101
|
Saleh A, Davies GE, Pascal V, Wright PW, Hodge DL, Cho EH, Lockett SJ, Abshari M, Anderson SK. Identification of probabilistic transcriptional switches in the Ly49 gene cluster: a eukaryotic mechanism for selective gene activation. Immunity 2004; 21:55-66. [PMID: 15345220 DOI: 10.1016/j.immuni.2004.06.005] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2004] [Revised: 05/11/2004] [Accepted: 05/18/2004] [Indexed: 11/17/2022]
Abstract
Murine natural killer cells selectively express members of the Ly49 family of class I MHC receptors; however, the molecular mechanism controlling probabilistic expression of Ly49 proteins has not been defined. A pair of overlapping, divergent promoters discovered in the Ly49g gene functions as a molecular switch that can produce a forward transcript containing the coding region of the gene (on position) or a noncoding transcript in the opposite direction (off position), and this element maintains transcription in the chosen direction. Competition of C/EBP and TBP transcription factors for overlapping binding sites determines the relative strength of the competing promoters and the probability of transcription in a given direction. Similar elements precede all Ly49 family members, and the relative strength of the forward promoter in each inhibitory Ly49 gene correlates with the percentage of natural killer cells that express a given receptor, supporting a promoter competition model of selective gene activation.
Collapse
Affiliation(s)
- Ali Saleh
- Laboratory of Experimental Immunology, Center for Cancer Research, National Cancer Institute, National Cancer Institute-Frederick, MD 21702, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
102
|
Abstract
During blastula and gastrula stages of Xenopus development, cells become progressively and asynchronously committed to a particular germ layer. We have analysed the expression of genes normally expressed in ectoderm, mesoderm or endoderm in individual cells from early and late gastrula embryos, by both in situ hybridization and single-cell RT-PCR. We show that at early gastrula stages, individual cells in the same region may express markers of two or more germ layers, and 'rogue' cells that express a marker outside its canonical domain are also observed at these stages. However, by the late gastrula stage, individual cells express markers that are more characteristic of their position in the embryo, and 'rogue' cells are seen less frequently. These observations exemplify at the gene expression level the observation that cells of the early gastrula are less committed to one germ layer than are cells of the late gastrula embryo. Ectodermal cells induced to form mesendoderm by the addition of Activin respond by activating expression of different mesodermal and endodermal markers in the same cell, recapitulating the response of marginal zone cells in the embryo.
Collapse
Affiliation(s)
- Fiona C Wardle
- Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Zoology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK.
| | | |
Collapse
|
103
|
Turner TE, Schnell S, Burrage K. Stochastic approaches for modelling in vivo reactions. Comput Biol Chem 2004; 28:165-78. [PMID: 15261147 DOI: 10.1016/j.compbiolchem.2004.05.001] [Citation(s) in RCA: 231] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2004] [Accepted: 05/02/2004] [Indexed: 11/23/2022]
Abstract
In recent years, stochastic modelling has emerged as a physically more realistic alternative for modelling in vivo reactions. There are numerous stochastic approaches available in the literature; most of these assume that observed random fluctuations are a consequence of the small number of reacting molecules. We review some important developments of the stochastic approach and consider its suitability for modelling intracellular reactions. We then describe recent efforts to include the fluctuation effects caused by the structural organisation of the cytoplasm and the limited diffusion of molecules due to macromolecular crowding.
Collapse
Affiliation(s)
- T E Turner
- Oxford Centre for Industrial and Applied Mathematics, Mathematical Institute, 24-29 St. Giles', Oxford OX1 3LB, UK.
| | | | | |
Collapse
|
104
|
Burrage K, Tian T, Burrage P. A multi-scaled approach for simulating chemical reaction systems. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2004; 85:217-34. [PMID: 15142745 DOI: 10.1016/j.pbiomolbio.2004.01.014] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In this paper we give an overview of some very recent work, as well as presenting a new approach, on the stochastic simulation of multi-scaled systems involving chemical reactions. In many biological systems (such as genetic regulation and cellular dynamics) there is a mix between small numbers of key regulatory proteins, and medium and large numbers of molecules. In addition, it is important to be able to follow the trajectories of individual molecules by taking proper account of the randomness inherent in such a system. We describe different types of simulation techniques (including the stochastic simulation algorithm, Poisson Runge-Kutta methods and the balanced Euler method) for treating simulations in the three different reaction regimes: slow, medium and fast. We then review some recent techniques on the treatment of coupled slow and fast reactions for stochastic chemical kinetics and present a new approach which couples the three regimes mentioned above. We then apply this approach to a biologically inspired problem involving the expression and activity of LacZ and LacY proteins in E. coli, and conclude with a discussion on the significance of this work.
