Characterization of genomic regulatory domains conserved across the genus Drosophila

In both vertebrates and insects, the conservation of local gene order among distantly related species (microsynteny) is higher than expected in the presence of highly conserved noncoding elements (HCNEs). Dense clusters of HCNEs, or HCNE peaks, have been proposed to mediate the regulation of sometimes distantly located genes, which are central for the developmental program of the organism. Thus, the regions encompassing HCNE peaks and their targets in different species would form genomic regulatory domains (GRDs), which should presumably enjoy an enhanced stability over evolutionary time. By leveraging genome rearrangement information from nine Drosophila species and using gene functional and phenotypic information, we performed a comprehensive characterization of the organization of microsynteny blocks harboring HCNE peaks and provide a functional portrait of the putative HCNE targets that reside therein. We found that Drosophila HCNE peaks tend to colocalize more often than expected and to be evenly distributed across chromosomal elements. Putative HCNE peak targets are characterized by a tight association with particular promoter motifs, higher incidence of severe mutant phenotypes, and evidence of a more precise regulation of gene expression during important developmental transitions. As for their physical organization, ~65% of these putative targets are separated by a median of two genes from their nearest HCNE peaks. These observations represent the first functional portrait of this euchromatic fraction of the Drosophila genome with distinctive evolutionary dynamics, which will facilitate future experimental studies on the interactions between HCNE peaks and their targets in a genetically tractable system such as Drosophila melanogaster.