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Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all



 



Microbiology: Manipulation of the manipulators

2017-02-27

Wolbachia bacteria infect insects and can cause mating incompatibilities, an outcome that is used to fight insect-transmitted disease. The proposed genes responsible illuminate this process and the disease-control mechanisms.



TIRR regulates 53BP1 by masking its histone methyl-lysine binding function

2017-02-27

A new protein, Tudor interacting repair regulator (TIRR), affects DNA repair by masking the chromatin interaction domain of 53BP1, thereby preventing its recruitment to double-strand breaks.



Earth’s first stable continents did not form by subduction

2017-02-27

The geodynamic environment in which Earth’s first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite–trondhjemite–granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have ‘arc-like’ signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today’s. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG ‘parents’, and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents—coupled with the high geothermal gradients—is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.



Prophage WO genes recapitulate and enhance Wolbachia-induced cytoplasmic incompatibility

2017-02-27

The genus Wolbachia is an archetype of maternally inherited intracellular bacteria that infect the germline of numerous invertebrate species worldwide. They can selfishly alter arthropod sex ratios and reproductive strategies to increase the proportion of the infected matriline in the population. The most common reproductive manipulation is cytoplasmic incompatibility, which results in embryonic lethality in crosses between infected males and uninfected females. Females infected with the same Wolbachia strain rescue this lethality. Despite more than 40 years of research and relevance to symbiont-induced speciation, as well as control of arbovirus vectors and agricultural pests, the bacterial genes underlying cytoplasmic incompatibility remain unknown. Here we use comparative and transgenic approaches to demonstrate that two differentially transcribed, co-diverging genes in the eukaryotic association module of prophage WO from Wolbachia strain wMel recapitulate and enhance cytoplasmic incompatibility. Dual expression in transgenic, uninfected males of Drosophila melanogaster crossed to uninfected females causes embryonic lethality. Each gene additively augments embryonic lethality in crosses between infected males and uninfected females. Lethality associates with embryonic defects that parallel those of wild-type cytoplasmic incompatibility and is notably rescued by wMel-infected embryos in all cases. The discovery of cytoplasmic incompatibility factor genes cifA and cifB pioneers genetic studies of prophage WO-induced reproductive manipulations and informs the continuing use of Wolbachia to control dengue and Zika virus transmission to humans.



Immunology: The chronicles of T-cell exhaustion

2017-02-22

T cells of the immune system often fail to target cancer cells because they enter a dysfunctional state known as exhaustion. Molecular analysis of T-cell exhaustion provides insights into the clinical use of these cells.



Biochemistry: Origin of a key player in methane biosynthesis

2017-02-22

The biosynthesis of a coenzyme in the microbial production of methane has been determined — completing the biosynthetic pathways for the family of compounds that includes chlorophyll, haem and vitamin B12.



Immunology: T-cell tweaks to target tumours

2017-02-22

Immune cells known as T cells can destroy tumour cells, but their clinical use requires complex preparation and the cells can lose effectiveness over time. A new approach might improve the efficiency of T-cell therapy.



Cardiovascular disease: Commonality with cancer

2017-02-22

Ageing is associated with an increased risk of cardiovascular disease caused by the rupture of inflamed cholesterol plaques in arteries. It emerges that this might be partly due to genetic mutations that cause cancerous changes in white blood cells.



Elucidation of the biosynthesis of the methane catalyst coenzyme F430

2017-02-22

The enzymes and pathway involved in the biosynthesis of coenzyme F430 are identified, completing our understanding of how members of the cyclic modified tetrapyrrole family are constructed.



Intragenic DNA methylation prevents spurious transcription initiation

2017-02-22

Intragenic DNA methylation, dependent on Dnmt3b, protects the gene body from spurious entry of RNA Polymerase II and aberrant transcription initiation events.



Targeting a CAR to the TRAC locus with CRISPR/Cas9 enhances tumour rejection

2017-02-22

Chimeric antigen receptors (CARs) are synthetic receptors that redirect and reprogram T cells to mediate tumour rejection. The most successful CARs used to date are those targeting CD19 (ref. 2), which offer the prospect of complete remission in patients with chemorefractory or relapsed B-cell malignancies. CARs are typically transduced into the T cells of a patient using γ-retroviral vectors or other randomly integrating vectors, which may result in clonal expansion, oncogenic transformation, variegated transgene expression and transcriptional silencing. Recent advances in genome editing enable efficient sequence-specific interventions in human cells, including targeted gene delivery to the CCR5 and AAVS1 loci. Here we show that directing a CD19-specific CAR to the T-cell receptor α constant (TRAC) locus not only results in uniform CAR expression in human peripheral blood T cells, but also enhances T-cell potency, with edited cells vastly outperforming conventionally generated CAR T cells in a mouse model of acute lymphoblastic leukaemia. We further demonstrate that targeting the CAR to the TRAC locus averts tonic CAR signalling and establishes effective internalization and re-expression of the CAR following single or repeated exposure to antigen, delaying effector T-cell differentiation and exhaustion. These findings uncover facets of CAR immunobiology and underscore the potential of CRISPR/Cas9 genome editing to advance immunotherapies.



