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Doğaner BA, Yan LK, Youk H. Autocrine Signaling and Quorum Sensing: Extreme Ends of a Common Spectrum. Trends Cell Biol 2016; 26:262-271. [DOI: 10.1016/j.tcb.2015.11.002] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 11/05/2015] [Accepted: 11/10/2015] [Indexed: 11/30/2022]
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52
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de Lucena RM, Elsztein C, Barros de Souza R, de Barros Pita W, Paiva SDSL, de Morais MA. Genetic Interaction between HOG1 and SLT2 Genes in Signalling the Cellular Stress Caused by Sulphuric Acid in Saccharomyces cerevisiae. J Mol Microbiol Biotechnol 2016; 25:423-7. [PMID: 26845706 DOI: 10.1159/000443309] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 12/09/2015] [Indexed: 11/19/2022] Open
Abstract
In fuel ethanol production, recycling of yeast biomass includes treatment of cells with diluted sulphuric acid in order to control bacterial population. However, this strategy might lead to a loss of cell viability, with potential negative consequences to the fermentation yield. In a recent paper we showed that the proteins Slt2 and Hog1 are essential for yeast tolerance to sulphuric acid. As a complement of the aforementioned work, we used DNA microarray technology to search for differentially expressed genes in hog1Δ and slt2Δ deletion mutants after treatment with sulphuric acid. Our results show how Slt2p and Hog1p could coordinate the interplay among protein kinase A (PKA), protein kinase C and high-osmolarity glycerol pathways. Moreover, the SSK22 and KDX1 genes may be part of this network, although their proteins were shown to be non-essential for cell growth/survival at low pH. These proteins might work by enhancing the signal which downregulates the PKA pathway leading to cell cycle arrest, in order to regenerate the integrity of yeast cell wall and cell homeostasis under acid shock.
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Affiliation(s)
- Rodrigo Mendonça de Lucena
- Interdepartmental Research Group in Metabolic Engineering, Federal University of Pernambuco, Recife, Brazil
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53
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A sex-inducing pheromone triggers cell cycle arrest and mate attraction in the diatom Seminavis robusta. Sci Rep 2016; 6:19252. [PMID: 26786712 PMCID: PMC4726125 DOI: 10.1038/srep19252] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 12/04/2015] [Indexed: 01/15/2023] Open
Abstract
Although sexual reproduction is believed to play a major role in the high diversification rates and species richness of diatoms, a mechanistic understanding of diatom life cycle control is virtually lacking. Diatom sexual signalling is controlled by a complex, yet largely unknown, pheromone system. Here, a sex-inducing pheromone (SIP+) of the benthic pennate diatom Seminavis robusta was identified by comparative metabolomics, subsequently purified, and physicochemically characterized. Transcriptome analysis revealed that SIP+ triggers the switch from mitosis-to-meiosis in the opposing mating type, coupled with the transcriptional induction of proline biosynthesis genes, and the release of the proline-derived attraction pheromone. The induction of cell cycle arrest by a pheromone, chemically distinct from the one used to attract the opposite mating type, highlights the existence of a sophisticated mechanism to increase chances of mate finding, while keeping the metabolic losses associated with the release of an attraction pheromone to a minimum.
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Alexander WG, Peris D, Pfannenstiel BT, Opulente DA, Kuang M, Hittinger CT. Efficient engineering of marker-free synthetic allotetraploids of Saccharomyces. Fungal Genet Biol 2015; 89:10-17. [PMID: 26555931 DOI: 10.1016/j.fgb.2015.11.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Revised: 11/02/2015] [Accepted: 11/03/2015] [Indexed: 01/19/2023]
Abstract
Saccharomyces interspecies hybrids are critical biocatalysts in the fermented beverage industry, including in the production of lager beers, Belgian ales, ciders, and cold-fermented wines. Current methods for making synthetic interspecies hybrids are cumbersome and/or require genome modifications. We have developed a simple, robust, and efficient method for generating allotetraploid strains of prototrophic Saccharomyces without sporulation or nuclear genome manipulation. S. cerevisiae×S. eubayanus, S. cerevisiae×S. kudriavzevii, and S. cerevisiae×S. uvarum designer hybrid strains were created as synthetic lager, Belgian, and cider strains, respectively. The ploidy and hybrid nature of the strains were confirmed using flow cytometry and PCR-RFLP analysis, respectively. This method provides an efficient means for producing novel synthetic hybrids for beverage and biofuel production, as well as for constructing tetraploids to be used for basic research in evolutionary genetics and genome stability.
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Affiliation(s)
- William G Alexander
- Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI 53706, United States; DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53706, United States
| | - David Peris
- Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI 53706, United States; DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53706, United States
| | - Brandon T Pfannenstiel
- Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI 53706, United States
| | - Dana A Opulente
- Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI 53706, United States
| | - Meihua Kuang
- Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI 53706, United States; Graduate Program in Cellular and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706, United States
| | - Chris Todd Hittinger
- Laboratory of Genetics, Genome Center of Wisconsin, Wisconsin Energy Institute, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI 53706, United States; DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53706, United States; Graduate Program in Cellular and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706, United States.
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56
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Lai A, Sato PM, Peisajovich SG. Evolution of synthetic signaling scaffolds by recombination of modular protein domains. ACS Synth Biol 2015; 4:714-22. [PMID: 25587847 DOI: 10.1021/sb5003482] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Signaling scaffolds are proteins that interact via modular domains with multiple partners, regulating signaling networks in space and time and providing an ideal platform from which to alter signaling functions. However, to better exploit scaffolds for signaling engineering, it is necessary to understand the full extent of their modularity. We used a directed evolution approach to identify, from a large library of randomly shuffled protein interaction domains, variants capable of rescuing the signaling defect of a yeast strain in which Ste5, the scaffold in the mating pathway, had been deleted. After a single round of selection, we identified multiple synthetic scaffold variants with diverse domain architectures, able to mediate mating pathway activation in a pheromone-dependent manner. The facility with which this signaling network accommodates changes in scaffold architecture suggests that the mating signaling complex does not possess a single, precisely defined geometry into which the scaffold has to fit. These relaxed geometric constraints may facilitate the evolution of signaling networks, as well as their engineering for applications in synthetic biology.
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Affiliation(s)
- Andicus Lai
- Department of Cell and Systems
Biology University of Toronto 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada
| | - Paloma M. Sato
- Department of Cell and Systems
Biology University of Toronto 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada
| | - Sergio G. Peisajovich
- Department of Cell and Systems
Biology University of Toronto 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada
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57
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Nguyen HA, Vu CL, Tu MP, Bui TL. Discovery of pathways in protein–protein interaction networks using a genetic algorithm. DATA KNOWL ENG 2015. [DOI: 10.1016/j.datak.2015.04.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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58
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Vaga S, Bernardo-Faura M, Cokelaer T, Maiolica A, Barnes CA, Gillet LC, Hegemann B, van Drogen F, Sharifian H, Klipp E, Peter M, Saez-Rodriguez J, Aebersold R. Phosphoproteomic analyses reveal novel cross-modulation mechanisms between two signaling pathways in yeast. Mol Syst Biol 2014; 10:767. [PMID: 25492886 PMCID: PMC4300490 DOI: 10.15252/msb.20145112] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cells respond to environmental stimuli via specialized signaling pathways. Concurrent stimuli trigger multiple pathways that integrate information, predominantly via protein phosphorylation. Budding yeast responds to NaCl and pheromone via two mitogen-activated protein kinase cascades, the high osmolarity, and the mating pathways, respectively. To investigate signal integration between these pathways, we quantified the time-resolved phosphorylation site dynamics after pathway co-stimulation. Using shotgun mass spectrometry, we quantified 2,536 phosphopeptides across 36 conditions. Our data indicate that NaCl and pheromone affect phosphorylation events within both pathways, which thus affect each other at more levels than anticipated, allowing for information exchange and signal integration. We observed a pheromone-induced down-regulation of Hog1 phosphorylation due to Gpd1, Ste20, Ptp2, Pbs2, and Ptc1. Distinct Ste20 and Pbs2 phosphosites responded differently to the two stimuli, suggesting these proteins as key mediators of the information exchange. A set of logic models was then used to assess the role of measured phosphopeptides in the crosstalk. Our results show that the integration of the response to different stimuli requires complex interconnections between signaling pathways.
