Genetic Changes to a Transcriptional Silencer Element Confers Phenotypic Diversity within and between Drosophila Species
(A) Schematic depicting the upstream regulatory region of ebony from a dark D. auraria strain aligned to the orthologous region of D. melanogaster. Gray boxes connecting D. auraria and D. melanogaster sequences indicate the relative position of perfectly conserved stretches. Positions of the minimal abdominal enhancer and silencer are shown above the D. melanogaster sequence are based on . Position of the D. auraria silencer element is based upon the truncation constructs shown below the conservation plot. Regions experimentally determined to be required for silencer activity are listed in black, while the region between the enhancer and silencer are shown in a gray gradient, as they may contribute to silencing activity. “A6 midline activity” was measured for each truncation construct, in which the fluorescent intensity of the midline was expressed as the percentage of the lateral A6 intensity ± S.E.M. (B) Activity of the dark (“PM”) strain full ebony upstream regulatory region, which recapitulates the midline repression of ebony observed by in situ hybridization (dotted lines). Dashed boxes indicate representative midline and lateral patches used to quantify midline activity. (C-D) The CD1 truncation construct (C), and the CD2 construct (D) both show midline repression similar to that observed in the full ebony upstream region. (E) The CD3 truncation construct shows uniform expression of GFP across the A6 body segment, reflecting the elimination of sequences required for repression.