Crystallization of silicon dioxide and compositional evolution of the Earth’s core

2017-02-22

The Earth’s core is about ten per cent less dense than pure iron (Fe), suggesting that it contains light elements as well as iron. Modelling of core formation at high pressure (around 40–60 gigapascals) and high temperature (about 3,500 kelvin) in a deep magma ocean predicts that both silicon (Si) and oxygen (O) are among the impurities in the liquid outer core. However, only the binary systems Fe–Si and Fe–O have been studied in detail at high pressures, and little is known about the compositional evolution of the Fe–Si–O ternary alloy under core conditions. Here we performed melting experiments on liquid Fe–Si–O alloy at core pressures in a laser-heated diamond-anvil cell. Our results demonstrate that the liquidus field of silicon dioxide (SiO2) is unexpectedly wide at the iron-rich portion of the Fe–Si–O ternary, such that an initial Fe–Si–O core crystallizes SiO2 as it cools. If crystallization proceeds on top of the core, the buoyancy released should have been more than sufficient to power core convection and a dynamo, in spite of high thermal conductivity, from as early on as the Hadean eon. SiO2 saturation also sets limits on silicon and oxygen concentrations in the present-day outer core.



Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy

2017-02-22

Lanthanide-doped glasses and crystals are attractive for laser applications because the metastable energy levels of the trivalent lanthanide ions facilitate the establishment of population inversion and amplified stimulated emission at relatively low pump power. At the nanometre scale, lanthanide-doped upconversion nanoparticles (UCNPs) can now be made with precisely controlled phase, dimension and doping level. When excited in the near-infrared, these UCNPs emit stable, bright visible luminescence at a variety of selectable wavelengths, with single-nanoparticle sensitivity, which makes them suitable for advanced luminescence microscopy applications. Here we show that UCNPs doped with high concentrations of thulium ions (Tm3+), excited at a wavelength of 980 nanometres, can readily establish a population inversion on their intermediate metastable 3H4 level: the reduced inter-emitter distance at high Tm3+ doping concentration leads to intense cross-relaxation, inducing a photon-avalanche-like effect that rapidly populates the metastable 3H4 level, resulting in population inversion relative to the 3H6 ground level within a single nanoparticle. As a result, illumination by a laser at 808 nanometres, matching the upconversion band of the 3H4 → 3H6 transition, can trigger amplified stimulated emission to discharge the 3H4 intermediate level, so that the upconversion pathway to generate blue luminescence can be optically inhibited. We harness these properties to realize low-power super-resolution stimulated emission depletion (STED) microscopy and achieve nanometre-scale optical resolution (nanoscopy), imaging single UCNPs; the resolution is 28 nanometres, that is, 1/36th of the wavelength. These engineered nanocrystals offer saturation intensity two orders of magnitude lower than those of fluorescent probes currently employed in stimulated emission depletion microscopy, suggesting a new way of alleviating the square-root law that typically limits the resolution that can be practically achieved by such techniques.



Prefrontal cortex output circuits guide reward seeking through divergent cue encoding

2017-02-22

Neurons that project from the prefrontal cortex to either the nucleus accumbens or paraventricular thalamus receive different inputs, differentially encode reward-predictive cues, and have opposing effects on reward seeking during cue presentation.



