Showing papers by "Eivind Valen published in 2014"

An atlas of active enhancers across human cell types and tissues

Abstract: Enhancers control the correct temporal and cell-type-specific activation of gene expression in multicellular eukaryotes. Knowing their properties, regulatory activity and targets is crucial to understand the regulation of differentiation and homeostasis. Here we use the FANTOM5 panel of samples, covering the majority of human tissues and cell types, to produce an atlas of active, in vivo-transcribed enhancers. We show that enhancers share properties with CpG-poor messenger RNA promoters but produce bidirectional, exosome-sensitive, relatively short unspliced RNAs, the generation of which is strongly related to enhancer activity. The atlas is used to compare regulatory programs between different cells at unprecedented depth, to identify disease-associated regulatory single nucleotide polymorphisms, and to classify cell-type-specific and ubiquitous enhancers. We further explore the utility of enhancer redundancy, which explains gene expression strength rather than expression patterns. The online FANTOM5 enhancer atlas represents a unique resource for studies on cell-type-specific enhancers and gene regulation.

A promoter-level mammalian expression atlas

Abstract: Regulated transcription controls the diversity, developmental pathways and spatial organization of the hundreds of cell types that make up a mammal Using single-molecule cDNA sequencing, we mapped transcription start sites (TSSs) and their usage in human and mouse primary cells, cell lines and tissues to produce a comprehensive overview of mammalian gene expression across the human body We find that few genes are truly 'housekeeping', whereas many mammalian promoters are composite entities composed of several closely separated TSSs, with independent cell-type-specific expression profiles TSSs specific to different cell types evolve at different rates, whereas promoters of broadly expressed genes are the most conserved Promoter-based expression analysis reveals key transcription factors defining cell states and links them to binding-site motifs The functions of identified novel transcripts can be predicted by coexpression and sample ontology enrichment analyses The functional annotation of the mammalian genome 5 (FANTOM5) project provides comprehensive expression profiles and functional annotation of mammalian cell-type-specific transcriptomes with wide applications in biomedical research

CHOPCHOP: a CRISPR/Cas9 and TALEN web tool for genome editing

Abstract: Major advances in genome editing have recently been made possible with the development of the TALEN and CRISPR/Cas9 methods. The speed and ease of implementing these technologies has led to an explosion of mutant and transgenic organisms. A rate-limiting step in efficiently applying TALEN and CRISPR/Cas9 methods is the selection and design of targeting constructs. We have developed an online tool, CHOPCHOP (https://chopchop.rc.fas.harvard.edu), to expedite the design process. CHOPCHOP accepts a wide range of inputs (gene identifiers, genomic regions or pasted sequences) and provides an array of advanced options for target selection. It uses efficient sequence alignment algorithms to minimize search times, and rigorously predicts off-target binding of single-guide RNAs (sgRNAs) and TALENs. Each query produces an interactive visualization of the gene with candidate target sites displayed at their genomic positions and color-coded according to quality scores. In addition, for each possible target site, restriction sites and primer candidates are visualized, facilitating a streamlined pipeline of mutant generation and validation. The ease-of-use and speed of CHOPCHOP make it a valuable tool for genome engineering.

Efficient Mutagenesis by Cas9 Protein-Mediated Oligonucleotide Insertion and Large-Scale Assessment of Single-Guide RNAs

Abstract: The CRISPR/Cas9 system has been implemented in a variety of model organisms to mediate site-directed mutagenesis. A wide range of mutation rates has been reported, but at a limited number of genomic target sites. To uncover the rules that govern effective Cas9-mediated mutagenesis in zebrafish, we targeted over a hundred genomic loci for mutagenesis using a streamlined and cloning-free method. We generated mutations in 85% of target genes with mutation rates varying across several orders of magnitude, and identified sequence composition rules that influence mutagenesis. We increased rates of mutagenesis by implementing several novel approaches. The activities of poor or unsuccessful single-guide RNAs (sgRNAs) initiating with a 5′ adenine were improved by rescuing 5′ end homogeneity of the sgRNA. In some cases, direct injection of Cas9 protein/sgRNA complex further increased mutagenic activity. We also observed that low diversity of mutant alleles led to repeated failure to obtain frame-shift mutations. This limitation was overcome by knock-in of a stop codon cassette that ensured coding frame truncation. Our improved methods and detailed protocols make Cas9-mediated mutagenesis an attractive approach for labs of all sizes.

Toddler: an embryonic signal that promotes cell movement via Apelin receptors.

Abstract: It has been assumed that most, if not all, signals regulating early development have been identified. Contrary to this expectation, we identified 28 candidate signaling proteins expressed during zebrafish embryogenesis, including Toddler, a short, conserved, and secreted peptide. Both absence and overproduction of Toddler reduce the movement of mesendodermal cells during zebrafish gastrulation. Local and ubiquitous production of Toddler promote cell movement, suggesting that Toddler is neither an attractant nor a repellent but acts globally as a motogen. Toddler drives internalization of G protein-coupled APJ/Apelin receptors, and activation of APJ/Apelin signaling rescues toddler mutants. These results indicate that Toddler is an activator of APJ/Apelin receptor signaling, promotes gastrulation movements, and might be the first in a series of uncharacterized developmental signals.

