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Rxivist combines biology preprints from bioRxiv and medRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 128,741 papers from 551,614 authors.

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in category molecular biology

3,856 results found. For more information, click each entry to expand.

41: Generation and validation of homozygous fluorescent knock-in cells using genome editing
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Posted 14 Sep 2017

Generation and validation of homozygous fluorescent knock-in cells using genome editing
4,706 downloads bioRxiv molecular biology

Birgit Koch, Bianca Nijmeijer, Moritz Kueblbeck, Yin Cai, Nike Walther, Jan Ellenberg

Gene tagging with fluorescent proteins (FPs) is essential to investigate the dynamic properties of cellular proteins. Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 technology (CRISPR/Cas9) technology is a powerful tool for inserting fluorescent markers into all alleles of the gene of interest and permits functionality and physiological expression of the fusion protein. It is essential to evaluate such genome-edited cell lines carefully in order to preclude off-target effects caused by either (i) incorrect insertion of the FP, (ii) perturbation of the fusion protein by the FP or (iii) non-specific genomic DNA damage by CRISPR/Cas9. In this protocol, we provide a step-by-step description of our systematic pipeline to generate and validate homozygous fluorescent knock-in cell lines. We have used the paired Cas9D10A nickase approach to efficiently insert tags into specific genomic loci via homology-directed repair (HDR) with minimal off-target effects. It is not only time- and cost-effective to perform whole genome sequencing of each cell clone, but also there are spontaneous genetic variations occurring in mammalian cell lines. Therefore we have developed an efficient validation pipeline of the generated cell lines consisting of junction PCR, Southern Blot analysis, Sanger sequencing, microscopy, Western blot analysis and live cell imaging for cell cycle dynamics which takes between 6-9 weeks. Using this pipeline, 70% of the targeted genes could be tagged homozygously with FPs and resulted in physiological levels and phenotypically functional expression of the fusion proteins. In contrast to a study that systematically tagged genes using CRISPR/Cas9 in human stem cells1, our approach resulted in homozygously tagged proteins of interests.

42: Rapid, field-deployable nucleobase detection and identification using FnCas9
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Posted 09 Apr 2020

Rapid, field-deployable nucleobase detection and identification using FnCas9
4,642 downloads bioRxiv molecular biology

Mohd. Azhar, Rhythm Phutela, Asgar Hussain Ansari, Dipanjali Sinha, Namrata Sharma, Manoj Kumar, Meghali Aich, Saumya Sharma, Riya Rauthan, Khushboo Singhal, Harsha Lad, Pradeep Kumar Patra, Govind Makharia, Giriraj Ratan Chandak, Debojyoti Chakraborty, Souvik Maiti

Detection of pathogenic sequences or variants in DNA and RNA through a point-of-care diagnostic approach is valuable for rapid clinical prognosis. In recent times, CRISPR based detection of nucleic acids have provided an economical and quicker alternative to sequencing-based platforms which are often difficult to implement in the field. Here, we present FnCas9 Editor Linked Uniform Detection Assay (FELUDA) that employs a highly accurate enzymatic readout for detecting nucleotide sequences, identifying nucleobase identity and inferring zygosity with precision. We demonstrate that FELUDA output can be adapted to multiple signal detection platforms and can be quickly designed and deployed for versatile applications including rapid diagnosis during infectious disease outbreaks like COVID-19. ### Competing Interest Statement D.C., S.M., M.A., R.P., A.S.A, D.S., N.S. and S.S. are authors in provisional patent applications that have been filed in relation to this work.

43: Purification of Cross-linked RNA-Protein Complexes by Phenol-Toluol Extraction
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Posted 30 May 2018

Purification of Cross-linked RNA-Protein Complexes by Phenol-Toluol Extraction
4,604 downloads bioRxiv molecular biology

Erika C Urdaneta, Carlos H. Vieira-Vieira, Timon Hick, Hans-Herrmann Wessels, Davide Figini, Rebecca Moschall, Jan Medenbach, Uwe Ohler, Sander Granneman, Matthias Selbach, Benedikt M Beckmann

Recent methodological advances allowed the identification of an increasing number of RNA-binding proteins (RBPs) and their RNA-binding sites. Most of those methods rely, however, on capturing proteins associated to polyadenylated RNAs which neglects RBPs bound to non-adenylate RNA classes (tRNA, rRNA, pre-mRNA) as well as the vast majority of species that lack poly-A tails in their mRNAs (including all archea and bacteria). To overcome these limitations, we have developed a novel protocol, Phenol Toluol extraction (PTex), that does not rely on a specific RNA sequence or motif for isolation of cross-linked ribonucleoproteins (RNPs), but rather purifies them based entirely on their physicochemical properties. PTex captures RBPs that bind to RNA as short as 30 nt, RNPs directly from animal tissue and can be used to simplify complex workflows such as PAR-CLIP. Finally, we provide a first global RNA-bound proteome of human HEK293 cells and Salmonella Typhimurium as a bacterial species.