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Affiliation(s)
- Stefania Vaga
- Department of Biology, Institute of Molecular Systems Biology ETH Zürich, Zürich, Switzerland
| | - Marti Bernardo-Faura
- European Molecular Biology Laboratory (EMBL), European Bioinformatics Institute (EBI), Cambridge, UK
| | - Thomas Cokelaer
- European Molecular Biology Laboratory (EMBL), European Bioinformatics Institute (EBI), Cambridge, UK
| | - Alessio Maiolica
- Department of Biology, Institute of Molecular Systems Biology ETH Zürich, Zürich, Switzerland
| | - Christopher A Barnes
- Department of Biology, Institute of Molecular Systems Biology ETH Zürich, Zürich, Switzerland Department of Biology, Institute of Biochemistry, ETH Zürich, Zürich, Switzerland
| | - Ludovic C Gillet
- Department of Biology, Institute of Molecular Systems Biology ETH Zürich, Zürich, Switzerland
| | - Björn Hegemann
- Department of Biology, Institute of Biochemistry, ETH Zürich, Zürich, Switzerland
| | - Frank van Drogen
- Department of Biology, Institute of Biochemistry, ETH Zürich, Zürich, Switzerland
| | - Hoda Sharifian
- Department of Biology, Institute of Biochemistry, ETH Zürich, Zürich, Switzerland
| | - Edda Klipp
- Department of Biology, Theoretical Biophysics, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Matthias Peter
- Department of Biology, Institute of Biochemistry, ETH Zürich, Zürich, Switzerland
| | - Julio Saez-Rodriguez
- European Molecular Biology Laboratory (EMBL), European Bioinformatics Institute (EBI), Cambridge, UK
| | - Ruedi Aebersold
- Department of Biology, Institute of Molecular Systems Biology ETH Zürich, Zürich, Switzerland Faculty of Science, University of Zurich, Zurich, Switzerland
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59
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Tehseen M, Dumancic M, Briggs L, Wang J, Berna A, Anderson A, Trowell S. Functional coupling of a nematode chemoreceptor to the yeast pheromone response pathway. PLoS One 2014; 9:e111429. [PMID: 25415379 PMCID: PMC4240545 DOI: 10.1371/journal.pone.0111429] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 09/25/2014] [Indexed: 12/22/2022] Open
Abstract
Sequencing of the Caenorhabditis elegans genome revealed sequences encoding more than 1,000 G-protein coupled receptors, hundreds of which may respond to volatile organic ligands. To understand how the worm's simple olfactory system can sense its chemical environment there is a need to characterise a representative selection of these receptors but only very few receptors have been linked to a specific volatile ligand. We therefore set out to design a yeast expression system for assigning ligands to nematode chemoreceptors. We showed that while a model receptor ODR-10 binds to C. elegans Gα subunits ODR-3 and GPA-3 it cannot bind to yeast Gα. However, chimaeras between the nematode and yeast Gα subunits bound to both ODR-10 and the yeast Gβγ subunits. FIG2 was shown to be a superior MAP-dependent promoter for reporter expression. We replaced the endogenous Gα subunit (GPA1) of the Saccharomyces cerevisiae (ste2Δ sst2Δ far1Δ) triple mutant ("Cyb") with a Gpa1/ODR-3 chimaera and introduced ODR-10 as a model nematode GPCR. This strain showed concentration-dependent activation of the yeast MAP kinase pathway in the presence of diacetyl, the first time that the native form of a nematode chemoreceptor has been functionally expressed in yeast. This is an important step towards en masse de-orphaning of C. elegans chemoreceptors.
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Affiliation(s)
- Muhammad Tehseen
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
| | - Mira Dumancic
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
| | - Lyndall Briggs
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
| | - Jian Wang
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
| | - Amalia Berna
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
| | - Alisha Anderson
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
| | - Stephen Trowell
- CSIRO Food Futures National Research Flagship & CSIRO Ecosystem Sciences, Australia, PO Box 1700, Canberra, ACT 2601, Australia
- * E-mail:
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60
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Scalco E, Stec K, Iudicone D, Ferrante MI, Montresor M. The dynamics of sexual phase in the marine diatom Pseudo-nitzschia multistriata (Bacillariophyceae). JOURNAL OF PHYCOLOGY 2014; 50:817-828. [PMID: 26988637 DOI: 10.1111/jpy.12225] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 07/06/2014] [Indexed: 06/05/2023]
Abstract
Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked to both the production of genotypic diversity and the formation of large-sized initial cells. Only cells below a certain size threshold can be sexualized, but various environmental factors can modulate the success of sexual reproduction. We investigated the role of cell density and physiological conditions of parental strains in affecting the success and timing of sexual reproduction in the marine heterothallic diatom Pseudo-nitzschia multistriata. We also studied the dynamics of the sexual phase in still conditions allowing cell sedimentation and in gently mixed conditions that keep cells in suspension. Our results showed that successful sexual reproduction can only be achieved when crossing parental strains in the exponential growth phase. Evidence was provided for the fact that sexual reproduction is a density-dependent event and requires a threshold cell concentration to start, although this might vary considerably amongst strains. Moreover, the onset of the sexual phase was coupled to a marked reduction in growth of the vegetative parental cells. The crosses carried out in physically mixed conditions produced a significantly reduced number of sexual stages as compared to crosses in still conditions, showing that mixing impairs sexualization. The results of our experiments suggest that the signaling that triggers the sexual phase is favored when cells can accumulate, reducing the distance between them and facilitating contacts and/or the perception of chemical cues. Information on the progression of the sexual phase in laboratory conditions help understanding the conditions at which sex occurs in the natural environment.
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Affiliation(s)
- Eleonora Scalco
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, 80121, Italy
| | - Krzysztof Stec
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, 80121, Italy
| | - Daniele Iudicone
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, 80121, Italy
| | | | - Marina Montresor
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, 80121, Italy
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61
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Willhite DG, Brigati JR, Selcer KE, Denny JE, Duck ZA, Wright SE. Pheromone responsiveness is regulated by components of the Gpr1p-mediated glucose sensing pathway inSaccharomyces cerevisiae. Yeast 2014; 31:361-74. [DOI: 10.1002/yea.3030] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 06/24/2014] [Accepted: 07/03/2014] [Indexed: 11/10/2022] Open
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Majumdar A, Scott SD, Deogun JS, Harris S. Yeast pheromone pathway modeling using Petri nets. BMC Bioinformatics 2014; 15 Suppl 7:S13. [PMID: 25080237 PMCID: PMC4110738 DOI: 10.1186/1471-2105-15-s7-s13] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Background Our environment is composed of biological components of varying magnitude. The
relationships between the different biological elements can be represented as a
biological network. The process of mating in S. cerevisiae is initiated
by secretion of pheromone by one of the cells. Our interest lies in one particular
question: how does a cell dynamically adapt the pathway to continue mating under
severe environmental changes or under mutation (which might result in the loss of
functionality of some proteins known to participate in the pheromone pathway). Our
work attempts to answer this question. To achieve this, we first propose a model
to simulate the pheromone pathway using Petri nets. Petri nets are directed graphs
that can be used for describing and modeling systems characterized as concurrent,
asynchronous, distributed, parallel, non-deterministic, and/or stochastic. We then
analyze our Petri net-based model of the pathway to investigate the following: 1)
Given the model of the pheromone response pathway, under what conditions does the
cell respond positively, i.e., mate? 2) What kinds of perturbations in the cell
would result in changing a negative response to a positive one? Method In our model, we classify proteins into two categories: core component proteins
(set ψ) and additional proteins (set λ). We randomly
generate our model's parameters in repeated simulations. To simulate the pathway,
we carry out three different experiments. In the experiments, we simply change the
concentration of the additional proteins (λ) available to the cell.
The concentration of proteins in ψ is varied consistently from 300
to 400. In Experiment 1, the range of values for λ is set to be 100
to 150. In Experiment 2, it is set to be 151 to 200. In Experiment 3, the set
λ is further split into σ and ς, with
the idea that proteins in σ are more important than those in
ς. The range of values for σ is set to be between
151 to 200 while that of ς is 100 to 150. Decision trees were
derived from each of the first two experiments to allow us to more easily analyze
the conditions under which the pheromone is expressed. Conclusion The simulation results reveal that a cell can overcome the detrimental effects of
the conditions by using more concentration of additional proteins in
λ. The first two experiments provide evidence that employing more
concentration of proteins might be one of the ways that the cell uses to adapt
itself in inhibiting conditions to facilitate mating. The results of the third
experiment reveal that in some case the protein set σ is sufficient
in regulating the response of the cell. Results of Experiments 4 and 5 reveal that
there are certain conditions (parameters) in the model that are more important in
determining whether a cell will respond positively or not.
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64
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Youk H, Lim WA. Secreting and sensing the same molecule allows cells to achieve versatile social behaviors. Science 2014; 343:1242782. [PMID: 24503857 PMCID: PMC4145839 DOI: 10.1126/science.1242782] [Citation(s) in RCA: 131] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Cells that secrete and sense the same signaling molecule are ubiquitous. To uncover the functional capabilities of the core "secrete-and-sense" circuit motif shared by these cells, we engineered yeast to secrete and sense the mating pheromone. Perturbing each circuit element revealed parameters that control the degree to which the cell communicated with itself versus with its neighbors. This tunable interplay of self-communication and neighbor communication enables cells to span a diverse repertoire of cellular behaviors. These include a cell being asocial by responding only to itself and social through quorum sensing, and an isogenic population of cells splitting into social and asocial subpopulations. A mathematical model explained these behaviors. The versatility of the secrete-and-sense circuit motif may explain its recurrence across species.
