Hyeshik Chang

Mathematical model helps scientists decide where to submit their papers

Nature 518, 7537 (2015). doi:10.1038/518009f

Author: Chris Woolston

A study that ranks ecology journals on the basis of citation numbers and review times attracts attention online.

Nature advance online publication 04 February 2015. doi:10.1038/nature14219

Authors: Timothy M. Colussi, David A. Costantino, Jianyu Zhu, John Paul Donohue, Andrei A. Korostelev, Zane A. Jaafar, Terra-Dawn M. Plank, Harry F. Noller & Jeffrey S. Kieft

The central dogma of gene expression (DNA to RNA to protein) is universal, but in different domains of life there are fundamental mechanistic differences within this pathway. For example, the canonical molecular signals used to initiate protein synthesis in bacteria and eukaryotes are mutually exclusive. However, the core structures and conformational dynamics of ribosomes that are responsible for the translation steps that take place after initiation are ancient and conserved across the domains of life. We wanted to explore whether an undiscovered RNA-based signal might be able to use these conserved features, bypassing mechanisms specific to each domain of life, and initiate protein synthesis in both bacteria and eukaryotes. Although structured internal ribosome entry site (IRES) RNAs can manipulate ribosomes to initiate translation in eukaryotic cells, an analogous RNA structure-based mechanism has not been observed in bacteria. Here we report our discovery that a eukaryotic viral IRES can initiate translation in live bacteria. We solved the crystal structure of this IRES bound to a bacterial ribosome to 3.8 Å resolution, revealing that despite differences between bacterial and eukaryotic ribosomes this IRES binds directly to both and occupies the space normally used by transfer RNAs. Initiation in both bacteria and eukaryotes depends on the structure of the IRES RNA, but in bacteria this RNA uses a different mechanism that includes a form of ribosome repositioning after initial recruitment. This IRES RNA bridges billions of years of evolutionary divergence and provides an example of an RNA structure-based translation initiation signal capable of operating in two domains of life.

To understand the evolutionary dynamics between transcription factor (TF) binding and gene expression in mammals, we compared transcriptional output and the binding intensities for three tissue-specific TFs in livers from four closely related mouse species. For each transcription factor, TF-dependent genes and the TF binding sites most likely to influence mRNA expression were identified by comparing mRNA expression levels between wild-type and TF knockout mice. Independent evolution was observed genome-wide between the rate of change in TF binding and the rate of change in mRNA expression across taxa, with the exception of a small number of TF-dependent genes. We also found that binding intensities are preferentially conserved near genes whose expression is dependent on the TF, and the conservation is shared among binding peaks in close proximity to each other near the TSS. Expression of TF-dependent genes typically showed an increased sensitivity to changes in binding levels as measured by mRNA abundance. Taken together, these results highlight a significant tolerance to evolutionary changes in TF binding intensity in mammalian transcriptional networks and suggest that some TF-dependent genes may be largely regulated by a single TF across evolution.

This protocol is used to denature and separate large mRNA molecules (0.5–10 kb) on agarose gels by electrophoretic size fractionation. Glyoxal (also called diformyl or ethanedial), the agent responsible for maintaining denaturation in this protocol, contains two carbonyl groups that react to form a cyclic ring structure with the imino and amino groups of guanine. It can also react with the amino groups of adenine and cytidine. When RNA is denatured in the presence of glyoxal, this covalent adduct prevents normal base pairing and maintains the RNA in a denatured state in agarose gels. Once formed, these adducts are stable at room temperature at pH <7.0; thus, there is no need to add glyoxal to the gel or to the gel buffers to maintain the RNA in the denatured state. Because the fully denatured RNA migrates through agarose gels according to its molecular mass, this method can be used to accurately size mRNA molecules. Following electrophoresis and reversal of glyoxalation, the RNA can be detected using a northern hybridization procedure.

