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Drosophila phototransduction is mediated via a G-protein-coupled PLC cascade. Recent evidence, including the demonstration that light evokes rapid contractions of the photoreceptors, suggested that the light-sensitive channels (TRP and TRPL) may be mechanically gated, together with protons released by PLC-mediated PIP2 hydrolysis. If mechanical gating is involved we predicted that the response to light should be influenced by altering the physical properties of the membrane. To achieve this, we used diet to manipulate the degree of saturation of membrane phospholipids. In flies reared on a yeast diet, lacking polyunsaturated fatty acids (PUFAs), mass spectrometry showed that the proportion of polyunsaturated phospholipids was sevenfold reduced (from 38 to ∼5%) but rescued by adding a single species of PUFA (linolenic or linoleic acid) to the diet. Photoreceptors from yeast-reared flies showed a 2- to 3-fold increase in latency and time to peak of the light response, without affecting quantum bump waveform. In the absence of Ca(2+) influx or in trp mutants expressing only TRPL channels, sensitivity to light was reduced up to ∼10-fold by the yeast diet, and essentially abolished in hypomorphic G-protein mutants (Gαq). PLC activity appeared little affected by the yeast diet; however, light-induced contractions measured by atomic force microscopy or the activation of ectopic mechanosensitive gramicidin channels were also slowed ∼2-fold. The results are consistent with mechanosensitive gating and provide a striking example of how dietary fatty acids can profoundly influence sensory performance in a classical G-protein-coupled signaling cascade.

Gene variants that disrupt TCR signaling can cause severe immune deficiency, yet less disruptive variants are sometimes associated with immune pathology. Null mutations of the gene encoding the scaffold protein Src homology 2 domain-containing leukocyte protein of 76 kDa (SLP-76), for example, cause an arrest of T cell positive selection, whereas a synthetic membrane-targeted allele allows limited positive selection but is associated with proinflammatory cytokine production and autoantibodies. Whether these and other enigmatic outcomes are due to a biochemical uncoupling of tolerogenic signaling, or simply a quantitative reduction of protein activity, remains to be determined. In this study we describe a splice variant of Lcp2 that reduced the amount of wild-type SLP-76 protein by ~90%, disrupting immunogenic and tolerogenic pathways to different degrees. Mutant mice produced excessive amounts of proinflammatory cytokines, autoantibodies, and IgE, revealing that simple quantitative reductions of SLP-76 were sufficient to trigger immune dysregulation. This allele reveals a dose-sensitive threshold for SLP-76 in the balance of immunity and immune dysregulation, a common disturbance of atypical clinical immune deficiencies.

Allogeneic hematopoietic stem cell transplantation (HSCT) can treat certain hematologic malignancies due to the graft versus leukemia (GvL) effect but is complicated by graft versus host disease (GvHD). Expression of the p110δ catalytic subunit of the phosphoinositide 3-kinase pathway is restricted to leukocytes, where it regulates proliferation, migration, and cytokine production. Here, in a mouse model of fully mismatched hematopoietic cell transplantation (HCT), we show that genetic inactivation of p110δ in T cells leads to milder GvHD, whereas GvL is preserved. Inactivation of p110δ in human lymphocytes reduced T cell allorecognition. We demonstrate that both allostimulation and granzyme B expression were dependent on p110δ in naive T cells, which are the main mediators of GvHD, whereas memory T cells were unaffected. Strikingly, p110δ is not mandatory for either naive or memory T cells to mediate GvL. Therefore, immunomodulation of selective naive T cell functions by p110δ inactivation improves the outcome of allogeneic HSCT.

Behaviours of complex biomolecular systems are often irreducible to the elementary properties of their individual components. Explanatory and predictive mathematical models are therefore useful for fully understanding and precisely engineering cellular functions. The development and analyses of these models require their adaptation to the problems that need to be solved and the type and amount of available genetic or molecular data. Quantitative and logic modelling are among the main methods currently used to model molecular and gene networks. Each approach comes with inherent advantages and weaknesses. Recent developments show that hybrid approaches will become essential for further progress in synthetic biology and in the development of virtual organisms.

