Fig. 3. Mapping of regulatory motifs essential for PLE-specific activity of the FoxE3 enhancer. (A-C) Representative transgenic embryos (stages 22-24) generated with the GFP reporter constructs shown on the left. Black arrows indicate the PLE. Numbers of embryos with GFP expression in the PLE and the total number of normally (or near normally) developing embryos injected with each construct are indicated on the right-hand side with percentages of the GFP-positive cases. The white line in A indicates the plane of the transverse section shown in the inset. The black arrow in the inset indicates GFP expression in the PLE overlying the optic vesicle. The embryo shown in C was generated by co-transgenesis, i.e. co-injection of the 462 bp enhancer of Xenopus FoxE3 amplified by PCR along with the βGFP cassette. (D) Identification of transcription factor-binding motifs essential for PLE-specific expression by mutation analysis. wt is the construct used in Fig. 3A (Xt462-βGFP). mt1-mt9 were generated from wt/Xt462-βGFP by introducing a base-substitution mutation (cross) into each of the conserved transcription factor-binding motifs. The bar chart shows the percentage of the embryos that showed GFP expression in the PLE among total developed embryos injected with the constructs shown on the left. Actual numbers of GFP-positive cases and total numbers of scored embryos are indicated in parentheses.