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Figure 7. The fibroblast growth factor mitogen activated protein kinase (FGF/MAPK) pathway regulates MKP3 expression during Xenopus development. All panels show XMKP3 expression pattern except K,L and Q-T, which show Fgf8 and Xbra expression, respectively. M-T: Injection of different mRNAs along with 300 pg of LacZ mRNA in one blastomere at the two-cell stage. The injection side was determined by XGal staining. A,B: Vegetal (A) and lateral (B) views of early gastrula embryos (stage 10) show that XMKP3 is expressed in the mesodermal marginal zone (B) and in the prospective neural ectoderm (B, arrowhead). C,D: Vegetal (A) and lateral (B) views of late gastrula embryos (stage 12). XMKP3 is expressed in all the prospective neuroectoderm (C and arrowhead in D). E-I: Dorsal views of different neurula stage embryos show similar XMKP3 mRNA distribution. At these stages, XMKP3 expression in the neuroectoderm becomes more restricted, being localized to the posterior neuroectoderm (F, red arrowhead), at the midbrain-hindbrain boundary (F, black arrowhead), and in two horseshoe-shaped bands in the anterior neuroectoderm (G, arrowheads). J: Lateral view of tail bud stage 34 embryos. XMKP3 is strongly detected in the branchial arch region (red arrowhead) and in the tail tip (black arrow). Indeed, these two domains of expression were the only ones detected in a previous report (Mason et al., [1996]). In addition, at this stage MKP3 is also expressed at the midbrain-hindbrain boundary (black arrowhead) and in the somites (red arrow). K,L: Anterior (K) and dorsal (L) views of stage 14 embryos showing the expression pattern of Fgf8. Note that Fgf8 and MKP3 are expressed in similar territories (compare K,G and F,L). M-P: Dorsal views of neurula embryos showing MKP3 expression in embryos injected with different mRNAs. These embryos are at a similar stage to the control embryo shown in H. Red and black arrowheads point at the uninjected (internal control) and the injected sides, respectively. Interfering (M) or increasing (N) Ras activity down-regulates or ectopically activates, respectively, MKP3 expression. Similarly, interfering (O) or increasing (P) FGF signaling down-regulates or ectopically activates, respectively, MKP3 expression. The effectiveness of these injections was determined by monitoring Xbra expression. Q-T: Interfering with FGF/MAPK pathway represses Xbra expression at early gastrula (vegetal views, Q,S) while increasing FGF/MAPK activity promotes ectopic Xbra expression at neurula stages (dorsal views, R,T). Compare the uninjected (red arrowheads) and the injected (black arrowheads) sides. Insets in Q and R show Xbra expression in control embryos at early gastrula and neurula stages, respectively. XMKP3, Xenopus extracellular signal-regulated kinase phosphatase 3. |
