Figure 4.

 Activation by FGF and components of the MAP kinase pathway of a reporter gene construct containing 2.1 kb of Xbra2 5′-flanking sequence. Activation of the same reporter in response to activin, and of a reporter containing 381 bp of flanking sequence, is dose dependent. (A) Normalized luciferase activity in animal caps injected with Xbra2.pGL2. One group of caps was also injected with v-Ras mRNA, a second with MEK1^S217E/S221E, and a third was treated with FGF-2. Analysis was performed at control stage 12.5. This experiment has been performed 3 times with MEK1^S217E/S221E alone, 10 times with v-Ras alone, and once with MEK1^S217E/S221E and v-Ras in the same experiment. Similar results were obtained each time. (B) Normalized luciferase activity in animal caps treated with FGF-2 or injected with different amounts of activin mRNA (in this experiment “low” represents 1 pg, “medium” represents 5 pg, and “high” represents 50 pg). Analysis was at control stage 12.5. Half of each group of caps was assayed for luciferase and β-galactosidase activities, and the other half was assayed for expression of endogenous Xbra2 by RNase protection. Note that high levels of activin suppress expression of both endogenous Xbra2 and the reporter construct. This experiment has been performed out three times, with similar results each time. (C) A similar experiment to that in B using −381Xbra2.pGL2 (in this experiment “low” represents 1 pg and “high” represents 100 pg activin RNA).