1
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Callan-Sidat A, Zewdu E, Cavallaro M, Liu J, Hebenstreit D. N-terminal tagging of RNA Polymerase II shapes transcriptomes more than C-terminal alterations. iScience 2024; 27:109914. [PMID: 38799575 PMCID: PMC11126984 DOI: 10.1016/j.isci.2024.109914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 02/14/2024] [Accepted: 05/03/2024] [Indexed: 05/29/2024] Open
Abstract
RNA polymerase II (Pol II) has a C-terminal domain (CTD) that is unstructured, consisting of a large number of heptad repeats, and whose precise function remains unclear. Here, we investigate how altering the CTD's length and fusing it with protein tags affects transcriptional output on a genome-wide scale in mammalian cells at single-cell resolution. While transcription generally appears to occur in burst-like fashion, where RNA is predominantly made during short bursts of activity that are interspersed with periods of transcriptional silence, the CTD's role in shaping these dynamics seems gene-dependent; global patterns of bursting appear mostly robust to CTD alterations. Introducing protein tags with defined structures to the N terminus cause transcriptome-wide effects, however. We find the type of tag to dominate characteristics of the resulting transcriptomes. This is possibly due to Pol II-interacting factors, including non-coding RNAs, whose expression correlates with the tags. Proteins involved in liquid-liquid phase separation appear prominently.
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Affiliation(s)
- Adam Callan-Sidat
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
- Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Emmanuel Zewdu
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
| | - Massimo Cavallaro
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
- School of Computing and Mathematical Sciences, University of Leicester, Leicester LE1 7RH, UK
| | - Juntai Liu
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK
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2
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Das S, Singh A, Shah P. Evaluating single-cell variability in proteasomal decay. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.22.554358. [PMID: 37662347 PMCID: PMC10473619 DOI: 10.1101/2023.08.22.554358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
Gene expression is a stochastic process that leads to variability in mRNA and protein abundances even within an isogenic population of cells grown in the same environment. This variation, often called gene-expression noise, has typically been attributed to transcriptional and translational processes while ignoring the contributions of protein decay variability across cells. Here we estimate the single-cell protein decay rates of two degron GFPs in Saccharomyces cerevisiae using time-lapse microscopy. We find substantial cell-to-cell variability in the decay rates of the degron GFPs. We evaluate cellular features that explain the variability in the proteasomal decay and find that the amount of 20s catalytic beta subunit of the proteasome marginally explains the observed variability in the degron GFP half-lives. We propose alternate hypotheses that might explain the observed variability in the decay of the two degron GFPs. Overall, our study highlights the importance of studying the kinetics of the decay process at single-cell resolution and that decay rates vary at the single-cell level, and that the decay process is stochastic. A complex model of decay dynamics must be included when modeling stochastic gene expression to estimate gene expression noise.
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Affiliation(s)
| | - Abhyudai Singh
- Department of Electrical and Computer Engineering, Biomedical Engineering, University of Delaware
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3
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Oehler M, Geisser L, Diernfellner ACR, Brunner M. Transcription activator WCC recruits deacetylase HDA3 to control transcription dynamics and bursting in Neurospora. SCIENCE ADVANCES 2023; 9:eadh0721. [PMID: 37390199 PMCID: PMC10313174 DOI: 10.1126/sciadv.adh0721] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 05/25/2023] [Indexed: 07/02/2023]
Abstract
RNA polymerase II initiates transcription either randomly or in bursts. We examined the light-dependent transcriptional activator White Collar Complex (WCC) of Neurospora to characterize the transcriptional dynamics of the strong vivid (vvd) promoter and the weaker frequency (frq) promoter. We show that WCC is not only an activator but also represses transcription by recruiting histone deacetylase 3 (HDA3). Our data suggest that bursts of frq transcription are governed by a long-lived refractory state established and maintained by WCC and HDA3 at the core promoter, whereas transcription of vvd is determined by WCC binding dynamics at an upstream activating sequence. Thus, in addition to stochastic binding of transcription factors, transcription factor-mediated repression may also influence transcriptional bursting.
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Affiliation(s)
- Michael Oehler
- Heidelberg University Biochemistry Center, Im Neuenheimer Feld 328, D-60120 Heidelberg, Germany
| | - Leonie Geisser
- Heidelberg University Biochemistry Center, Im Neuenheimer Feld 328, D-60120 Heidelberg, Germany
| | - Axel C. R. Diernfellner
- Heidelberg University Biochemistry Center, Im Neuenheimer Feld 328, D-60120 Heidelberg, Germany
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4
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Alachkar N, Norton D, Wolkensdorfer Z, Muldoon M, Paszek P. Variability of the innate immune response is globally constrained by transcriptional bursting. Front Mol Biosci 2023; 10:1176107. [PMID: 37441161 PMCID: PMC10333517 DOI: 10.3389/fmolb.2023.1176107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Accepted: 06/15/2023] [Indexed: 07/15/2023] Open
Abstract
Transcription of almost all mammalian genes occurs in stochastic bursts, however the fundamental control mechanisms that allow appropriate single-cell responses remain unresolved. Here we utilise single cell genomics data and stochastic models of transcription to perform global analysis of the toll-like receptor (TLR)-induced gene expression variability. Based on analysis of more than 2000 TLR-response genes across multiple experimental conditions we demonstrate that the single-cell, gene-by-gene expression variability can be empirically described by a linear function of the population mean. We show that response heterogeneity of individual genes can be characterised by the slope of the mean-variance line, which captures how cells respond to stimulus and provides insight into evolutionary differences between species. We further demonstrate that linear relationships theoretically determine the underlying transcriptional bursting kinetics, revealing different regulatory modes of TLR response heterogeneity. Stochastic modelling of temporal scRNA-seq count distributions demonstrates that increased response variability is associated with larger and more frequent transcriptional bursts, which emerge via increased complexity of transcriptional regulatory networks between genes and different species. Overall, we provide a methodology relying on inference of empirical mean-variance relationships from single cell data and new insights into control of innate immune response variability.
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Affiliation(s)
- Nissrin Alachkar
- Division of Immunology, Immunity to Infection and Respiratory Medicine, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom
| | - Dale Norton
- Division of Immunology, Immunity to Infection and Respiratory Medicine, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom
| | - Zsofia Wolkensdorfer
- Division of Immunology, Immunity to Infection and Respiratory Medicine, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom
| | - Mark Muldoon
- Department of Mathematics, University of Manchester, Manchester, United Kingdom
| | - Pawel Paszek
- Division of Immunology, Immunity to Infection and Respiratory Medicine, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom
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5
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A transcriptional cycling model recapitulates chromatin-dependent features of noisy inducible transcription. PLoS Comput Biol 2022; 18:e1010152. [PMID: 36084132 PMCID: PMC9491597 DOI: 10.1371/journal.pcbi.1010152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 09/21/2022] [Accepted: 08/12/2022] [Indexed: 11/23/2022] Open
Abstract
Activation of gene expression in response to environmental cues results in substantial phenotypic heterogeneity between cells that can impact a wide range of outcomes including differentiation, viral activation, and drug resistance. An important source of gene expression noise is transcriptional bursting, or the process by which transcripts are produced during infrequent bursts of promoter activity. Chromatin accessibility impacts transcriptional bursting by regulating the assembly of transcription factor and polymerase complexes on promoters, suggesting that the effect of an activating signal on transcriptional noise will depend on the initial chromatin state at the promoter. To explore this possibility, we simulated transcriptional activation using a transcriptional cycling model with three promoter states that represent chromatin remodeling, polymerase binding and pause release. We initiated this model over a large parameter range representing target genes with different chromatin environments, and found that, upon increasing the polymerase pause release rate to activate transcription, changes in gene expression noise varied significantly across initial promoter states. This model captured phenotypic differences in activation of latent HIV viruses integrated at different chromatin locations and mediated by the transcription factor NF-κB. Activating transcription in the model via increasing one or more of the transcript production rates, as occurs following NF-κB activation, reproduced experimentally measured transcript distributions for four different latent HIV viruses, as well as the bimodal pattern of HIV protein expression that leads to a subset of reactivated virus. Importantly, the parameter ‘activation path’ differentially affected gene expression noise, and ultimately viral activation, in line with experimental observations. This work demonstrates how upstream signaling pathways can be connected to biological processes that underlie transcriptional bursting, resulting in target gene-specific noise profiles following stimulation of a single upstream pathway. Many genes are transcribed in infrequent bursts of mRNA production through a process called transcriptional bursting, which contributes to variability in responses between cells. Heterogeneity in cell responses can have important biological impacts, such as whether a cell supports viral replication or responds to a drug, and thus there is an effort to describe this process with mathematical models to predict biological outcomes. Previous models described bursting as a transition between an “OFF” state or an “ON” state, an elegant and simple mathematical representation of complex molecular mechanisms, but one which failed to capture how upstream activation signals affected bursting. To address this, we added an additional promoter state to better reflect biological mechanisms underlying bursting. By fitting this model to variable activation of quiescent HIV infections in T cells, we showed that our model more accurately described viral expression variability across cells in response to an upstream stimulus. Our work highlights how mathematical models can be further developed to understand complex biological mechanisms and suggests ways to connect transcriptional bursting to upstream activation pathways.