44: DNA Break-Induced Epigenetic Drift as a Cause of Mammalian Aging
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Posted 21 Oct 2019

DNA Break-Induced Epigenetic Drift as a Cause of Mammalian Aging
4,465 downloads bioRxiv molecular biology

Motoshi Hayano, Jae-Hyun Yang, Michael S. Bonkowski, Joao A. Amorim, Jaime M. Ross, Giuseppe Coppotelli, Patrick T. Griffin, Yap Ching Chew, Wei Guo, Xiaojing Yang, Daniel L. Vera, Elias L. Salfati, Abhirup Das, Sachin Thakur, Alice E Kane, Sarah J. Mitchell, Yasuaki Mohri, Emi K. Nishimura, Laura Schaevitz, Neha Garg, Ana-Maria Balta, Meghan A Rego, Meredith Gregory-Ksander, Tatjana C. Jakobs, Lei Zhong, Hiroko Wakimoto, Raul Mostoslavsky, Amy J Wagers, Kazuo Tsubota, Stephen J Bonasera, Carlos M. Palmeira, Jonathan G Seidman, Christine E. Seidman, Norman S. Wolf, Jill A. Kreiling, John M Sedivy, George F. Murphy, Philipp Oberdoerffer, Bruce R. Ksander, Luis A. Rajman, David A. Sinclair

There are numerous hallmarks of aging in mammals, but no unifying cause has been identified. In budding yeast, aging is associated with a loss of epigenetic information that occurs in response to genome instability, particularly DNA double-strand breaks (DSBs). Mammals also undergo predictable epigenetic changes with age, including alterations to DNA methylation patterns that serve as epigenetic "age" clocks, but what drives these changes is not known. Using a transgenic mouse system called "ICE" (for inducible changes to the epigenome), we show that a tissue's response to non-mutagenic DSBs reorganizes the epigenome and accelerates physiological, cognitive, and molecular changes normally seen in older mice, including advancement of the epigenetic clock. These findings implicate DSB-induced epigenetic drift as a conserved cause of aging from yeast to mammals.

45: Accurate detection of m6A RNA modifications in native RNA sequences
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Posted 21 Jan 2019

Accurate detection of m6A RNA modifications in native RNA sequences
4,387 downloads bioRxiv molecular biology

Huanle Liu, Oguzhan Begik, Morghan C Lucas, Christopher Mason, Schraga Schwartz, John S Mattick, Martin A. Smith, Eva Maria Novoa

The field of epitranscriptomics has undergone an enormous expansion in the last few years; however, a major limitation is the lack of generic methods to map RNA modifications transcriptome-wide. Here we show that using Oxford Nanopore Technologies, N6-methyladenosine (m6A) RNA modifications can be detected with high accuracy, in the form of systematic errors and decreased base-calling qualities. Our results open new avenues to investigate the universe of RNA modifications with single nucleotide resolution, in individual RNA molecules.

46: A Scalable, Easy-to-Deploy, Protocol for Cas13-Based Detection of SARS-CoV-2 Genetic Material
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Posted 21 Apr 2020

A Scalable, Easy-to-Deploy, Protocol for Cas13-Based Detection of SARS-CoV-2 Genetic Material
4,339 downloads bioRxiv molecular biology

Jennifer N. Rauch, Eric Valois, Sabrina C Solley, Friederike Braig, Ryan S Lach, Morgane Audouard, Jose Carlos Ponce-Rojas, Michael S. Costello, Naomi J Baxter, Kenneth S Kosik, Carolina Arias, Diego Acosta-Alvear, Maxwell Z. Wilson

The COVID-19 pandemic has created massive demand for widespread, distributed tools for detecting SARS-CoV-2 genetic material. The hurdles to scalable testing include reagent and instrument accessibility, availability of highly-trained personnel, and large upfront investment. Here we showcase an orthogonal pipeline we call CREST (Cas13-based, Rugged, Equitable, Scalable Testing) that addresses some of these hurdles. Specifically, CREST pairs commonplace and reliable biochemical methods (PCR) with low-cost instrumentation, without sacrificing detection sensitivity. By taking advantage of simple fluorescence visualizers, CREST allows for a binary interpretation of results. CREST may provide a point- of-care solution to increase the distribution of COVID-19 surveillance. ### Competing Interest Statement The authors have declared no competing interest.

