Life Sciences Research for Lifelong Health


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Title / Authors / Details Open Access Download

Ligand-dependent opening of the multiple AMPA receptor conductance States: a concerted model.
Dutta-Roy R, Rosenmund C, Edelstein SJ, Le Novère N

Modulation of the properties of AMPA receptors at the post-synaptic membrane is one of the main suggested mechanisms underlying fast synaptic transmission in the central nervous system of vertebrates. Electrophysiological recordings of single channels stimulated with agonists showed that both recombinant and native AMPA receptors visit multiple conductance states in an agonist concentration dependent manner. We propose an allosteric model of the multiple conductance states based on concerted conformational transitions of the four subunits, as an iris diaphragm. Our model predicts that the thermodynamic behaviour of the conductance states upon full and partial agonist stimulations can be described with increased affinity of receptors as they progress to higher conductance states. The model also predicts the existence of AMPA receptors in non-liganded conductive substates. However, the probability of spontaneous openings decreases with increasing conductances. Finally, we predict that the large conductance states are stabilized within the rise phase of a whole-cell EPSC in glutamatergic hippocampal neurons. Our model provides a mechanistic link between ligand concentration and conductance states that can explain thermodynamic and kinetic features of AMPA receptor gating.

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PloS one, 10, 1932-6203, e0116616, 2015

PMID: 25629405

Open Access

Premature thymic involution is independent of structural plasticity of the thymic stroma.
Franckaert D, Schlenner SM, Heirman N, Gill J, Skogberg G, Ekwall O, Put K, Linterman MA, Dooley J, Liston A

The thymus is the organ devoted to T-cell production. The thymus undergoes multiple rounds of atrophy and redevelopment before degenerating with age in a process known as involution. This process is poorly understood, despite the influence the phenomenon has on peripheral T-cell numbers. Here we have investigated the FVB/N mouse strain, which displays premature thymic involution. We find multiple architectural and cellular features that precede thymic involution, including disruption of the epithelial-endothelial relationship and a progressive loss of pro-T cells. The architectural features, reminiscent of the human thymus, are intrinsic to the non-hematopoietic compartment and are neither necessary nor sufficient for thymic involution. By contrast, the loss of pro-T cells is intrinsic to the hematopoietic compartment, and is sufficient to drive premature involution. These results identify pro-T-cell loss as the main driver of premature thymic involution, and highlight the plasticity of the thymic stroma, capable of maintaining function across diverse inter-strain architectures. This article is protected by copyright. All rights reserved.

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European journal of immunology, , 1521-4141, , 2015

PMID: 25627671

Selective impairment of methylation maintenance is the major cause of DNA methylation reprogramming in the early embryo.
Arand J, Wossidlo M, Lepikhov K, Peat JR, Reik W, Walter J

DNA methylomes are extensively reprogrammed during mouse pre-implantation and early germ cell development. The main feature of this reprogramming is a genome-wide decrease in 5-methylcytosine (5mC). Standard high-resolution single-stranded bisulfite sequencing techniques do not allow discrimination of the underlying passive (replication-dependent) or active enzymatic mechanisms of 5mC loss. We approached this problem by generating high-resolution deep hairpin bisulfite sequencing (DHBS) maps, allowing us to follow the patterns of symmetric DNA methylation at CpGs dyads on both DNA strands over single replications.

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Epigenetics & chromatin, 8, 1756-8935, 1, 2015

PMID: 25621012

Open Access

Modulation of calmodulin lobes by different targets: an allosteric model with hemiconcerted conformational transitions.
Lai M, Brun D, Edelstein SJ, Le Novère N

Calmodulin is a calcium-binding protein ubiquitous in eukaryotic cells, involved in numerous calcium-regulated biological phenomena, such as synaptic plasticity, muscle contraction, cell cycle, and circadian rhythms. It exibits a characteristic dumbell shape, with two globular domains (N- and C-terminal lobe) joined by a linker region. Each lobe can take alternative conformations, affected by the binding of calcium and target proteins. Calmodulin displays considerable functional flexibility due to its capability to bind different targets, often in a tissue-specific fashion. In various specific physiological environments (e.g. skeletal muscle, neuron dendritic spines) several targets compete for the same calmodulin pool, regulating its availability and affinity for calcium. In this work, we sought to understand the general principles underlying calmodulin modulation by different target proteins, and to account for simultaneous effects of multiple competing targets, thus enabling a more realistic simulation of calmodulin-dependent pathways. We built a mechanistic allosteric model of calmodulin, based on an hemiconcerted framework: each calmodulin lobe can exist in two conformations in thermodynamic equilibrium, with different affinities for calcium and different affinities for each target. Each lobe was allowed to switch conformation on its own. The model was parameterised and validated against experimental data from the literature. In spite of its simplicity, a two-state allosteric model was able to satisfactorily represent several sets of experiments, in particular the binding of calcium on intact and truncated calmodulin and the effect of different skMLCK peptides on calmodulin's saturation curve. The model can also be readily extended to include multiple targets. We show that some targets stabilise the low calcium affinity T state while others stabilise the high affinity R state. Most of the effects produced by calmodulin targets can be explained as modulation of a pre-existing dynamic equilibrium between different conformations of calmodulin's lobes, in agreement with linkage theory and MWC-type models.