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6
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Loell K, Wu Y, Staller MV, Cohen B. Activation domains can decouple the mean and noise of gene expression. Cell Rep 2022; 40:111118. [PMID: 35858548 PMCID: PMC9912357 DOI: 10.1016/j.celrep.2022.111118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 01/18/2022] [Accepted: 06/28/2022] [Indexed: 11/03/2022] Open
Abstract
Regulatory mechanisms set a gene's average level of expression, but a gene's expression constantly fluctuates around that average. These stochastic fluctuations, or expression noise, play a role in cell-fate transitions, bet hedging in microbes, and the development of chemotherapeutic resistance in cancer. An outstanding question is what regulatory mechanisms contribute to noise. Here, we demonstrate that, for a fixed mean level of expression, strong activation domains (ADs) at low abundance produce high expression noise, while weak ADs at high abundance generate lower expression noise. We conclude that differences in noise can be explained by the interplay between a TF's nuclear concentration and the strength of its AD's effect on mean expression, without invoking differences between classes of ADs. These results raise the possibility of engineering gene expression noise independently of mean levels in synthetic biology contexts and provide a potential mechanism for natural selection to tune the noisiness of gene expression.
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Affiliation(s)
- Kaiser Loell
- Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO 63108, USA,The Edison Family Center for Genome Sciences & Systems Biology, Washington University School of Medicine in St. Louis, St. Louis, MO 63108, USA
| | - Yawei Wu
- Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO 63108, USA,The Edison Family Center for Genome Sciences & Systems Biology, Washington University School of Medicine in St. Louis, St. Louis, MO 63108, USA
| | - Max V. Staller
- Center for Computational Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Barak Cohen
- Department of Genetics, Washington University School of Medicine in St. Louis, St. Louis, MO 63108, USA; The Edison Family Center for Genome Sciences & Systems Biology, Washington University School of Medicine in St. Louis, St. Louis, MO 63108, USA.
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7
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Yang X, Luo S, Zhang Z, Wang Z, Zhou T, Zhang J. Silent transcription intervals and translational bursting lead to diverse phenotypic switching. Phys Chem Chem Phys 2022; 24:26600-26608. [DOI: 10.1039/d2cp03703c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
For complex process of gene expression, we use theoretical analysis and stochastic simulations to study the phenotypic diversity induced by silent transcription intervals and translational bursting.
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Affiliation(s)
- Xiyan Yang
- School of Financial Mathematics and Statistics, Guangdong University of Finance, Guangzhou 510521, P. R. China
| | - Songhao Luo
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, P. R. China
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, P. R. China
| | - Zhenquan Zhang
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, P. R. China
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, P. R. China
| | - Zihao Wang
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, P. R. China
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, P. R. China
| | - Tianshou Zhou
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, P. R. China
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, P. R. China
| | - Jiajun Zhang
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, P. R. China
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, P. R. China
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8
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Chen M, Luo S, Cao M, Guo C, Zhou T, Zhang J. Exact distributions for stochastic gene expression models with arbitrary promoter architecture and translational bursting. Phys Rev E 2022; 105:014405. [PMID: 35193181 DOI: 10.1103/physreve.105.014405] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Accepted: 12/14/2021] [Indexed: 11/07/2022]
Abstract
Gene expression in individual cells is inherently variable and sporadic, leading to cell-to-cell variability in mRNA and protein levels. Recent single-cell and single-molecule experiments indicate that promoter architecture and translational bursting play significant roles in controlling gene expression noise and generating the phenotypic diversity that life exhibits. To quantitatively understand the impact of these factors, it is essential to construct an accurate mathematical description of stochastic gene expression and find the exact analytical results, which is a formidable task. Here, we develop a stochastic model of bursty gene expression, which considers the complex promoter architecture governing the variability in mRNA expression and a general distribution characterizing translational burst. We derive the analytical expression for the corresponding protein steady-state distribution and all moment statistics of protein counts. We show that the total protein noise can be decomposed into three parts: the low-copy noise of protein due to probabilistic individual birth and death events, the noise due to stochastic switching between promoter states, and the noise resulting from translational busting. The theoretical results derived provide quantitative insights into the biochemical mechanisms of stochastic gene expression.
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Affiliation(s)
- Meiling Chen
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, People's Republic of China.,School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
| | - Songhao Luo
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, People's Republic of China.,School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
| | - Mengfang Cao
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, People's Republic of China.,School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
| | - Chengjun Guo
- School of Mathematics and Statistics, Guangdong University of Technology, Guangzhou 510275, People's Republic of China
| | - Tianshou Zhou
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, People's Republic of China.,School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
| | - Jiajun Zhang
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, People's Republic of China.,School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
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9
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Zhang J, Cavallaro M, Hebenstreit D. Timing RNA polymerase pausing with TV-PRO-seq. CELL REPORTS METHODS 2021; 1:None. [PMID: 34723238 PMCID: PMC8547241 DOI: 10.1016/j.crmeth.2021.100083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 08/03/2021] [Accepted: 08/18/2021] [Indexed: 11/28/2022]
Abstract
Transcription of many genes in metazoans is subject to polymerase pausing, which is the transient stop of transcriptionally engaged polymerases. This is known to mainly occur in promoter-proximal regions but it is not well understood. In particular, a genome-wide measurement of pausing times at high resolution has been lacking. We present here the time-variant precision nuclear run-on and sequencing (TV-PRO-seq) assay, an extension of the standard PRO-seq that allows us to estimate genome-wide pausing times at single-base resolution. Its application to human cells demonstrates that, proximal to promoters, polymerases pause more frequently but for shorter times than in other genomic regions. Comparison with single-cell gene expression data reveals that the polymerase pausing times are longer in highly expressed genes, while transcriptionally noisier genes have higher pausing frequencies and slightly longer pausing times. Analyses of histone modifications suggest that the marker H3K36me3 is related to the polymerase pausing.