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Affiliation(s)
- Hyun Youk
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94158, USA
- Center for Systems and Synthetic Biology, University of California San Francisco, San Francisco, CA 94158, USA
| | - Wendell A. Lim
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94158, USA
- Center for Systems and Synthetic Biology, University of California San Francisco, San Francisco, CA 94158, USA
- Howard Hughes Medical Institute, University of California San Francisco, San Francisco, CA 94158, USA
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65
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Ultrasensitivity in independent multisite systems. J Math Biol 2013; 69:977-99. [PMID: 24046085 DOI: 10.1007/s00285-013-0727-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 08/08/2013] [Indexed: 10/26/2022]
Abstract
Multisite modifications are widely recognized as an essential feature of many switch-like responses in signal transduction. It is usually assumed that the modification of one site directly or indirectly increases the rate of modification of neighboring sites. In this paper we provide a new set of assumptions for a multisite system to become highly ultrasensitive even in the absence of cooperativity or allostery. We assume that the individual sites are modified independently of each other, and that protein activity is an ultrasensitive function of the fraction of modified sites. These assumptions are particularly useful in the context of multisite systems with a large (8+) number of sites. We estimate the apparent Hill coefficient of the dose responses in the sequential and nonsequential cases, highlight their different qualitative properties, and discuss a formula to approximate dose responses in the nonsequential case. As an example we describe a model of bacterial chemotaxis that features robust ultrasensitivity and perfect adaptation over a wide range of ligand concentrations, based on non-allosteric multisite behavior at the level of receptors and flagella. We also include a model of the inactivation of the yeast pheromone protein Ste5 by cell cycle proteins.
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66
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Jaehnig EJ, Kuo D, Hombauer H, Ideker TG, Kolodner RD. Checkpoint kinases regulate a global network of transcription factors in response to DNA damage. Cell Rep 2013; 4:174-88. [PMID: 23810556 DOI: 10.1016/j.celrep.2013.05.041] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Revised: 04/04/2013] [Accepted: 05/24/2013] [Indexed: 01/01/2023] Open
Abstract
DNA damage activates checkpoint kinases that induce several downstream events, including widespread changes in transcription. However, the specific connections between the checkpoint kinases and downstream transcription factors (TFs) are not well understood. Here, we integrate kinase mutant expression profiles, transcriptional regulatory interactions, and phosphoproteomics to map kinases and downstream TFs to transcriptional regulatory networks. Specifically, we investigate the role of the Saccharomyces cerevisiae checkpoint kinases (Mec1, Tel1, Chk1, Rad53, and Dun1) in the transcriptional response to DNA damage caused by methyl methanesulfonate. The result is a global kinase-TF regulatory network in which Mec1 and Tel1 signal through Rad53 to synergistically regulate the expression of more than 600 genes. This network involves at least nine TFs, many of which have Rad53-dependent phosphorylation sites, as regulators of checkpoint-kinase-dependent genes. We also identify a major DNA damage-induced transcriptional network that regulates stress response genes independently of the checkpoint kinases.
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Affiliation(s)
- Eric J Jaehnig
- Ludwig Institute for Cancer Research, University of California School of Medicine, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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67
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Bauer MA, Carmona-Gutiérrez D, Ruckenstuhl C, Reisenbichler A, Megalou EV, Eisenberg T, Magnes C, Jungwirth H, Sinner FM, Pieber TR, Fröhlich KU, Kroemer G, Tavernarakis N, Madeo F. Spermidine promotes mating and fertilization efficiency in model organisms. Cell Cycle 2013; 12:346-52. [PMID: 23255134 PMCID: PMC3575463 DOI: 10.4161/cc.23199] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Spermidine is a naturally occurring polyamine involved in multiple biological processes, including DNA metabolism, autophagy and aging. Like other polyamines, spermidine is also indispensable for successful reproduction at several stages. However, a direct influence on the actual fertilization process, i.e., the fusion of an oocyte with a spermatocyte, remains uncertain. To explore this possibility, we established the mating process in the yeast Saccharomyces cerevisiae as a model for fertilization in higher eukaryotes. During human fertilization, the sperm capacitates and the acrosome reaction is necessary for penetration of the oocyte. Similarly, sexually active yeasts form a protrusion called "shmoo" as a prerequisite for mating. In this study, we demonstrate that pheromone-induced shmoo formation requires spermidine. In addition, we show that spermidine is essential for mating in yeast as well as for egg fertilization in the nematode Caenorhabditis elegans. In both cases, this occurs independently from autophagy. In synthesis, we identify spermidine as an important mating component in unicellular and multicellular model organisms, supporting an unprecedented evolutionary conservation of the mechanisms governing fertilization-related cellular fusion.
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Affiliation(s)
- Maria Anna Bauer
- Institute of Molecular Biosciences; Karl-Franzens University of Graz; Graz, Austria
| | | | | | - Angela Reisenbichler
- Institute of Molecular Biosciences; Karl-Franzens University of Graz; Graz, Austria
| | - Evgenia V. Megalou
- Institute of Molecular Biology and Biotechnology; Foundation for Research and Technology-Hellas; Heraklion, Greece
| | - Tobias Eisenberg
- Institute of Molecular Biosciences; Karl-Franzens University of Graz; Graz, Austria
| | - Christoph Magnes
- Institute of Medical Technologies and Health Management; Joanneum Research; Graz, Austria
- Department of Internal Medicine; Division of Diabetes and Metabolism; Medical University of Graz; Graz, Austria
| | - Helmut Jungwirth
- Institute of Molecular Biosciences; Karl-Franzens University of Graz; Graz, Austria
| | - Frank M. Sinner
- Institute of Medical Technologies and Health Management; Joanneum Research; Graz, Austria
- Department of Internal Medicine; Division of Diabetes and Metabolism; Medical University of Graz; Graz, Austria
| | - Thomas R. Pieber
- Institute of Medical Technologies and Health Management; Joanneum Research; Graz, Austria
- Department of Internal Medicine; Division of Diabetes and Metabolism; Medical University of Graz; Graz, Austria
| | - Kai-Uwe Fröhlich
- Institute of Molecular Biosciences; Karl-Franzens University of Graz; Graz, Austria
| | - Guido Kroemer
- INSERM; U848 and Institut Gustave Roussy; Villejuif, France
- Metabolomics Platform; Institut Gustave Roussy; Villejuif, France
- Centre de Recherche des Cordeliers; Paris, France
- Pôle de Biologie; Hôpital Européen Georges Pompidou; Assistance Publique–Hôpitaux de Paris (AP-HP); Paris, France
- Université Paris Descartes/Paris 5; Sorbonne Paris Cité; Paris, France
| | - Nektarios Tavernarakis
- Institute of Molecular Biology and Biotechnology; Foundation for Research and Technology-Hellas; Heraklion, Greece
| | - Frank Madeo
- Institute of Molecular Biosciences; Karl-Franzens University of Graz; Graz, Austria
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68
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Witzel F, Maddison L, Blüthgen N. How scaffolds shape MAPK signaling: what we know and opportunities for systems approaches. Front Physiol 2012; 3:475. [PMID: 23267331 PMCID: PMC3527831 DOI: 10.3389/fphys.2012.00475] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 12/04/2012] [Indexed: 11/13/2022] Open
Abstract
Scaffolding proteins add a new layer of complexity to the dynamics of cell signaling. Above their basic function to bring several components of a signaling pathway together, recent experimental research has found that scaffolds influence signaling in a much more complex way: scaffolds can exert some catalytic function, influence signaling by allosteric mechanisms, are feedback-regulated, localize signaling activity to distinct regions of the cell or increase pathway fidelity. Here we review experimental and theoretical approaches that address the function of two MAPK scaffolds, Ste5, a scaffold of the yeast mating pathway and KSR1/2, a scaffold of the classical mammalian MAPK signaling pathway. For the yeast scaffold Ste5, detailed mechanistic models have been valuable for the understanding of its function. For scaffolds in mammalian signaling, however, models have been rather generic and sketchy. For example, these models predicted narrow optimal scaffold concentrations, but when revisiting these models by assuming typical concentrations, rather a range of scaffold levels optimally supports signaling. Thus, more realistic models are needed to understand the role of scaffolds in mammalian signal transduction, which opens a big opportunity for systems biology.
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Affiliation(s)
- Franziska Witzel
- Institute of Pathology, Charité-Universitätsmedizin Berlin Berlin, Germany ; Institute for Theoretical Biology, Humboldt University Berlin Berlin, Germany
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69
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Lien EC, Nagiec MJ, Dohlman HG. Proper protein glycosylation promotes mitogen-activated protein kinase signal fidelity. Biochemistry 2012; 52:115-24. [PMID: 23210626 DOI: 10.1021/bi3009483] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The ability of cells to sense and respond appropriately to changing environmental conditions is often mediated by signal transduction pathways that employ mitogen-activated protein kinases (MAPKs). In the yeast Saccharomyces cerevisiae, the high-osmolarity glycerol (HOG) and filamentous growth (FG) pathways are activated following hyperosmotic stress and nutrient deprivation, respectively. Whereas the HOG pathway requires the MAPK Hog1, the FG pathway employs the MAPK Kss1. We conducted a comprehensive screen of nearly 5000 gene deletion strains for mutants that exhibit inappropriate cross-talk between the HOG and FG pathways. We identified two novel mutants, mnn10Δ and mnn11Δ, that allow activation of Kss1 under conditions that normally stimulate Hog1. MNN10 and MNN11 encode mannosyltransferases that are part of the N-glycosylation machinery within the Golgi apparatus; deletion of either gene results in N-glycosylated proteins that have shorter mannan chains. Deletion of the cell surface mucin Msb2 suppressed the mnn11Δ phenotype, while mutation of a single glycosylation site within Msb2 was sufficient to confer inappropriate activation of Kss1 by salt stress. These findings reveal new components of the N-glycosylation machinery needed to ensure MAPK signaling fidelity.
