Mammalian genomes are pervasively transcribed to produce thousands of long non-coding RNAs (lncRNAs) A few of these lncRNAs have been shown to recruit regulatory complexes through RNA-protein interactions to influence the expression of nearby genes, and it has been suggested that many other lncRNAs can also act as local regulators Such local functions could explain the observation that lncRNA expression is often correlated with the expression of nearby genes However, these correlations have been challenging to dissect and could alternatively result from processes that are not mediated by the lncRNA transcripts themselves For example, some gene promoters have been proposed to have dual functions as enhancers, and the process of transcription itself may contribute to gene regulation by recruiting activating factors or remodelling nucleosomes Here we use genetic manipulation in mouse cell lines to dissect 12 genomic loci that produce lncRNAs and find that 5 of these loci influence the expression of a neighbouring gene in cis Notably, none of these effects requires the specific lncRNA transcripts themselves and instead involves general processes associated with their production, including enhancer-like activity of gene promoters, the process of transcription, and the splicing of the transcript Furthermore, such effects are not limited to lncRNA loci: we find that four out of six protein-coding loci also influence the expression of a neighbour These results demonstrate that cross-talk among neighbouring genes is a prevalent phenomenon that can involve multiple mechanisms and cis-regulatory signals, including a role for RNA splice sites These mechanisms may explain the function and evolution of some genomic loci that produce lncRNAs and broadly contribute to the regulation of both coding and non-coding genes

Local regulation of gene expression by lncRNA promoters, transcription and splicing

Precise spatio-temporal control of gene activity is essential for organismal development, growth, and survival in a changing environment. Decisive steps in gene regulation involve the pausing of RNA polymerase II (Pol II) in early elongation, and the controlled release of paused polymerase into productive RNA synthesis. Here we describe the factors that enable pausing and the events that trigger Pol II release into the gene. We also discuss open questions in the field concerning the stability of paused Pol II, nucleosomes as obstacles to elongation, and potential roles of pausing in defining the precision and dynamics of gene expression.

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Promoter-proximal pausing of RNA polymerase II: a nexus of gene regulation

The epigenetic modifications of histones are versatile marks that are intimately connected to development and disease pathogenesis including human cancers. In this review, we will discuss the many different types of histone modifications and the biological processes with which they are involved. Specifically, we review the enzymatic machineries and modifications that are involved in cancer development and progression, and how to apply currently available small molecule inhibitors for histone modifiers as tool compounds to study the functional significance of histone modifications and their clinical implications.

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Epigenetic modifications of histones in cancer

The human gene catalogue is essentially complete, but we lack an equivalently vetted inventory of bona fide human enhancers. Hundreds of thousands of candidate enhancers have been nominated via biochemical annotations; however, only a handful of these have been validated and confidently linked to their target genes. Here we review emerging technologies for discovering, characterizing and validating human enhancers at scale. We furthermore propose a new framework for operationally defining enhancers that accommodates the heterogeneous and complementary results that are emerging from reporter assays, biochemical measurements and CRISPR screens. In this Review, Gasperini, Tome and Shendure discuss the evolving definitions of transcriptional enhancers, as well as diverse modern experimental tools to identify them. The authors describe how these diverse mindsets and methods provide differing but complementary insights into enhancers, each with notable strengths and caveats. They discuss how such views and approaches might be combined in a comprehensive catalogue of functional enhancers.

Towards a comprehensive catalogue of validated and target-linked human enhancers

Gene expression is regulated by promoters, which initiate transcription, and enhancers, which control their temporal and spatial activity However, the discovery that mammalian enhancers also initiate transcription questions the inherent differences between enhancers and promoters Here, we investigate the transcriptional properties of enhancers during Drosophila embryogenesis using characterized developmental enhancers We show that while the timing of enhancer transcription is generally correlated with enhancer activity, the levels and directionality of transcription are highly varied among active enhancers To assess how this impacts function, we developed a dual transgenic assay to simultaneously measure enhancer and promoter activities from a single element in the same embryo Extensive transgenic analysis revealed a relationship between the direction of endogenous transcription and the ability to function as an enhancer or promoter in vivo, although enhancer RNA (eRNA) production and activity are not always strictly coupled Some enhancers (mainly bidirectional) can act as weak promoters, producing overlapping spatio-temporal expression Conversely, bidirectional promoters often act as strong enhancers, while unidirectional promoters generally cannot The balance between enhancer and promoter activity is generally reflected in the levels and directionality of eRNA transcription and is likely an inherent sequence property of the elements themselves

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The degree of enhancer or promoter activity is reflected by the levels and directionality of eRNA transcription.

We provide a protocol for precision nuclear run-on sequencing (PRO-seq) and its variant, PRO-cap, which map the location of active RNA polymerases (PRO-seq) or transcription start sites (TSSs) (PRO-cap) genome-wide at high resolution. The density of RNA polymerases at a particular genomic locus directly reflects the level of nascent transcription at that region. Nuclei are isolated from cells and, under nuclear run-on conditions, transcriptionally engaged RNA polymerases incorporate one or, at most, a few biotin-labeled nucleotide triphosphates (biotin-NTPs) into the 3' end of nascent RNA. The biotin-labeled nascent RNA is used to prepare sequencing libraries, which are sequenced from the 3' end to provide high-resolution positional information for the RNA polymerases. PRO-seq provides much higher sensitivity than ChIP-seq, and it generates a much larger fraction of usable sequence reads than ChIP-seq or NET-seq (native elongating transcript sequencing). Similarly to NET-seq, PRO-seq maps the RNA polymerase at up to base-pair resolution with strand specificity, but unlike NET-seq it does not require immunoprecipitation. With the protocol provided here, PRO-seq (or PRO-cap) libraries for high-throughput sequencing can be generated in 4-5 working days. The method has been applied to human, mouse, Drosophila melanogaster and Caenorhabditis elegans cells and, with slight modifications, to yeast.

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Katie Munson

Papers

Base-pair-resolution genome-wide mapping of active RNA polymerases using precision nuclear run-on (PRO-seq)