Complement drives glucosylceramide accumulation and tissue inflammation in Gaucher disease

2017-02-22

Gaucher disease is caused by mutations in GBA1, which encodes the lysosomal enzyme glucocerebrosidase (GCase). GBA1 mutations drive extensive accumulation of glucosylceramide (GC) in multiple innate and adaptive immune cells in the spleen, liver, lung and bone marrow, often leading to chronic inflammation. The mechanisms that connect excess GC to tissue inflammation remain unknown. Here we show that activation of complement C5a and C5a receptor 1 (C5aR1) controls GC accumulation and the inflammatory response in experimental and clinical Gaucher disease. Marked local and systemic complement activation occurred in GCase-deficient mice or after pharmacological inhibition of GCase and was associated with GC storage, tissue inflammation and proinflammatory cytokine production. Whereas all GCase-inhibited mice died within 4–5 weeks, mice deficient in both GCase and C5aR1, and wild-type mice in which GCase and C5aR were pharmacologically inhibited, were protected from these adverse effects and consequently survived. In mice and humans, GCase deficiency was associated with strong formation of complement-activating GC-specific IgG autoantibodies, leading to complement activation and C5a generation. Subsequent C5aR1 activation controlled UDP-glucose ceramide glucosyltransferase production, thereby tipping the balance between GC formation and degradation. Thus, extensive GC storage induces complement-activating IgG autoantibodies that drive a pathway of C5a generation and C5aR1 activation that fuels a cycle of cellular GC accumulation, innate and adaptive immune cell recruitment and activation in Gaucher disease. As enzyme replacement and substrate reduction therapies are expensive and still associated with inflammation, increased risk of cancer and Parkinson disease, targeting C5aR1 may serve as a treatment option for patients with Gaucher disease and, possibly, other lysosomal storage diseases.



Reconstitution of the tubular endoplasmic reticulum network with purified components

2017-02-22

Organelles display characteristic morphologies that are intimately tied to their cellular function, but how organelles are shaped is poorly understood. The endoplasmic reticulum is particularly intriguing, as it comprises morphologically distinct domains, including a dynamic network of interconnected membrane tubules. Several membrane proteins have been implicated in network formation, but how exactly they mediate network formation and whether they are all required are unclear. Here we reconstitute a dynamic tubular membrane network with purified endoplasmic reticulum proteins. Proteoliposomes containing the membrane-fusing GTPase Sey1p (refs 6, 7) and the curvature-stabilizing protein Yop1p (refs 8, 9) from Saccharomyces cerevisiae form a tubular network upon addition of GTP. The tubules rapidly fragment when GTP hydrolysis of Sey1p is inhibited, indicating that network maintenance requires continuous membrane fusion and that Yop1p favours the generation of highly curved membrane structures. Sey1p also forms networks with other curvature-stabilizing proteins, including reticulon and receptor expression-enhancing proteins (REEPs) from different species. Atlastin, the vertebrate orthologue of Sey1p, forms a GTP-hydrolysis-dependent network on its own, serving as both a fusion and curvature-stabilizing protein. Our results show that organelle shape can be generated by a surprisingly small set of proteins and represents an energy-dependent steady state between formation and disassembly.



Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness

2017-02-20

A wide variety of high-performance applications require materials for which shape control is maintained under substantial stress, and that have minimal density. Bio-inspired hexagonal and square honeycomb structures and lattice materials based on repeating unit cells composed of webs or trusses, when made from materials of high elastic stiffness and low density, represent some of the lightest, stiffest and strongest materials available today. Recent advances in 3D printing and automated assembly have enabled such complicated material geometries to be fabricated at low (and declining) cost. These mechanical metamaterials have properties that are a function of their mesoscale geometry as well as their constituents, leading to combinations of properties that are unobtainable in solid materials; however, a material geometry that achieves the theoretical upper bounds for isotropic elasticity and strain energy storage (the Hashin–Shtrikman upper bounds) has yet to be identified. Here we evaluate the manner in which strain energy distributes under load in a representative selection of material geometries, to identify the morphological features associated with high elastic performance. Using finite-element models, supported by analytical methods, and a heuristic optimization scheme, we identify a material geometry that achieves the Hashin–Shtrikman upper bounds on isotropic elastic stiffness. Previous work has focused on truss networks and anisotropic honeycombs, neither of which can achieve this theoretical limit. We find that stiff but well distributed networks of plates are required to transfer loads efficiently between neighbouring members. The resulting low-density mechanical metamaterials have many advantageous properties: their mesoscale geometry can facilitate large crushing strains with high energy absorption, optical bandgaps and mechanically tunable acoustic bandgaps, high thermal insulation, buoyancy, and fluid storage and transport. Our relatively simple design can be manufactured using origami-like sheet folding and bonding methods.