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Affiliation(s)
- Evan C Lien
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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70
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Seibel C, Tisch D, Kubicek CP, Schmoll M. The role of pheromone receptors for communication and mating in Hypocrea jecorina (Trichoderma reesei). Fungal Genet Biol 2012; 49:814-24. [PMID: 22884620 PMCID: PMC3462998 DOI: 10.1016/j.fgb.2012.07.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 07/12/2012] [Accepted: 07/23/2012] [Indexed: 11/04/2022]
Abstract
Discovery of sexual development in the ascomycete Trichoderma reesei (Hypocrea jecorina) as well as detection of a novel class of peptide pheromone precursors in this fungus indicates promising insights into its physiology and lifestyle. Here we investigated the role of the two pheromone receptors HPR1 and HPR2 in the H. jecorina pheromone-system. We found that these pheromone receptors show an unexpectedly high genetic variability among H. jecorina strains. HPR1 and HPR2 confer female fertility in their cognate mating types (MAT1-1 or MAT1-2, respectively) and mediate induction of fruiting body development. One compatible pheromone precursor–pheromone receptor pair (hpr1–hpp1 or hpr2–ppg1) in mating partners was sufficient for sexual development. Additionally, pheromone receptors were essential for ascospore development, hence indicating their involvement in post-fertilisation events. Neither pheromone precursor genes nor pheromone receptor genes of H. jecorina were transcribed in a strictly mating type dependent manner, but showed enhanced expression levels in the cognate mating type. In the presence of a mating partner under conditions favoring sexual development, transcript levels of pheromone precursors were significantly increased, while those of pheromone receptor genes do not show this trend. In the female sterile T. reesei strain QM6a, transcriptional responses of pheromone precursor and pheromone receptor genes to a mating partner were clearly altered compared to the female fertile wild-type strain CBS999.97. Consequently, a delayed and inappropriate response to the mating partner may be one aspect causing female sterility in QM6a.
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Affiliation(s)
- Christian Seibel
- Research Area Gene Technology and Applied Biochemistry, Institute of Chemical Engineering, Vienna University of Technology, 1060 Vienna, Austria
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71
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Bayram Ö, Bayram ÖS, Ahmed YL, Maruyama JI, Valerius O, Rizzoli SO, Ficner R, Irniger S, Braus GH. The Aspergillus nidulans MAPK module AnSte11-Ste50-Ste7-Fus3 controls development and secondary metabolism. PLoS Genet 2012; 8:e1002816. [PMID: 22829779 PMCID: PMC3400554 DOI: 10.1371/journal.pgen.1002816] [Citation(s) in RCA: 121] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Accepted: 05/22/2012] [Indexed: 12/25/2022] Open
Abstract
The sexual Fus3 MAP kinase module of yeast is highly conserved in eukaryotes and transmits external signals from the plasma membrane to the nucleus. We show here that the module of the filamentous fungus Aspergillus nidulans (An) consists of the AnFus3 MAP kinase, the upstream kinases AnSte7 and AnSte11, and the AnSte50 adaptor. The fungal MAPK module controls the coordination of fungal development and secondary metabolite production. It lacks the membrane docking yeast Ste5 scaffold homolog; but, similar to yeast, the entire MAPK module's proteins interact with each other at the plasma membrane. AnFus3 is the only subunit with the potential to enter the nucleus from the nuclear envelope. AnFus3 interacts with the conserved nuclear transcription factor AnSte12 to initiate sexual development and phosphorylates VeA, which is a major regulatory protein required for sexual development and coordinated secondary metabolite production. Our data suggest that not only Fus3, but even the entire MAPK module complex of four physically interacting proteins, can migrate from plasma membrane to nuclear envelope.
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Affiliation(s)
- Özgür Bayram
- Institute of Microbiology and Genetics, Department of Molecular Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Özlem Sarikaya Bayram
- Institute of Microbiology and Genetics, Department of Molecular Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Yasar Luqman Ahmed
- Department of Molecular Structural Biology, Institute for Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Jun-ichi Maruyama
- Institute of Microbiology and Genetics, Department of Molecular Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Oliver Valerius
- Institute of Microbiology and Genetics, Department of Molecular Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Silvio O. Rizzoli
- European Neuroscience Institute, Deutsche Forschungsgemeinschaft Center for Molecular Physiology of the Brain/Excellence Cluster 171, Göttingen, Germany
| | - Ralf Ficner
- Department of Molecular Structural Biology, Institute for Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Stefan Irniger
- Institute of Microbiology and Genetics, Department of Molecular Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
| | - Gerhard H. Braus
- Institute of Microbiology and Genetics, Department of Molecular Microbiology and Genetics, Georg-August-Universität, Göttingen, Germany
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72
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Neighbor overlap is enriched in the yeast interaction network: analysis and implications. PLoS One 2012; 7:e39662. [PMID: 22761860 PMCID: PMC3383679 DOI: 10.1371/journal.pone.0039662] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 05/26/2012] [Indexed: 11/19/2022] Open
Abstract
The yeast protein-protein interaction network has been shown to have distinct topological features such as a scale free degree distribution and a high level of clustering. Here we analyze an additional feature which is called Neighbor Overlap. This feature reflects the number of shared neighbors between a pair of proteins. We show that Neighbor Overlap is enriched in the yeast protein-protein interaction network compared with control networks carefully designed to match the characteristics of the yeast network in terms of degree distribution and clustering coefficient. Our analysis also reveals that pairs of proteins with high Neighbor Overlap have higher sequence similarity, more similar GO annotations and stronger genetic interactions than pairs with low ones. Finally, we demonstrate that pairs of proteins with redundant functions tend to have high Neighbor Overlap. We suggest that a combination of three mechanisms is the basis for this feature: The abundance of protein complexes, selection for backup of function, and the need to allow functional variation.
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73
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Taslimi A, Mathew E, Celić A, Wessel S, Dumont ME. Identifying functionally important conformational changes in proteins: activation of the yeast α-factor receptor Ste2p. J Mol Biol 2012; 418:367-78. [PMID: 22387470 DOI: 10.1016/j.jmb.2012.02.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2011] [Revised: 02/13/2012] [Accepted: 02/18/2012] [Indexed: 11/29/2022]
Abstract
We have developed a procedure in which disulfide cross-links are used to identify regions of proteins that undergo functionally important intramolecular motion. The approach was applied to the identification of disulfide bonds that stabilize the active state of the yeast α-mating pheromone receptor Ste2p, a member of the superfamily of G protein-coupled receptors. Cysteine residues were introduced at random positions in targeted regions of a starting allele of Ste2p that completely lacks cysteines. Libraries of mutated receptors were then screened for alleles that exhibit constitutive signaling. Two strongly activated alleles were recovered containing cysteine residues in transmembrane (TM) segments 5 and 6. Constitutive activity of these alleles was dependent on the presence of both introduced cysteines and was sensitive to reducing agent. Cross-linked peptides derived from the mutant receptors were detected by immunoblotting. Additional sites of cross-linking between TM segments 5 and 6 that did not lead to constitutive activation were also identified. These results indicate that relative motion of the TM segments 5 and 6 in the extracellular half of the membrane is sufficient to activate the receptor and that TM segment 6, but not TM segment 5, exhibits rotational mobility that is not associated with receptor activation.
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Affiliation(s)
- Amir Taslimi
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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74
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Chou CS, Bardwell L, Nie Q, Yi TM. Noise filtering tradeoffs in spatial gradient sensing and cell polarization response. BMC SYSTEMS BIOLOGY 2011; 5:196. [PMID: 22166067 PMCID: PMC3268761 DOI: 10.1186/1752-0509-5-196] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Accepted: 12/13/2011] [Indexed: 12/29/2022]
Abstract
BACKGROUND Cells sense chemical spatial gradients and respond by polarizing internal components. This process can be disrupted by gradient noise caused by fluctuations in chemical concentration. RESULTS We investigated how external gradient noise affects spatial sensing and response focusing on noise-filtering and the resultant tradeoffs. First, using a coarse-grained mathematical model of gradient-sensing and cell polarity, we characterized three negative consequences of noise: Inhibition of the extent of polarization, degradation of directional accuracy, and production of a noisy output polarization. Next, we explored filtering strategies and discovered that a combination of positive feedback, multiple signaling stages, and time-averaging produced good results. There was an important tradeoff, however, because filtering resulted in slower polarization. Simulations demonstrated that a two-stage filter-amplifier resulted in a balanced outcome. Then, we analyzed the effect of noise on a mechanistic model of yeast cell polarization in response to gradients of mating pheromone. This analysis showed that yeast cells likely also combine the above three filtering mechanisms into a filter-amplifier structure to achieve impressive spatial-noise tolerance, but with the consequence of a slow response time. Further investigation of the amplifier architecture revealed two positive feedback loops, a fast inner and a slow outer, both of which contributed to noise-tolerant polarization. This model also made specific predictions about how orientation performance depended upon the ratio between the gradient slope (signal) and the noise variance. To test these predictions, we performed microfluidics experiments measuring the ability of yeast cells to orient to shallow gradients of mating pheromone. The results of these experiments agreed well with the modeling predictions, demonstrating that yeast cells can sense gradients shallower than 0.1% μm-1, approximately a single receptor-ligand molecule difference between front and back, on par with motile eukaryotic cells. CONCLUSIONS Spatial noise impedes the extent, accuracy, and smoothness of cell polarization. A combined filtering strategy implemented by a filter-amplifier architecture with slow dynamics was effective. Modeling and experimental data suggest that yeast cells employ these elaborate mechanisms to filter gradient noise resulting in a slow but relatively accurate polarization response.