Collapse
Affiliation(s)
- Kevin Burrage
- Department of Mathematics, Advanced Computational Modelling Centre, University of Queensland, Brisbane QLD4072, Australia.
| | | | | |
Collapse
|
105
|
Pirone JR, Elston TC. Fluctuations in transcription factor binding can explain the graded and binary responses observed in inducible gene expression. J Theor Biol 2004; 226:111-21. [PMID: 14637060 DOI: 10.1016/j.jtbi.2003.08.008] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Inducible genes are expressed in the presence of an external stimulus. Individual cells may exhibit either a binary or graded response to such signals. It has been hypothesized that the chemical kinetics of transcription factor/DNA interactions can account for both these scenarios (EMBO J. 9(9) (1990) 2835; BioEssays 14(5) (1992) 341). To explore this question, we have conducted work based on the experimental results of Fiering et al. (Genes Dev. 4 (10) (1990) 1823). In these experiments, three upstream NF-AT binding sites control transcription of the lacZ gene, which codes for the enzyme beta-Galactosidase. The experimental data show a binary response for this system. We consider the effects of fluctuations in NF-AT binding on the response of the system. Our modeling results are in good qualitative agreement with the experimental data, and illustrate how the binary and graded responses can stem from the same underlying mechanism.
Collapse
Affiliation(s)
- Jason R Pirone
- Biomathematics Graduate Program and Department of Environmental and Molecular Toxicology, Campus Box 8203, North Carolina State University, Raleigh, NC 27695-8203, USA.
| | | |
Collapse
|
106
|
Golubev A, Khrustalev S, Butov A. An in silico investigation into the causes of telomere length heterogeneity and its implications for the Hayflick limit. J Theor Biol 2004; 225:153-70. [PMID: 14575650 DOI: 10.1016/s0022-5193(03)00229-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
UNLABELLED In telomerase-negative cell populations the mean telomere length (TL) decreases with increasing population doubling number (PD). A critically small TL is believed to stop cell proliferation at a cell-, age- and species-specific PD thus defining the Hayflick limit. However, positively skewed TL distributions are broad compared to differences between initial and final mean TL and strongly overlap at middle and late PD, which is inconsistent with a limiting role of TL. We used computer-assisted modelling to define what set of premises may account for the above. Our model incorporates the following concepts. DNA end replication problem: telomeres loose 1 shortening unit (SU) upon each cell division. Free radical-caused TL decrease: telomeres experience random events resulting in the loss of a random SU number within a remaining TL. Stochasticity of gene expression and cell differentiation: cells experience random events inducing mitoses or committing cells to proliferation arrest, the latter option requiring a specified number of mitoses to be passed. Cells whose TL reaches 1SU cannot divide. The proliferation kinetics of such virtual cells conforms to the transition probability model of cell cycle. When no committing events occur and at realistic SU estimates of the initial TL, maximal PD values far exceed the Hayflick limit observed in normal cells and are consistent with the crisis stage entered by transformed cells that have surpassed the Hayflick limit. At intermediate PD, symmetrical TL distributions are yielded. Upon introduction of committing events making the ratio of the rates of proliferating and committing events (P/C) range from 1.10 to 1.25, TL distributions at intermediate PD become positively skewed, and virtual cell clones show bimodal size distributions. At P/C as high as 1.25 the majority of virtual cells at maximal PD contain telomeres with TL>1SU. A 10% increase in P/C within the 1.10-1.25 range produces a two-fold increase in the maximal PD, which can reach values of up to 25 observed in rodent and some human cells. Increasing the number of committed mitoses from 0 to 10 can increases PD to about 50 observed in human fibroblasts. Introduction of the random TL breakage makes the shapes of TL distributions quite dissimilar from those observed in real cells. CONCLUSIONS Telomere length decrease is a correlate of cell proliferation that cannot alone account for the Hayflick limit, which primarily depends on parameters of cell population kinetics. Free radical damage influences the Hayflick limit not through TL but rather by affecting the ratio of the rates of events that commit cells to mitoses or to proliferation arrest.
