Temporal flexibility of gene regulatory network underlies a novel wing pattern in flies

Organisms have evolved endless morphological, physiological, and
behavioral novel traits during the course of evolution. Novel traits were
proposed to evolve mainly by orchestration of preexisting genes. Over the
past two decades, biologists have shown that co-option of gene regulatory
networks (GRNs) indeed underlies numerous evolutionary novelties. However,
very little is known about the actual GRN properties that allow such
redeployment. Here we have investigated the generation and evolution of
the complex wing pattern of the fly Samoaia leonensis. We show that the
transcription factor Engrailed is recruited independently from the other
players of the anterior-posterior specification network to generate a new
wing pattern. We argue that partial co-option is made possible because (i)
the anterior-posterior specification GRN is flexible over time in the
developing wing and (ii) this flexibility results from the fact every
single gene of the GRN possesses its own functional time window. We
propose that the temporal flexibility of a GRN is a general prerequisite
for its possible co-option during the course of evolution.