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Affiliation(s)
- Jie Zhang
- School of Life Sciences, Gibbet Hill Campus, the University of Warwick, CV4 7AL Coventry, UK
| | - Massimo Cavallaro
- School of Life Sciences, Gibbet Hill Campus, the University of Warwick, CV4 7AL Coventry, UK
- Mathematics Institute and Zeeman Institute for Systems Biology and Infectious Disease Epidemiology Research, the University of Warwick, CV4 7AL Coventry, UK
| | - Daniel Hebenstreit
- School of Life Sciences, Gibbet Hill Campus, the University of Warwick, CV4 7AL Coventry, UK
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10
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Modi S, Dey S, Singh A. Noise suppression in stochastic genetic circuits using PID controllers. PLoS Comput Biol 2021; 17:e1009249. [PMID: 34319990 PMCID: PMC8360635 DOI: 10.1371/journal.pcbi.1009249] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 08/12/2021] [Accepted: 07/05/2021] [Indexed: 01/01/2023] Open
Abstract
Inside individual cells, protein population counts are subject to molecular noise due to low copy numbers and the inherent probabilistic nature of biochemical processes. We investigate the effectiveness of proportional, integral and derivative (PID) based feedback controllers to suppress protein count fluctuations originating from two noise sources: bursty expression of the protein, and external disturbance in protein synthesis. Designs of biochemical reactions that function as PID controllers are discussed, with particular focus on individual controllers separately, and the corresponding closed-loop system is analyzed for stochastic controller realizations. Our results show that proportional controllers are effective in buffering protein copy number fluctuations from both noise sources, but this noise suppression comes at the cost of reduced static sensitivity of the output to the input signal. In contrast, integral feedback has no effect on the protein noise level from stochastic expression, but significantly minimizes the impact of external disturbances, particularly when the disturbance comes at low frequencies. Counter-intuitively, integral feedback is found to amplify external disturbances at intermediate frequencies. Next, we discuss the design of a coupled feedforward-feedback biochemical circuit that approximately functions as a derivate controller. Analysis using both analytical methods and Monte Carlo simulations reveals that this derivative controller effectively buffers output fluctuations from bursty stochastic expression, while maintaining the static input-output sensitivity of the open-loop system. In summary, this study provides a systematic stochastic analysis of biochemical controllers, and paves the way for their synthetic design and implementation to minimize deleterious fluctuations in gene product levels. In the noisy cellular environment, biochemical species such as genes, RNAs and proteins that often occur at low molecular counts, are subject to considerable stochastic fluctuations in copy numbers over time. How cellular biochemical processes function reliably in the face of such randomness is an intriguing fundamental problem. Increasing evidence suggests that random fluctuations (noise) in protein copy numbers play important functional roles, such as driving genetically identical cells to different cell fates. Moreover, many disease states have been attributed to elevated noise levels in specific proteins. Here we systematically investigate design of biochemical systems that function as proportional, integral and derivative-based feedback controllers to suppress protein count fluctuations arising from bursty expression of the protein and external disturbance in protein synthesis. Our results show that different controllers are effective in buffering different noise components, and identify ranges of feedback gain for minimizing deleterious fluctuations in protein levels.
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Affiliation(s)
- Saurabh Modi
- Department of Biomedical Engineering, University of Delaware, Newark, Delaware, United States of America
| | - Supravat Dey
- Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware, United States of America
| | - Abhyudai Singh
- Department of Biomedical Engineering, University of Delaware, Newark, Delaware, United States of America
- Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware, United States of America
- * E-mail:
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11
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Desai RV, Chen X, Martin B, Chaturvedi S, Hwang DW, Li W, Yu C, Ding S, Thomson M, Singer RH, Coleman RA, Hansen MMK, Weinberger LS. A DNA repair pathway can regulate transcriptional noise to promote cell fate transitions. Science 2021; 373:science.abc6506. [PMID: 34301855 DOI: 10.1126/science.abc6506] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 07/08/2021] [Indexed: 12/13/2022]
Abstract
Stochastic fluctuations in gene expression ("noise") are often considered detrimental, but fluctuations can also be exploited for benefit (e.g., dither). We show here that DNA base excision repair amplifies transcriptional noise to facilitate cellular reprogramming. Specifically, the DNA repair protein Apex1, which recognizes both naturally occurring and unnatural base modifications, amplifies expression noise while homeostatically maintaining mean expression levels. This amplified expression noise originates from shorter-duration, higher-intensity transcriptional bursts generated by Apex1-mediated DNA supercoiling. The remodeling of DNA topology first impedes and then accelerates transcription to maintain mean levels. This mechanism, which we refer to as "discordant transcription through repair" ("DiThR," which is pronounced "dither"), potentiates cellular reprogramming and differentiation. Our study reveals a potential functional role for transcriptional fluctuations mediated by DNA base modifications in embryonic development and disease.
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Affiliation(s)
- Ravi V Desai
- Gladstone/UCSF Center for Cell Circuitry, Gladstone Institutes, San Francisco, CA 94158, USA.,Medical Scientist Training Program and Tetrad Graduate Program, University of California, San Francisco, CA 94158, USA
| | - Xinyue Chen
- Gladstone/UCSF Center for Cell Circuitry, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Benjamin Martin
- Gladstone/UCSF Center for Cell Circuitry, Gladstone Institutes, San Francisco, CA 94158, USA.,Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, the Netherlands
| | - Sonali Chaturvedi
- Gladstone/UCSF Center for Cell Circuitry, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Dong Woo Hwang
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Weihan Li
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Chen Yu
- Gladstone Institute of Cardiovascular Disease, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Sheng Ding
- Gladstone Institute of Cardiovascular Disease, Gladstone Institutes, San Francisco, CA 94158, USA.,School of Pharmaceutical Sciences, Tsinghua University, Beijing 100084, China
| | - Matt Thomson
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Robert H Singer
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Robert A Coleman
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Maike M K Hansen
- Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, the Netherlands
| | - Leor S Weinberger
- Gladstone/UCSF Center for Cell Circuitry, Gladstone Institutes, San Francisco, CA 94158, USA. .,Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158, USA.,Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158, USA
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12
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Patel HP, Brouwer I, Lenstra TL. Optimized protocol for single-molecule RNA FISH to visualize gene expression in S. cerevisiae. STAR Protoc 2021; 2:100647. [PMID: 34278333 PMCID: PMC8264745 DOI: 10.1016/j.xpro.2021.100647] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Single-molecule RNA fluorescence in situ hybridization (smFISH) allows subcellular visualization, localization, and quantification of endogenous RNA molecules in fixed cells. The spatial and intensity information of each RNA can be used to distinguish mature from nascent transcripts inside each cell, revealing both past and instantaneous transcriptional activity. Here, we describe an optimized protocol for smFISH in Saccharomyces cerevisiae with optimized lyticase digestion time and hybrization steps for more homogenous results. For complete details on the use and execution of this protocol, please refer to Donovan et al. (2019). Optimized protocol for single-molecule RNA FISH in S. cerevisiae Includes sample preparation, imaging setup, and image analysis Visualizes mature and nascent transcripts inside each cell
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Affiliation(s)
- Heta P. Patel
- Division of Gene Regulation, The Netherlands Cancer Institute, Oncode Institute, 1066CX Amsterdam, the Netherlands
- Corresponding author
| | - Ineke Brouwer
- Division of Gene Regulation, The Netherlands Cancer Institute, Oncode Institute, 1066CX Amsterdam, the Netherlands
| | - Tineke L. Lenstra
- Division of Gene Regulation, The Netherlands Cancer Institute, Oncode Institute, 1066CX Amsterdam, the Netherlands
- Corresponding author
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13
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Bass VL, Wong VC, Bullock ME, Gaudet S, Miller‐Jensen K. TNF stimulation primarily modulates transcriptional burst size of NF-κB-regulated genes. Mol Syst Biol 2021; 17:e10127. [PMID: 34288498 PMCID: PMC8290835 DOI: 10.15252/msb.202010127] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 06/03/2021] [Accepted: 06/07/2021] [Indexed: 12/12/2022] Open
Abstract
Cell-to-cell heterogeneity is a feature of the tumor necrosis factor (TNF)-stimulated inflammatory response mediated by the transcription factor NF-κB, motivating an exploration of the underlying sources of this noise. Here, we combined single-transcript measurements with computational models to study transcriptional noise at six NF-κB-regulated inflammatory genes. In the basal state, NF-κB-target genes displayed an inverse correlation between mean and noise characteristic of transcriptional bursting. By analyzing transcript distributions with a bursting model, we found that TNF primarily activated transcription by increasing burst size while maintaining burst frequency for gene promoters with relatively high basal histone 3 acetylation (AcH3) that marks open chromatin environments. For promoters with lower basal AcH3 or when AcH3 was decreased with a small molecule drug, the contribution of burst frequency to TNF activation increased. Finally, we used a mathematical model to show that TNF positive feedback amplified gene expression noise resulting from burst size-mediated transcription, leading to a subset of cells with high TNF protein expression. Our results reveal potential sources of noise underlying intercellular heterogeneity in the TNF-mediated inflammatory response.