Electrophoretic size fractionation can be used to denature and separate large mRNA molecules (0.5–10 kb) on formaldehyde-containing agarose gels. Formaldehyde contains a carbonyl group that reacts to form Schiff bases with the imino or amino groups of guanine, adenine, and cytosine. These covalent adducts prevent normal base pairing and maintain the RNA in a denatured state. Because these adducts are unstable, formaldehyde must be present in the gel to maintain the RNA in the denatured state. This protocol describes the preparation of an agarose gel with formaldehyde and its setup in a horizontal electrophoresis apparatus. RNA samples are prepared and denatured in a solution of formamide and formaldehyde and, with 0.5- to 10-kb size markers, subjected to electrophoresis through the gel. Following electrophoresis, the gel is stained to visualize RNA markers or rRNA using one of several different types of stains.

Publication date: 19 February 2015
Source:Molecular Cell, Volume 57, Issue 4
Author(s): Peiying Ye , Yu Liu , Chong Chen , Fei Tang , Qi Wu , Xiang Wang , Chang-Gong Liu , Xiuping Liu , Runhua Liu , Yang Liu , Pan Zheng
mTOR senses nutrient and energy status to regulate cell survival and metabolism in response to environmental changes. Surprisingly, targeted mutation of Tsc1, a negative regulator of mTORC1, caused a broad reduction in miRNAs due to Drosha degradation. Conversely, targeted mutation of Raptor, an essential component of mTORC1, increased miRNA biogenesis. mTOR activation increased expression of Mdm2, which is hereby identified as the necessary and sufficient ubiquitin E3 ligase for Drosha. Drosha was induced by nutrient and energy deprivation and conferred resistance to glucose deprivation. Using a high-throughput screen of a miRNA library, we identified four miRNAs that were necessary and sufficient to protect cells against glucose-deprivation-induced apoptosis. These miRNA was regulated by glucose through the mTORC1-MDM2-DROSHA axis. Taken together, our data reveal an mTOR-Mdm2-Drosha pathway in mammalian cells that broadly regulates miRNA biogenesis as a response to alteration in cellular environment.

Graphical abstract

Teaser

Ye et al. connect mTOR signaling to miRNA biogenesis, showing that mTOR increases expression of Mdm2 and that Mdm2 is a ubiquitin E3 ligase for Drosha. They show that Drosha is induced by nutrient deprivation and confers resistance to glucose deprivation.

Publication date: March 2015
Source:Trends in Biotechnology, Volume 33, Issue 3
Author(s): Xiaopei Qiu , Hong Zhang , Helian Yu , Tianlun Jiang , Yang Luo
Duplex-specific nucleases (DSNs) are promising tools for bioanalysis because of their unique ability to cleave DNA within duplexes while keeping a single strand intact. There is prevalent use of DSNs in both biomedical and biological science applications, such as cDNA library construction, circulating miRNA detection, telomeric overhang detection, and SNP recognition. We present an overview of the current knowledge of DSNs, with special emphasis on DSN-mediated isothermal signal amplification strategies for trace miRNA detection. Continued innovation to address key challenges, such as amplification-free approaches, will open up new avenues in the field of miRNA profiling, offering opportunities for improved personalized medicine, preventive medicine, and translational medicine.

Background: Long noncoding RNAs (lncRNAs) have been implicated in diverse biological processes. In contrast to extensive genomic annotation of lncRNA transcripts, far fewer have been characterized for subcellular localization and cell-to-cell variability. Addressing this requires systematic, direct visualization of lncRNAs in single cells at single-molecule resolution. Results: We use single-molecule RNA-FISH to systematically quantify and categorize the subcellular localization patterns of a representative set of 61 lncRNAs in three different cell types. Our survey yields high-resolution quantification and stringent validation of the number and spatial positions of these lncRNA, with an mRNA set for comparison. Using this highly quantitative image-based dataset, we observe a variety of subcellular localization patterns, ranging from bright sub-nuclear foci to almost exclusively cytoplasmic localization. We also find that the low abundance of lncRNAs observed from cell population measurements cannot be explained by high expression in a small subset of `jackpot? cells. Additionally, nuclear lncRNA foci dissolve during mitosis and become widely dispersed, suggesting these lncRNAs are not mitotic bookmarking factors. Moreover, we see that divergently transcribed lncRNAs do not always correlate with their cognate mRNA, nor do they have a characteristic localization pattern. Conclusions: Our systematic, high-resolution survey of lncRNA localization reveals aspects of lncRNAs that are similar to mRNAs, such as cell-to-cell variability, but also several distinct properties. These characteristics may correspond to particular functional roles. Our study also provides a quantitative description of lncRNAs at the single-cell level and a universally applicable framework for future study and validation of lncRNAs.

