Our results demonstrate the power of genetic network co-option to redeploy a genetic network into a new tissue context. Yet, novelties are more than mere iterations of repeated structures. We reflect on how they derive unique features by elaborating their network architecture.

Misexpression of the active form of shavenbaby in the naïve aedeagal sheath of D. melanogaster was sufficient to induce small trichomes.
This is one of the first times that genetic network co-option has been recapitulated through experimental manipulations.

Disruption of shavenbaby via mosaic CRISPR caused the truncation of trichome height, showing the important role of shavenbaby, but also indicating that there are likely other redundant transcription factors as well

Additionally, we find that the trichome genetic network was partially co-opted into the aedeagal sheath as 14 (purple) out of 23 direct targets of shavenbaby we tested have gained expression in the D. eugracilis aedeagal sheath

The novel unicellular outgrowths of D. eugracilis have evolved expression of the key trichome transcription factor shavenbaby, named for its mutant phenotype, in which trichome morphology is disrupted

We found that each of these outgrowths develop as an actin-rich (magenta) extension of a single cell (apical cell junctions grey), similar to trichomes, hair-like structures that cover the larvae and much of the adult cuticle

We developed the rapidly evolving drosophilid terminalia as a model to explore the genetic basis of novelty. D. eugracilis has over 150 differently sized outgrowths on its aedeagal sheath which appear to be absent from other species of Drosophila, including D. melanogaster.

Our new @CurrentBiology paper provides a rare glimpse into a morphological novelty in Drosophila eugracilis
In it, @gavinrrice and colleagues, infer and reproduce the likely initial steps of a novelty's formation
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