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Affiliation(s)
- Ching-Shan Chou
- Center for Complex Biological Systems, Department of Developmental and Cell Biology, University of California-Irvine, CA 92697, USA
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75
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Rappaport N, Barkai N. Disentangling signaling gradients generated by equivalent sources. J Biol Phys 2011; 38:267-78. [PMID: 23450187 DOI: 10.1007/s10867-011-9240-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Accepted: 08/23/2011] [Indexed: 10/17/2022] Open
Abstract
Yeast cells approach a mating partner by polarizing along a gradient of mating pheromones that are secreted by cells of the opposite mating type. The Bar1 protease is secreted by a-cells and, paradoxically, degrades the α-factor pheromones which are produced by cells of the opposite mating type and trigger mating in a-cells. This degradation may assist in the recovery from pheromone signaling but has also been shown to play a positive role in mating. Previous studies suggested that widely diffusing protease can bias the pheromone gradient towards the closest secreting cell. Here, we show that restricting the Bar1 protease to the secreting cell itself, preventing its wide diffusion, facilitates discrimination between equivalent mating partners. This may be mostly relevant during spore germination, where most mating events occur in nature.
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Affiliation(s)
- Noa Rappaport
- Departments of Molecular Genetics and Physics of Complex Systems, Weizmann Institute of Science, Rehovot, 76100 Israel
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76
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Jones SK, Bennett RJ. Fungal mating pheromones: choreographing the dating game. Fungal Genet Biol 2011; 48:668-76. [PMID: 21496492 PMCID: PMC3100450 DOI: 10.1016/j.fgb.2011.04.001] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2010] [Revised: 02/23/2011] [Accepted: 04/05/2011] [Indexed: 01/11/2023]
Abstract
Pheromones are ubiquitous from bacteria to mammals - a testament to their importance in regulating inter-cellular communication. In fungal species, they play a critical role in choreographing interactions between mating partners during the program of sexual reproduction. Here, we describe how fungal pheromones are synthesized, their interactions with G protein-coupled receptors, and the signals propagated by this interaction, using Saccharomyces cerevisiae as a reference point. Divergence from this model system is compared amongst the ascomycetes and basidiomycetes, which reveals the wealth of information that has been gleaned from studying pheromone-driven processes across a wide spectrum of the fungal kingdom.
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Affiliation(s)
- Stephen K. Jones
- Graduate Program in Molecular Biology, Cellular Biology, and Biochemistry, Brown University, Providence, RI 02912
| | - Richard J. Bennett
- Graduate Program in Molecular Biology, Cellular Biology, and Biochemistry, Brown University, Providence, RI 02912
- Department of Molecular Microbiology and Immunology, Brown University, Providence, RI 02912
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77
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The Gα subunit signals through the Ste50 protein during the mating pheromone response in the yeast Kluyveromyces lactis. EUKARYOTIC CELL 2011; 10:540-6. [PMID: 21335532 DOI: 10.1128/ec.00285-10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Yeast mating signal transduction pathways require a heterotrimeric G protein composed of Gα, Gβ, and Gγ subunits connected to a mitogen-activated protein kinase (MAPK) module. While in Saccharomyces cerevisiae elimination of Gα induces constitutive activation of the mating pathway, in Kluyveromyces lactis it produces partial sterility, which indicates that K. lactis Gα (KlGα) is required to positively activate mating. We use physical interaction experiments to determine that KlGα interacts with the adaptor protein KlSte50p. The Ras association (RA) domain of KlSte50p favored interaction with the GDP-bound KlGα subunit, and when the KlGα protein is constitutively activated, the interaction drops significantly. Additionally, KlSte50p strongly associates with the MAPK kinase kinase (MAPKKK) KlSte11p through its sterile alpha motif (SAM) domain. Genetic experiments placed KlSte50p downstream of the G protein α subunit, indicating that KlGα may stimulate the mating pathway via KlSte50p. Fusion of KlSte50p to the KlGβ subunit partially eliminated the requirement of KlGα for mating, indicating that one contribution of KlGα to the mating pathway is to facilitate plasma membrane anchoring of KlSte50p.
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78
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Liu X, Nie X, Ding Y, Chen J. Asc1, a WD-repeat protein, is required for hyphal development and virulence in Candida albicans. Acta Biochim Biophys Sin (Shanghai) 2010; 42:793-800. [PMID: 20929924 DOI: 10.1093/abbs/gmq093] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Candida albicans is a human pathogenic fungus which can undergo a morphological transition from yeast to hyphae in response to a variety of environmental stimuli. We analyzed a C. albicans Asc1 (Absence of growth Suppressor of Cyp1) protein which is entirely composed of seven repeats of the WD domain, and is conserved from fungi to metazoan. Deleting the ASC1 in C. albicans led to a profound defect in hyphal development under hypha-inducing conditions examined. Furthermore, deletion of the ASC1 attenuated virulence of C. albicans in a mouse model of systemic infection. These data strongly suggested that the conserved WD-repeat protein Asc1 is required for morphogenesis and pathogenesis of C. albicans.
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Affiliation(s)
- Xiaoyan Liu
- Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, China
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79
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Cellular responses to extracellular guidance cues. EMBO J 2010; 29:2734-45. [PMID: 20717143 DOI: 10.1038/emboj.2010.170] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Accepted: 07/05/2010] [Indexed: 01/20/2023] Open
Abstract
Extracellular guidance cues have a key role in orchestrating cell behaviour. They can take many forms, including soluble and cell-bound ligands (proteins, lipids, peptides or small molecules) and insoluble matrix substrates, but to act as guidance cues, they must be presented to the cell in a spatially restricted manner. Cells that recognize such cues respond by activating intracellular signal transduction pathways in a spatially restricted manner and convert the extracellular information into intracellular polarity. Although extracellular cues influence a broad range of cell polarity decisions, such as mitotic spindle orientation during asymmetric cell division, or the establishment of apical-basal polarity in epithelia, this review will focus specifically on guidance cues that promote cell migration (chemotaxis), or localized cell shape changes (chemotropism).
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80
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Witzany G. Uniform categorization of biocommunication in bacteria, fungi and plants. World J Biol Chem 2010; 1:160-80. [PMID: 21541001 PMCID: PMC3083953 DOI: 10.4331/wjbc.v1.i5.160] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 05/11/2010] [Accepted: 05/18/2010] [Indexed: 02/05/2023] Open
Abstract
This article describes a coherent biocommunication categorization for the kingdoms of bacteria, fungi and plants. The investigation further shows that, besides biotic sign use in trans-, inter- and intraorganismic communication processes, a common trait is interpretation of abiotic influences as indicators to generate an appropriate adaptive behaviour. Far from being mechanistic interactions, communication processes within organisms and between organisms are sign-mediated interactions. Sign-mediated interactions are the precondition for every cooperation and coordination between at least two biological agents such as cells, tissues, organs and organisms. Signs of biocommunicative processes are chemical molecules in most cases. The signs that are used in a great variety of signaling processes follow syntactic (combinatorial), pragmatic (context-dependent) and semantic (content-specific) rules. These three levels of semiotic rules are helpful tools to investigate communication processes throughout all organismic kingdoms. It is not the aim to present the latest empirical data concerning communication in these three kingdoms but to present a unifying perspective that is able to interconnect transdisciplinary research on bacteria, fungi and plants.
