Meeting Abstract
How the gene regulatory networks (GRNs) underlying morphological characters are built is a major subject of interest in the field of evolutionary developmental biology. Network co-option, a mechanism in which pre-existing transcriptional circuits are redeployed to a new developmental setting, has been proposed to facilitate the rapid evolution of GRNs. Although several examples implicate the contribution of network co-option to the evolution of novel structures, examples that analyze this process at the level of regulatory DNA are currently lacking. We study the posterior lobe, a genital structure that recently evolved within the Drosophila melanogaster clade. We discovered that the regulatory regions responsible for the genital activity of several posterior lobe developmental genes are also active in completely unrelated structures, including the larval posterior spiracles and embryonic midgut. Further, we identified several transcription factor binding sites necessary for both the derived and ancestral activities, providing strong molecular evidence for network co-option. One major challenge concerning the network co-option mechanism, however, is that it is predicted to create pleiotropic constraint between the derived and ancestral networks. To address this, we analyzed the activity of co-opted regulatory DNA from species exhibiting highly-divergent posterior lobe morphologies. We discovered modifications to co-opted regulatory DNA that altered only genital activity, indicating that it is possible to incur mutations that enact modular effects to the derived tissue without disrupting the ancestral activity.
