In locus analysis of patterning evolution of the BMP type II receptor Wishful thinking.

Proper tissue patterning is an essential step during organ formation. During this process, genes are expressed in distinct patterns, defining boundaries for future functional domains. The bone morphogenetic protein (BMP) signaling pathway sets the anterior domain during eggshell patterning. Previously, the Drosophila melanogaster homolog of BMPR2, Wishful thinking (WIT), was shown to be required for BMP signaling and patterning during eggshell formation. Expressed in a conserved anterior pattern, the width of wit patterning in the follicular epithelium is evolutionarily divergent between Drosophila species. We used genome editing to demonstrate how the gene pattern divergence is controlled in cis within the wit locus of D. virilis Furthermore, unlike direct targets of BMP signaling, we demonstrate how one transcription factor binding site shapes the pattern of WIT in D. melanogaster by negative regulation. However, changes in this site are not sufficient to explain the evolution of wit patterning, suggesting that a positive regulatory element that controls pattern divergence remains to be discovered.