Collapse
Affiliation(s)
- A Golubev
- Research Institute of Experimental Medicine, St. Petersburg, Russia.
| | | | | |
Collapse
|
107
|
French CT, Hanneman WH, Chubb LS, Billings RE, Andersen ME. Induction of CYP1A1 in primary rat hepatocytes by 3,3',4,4',5-pentachlorobiphenyl: evidence for a switch circuit element. Toxicol Sci 2004; 78:276-86. [PMID: 15014209 DOI: 10.1093/toxsci/kfh105] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In vivo induction of CYP1A1 in hepatocytes by aryl hydrocarbon receptor agonists is heterogeneous. Using immunohistochemistry, cells appear to be either induced or not induced as if the response of an individual cell is better represented as a switch. We have examined induction of CYP1A1 in vitro in primary rat hepatocytes to distinguish the responses of populations of cells and responses of individual cells. Cells were treated with various concentrations of the aryl hydrocarbon receptor agonist, 3,3',4,4',5-pentachlorobiphenyl. Concentration-response and time-course responses were determined for the population of cells by Western blotting for CYP1A1 protein and by real-time RT-PCR for CYP1A1 mRNA. Individual cell responses were visualized by immunocytochemistry (ICC) for protein and by in situ hybridization (ISH) for mRNA. CYP1A1 mRNA was quantified by frequency distribution analysis of grains observed on the ISH slides. Population responses showed time- and concentration-related increases in induction. Single cell responses appeared as all-or-none in the field, with cells appearing to be induced and others appearing to be not induced. Even at the highest concentrations (2.5 x 10(-7) M), some hepatocytes remained unresponsive. Distribution frequencies of single cell induction were more consistent with a switch with variable levels of induction in cells depending on treatment concentration. Combined with the reports from in vivo studies, our results support a switch with rheostat behavior for individual hepatocytes. Mechanistic studies in liver cell lines that are confirmed to exhibit switch-like induction of single cells will be necessary to assess the molecular pathways of this circuit element.
Collapse
Affiliation(s)
- C Tenley French
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA
| | | | | | | | | |
Collapse
|
108
|
Kienzle N, Baz A, Kelso A. Profiling the CD8lowphenotype, an alternative career choice for CD8 T cells during primary differentiation. Immunol Cell Biol 2004; 82:75-83. [PMID: 14984598 DOI: 10.1111/j.1440-1711.2004.01210.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
A CD8+ T cell of naive phenotype has multiple career choices during its primary differentiation into an effector cell population. One of these career options is becoming a CD8low T cell. We have previously shown by in vitro studies that CD8low T cells have lost expression of CD8 surface protein and mRNA and are poorly cytolytic. In line with poor cytolytic function, CD8low T cells express low levels of perforin and granzyme B and C, mediators of the granule-exocytosis machinery. However, CD8low T cells express IFN-gamma and substantial amounts of IL-4, the signature cytokines of type 1 and type 2 T-cell polarization, respectively. Here, we argue that the CD8low phenotype is an alternative career choice for any naive CD8+ T cell during primary activation but that the probability of choosing this option is greatly enhanced by both IL-4 and strong activation conditions. CD8low T cells have downregulated CD8 alpha/beta heterodimers and no preferential CD8 alpha/alpha homodimer expression. As shown by anti-CD8 Ab blocking experiments, surface CD8 substantially contributes to the CD8 T cell's effector function (i.e. cytokine expression and cytolytic activity). The distinct effector profile of CD8low T cells gives an example of the complexity of different CD8 T cell careers during primary effector differentiation.
Collapse
Affiliation(s)
- Norbert Kienzle
- Cooperative Research Centre for Vaccine Technology, Queensland Institute of Medical Research, Brisbane 4006, Australia.
| | | | | |
Collapse
|
109
|
Burrage K, Burrage PM, Tian T. Numerical methods for strong solutions of stochastic differential equations: an overview. Proc Math Phys Eng Sci 2004. [DOI: 10.1098/rspa.2003.1247] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- K. Burrage
- Department of Mathematics and Advanced Computational Modelling Centre, University of Queensland, Brisbane 4072, Australia
| | - P. M. Burrage
- Department of Mathematics and Advanced Computational Modelling Centre, University of Queensland, Brisbane 4072, Australia
| | - T. Tian
- Department of Mathematics and Advanced Computational Modelling Centre, University of Queensland, Brisbane 4072, Australia
| |
Collapse
|
110
|
Ye M, Iwasaki H, Laiosa CV, Stadtfeld M, Xie H, Heck S, Clausen B, Akashi K, Graf T. Hematopoietic Stem Cells Expressing the Myeloid Lysozyme Gene Retain Long-Term, Multilineage Repopulation Potential. Immunity 2003; 19:689-99. [PMID: 14614856 DOI: 10.1016/s1074-7613(03)00299-1] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Single cell PCR studies showed that hematopoietic stem cells (HSCs) express a variety of lineage-affiliated genes. However, it remains unclear whether these cells exhibiting "lineage priming" represent bona fide stem cells or a subpopulation earmarked for differentiation. Here we have used a Cre-Lox approach to follow the fate of cells expressing a lineage-affiliated marker. We crossed lysozyme Cre mice with yellow fluorescent protein (EYFP) reporter mice and found EYFP gene expression not only in myelomonocytic cells but also in a fraction of HSCs as well as B cells and T cells. Transplantation of EYFP+ HSCs into primary and secondary recipients generated mice in which all hematopoietic cells were EYFP+. In contrast, crosses between CD19 Cre and lck Cre mice with reporter mice showed no EYFP expression in HSCs or intermediate progenitors. Our results demonstrate that lysozyme expression does not mark myeloid commitment and that long-term repopulation potential is maintained in primed HSCs.