Related Articles

Re: lin28 sustains early renal progenitors and induces wilms tumor.

J Urol. 2015 Feb;193(2):730-1

Authors: Atala A

PMID: 25617308 [PubMed - in process]

Related Articles

Detecting riboSNitches with RNA folding algorithms: a genome-wide benchmark.

Nucleic Acids Res. 2015 Jan 23;

Authors: Corley M, Solem A, Qu K, Chang HY, Laederach A

Abstract
Ribonucleic acid (RNA) secondary structure prediction continues to be a significant challenge, in particular when attempting to model sequences with less rigidly defined structures, such as messenger and non-coding RNAs. Crucial to interpreting RNA structures as they pertain to individual phenotypes is the ability to detect RNAs with large structural disparities caused by a single nucleotide variant (SNV) or riboSNitches. A recently published human genome-wide parallel analysis of RNA structure (PARS) study identified a large number of riboSNitches as well as non-riboSNitches, providing an unprecedented set of RNA sequences against which to benchmark structure prediction algorithms. Here we evaluate 11 different RNA folding algorithms' riboSNitch prediction performance on these data. We find that recent algorithms designed specifically to predict the effects of SNVs on RNA structure, in particular remuRNA, RNAsnp and SNPfold, perform best on the most rigorously validated subsets of the benchmark data. In addition, our benchmark indicates that general structure prediction algorithms (e.g. RNAfold and RNAstructure) have overall better performance if base pairing probabilities are considered rather than minimum free energy calculations. Although overall aggregate algorithmic performance on the full set of riboSNitches is relatively low, significant improvement is possible if the highest confidence predictions are evaluated independently.

PMID: 25618847 [PubMed - as supplied by publisher]

Eukaryotic translation initiation commences at the initiation codon near the 5′ end of mRNA by a 40S ribosomal subunit, and the recruitment of a 40S ribosome to an mRNA is facilitated by translation initiation factors interacting with the m7G cap and/or poly(A) tail. The 40S ribosome recruited to an mRNA...

Motivation: Abstract shape analysis, first proposed in 2004, allows one to extract several relevant structures from the folding space of an RNA sequence, preferable to focusing in a single structure of minimal free energy. We report recent extensions to this approach.

Results: We have rebuilt the original RNAshapes as a repository of components that allows us to integrate several established tools for RNA structure analysis: RNAshapes, RNAalishapes and pknotsRG, including its recent extension pKiss. As a spin-off, we obtain heretofore unavailable functionality: e. g. with pKiss, we can now perform abstract shape analysis for structures holding pseudoknots up to the complexity of kissing hairpin motifs. The new tool pAliKiss can predict kissing hairpin motifs from aligned sequences. Along with the integration, the functionality of the tools was also extended in manifold ways.

Availability and implementation: As before, the tool is available on the Bielefeld Bioinformatics server at http://bibiserv.cebitec.uni-bielefeld.de/rnashapesstudio.