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Affiliation(s)
- Günther Witzany
- Guenther Witzany, Telos-Philosophische Praxis, Vogelsangstrasse 18c, A-5111-Buermoos, Austria
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81
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Chavel CA, Dionne HM, Birkaya B, Joshi J, Cullen PJ. Multiple signals converge on a differentiation MAPK pathway. PLoS Genet 2010; 6:e1000883. [PMID: 20333241 PMCID: PMC2841618 DOI: 10.1371/journal.pgen.1000883] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Accepted: 02/14/2010] [Indexed: 12/12/2022] Open
Abstract
An important emerging question in the area of signal transduction is how information from different pathways becomes integrated into a highly coordinated response. In budding yeast, multiple pathways regulate filamentous growth, a complex differentiation response that occurs under specific environmental conditions. To identify new aspects of filamentous growth regulation, we used a novel screening approach (called secretion profiling) that measures release of the extracellular domain of Msb2p, the signaling mucin which functions at the head of the filamentous growth (FG) MAPK pathway. Secretion profiling of complementary genomic collections showed that many of the pathways that regulate filamentous growth (RAS, RIM101, OPI1, and RTG) were also required for FG pathway activation. This regulation sensitized the FG pathway to multiple stimuli and synchronized it to the global signaling network. Several of the regulators were required for MSB2 expression, which identifies the MSB2 promoter as a target “hub” where multiple signals converge. Accessibility to the MSB2 promoter was further regulated by the histone deacetylase (HDAC) Rpd3p(L), which positively regulated FG pathway activity and filamentous growth. Our findings provide the first glimpse of a global regulatory hierarchy among the pathways that control filamentous growth. Systems-level integration of signaling circuitry is likely to coordinate other regulatory networks that control complex behaviors. Signal integration is an essential feature of information flow through signal transduction pathways. The mechanisms by which signals from multiple pathways become integrated into a coordinated response remain unclear. We show that multiple pathways that regulate filamentous growth converge on a differentiation-dependent MAPK pathway. Our findings indicate that more extensive communication occurs between signaling pathways that control the filamentation response than has previously been appreciated. We suggest that global communication hierarchies regulate information flow in other systems, particularly higher eukaryotes where multiple pathways typically function simultaneously to modulate a complex response.
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Affiliation(s)
- Colin A. Chavel
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York, United States of America
| | - Heather M. Dionne
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York, United States of America
| | - Barbara Birkaya
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York, United States of America
| | - Jyoti Joshi
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York, United States of America
| | - Paul J. Cullen
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York, United States of America
- * E-mail:
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82
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Kinkhabwala A, Bastiaens PIH. Spatial aspects of intracellular information processing. Curr Opin Genet Dev 2010; 20:31-40. [PMID: 20096560 DOI: 10.1016/j.gde.2009.12.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Revised: 12/18/2009] [Accepted: 12/29/2009] [Indexed: 12/24/2022]
Abstract
The computational properties of intracellular biochemical networks, for which the cell is assumed to be a 'well-mixed' reactor, have already been widely characterized. What has so far not received systematic treatment is the important role of space in many intracellular computations. Spatial network computations can be divided into two broad categories: those required for essential spatial processes (e.g. polarization, chemotaxis, division, and development) and those for which space is simply used as an extra dimension to expand the computational power of the network. Several pertinent recent examples of each category are discussed that illustrate the often conceptually subtle role of space in the processing of intracellular information.
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Affiliation(s)
- Ali Kinkhabwala
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
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83
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Dse1 may control cross talk between the pheromone and filamentation pathways in yeast. Curr Genet 2009; 55:611-21. [PMID: 19820940 DOI: 10.1007/s00294-009-0274-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2009] [Revised: 09/18/2009] [Accepted: 09/20/2009] [Indexed: 10/20/2022]
Abstract
The filamentous/invasive growth pathway is activated by nutrient limitation in the haploid form of the yeast Saccharomyces cerevisiae, whereas exposure to mating-pheromone causes cells to differentiate into gametes. Although these two pathways respond to very different stimuli and generate very different responses, they utilize many of the same signaling components. This implies the need for robust mechanisms to maintain signal fidelity. Dse1 was identified in an allele-specific suppressor screen for proteins that interact with the pheromone-responsive Gbetagamma, and found to bind both to a Gbetagamma-affinity column, and to the shared MEKK, Ste11. Although overexpression of Dse1 stimulated invasive growth and transcription of both filamentation and mating-specific transcriptional reporters, deletion of DSE1 had no effect on these outputs. In contrast, pheromone hyper-induced transcription of the filamentation reporter in cells lacking Dse1 and in cells expressing a mutant form of Gbeta that exhibits diminished interaction with Dse1. Thus, the interaction of Dse1 with both Gbeta and Ste11 may be designed to control cross talk between the pheromone and filamentation pathways.
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84
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Pitoniak A, Birkaya B, Dionne HM, Vadaie N, Cullen PJ. The signaling mucins Msb2 and Hkr1 differentially regulate the filamentation mitogen-activated protein kinase pathway and contribute to a multimodal response. Mol Biol Cell 2009; 20:3101-14. [PMID: 19439450 DOI: 10.1091/mbc.e08-07-0760] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A central question in the area of signal transduction is why pathways utilize common components. In the budding yeast Saccharomyces cerevisiae, the HOG and filamentous growth (FG) MAPK pathways require overlapping components but are thought to be induced by different stimuli and specify distinct outputs. To better understand the regulation of the FG pathway, we examined FG in one of yeast's native environments, the grape-producing plant Vitis vinifera. In this setting, different aspects of FG were induced in a temporal manner coupled to the nutrient cycle, which uncovered a multimodal feature of FG pathway signaling. FG pathway activity was modulated by the HOG pathway, which led to the finding that the signaling mucins Msb2p and Hkr1p, which operate at the head of the HOG pathway, differentially regulate the FG pathway. The two mucins exhibited different expression and secretion patterns, and their overproduction induced nonoverlapping sets of target genes. Moreover, Msb2p had a function in cell polarization through the adaptor protein Sho1p that Hkr1p did not. Differential MAPK activation by signaling mucins brings to light a new point of discrimination between MAPK pathways.
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Affiliation(s)
- Andrew Pitoniak
- Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14260-1300, USA
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85
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Hog1 mitogen-activated protein kinase (MAPK) interrupts signal transduction between the Kss1 MAPK and the Tec1 transcription factor to maintain pathway specificity. EUKARYOTIC CELL 2009; 8:606-16. [PMID: 19218425 DOI: 10.1128/ec.00005-09] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In Saccharomyces cerevisiae, the mating, filamentous growth (FG), and high-osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) signaling pathways share components and yet mediate distinct responses to different extracellular signals. Cross talk is suppressed between the mating and FG pathways because mating signaling induces the destruction of the FG transcription factor Tec1. We show here that HOG pathway activation results in phosphorylation of the FG MAPK, Kss1, and the MAPKK, Ste7. However, FG transcription is not activated because HOG signaling prevents the activation of Tec1. In contrast to the mating pathway, we find that the mechanism involves the inhibition of DNA binding by Tec1 rather than its destruction. We also find that nuclear accumulation of Tec1 is not affected by HOG signaling. Inhibition by Hog1 is apparently indirect since it does not require any of the consensus S/TP MAPK phosphorylation sites on Tec1, its DNA-binding partner Ste12, or the associated regulators Dig1 or Dig2. It also does not require the consensus MAPK sites of the Ste11 activator Ste50, in contrast to a recent proposal for a role for negative feedback in specificity. Our results demonstrate that HOG signaling interrupts the FG pathway signal transduction between the phosphorylation of Kss1 and the activation of DNA binding by Tec1.
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86
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Halperin Y, Linhart C, Ulitsky I, Shamir R. Allegro: analyzing expression and sequence in concert to discover regulatory programs. Nucleic Acids Res 2009; 37:1566-79. [PMID: 19151090 PMCID: PMC2655690 DOI: 10.1093/nar/gkn1064] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
A major goal of system biology is the characterization of transcription factors and microRNAs (miRNAs) and the transcriptional programs they regulate. We present Allegro, a method for de-novo discovery of cis-regulatory transcriptional programs through joint analysis of genome-wide expression data and promoter or 3' UTR sequences. The algorithm uses a novel log-likelihood-based, non-parametric model to describe the expression pattern shared by a group of co-regulated genes. We show that Allegro is more accurate and sensitive than existing techniques, and can simultaneously analyze multiple expression datasets with more than 100 conditions. We apply Allegro on datasets from several species and report on the transcriptional modules it uncovers. Our analysis reveals a novel motif over-represented in the promoters of genes highly expressed in murine oocytes, and several new motifs related to fly development. Finally, using stem-cell expression profiles, we identify three miRNA families with pivotal roles in human embryogenesis.
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Affiliation(s)
- Yonit Halperin
- School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel
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87
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Abstract
The functional coupling of heterologous G protein-coupled receptors (GPCRs) to the pheromone-response pathway of the budding yeast Saccharomyces cerevisiae is well established as an experimental system for ligand identification and for characterizing receptor pharmacology and signal transduction mechanisms. A number of groups have developed yeast strains using various modifications to this signaling pathway, especially manipulation of the G protein alpha subunit Gpa1p, to facilitate coupling of a wide range of mammalian GPCRs. The attraction of these systems is the simplicity and low cost of yeast cell culture enabling the assays to be set up rapidly in academic or industrial labs without the requirement for expensive technical equipment. Furthermore, haploid yeasts contain only a single GPCR capable of activating the pathway, which can be deleted and replaced with a mammalian GPCR providing a cell-based functional assay in a eukaryotic host free from endogenous responses. The yeast strains used for this purpose are highly engineered and may be covered by intellectual property for commercial applications in some countries. However, they can usually be obtained from the host labs for research purposes covered by a Material Transfer Agreement and/or licence where appropriate. The protocols herein assume that such strains have been acquired and begin with introduction of the heterologous GPCR into the engineered yeast cell. Assays are configured such that agonism of the GPCR leads to induction of a reporter gene and/or growth of the yeast. A number of parameters may be optimized to generate robust experimental formats, in high-density microtiter plates, that may be used for ligand identification and pharmacological characterization.
