Figure 2.

 Determination of siamois promoter regions responsive to a dorsally localized endogenous activity. (A) Regions of the siamois promoter responsive to the dorsalizing activity. The indicated constructs were injected into the marginal zone of dorsal (D) or ventral (V) blastomeres at the four-cell stage. The mean and standard error, in RLUs, from three pools of five embryos each are shown. The average fold induction (D/V Ratio) for each construct is indicated above each data set. (N.S.) No significant dorsal vs. ventral difference. (B) siamois activation by the endogenous dorsalizing activity requires the proximal promoter region. The 0.8-kb and Δ−45/−357 reporter constructs were assayed as described above. The siamois promoter is no longer responsive to the endogenous dorsalizing activity when the proximal region containing the three Lef/Tcf sites is deleted.