Survival of tissue-resident memory T cells requires exogenous lipid uptake and metabolism

2017-02-20

Tissue-resident memory T (TRM) cells persist indefinitely in epithelial barrier tissues and protect the host against pathogens. However, the biological pathways that enable the long-term survival of TRM cells are obscure. Here we show that mouse CD8+ TRM cells generated by viral infection of the skin differentially express high levels of several molecules that mediate lipid uptake and intracellular transport, including fatty-acid-binding proteins 4 and 5 (FABP4 and FABP5). We further show that T-cell-specific deficiency of Fabp4 and Fabp5 (Fabp4/Fabp5) impairs exogenous free fatty acid (FFA) uptake by CD8+ TRM cells and greatly reduces their long-term survival in vivo, while having no effect on the survival of central memory T (TCM) cells in lymph nodes. In vitro, CD8+ TRM cells, but not CD8+ TCM cells, demonstrated increased mitochondrial oxidative metabolism in the presence of exogenous FFAs; this increase was not seen in Fabp4/Fabp5 double-knockout CD8+ TRM cells. The persistence of CD8+ TRM cells in the skin was strongly diminished by inhibition of mitochondrial FFA β-oxidation in vivo. Moreover, skin CD8+ TRM cells that lacked Fabp4/Fabp5 were less effective at protecting mice from cutaneous viral infection, and lung Fabp4/Fabp5 double-knockout CD8+ TRM cells generated by skin vaccinia virus (VACV) infection were less effective at protecting mice from a lethal pulmonary challenge with VACV. Consistent with the mouse data, increased FABP4 and FABP5 expression and enhanced extracellular FFA uptake were also demonstrated in human CD8+ TRM cells in normal and psoriatic skin. These results suggest that FABP4 and FABP5 have a critical role in the maintenance, longevity and function of CD8+ TRM cells, and suggest that CD8+ TRM cells use exogenous FFAs and their oxidative metabolism to persist in tissue and to mediate protective immunity.



Light-induced structural changes and the site of O=O bond formation in PSII caught by XFEL

2017-02-20

Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC). The structure of PSII has been analysed at 1.9 Å resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn4CaO5 cluster organized in an asymmetric, ‘distorted-chair’ form. This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the ‘radiation damage-free’ structure. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures. Here we describe the structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 Å using time-resolved serial femtosecond crystallography with an XFEL provided by the SPring-8 ångström compact free-electron laser. An isomorphous difference Fourier map between the two-flash and dark-adapted states revealed two areas of apparent changes: around the QB/non-haem iron and the Mn4CaO5 cluster. The changes around the QB/non-haem iron region reflected the electron and proton transfers induced by the two-flash illumination. In the region around the OEC, a water molecule located 3.5 Å from the Mn4CaO5 cluster disappeared from the map upon two-flash illumination. This reduced the distance between another water molecule and the oxygen atom O4, suggesting that proton transfer also occurred. Importantly, the two-flash-minus-dark isomorphous difference Fourier map showed an apparent positive peak around O5, a unique μ4-oxo-bridge located in the quasi-centre of Mn1 and Mn4 (refs 4,5). This suggests the insertion of a new oxygen atom (O6) close to O5, providing an O=O distance of 1.5 Å between these two oxygen atoms. This provides a mechanism for the O=O bond formation consistent with that proposed previously.



Cell biology: Stretched divisions

2017-02-15

Many organ surfaces are covered by a protective epithelial-cell layer. It emerges that such layers are maintained by cell stretching that triggers cell division mediated by the force-sensitive ion-channel protein Piezo1.



Whole-genome landscape of pancreatic neuroendocrine tumours

2017-02-15

The genomes of 102 primary pancreatic neuroendocrine tumours have been sequenced, revealing mutations in genes with functions such as chromatin remodelling, DNA damage repair, mTOR activation and telomere maintenance, and a greater-than-expected contribution from germ line mutations.



Untimely expression of gametogenic genes in vegetative cells causes uniparental disomy

2017-02-15

Uniparental disomy (UPD), in which an individual contains a pair of homologous chromosomes originating from only one parent, is a frequent phenomenon that is linked to congenital disorders and various cancers. UPD is thought to result mostly from pre- or post-zygotic chromosome missegregation. However, the factors that drive UPD remain unknown. Here we use the fission yeast Schizosaccharomyces pombe as a model to investigate UPD, and show that defects in the RNA interference (RNAi) machinery or in the YTH domain-containing RNA elimination factor Mmi1 cause high levels of UPD in vegetative diploid cells. This phenomenon is not due to defects in heterochromatin assembly at centromeres. Notably, in cells lacking RNAi components or Mmi1, UPD is associated with the untimely expression of gametogenic genes. Deletion of the upregulated gene encoding the meiotic cohesin Rec8 or the cyclin Crs1 suppresses UPD in both RNAi and mmi1 mutants. Moreover, overexpression of Rec8 is sufficient to trigger UPD in wild-type cells. Rec8 expressed in vegetative cells localizes to chromosomal arms and to the centromere core, where it is required for localization of the cohesin subunit Psc3. The centromeric localization of Rec8 and Psc3 promotes UPD by uniquely affecting chromosome segregation, causing a reductional segregation of one homologue. Together, these findings establish the untimely vegetative expression of gametogenic genes as a causative factor of UPD, and provide a solid foundation for understanding this phenomenon, which is linked to diverse human diseases.



