bar: 50 μm.