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  • 1
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    Stochastic coordination of multiple actuators reduces latency and improves chemotactic response in bacteria [Biophysics and Computational Biology] (2012)
    National Academy of Sciences
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    Publication Date: 2012-01-18
    Description: Individual neuronal, signal transduction, and regulatory pathways often control multiple stochastic downstream actuators, which raises the question of how coordinated response to a single input can be achieved when individual actuators fluctuate independently. In Escherichia coli, the bacterial chemotaxis pathway controls the activity of multiple flagellar motors to generate the run-and-tumble motion of the cell. High-resolution microscopy experiments have identified the key conformational changes adopted by individual flagella during this process. By incorporating these observations into a stochastic model of the flagellar bundle, we demonstrate that the presence of multiple motors imposes a trade-off on chemotactic performance. Multiple motors reduce the latency of the response below the time scale of the stochastic switching of a single motor, which improves performance on steep gradients of attractants. However, the uncoordinated switching of multiple motors interrupts and shortens cell runs, which thereby reduces signal detection and performance on shallow gradients. Remarkably, when slow fluctuations generated by the adaptation mechanism of the chemotaxis system are incorporated in the model at levels measured in experiments, the chemotactic sensitivity and performance in shallow gradients is partially restored with marginal effects for steep gradients. The noise is beneficial because it simultaneously generates long events in the statistics of individual motors and coordinates the motors to generate a long tail in the run length distribution of the cell. Occasional long runs are known to enhance exploration of random walkers. Here we show that they have the additional benefit of enhancing the sensitivity of the bacterium to very shallow gradients.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 2
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    Interdependence of behavioural variability and response to small stimuli in bacteria (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-11-16
    Description: The chemotaxis signalling network in Escherichia coli that controls the locomotion of bacteria is a classic model system for signal transduction. This pathway modulates the behaviour of flagellar motors to propel bacteria towards sources of chemical attractants. Although this system relaxes to a steady state in response to environmental changes, the signalling events within the chemotaxis network are noisy and cause large temporal variations of the motor behaviour even in the absence of stimulus. That the same signalling network governs both behavioural variability and cellular response raises the question of whether these two traits are independent. Here, we experimentally establish a fluctuation-response relationship in the chemotaxis system of living bacteria. Using this relationship, we demonstrate the possibility of inferring the cellular response from the behavioural variability measured before stimulus. In monitoring the pre- and post-stimulus switching behaviour of individual bacterial motors, we found that variability scales linearly with the response time for different functioning states of the cell. This study highlights that the fundamental relationship between fluctuation and response is not constrained to physical systems at thermodynamic equilibrium but is extensible to living cells. Such a relationship not only implies that behavioural variability and cellular response can be coupled traits, but it also provides a general framework within which we can examine how the selection of a network design shapes this interdependence.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230254/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230254/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Park, Heungwon -- Pontius, William -- Guet, Calin C -- Marko, John F -- Emonet, Thierry -- Cluzel, Philippe -- 1U54CA143869-01/CA/NCI NIH HHS/ -- P50 GM081892/GM/NIGMS NIH HHS/ -- P50 GM081892-04/GM/NIGMS NIH HHS/ -- R01 AI059195-03/AI/NIAID NIH HHS/ -- R01AI059195-03/AI/NIAID NIH HHS/ -- U54 CA143869/CA/NCI NIH HHS/ -- U54 CA143869-01/CA/NCI NIH HHS/ -- England -- Nature. 2010 Dec 9;468(7325):819-23. doi: 10.1038/nature09551. Epub 2010 Nov 14.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉The James Franck Institute, The Institute for Biophysical Dynamics, and The Department of Physics, University of Chicago, Chicago, Illinois 60637, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21076396" target="_blank"〉PubMed〈/a〉
    Keywords: Aspartic Acid/metabolism/pharmacology ; Calibration ; Chemotaxis/drug effects/*physiology ; Chromatography, High Pressure Liquid ; *Environment ; Escherichia coli/*cytology/drug effects/*physiology ; Flagella/drug effects/physiology ; Molecular Motor Proteins/metabolism ; Rotation ; *Signal Transduction/drug effects ; Stochastic Processes ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Stochastic coordination of multiple actuators reduces latency and improves chemotactic response in bacteria (2011)
    National Academy of Sciences
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    Publication Date: 2011-12-27
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 4
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    Mismatch repair-signature mutations activate gene enhancers across human colorectal cancer epigenomes (2019)
    eLife Sciences Publications
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    Publication Date: 2019-02-13
    Description: Commonly-mutated genes have been found for many cancers, but less is known about mutations in cis-regulatory elements. We leverage gains in tumor-specific enhancer activity, coupled with allele-biased mutation detection from H3K27ac ChIP-seq data, to pinpoint potential enhancer-activating mutations in colorectal cancer (CRC). Analysis of a genetically-diverse cohort of CRC specimens revealed that microsatellite instable (MSI) samples have a high indel rate within active enhancers. Enhancers with indels show evidence of positive selection, increased target gene expression, and a subset is highly recurrent. The indels affect short homopolymer tracts of A/T and increase affinity for FOX transcription factors. We further demonstrate that signature mismatch-repair (MMR) mutations activate enhancers using a xenograft tumor metastasis model, where mutations are induced naturally via CRISPR/Cas9 inactivation of MLH1 prior to tumor cell injection. Our results suggest that MMR signature mutations activate enhancers in CRC tumor epigenomes to provide a selective advantage.
    Electronic ISSN: 2050-084X
    Topics: Biology , Medicine , Natural Sciences in General
    Published by eLife Sciences Publications
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