47: Microbial community composition and diversity via 16S rRNA gene amplicons: evaluating the Illumina platform
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Posted 06 Oct 2014

Microbial community composition and diversity via 16S rRNA gene amplicons: evaluating the Illumina platform
4,284 downloads bioRxiv molecular biology

Lucas Sinclair, Omneya Ahmed Osman, Stefan Bertilsson, Alexander Eiler

As new sequencing technologies become cheaper and older ones disappear, laboratories switch vendors and platforms. Validating the new setups is a crucial part of conducting rigorous scientific research. Here we report on the reliability and biases of performing bacterial 16S rRNA gene amplicon paired-end sequencing on the MiSeq Illumina platform. We designed a protocol using 50 barcode pairs to run samples in parallel and coded a pipeline to process the data. Sequencing the same sediment sample in 248 replicates as well as 70 samples from alkaline soda lakes, we evaluated the performance of the method with regards to estimates of alpha and beta diversity. Using different purification and DNA quantification procedures we always found up to 5-fold differences in the yield of sequences between individually barcodes samples. Using either a one-step or a two-step PCR preparation resulted in significantly different estimates in both alpha and beta diversity. Comparing with a previous method based on 454 pyrosequencing, we found that our Illumina protocol performed in a similar manner -- with the exception for evenness estimates where correspondence between the methods was low. We further quantified the data loss at every processing step eventually accumulating to 50\% of the raw reads. When evaluating different OTU clustering methods, we observed a stark contrast between the results of QIIME with default settings and the more recent UPARSE algorithm when it comes to the number of OTUs generated. Still, overall trends in alpha and beta diversity corresponded highly using both clustering methods. Our procedure performed well considering the precisions of alpha and beta diversity estimates, with insignificant effects of individual barcodes. Comparative analyses suggest that 454 and Illumina sequence data can be combined if the same PCR protocol and bioinformatic workflows are used for describing patterns in richness, beta-diversity and taxonomic composition. (version 1.1 resubmitted to PLOS one 2014-Sept-08)

48: Evolutionary persistence of DNA methylation for millions of years after ancient loss of a de novo methyltransferase
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Posted 13 Jun 2017

Evolutionary persistence of DNA methylation for millions of years after ancient loss of a de novo methyltransferase
4,249 downloads bioRxiv molecular biology

Sandra Catania, Phillip A. Dumesic, Harold Pimentel, Ammar Nasif, Caitlin I Stoddard, Jordan E Burke, Jolene Diedrich, Sophie Cook, Terrance Shea, Elizabeth Geinger, Robert Lintner, John Robert Yates, Petra Hajkova, Geeta J. Narlikar, Christina A. Cuomo, Jonathan K Pritchard, Hiten D. Madhani

Cytosine methylation of DNA is a widespread modification of DNA that plays numerous critical roles, yet has been lost many times in diverse eukaryotic lineages. In the yeast Cryptococcus neoformans , CG methylation occurs in transposon-rich repeats and requires the DNA methyltransferase, Dnmt5. We show that Dnmt5 displays exquisite maintenance-type specificity in vitro and in vivo and utilizes similar in vivo cofactors as the metazoan maintenance methylase Dnmt1. Remarkably, phylogenetic and functional analysis revealed that the ancestral species lost the gene for a de novo methylase, DnmtX, between 50-150 MYA. We examined how methylation has persisted since the ancient loss of DnmtX. Experimental and comparative studies reveal efficient replication of methylation patterns in C. neoformans , rare stochastic methylation loss and gain events, and the action of natural selection. We propose that an epigenome has been propagated for >50 MY through a process analogous to Darwinian evolution of the genome.

