Craniofacial defects induced by Macondo crude oil exposure were correlated with defects in neural crest development. (A-F) Alcian blue staining of head and jaw cartilage in 4 dpf control (A, D) and severely (B, E) or moderately (C, F) affected WAF-treated embryos. WAF-treated embryos had a variable reduction in the size of all cartilage components, notably a lack of anterior extension of jaw elements and a dramatic reduction in posterior pharyngeal arches (B, C, E, F). (G-L) Whole mount in situ hybridization of crestin expression in neural crest cells. crestin expression is normal in the trunks of control and WAF-treated embryos (G, I, K, bracket; circles in G, I, K represent magnified view in H, J, L). However, crestin expression was variably reduced specifically in the anterior migratory streams, an area of cells that will populate the pharyngeal arches (H, J, L, arrowheads and bracket). (M, N) Cranial neural crest forming pharyngeal arches (p1-5) at 31 hpf as visualized by fli driven expression of GFP. One of the posterior-most pharyngeal arches is missing in WAF treated embryos (N, arrows) as compared to controls (M, 3, 4, 5). (O, P) dlx2 expression in the region of pharyngeal arches is reduced in 26 hpf WAF-treated embryos (P, p1, arrow, bracket) as compared to controls (O). dlx2 expression is nearly lost in the most posterior regions of the presumptive pharyngeal arches (P, bracket) despite robust expression still seen in the forebrain. Abbreviations: bh, basihyal cartilage; cb1-5, ceratobranchial branches; ch, ceratohyal; m, Meckel's; pq, palatoquadrate. Scale bars = 200 μm, A-F; 100 μm, G-L.