Nuclear stability and transcriptional directionality separate functionally distinct RNA species

Abstract: Mammalian genomes are pervasively transcribed, yielding a complex transcriptome with high variability in composition and cellular abundance. Although recent efforts have identified thousands of new long non-coding (lnc) RNAs and demonstrated a complex transcriptional repertoire produced by protein-coding (pc) genes, limited progress has been made in distinguishing functional RNA from spurious transcription events. This is partly due to present RNA classification, which is typically based on technical rather than biochemical criteria. Here we devise a strategy to systematically categorize human RNAs by their sensitivity to the ribonucleolytic RNA exosome complex and by the nature of their transcription initiation. These measures are surprisingly effective at correctly classifying annotated transcripts, including lncRNAs of known function. The approach also identifies uncharacterized stable lncRNAs, hidden among a vast majority of unstable transcripts. The predictive power of the approach promises to streamline the functional analysis of known and novel RNAs.

Genome-wide nucleosome map and cytosine methylation levels of an ancient human genome

Abstract: Epigenetic information is available from contemporary organisms, but is difficult to track back in evolutionary time. Here, we show that genome-wide epigenetic information can be gathered directly from next-generation sequence reads of DNA isolated from ancient remains. Using the genome sequence data generated from hair shafts of a 4000-yr-old Paleo-Eskimo belonging to the Saqqaq culture, we generate the first ancient nucleosome map coupled with a genome-wide survey of cytosine methylation levels. The validity of both nucleosome map and methylation levels were confirmed by the recovery of the expected signals at promoter regions, exon/intron boundaries, and CTCF sites. The top-scoring nucleosome calls revealed distinct DNA positioning biases, attesting to nucleotide-level accuracy. The ancient methylation levels exhibited high conservation over time, clustering closely with modern hair tissues. Using ancient methylation information, we estimated the age at death of the Saqqaq individual and illustrate how epigenetic information can be used to infer ancient gene expression. Similar epigenetic signatures were found in other fossil material, such as 110,000- to 130,000-yr-old bones, supporting the contention that ancient epigenomic information can be reconstructed from a deep past. Our findings lay the foundation for extracting epigenomic information from ancient samples, allowing shifts in epialleles to be tracked through evolutionary time, as well as providing an original window into modern epigenomics.

ErbB2 upregulates the Na+,HCO3−-cotransporter NBCn1/SLC4A7 in human breast cancer cells via Akt, ERK, Src, and Krüppel-like factor 4

Abstract: Misregulation of acid-base transport plays central roles in cancer development. We previously demonstrated the strong up-regulation of the Na(+),HCO3(-) cotransporter NBCn1 (SLC4A7) in MCF-7 breast cancer cells by a truncated, constitutively active ErbB2 (HER2) receptor, ΔNErbB2, and showed that NBCn1 expression and activity are increased in breast cancer tissue from patients. Here, we present the first in-depth characterization of an SLC4A7 promoter and identify its minimal ΔNErbB2-sensitive region. Inhibition or siRNA-mediated knockdown of PI3K, Akt1, ERK1/2, or Src decreased the NBCn1 protein level in ΔNErbB2-expressing MCF-7 cells by ~50, 60, 30 and 35%, respectively. Further, knockdown of the transcription factor Kruppel-like factor 4 (KLF4) reduced NBCn1 protein expression by ~40%, and KLF4 overexpression increased NBCn1 expression by 50-80%. In contrast, knockdown of the closely related transcription factor specificity protein 1 (Sp1) or transfection with dominant-negative Sp1 increased NBCn1 expression by ~35 and ~50%, respectively. NBCn1 expression was also increased by stimulation of full-length ErbB1, -2, and -3 receptors in SKBr3 cells (1.5- and 2-fold by NRG1 or EGF, respectively) or after their exogenous expression in MCF-7 cells. Finally, stimulation with NRG1 or EGF more than doubled acid extrusion capacity in SKBr3 cells. In conclusion, NBCn1 is strongly upregulated by ErbB receptor signaling in a manner involving opposite effects of KLF4 and Sp1, transcription factors with central roles in cancer development. ErbB-induced up-regulation of NBCn1-mediated acid extrusion may play important physiological and pathophysiological roles in the breast epithelium and other tissues with high ErbB receptor levels.

Nuclear stability and transcriptional directionality separate functionally distinct RNA species

Abstract: Mammalian genomes are pervasively transcribed, yielding a complex transcriptome with high variability in composition and cellular abundance. While recent efforts have identified thousands of new long non-coding (lnc) RNAs and demonstrated a complex transcriptional repertoire produced by protein-coding (pc) genes, limited progress has been made in distinguishing functional RNA from spurious transcription events. This is partly due to present RNA classification, which is typically based on technical rather than biochemical criteria. Here we devise a strategy to systematically categorize human RNAs by their sensitivity to the ribonucleolytic RNA exosome complex and by the nature of their transcription initiation. These measures are surprisingly effective at correctly classifying annotated transcripts, including lncRNAs of known function. The approach also identifies uncharacterized stable lncRNAs, hidden among a vast majority of unstable transcripts. The predictive power of the approach promises to streamline the functional analysis of known and novel RNAs.