Project description:Enhancers are critical cis-regulatory elements controlling gene expression during cell development and differentiation. However, genome-wide enhancer characterization has been challenging due to the lack of a well-defined relationship between enhancers and genes. Here, we applied a massively parallel reporter assay on Arabidopsis to measure enhancer activities across the genome. We identified 4327 enhancers with various combinations of epigenetic modifications distinctively different from animal enhancers. Furthermore, we showed that enhancers differ from promoters in their preference for transcription factors. Although some enhancers are not conserved and overlap with transposable elements forming clusters, enhancers are generally conserved across thousand Arabidopsis species, suggesting they are selected under evolution pressure and could play critical roles in the regulation of important genes. Moreover, comparison analysis reveals that enhancers identified by different strategies do not overlap, suggesting these methods are complementary in nature. In sum, our work provides an additional catalog of enhancers and lays the foundation for further investigation into enhancers’ functional mechanisms in plants.
Project description:We employ a massively parallel reporter assay (MPRA) to measure the ex vivo activities of hundreds of K562 and HepG2 enhancers with known transcription factor motif instances. For seven selected motifs that correspond to known or predicted activators and repressors in the two cell types, we make directed modifications of the bases corresponding to these motifs and observe the changes in enhancer activity. Reporter mRNA-seq from HepG2 and K562 cells transfected with a ~55,000-plex MPRA plasmid pool containing 5,418 mutated human enhancer sequences, each linked to 10 distinct 10-nt tags. The reporter mRNA tags facilitate quantitation of their abundances. The same tags were also sequenced from the transfected MPRA plasmid pool to facilitate normalization to plasmid copy numbers.
Project description:We apply a massively parallel reporter assay (MPRA) that relies on mRNA and plasmid tag sequencing (Tag-Seq) to compare the regulatory activities of more than 27,000 distinct variants of two inducible enhancers in human cells: a synthetic cAMP-regulated enhancer and the virus-inducible interferon beta enhancer. The resulting data define accurate maps of functional transcription factor binding sites in both enhancers at single-nucleotide resolution and can be used the to train quantitative sequence-activity models (QSAMs). Reporter Tag-Seq from HEK293 cells transfected with each of six MPRA plasmid pools, with and without stimulation (forskolin or Sendai virus). The reporter mRNAs contain unique 10 nucleotide tags that facilitates quantitation of their abundances. The same tags were also sequenced from each ransfected plasmid pool to facilitate normalization to plasmid copy numbers. The reporter constructs were designed according to two different mutagenesis strategies: 'single-hit scanning' and 'multi-hit sampling'. The specific variants are included in the processed data files.
Project description:We apply a massively parallel reporter assay (MPRA) that relies on mRNA and plasmid tag sequencing (Tag-Seq) to compare the regulatory activities of more than 27,000 distinct variants of two inducible enhancers in human cells: a synthetic cAMP-regulated enhancer and the virus-inducible interferon beta enhancer. The resulting data define accurate maps of functional transcription factor binding sites in both enhancers at single-nucleotide resolution and can be used the to train quantitative sequence-activity models (QSAMs).
Project description:We employ a massively parallel reporter assay (MPRA) to measure the ex vivo activities of hundreds of K562 and HepG2 enhancers with known transcription factor motif instances. For seven selected motifs that correspond to known or predicted activators and repressors in the two cell types, we make directed modifications of the bases corresponding to these motifs and observe the changes in enhancer activity.
Project description:We performed a Massively Parallel Reporter Assay (MPRA) to screen >30,000 human-specific substitutions in ChIP-seq-identified Human Gain Enhancers (HGEs) and Human Accelerated Regions (HARs), highly conserved non-coding regions that show accelerated sequence evolution in humans. After comparing human and chimpanzee reference alleles, we used a second MPRA to deconvolute individual substitutions within differentially active enhancers from substitutions in the same fragment and from other variants (human segregating variants or chimpanzee-specific variants) to isolate their specific effects on enhancer activity.
Project description:Cone-rod homeobox (CRX) is a paired-like homeodomain transcription factor (TF) and a master regulator of photoreceptor development in vertebrates. The in vitro DNA binding preferences of CRX have been described in detail, but the degree to which in vitro binding affinity is correlated with in vivo enhancer activity is not known. In addition, paired-class homeodomain TFs can bind DNA cooperatively as both homodimers and heterodimers at inverted TAAT half-sites separated by two or three nucleotides. This dimeric configuration is thought to mediate target specificity, but whether monomeric and dimeric sites encode distinct levels of activity is not known. Here, we use a massively parallel reporter assay, CRE-seq, to determine how local sequence context shapes the regulatory activity of CRX binding sites in mouse photoreceptors. We assay inactivating mutations in >1700 TFBSs, and we find that dimeric CRX binding sites act as stronger enhancers than monomeric CRX binding sites. Furthermore, the activity of dimeric half-sites is cooperative, dependent on a strict three-base-pair spacing, and tuned by the identity of the spacer nucleotides. Saturating single-nucleotide mutagenesis of 195 CRX binding sites shows that, on average, changes in TFBS affinity are correlated with changes in regulatory activity, but this relationship is obscured when considering mutations across multiple CREs. Taken together, these results demonstrate that the activity of CRX binding sites is highly dependent on sequence context, providing insight into photoreceptor gene regulation and illustrating functional principles of homeodomain binding sites that may be conserved in other cell types.
Project description:We designed 4 oligonucleotide libraries containing either a retained intron, a cassette exon, tandem 5' or tandem 3' splice sites, cloned them into dedicated reporter constructs, transfected and integrated these constructs in the genome of K562 cells, and performed targeted RNA sequencing to determine RNA splicing ratios and a FACSseq approach to determine protein isoform ratios.
Project description:A massively parallel reporter assay, MPRA, was conducted in mouse embryonic stem cells (mESC). Synthetic cis-regulatory elements comprised of binding sites for pluripotency transcription factors and genomic sequences with comparable binding sites configurations were used in the assay. Transcripts of dsRed were amplified via PCR from the end of the transcript to sequence 3' UTR barcodes.