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PLoS computational biology, 11, 1553-7358, e1004063, 2015

PMID: 25611683

Open Access

Regulatory T cells and control of the germinal centre response.
Vanderleyden I, Linterman MA, Smith KG

Germinal centres (GCs) are specialised lymphoid microenvironments that form in secondary B-cell follicles upon exposure to T-dependent antigens. In the GC, clonal expansion, selection and differentiation of GC B cells result in the production of high-affinity plasma cells and memory B cells that provide protection against subsequent infection. The GC is carefully regulated to fulfil its critical role in defence against infection and to ensure that immunological tolerance is not broken in the process. The GC response can be controlled by a number of mechanisms, one of which is by forkhead box p3 expressing regulatory T (Treg) cells, a suppressive population of CD4+ T cells. A specialised subset of Treg cells - follicular regulatory T (Tfr) cells - form after immunisation and are able to access the GC, where they control the size and output of the response. Our knowledge of Treg cell control of the GC is expanding. In this review we will discuss recent advances in the field, with a particular emphasis on the differentiation and function of Tfr cells in the GC.

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Arthritis research & therapy, 16, 1478-6362, 471, 2014

PMID: 25606598

Open Access

The regulatory subunits of PI3Kγ control distinct neutrophil responses.
Deladeriere A, Gambardella L, Pan D, Anderson KE, Hawkins PT, Stephens LR

Neutrophils, which migrate toward inflamed sites and kill pathogens by producing reactive oxygen species (ROS), are important in the defense against bacterial and fungal pathogens, but their inappropriate regulation causes various chronic inflammatory diseases. Phosphoinositide 3-kinase γ (PI3Kγ) functions downstream of proinflammatory G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors (GPCRs) in neutrophils and is a therapeutic target. In neutrophils, PI3Kγ consists of a p110γ catalytic subunit, which is activated by the guanosine triphosphatase Ras, and either a p84 or p101 regulatory subunit. Loss or inhibition of p110γ or expression of a Ras-insensitive variant p110γ (p110γ(DASAA/DASAA)) impairs PIP3 production, Akt phosphorylation, migration, and ROS formation in response to GPCR activation. The p101 subunit binds to, and mediates PI3Kγ activation by, G protein βγ subunits, and p101(-/-) neutrophils have a similar phenotype to that of p110γ(-/-) neutrophils, except that ROS responses are normal. We found that p84(-/-) neutrophils displayed reduced GPCR-stimulated PIP3 and Akt signaling, which was indistinguishable from that of p101(-/-) neutrophils. However, p84(-/-) neutrophils produced less ROS and exhibited normal migration in response to GPCR stimulation. These data suggest that p84-containing PI3Kγ controls GPCR-dependent ROS production. Thus, the PI3Kγ regulatory subunits enable PI3Kγ to mediate distinct neutrophil responses, which may occur by targeting PIP3 signaling into spatially distinct domains.

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Science signaling, 8, 1937-9145, ra8, 2015

PMID: 25605974

Acetyl-CoA Synthetase 2 Promotes Acetate Utilization and Maintains Cancer Cell Growth under Metabolic Stress.
Schug ZT, Peck B, Jones DT, Zhang Q, Grosskurth S, Alam IS, Goodwin LM, Smethurst E, Mason S, Blyth K, McGarry L, James D, Shanks E, Kalna G, Saunders RE, Jiang M, Howell M, Lassailly F, Thin MZ, Spencer-Dene B, Stamp G, van den Broek NJ, Mackay G, Bulusu V, Kamphorst JJ, Tardito S, Strachan D, Harris AL, Aboagye EO, Critchlow SE, Wakelam MJ, Schulze A, Gottlieb E

A functional genomics study revealed that the activity of acetyl-CoA synthetase 2 (ACSS2) contributes to cancer cell growth under low-oxygen and lipid-depleted conditions. Comparative metabolomics and lipidomics demonstrated that acetate is used as a nutritional source by cancer cells in an ACSS2-dependent manner, and supplied a significant fraction of the carbon within the fatty acid and phospholipid pools. ACSS2 expression is upregulated under metabolically stressed conditions and ACSS2 silencing reduced the growth of tumor xenografts. ACSS2 exhibits copy-number gain in human breast tumors, and ACSS2 expression correlates with disease progression. These results signify a critical role for acetate consumption in the production of lipid biomass within the harsh tumor microenvironment.

