Fig. 1. Phylogenetic footprinting and regulatory element expression analysis of nodal. (A) Diagram showing the position of the P. lividus nodal gene in the BAC (top) and the region used for the phylogenetic footprinting analysis (brackets). (B) 15 kb of sequence surrounding the P. lividus nodal gene was aligned with 15 kb of S. purpuratus (Sp) and 9 kb of L. variegatus (Lv) genomic sequence using Vista. The two exons are labeled in blue and non-coding sequence showing more than 75% homology in pink. (C) Enlargement of the two non-coding conserved regions used for the expression and deletion analyses. Broken lines delineate the sequences used for the deletion analysis in D. (D) P. lividus genomic DNA sequence was used to drive GFP expression in P. lividus embryos. Merged GFP-fluorescent and DIC images of pluteus-stage embryos illustrating the results of the deletion analysis.