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Affiliation(s)
- Simon J Dowell
- Department of Biological Reagent and Assay Development, GlaxoSmithKline, Hertfordshire, UK
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88
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Moore TI, Chou CS, Nie Q, Jeon NL, Yi TM. Robust spatial sensing of mating pheromone gradients by yeast cells. PLoS One 2008; 3:e3865. [PMID: 19052645 PMCID: PMC2586657 DOI: 10.1371/journal.pone.0003865] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 10/29/2008] [Indexed: 01/27/2023] Open
Abstract
Projecting or moving up a chemical gradient is a universal behavior of living organisms. We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone α-factor produced in a microfluidics chamber; the focus was on bar1Δ strains, which do not degrade the pheromone input. The yeast cells exhibited good accuracy with the mating projection typically pointing in the correct direction up the gradient (∼80% under certain conditions), excellent sensitivity to shallow gradients, and broad dynamic range so that gradient-sensing was relatively robust over a 1000-fold range of average α-factor concentrations. Optimal directional sensing occurred at lower concentrations (5 nM) close to the Kd of the receptor and with steeper gradient slopes. Pheromone supersensitive mutations (sst2Δ and ste2300Δ) that disrupt the down-regulation of heterotrimeric G-protein signaling caused defects in both sensing and response. Interestingly, yeast cells employed adaptive mechanisms to increase the robustness of the process including filamentous growth (i.e. directional distal budding) up the gradient at low pheromone concentrations, bending of the projection to be more aligned with the gradient, and forming a more accurate second projection when the first projection was in the wrong direction. Finally, the cells were able to amplify a shallow external gradient signal of α-factor to produce a dramatic polarization of signaling proteins at the front of the cell. Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization. Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.
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Affiliation(s)
- Travis I. Moore
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
| | - Ching-Shan Chou
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Mathematics, University of California Irvine, Irvine, California, United States of America
| | - Qing Nie
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Mathematics, University of California Irvine, Irvine, California, United States of America
| | - Noo Li Jeon
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Biomedical Engineering, University of California Irvine, Irvine, California, United States of America
| | - Tau-Mu Yi
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- * E-mail:
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89
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Xue C, Hsueh YP, Heitman J. Magnificent seven: roles of G protein-coupled receptors in extracellular sensing in fungi. FEMS Microbiol Rev 2008; 32:1010-32. [PMID: 18811658 DOI: 10.1111/j.1574-6976.2008.00131.x] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
G protein-coupled receptors (GPCRs) represent the largest family of transmembrane receptors and are responsible for transducing extracellular signals into intracellular responses that involve complex intracellular-signaling networks. This review highlights recent research advances in fungal GPCRs, including classification, extracellular sensing, and G protein-signaling regulation. The involvement of GPCRs in pheromone and nutrient sensing has been studied extensively over the past decade. Following recent advances in fungal genome sequencing projects, a panoply of GPCR candidates has been revealed and some have been documented to play key roles sensing diverse extracellular signals, such as pheromones, sugars, amino acids, nitrogen sources, and even photons. Identification and deorphanization of additional putative GPCRs may require the development of new research tools. Here, we compare research on GPCRs in fungi with information derived from mammalian systems to provide a useful road map on how to better understand ligand-GPCR-G protein interactions in general. We also emphasize the utility of yeast as a discovery tool for systemic studies of GPCRs from other organisms.
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Affiliation(s)
- Chaoyang Xue
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC, USA
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90
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Uncovering mechanisms of bistability in biological systems. Curr Opin Biotechnol 2008; 19:381-8. [PMID: 18634875 DOI: 10.1016/j.copbio.2008.06.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Accepted: 06/15/2008] [Indexed: 12/14/2022]
Abstract
As the systems biology era progresses, theoreticians and experimentalists continue uncovering the molecular mechanisms that underlie the regulation of complex cellular phenomena, including those governing proliferation, differentiation, and death. The discovery of bistability in cellular responses and their signaling pathways has become a recurring theme, and prompted strong interest in understanding both the design and function of these networks. Modeling these systems has been crucial in assisting experimentalists to better understand how this and other types of behavior can emerge from a subset of regulators, and also to analyze and identify systems-level characteristics that would otherwise be difficult to intuit. In this review, recent advances in both theoretical and experimental work investigating the mechanistic as well as biological basis for bistability will be presented. These will include the role of positive feedback loops, the potential function of dual phosphorylation cycles, and substrate competition as a means of generating ultrasensitivity.
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91
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Heterotrimeric G-protein subunit function in Candida albicans: both the alpha and beta subunits of the pheromone response G protein are required for mating. EUKARYOTIC CELL 2008; 7:1591-9. [PMID: 18658257 DOI: 10.1128/ec.00077-08] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A pheromone-mediated signaling pathway that couples seven-transmembrane-domain (7-TMD) receptors to a mitogen-activated protein kinase module controls Candida albicans mating. 7-TMD receptors are typically connected to heterotrimeric G proteins whose activation regulates downstream effectors. Two Galpha subunits in C. albicans have been identified previously, both of which have been implicated in aspects of pheromone response. Cag1p was found to complement the mating pathway function of the pheromone receptor-coupled Galpha subunit in Saccharomyces cerevisiae, and Gpa2p was shown to have a role in the regulation of cyclic AMP signaling in C. albicans and to repress pheromone-mediated arrest. Here, we show that the disruption of CAG1 prevented mating, inactivated pheromone-mediated arrest and morphological changes, and blocked pheromone-mediated gene expression changes in opaque cells of C. albicans and that the overproduction of CAG1 suppressed the hyperactive cell cycle arrest exhibited by sst2 mutant cells. Because the disruption of the STE4 homolog constituting the only C. albicans gene for a heterotrimeric Gbeta subunit also blocked mating and pheromone response, it appears that in this fungal pathogen the Galpha and Gbeta subunits do not act antagonistically but, instead, are both required for the transmission of the mating signal.
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92
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93
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Grafahrend-Belau E, Schreiber F, Heiner M, Sackmann A, Junker BH, Grunwald S, Speer A, Winder K, Koch I. Modularization of biochemical networks based on classification of Petri net t-invariants. BMC Bioinformatics 2008; 9:90. [PMID: 18257938 PMCID: PMC2277402 DOI: 10.1186/1471-2105-9-90] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Accepted: 02/08/2008] [Indexed: 11/10/2022] Open
Abstract
Background Structural analysis of biochemical networks is a growing field in bioinformatics and systems biology. The availability of an increasing amount of biological data from molecular biological networks promises a deeper understanding but confronts researchers with the problem of combinatorial explosion. The amount of qualitative network data is growing much faster than the amount of quantitative data, such as enzyme kinetics. In many cases it is even impossible to measure quantitative data because of limitations of experimental methods, or for ethical reasons. Thus, a huge amount of qualitative data, such as interaction data, is available, but it was not sufficiently used for modeling purposes, until now. New approaches have been developed, but the complexity of data often limits the application of many of the methods. Biochemical Petri nets make it possible to explore static and dynamic qualitative system properties. One Petri net approach is model validation based on the computation of the system's invariant properties, focusing on t-invariants. T-invariants correspond to subnetworks, which describe the basic system behavior. With increasing system complexity, the basic behavior can only be expressed by a huge number of t-invariants. According to our validation criteria for biochemical Petri nets, the necessary verification of the biological meaning, by interpreting each subnetwork (t-invariant) manually, is not possible anymore. Thus, an automated, biologically meaningful classification would be helpful in analyzing t-invariants, and supporting the understanding of the basic behavior of the considered biological system. Methods Here, we introduce a new approach to automatically classify t-invariants to cope with network complexity. We apply clustering techniques such as UPGMA, Complete Linkage, Single Linkage, and Neighbor Joining in combination with different distance measures to get biologically meaningful clusters (t-clusters), which can be interpreted as modules. To find the optimal number of t-clusters to consider for interpretation, the cluster validity measure, Silhouette Width, is applied. Results We considered two different case studies as examples: a small signal transduction pathway (pheromone response pathway in Saccharomyces cerevisiae) and a medium-sized gene regulatory network (gene regulation of Duchenne muscular dystrophy). We automatically classified the t-invariants into functionally distinct t-clusters, which could be interpreted biologically as functional modules in the network. We found differences in the suitability of the various distance measures as well as the clustering methods. In terms of a biologically meaningful classification of t-invariants, the best results are obtained using the Tanimoto distance measure. Considering clustering methods, the obtained results suggest that UPGMA and Complete Linkage are suitable for clustering t-invariants with respect to the biological interpretability. Conclusion We propose a new approach for the biological classification of Petri net t-invariants based on cluster analysis. Due to the biologically meaningful data reduction and structuring of network processes, large sets of t-invariants can be evaluated, allowing for model validation of qualitative biochemical Petri nets. This approach can also be applied to elementary mode analysis.