Cellular senescence has been implicated in tumor suppression, development, and aging and is accompanied by large-scale chromatin rearrangements, forming senescence-associated heterochromatic foci (SAHF). However, how the chromatin is reorganized during SAHF formation is poorly understood. Furthermore, heterochromatin formation in senescence appears to contrast with loss of heterochromatin in Hutchinson-Gilford progeria. We mapped architectural changes in genome organization in cellular senescence using Hi-C. Unexpectedly, we find a dramatic sequence- and lamin-dependent loss of local interactions in heterochromatin. This change in local connectivity resolves the paradox of opposing chromatin changes in senescence and progeria. In addition, we observe a senescence-specific spatial clustering of heterochromatic regions, suggesting a unique second step required for SAHF formation. Comparison of embryonic stem cells (ESCs), somatic cells, and senescent cells shows a unidirectional loss in local chromatin connectivity, suggesting that senescence is an endpoint of the continuous nuclear remodelling process during differentiation.

On the Semantic Web, in life sciences in particular, data is often distributed via multiple resources. Each of these sources is likely to use their own IRI (International Resource Identifier) for conceptually the same resource or database record. The lack of correspondence between identifiers introduces a barrier when executing federated SPARQL queries across life science data.

Hematopoietic stem cells (HSCs) possess the ability to generate all hematopoietic cell types and to self-renew over long periods, but the mechanisms that regulate their unique properties are incompletely understood. Herein, we show that homozygous deletion of the miR-29a/b-1 bicistron results in decreased numbers of hematopoietic stem and progenitor cells (HSPCs), decreased HSC self-renewal, and increased HSC cell cycling and apoptosis. The HSPC phenotype is specifically due to loss of miR-29a, because miR-29b expression is unaltered in miR-29a/b-1-null HSCs, and only ectopic expression of miR-29a restores HSPC function both in vitro and in vivo. HSCs lacking miR-29a/b-1 exhibit widespread transcriptional dysregulation and adopt gene expression patterns similar to normal committed progenitors. A number of predicted miR-29 target genes, including Dnmt3a, are significantly upregulated in miR-29a/b-1-null HSCs. The loss of negative regulation of Dnmt3a by miR-29a is a major contributor to the miR-29a/b-1-null HSPC phenotype, as both in vitro Dnmt3a short hairpin RNA knockdown assays and a genetic haploinsufficiency model of Dnmt3a restored the frequency and long-term reconstitution capacity of HSCs from miR-29a/b-1-deficient mice. Overall, these data demonstrate that miR-29a is critical for maintaining HSC function through its negative regulation of Dnmt3a.

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.

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.

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.

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.

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.

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.

Basal cell carcinoma (BCC) is the most commonly diagnosed cancer. While most BCCs are amenable to surgery, some tumors can reach a more advanced stage or metastasize, and become ineligible for surgical resection or radiotherapy. Abnormal activation of the Hedgehog (Hh) pathway is a key driver in BCC pathophysiology. Consequently, inhibitors of the Hh pathway have been developed. Molecules that inhibit the receptor protein Smoothened (SMO) are the most advanced in clinical development. Vismodegib is the first-in-class SMO inhibitor and has been approved in a number of countries for the treatment of metastatic or locally advanced BCC. Several molecules have demonstrated antitumoral activity, but treatment may be limited in duration by a number of side effects, and it is not yet established whether these agents are truly curative or whether continued treatment will be required. Resistance to SMO inhibition has been reported in the clinic for which incidence and mechanisms must be elucidated to inform future therapeutic strategies. Intermittent dosing regimens to improve tolerability, as well as neoadjuvant use of Hh pathway inhibitors, are currently under investigation. Here, we review the most recent outcomes obtained with Hh inhibitors under clinical investigation in BCC.

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.

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).

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.

The microbiota of the human gut is gaining broad attention owing to its association with a wide range of diseases, ranging from metabolic disorders (e.g. obesity and type 2 diabetes) to autoimmune diseases (such as inflammatory bowel disease and type 1 diabetes), cancer and even neurodevelopmental disorders (e.g. autism). Having been increasingly used in biomedical research, mice have become the model of choice for most studies in this emerging field. Mouse models allow perturbations in gut microbiota to be studied in a controlled experimental setup, and thus help in assessing causality of the complex host-microbiota interactions and in developing mechanistic hypotheses. However, pitfalls should be considered when translating gut microbiome research results from mouse models to humans. In this Special Article, we discuss the intrinsic similarities and differences that exist between the two systems, and compare the human and murine core gut microbiota based on a meta-analysis of currently available datasets. Finally, we discuss the external factors that influence the capability of mouse models to recapitulate the gut microbiota shifts associated with human diseases, and investigate which alternative model systems exist for gut microbiota research.

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.

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.

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.

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.

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.

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.