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      Functional annotation of native enhancers with a Cas9 -histone demethylase fusion

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          Abstract

          Understanding of mammalian enhancer function is limited by the lack of a technology to rapidly and thoroughly test their cell type-specific function. Here, we use a nuclease-deficient (d)Cas9 histone demethylase fusion to functionally characterize previously described and novel enhancer elements for their roles in the embryonic stem cell state. Further, we distinguish the mechanism of action of dCas9-LSD1 at enhancers from previous dCas9-effectors.

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          Most cited references20

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          RSEM: accurate transcript quantification from RNA-Seq data with or without a reference genome

          Background RNA-Seq is revolutionizing the way transcript abundances are measured. A key challenge in transcript quantification from RNA-Seq data is the handling of reads that map to multiple genes or isoforms. This issue is particularly important for quantification with de novo transcriptome assemblies in the absence of sequenced genomes, as it is difficult to determine which transcripts are isoforms of the same gene. A second significant issue is the design of RNA-Seq experiments, in terms of the number of reads, read length, and whether reads come from one or both ends of cDNA fragments. Results We present RSEM, an user-friendly software package for quantifying gene and isoform abundances from single-end or paired-end RNA-Seq data. RSEM outputs abundance estimates, 95% credibility intervals, and visualization files and can also simulate RNA-Seq data. In contrast to other existing tools, the software does not require a reference genome. Thus, in combination with a de novo transcriptome assembler, RSEM enables accurate transcript quantification for species without sequenced genomes. On simulated and real data sets, RSEM has superior or comparable performance to quantification methods that rely on a reference genome. Taking advantage of RSEM's ability to effectively use ambiguously-mapping reads, we show that accurate gene-level abundance estimates are best obtained with large numbers of short single-end reads. On the other hand, estimates of the relative frequencies of isoforms within single genes may be improved through the use of paired-end reads, depending on the number of possible splice forms for each gene. Conclusions RSEM is an accurate and user-friendly software tool for quantifying transcript abundances from RNA-Seq data. As it does not rely on the existence of a reference genome, it is particularly useful for quantification with de novo transcriptome assemblies. In addition, RSEM has enabled valuable guidance for cost-efficient design of quantification experiments with RNA-Seq, which is currently relatively expensive.
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            A unique chromatin signature uncovers early developmental enhancers in humans.

            Cell-fate transitions involve the integration of genomic information encoded by regulatory elements, such as enhancers, with the cellular environment. However, identification of genomic sequences that control human embryonic development represents a formidable challenge. Here we show that in human embryonic stem cells (hESCs), unique chromatin signatures identify two distinct classes of genomic elements, both of which are marked by the presence of chromatin regulators p300 and BRG1, monomethylation of histone H3 at lysine 4 (H3K4me1), and low nucleosomal density. In addition, elements of the first class are distinguished by the acetylation of histone H3 at lysine 27 (H3K27ac), overlap with previously characterized hESC enhancers, and are located proximally to genes expressed in hESCs and the epiblast. In contrast, elements of the second class, which we term 'poised enhancers', are distinguished by the absence of H3K27ac, enrichment of histone H3 lysine 27 trimethylation (H3K27me3), and are linked to genes inactive in hESCs and instead are involved in orchestrating early steps in embryogenesis, such as gastrulation, mesoderm formation and neurulation. Consistent with the poised identity, during differentiation of hESCs to neuroepithelium, a neuroectoderm-specific subset of poised enhancers acquires a chromatin signature associated with active enhancers. When assayed in zebrafish embryos, poised enhancers are able to direct cell-type and stage-specific expression characteristic of their proximal developmental gene, even in the absence of sequence conservation in the fish genome. Our data demonstrate that early developmental enhancers are epigenetically pre-marked in hESCs and indicate an unappreciated role of H3K27me3 at distal regulatory elements. Moreover, the wealth of new regulatory sequences identified here provides an invaluable resource for studies and isolation of transient, rare cell populations representing early stages of human embryogenesis.
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              Orthogonal Cas9 Proteins for RNA-Guided Gene Regulation and Editing

              The Cas9 protein from the Streptococcus pyogenes CRISPR-Cas immune system has been adapted for both RNA-guided genome editing and gene regulation in a variety of organisms, but can mediate only a single activity at a time within any given cell. Here we characterize a set of fully orthogonal Cas9 proteins and demonstrate their ability to mediate simultaneous and independently targeted gene regulation and editing in bacteria and in human cells. We find that Cas9 orthologs display consistent patterns in their recognition of target sequences and identify a highly targetable protein from Neisseria meningitidis. Our results provide a basal set of orthogonal RNA-guided proteins for controlling biological systems and establish a general methodology for characterizing additional proteins and adapting them to eukaryotic cells.
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                Author and article information

                Journal
                101215604
                32338
                Nat Methods
                Nat. Methods
                Nature methods
                1548-7091
                1548-7105
                1 March 2015
                16 March 2015
                May 2015
                01 November 2015
                : 12
                : 5
                : 401-403
                Affiliations
                [1 ] Diabetes Center of Excellence, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
                [2 ] Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
                [3 ] Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA
                Author notes
                Correspondence: René Maehr ( rene.maehr@ 123456umassmed.edu )
                Article
                NIHMS666544
                10.1038/nmeth.3325
                4414811
                25775043
                639440df-3ac0-4bca-b319-022fed8938b6
                History
                Categories
                Article

                Life sciences
                Life sciences

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