cis-regulatory evolution

Dissecting sources of quantitative gene expression pattern divergence between Drosophila species

Zeba Wunderlich¹, Meghan D Bragdon¹, Kelly B Eckenrode¹, Tara Lydiard-Martin¹, Sivanne Pearl-Waserman¹ & Angela H DePace¹

The function of a transcriptional circuit is compared in three closely related species of Drosophila. Using quantitative imaging of gene expression, targeted transgenic reporter fly lines, and a computational framework, the sources of their differing expression outputs are identified.

• The logic of the transcriptional circuit controlling expression of the embryonic hunchback posterior stripe is highly conserved between three Drosophila species (D. melanogaster, D. yakuba, and D. pseudoobscura), despite observed differences in the hunchback posterior stripe expression pattern.
• Quantitative expression differences in the hunchback posterior stripe are largely, but not entirely, due to changes in the expression patterns of upstream regulators.
• The set of orthologous cis-regulatory elements (CREs) underlying this circuit direct similar expression patterns in concordance with previous qualitative studies; however, the expression patterns they direct are quantitatively distinct.
• These results indicate that small-scale sequence changes in CREs can impact their function and has broad implications for understanding the importance of transcription factor binding site architecture in CRE function.