Contact: bibi-help@cebitec.uni-bielefeld.de

Publication date: 12 February 2015
Source:Cell, Volume 160, Issue 4
Author(s): Claus-D. Kuhn , Jeremy E. Wilusz , Yuxuan Zheng , Peter A. Beal , Leemor Joshua-Tor
Transcription in eukaryotes produces a number of long noncoding RNAs (lncRNAs). Two of these, MALAT1 and Menβ, generate a tRNA-like small RNA in addition to the mature lncRNA. The stability of these tRNA-like small RNAs and bona fide tRNAs is monitored by the CCA-adding enzyme. Whereas CCA is added to stable tRNAs and tRNA-like transcripts, a second CCA repeat is added to certain unstable transcripts to initiate their degradation. Here, we characterize how these two scenarios are distinguished. Following the first CCA addition cycle, nucleotide binding to the active site triggers a clockwise screw motion, producing torque on the RNA. This ejects stable RNAs, whereas unstable RNAs are refolded while bound to the enzyme and subjected to a second CCA catalytic cycle. Intriguingly, with the CCA-adding enzyme acting as a molecular vise, the RNAs proofread themselves through differential responses to its interrogation between stable and unstable substrates.

Graphical abstract

Teaser

The CCA-adding enzyme acts as a molecular vise to produce torque on RNA substrates, and the RNAs proofread themselves through differential responses to this interrogation between stable and unstable substrates.

Publication date: 29 January 2015
Source:Cell, Volume 160, Issue 3
Author(s): Hsin-Yue Tsai , Chun-Chieh G. Chen , Darryl Conte Jr. , James J. Moresco , Daniel A. Chaves , Shohei Mitani , John R. Yates III , Ming-Daw Tsai , Craig C. Mello
Effective silencing by RNA-interference (RNAi) depends on mechanisms that amplify and propagate the silencing signal. In some organisms, small-interfering RNAs (siRNAs) are amplified from target mRNAs by RNA-dependent RNA polymerase (RdRP). Both RdRP recruitment and mRNA silencing require Argonaute proteins, which are generally thought to degrade RNAi targets by directly cleaving them. However, in C. elegans, the enzymatic activity of the primary Argonaute, RDE-1, is not required for silencing activity. We show that RDE-1 can instead recruit an endoribonuclease, RDE-8, to target RNA. RDE-8 can cleave RNA in vitro and is needed for the production of 3′ uridylated fragments of target mRNA in vivo. We also find that RDE-8 promotes RdRP activity, thereby ensuring amplification of siRNAs. Together, our findings suggest a model in which RDE-8 cleaves target mRNAs to mediate silencing, while generating 3′ uridylated mRNA fragments to serve as templates for the RdRP-directed amplification of the silencing signal.

Graphical abstract

Teaser

Although Argonaute proteins are ribonuclease homologs, their enzymatic activity is not required for RNAi in C. elegans. Tsai et al. identify RDE-8 as a conserved endoribonuclease that promotes cleavage and uridylation of RNAi targets, which are then used as templates for siRNA amplification. The findings suggest how Argonautes promote both mRNA silencing and the amplification of the silencing signal without directly cleaving their mRNA targets.

Nature Methods 12, 97 (2015). doi:10.1038/nmeth.3262

Authors: Marc Streit & Nils Gehlenborg

Use inherent properties of time to create effective visualizations.

Integrated genome and transcriptome sequencing of the same cell.

Nat Biotechnol. 2015 Jan 19;

Authors: Dey SS, Kester L, Spanjaard B, Bienko M, van Oudenaarden A

Abstract
Single-cell genomics and single-cell transcriptomics have emerged as powerful tools to study the biology of single cells at a genome-wide scale. However, a major challenge is to sequence both genomic DNA and mRNA from the same cell, which would allow direct comparison of genomic variation and transcriptome heterogeneity. We describe a quasilinear amplification strategy to quantify genomic DNA and mRNA from the same cell without physically separating the nucleic acids before amplification. We show that the efficiency of our integrated approach is similar to existing methods for single-cell sequencing of either genomic DNA or mRNA. Further, we find that genes with high cell-to-cell variability in transcript numbers generally have lower genomic copy numbers, and vice versa, suggesting that copy number variations may drive variability in gene expression among individual cells. Applications of our integrated sequencing approach could range from gaining insights into cancer evolution and heterogeneity to understanding the transcriptional consequences of copy number variations in healthy and diseased tissues.