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Affiliation(s)
- Victor L Bass
- Department of Molecular, Cellular, and Developmental BiologyYale UniversityNew HavenCTUSA
- Present address:
Neuro‐Immune Regulome UnitNational Eye InstituteNational Institutes of HealthBethesdaMDUSA
| | - Victor C Wong
- Department of Molecular, Cellular, and Developmental BiologyYale UniversityNew HavenCTUSA
- Present address:
Janelia Research CampusHoward Hughes Medical InstituteAshburnVAUSA
| | - M Elise Bullock
- Department of Biomedical EngineeringYale UniversityNew HavenCTUSA
| | - Suzanne Gaudet
- Department of Cancer Biology and Center for Cancer Systems BiologyDana‐Farber Cancer InstituteBostonMAUSA
- Department of GeneticsHarvard Medical SchoolBostonMAUSA
- Present address:
Novartis Institute for BioMedical ResearchCambridgeMAUSA
| | - Kathryn Miller‐Jensen
- Department of Molecular, Cellular, and Developmental BiologyYale UniversityNew HavenCTUSA
- Department of Biomedical EngineeringYale UniversityNew HavenCTUSA
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14
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Blanco A, Mahajan T, Coronado RA, Ma K, Demma DR, Dar RD. Synergistic Chromatin-Modifying Treatments Reactivate Latent HIV and Decrease Migration of Multiple Host-Cell Types. Viruses 2021; 13:v13061097. [PMID: 34201394 PMCID: PMC8228244 DOI: 10.3390/v13061097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/29/2021] [Accepted: 06/02/2021] [Indexed: 11/29/2022] Open
Abstract
Upon infection of its host cell, human immunodeficiency virus (HIV) establishes a quiescent and non-productive state capable of spontaneous reactivation. Diverse cell types harboring the provirus form a latent reservoir, constituting a major obstacle to curing HIV. Here, we investigate the effects of latency reversal agents (LRAs) in an HIV-infected THP-1 monocyte cell line in vitro. We demonstrate that leading drug treatments synergize activation of the HIV long terminal repeat (LTR) promoter. We establish a latency model in THP-1 monocytes using a replication incompetent HIV reporter vector with functional Tat, and show that chromatin modifiers synergize with a potent transcriptional activator to enhance HIV reactivation, similar to T-cells. Furthermore, leading reactivation cocktails are shown to differentially affect latency reactivation and surface expression of chemokine receptor type 4 (CXCR4), leading to altered host cell migration. This study investigates the effect of chromatin-modifying LRA treatments on HIV latent reactivation and cell migration in monocytes. As previously reported in T-cells, epigenetic mechanisms in monocytes contribute to controlling the relationship between latent reactivation and cell migration. Ultimately, advanced “Shock and Kill” therapy needs to successfully target and account for all host cell types represented in a complex and composite latency milieu.
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Affiliation(s)
- Alexandra Blanco
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; (A.B.); (T.M.); (R.A.C.); (K.M.); (D.R.D.)
| | - Tarun Mahajan
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; (A.B.); (T.M.); (R.A.C.); (K.M.); (D.R.D.)
| | - Robert A. Coronado
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; (A.B.); (T.M.); (R.A.C.); (K.M.); (D.R.D.)
| | - Kelly Ma
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; (A.B.); (T.M.); (R.A.C.); (K.M.); (D.R.D.)
| | - Dominic R. Demma
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; (A.B.); (T.M.); (R.A.C.); (K.M.); (D.R.D.)
| | - Roy D. Dar
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; (A.B.); (T.M.); (R.A.C.); (K.M.); (D.R.D.)
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Correspondence: ; Tel.: +1-(217)-265-0708
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15
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Chen M, Zhou T, Zhang J. Correlation between external regulators governs the mean-noise relationship in stochastic gene expression. MATHEMATICAL BIOSCIENCES AND ENGINEERING : MBE 2021; 18:4713-4730. [PMID: 34198461 DOI: 10.3934/mbe.2021239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Gene transcription in single cells is inherently a probabilistic process. The relationship between variance ($ \sigma^{2} $) and mean expression ($ \mu $) is of paramount importance for investigations into the evolutionary origins and consequences of noise in gene expression. It is often formulated as $ \log \left({{{\sigma}^{2}}}/{{{\mu}^{2}}}\; \right) = \beta\log\mu+\log\alpha $, where $ \beta $ is a key parameter since its sign determines the qualitative dependence of noise on mean. We reveal that the sign of $ \beta $ is controlled completely by external regulation, but independent of promoter structure. Specifically, it is negative if regulators as stochastic variables are independent but positive if they are correlated. The essential mechanism revealed here can well interpret diverse experimental phenomena underlying expression noise. Our results imply that external regulation rather than promoter sequence governs the mean-noise relationship.
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Affiliation(s)
- Meiling Chen
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, China
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, China
| | - Tianshou Zhou
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, China
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, China
| | - Jiajun Zhang
- Guangdong Province Key Laboratory of Computational Science, Guangzhou 510275, China
- School of Mathematics, Sun Yat-Sen University, Guangzhou 510275, China
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16
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Rivera HE, Aichelman HE, Fifer JE, Kriefall NG, Wuitchik DM, Wuitchik SJS, Davies SW. A framework for understanding gene expression plasticity and its influence on stress tolerance. Mol Ecol 2021; 30:1381-1397. [PMID: 33503298 DOI: 10.1111/mec.15820] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 12/10/2020] [Accepted: 01/20/2021] [Indexed: 12/18/2022]
Abstract
Phenotypic plasticity can serve as a stepping stone towards adaptation. Recently, studies have shown that gene expression contributes to emergent stress responses such as thermal tolerance, with tolerant and susceptible populations showing distinct transcriptional profiles. However, given the dynamic nature of gene expression, interpreting transcriptomic results in a way that elucidates the functional connection between gene expression and the observed stress response is challenging. Here, we present a conceptual framework to guide interpretation of gene expression reaction norms in the context of stress tolerance. We consider the evolutionary and adaptive potential of gene expression reaction norms and discuss the influence of sampling timing, transcriptomic resilience, as well as complexities related to life history when interpreting gene expression dynamics and how these patterns relate to host tolerance. We highlight corals as a case study to demonstrate the value of this framework for non-model systems. As species face rapidly changing environmental conditions, modulating gene expression can serve as a mechanistic link from genetic and cellular processes to the physiological responses that allow organisms to thrive under novel conditions. Interpreting how or whether a species can employ gene expression plasticity to ensure short-term survival will be critical for understanding the global impacts of climate change across diverse taxa.
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Affiliation(s)
- Hanny E Rivera
- Department of Biology, Boston University, Boston, MA, USA
| | | | - James E Fifer
- Department of Biology, Boston University, Boston, MA, USA
| | | | | | - Sara J S Wuitchik
- Department of Biology, Boston University, Boston, MA, USA.,FAS Informatics, Harvard University, Cambridge, MA, USA
| | - Sarah W Davies
- Department of Biology, Boston University, Boston, MA, USA
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17
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Cavallaro M, Walsh MD, Jones M, Teahan J, Tiberi S, Finkenstädt B, Hebenstreit D. 3 '-5 ' crosstalk contributes to transcriptional bursting. Genome Biol 2021; 22:56. [PMID: 33541397 PMCID: PMC7860045 DOI: 10.1186/s13059-020-02227-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2020] [Accepted: 12/08/2020] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND Transcription in mammalian cells is a complex stochastic process involving shuttling of polymerase between genes and phase-separated liquid condensates. It occurs in bursts, which results in vastly different numbers of an mRNA species in isogenic cell populations. Several factors contributing to transcriptional bursting have been identified, usually classified as intrinsic, in other words local to single genes, or extrinsic, relating to the macroscopic state of the cell. However, some possible contributors have not been explored yet. Here, we focus on processes at the 3 ' and 5 ' ends of a gene that enable reinitiation of transcription upon termination. RESULTS Using Bayesian methodology, we measure the transcriptional bursting in inducible transgenes, showing that perturbation of polymerase shuttling typically reduces burst size, increases burst frequency, and thus limits transcriptional noise. Analysis based on paired-end tag sequencing (PolII ChIA-PET) suggests that this effect is genome wide. The observed noise patterns are also reproduced by a generative model that captures major characteristics of the polymerase flux between the ends of a gene and a phase-separated compartment. CONCLUSIONS Interactions between the 3 ' and 5 ' ends of a gene, which facilitate polymerase recycling, are major contributors to transcriptional noise.