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Cancer cell, 27, 1878-3686, 57-71, 2015

PMID: 25584894

Open Access

ERES: sites for autophagosome biogenesis and maturation?
Sanchez-Wandelmer J, Ktistakis NT, Reggiori F

Autophagosomes are the hallmark of autophagy, but despite their central role in this degradative pathway that involves vesicle transport to lysosomes or vacuoles, the mechanism underlying their biogenesis still remains largely unknown. Our current concepts about autophagosome biogenesis are based on models suggesting that a small autonomous cisterna grows into an autophagosome through expansion at its extremities. Recent findings have revealed that endoplasmic reticulum (ER) exit sites (ERES), specialized ER regions where proteins are sorted into the secretory system, are key players in the formation of autophagosomes. Owing to the morphological connection of nascent autophagosomes with the ER, this has raised several questions that challenge our current perception of autophagosome biogenesis, such as are ERES the compartments where autophagosome formation takes place? What is the functional relevance of this connection? Are these compartments providing essential molecules for the generation of autophagosomes and/or are they structural platforms where these vesicles emerge? In this Hypothesis, we discuss recent data that have implicated the ERES in autophagosome biogenesis and we propose two models to describe the possible role of this compartment at different steps in the process of autophagosome biogenesis. This article is part of a Focus on Autophagosome biogenesis. For further reading, please see related articles: 'Membrane dynamics in autophagosome biogenesis' by Sven R. Carlsson and Anne Simonsen (J. Cell Sci. 128, 193-205) and 'WIPI proteins: essential PtdIns3P effectors at the nascent autophagosome' by Tassula Proikas-Cezanne et al. (J. Cell Sci. 128, 207-217).

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Journal of cell science, 128, 1477-9137, 185-192, 2015

PMID: 25568152

Open Access

Finding Our Way through Phenotypes
Deans AR, Lewis SE, Huala E, Anzaldo SS, Ashburner M, Balhoff JP, Blackburn DC, Blake JA, Burleigh JG, Chanet B, Cooper LD, Courtot M, Csösz S, Cui H, Dahdul W, Das S, Dececchi TA, Dettai A, Diogo R, Druzinsky RE, Dumontier M, Franz NM, Friedrich F, Gkoutos GV, Haendel M, Harmon LJ, Hayamizu TF, He Y, Hines HM, Ibrahim N, Jackson LM, Jaiswal P, James-Zorn C, Köhler S, Lecointre G, Lapp H, Lawrence CJ, Le Novère N, Lundberg JG, Macklin J, Mast AR, Midford PE, Mikó I, Mungall CJ, Oellrich A, Osumi-Sutherland D, Parkinson H, Ramírez MJ, Richter S, Robinson PN, Ruttenberg A, Schulz KS, Segerdell E, Seltmann KC, Sharkey MJ, Smith AD, Smith B, Specht CD, Squires RB, Thacker RW, Thessen A, Fernandez-Triana J, Vihinen M, Vize PD, Vogt L, Wall CE, Walls RL, Westerfeld M, Wharton RA, Wirkner CS, Woolley JB, Yoder MJ, Zorn AM, Mabee P

Despite a large and multifaceted effort to understand the vast landscape of phenotypic data, their current form inhibits productive data analysis. The lack of a community-wide, consensus-based, human- and machine-interpretable language for describing phenotypes and their genomic and environmental contexts is perhaps the most pressing scientific bottleneck to integration across many key fields in biology, including genomics, systems biology, development, medicine, evolution, ecology, and systematics. Here we survey the current phenomics landscape, including data resources and handling, and the progress that has been made to accurately capture relevant data descriptions for phenotypes. We present an example of the kind of integration across domains that computable phenotypes would enable, and we call upon the broader biology community, publishers, and relevant funding agencies to support efforts to surmount today's data barriers and facilitate analytical reproducibility.

