Bmp activity is selectively down-regulated in ectomesenchyme precursors.
(A) Confocal projection of pSMAD1/5/8 immunostaining at 12 hpf shows that all sox10:GFP-positive CNCCs display high pSMAD1/5/8. (B–D) At 16.5 hpf, a projection (B) and a high-magnification section (C, boxed area in B) show that pSMAD1/5/8 remains high in the dorsal non-ectomesenchyme but is lower in the more ventral ectomesenchyme. An orthogonal section (D, taken at the level of the line in C) shows that high pSMAD1/5/8 CNCCs remain in the neural epithelium whereas low pSMAD1/5/8 CNCCs are positioned more medial and ventral. The eye also displays high pSMAD1/5/8. Abbreviations: D, dorsal; V, ventral; A, anterior; P, posterior; M, medial; L, lateral; m, mandibular arch ectomesenchyme; h, hyoid arch ectomesenchyme; n, non-ectomesenchyme; e, ectomesenchyme; ve, ventral epithelium. Scale bar = 50 µm.