49: A one-enzyme RT-qPCR assay for SARS-CoV-2, and procedures for reagent production
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Posted 31 Mar 2020

A one-enzyme RT-qPCR assay for SARS-CoV-2, and procedures for reagent production
4,227 downloads bioRxiv molecular biology

Sanchita Bhadra, Andre C Maranhao, Andrew D. Ellington

Given the scale of the ongoing COVID-19 pandemic, the need for reliable, scalable testing, and the likelihood of reagent shortages, especially in resource-poor settings, we have developed a RT-qPCR assay that relies on an alternative to conventional viral reverse transcriptases, a thermostable reverse transcriptase / DNA polymerase (RTX). Here we show that RTX performs comparably to the other assays sanctioned by the CDC and validated in kit format. We demonstrate two modes of RTX use - (i) dye-based RT-qPCR assays that require only RTX polymerase, and (ii) TaqMan RT-qPCR assays that use a combination of RTX and Taq DNA polymerases (as the RTX exonuclease does not degrade a TaqMan probe). We also provide straightforward recipes for the purification of this alternative reagent. We anticipate that in low resource or point-of-need settings researchers could obtain the available constructs from Addgene or our lab and begin to develop their own assays, within whatever regulatory framework exists for them. ### Competing Interest Statement The authors have declared no competing interest.

50: “Unexpected mutations after CRISPR-Cas9 editing in vivo” are most likely pre-existing sequence variants and not nuclease-induced mutations
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Posted 05 Jul 2017

“Unexpected mutations after CRISPR-Cas9 editing in vivo” are most likely pre-existing sequence variants and not nuclease-induced mutations
4,218 downloads bioRxiv molecular biology

Caleb A. Lareau, Kendell Clement, Jonathan Y Hsu, Vikram Pattanayak, J. Keith Joung, Martin J Aryee, Luca Pinello

Schaefer et al. recently advanced the provocative conclusion that CRISPR-Cas9 nuclease can induce off-target alterations at genomic loci that do not resemble the intended on-target site. Using high-coverage whole genome sequencing (WGS), these authors reported finding SNPs and indels in two CRISPR-Cas9-treated mice that were not present in a single untreated control mouse. On the basis of this association, Schaefer et al. concluded that these sequence variants were caused by CRISPR-Cas9. This new proposed CRISPR-Cas9 off-target activity runs contrary to previously published work and, if the authors are correct, could have profound implications for research and therapeutic applications. Here we demonstrate that the simplest interpretation of Schaefer et al.'s data is that the two CRISPR-Cas9-treated mice are actually more closely related genetically to each other than to the control mouse. This strongly suggests that the so-called “unexpected mutations” simply represent SNPs and indels shared in common by these mice prior to nuclease treatment. In addition, given the genomic and sequence distribution profiles of these variants, we show that it is challenging to explain how CRISPR-Cas9 might be expected to induce such changes. Finally, we argue that the lack of appropriate controls in Schaefer et al.'s experimental design precludes assignment of causality to CRISPR-Cas9. Given these substantial issues, we urge Schaefer et al. to revise or re-state the original conclusions of their published work so as to avoid leaving misleading and unsupported statements to persist in the literature.

51: An improved auxin-inducible degron system preserves native protein levels and enables rapid and specific protein depletion
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Posted 22 Mar 2019

An improved auxin-inducible degron system preserves native protein levels and enables rapid and specific protein depletion
4,191 downloads bioRxiv molecular biology

Kizhakke Mattada Sathyan, Brian D McKenna, Warren D. Anderson, Fabiana M. Duarte, Leighton Core, Michael J. Guertin

Rapid perturbation of protein function permits the ability to define primary molecular responses while avoiding down-stream cumulative effects of protein dysregulation. The auxin-inducible degron (AID) system was developed as a tool to achieve rapid and inducible protein degradation in non-plant systems. However, tagging proteins at their endogenous loci results in chronic, auxin-independent degradation by the proteasome. To correct this deficiency, we expressed the Auxin Response Transcription Factor (ARF) in an improved inducible degron system. ARF is absent from previously engineered AID systems, but ARF is a critical component of native auxin signaling. In plants, ARF directly interacts with AID in the absence of auxin and we found that expression of the ARF Phox and Bem1 (PB1) domain suppresses constitutive degradation of AID-tagged proteins. Moreover, the rate of auxin-induced AID degradation is substantially faster in the ARF-AID system. To test the ARF-AID system in a quantitative and sensitive manner, we measured genome-wide changes in nascent transcription after rapidly depleting the ZNF143 transcription factor. Transciptional profiling indicates that ZNF143 activates transcription in cis and ZNF143 regulates promoter-proximal paused RNA Polymerase density. Rapidly inducible degradation systems that preserve the target protein’s native expression levels and patterns will revolutionize the study of biological systems by enabling specific and temporally defined protein dysregulation.