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PLoS Biology, 13, 1, , 2015

PMID: 25562316

Open Access

miR-155 augments CD8+ T-cell antitumor activity in lymphoreplete hosts by enhancing responsiveness to homeostatic γc cytokines.
Ji Y, Wrzesinski C, Yu Z, Hu J, Gautam S, Hawk NV, Telford WG, Palmer DC, Franco Z, Sukumar M, Roychoudhuri R, Clever D, Klebanoff CA, Surh CD, Waldmann TA, Restifo NP, Gattinoni L

Lymphodepleting regimens are used before adoptive immunotherapy to augment the antitumor efficacy of transferred T cells by removing endogenous homeostatic "cytokine sinks." These conditioning modalities, however, are often associated with severe toxicities. We found that microRNA-155 (miR-155) enabled tumor-specific CD8(+) T cells to mediate profound antitumor responses in lymphoreplete hosts that were not potentiated by immune-ablation. miR-155 enhanced T-cell responsiveness to limited amounts of homeostatic γc cytokines, resulting in delayed cellular contraction and sustained cytokine production. miR-155 restrained the expression of the inositol 5-phosphatase Ship1, an inhibitor of the serine-threonine protein kinase Akt, and multiple negative regulators of signal transducer and activator of transcription 5 (Stat5), including suppressor of cytokine signaling 1 (Socs1) and the protein tyrosine phosphatase Ptpn2. Expression of constitutively active Stat5a recapitulated the survival advantages conferred by miR-155, whereas constitutive Akt activation promoted sustained effector functions. Our results indicate that overexpression of miR-155 in tumor-specific T cells can be used to increase the effectiveness of adoptive immunotherapies in a cell-intrinsic manner without the need for life-threatening, lymphodepleting maneuvers.

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Proceedings of the National Academy of Sciences of the United States of America, 112, 1091-6490, 476-81, 2015

PMID: 25548153

P-Rex and Vav Rac-GEFs in platelets control leukocyte recruitment to sites of inflammation.
Pan D, Amison RT, Riffo-Vasquez Y, Spina D, Cleary SJ, Wakelam MJ, Page CP, Pitchford SC, Welch HC

The small GTPase Rac is required for neutrophil recruitment during inflammation, but its GEF activators seem dispensable for this process, which led us to investigate the possibility of cooperation between Rac-GEF families. Thioglycollate-induced neutrophil recruitment into the peritoneum was more severely impaired in P-Rex1(-/-) Vav1(-/-) (P1V1) or P-Rex1(-/-) Vav3(-/-) (P1V3) mice than in P-Rex null or Vav null mice, suggesting cooperation between P-Rex and Vav Rac-GEFs in this process. Neutrophil transmigration and airway infiltration were all but lost in P1V1 and P1V3 mice during LPS-induced pulmonary inflammation, with altered ICAM1-dependent slow neutrophil rolling and strongly reduced L- and E-selectin dependent adhesion in airway postcapillary venules. Analysis of adhesion molecule expression, neutrophil adhesion, spreading and migration suggested these defects to be only partially neutrophil-intrinsic and not obviously involving vascular endothelial cells. Instead, P1V1 and P1V3 platelets recapitulated the impairment of LPS-induced intravascular neutrophil adhesion and recruitment, revealing P-Rex and Vav expression in platelets to be crucial. Similarly, during ovalbumin-induced allergic inflammation, pulmonary recruitment of P1V1 and P1V3 eosinophils, monocytes and lymphocytes was compromised in a platelet-dependent manner, and airway inflammation essentially abolished, resulting in improved airway responsiveness. Therefore, platelet P-Rex and Vav family Rac-GEFs play important proinflammatory roles in leukocyte recruitment.

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Blood, , 1528-0020, , 2014

PMID: 25538043

Open Access

Functional drug screening reveals anticonvulsants as enhancers of mTOR-independent autophagic killing of Mycobacterium tuberculosis through inositol depletion.
Schiebler M, Brown K, Hegyi K, Newton SM, Renna M, Hepburn L, Klapholz C, Coulter S, Obregón-Henao A, Henao Tamayo M, Basaraba R, Kampmann B, Henry KM, Burgon J, Renshaw SA, Fleming A, Kay RR, Anderson KE, Hawkins PT, Ordway DJ, Rubinsztein DC, Floto RA

Mycobacterium tuberculosis (MTB) remains a major challenge to global health made worse by the spread of multidrug resistance. We therefore examined whether stimulating intracellular killing of mycobacteria through pharmacological enhancement of macroautophagy might provide a novel therapeutic strategy. Despite the resistance of MTB to killing by basal autophagy, cell-based screening of FDA-approved drugs revealed two anticonvulsants, carbamazepine and valproic acid, that were able to stimulate autophagic killing of intracellular M. tuberculosis within primary human macrophages at concentrations achievable in humans. Using a zebrafish model, we show that carbamazepine can stimulate autophagy in vivo and enhance clearance of M. marinum, while in mice infected with a highly virulent multidrug-resistant MTB strain, carbamazepine treatment reduced bacterial burden, improved lung pathology and stimulated adaptive immunity. We show that carbamazepine induces antimicrobial autophagy through a novel, evolutionarily conserved, mTOR-independent pathway controlled by cellular depletion of myo-inositol. While strain-specific differences in susceptibility to in vivo carbamazepine treatment may exist, autophagy enhancement by repurposed drugs provides an easily implementable potential therapy for the treatment of multidrug-resistant mycobacterial infection.