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Affiliation(s)
- Massimo Cavallaro
- School of Life Sciences, University of Warwick, Coventry, UK.
- Mathematics Institute and Zeeman Institute for Systems Biology and Infectious Disease Epidemiology Research, University of Warwick, Coventry, UK.
- Department of Statistics, University of Warwick, Coventry, UK.
| | - Mark D Walsh
- School of Life Sciences, University of Warwick, Coventry, UK
| | - Matt Jones
- School of Life Sciences, University of Warwick, Coventry, UK
| | - James Teahan
- Department of Chemistry, University of Warwick, Coventry, UK
| | - Simone Tiberi
- Institute of Molecular Life Sciences and Swiss Institute of Bioinformatics, University of Zurich, Zurich, Switzerland
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18
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Guinn MT, Wan Y, Levovitz S, Yang D, Rosner MR, Balázsi G. Observation and Control of Gene Expression Noise: Barrier Crossing Analogies Between Drug Resistance and Metastasis. Front Genet 2020; 11:586726. [PMID: 33193723 PMCID: PMC7662081 DOI: 10.3389/fgene.2020.586726] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 09/29/2020] [Indexed: 12/12/2022] Open
Affiliation(s)
- Michael Tyler Guinn
- Biomedical Engineering Department, Stony Brook University, Stony Brook, NY, United States.,Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, NY, United States.,Stony Brook Medical Scientist Training Program, Stony Brook, NY, United States
| | - Yiming Wan
- Biomedical Engineering Department, Stony Brook University, Stony Brook, NY, United States.,Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, NY, United States
| | - Sarah Levovitz
- Biomedical Engineering Department, Stony Brook University, Stony Brook, NY, United States.,Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, NY, United States
| | - Dongbo Yang
- Ben May Department for Cancer Research, The University of Chicago, Chicago, IL, United States
| | - Marsha R Rosner
- Ben May Department for Cancer Research, The University of Chicago, Chicago, IL, United States
| | - Gábor Balázsi
- Biomedical Engineering Department, Stony Brook University, Stony Brook, NY, United States.,Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, NY, United States
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19
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Dibaeinia P, Sinha S. SERGIO: A Single-Cell Expression Simulator Guided by Gene Regulatory Networks. Cell Syst 2020; 11:252-271.e11. [PMID: 32871105 PMCID: PMC7530147 DOI: 10.1016/j.cels.2020.08.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 03/18/2020] [Accepted: 08/04/2020] [Indexed: 12/14/2022]
Abstract
A common approach to benchmarking of single-cell transcriptomics tools is to generate synthetic datasets that statistically resemble experimental data. However, most existing single-cell simulators do not incorporate transcription factor-gene regulatory interactions that underlie expression dynamics. Here, we present SERGIO, a simulator of single-cell gene expression data that models the stochastic nature of transcription as well as regulation of genes by multiple transcription factors according to a user-provided gene regulatory network. SERGIO can simulate any number of cell types in steady state or cells differentiating to multiple fates. We show that datasets generated by SERGIO are statistically comparable to experimental data generated by Illumina HiSeq2000, Drop-seq, Illumina 10X chromium, and Smart-seq. We use SERGIO to benchmark several single-cell analysis tools, including GRN inference methods, and identify Tcf7, Gata3, and Bcl11b as key drivers of T cell differentiation by performing in silico knockout experiments. SERGIO is freely available for download here: https://github.com/PayamDiba/SERGIO.
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Affiliation(s)
- Payam Dibaeinia
- Department of Computer Science, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Saurabh Sinha
- Department of Computer Science, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA; Carl R. Woese Institute of Genomic Biology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA; Cancer Center at Illinois, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
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20
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Gene-Specific Linear Trends Constrain Transcriptional Variability of the Toll-like Receptor Signaling. Cell Syst 2020; 11:300-314.e8. [PMID: 32918862 PMCID: PMC7521480 DOI: 10.1016/j.cels.2020.08.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 04/08/2020] [Accepted: 08/06/2020] [Indexed: 12/13/2022]
Abstract
Single-cell gene expression is inherently variable, but how this variability is controlled in response to stimulation remains unclear. Here, we use single-cell RNA-seq and single-molecule mRNA counting (smFISH) to study inducible gene expression in the immune toll-like receptor system. We show that mRNA counts of tumor necrosis factor α conform to a standard stochastic switch model, while transcription of interleukin-1β involves an additional regulatory step resulting in increased heterogeneity. Despite different modes of regulation, systematic analysis of single-cell data for a range of genes demonstrates that the variability in transcript count is linearly constrained by the mean response over a range of conditions. Mathematical modeling of smFISH counts and experimental perturbation of chromatin state demonstrates that linear constraints emerge through modulation of transcriptional bursting along with gene-specific relationships. Overall, our analyses demonstrate that the variability of the inducible single-cell mRNA response is constrained by transcriptional bursting. Single-cell TNF-α and IL-1β mRNA responses are differentially controlled Variability of TLR-induced responses scale linearly with mean mRNA counts Gene-specific constraints emerge via modulation of transcriptional bursting Chromatin state regulates transcriptional bursting of IL-1β
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21
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Waymack R, Fletcher A, Enciso G, Wunderlich Z. Shadow enhancers can suppress input transcription factor noise through distinct regulatory logic. eLife 2020; 9:59351. [PMID: 32804082 PMCID: PMC7556877 DOI: 10.7554/elife.59351] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 08/14/2020] [Indexed: 12/26/2022] Open
Abstract
Shadow enhancers, groups of seemingly redundant enhancers, are found in a wide range of organisms and are critical for robust developmental patterning. However, their mechanism of action is unknown. We hypothesized that shadow enhancers drive consistent expression levels by buffering upstream noise through a separation of transcription factor (TF) inputs at the individual enhancers. By measuring the transcriptional dynamics of several Kruppel shadow enhancer configurations in live Drosophila embryos, we showed that individual member enhancers act largely independently. We found that TF fluctuations are an appreciable source of noise that the shadow enhancer pair can better buffer than duplicated enhancers. The shadow enhancer pair is also uniquely able to maintain low levels of expression noise across a wide range of temperatures. A stochastic model demonstrated the separation of TF inputs is sufficient to explain these findings. Our results suggest the widespread use of shadow enhancers is partially due to their noise suppressing ability. In all higher organisms, life begins with a single cell. During the early stages of development, this single cell grows and divides multiple times to develop into the many different kinds of cells that make up an organism. This is a highly regulated process during which cells receive instructions telling them what kind of cell to become. These instructions are relayed via genes, and a particular combination of activated genes determines the cell’s fate. Specific pieces of DNA, known as enhancers, act as switches that control when and where genes are active, while so-called shadow enhancers are found in groups and work together to turn on the same gene in a similar way. Shadow enhancers are often active during the early stages of life to direct the formation of specialized cells in different parts of the body. But so far, it has been unclear why it is beneficial to the divide the role of activating genes across several shadow enhancers rather than a single one. Here, Waymack et al. examined shadow enhancers around a gene called Kruppel in embryos of the fruit fly Drosophila melanogaster. Manipulating the shadow enhancers showed that they help to make gene activity more resistant to changes. Factors such as fluctuations in temperature have different effects on each shadow enhancer. Having several shadow enhancers working together ensures that, whatever happens, the right genes still get activated. For genes like Kruppel, which are key for healthy development, the ability to withstand unexpected changes is a valuable evolutionary benefit. The study of Waymack et al. reveals why shadow enhancers are involved in the regulation of many genes, which may help to better understand developmental defects. Many conditions caused by such defects are influenced by both genetics and the environment. Genetic illnesses can vary in severity, which may be related to the roles of shadow enhancers. As such, studying shadow enhancers could lead to new approaches for treating genetic diseases.