PMID: 25599178 [PubMed - as supplied by publisher]

Despite the great importance of nucleic acid–protein interactions in the cell, our understanding of their physico-chemical basis remains incomplete. In order to address this challenge, we have for the first time determined potentials of mean force and the associated absolute binding free energies between all standard RNA/DNA nucleobases and amino-acid sidechain analogs in high- and low-dielectric environments using molecular dynamics simulations and umbrella sampling. A comparison against a limited set of available experimental values for analogous systems attests to the quality of the computational approach and the force field used. Overall, our analysis provides a microscopic picture behind nucleobase/sidechain interaction preferences and creates a unified framework for understanding and sculpting nucleic acid–protein interactions in different contexts. Here, we use this framework to demonstrate a strong relationship between nucleobase density profiles of mRNAs and nucleobase affinity profiles of their cognate proteins and critically analyze a recent hypothesis that the two may be capable of direct, complementary interactions.

Ribosome profiling identifies ribosome positions on translated mRNAs. A prominent feature of published datasets is the near complete absence of ribosomes in 3' untranslated regions (3'UTR) although substantial ribosome density can be observed on non-coding RNAs. Here we perform ribosome profiling in cultured Drosophila and human cells and show that different features of translation are revealed depending on the nuclease and the digestion conditions used. Most importantly, we observe high abundance of ribosome protected fragments in 3'UTRs of thousands of genes without manipulation of translation termination. Affinity purification of ribosomes indicates that the 3'UTR reads originate from ribosome protected fragments. Association of ribosomes with the 3'UTR may be due to ribosome migration through the stop codon or 3'UTR mRNA binding to ribosomes on the coding sequence. This association depends primarily on the relative length of the 3'UTR and may be related to translational regulation or ribosome recycling, for which the efficiency is known to inversely correlate with 3'UTR length. Together our results indicate that ribosome profiling is highly dependent on digestion conditions and that ribosomes commonly associate with the 3'UTR, which may have a role in translational regulation.

In post-transcriptional regulation, an mRNA molecule is bound by many proteins and/or miRNAs to modulate its function. To enable combinatorial gene regulation, these binding partners of an RNA must communicate with each other, exhibiting cooperativity. Even in the absence of direct physical interactions between the binding partners, such cooperativity can be mediated through RNA secondary structures, since they affect the accessibility of the binding sites. Here we propose a quantitative measure of this structure-mediated cooperativity that can be numerically calculated for an arbitrary RNA sequence. Focusing on an RNA with two binding sites, we derive a characteristic difference of free energy differences, i.e. G, as a measure of the effect of the occupancy of one binding site on the binding strength of another. We apply this measure to a large number of human and Caenorhabditis elegans mRNAs, and find that structure-mediated cooperativity is a generic feature. Interestingly, this cooperativity not only affects binding sites in close proximity along the sequence but also configurations in which one binding site is located in the 5'UTR and the other is located in the 3'UTR of the mRNA. Furthermore, we find that this end-to-end cooperativity is determined by the UTR sequences while the sequences of the coding regions are irrelevant.

MicroRNAs (miRNAs) originate from stem-loop-containing precursors (pre-miRNAs, pri-miRNAs) and mature by means of the Drosha and Dicer endonucleases and their associated factors. The let-7 miRNAs have prominent roles in developmental differentiation and in regulating cell proliferation. In cancer, the tumor suppressor function of let-7 is abrogated by overexpression of Lin28, one of several RNA-binding proteins that regulate let-7 biogenesis by interacting with conserved motifs in let-7 precursors close to the Dicer cleavage site. Using in vitro assays, we have identified a binding site for short modified oligoribonucleotides (‘looptomirs’) overlapping that of Lin28 in pre-let-7a-2. These looptomirs selectively antagonize the docking of Lin28, but still permit processing of pre-let-7a-2 by Dicer. Looptomirs restored synthesis of mature let-7 and inhibited growth and clonogenic potential in Lin28 overexpressing hepatocarcinoma cells, thereby demonstrating a promising new means to rescue defective miRNA biogenesis in Lin28-dependent cancers.