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EMBO molecular medicine, 7, 1757-4684, 127-39, 2014

PMID: 25535254

Open Access

Promiscuous Foxp3-cre activity reveals a differential requirement for CD28 in Foxp3(+) and Foxp3(-) T cells.
Franckaert D, Dooley J, Roos E, Floess S, Huehn J, Luche H, Fehling HJ, Liston A, Linterman MA, Schlenner SM

Costimulatory signals by CD28 are critical for thymic regulatory T-cell (Treg) development. To determine the functional relevance of CD28 for peripheral Treg post thymic selection, we crossed the widely used Forkhead box protein 3 (Foxp3)-CreYFP mice to mice bearing a conditional Cd28 allele. Treg-specific CD28 deficiency provoked a severe autoimmune syndrome as a result of a strong disadvantage in competitive fitness and proliferation of CD28-deficient Tregs. By contrast, Treg survival and lineage integrity were not affected by the lack of CD28. This data demonstrate that, even after the initial induction requirement, Treg maintain a higher dependency on CD28 signalling than conventional T cells for homeostasis. In addition, we found the Foxp3-CreYFP allele to be a hypomorph, with reduced Foxp3 protein levels. Furthermore, we report here the stochastic activity of the Foxp3-CreYFP allele in non-Tregs, sufficient to recombine some conditional alleles (including Cd28) but not others (including R26-RFP). This hypomorphism and 'leaky' expression of the Foxp3-CreYFP allele should be considered when analysing the conditionally mutated Treg.Immunology and Cell Biology advance online publication, 23 December 2014; doi:10.1038/icb.2014.108.

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Immunology and cell biology, , 1440-1711, , 2014

PMID: 25533288

Open Access

Treg cells and CTLA-4: the ball and chain of the germinal center response.
Linterman MA, Denton AE

The mechanism by which regulatory T cells control the germinal center response is unknown. In this issue of Immunity, Wing et al. (2014) and Sage et al. (2014) demonstrate that CTLA-4 is a critical effector molecule used by regulatory T cells to control the germinal center.

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Immunity, 41, 1097-4180, 876-8, 2014

PMID: 25526300

PI3K signalling in inflammation.
Hawkins PT, Stephens LR

PI3Ks regulate several key events in the inflammatory response to damage and infection. There are four Class I PI3K isoforms (PI3Kα,β,γ,δ), three Class II PI3K isoforms (PI3KC2α, C2β, C2γ) and a single Class III PI3K. The four Class I isoforms synthesise the phospholipid 'PIP3'. PIP3 is a 'second messenger' used by many different cell surface receptors to control cell movement, growth, survival and differentiation. These four isoforms have overlapping functions but each is adapted to receive efficient stimulation by particular receptor sub-types. PI3Kγ is highly expressed in leukocytes and plays a particularly important role in chemokine-mediated recruitment and activation of innate immune cells at sites of inflammation. PI3Kδ is also highly expressed in leukocytes and plays a key role in antigen receptor and cytokine-mediated B and T cell development, differentiation and function. Class III PI3K synthesises the phospholipid PI3P, which regulates endosome-lysosome trafficking and the induction of autophagy, pathways involved in pathogen killing, antigen processing and immune cell survival. Much less is known about the function of Class II PI3Ks, but emerging evidence indicates they can synthesise PI3P and PI34P2 and are involved in the regulation of endocytosis. The creation of genetically-modified mice with altered PI3K signalling, together with the development of isoform-selective, small-molecule PI3K inhibitors, has allowed the evaluation of the individual roles of Class I PI3K isoforms in several mouse models of chronic inflammation. Selective inhibition of PI3Kδ, γ or β has each been shown to reduce the severity of inflammation in one or more models of autoimmune disease, respiratory disease or allergic inflammation, with dual γ/δ or β/δ inhibition generally proving more effective. The inhibition of Class I PI3Ks may therefore offer a therapeutic opportunity to treat non-resolving inflammatory pathologies in humans. This article is part of a Special Issue entitled Phosphoinositides.