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Affiliation(s)
- Rachel Waymack
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, United States
| | - Alvaro Fletcher
- Mathematical, Computational, and Systems Biology Graduate Program, University of California, Irvine, Irvine, United States
| | - German Enciso
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, United States.,Department of Mathematics, University of California, Irvine, Irvine, United States
| | - Zeba Wunderlich
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, United States
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22
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Enhancement of gene expression noise from transcription factor binding to genomic decoy sites. Sci Rep 2020; 10:9126. [PMID: 32499583 PMCID: PMC7272470 DOI: 10.1038/s41598-020-65750-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2019] [Accepted: 05/08/2020] [Indexed: 12/29/2022] Open
Abstract
The genome contains several high-affinity non-functional binding sites for transcription factors (TFs) creating a hidden and unexplored layer of gene regulation. We investigate the role of such “decoy sites” in controlling noise (random fluctuations) in the level of a TF that is synthesized in stochastic bursts. Prior studies have assumed that decoy-bound TFs are protected from degradation, and in this case decoys function to buffer noise. Relaxing this assumption to consider arbitrary degradation rates for both bound/unbound TF states, we find rich noise behaviors. For low-affinity decoys, noise in the level of unbound TF always monotonically decreases to the Poisson limit with increasing decoy numbers. In contrast, for high-affinity decoys, noise levels first increase with increasing decoy numbers, before decreasing back to the Poisson limit. Interestingly, while protection of bound TFs from degradation slows the time-scale of fluctuations in the unbound TF levels, the decay of bound TFs leads to faster fluctuations and smaller noise propagation to downstream target proteins. In summary, our analysis reveals stochastic dynamics emerging from nonspecific binding of TFs and highlights the dual role of decoys as attenuators or amplifiers of gene expression noise depending on their binding affinity and stability of the bound TF.
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23
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Giri R, Papadopoulos DK, Posadas DM, Potluri HK, Tomancak P, Mani M, Carthew RW. Ordered patterning of the sensory system is susceptible to stochastic features of gene expression. eLife 2020; 9:e53638. [PMID: 32101167 PMCID: PMC7064346 DOI: 10.7554/elife.53638] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 02/25/2020] [Indexed: 01/23/2023] Open
Abstract
Sensory neuron numbers and positions are precisely organized to accurately map environmental signals in the brain. This precision emerges from biochemical processes within and between cells that are inherently stochastic. We investigated impact of stochastic gene expression on pattern formation, focusing on senseless (sens), a key determinant of sensory fate in Drosophila. Perturbing microRNA regulation or genomic location of sens produced distinct noise signatures. Noise was greatly enhanced when both sens alleles were present in homologous loci such that each allele was regulated in trans by the other allele. This led to disordered patterning. In contrast, loss of microRNA repression of sens increased protein abundance but not sensory pattern disorder. This suggests that gene expression stochasticity is a critical feature that must be constrained during development to allow rapid yet accurate cell fate resolution.
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Affiliation(s)
- Ritika Giri
- Department of Molecular Biosciences, Northwestern UniversityEvanstonUnited States
- NSF-Simons Center for Quantitative Biology, Northwestern UniversityEvanstonUnited States
| | | | - Diana M Posadas
- Department of Molecular Biosciences, Northwestern UniversityEvanstonUnited States
| | - Hemanth K Potluri
- Department of Molecular Biosciences, Northwestern UniversityEvanstonUnited States
| | - Pavel Tomancak
- Max Planck Institute of Cell Biology and GeneticsDresdenGermany
| | - Madhav Mani
- Department of Molecular Biosciences, Northwestern UniversityEvanstonUnited States
- NSF-Simons Center for Quantitative Biology, Northwestern UniversityEvanstonUnited States
- Department of Engineering Sciences and Applied Mathematics, Northwestern UniversityEvanstonUnited States
| | - Richard W Carthew
- Department of Molecular Biosciences, Northwestern UniversityEvanstonUnited States
- NSF-Simons Center for Quantitative Biology, Northwestern UniversityEvanstonUnited States
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24
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Rodrigo G. Ab initio scaling laws between noise and mean of gene expression. Phys Rev E 2020; 100:032415. [PMID: 31640034 DOI: 10.1103/physreve.100.032415] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Indexed: 12/17/2022]
Abstract
Gene expression is inherently noisy due to fluctuations occurring at the molecular level. From a top-down perspective, noise has been traditionally decomposed into an intrinsic component that scales inversely with the mean expression level and an extrinsic component that is constant in absence of regulatory changes. Here, we adopt a bottom-up approach to reveal that extrinsic noise, by itself, can follow the aforementioned decomposition, which entails that one component of it can be confounded with intrinsic noise. Analytical expressions of the noise-mean relationship were derived for different scenarios, which were in part supported by numerical simulations.
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Affiliation(s)
- Guillermo Rodrigo
- Institute for Integrative Systems Biology (I2SysBio), CSIC-University Valencia, 46980 Paterna, Spain
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25
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Bohn-Wippert K, Tevonian EN, Lu Y, Huang MY, Megaridis MR, Dar RD. Cell Size-Based Decision-Making of a Viral Gene Circuit. Cell Rep 2019; 25:3844-3857.e5. [PMID: 30590053 PMCID: PMC7050911 DOI: 10.1016/j.celrep.2018.12.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Revised: 07/23/2018] [Accepted: 11/30/2018] [Indexed: 12/22/2022] Open
Abstract
Latently infected T cells able to reinitiate viral propagation throughout the body remain a major barrier to curing HIV. Distinguishing between latently infected cells and uninfected cells will advance efforts for viral eradication. HIV decision-making between latency and active replication is stochastic, and drug cocktails that increase bursts of viral gene expression enhance reactivation from latency. Here, we show that a larger host-cell size provides a natural cellular mechanism for enhancing burst size of viral expression and is necessary to destabilize the latent state and bias viral decision-making. Latently infected Jurkat and primary CD4+ T cells reactivate exclusively in larger activated cells, while smaller cells remain silent. In addition, reactivation is cell-cycle dependent and can be modulated with cell-cycle-arresting compounds. Cell size and cell-cycle dependent decision-making of viral circuits may guide stochastic design strategies and applications in synthetic biology and may provide important determinants to advance diagnostics and therapies. Bohn-Wippert et al. investigate reactivation of T cells latently infected with HIV. They discover that only larger cells exit latency, while smaller cells remain silent. Viral expression bursts are cell size and cell-cycle dependent, presenting dynamic cell states, capable of active control, as sources of viral fate determination.
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Affiliation(s)
- Kathrin Bohn-Wippert
- Department of Bioengineering, University of Illinois at Urbana-Champaign, 321 Everitt Laboratory, 1406 West Green Street, Urbana, IL 61801, USA
| | - Erin N Tevonian
- Department of Bioengineering, University of Illinois at Urbana-Champaign, 321 Everitt Laboratory, 1406 West Green Street, Urbana, IL 61801, USA
| | - Yiyang Lu
- Department of Bioengineering, University of Illinois at Urbana-Champaign, 321 Everitt Laboratory, 1406 West Green Street, Urbana, IL 61801, USA
| | - Meng-Yao Huang
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801, USA
| | - Melina R Megaridis
- Department of Bioengineering, University of Illinois at Urbana-Champaign, 321 Everitt Laboratory, 1406 West Green Street, Urbana, IL 61801, USA
| | - Roy D Dar
- Department of Bioengineering, University of Illinois at Urbana-Champaign, 321 Everitt Laboratory, 1406 West Green Street, Urbana, IL 61801, USA; Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 306 North Wright St, Urbana, IL 61801, USA; Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801, USA; Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, 1206 West Gregory Drive, Urbana, IL 61801, USA.
