Caudal and Hunchback binding sites co-evolve in orthologous eve stripe 2 enhancers.

(A) Enrichment scores for predicted Hb and Cad binding sites in orthologous eve stripe 2 and eve3+7 sequences from different Drosophilid and Sepsid species [51]. Scores were calculated by comparing the number of predicted sites to an expected value calculated from the genomic background [52]. Scores for Drosophila melanogaster enhancers are indicated in magenta. Spearman correlation and p-value are displayed for each set of enhancers. (B) Summary of current findings. Top: levels of Hb protein (blue), Cad protein (red) and Eve protein (grey) are plotted as a function of anterior-posterior position. Data were taken from the FlyEx database [75]. Bottom: cartoon indicating Hb function in eve2+7 at different locations in the embryo. In the anterior, Cad levels are low, so Hb represses eve2+7. In the trunk, Cad binding to eve2+7 prevents Hb repression.