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Fig. 6. Neural crest derivatives fail to differentiate in Id3-injected embryos. (A) Forced Id3 expression leads to the formation of substantially fewer melanocytes on the injected side (arrowhead) of embryos that were injected in one cell at the two-cell stage. (B,C) Embryos injected bilaterally with Id3 mRNA (C) show more dramatic deficits in melanocyte formation (arrows) and also have reduced or absent dorsal fins as compared to sibling control embryos (B). (D) Following forced expression of Id3, neural crest cells that populate the branchial arches fail to give rise to chondrocytes, as visualized by Sox9 expression (black arrows) on the injected (D) versus control (E) side of the embryo. Expression of Sox9 in the developing ear (red arrows) is unperturbed by Id3 expression. (F) The differentiation of N-tubulin-expressing primary neurons is also inhibited on the Id3-injected side of the embryo (arrowhead). (G) Rohon-Beard sensory neurons, as marked by expression of brn3, are particularly sensitive to Id3 (injected side marked by arrowhead and β-gal staining, blue). (H) The effects of Id3 in these experiments are directly on the ectoderm. In situ hybridization for muscle actin expression shows that the underlying mesoderm is unperturbed on the injected side of the embryo. |
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Fig. 5. (A) In situ hybridization showing Sox10 expression just after the onset of neural crest migration. At these stages, Sox10 marks the entire neural crest stem cell population. (B) Double in situ hybridization showing expression of Sox10 (cyan) and N-tubulin (magenta) at stage 28. Sox10 expression at these stages is restricted to glia in the peripheral ganglia and CNS (aqua) as well as to melanoblasts (not shown). (C,D) Forced expression of Id3 leads to the persistence of Sox10 expression in neural crest cells migrating to the pharyngeal pouches on the injected side of the embryo (C, arrows). At this stage, expression of Sox10 has normally been downregulated in all neural crest cells except those committing to a glial or melanocyte fate, as seen on the uninjected side of the embryo (D). (E,F) No significant difference is seen in the number of migratory neural crest precursor cells following forced Id3 expression, as visualized by comparing expressing of Twist on the Id3-injected (E) versus uninjected (F) side of the embryo. (G,H) Overexpression of Slug leads to expanded expression of markers of neural crest precursor cells on the injected side of the embryo (arrowheads) at neural plate stages. (I,J) In contrast to forced Id3 expression, Slug expression does not lead to persistent expression of Sox10 in migrating neural crest cells (arrows indicate location of migratory neural crest cells). |