RNA-binding proteins (RBPs) are important regulators of eukaryotic gene expression. Genomes typically encode dozens to hundreds of proteins containing RNA-binding domains, which collectively recognize diverse RNA sequences and structures. Recent advances in high-throughput methods for assaying the targets of RBPs in vitro and in vivo allow large-scale derivation of RNA-binding motifs as well as determination of RNA–protein interactions in living cells. In parallel, many computational methods have been developed to analyze and interpret these data. The interplay between RNA secondary structure and RBP binding has also been a growing theme. Integrating RNA–protein interaction data with observations of post-transcriptional regulation will enhance our understanding of the roles of these important proteins.

Article

Strand-specific RNA-seq (ssRNA-seq) data often lack information on 5′ and 3′ ends of transcripts. Here the authors present a novel method for ssRNA-seq that enables the simultaneous profiling of gene expression, TSSs and polyadenylation sites at near-base resolution with a single library.

Nature Communications doi: 10.1038/ncomms7002

Authors: Saurabh Agarwal, Todd S. Macfarlan, Maureen A. Sartor, Shigeki Iwase

Nature Chemical Biology 11, 96 (2015). doi:10.1038/nchembio.1745

Author: Joshua M. Finkelstein

Publication date: 22 January 2015
Source:Molecular Cell, Volume 57, Issue 2
Author(s): Boris Slobodin , Reuven Agami
A new study published in this issue of Molecular Cell (Oktaba et al., 2015) suggests widespread involvement of promoters in the regulation of alternative cleavage and polyadenylation of mRNAs in Drosophila neurons.

Teaser

A new study published in this issue of Molecular Cell (Oktaba et al.) suggests widespread involvement of promoters in the regulation of alternative cleavage and polyadenylation of mRNAs in Drosophila neurons.

MYC regulates the non-coding transcriptome.

Oncotarget. 2014 Dec 30;5(24):12543-54

Authors: Hart JR, Roberts TC, Weinberg MS, Morris KV, Vogt PK

Abstract
Using RNA-seq (RNA sequencing) of ribosome-depleted RNA, we have identified 1,273 lncRNAs (long non-coding RNAs) in P493-6 human B-cells. Of these, 534 are either up- or downregulated in response to MYC overexpression. An increase in MYC occupancy near their TSS (transcription start sites) was observed for MYC-responsive lncRNAs suggesting these are direct MYC targets. MYC binds to the same TSS across several cell lines, but the number of TSS bound depends on cellular MYC levels and increases with higher MYC concentrations. Despite this concordance in promoter binding, a majority of expressed lncRNAs are specific for one cell line, suggesting a determinant role of additional, possibly differentiation-specific factors in the activity of MYC-bound lncRNA promoters. A significant fraction of the lncRNA transcripts lack polyadenylation. The RNA-seq data were confirmed on eight selected lncRNAs by NRO (nuclear run-on) and RT-qPCR (quantitative reverse transcription PCR).

PMID: 25587025 [PubMed - in process]

The field of non-coding RNA biology has been hampered by the lack of availability of a comprehensive, up-to-date collection of accessioned RNA sequences. Here we present the first release of RNAcentral, a database that collates and integrates information from an international consortium of established RNA sequence databases. The initial release contains over 8.1 million sequences, including representatives of all major functional classes. A web portal (http://rnacentral.org) provides free access to data, search functionality, cross-references, source code and an integrated genome browser for selected species.

Publication date: March 2015
Source:Trends in Cell Biology, Volume 25, Issue 3
Author(s): Harvey F. Lodish
The demands of family life are crucial factors in successfully retaining women in science. Retention efforts should focus on creating a family-friendly environment within the laboratory and the institute. Based on my own experiences, I suggest ways to attract top young scientists and support their development into leading researchers.

