sulf1 morphants have a loss of dermomyotome cells that can be partially rescued by BMP inhibition. (A–C) Cross-sections of control fish (A), sulf1 morphants treated with DMSO as a vehicle control (B) or sulf1 morphants treated with 2 μM LDN193189 (C) beginning at 12 hpf. Fish was fixed at 48 hpf and labeled with phalloidin to label actin-rich muscle fibrils. While sulf1 morphants have a decrease in the density of muscle fibers and lack a defined horizontal myoseptum compared to controls, the density of muscle fibers and myoseptum are partially rescued in morphants treated with LDN to decrease BMP signaling. (D–F) Whole-mount views of control (D), sulf1 morphant (E), and sulf1 morphant fish treated with 2 μM LDN193189 (F) fixed at 24 hpf and labeled with an antibody against Pax7, which strongly labels neural crest derived cells and also labels dermomyotome cells. Images are taken around the proctodeum (approximately somite 15). (D) Control fish have Pax7-expressing dermomyotome cells throughout each somite, with a distinct population of elongate cells along the developing horizontal myoseptum (arrows). (E) sulf1 morphants have fewer Pax7-expressing dermomyotome cells across the somite, and in particular have no elongate cells running along the horizontal myoseptum. (F) Treatment of sulf1 morphants with LDN193189 increases the number of Pax7-expressing dermomyotome cells in each somite, including restoring the population of elongate cells along the horizontal myoseptum (arrows). (F) Quantification of the number of Pax7-expressing dermomyotome cells in each somite (excluding strongly labeled neural crest cells), from control (blue), sulf1 morphants treated with DMSO (red) and sulf1 morphants treated with 2 μM LDN193189 beginning at 12 hpf (green). Statistical significance is shown by asterisks (p<0.001 for each comparison; ANOVA). Scale bars: A–C: 50 μm; D–F: 50 μm.
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