Collapse
Affiliation(s)
- Min Ye
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
111
|
Louis M, Holm L, Sánchez L, Kaufman M. A Theoretical Model for the Regulation of Sex-lethal, a Gene That Controls Sex Determination and Dosage Compensation in Drosophila melanogaster. Genetics 2003; 165:1355-84. [PMID: 14668388 PMCID: PMC1462829 DOI: 10.1093/genetics/165.3.1355] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Cell fate commitment relies upon making a choice between different developmental pathways and subsequently remembering that choice. Experimental studies have thoroughly investigated this central theme in biology for sex determination. In the somatic cells of Drosophila melanogaster, Sex-lethal (Sxl) is the master regulatory gene that specifies sexual identity. We have developed a theoretical model for the initial sex-specific regulation of Sxl expression. The model is based on the well-documented molecular details of the system and uses a stochastic formulation of transcription. Numerical simulations allow quantitative assessment of the role of different regulatory mechanisms in achieving a robust switch. We establish on a formal basis that the autoregulatory loop involved in the alternative splicing of Sxl primary transcripts generates an all-or-none bistable behavior and constitutes an efficient stabilization and memorization device. The model indicates that production of a small amount of early Sxl proteins leaves the autoregulatory loop in its off state. Numerical simulations of mutant genotypes enable us to reproduce and explain the phenotypic effects of perturbations induced in the dosage of genes whose products participate in the early Sxl promoter activation.
Collapse
Affiliation(s)
- Matthieu Louis
- The European Bioinformatics Institute, EMBL Outstation, Cambridge CB10 1SD, United Kingdom.
| | | | | | | |
Collapse
|
112
|
Schroder K, Hertzog PJ, Ravasi T, Hume DA. Interferon-gamma: an overview of signals, mechanisms and functions. J Leukoc Biol 2003; 75:163-89. [PMID: 14525967 DOI: 10.1189/jlb.0603252] [Citation(s) in RCA: 2905] [Impact Index Per Article: 138.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.
Collapse
Affiliation(s)
- Kate Schroder
- Institute for Molecular Bioscience, University of Queensland, St. Lucia, Brisbane 4072, Australia.
| | | | | | | |
Collapse
|
113
|
Berens C, Hillen W. Gene regulation by tetracyclines. Constraints of resistance regulation in bacteria shape TetR for application in eukaryotes. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:3109-21. [PMID: 12869186 DOI: 10.1046/j.1432-1033.2003.03694.x] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Tet repressor protein (TetR) regulates transcription of a family of tetracycline (tc) resistance determinants in Gram-negative bacteria. The resistance protein TetA, a membrane-spanning H+-[tc.M]+ antiporter, must be sensitively regulated because its expression is harmful in the absence of tc, yet it has to be expressed before the drugs' concentration reaches cytoplasmic levels inhibitory for protein synthesis. Consequently, TetR shows highly specific tetO binding to reduce basal expression and high affinity to tc to ensure sensitive induction. Tc can cross biological membranes by diffusion enabling this inducer to penetrate the majority of cells. These regulatory and pharmacological properties are the basis for application of TetR to selectively control the expression of single genes in lower and higher eukaryotes. TetR can be used for that purpose in some organisms without further modifications. In mammals and in a large variety of other organisms, however, eukaryotic transcriptional activator or repressor domains are fused to TetR to turn it into an efficient regulator. Mechanistic understanding and the ability to engineer and screen for mutants with specific properties allow tailoring of the DNA recognition specificity, the response to inducer tc and the dimerization specificity of TetR-based eukaryotic regulators. This review provides an overview of the TetR properties as they evolved in bacteria, the functional modifications necessary to transform it into a convenient, specific and efficient regulator for use in eukaryotes and how the interplay between structure--function studies in bacteria and specific requirements of particular applications in eukaryotes have made it a versatile and highly adaptable regulatory system.