52: RNA-protein interaction mapping via MS2 or Cas13-based APEX targeting
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Posted 28 Feb 2020

RNA-protein interaction mapping via MS2 or Cas13-based APEX targeting
4,012 downloads bioRxiv molecular biology

Shuo Han, Boxuan Simen Zhao, Samuel A. Myers, Steven A Carr, Chuan He, Alice Y Ting

RNA-protein interactions underlie a wide range of cellular processes. Improved methods are needed to systematically map RNA-protein interactions in living cells in an unbiased manner. Capitalizing on the ability of the engineered peroxidase APEX2 to identify protein interaction partners via proximity-dependent biotinylation, we used two approaches to target APEX2 to specific cellular RNAs. Both an MS2-MCP system and an engineered CRISPR-Cas13 system were able to deliver APEX2 to the human telomerase RNA hTR with high specificity. One-minute proximity biotinylation captured endogenous protein interaction partners of hTR, including more than a dozen proteins not previously linked to hTR. We validated the unexpected interaction between hTR and the N6-methyladenosine (m6A) demethylase ALKBH5. Further investigation showed that endogenous hTR is modified by m6A, which can be erased by ALKBH5, and that ALKBH5 influences both telomerase complex assembly and activity. These results highlight the ability of MS2- and Cas13-targeted APEX2 to identify novel RNA-protein interactions in living cells.

53: High-resolution interrogation of functional elements in the noncoding genome
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Posted 18 Apr 2016

High-resolution interrogation of functional elements in the noncoding genome
4,005 downloads bioRxiv molecular biology

Neville E Sanjana, Jason Wright, Kaijie Zheng, Ophir Shalem, Pierre Fontanillas, Julia Joung, Christine Cheng, Aviv Regev, Feng Zhang

The noncoding genome plays a major role in gene regulation and disease yet we lack tools for rapid identification and manipulation of noncoding elements. Here, we develop a large-scale CRISPR screen employing ~18,000 sgRNAs targeting >700 kb of noncoding sequence in an unbiased manner surrounding three genes (NF1, NF2, and CUL3) involved in resistance to the BRAF inhibitor vemurafenib in the BRAF-mutant melanoma cell line A375. We identify specific noncoding locations near genes that modulate drug resistance when mutated. These sites have predictive hallmarks of noncoding function, such as physical interaction with gene promoters, evolutionary conservation and tissue-specific chromatin accessibility. At a subset of identified elements at the CUL3 locus, we show that engineered mutations lead to a loss of gene expression associated with changes in transcription factor occupancy and in long-range and local epigenetic environments, implicating these sites in gene regulation and chemotherapeutic resistance. This demonstration of an unbiased mutagenesis screen across large noncoding regions expands the potential of pooled CRISPR screens for fundamental genomic discovery and for elucidating biologically relevant mechanisms of gene regulation.

54: High-surety isothermal amplification and detection of SARS-CoV-2, including with crude enzymes
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Posted 14 Apr 2020

High-surety isothermal amplification and detection of SARS-CoV-2, including with crude enzymes
3,932 downloads bioRxiv molecular biology

Sanchita Bhadra, Timothy E Riedel, Simren Lakhotia, Nicholas D Tran, Andrew D. Ellington

Isothermal nucleic acid amplification tests (iNAT), such as loop-mediated isothermal amplification (LAMP), are good alternatives to polymerase chain reaction (PCR)-based amplification assays, especially for point-of-care and low resource use, in part because they can be carried out with relatively simple instrumentation. However, iNATs can generate spurious amplicons, especially in the absence of target sequences, resulting in false positive results. This is especially true if signals are based on non-sequence-specific probes, such as intercalating dyes or pH changes. In addition, pathogens often prove to be moving, evolving targets, and can accumulate mutations that will lead to inefficient primer binding and thus false negative results. Internally redundant assays targeting different regions of the target sequence can help to reduce such false negatives. Here we describe rapid conversion of three previously described SARS-CoV-2 LAMP assays that relied on non-sequence-specific readout into assays that can be visually read using sequence-specific fluorogenic oligonucleotide strand exchange (OSD) probes. We evaluate one-pot operation of both individual and multiplex LAMP-OSD assays and demonstrate detection of SARS-CoV-2 virions in crude human saliva. ### Competing Interest Statement The authors have declared no competing interest.

