Donya Shodja - Rebeiz Lab
"Expansion of a pre-existing signaling center underlies the evolution of a morphological novelty in the Drosophila genitalia"
Friday, April 2nd, 2021
12:10 PM
Virtual Zoom seminar
Abstract:
How new morphological structures (“morphological novelties”) arise during evolution has been a long standing question in biology. Work on morphological novelties has frequently implicated a role for signaling pathways in their origination. In particular, the frequent appearance of signaling pathway ligands in spatial association with novel morphological structures suggests that the evolution of ligand expression is critical to installing the genetic programs underlying novelties. However, we currently lack an understanding of how the regulation of these pathways are altered to establish their roles in the development of novel morphologies. To investigate this problem, I examined the role of Notch signaling during the evolution of a recently evolved structure, the posterior lobe of the fruit fly Drosophila melanogaster. This structure is a cuticular outgrowth on the genitalia of males within the melanogaster clade. The ligand for the Notch signaling pathway, Delta, is required for posterior lobe development, and its expression has been expanded in lobe-forming species. We’ve identified partially redundant transcriptional enhancers of Delta, and show that changes both within the Delta locus, as well as upstream of Delta have occurred to generate patterns of expression associated with posterior lobe development. While these enhancers regulate Delta expression, their activities differ in both time and space. Surprisingly, our analysis demonstrates that these enhancers activate Delta over an extended period of days, likely serving multiple roles in patterning genital tissues. This work reveals that a novel role of posterior lobe development was added to an ancient signaling center with different roles that emerge over days of development. This paints a very different picture of how new traits arise: by adding and building upon pre-existing signals.