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Biochimica et biophysica acta, 1851, 0006-3002, 882-97, 2015

PMID: 25514767

Open Access

Unexpected DNA loss mediated by the DNA binding activity of ribonuclease A.
Donà F, Houseley J

Ribonuclease A (RNase A) is widely used in molecular biology research both for analytical assays and for nucleic acid preparation. The catalytic mechanism of RNase A is well understood and absolutely precludes activity on DNA; however anecdotal reports of DNA degradation by RNase A are not uncommon. Here we describe a mechanism by which RNase A treatment can lead to apparent DNA degradation. This results from the surprising finding that RNase A remains functional in a phenol:chloroform mixture, to our knowledge the only enzyme that survives this highly denaturing solvent environment. Although RNase A does not cleave the DNA backbone it is capable of binding to DNA, forming stable RNase A-DNA complexes that partition to the interphase or organic phase during phenol:chloroform purification. The unexpected survival of the RNase A DNA-binding activity in phenol means that these complexes are not dissolved and a substantial amount of RNase A-bound DNA is permanently removed from the aqueous phase and lost on phase separation. This effect will impact DNA recovery from multiple procedures and is likely to represent a source of sequence bias in genome-wide studies. Our results also indicate that the results of analytical studies performed using RNase A must be considered with care.

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PloS one, 9, 1932-6203, e115008, 2014

PMID: 25502562

Open Access

Live-cell imaging for the assessment of the dynamics of autophagosome formation: Focus on early steps.
Karanasios E, Ktistakis NT

Autophagy is a cytosolic degradative pathway, which through a series of complicated membrane rearrangements leads to the formation of a unique double membrane vesicle, the autophagosome. The use of fluorescent proteins has allowed visualizing the autophagosome formation in live cells and in real time, almost 40years after electron microscopy studies observed these structures for the first time. In the last decade, live-cell imaging has been extensively used to study the dynamics of autophagosome formation in cultured mammalian cells. Hereby we will discuss how the live-cell imaging studies have tried to settle the debate about the origin of the autophagosome membrane and how they have described the way different autophagy proteins coordinate in space and time in order to drive autophagosome formation.

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Methods (San Diego, Calif.), , 1095-9130, , 2014

PMID: 25498007

Genome-wide bisulfite sequencing in zygotes identifies demethylation targets and maps the contribution of TET3 oxidation.
Peat JR, Dean W, Clark SJ, Krueger F, Smallwood SA, Ficz G, Kim JK, Marioni JC, Hore TA, Reik W

Fertilization triggers global erasure of paternal 5-methylcytosine as part of epigenetic reprogramming during the transition from gametic specialization to totipotency. This involves oxidation by TET3, but our understanding of its targets and the wider context of demethylation is limited to a small fraction of the genome. We employed an optimized bisulfite strategy to generate genome-wide methylation profiles of control and TET3-deficient zygotes, using SNPs to access paternal alleles. This revealed that in addition to pervasive removal from intergenic sequences and most retrotransposons, gene bodies constitute a major target of zygotic demethylation. Methylation loss is associated with zygotic genome activation and at gene bodies is also linked to increased transcriptional noise in early development. Our data map the primary contribution of oxidative demethylation to a subset of gene bodies and intergenic sequences and implicate redundant pathways at many loci. Unexpectedly, we demonstrate that TET3 activity also protects certain CpG islands against methylation buildup.

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Cell reports, 9, 2211-1247, 1990-2000, 2014

PMID: 25497087

Open Access

COMBINE archive and OMEX format: one file to share all information to reproduce a modeling project.
Bergmann FT, Adams R, Moodie S, Cooper J, Glont M, Golebiewski M, Hucka M, Laibe C, Miller AK, Nickerson DP, Olivier BG, Rodriguez N, Sauro HM, Scharm M, Soiland-Reyes S, Waltemath D, Yvon F, Le Novère N