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Affiliation(s)
- Eva Grafahrend-Belau
- Technical University of Applied Sciences Berlin, FB VI/FB V, Bioinformatics/Biotechnology, Seestr, 64, 13347 Berlin, Germany.
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94
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Ka M, Park YU, Kim J. The DEAD-box RNA helicase, Dhh1, functions in mating by regulating Ste12 translation in Saccharomyces cerevisiae. Biochem Biophys Res Commun 2008; 367:680-6. [PMID: 18182159 DOI: 10.1016/j.bbrc.2007.12.169] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Accepted: 12/26/2007] [Indexed: 01/11/2023]
Abstract
The DEAD-box RNA helicase, Dhh1, is a member of a highly conserved subfamily designated RCK/p54 helicases. Dhh1 functions as mRNA decapping activator, and is localized to discrete cytoplasmic foci known as processing bodies (P-bodies). Here, we describe the essential roles of Dhh1 in the yeast mating pathway. A dhh1 deletion mutation caused a significant decrease in the protein level of Ste12, a mating-specific transcription factor, resulting in severe mating defects. We examined the accumulation of Dhh1-GFP in P-bodies during mating. Following pheromone treatment, the P-body intensity and number increased in wild-type cells, while dhh1 mutant cells failed to show P-body formation. Both the mating and P-body phenotypes of dhh1 were suppressed by overexpression of STE12 or CAF20 encoding an eIF4E inhibitor. In wild-type cells, CAF20 overexpression led to an increased level of Ste12 protein as well as highly developed P-bodies. We propose that Dhh1 and Caf20 regulate the Ste12 protein expression and the Ste12 protein level is associated with P-body formation during mating.
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Affiliation(s)
- Minhan Ka
- Department of Microbiology, School of Bioscience and Biotechnology, Chungnam National University, Yuseong-Gu, Gung-Dong 220, Daejeon 305-764, Republic of Korea
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95
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Protein kinases involved in mating and osmotic stress in the yeast Kluyveromyces lactis. EUKARYOTIC CELL 2007; 7:78-85. [PMID: 18024598 DOI: 10.1128/ec.00362-07] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Systematic disruption of genes encoding kinases and mitogen-activated protein kinases (MAPKs) was performed in Kluyveromyces lactis haploid cells. The mutated strains were assayed by their capacity to mate and to respond to hyperosmotic stress. The K. lactis Ste11p (KlSte11p) MAPK kinase kinase (MAPKKK) was found to act in both mating and osmoresponse pathways while the scaffold KlSte5p and the MAPK KlFus3p appeared to be specific for mating. The p21-activated kinase KlSte20p and the kinase KlSte50p participated in both pathways. Protein association experiments showed interaction of KlSte50p and KlSte20p with Galpha and Gbeta, respectively, the G protein subunits involved in the mating pathway. Both KlSte50p and KlSte20p also showed interaction with KlSte11p. Disruption mutants of the K. lactis PBS2 (KlPBS2) and KlHOG1 genes of the canonical osmotic response pathway resulted in mutations sensitive to high salt and high sorbitol but dispensable for mating. Mutations that eliminate the MAPKK KlSte7p activity had a strong effect on mating and also showed sensitivity to osmotic stress. Finally, we found evidence of physical interaction between KlSte7p and KlHog1p, in addition to diminished Hog1p phosphorylation after a hyperosmotic shock in cells lacking KlSte7p. This study reveals novel roles for components of transduction systems in yeast.
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96
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Blackwell E, Kim HJN, Stone DE. The pheromone-induced nuclear accumulation of the Fus3 MAPK in yeast depends on its phosphorylation state and on Dig1 and Dig2. BMC Cell Biol 2007; 8:44. [PMID: 17963515 PMCID: PMC2219999 DOI: 10.1186/1471-2121-8-44] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Accepted: 10/26/2007] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Like mammalian MAP kinases, the mating-specific Fus3 MAPK of yeast accumulates in the nuclei of stimulated cells. Because Fus3 does not appear to be subjected to active nucleo-cytoplasmic transport, it is not clear how its activation by mating pheromone effects the observed change in its localization. One possibility is that the activation of Fus3 changes its affinity for nuclear and cytoplasmic tethers. RESULTS Dig1, Dig2, and Ste12 are nuclear proteins that interact with Fus3. We found that the pheromone-induced nuclear accumulation of a Fus3-GFP reporter is reduced in cells lacking Dig1 or Dig2, whereas Fus3T180AY182A-GFP localization was unaffected by the absence of these proteins. This suggests that Dig1 and Dig2 contribute to the retention of phosphorylated Fus3 in the nucleus. Moreover, overexpression of Ste12 caused the hyper-accumulation of Fus3-GFP (but not Fus3T180AY182A-GFP) in the nuclei of pheromone-treated cells, suggesting that Ste12 also plays a role in the nuclear retention of phosphorylated Fus3, either by directly interacting with it or by transcribing genes whose protein products are Fus3 tethers. We have previously reported that overexpression of the Msg5 phosphatase inhibits the nuclear localization of Fus3. Here we show that this effect depends on the phosphatase activity of Msg5, and provide evidence that both nuclear and cytoplasmic Msg5 can affect the localization of Fus3. CONCLUSION Our data are consistent with a model in which the pheromone-induced phosphorylation of Fus3 increases its affinity for nuclear tethers, which contributes to its nuclear accumulation and is antagonized by Msg5.
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Affiliation(s)
- Ernest Blackwell
- Laboratory for Molecular Biology, University of Illinois at Chicago, Chicago, Illinois 60607, USA
| | - Hye-Jin N Kim
- Laboratory for Molecular Biology, University of Illinois at Chicago, Chicago, Illinois 60607, USA
| | - David E Stone
- Laboratory for Molecular Biology, University of Illinois at Chicago, Chicago, Illinois 60607, USA
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97
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Zhao X, Mehrabi R, Xu JR. Mitogen-activated protein kinase pathways and fungal pathogenesis. EUKARYOTIC CELL 2007; 6:1701-14. [PMID: 17715363 PMCID: PMC2043402 DOI: 10.1128/ec.00216-07] [Citation(s) in RCA: 263] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Xinhua Zhao
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, USA
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98
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Zeller CE, Parnell SC, Dohlman HG. The RACK1 ortholog Asc1 functions as a G-protein beta subunit coupled to glucose responsiveness in yeast. J Biol Chem 2007; 282:25168-76. [PMID: 17591772 DOI: 10.1074/jbc.m702569200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
According to the prevailing paradigm, G-proteins are composed of three subunits, an alpha subunit with GTPase activity and a tightly associated betagamma subunit complex. In the yeast Saccharomyces cerevisiae there are two known Galpha proteins (Gpa1 and Gpa2) but only one Gbetagamma, which binds only to Gpa1. Here we show that the yeast ortholog of RACK1 (receptor for activated protein kinase C1) Asc1 functions as the Gbeta for Gpa2. As with other known Gbeta proteins, Asc1 has a 7-WD domain structure, interacts directly with the Galpha in a guanine nucleotide-dependent manner, and inhibits Galpha guanine nucleotide exchange activity. In addition, Asc1 binds to the effector enzyme adenylyl cyclase (Cyr1), and diminishes the production of cAMP in response to glucose stimulation. Thus, whereas Gpa2 promotes glucose signaling through elevated production of cAMP, Asc1 has opposing effects on these same processes. Our findings reveal the existence of an unusual Gbeta subunit, one having multiple functions within the cell in addition to serving as a signal transducer for cell surface receptors and intracellular effectors.
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Affiliation(s)
- Corinne E Zeller
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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99
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100
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Ingolia NT, Murray AW. Positive-feedback loops as a flexible biological module. Curr Biol 2007; 17:668-77. [PMID: 17398098 PMCID: PMC1914375 DOI: 10.1016/j.cub.2007.03.016] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 02/12/2007] [Accepted: 03/01/2007] [Indexed: 01/08/2023]
Abstract
BACKGROUND Bistability in genetic networks allows cells to remember past events and to make discrete decisions in response to graded signals. Bistable behavior can result from positive feedback, but feedback loops can have other roles in signal transduction as well. RESULTS We introduced positive feedback into the budding-yeast pheromone response to convert it into a bistable system. In the presence of feedback, transient induction with high pheromone levels caused persistent pathway activation, whereas at lower levels a fraction of cells became persistently active but the rest inactivated completely. We also generated mutations that quantitatively tuned the basal and induced expression levels of the feedback promoter and showed that they qualitatively changed the behavior of the system. Finally, we developed a simple stochastic model of our positive-feedback system and showed the agreement between our simulations and experimental results. CONCLUSIONS The positive-feedback loop can display several different behaviors, including bistability, and can switch between them as a result of simple mutations.
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Affiliation(s)
- Nicholas T. Ingolia
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138 USA
| | - Andrew W. Murray
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138 USA
- *To whom correspondence should be addressed, E-mail: ; Phone: (617) 496-1350
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