55: Spatial single-cell profiling of intracellular metabolomes in situ
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Posted 02 Jan 2019

Spatial single-cell profiling of intracellular metabolomes in situ
3,919 downloads bioRxiv molecular biology

Luca Rappez, Mira Stadler, Sergio Triana, Prasad Phapale, Mathias Heikenwalder, Theodore Alexandrov

The recently unveiled extent of cellular heterogeneity demands for single-cell investigations of intracellular metabolomes to reveal their roles in intracellular processes, molecular microenvironment and cell-cell interactions. To address this, we developed SpaceM, a method for in situ spatial single-cell metabolomics of cell monolayers which detects >100 metabolites in >10000 individual cells together with fluorescence and morpho-spatial cellular features. We discovered that the intracellular metabolomes of co-cultured human HeLa cells and mouse NIH3T3 fibroblasts predict the cell type with 90.4% accuracy and revealed a short-distance metabolic intermixing between HeLa and NIH3T3. We characterized lipid classes composing lipid droplets in steatotic differentiated human hepatocytes, and discovered a preferential accumulation of long-chain phospholipids, a co-regulation of oleic and linoleic acids, and an association of phosphatidylinositol monophosphate with high cell-cell contact. SpaceM provides single-cell metabolic, phenotypic, and spatial information and enables spatio-molecular investigations of intracellular metabolomes in a variety of cellular models.

56: SARS-CoV-2 detection from nasopharyngeal swab samples without RNA extraction
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Posted 30 Mar 2020

SARS-CoV-2 detection from nasopharyngeal swab samples without RNA extraction
3,904 downloads bioRxiv molecular biology

Carolina Beltrán-Pavez, Chantal L. Márquez, Gabriela Muñoz, Fernando Valiente-Echeverría, Aldo Gaggero, Ricardo Soto-Rifo, Gonzalo P. Barriga

The ongoing COVID-19 pandemic has reached more than 200 countries and territories worldwide. Given the large requirement of SARS-CoV-2 diagnosis and considering that RNA extraction kits are in short supply, we investigated whether two commercial RT-qPCR kits were compatible with direct SARS-CoV-2 detection from nasopharyngeal swab samples. We show that one of the tested kits is fully compatible with direct SARS-CoV-2 detection suggesting that omission of RNA extraction step should be considered in SARS-CoV-2 diagnosis.

57: Single-cell isoform RNA sequencing (ScISOr-Seq) across thousands of cells reveals isoforms of cerebellar cell types.
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Posted 08 Jul 2018

Single-cell isoform RNA sequencing (ScISOr-Seq) across thousands of cells reveals isoforms of cerebellar cell types.
3,895 downloads bioRxiv molecular biology

Ishaan Gupta, Paul G Collier, Bettina Haase, Ahmed Mahfouz, Anoushka Joglekar, Taylor Floyd, Frank Koopmans, Ben Barres, August B Smit, Steven Sloan, Wenjie Luo, Olivier Fedrigo, M Elizabeth Ross, Hagen U Tilgner

Full-length isoform sequencing has advanced our knowledge of isoform biology. However, apart from applying full-length isoform sequencing to very few single cells, isoform sequencing has been limited to bulk tissue, cell lines, or sorted cells. Single splicing events have been described for <=200 single cells with great statistical success, but these methods do not describe full-length mRNAs. Single cell short-read 3' sequencing has allowed identification of many cell sub-types, but full-length isoforms for these cell types have not been profiled. Using our new method of single-cell-isoform-RNA-sequencing (ScISOr-Seq) we determine isoform-expression in thousands of individual cells from a heterogeneous bulk tissue (cerebellum), without specific antibody-fluorescence activated cell sorting. We elucidate isoform usage in high-level cell types such as neurons, astrocytes and microglia and finer sub-types, such as Purkinje cells and Granule cells, including the combination patterns of distant splice sites, which for individual molecules requires long reads. We produce an enhanced genome annotation revealing cell-type specific expression of known and 16,872 novel (with respect to mouse Gencode version 10) isoforms (see isoformatlas.com).