Collapse
Affiliation(s)
- Christian Berens
- Lehrstuhl für Mikrobiologie, Institut für Mikrobiologie, Biochemie und Genetik, Friedrich-Alexander Universität Erlangen-Nürnberg, Germany
| | | |
Collapse
|
114
|
Abstract
Genomic imprinting is traditionally defined as an epigenetic process leading to parental origin-dependent monoallelic expression of some genes. The current paradigm considers this unusual expression mode as the biological raison d être of imprinting. The present chapter proposes a critical review of our ideas about genomic imprinting in light of more recent investigatory progress. Many observations are difficult to explain on the basis of the current paradigm. Studies of allelic expression of many imprinted genes and other characteristics of chromatin domains containing clustered imprinted genes, such as replication and chromatin structure, revealed an unexpectedly complex situation that challenged the role of genomic imprinting as a mechanism of transcriptional regulation. The emerging picture is that parental imprinting is a feature of large chromatin domains with their own domain-wide characteristics. The primary biological function of imprinting may reside in the differential chromatin structure of the parental chromosomal regions and not in the monoallelic expression of some of the genes contained within them.
Collapse
Affiliation(s)
- Andras Paldi
- Institut Jacques Monod, CNRS, Ecole Pratique des Hautes Etudes, 75005 Paris, France
| |
Collapse
|
115
|
Blake WJ, KAErn M, Cantor CR, Collins JJ. Noise in eukaryotic gene expression. Nature 2003; 422:633-7. [PMID: 12687005 DOI: 10.1038/nature01546] [Citation(s) in RCA: 1051] [Impact Index Per Article: 50.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2002] [Accepted: 03/07/2003] [Indexed: 11/09/2022]
Abstract
Transcription in eukaryotic cells has been described as quantal, with pulses of messenger RNA produced in a probabilistic manner. This description reflects the inherently stochastic nature of gene expression, known to be a major factor in the heterogeneous response of individual cells within a clonal population to an inducing stimulus. Here we show in Saccharomyces cerevisiae that stochasticity (noise) arising from transcription contributes significantly to the level of heterogeneity within a eukaryotic clonal population, in contrast to observations in prokaryotes, and that such noise can be modulated at the translational level. We use a stochastic model of transcription initiation specific to eukaryotes to show that pulsatile mRNA production, through reinitiation, is crucial for the dependence of noise on transcriptional efficiency, highlighting a key difference between eukaryotic and prokaryotic sources of noise. Furthermore, we explore the propagation of noise in a gene cascade network and demonstrate experimentally that increased noise in the transcription of a regulatory protein leads to increased cell-cell variability in the target gene output, resulting in prolonged bistable expression states. This result has implications for the role of noise in phenotypic variation and cellular differentiation.
Collapse
Affiliation(s)
- William J Blake
- Center for BioDynamics, Center for Advanced Biotechnology, Bioinformatics Program, and Department of Biomedical Engineering, Boston University, 44 Cummington Street, Boston, Massachusetts 02215, USA
| | | | | | | |
Collapse
|
116
|
Norris AJ, Stirland JA, McFerran DW, Seymour ZC, Spiller DG, Loudon ASI, White MRH, Davis JRE. Dynamic patterns of growth hormone gene transcription in individual living pituitary cells. Mol Endocrinol 2003; 17:193-202. [PMID: 12554747 DOI: 10.1210/me.2002-0201] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Real-time imaging of the GH gene promoter linked to luciferase in living pituitary cells has revealed surprising heterogeneity and variety of dynamic patterns of gene expression. Cells treated with either forskolin or thyroid hormone generated a consistent and characteristic temporal response from cell populations, but detailed analysis of individual cells revealed different patterns. Approximately 25-26% of cells displayed no response, 25-33% of cells exhibited a sustained progressive rise in luciferase activity, and 41-50% showed a transient phasic, or oscillatory response, after given stimuli. In cells treated consecutively with the two stimuli, the population response to the second stimulus was augmented. Single-cell analysis revealed that this was partly due to an increased number of cells responding, but also that the prevalence of response patterns changed: cells that responded to an initial stimulus were more likely to respond subsequently in a progressive sustained manner. In conclusion, these studies have indicated that GH promoter activity in individual living pituitary cells is unstable and possibly stochastic, with dynamic variations from hour to hour. The prevalence of different temporal patterns of response to hormonal stimulation among a population of cells is altered by the endocrine history of those cells.
