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The embryonic expression patterns of two additional members of the transcription factor TFAP2 family in Xenopus laevis, TFAP2beta and TFAP2gamma, are described. Both genes share overlapping expression domains with the previously characterized TFAP2alpha in this species, although differences exist. All three genes are expressed in the neural crest (NC) region at late gastrula to early neurula stages. TFAP2alpha and TFAP2gamma are also expressed in outer, epidermal cells, while TFAP2beta is essentially NC-specific. All three are induced by Wnt/beta-catenin -- BMP signals and all bind to a consensus TFAP2 recognition site from an epidermal keratin gene.
Fig. 2. Expression patterns. (A) Northern blot analysis. Whole embryonic RNA isolated from various stages separated on denaturing agarose gels and probed with radiolabeled DNA for TFAP2α, TFAP2β, and TFAP2γ, as indicated. TFAP2α and TFAP2γ RNAs migrate as multiple bands. Ethidium bromide staining of 28S RNA shown as loading control. (B) Whole mount in situ hybridization. The embryonic stages are indicated to the left of the images. dors., dorsal view (anterior towards top); lat., lateral view (anterior towards right). Pronephric duct expression for TFAP2α and TFAP2β indicated by black arrowheads. In some cases (e.g., TFAP2γ, stage 17 dorsal), the deep and superficial signals yield different colors; this is an artifact of the BM-purple staining reaction. Pax8 expression in the placodal region indicated with arrowheads.
Fig. 3. Cross-sections. Sibling embryos (Fig. 2) hybridized to TFAP2α (A and F), TFAP2β (B and G), TFAP2γ (C), Slug (D), and Pax8 (E) were embedded in JB4 and cut into 10 μ sections. Shown are sections about 300 μ from the anterior end of the embryos for (A)–(E) and about 550 μ, in the mid-anterior region for (F) and (G). A–E, stage 14; F–G, stage 17. The notochord is indicated in each section by a dotted outline, and the medial boundary of expression with arrowheads.
Fig. 4. Deep versus superficial hybridization. Stage 14 embryos were fixed and hybridized in whole mount in situ to probes for (A) TFAP2α and (C) TFAP2γ. Conditions were adjusted to optimize deep cell hybridization: Proteinase K treatment was increased slightly, and the color development time was increased. For Slug (D) and TFAP2β (B), the images were magnified from Fig. 3B. Following hybridization embryos were embedded in JB4 and cut into 10 μ sections. The sections shown were located 300 μ from the anterior tip of the embryos. Hybridization to superficial cells is indicated with black arrows, and to deep, NC cells with red. The bar in (D) represents 100 μ.