58: Simplifying the combined use of CRISPR-Cas9 and Cre-loxP technologies for the efficient generation of targeted conditional gene knockouts in mammalian cells
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Posted 19 Dec 2017

Simplifying the combined use of CRISPR-Cas9 and Cre-loxP technologies for the efficient generation of targeted conditional gene knockouts in mammalian cells
3,769 downloads bioRxiv molecular biology

Tzahi Noiman, Chaim Kahana

Gene knockout technologies have contributed fundamentally to our understanding of the cellular functions of various genes. Two prevalent systems used for the efficient elimination of the expression of specific genes are the Cre-LoxP system and the CRISPR-Cas9 system. Here we present a simple method that combines the use of CRISPR-Cas9 and Cre-loxP for the conditional deletion of essential genes in mammalian cells. First, an inducible Cre recombinase is stably expressed in the cells. Next CRISPR-Cas9 is used to knockout an essential gene, whose function is complemented by stable expression of a FLAG-tagged version of the same protein encoded from a floxed transcription unit containing silent mutations, making it refractory to the CRISPR-Cas9 guide. This FLAG-tagged protein can be deleted by activating the expressed Cre protein enabling evaluation of the cellular consequences of its deletion. We have further used this system to evaluate potential mutants of the tested gene.

59: Erosion of the Epigenetic Landscape and Loss of Cellular Identity as a Cause of Aging in Mammals
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Posted 19 Oct 2019

Erosion of the Epigenetic Landscape and Loss of Cellular Identity as a Cause of Aging in Mammals
3,726 downloads bioRxiv molecular biology

Jae-Hyun Yang, Patrick T. Griffin, Daniel L. Vera, John K. Apostolides, Motoshi Hayano, Margarita V. Meer, Elias L. Salfati, Qiao Su, Elizabeth M Munding, Marco Blanchette, Mital Bhakta, Zhixun Dou, Caiyue Xu, Jeffrey W. Pippin, Michael L. Creswell, Brendan L. O’Connell, Richard E. Green, Benjamin A Garcia, Shelley L Berger, Philipp Oberdoerffer, Stuart J. Shankland, Vadim N Gladyshev, Luis A. Rajman, Andreas R Pfenning, David A. Sinclair

All living things experience entropy, manifested as a loss of inherited genetic and epigenetic information over time. As budding yeast cells age, epigenetic changes result in a loss of cell identity and sterility, both hallmarks of yeast aging. In mammals, epigenetic information is also lost over time, but what causes it to be lost and whether it is a cause or a consequence of aging is not known. Here we show that the transient induction of genomic instability, in the form of a low number of non-mutagenic DNA breaks, accelerates many of the chromatin and tissue changes seen during aging, including the erosion of the epigenetic landscape, a loss of cellular identity, advancement of the DNA methylation clock and cellular senescence. These data support a model in which a loss of epigenetic information is a cause of aging in mammals.

60: In-cell architecture of an actively transcribing-translating expressome
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Posted 28 Feb 2020

In-cell architecture of an actively transcribing-translating expressome
3,719 downloads bioRxiv molecular biology

Francis J. O’Reilly, Liang Xue, Andrea Graziadei, Ludwig Sinn, Swantje Lenz, Dimitry Tegunov, Cedric Blötz, Wim J. H. Hagen, Patrick Cramer, Jörg Stülke, Julia Mahamid, Juri Rappsilber

Structural biology performed inside cells can capture molecular machines in action within their native context. Here we develop an integrative in-cell structural approach using the genome-reduced human pathogen Mycoplasma pneumoniae. We combine whole-cell crosslinking mass spectrometry, cellular cryo-electron tomography, and integrative modeling to determine an in-cell architecture of a transcribing and translating expressome at sub-nanometer resolution. The expressome comprises RNA polymerase (RNAP), the ribosome, and the transcription elongation factors NusG and NusA. We pinpoint NusA at the interface between a NusG-bound elongating RNAP and the ribosome, and propose it could mediate transcription-translation coupling. Translation inhibition dissociates the expressome, whereas transcription inhibition stalls and rearranges it, demonstrating that the active expressome architecture requires both translation and transcription elongation within the cell.

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