Collapse
Affiliation(s)
- A J Norris
- Endocrine Sciences Research Group, Faculty of Medicine, University of Manchester, Manchester M13 9PT, United Kingdom
| | | | | | | | | | | | | | | |
Collapse
|
117
|
Hume DA, Ross IL, Himes SR, Sasmono RT, Wells CA, Ravasi T. The mononuclear phagocyte system revisited. J Leukoc Biol 2002. [DOI: 10.1189/jlb.72.4.621] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Affiliation(s)
- David A. Hume
- Institute for Molecular Bioscience, University of Queensland, Australia
| | - Ian L. Ross
- Institute for Molecular Bioscience, University of Queensland, Australia
| | - S. Roy Himes
- Institute for Molecular Bioscience, University of Queensland, Australia
| | - R. Tedjo Sasmono
- Institute for Molecular Bioscience, University of Queensland, Australia
| | | | - Timothy Ravasi
- Institute for Molecular Bioscience, University of Queensland, Australia
| |
Collapse
|
118
|
Louis M, Becskei A. Binary and graded responses in gene networks. SCIENCE'S STKE : SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT 2002; 2002:pe33. [PMID: 12149512 DOI: 10.1126/stke.2002.143.pe33] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Although gene expression can be regulated in a graded or a binary fashion, the majority of eukaryotic genes are either fully activated or not expressed at all in individual cells. This binary response might be an inherent property of many eukaryotic promoters. Analysis of transcription under the control of yeast GAL1 promoter suggests, however, that graded and binary modes of transcription are not mutually exclusive, but that both can occur at the same promoter when the activity of different signaling pathways is varied. In view of that, it can be expected that forthcoming experimental studies on the combinatorial effects of signaling and transcriptional mechanisms will reveal new strategies for generating graded or binary responses.
Collapse
Affiliation(s)
- Matthieu Louis
- EMBL-EBI, Structural Genomics Group, Cambridge CB10 1SD, UK
| | | |
Collapse
|
119
|
Kuznetsov VA, Knott GD, Bonner RF. General statistics of stochastic process of gene expression in eukaryotic cells. Genetics 2002; 161:1321-32. [PMID: 12136033 PMCID: PMC1462190 DOI: 10.1093/genetics/161.3.1321] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Thousands of genes are expressed at such very low levels (< or =1 copy per cell) that global gene expression analysis of rarer transcripts remains problematic. Ambiguity in identification of rarer transcripts creates considerable uncertainty in fundamental questions such as the total number of genes expressed in an organism and the biological significance of rarer transcripts. Knowing the distribution of the true number of genes expressed at each level and the corresponding gene expression level probability function (GELPF) could help resolve these uncertainties. We found that all observed large-scale gene expression data sets in yeast, mouse, and human cells follow a Pareto-like distribution model skewed by many low-abundance transcripts. A novel stochastic model of the gene expression process predicts the universality of the GELPF both across different cell types within a multicellular organism and across different organisms. This model allows us to predict the frequency distribution of all gene expression levels within a single cell and to estimate the number of expressed genes in a single cell and in a population of cells. A random "basal" transcription mechanism for protein-coding genes in all or almost all eukaryotic cell types is predicted. This fundamental mechanism might enhance the expression of rarely expressed genes and, thus, provide a basic level of phenotypic diversity, adaptability, and random monoallelic expression in cell populations.
Collapse
Affiliation(s)
- V A Kuznetsov
- Laboratory of Integrative and Medical Biophysics, National Institute of Child Health and Human Development/NIH, Bldg. 13, Rm. 3W16, Bethesda, MD 20892-5772, USA.
| | | | | |
Collapse
|
120
|
Kaushansky K, Drachman JG. The molecular and cellular biology of thrombopoietin: the primary regulator of platelet production. Oncogene 2002; 21:3359-67. [PMID: 12032774 DOI: 10.1038/sj.onc.1205323] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The term thrombopoietin (TPO) was first coined in 1958 and used to describe the humoral substance responsible for causing the platelet count to rise in response to thrombocytopenic stimuli. Despite much progress during the 1980s in the purification and characterization of the humoral regulators of lymphocyte, erythrocyte, monocyte and granulocyte production, the successful search to purify and molecularly clone thrombopoietin did not begin until the oncogene v-mpl was discovered in 1990. Since that time the proto-oncogene c-mpl was identified and, based on homology arguments, believed to encode a hematopoietic cytokine receptor, a hypothesis later proven when the cytoplasmic domain was linked to the ligand binding domain of the IL-4 receptor and shown to support the IL-4 induced growth of hematopoietic cells (Skoda et al., 1993). Finally, two different strategies using c-mpl lead to the identification of a novel ligand for the receptor in 1994 (de Sauvage et al., 1994; Lok et al., 1994; Bartley et al., 1994), a protein that displays all the biologic properties of TPO. This review attempts to distill what has been learned of the molecular and cellular biology of TPO and its receptor during the past several years, and links this information to several new insights into human disease and its treatment.
