Abstracts (first author)
Positive selection drives the transcriptional evolution of the Drosophila chemosensory gene families
The chemosensory system is involved in critical processes such as nutrition, reproduction and social communication, being therefore crucial for the survival of animals. In insects, the early steps of the chemosensory process are mediated by proteins encoded in multigene families, including extracellular ligand-binding proteins (OBPs, CSPs and CheBs) and membrane receptor proteins (ORs, GRs and IRs). Since the ability to discriminate chemical stimuli (and thus the individual fitness) depends on such gene families, positive selection may promote their transcriptional evolution as an adaptation to external environment changes.
Here we examined the transcriptional changes underlying the adaptive evolution of the chemosensory gene families. In particular, we analysed the OBP gene cluster organisation, the turnover of cis-regulatory elements, and the patterns of polymorphism and divergence at the upstream regions of the genes of these chemosensory families. For that, we integrated information from diverse genome-wide data sets, such as the expression pattern, chromatin state and promoter architecture of the confined genes.
We found that chromatin domains play an important role in the maintenance of the OBP clusters by restricting the location of genes to regions with the appropriate transcriptional environment: low expression intensity, high expression breadth and noise. These elevated noise levels may be adaptive, by increasing the behavioural plasticity in front external changing environments. Moreover, we also identified the positive selection signature at the nucleotide variability of the upstream chemosensory regions, as well as in the turnover of cis-regulatory elements. Therefore, our results show that positive selection has driven the transcriptional evolution of the chemosensory gene families.