Sequence comparison of vertebrate Pax6 genes reveals three conserved regions upstream from the P0 promoter. (A) Genomic organisation of the mouse and zebrafish Pax6 genes composed of 17 exons (red boxes) and three promoters P0, P1 and Pα (arrows). Comparison of the three gene sequences revealed evolutionary conserved non-coding regions (blue boxes), notably three regions A, B and C located upstream the P0 promoter. Scale bar: 5 kb. (B) Multiple sequence alignment of the three conserved regions A, B and C from the human, mouse, chick, xenopus, fugu, tetraodon (except the B region, not found), and both zebrafish pax6 genes. The colour within the sequence alignment indicates the degree of similarity: yellow indicates complete identity between all species; blue indicates identity for at least 50% of the different sequences. Red stars represent nucleotide positions conserved in all vertebrates (including pax6b) but divergent in pax6a. Consensus sites for the binding of PBX1 and/or MEIS are underlined. PA1, PA2, PC1 and PC3 show the location of the conserved DNA elements used in EMSAs. EE corresponds to the lens/ectodermal enhancer described by Zhang et al, 2002.