BackgroundWith the ever increasing use of computational models in the biosciences, the need to share models and reproduce the results of published studies efficiently and easily is becoming more important. To this end, various standards have been proposed that can be used to describe models, simulations, data or other essential information in a consistent fashion. These constitute various separate components required to reproduce a given published scientific result.ResultsWe describe the Open Modeling EXchange format (OMEX). Together with the use of other standard formats from the Computational Modeling in Biology Network (COMBINE), OMEX is the basis of the COMBINE Archive, a single file that supports the exchange of all the information necessary for a modeling and simulation experiment in biology. An OMEX file is a ZIP container that includes a manifest file, listing the content of the archive, an optional metadata file adding information about the archive and its content, and the files describing the model. The content of a COMBINE Archive consists of files encoded in COMBINE standards whenever possible, but may include additional files defined by an Internet Media Type. Several tools that support the COMBINE Archive are available, either as independent libraries or embedded in modeling software.ConclusionsThe COMBINE Archive facilitates the reproduction of modeling and simulation experiments in biology by embedding all the relevant information in one file. Having all the information stored and exchanged at once also helps in building activity logs and audit trails. We anticipate that the COMBINE Archive will become a significant help for modellers, as the domain moves to larger, more complex experiments such as multi-scale models of organs, digital organisms, and bioengineering.

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BMC bioinformatics, 15, 1471-2105, 369, 2014

PMID: 25494900

Open Access

V-ATPase and osmotic imbalances activate endolysosomal LC3 lipidation.
Florey O, Gammoh N, Kim SE, Jiang X, Overholtzer M

Recently a noncanonical activity of autophagy proteins has been discovered that targets lipidation of microtubule-associated protein 1 light chain 3 (LC3) onto macroendocytic vacuoles, including macropinosomes, phagosomes, and entotic vacuoles. While this pathway is distinct from canonical autophagy, the mechanism of how these nonautophagic membranes are targeted for LC3 lipidation remains unclear. Here we present evidence that this pathway requires activity of the vacuolar-type H(+)-ATPase (V-ATPase) and is induced by osmotic imbalances within endolysosomal compartments. LC3 lipidation by this mechanism is induced by treatment of cells with the lysosomotropic agent chloroquine, and through exposure to the Heliobacter pylori pore-forming toxin VacA. These data add novel mechanistic insights into the regulation of noncanonical LC3 lipidation and its associated processes, including LC3-associated phagocytosis (LAP), and demonstrate that the widely and therapeutically used drug chloroquine, which is conventionally used to inhibit autophagy flux, is an inducer of LC3 lipidation.

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Autophagy, , 1554-8635, 0, 2014

PMID: 25484071

Redundant mechanisms to form silent chromatin at pericentromeric regions rely on BEND3 and DNA methylation.
Saksouk N, Barth TK, Ziegler-Birling C, Olova N, Nowak A, Rey E, Mateos-Langerak J, Urbach S, Reik W, Torres-Padilla ME, Imhof A, Déjardin J

Constitutive heterochromatin is typically defined by high levels of DNA methylation and H3 lysine 9 trimethylation (H3K9Me3), whereas facultative heterochromatin displays DNA hypomethylation and high H3 lysine 27 trimethylation (H3K27Me3). The two chromatin types generally do not coexist at the same loci, suggesting mutual exclusivity. During development or in cancer, pericentromeric regions can adopt either epigenetic state, but the switching mechanism is unknown. We used a quantitative locus purification method to characterize changes in pericentromeric chromatin-associated proteins in mouse embryonic stem cells deficient for either the methyltransferases required for DNA methylation or H3K9Me3. DNA methylation controls heterochromatin architecture and inhibits Polycomb recruitment. BEND3, a protein enriched on pericentromeric chromatin in the absence of DNA methylation or H3K9Me3, allows Polycomb recruitment and H3K27Me3, resulting in a redundant pathway to generate repressive chromatin. This suggests that BEND3 is a key factor in mediating a switch from constitutive to facultative heterochromatin.

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Molecular cell, 56, 1097-4164, 580-94, 2014

PMID: 25457167

Transcriptional profiles reveal a stepwise developmental program of memory CD8(+) T cell differentiation.
Roychoudhuri R,Lefebvre F,Honda M,Pan L,Ji Y,Klebanoff CA,Nichols CN,Fourati S,Hegazy AN,Goulet JP,Gattinoni L,Nabel GJ,Gilliet M,Cameron M,Restifo NP,Sekaly RP,Flatz L

The generation of CD8(+) T-cell memory is a major aim of vaccination. While distinct subsets of CD8(+) T-cells are generated following immunization that differ in their ability to confer long-term immunity against infection, the transcriptional profiles of these subsets within endogenous vaccine-induced CD8(+) T cell responses have not been resolved. Here, we measure global transcriptional profiles of endogenous effector (TEFF), effector memory (TEM) and central memory (TCM) CD8(+) T-cells arising from immunization with three distinct prime-boost vaccine regimens. While a proportion of transcripts were uniquely regulated within distinct CD8(+) T cell populations, we observed progressive up- or down-regulation in the expression of a majority of differentially expressed transcripts when subsets were compared in the order TN>TCM>TEM>TEFF. Strikingly, when we compared global differences in gene expression between TN, TCM, TEM and TEFF cells with known transcriptional changes that result when CD8(+) T cells repetitively encounter antigen, our analysis overwhelmingly favored a model whereby cumulative antigen stimulation drives differentiation specifically from TN>TCM>TEM>TEFF and this was common to all vaccines tested. These findings provide insight into the molecular basis of immunological memory and identify potential biomarkers for characterization of vaccine-induced responses and prediction of vaccine efficacy.