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26
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Friedrich D, Friedel L, Finzel A, Herrmann A, Preibisch S, Loewer A. Stochastic transcription in the p53-mediated response to DNA damage is modulated by burst frequency. Mol Syst Biol 2019; 15:e9068. [PMID: 31885199 PMCID: PMC6886302 DOI: 10.15252/msb.20199068] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 11/04/2019] [Accepted: 11/07/2019] [Indexed: 12/15/2022] Open
Abstract
Discontinuous transcription has been described for different mammalian cell lines and numerous promoters. However, our knowledge of how the activity of individual promoters is adjusted by dynamic signaling inputs from transcription factors is limited. To address this question, we characterized the activity of selected target genes that are regulated by pulsatile accumulation of the tumor suppressor p53 in response to ionizing radiation. We performed time-resolved measurements of gene expression at the single-cell level by smFISH and used the resulting data to inform a mathematical model of promoter activity. We found that p53 target promoters are regulated by frequency modulation of stochastic bursting and can be grouped along three archetypes of gene expression. The occurrence of these archetypes cannot solely be explained by nuclear p53 abundance or promoter binding of total p53. Instead, we provide evidence that the time-varying acetylation state of p53's C-terminal lysine residues is critical for gene-specific regulation of stochastic bursting.
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Affiliation(s)
- Dhana Friedrich
- Department for BiologyTechnische Universität DarmstadtDarmstadtGermany
- Berlin Institute for Medical Systems BiologyMax Delbrück Center in the Helmholtz AssociationBerlinGermany
- Department for BiologyHumboldt Universität zu BerlinBerlinGermany
| | - Laura Friedel
- Department for BiologyTechnische Universität DarmstadtDarmstadtGermany
| | - Ana Finzel
- Berlin Institute for Medical Systems BiologyMax Delbrück Center in the Helmholtz AssociationBerlinGermany
| | - Andreas Herrmann
- Department for BiologyHumboldt Universität zu BerlinBerlinGermany
| | - Stephan Preibisch
- Berlin Institute for Medical Systems BiologyMax Delbrück Center in the Helmholtz AssociationBerlinGermany
- Janelia Research CampusHoward Hughes Medical InstituteVAAshburnUSA
| | - Alexander Loewer
- Department for BiologyTechnische Universität DarmstadtDarmstadtGermany
- Berlin Institute for Medical Systems BiologyMax Delbrück Center in the Helmholtz AssociationBerlinGermany
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27
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Abstract
Numerous studies based on new single-cell and single-gene techniques show that individual genes can be transcribed in short bursts or pulses accompanied by changes in pulsing frequencies. Since so many examples of such discontinuous or fluctuating transcription have been found from prokaryotes to mammals, it now seems to be a common mode of gene expression. In this review we discuss the occurrence of the transcriptional fluctuations, the techniques used for their detection, their putative causes, kinetic characteristics, and probable physiological significance.
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Affiliation(s)
- Evgeny Smirnov
- a Institute of Biology and Medical Genetics , First Faculty of Medicine , Charles University and General University Hospital in Prague , Prague , Czech Republic
| | - Matúš Hornáček
- a Institute of Biology and Medical Genetics , First Faculty of Medicine , Charles University and General University Hospital in Prague , Prague , Czech Republic
| | - Tomáš Vacík
- a Institute of Biology and Medical Genetics , First Faculty of Medicine , Charles University and General University Hospital in Prague , Prague , Czech Republic
| | - Dušan Cmarko
- a Institute of Biology and Medical Genetics , First Faculty of Medicine , Charles University and General University Hospital in Prague , Prague , Czech Republic
| | - Ivan Raška
- a Institute of Biology and Medical Genetics , First Faculty of Medicine , Charles University and General University Hospital in Prague , Prague , Czech Republic
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28
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Wong VC, Bass VL, Bullock ME, Chavali AK, Lee REC, Mothes W, Gaudet S, Miller-Jensen K. NF-κB-Chromatin Interactions Drive Diverse Phenotypes by Modulating Transcriptional Noise. Cell Rep 2019; 22:585-599. [PMID: 29346759 DOI: 10.1016/j.celrep.2017.12.080] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 11/27/2017] [Accepted: 12/21/2017] [Indexed: 10/18/2022] Open
Abstract
Noisy gene expression generates diverse phenotypes, but little is known about mechanisms that modulate noise. Combining experiments and modeling, we studied how tumor necrosis factor (TNF) initiates noisy expression of latent HIV via the transcription factor nuclear factor κB (NF-κB) and how the HIV genomic integration site modulates noise to generate divergent (low-versus-high) phenotypes of viral activation. We show that TNF-induced transcriptional noise varies more than mean transcript number and that amplification of this noise explains low-versus-high viral activation. For a given integration site, live-cell imaging shows that NF-κB activation correlates with viral activation, but across integration sites, NF-κB activation cannot account for differences in transcriptional noise and phenotypes. Instead, differences in transcriptional noise are associated with differences in chromatin state and RNA polymerase II regulation. We conclude that, whereas NF-κB regulates transcript abundance in each cell, the chromatin environment modulates noise in the population to support diverse HIV activation in response to TNF.
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Affiliation(s)
- Victor C Wong
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Victor L Bass
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - M Elise Bullock
- Department of Biomedical Engineering, Yale University, New Haven, CT 06520, USA
| | - Arvind K Chavali
- Department of Biomedical Engineering, Yale University, New Haven, CT 06520, USA
| | - Robin E C Lee
- Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Walther Mothes
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06536, USA
| | - Suzanne Gaudet
- Department of Cancer Biology and Center for Cancer Systems Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
| | - Kathryn Miller-Jensen
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Department of Biomedical Engineering, Yale University, New Haven, CT 06520, USA.
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29
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Simulating multiple faceted variability in single cell RNA sequencing. Nat Commun 2019; 10:2611. [PMID: 31197158 PMCID: PMC6565723 DOI: 10.1038/s41467-019-10500-w] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 05/16/2019] [Indexed: 01/06/2023] Open
Abstract
The abundance of new computational methods for processing and interpreting transcriptomes at a single cell level raises the need for in silico platforms for evaluation and validation. Here, we present SymSim, a simulator that explicitly models the processes that give rise to data observed in single cell RNA-Seq experiments. The components of the SymSim pipeline pertain to the three primary sources of variation in single cell RNA-Seq data: noise intrinsic to the process of transcription, extrinsic variation indicative of different cell states (both discrete and continuous), and technical variation due to low sensitivity and measurement noise and bias. We demonstrate how SymSim can be used for benchmarking methods for clustering, differential expression and trajectory inference, and for examining the effects of various parameters on their performance. We also show how SymSim can be used to evaluate the number of cells required to detect a rare population under various scenarios. Simulated single cell RNA sequencing data is useful for method development and comparison. Here, the authors developed SymSim, a simulator that explicitly models the main factors of variation in single cell data.
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30
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Carey JN, Goulian M. A bacterial signaling system regulates noise to enable bet hedging. Curr Genet 2018; 65:65-70. [PMID: 29947971 DOI: 10.1007/s00294-018-0856-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Revised: 06/05/2018] [Accepted: 06/06/2018] [Indexed: 11/26/2022]
Abstract
Phenotypic diversity helps populations persist in changing and often unpredictable environments. One diversity-generating strategy is for individuals to switch randomly between phenotypic states such that one subpopulation has high fitness in the present environment, and another subpopulation has high fitness in an environment that might be encountered in the future. This sort of biological bet hedging can be found in all domains of life. Here, we discuss a recently described example from the bacterium Escherichia coli. When exposed to both oxygen and trimethylamine oxide (TMAO), E. coli hedges its bets on the possibility of oxygen loss by generating high cell-to-cell variability in the expression of the TMAO respiratory system. If oxygen is rapidly depleted from the environment, only those cells that had been expressing the TMAO respiratory system at high levels can continue to grow. This particular bet-hedging scheme possesses some unusual characteristics, most notably the decoupling of gene expression noise from the mean expression level. This decoupling allows bacteria to sense oxygen and regulate the amount of variability in TMAO reductase expression (that is, to turn bet hedging on or off) without having to adjust the mean TMAO reductase expression level. In this review, we discuss the features of the TMAO signaling pathway that permit the decoupling of gene expression noise from the mean and the regulation of bet hedging. We also highlight some open questions regarding the TMAO respiratory system and its regulatory architecture that may be relevant to many signaling systems.
