Adaptive substitutions underlying cardiac glycoside insensitivity in insects exhibit epistasis in vivo.

Predicting how species will respond to selection pressures requires understanding the factors that constrain their evolution. We use genome engineering of Drosophila to investigate constraints on the repeated evolution of unrelated herbivorous insects to toxic cardiac glycosides, which primarily occurs via a small subset of possible functionally-relevant substitutions to Na+,K+-ATPase. Surprisingly, we find that frequently observed adaptive substitutions at two sites, 111 and 122, are lethal when homozygous and adult heterozygotes exhibit dominant neural dysfunction. We identify a phylogenetically correlated substitution, A119S, that partially ameliorates the deleterious effects of substitutions at 111 and 122. Despite contributing little to cardiac glycoside-insensitivity in vitro, A119S, like substitutions at 111 and 122, substantially increases adult survivorship upon cardiac glycoside exposure. Our results demonstrate the importance of epistasis in constraining adaptive paths. Moreover, by revealing distinct effects of substitutions in vitro and in vivo, our results underscore the importance of evaluating the fitness of adaptive substitutions and their interactions in whole organisms.

Different Evolutionary Strategies To Conserve Chromatin Boundary Function in the Bithorax Complex.

Chromatin boundary elements subdivide chromosomes in multicellular organisms into physically independent domains. In addition to this architectural function, these elements also play a critical role in gene regulation. Here we investigated the evolution of a Drosophila Bithorax complex boundary element called Fab-7, which is required for the proper parasegment specific expression of the homeotic Abd-B gene. Using a "gene" replacement strategy, we show that Fab-7 boundaries from two closely related species, D. erecta and D. yakuba, and a more distant species, D. pseudoobscura, are able to substitute for the melanogaster boundary. Consistent with this functional conservation, the two known Fab-7 boundary factors, Elba and LBC, have recognition sequences in the boundaries from all species. However, the strategies used for maintaining binding and function in the face of sequence divergence is different. The first is conventional, and depends upon conservation of the 8 bp Elba recognition sequence. The second is unconventional, and takes advantage of the unusually large and flexible sequence recognition properties of the LBC boundary factor, and the deployment of multiple LBC recognition elements in each boundary. In the former case, binding is lost when the recognition sequence is altered. In the latter case, sequence divergence is accompanied by changes in the number, relative affinity, and location of the LBC recognition elements.

Ferret: a user-friendly Java tool to extract data from the 1000 Genomes Project.

UNLABELLED: The 1000 Genomes (1KG) Project provides a near-comprehensive resource on human genetic variation in worldwide reference populations. 1KG variants can be accessed through a browser and through the raw and annotated data that are regularly released on an ftp server. We developed Ferret, a user-friendly Java tool, to easily extract genetic variation information from these large and complex data files. From a locus, gene(s) or SNP(s) of interest, Ferret retrieves genotype data for 1KG SNPs and indels, and computes allelic frequencies for 1KG populations and optionally, for the Exome Sequencing Project populations. By converting the 1KG data into files that can be imported into popular pre-existing tools (e.g. PLINK and HaploView), Ferret offers a straightforward way, even for non-bioinformatics specialists, to manipulate, explore and merge 1KG data with the user's dataset, as well as visualize linkage disequilibrium pattern, infer haplotypes and design tagSNPs. AVAILABILITY AND IMPLEMENTATION: Ferret tool and source code are publicly available at http://limousophie35.github.io/Ferret/ CONTACT: ferret@nih.gov SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.