Publication date: 5 February 2015
Source:Molecular Cell, Volume 57, Issue 3
Author(s): Chen Davidovich , Xueyin Wang , Catherine Cifuentes-Rojas , Karen J. Goodrich , Anne R. Gooding , Jeannie T. Lee , Thomas R. Cech
Polycomb repressive complex-2 (PRC2) is a histone methyltransferase required for epigenetic silencing during development and cancer. Early works suggested binding specificity of PRC2 to certain long non-coding RNAs for recruitment to chromatin. More recent studies provided evidence both in favor and against this idea. Here, we bridge the two existing models of PRC2-RNA interaction. RepA RNA is a good binding partner for PRC2, while multiple non-relevant RNAs, including bacterial mRNAs, also bind PRC2; K d s depend to some extent on the experimental conditions. Human and mouse PRC2 have broadly similar RNA-binding properties in vitro. Examination of evidence supporting an existing model for site-specific recruitment of PRC2 by a well-defined RNA motif in cells reveals that results are PRC2 independent. We conclude that promiscuous and specific RNA-binding activities of PRC2 in vitro are not mutually exclusive, and that binding specificity in vivo remains to be demonstrated.

Graphical abstract

Teaser

Davidovich et al. show that PRC2 binds RepA lncRNA and non-cognate RNAs with good affinity. Therefore, promiscuous and specific RNA-binding activities of PRC2 are not mutually exclusive. They demonstrate and discuss experimental considerations that are required to assess RNA binding specificity by PRC2.

Small indels induced by CRISPR/Cas9 in the 5' region of microRNA lead to its depletion and Drosha processing retardance.

RNA Biol. 2015 Jan 15;:0

Authors: Jiang Q, Meng X, Meng L, Chang N, Xiong J, Cao H, Liang Z

Abstract
Abstract MicroRNA knockout by genome editing technologies is promising. In order to extend the application of the technology and to investigate the function of a specific miRNA, we used CRISPR/Cas9 to deplete human miR-93 from a cluster by targeting its 5' region in HeLa cells. Various small indels were induced in the targeted region containing the Drosha processing site and seed sequences. Interestingly, we found that even a single nucleotide deletion led to complete knockout of the target miRNA with high specificity. Functional knockout was confirmed by phenotype analysis. Furthermore, de novo microRNAs were not found by RNA-seq. Nevertheless, expression of the pri-microRNAs was increased. When combined with structural analysis, the data indicated that biogenesis was impaired. Altogether, we showed that small indels in the 5' region of a microRNA result in sequence depletion as well as Drosha processing retard.

PMID: 25590615 [PubMed - as supplied by publisher]

Publication date: 20 January 2015
Source:Cell Reports, Volume 10, Issue 3
Author(s): Paul B. Essers , Julie Nonnekens , Yvonne J. Goos , Marco C. Betist , Marjon D. Viester , Britt Mossink , Nico Lansu , Hendrik C. Korswagen , Rob Jelier , Arjan B. Brenkman , Alyson W. MacInnes
The biogenesis of ribosomes and their coordination of protein translation consume an enormous amount of cellular energy. As such, it has been established that the inhibition of either process can extend eukaryotic lifespan. Here, we used next-generation sequencing to compare ribosome-associated RNAs from normal strains of Caenorhabditis elegans to those carrying the life-extending daf-2 mutation. We found a long noncoding RNA (lncRNA), transcribed telomeric sequence 1 (tts-1), on ribosomes of the daf-2 mutant. Depleting tts-1 in daf-2 mutants increases ribosome levels and significantly shortens their extended lifespan. We find tts-1 is also required for the longer lifespan of the mitochondrial clk-1 mutants but not the feeding-defective eat-2 mutants. In line with this, the clk-1 mutants express more tts-1 and fewer ribosomes than the eat-2 mutants. Our results suggest that the expression of tts-1 functions in different longevity pathways to reduce ribosome levels in a way that promotes life extension.

Graphical abstract

Teaser

Essers et al. find a long noncoding RNA, transcribed telomeric sequence 1 (tts-1), on ribosomes of C. elegans carrying the life-extending daf-2 insulin receptor mutation as well as the clk-1 mitochondrial mutant. They then demonstrate that this RNA is required for the life-extension phenotypes and that its depletion results in increasing ribosome levels.