Multi-enhancer transcriptional hubs confer phenotypic robustness

Abstract

AbstractWe had previously shown inDrosophila melanogasterembryos that low-affinity Ultrabithorax (Ubx)-responsiveshavenbaby(svb) enhancers drive robust expression using localized transcriptional environments and that activesvbenhancers tended to colocalize, even when placed on different chromosomes (Tsai et al., 2017). Here, we test the hypothesis that these multi-enhancer “hubs” improve robustness by increasing transcription factor retention near transcription sites. Deleting a redundant enhancer from thesvblocus led to reduced trichome numbers in embryos raised at elevated temperatures. Using high-resolution fluorescence microscopy, we observed lower Ubx concentration and transcriptional output in this deletion allele. Transcription sites of the fullsvb cis-regulatory region inserted into a different chromosome colocalized with thesvblocus, increasing Ubx concentration, the transcriptional output ofsvb, and partially rescuing the phenotype. Thus, multiple enhancers could reinforce a local transcriptional hub to buffer against environmental stresses and genetic perturbations, providing a mechanism for phenotypical robustness.Impact statementMultiple enhancers in physical proximity can reinforce shared transcriptional “hubs” to retain transcription factors, providing a buffer during environmental stresses and genetic perturbations to preserve phenotypic robustness.