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Figure 1 Comparison of neurula stage expression of AP2α and other NC marker genes. (A) Whole-mount in situ hybridization with probes for AP2α, Slug, and Sox9 are shown in dorsal and lateral views. AP2α transcripts appear to extend more laterally than for the other two genes. This is shown more clearly in cross section in B, where the bracket indicates the Slug domain and the arrows point to the more extensive lateral AP2α. Note that under the conditions used here the epidermal expression of AP2α, which is considerably lower than for NC, is not apparent. The notochord is indicated by n. (Magnifications: A, ×7; B, ×42.) |
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Figure 4 Ectopic expression of AP2α converts neural plate into NC. Whole-mount in situ hybridization of probes for Slug, Sox9 (NC), and Sox2 (neural plate) to embryos injected at the 16-cell stage with 100 pg of RNA encoding AP2α, along with β-galactosidase lineage tracer RNA (5-bromo-4-chloro-3-indolyl-β-d-galactoside, turquoise staining). Discrete domains of intense ectopic expression of both NC marker genes was observed (arrows) within the neural plate. Endogenous Slug and Sox9 expression is indicated by the arrowheads. Concomitant repression of neural plate identity also occurred, as indicated by the reduction in Sox2 expression (arrow). (Magnification: ×22.) |
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Figure 2 NC expression of AP2α depends on Wnt signaling. Whole-mount in situ hybridizations with NC markers Sox9, Slug, and AP2α to embryos injected into one cell at the two-cell stage with 100 pg of plasmid DNA encoding Xenopus Xwnt-1 (Left) and Xwnt-3A (Center), or 1 ng RNA encoding GSK3β (Right), along with a β-galactosidase lineage tracer (red staining). In all cases the injected side is oriented to the right (red staining). Both Wnt treatments resulted in lateral and posterior expansion of NC territory, including expression of AP2α as well as the other NC markers. The reciprocal treatment with GSK3β, which interferes with downstream Wnt signaling (50), had the opposite effect: AP2α, Sox9 and Slug all were repressed. (Magnification: ×15.) |
