An IMP-Brandeis collaboration reveals the evolution of regulatory sequences in Drosophilids
By Yuliya Sytnikova and Nelson Lau
Enhancers are cis-regulatory DNA sequences that influence the promoters of genes, but identifying enhancers is not a straightforward process. Previously, the Stark lab developed a method for genome-wide enhancer detection called STARR-seq, (Arnold, Gerlach et al. 2013), that allowed them to identify thousands of enhancer sequences around the Drosophila melanogaster genome. In the most recent issue of Nature Genetics, a collaboration between the Stark lab of the IMP (Institute of Molecular Pathology) in Vienna, Austria, and the Lau lab at Brandeis University examines this hypothesis by studying the conservation of enhancer regulatory regions during Drosophilid fly evolution.
To ask if enhancers from D. melanogaster enhancers are also conserved in other Drosophila species in their sequences and locations, the Stark lab extended the STARR-Seq approach to D.yakuba and D.ananassae, which are separated from D.melanogaster by 11 and 40 million years ago, respectively (Arnold, Gerlach et al. 2014). Interestingly, this study also revealed hundreds of new sequences that gained enhancer function differentially between D.yakuba, D.ananassae, and D.melanogaster.
However, to test if these new sequences meaningfully direct different gene expression changes, the Lau lab conducted a targeted mRNA profiling experiment in purified endogenous follicle cells from D.yakuba and D.ananassae. The Stark lab had initiated the STARR-Seq analysis in an Ovarian Somatic Cell (OSC) line, which originated from the follicle cells of D.melanogaster, therefore the profiling of endogenous follicle cells from D.yakuba and D.ananassae was critical. The Lau lab achieved this using a methodology they developed for profiling Piwi-interacting RNAs from these cells (Matts, Synikova et al. 2013).
Figure 6: Evolution of enhancer activity in OSCs and gene expression in follicle cells in vivo.
Arnold CD, Gerlach D, Spies D, Matts JA, Sytnikova YA, Pagani M, Lau NC, Stark A. Nat Genet. 2014 Jun 8. doi: 10.1038/ng.3009. [Epub ahead of print] Quantitative genome-wide enhancer activity maps for five Drosophila species show functional enhancer conservation and turnover during cis-regulatory evolution.
Matts JA, Sytnikova Y, Chirn GW, Igloi GL, Lau NC. Methods Mol Biol. 2014;1093:123-36. doi: 10.1007/978-1-62703-694-8_10. Small RNA library construction from minute biological samples.