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Vaccine, , 1873-2518, , 2014

PMID: 25446821

Axonal transport declines with age in two distinct phases separated by a period of relative stability.
Milde S, Adalbert R, Elaman MH, Coleman MP

Axonal transport is critical for supplying newly synthesized proteins, organelles, mRNAs, and other cargoes from neuronal cell bodies into axons. Its impairment in many neurodegenerative conditions appears likely to contribute to pathogenesis. Axonal transport also declines during normal aging, but little is known about the timing of these changes, or about the effect of aging on specific cargoes in individual axons. This is important for understanding mechanisms of age-related axon loss and age-related axonal disorders. Here we use fluorescence live imaging of peripheral nerve and central nervous system tissue explants to investigate vesicular and mitochondrial axonal transport. Interestingly, we identify 2 distinct periods of change, 1 period during young adulthood and the other in old age, separated by a relatively stable plateau during most of adult life. We also find that after tibial nerve regeneration, even in old animals, neurons are able to support higher transport rates of each cargo for a prolonged period. Thus, the age-related decline in axonal transport is not an inevitable consequence of either aging neurons or an aging systemic milieu.

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Neurobiology of aging, , 1558-1497, , 2014

PMID: 25443288

Open Access

Akt inhibition enhances expansion of potent tumor-specific lymphocytes with memory cell characteristics.
Crompton JG, Sukumar M, Roychoudhuri R, Clever D, Gros A, Eil RL, Tran E, Hanada K, Yu Z, Palmer DC, Kerkar SP, Michalek RD, Upham T, Leonardi A, Acquavella N, Wang E, Marincola FM, Gattinoni L, Muranski P, Sundrud MS, Klebanoff CA, Rosenberg SA, Fearon DT, Restifo NP

Adoptive cell therapy (ACT) using autologous tumor-infiltrating lymphocytes (TIL) results in complete regression of advanced cancer in some patients, but the efficacy of this potentially curative therapy may be limited by poor persistence of TIL after adoptive transfer. Pharmacologic inhibition of the serine/threonine kinase Akt has recently been shown to promote immunologic memory in virus-specific murine models, but whether this approach enhances features of memory (e.g., long-term persistence) in TIL that are characteristically exhausted and senescent is not established. Here, we show that pharmacologic inhibition of Akt enables expansion of TIL with the transcriptional, metabolic, and functional properties characteristic of memory T cells. Consequently, Akt inhibition results in enhanced persistence of TIL after adoptive transfer into an immunodeficient animal model and augments antitumor immunity of CD8 T cells in a mouse model of cell-based immunotherapy. Pharmacologic inhibition of Akt represents a novel immunometabolomic approach to enhance the persistence of antitumor T cells and improve the efficacy of cell-based immunotherapy for metastatic cancer.

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Cancer research, 75, 1538-7445, 296-305, 2015

PMID: 25432172

Epigenetic memory of the first cell fate decision prevents complete ES cell reprogramming into trophoblast.
F Cambuli, A Murray, W Dean, D Dudzinska, F Krueger, S Andrews, CE Senner, S Cook, M Hemberger

Embryonic (ES) and trophoblast (TS) stem cells reflect the first, irrevocable cell fate decision in development that is reinforced by distinct epigenetic lineage barriers. Nonetheless, ES cells can seemingly acquire TS-like characteristics upon manipulation of lineage-determining transcription factors or activation of the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway. Here we have interrogated the progression of reprogramming in ES cell models with regulatable Oct4 and Cdx2 transgenes or conditional Erk1/2 activation. Although trans-differentiation into TS-like cells is initiated, lineage conversion remains incomplete in all models, underpinned by the failure to demethylate a small group of TS cell genes. Forced expression of these non-reprogrammed genes improves trans-differentiation efficiency, but still fails to confer a stable TS cell phenotype. Thus, even ES cells in ground-state pluripotency cannot fully overcome the boundaries that separate the first cell lineages but retain an epigenetic memory of their ES cell origin.

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Nat Commun., 26, 5, 5538, 2014

PMID: 25423963

Open Access