Collapse
Affiliation(s)
- Kenneth Kaushansky
- Division of Hematology, University of Washington School of Medicine, 1959 NE Pacific Street, Seattle, Washington, WA 98195, USA.
| | | |
Collapse
|
121
|
Li G, Song YH, Wu KF, Lin YM, Cao ZY, Zheng GG. Clone and expression of mutant M-CSF and its receptor from human leukemic cell line J6-1. Leuk Res 2002; 26:377-82. [PMID: 11839381 DOI: 10.1016/s0145-2126(01)00139-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Macrophage colony-stimulating factor (M-CSF) plays important roles in hematopoietic and immunologic systems. Some isoforms or mutations have been demonstrated including membrane-bound and cellular M-CSF, which associated with some leukemia, lymphoma and other solid tumors. We previously reported that the M-CSF-like membrane-associated factor (MAF-J6-1) and its receptor was found from human leukemic cell line J6-1. In this report, the cDNA of MAF-J6-1 and its receptor were cloned. The cDNA sequence of MAF-J6-1 shows a 768bp open reading frame (ORF) with 99.2% homology to m-M-CSF, but six site mutations, including two synonymous mutations and four missense mutations. The cDNA of MAF-J6-1-R has a 2916bp ORF shared 99.6% homology with M-CSF-R, but 13 site mutations, including six synonymous mutations and seven missense mutations. At the same time, a 1662bp mutant s-M-CSF cDNA, which has 10 site mutations including three synonymous mutations and seven missense mutations, was cloned from J6-1 cells. The cDNAs of MAF-J6-1 and MAF-J6-1-R were inserted into a mammalian expression plasmid pTARGET and were expressed in COS-7 cells that demonstrated by their specific MAb. COS-7 cells transfected with MAF-J6-1-R show obvious protein tyrosine kinase (PTK) activity. Our present work shows that MAF-J6-1 and its receptor are mutations of M-CSF and its receptor.
Collapse
Affiliation(s)
- Ge Li
- National Laboratory of Experimental Hematology, Institute of Hematology, Chinese Academy of Medical Sciences, Peking Union Medical College, Tianjin, PR China
| | | | | | | | | | | |
Collapse
|
122
|
Abstract
Tissue engineering and cellular therapies, either on their own or in combination with therapeutic gene delivery, have the potential to significantly impact medicine. Implementation of technologies based on these approaches requires a readily available source of cells for the generation of cells and tissues outside a living body. Because of their unique capacity to regenerate functional tissue for the lifetime of an organism, stem cells are an attractive "raw material" for multiple biotechnological applications. By definition they are self-renewing because on cell division they can generate daughter stem cells. They are also multipotent because they can differentiate into numerous specialized, functional cells. Recent findings have shown that stem cells exist in most, if not all, tissues, and that stem cell tissue specificity may be more flexible than originally thought. Although the potential for producing novel cell-based products from stem cells is large, currently there are no effective technologically relevant methodologies for culturing stem cells outside the body, or for reproducibly stimulating them to differentiate into functional cells. A mechanistic understanding of the parameters important in the control of stem cell self-renewal and lineage commitment is thus necessary to guide the development of bioprocesses for the ex vivo culture of stem cells and their derivates.
Collapse
Affiliation(s)
- P W Zandstra
- Institute of Biomaterials and Biomedical Engineering, Department of Chemical Engineering and Applied Chemistry, University of Toronto, Canada.
| | | |
Collapse
|
123
|
Abstract
Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.
Collapse
Affiliation(s)
- David G Skalnik
- Department of Pediatrics, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
| |
Collapse
|
124
|
Abstract
The recent discovery of thrombopoietin has enhanced our understanding of both hematopoiesis and platelet production. Thrombopoietin supports hematopoietic stem cell survival and expansion as well as promoting all aspects of megakaryocyte development. The hormone displays many structural similarities to other members of the hematopoietic cytokine family and some notable differences, and regulation of its expression requires both receptor-mediated removal and other mechanisms. Thrombopoietin induces receptor dimerization and tyrosine phosphorylation, and a series of signaling events including activation of JAK/STAT, Shc/Ras/MAPK and PI3K/Akt; these pathways overlap with those induced by other cytokines, but the differences that lead to the unique biological effects of the hormone are gradually being uncovered. Our growing appreciation of how cytokine signaling pathways are translated into megakaryocyte development is discussed.