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Affiliation(s)
- Jeffrey N Carey
- Graduate Group in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
- School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Mark Goulian
- Graduate Group in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
- Department of Biology and Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, 19104, USA.
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31
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Norred SE, Caveney PM, Chauhan G, Collier LK, Collier CP, Abel SM, Simpson ML. Macromolecular Crowding Induces Spatial Correlations That Control Gene Expression Bursting Patterns. ACS Synth Biol 2018; 7:1251-1258. [PMID: 29687993 DOI: 10.1021/acssynbio.8b00139] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Recent superresolution microscopy studies in E. coli demonstrate that the cytoplasm has highly variable local concentrations where macromolecular crowding plays a central role in establishing membrane-less compartmentalization. This spatial inhomogeneity significantly influences molecular transport and association processes central to gene expression. Yet, little is known about how macromolecular crowding influences gene expression bursting-the episodic process where mRNA and proteins are produced in bursts. Here, we simultaneously measured mRNA and protein reporters in cell-free systems, showing that macromolecular crowding decoupled the well-known relationship between fluctuations in the protein population (noise) and mRNA population statistics. Crowded environments led to a 10-fold increase in protein noise even though there were only modest changes in the mRNA population and fluctuations. Instead, cell-like macromolecular crowding created an inhomogeneous spatial distribution of mRNA ("spatial noise") that led to large variability in the protein production burst size. As a result, the mRNA spatial noise created large temporal fluctuations in the protein population. These results highlight the interplay between macromolecular crowding, spatial inhomogeneities, and the resulting dynamics of gene expression, and provide insights into using these organizational principles in both cell-based and cell-free synthetic biology.
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Affiliation(s)
- S Elizabeth Norred
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- Bredesen Center for Interdisciplinary Research and Graduate Education , University of Tennessee Knoxville and Oak Ridge National Laboratory , Knoxville , Tennessee 37996 , United States
| | - Patrick M Caveney
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- Bredesen Center for Interdisciplinary Research and Graduate Education , University of Tennessee Knoxville and Oak Ridge National Laboratory , Knoxville , Tennessee 37996 , United States
| | - Gaurav Chauhan
- Chemical and Biomolecular Engineering Department , University of Tennessee Knoxville , Knoxville , Tennessee 37996 , United States
| | - Lauren K Collier
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - C Patrick Collier
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Steven M Abel
- Chemical and Biomolecular Engineering Department , University of Tennessee Knoxville , Knoxville , Tennessee 37996 , United States
| | - Michael L Simpson
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- Bredesen Center for Interdisciplinary Research and Graduate Education , University of Tennessee Knoxville and Oak Ridge National Laboratory , Knoxville , Tennessee 37996 , United States
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32
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Megaridis MR, Lu Y, Tevonian EN, Junger KM, Moy JM, Bohn-Wippert K, Dar RD. Fine-tuning of noise in gene expression with nucleosome remodeling. APL Bioeng 2018; 2:026106. [PMID: 31069303 PMCID: PMC6481717 DOI: 10.1063/1.5021183] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 03/16/2018] [Indexed: 01/08/2023] Open
Abstract
Engineering stochastic fluctuations of gene expression (or “noise”) is integral to precisely bias cellular-fate decisions and statistical phenotypes in both single-cell and multi-cellular systems. Epigenetic regulation has been shown to constitute a large source of noise, and thus, engineering stochasticity is deeply intertwined with epigenetics. Here, utilizing chromatin remodeling, we report that Caffeic acid phenethyl ester (CA) and Pyrimethamine (PYR), two inhibitors of BAF250a, a subunit of the Brahma-associated factor (BAF) nucleosome remodeling complex, enable differential and tunable control of noise in transcription and translation from the human immunodeficiency virus long terminal repeat promoter in a dose and time-dependent manner. CA conserves noise levels while increasing mean abundance, resulting in direct tuning of the transcriptional burst size, while PYR strictly increases transcriptional initiation frequency while conserving a constant transcriptional burst size. Time-dependent treatment with CA reveals non-continuous tuning with noise oscillating at a constant mean abundance at early time points and the burst size increasing for treatments after 5 h. Treatments combining CA and Protein Kinase C agonists result in an even larger increase of abundance while conserving noise levels with a highly non-linear increase in variance of up to 63× untreated controls. Finally, drug combinations provide non-antagonistic combinatorial tuning of gene expression noise and map a noise phase space for future applications with viral and synthetic gene vectors. Active remodeling of nucleosomes and BAF-mediated control of gene expression noise expand a toolbox for the future design and engineering of stochasticity in living systems.
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Affiliation(s)
- Melina R Megaridis
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Yiyang Lu
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Erin N Tevonian
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Kendall M Junger
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Jennifer M Moy
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Kathrin Bohn-Wippert
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Nicolas D, Phillips NE, Naef F. What shapes eukaryotic transcriptional bursting? MOLECULAR BIOSYSTEMS 2018; 13:1280-1290. [PMID: 28573295 DOI: 10.1039/c7mb00154a] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Isogenic cells in a common environment present a large degree of heterogeneity in gene expression. Part of this variability is attributed to transcriptional bursting: the stochastic activation and inactivation of promoters that leads to the discontinuous production of mRNA. The diversity in bursting patterns displayed by different genes suggests the existence of a connection between bursting and gene regulation. Experimental strategies such as single-molecule RNA FISH, MS2-GFP or short-lived protein reporters allow the quantification of transcriptional bursting and the comparison of bursting kinetics between conditions, allowing therefore the identification of molecular mechanisms modulating transcriptional bursting. In this review we recapitulate the impact on transcriptional bursting of different molecular aspects of transcription such as the chromatin environment, nucleosome occupancy, histone modifications, the number and affinity of regulatory elements, DNA looping and transcription factor availability. More specifically, we examine their role in tuning the burst size or the burst frequency. While some molecular mechanisms involved in transcription such as histone marks can affect every aspect of bursting, others predominantly influence the burst size (e.g. the number and affinity of cis-regulatory elements) or frequency (e.g. transcription factor availability).
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Affiliation(s)
- Damien Nicolas
- The Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
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Aull KH, Tanner EJ, Thomson M, Weinberger LS. Transient Thresholding: A Mechanism Enabling Noncooperative Transcriptional Circuitry to Form a Switch. Biophys J 2017; 112:2428-2438. [PMID: 28591615 DOI: 10.1016/j.bpj.2017.05.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 04/20/2017] [Accepted: 05/01/2017] [Indexed: 01/27/2023] Open
Abstract
Threshold generation in fate-selection circuits is often achieved through deterministic bistability, which requires cooperativity (i.e., nonlinear activation) and associated hysteresis. However, the Tat positive-feedback loop that controls HIV's fate decision between replication and proviral latency lacks self-cooperativity and deterministic bistability. Absent cooperativity, it is unclear how HIV can temporarily remain in an off-state long enough for the kinetically slower epigenetic silencing mechanisms to act-expression fluctuations should rapidly trigger active positive feedback and replication, precluding establishment of latency. Here, using flow cytometry and single-cell imaging, we find that the Tat circuit exhibits a transient activation threshold. This threshold largely disappears after ∼40 h-accounting for the lack of deterministic bistability-and promoter activation shortens the lifetime of this transient threshold. Continuous differential equation models do not recapitulate this phenomenon. However, chemical reaction (master equation) models where the transcriptional transactivator and promoter toggle between inactive and active states can recapitulate the phenomenon because they intrinsically create a single-molecule threshold transiently requiring excess molecules in the inactive state to achieve at least one molecule (rather than a continuous fractional value) in the active state. Given the widespread nature of promoter toggling and transcription factor modifications, transient thresholds may be a general feature of inducible promoters.
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Affiliation(s)
- Katherine H Aull
- Bioinformatics Graduate Group, University of California, San Francisco, San Francisco, California
| | - Elizabeth J Tanner
- Gladstone Institutes (Virology and Immunology), San Francisco, California
| | - Matthew Thomson
- Division of Biology and Biological Engineering, Caltech, Pasadena, California
| | - Leor S Weinberger
- Gladstone Institutes (Virology and Immunology), San Francisco, California; Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California.
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