Collapse
Affiliation(s)
- Amy E Geddis
- Division of Hematology, University of Washington School of Medicine, Box 357710, 1959 NE Pacific Street, Seattle, WA 98195, USA
| | | | | |
Collapse
|
125
|
Ravasi T, Wells C, Forest A, Underhill DM, Wainwright BJ, Aderem A, Grimmond S, Hume DA. Generation of diversity in the innate immune system: macrophage heterogeneity arises from gene-autonomous transcriptional probability of individual inducible genes. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 168:44-50. [PMID: 11751944 DOI: 10.4049/jimmunol.168.1.44] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Microbial products such as LPS stimulate macrophages to produce a wide diversity of inducible gene products needed for immediate host defense and priming of an appropriate acquired immune response. In this study, we have examined LPS-inducible gene expression in subclones of a mouse macrophage cell line, RAW264, using cDNA microarrays. Even archetypal target genes such as TNF-alpha were not induced in all subclones, and there was no absolute correlation between expression of pairs of genes. Nevertheless, the array analysis revealed clusters of genes that were more likely to be coexpressed. RAW264 cells stably transfected with luciferase reporter genes driven by LPS-responsive promoters revealed the same kind of clonal heterogeneity. The results indicate that each LPS-inducible gene has its own inherent probability of activation in response to LPS.
Collapse
Affiliation(s)
- Timothy Ravasi
- Institute for Molecular Bioscience, and Cooperative Research Center for Chronic Inflammatory Diseases, University of Queensland, Brisbane, Queensland 4072, Australia
| | | | | | | | | | | | | | | |
Collapse
|
126
|
Himes SR, Tagoh H, Goonetilleke N, Sasmono T, Oceandy D, Clark R, Bonifer C, Hume DA. A highly conserved c‐
fms
gene intronic element controls macrophage‐specific and regulated expression. J Leukoc Biol 2001. [DOI: 10.1189/jlb.70.5.812] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Affiliation(s)
- S. Roy Himes
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia, 4072 and
| | - Hiromi Tagoh
- University of Leeds, Molecular Medicine Unit, St. James University Hospital, Leeds, United Kingdom
| | - Nilukshi Goonetilleke
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia, 4072 and
| | - Tedjo Sasmono
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia, 4072 and
| | - Delvac Oceandy
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia, 4072 and
| | - Richard Clark
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia, 4072 and
| | - Constanze Bonifer
- University of Leeds, Molecular Medicine Unit, St. James University Hospital, Leeds, United Kingdom
| | - David A. Hume
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia, 4072 and
| |
Collapse
|
127
|
Ohlsson R, Paldi A, Graves JA. Did genomic imprinting and X chromosome inactivation arise from stochastic expression? Trends Genet 2001; 17:136-41. [PMID: 11226606 DOI: 10.1016/s0168-9525(00)02211-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Both X chromosome inactivation and autosomal genomic imprinting generate a functional hemizygosity. Here we consider models that explain the evolution of genomic imprinting and X chromosome inactivation from novel perspectives. Specifically, we suggest that random (in)activation events are common in genes and gene clusters with a low probability of transcription. These generate variability that natural selection has acted on to evolve stable monoallelic expression. Possible selection forces might include a need for dosage compensation and the prevention of biallelic silencing where a total switch off would be lethal. Two different mechanisms can accomplish regular monoallelic expression - genomic imprinting and gene counting.
Collapse
Affiliation(s)
- R Ohlsson
- Dept of Genetics and Development, Evolution Biology Centre, Uppsala University, Norbyvägen 18A, S-752 36 Uppsala, Sweden.
| | | | | |
Collapse
|
128
|
Abstract
Studies of nuclear architecture reveal that the dynamic properties of proteins in the nucleus are critical for their function. The high mobility of proteins ensures their availability throughout the nucleus; their dynamic interplay generates an ever-changing, but overall stable, architectural framework, within which nuclear processes take place. As a consequence, overall nuclear morphology is determined by the functional interactions of nuclear components. The observed dynamic properties of nuclear proteins are consistent with a central role for stochastic mechanisms in gene expression and nuclear architecture.
Collapse
Affiliation(s)
- T Misteli
- National Cancer Institute, Bethesda, MD 20892-5002, USA.
| |
Collapse
|