Mechanical stretch triggers rapid epithelial cell division through Piezo1

2017-02-15

Despite acting as a barrier for the organs they encase, epithelial cells turn over at some of the fastest rates in the body. However, epithelial cell division must be tightly linked to cell death to preserve barrier function and prevent tumour formation. How does the number of dying cells match those dividing to maintain constant numbers? When epithelial cells become too crowded, they activate the stretch-activated channel Piezo1 to trigger extrusion of cells that later die. However, it is unclear how epithelial cell division is controlled to balance cell death at the steady state. Here we show that mammalian epithelial cell division occurs in regions of low cell density where cells are stretched. By experimentally stretching epithelia, we find that mechanical stretch itself rapidly stimulates cell division through activation of the Piezo1 channel. To stimulate cell division, stretch triggers cells that are paused in early G2 phase to activate calcium-dependent phosphorylation of ERK1/2, thereby activating the cyclin B transcription that is necessary to drive cells into mitosis. Although both epithelial cell division and cell extrusion require Piezo1 at the steady state, the type of mechanical force controls the outcome: stretch induces cell division, whereas crowding induces extrusion. How Piezo1-dependent calcium transients activate two opposing processes may depend on where and how Piezo1 is activated, as it accumulates in different subcellular sites with increasing cell density. In sparse epithelial regions in which cells divide, Piezo1 localizes to the plasma membrane and cytoplasm, whereas in dense regions in which cells extrude, it forms large cytoplasmic aggregates. Because Piezo1 senses both mechanical crowding and stretch, it may act as a homeostatic sensor to control epithelial cell numbers, triggering extrusion and apoptosis in crowded regions and cell division in sparse regions.



SZT2 dictates GATOR control of mTORC1 signalling

2017-02-15

Mechanistic target of rapamycin complex 1 (TORC1) integrates nutrient signals to control cell growth and organismal homeostasis across eukaryotes. The evolutionarily conserved GATOR complex regulates mTORC1 signalling through Rag GTPases, and GATOR1 displays GTPase activating protein (GAP) activity for RAGA and RAGB (RAGA/B) and GATOR2 has been proposed to be an inhibitor of GATOR1. Furthermore, the metazoan-specific SESN proteins function as guanine nucleotide dissociation inhibitors (GDIs) for RAGA/B, and interact with GATOR2 with unknown effects. Here we show that SZT2 (seizure threshold 2), a metazoan-specific protein mutated in epilepsy, recruits a fraction of mammalian GATOR1 and GATOR2 to form a SZT2-orchestrated GATOR (SOG) complex with an essential role in GATOR- and SESN-dependent nutrient sensing and mTORC1 regulation. The interaction of SZT2 with GATOR1 and GATOR2 was synergistic, and an intact SOG complex was required for its localization at the lysosome. SZT2 deficiency resulted in constitutive mTORC1 signalling in cells under nutrient-deprived conditions and neonatal lethality in mice, which was associated with failure to inactivate mTORC1 during fasting. Hyperactivation of mTORC1 in SZT2-deficient cells could be partially corrected by overexpression of the GATOR1 component DEPDC5, and by the lysosome-targeted GATOR2 component WDR59 or lysosome-targeted SESN2. These findings demonstrate that SZT2 has a central role in dictating GATOR-dependent nutrient sensing by promoting lysosomal localization of SOG, and reveal an unexpected function of lysosome-located GATOR2 in suppressing mTORC1 signalling through SESN recruitment.



KICSTOR recruits GATOR1 to the lysosome and is necessary for nutrients to regulate mTORC1

2017-02-15

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of cell growth that responds to diverse environmental signals and is deregulated in many human diseases, including cancer and epilepsy. Amino acids are a key input to this system, and act through the Rag GTPases to promote the translocation of mTORC1 to the lysosomal surface, its site of activation. Multiple protein complexes regulate the Rag GTPases in response to amino acids, including GATOR1, a GTPase activating protein for RAGA, and GATOR2, a positive regulator of unknown molecular function. Here we identify a protein complex (KICSTOR) that is composed of four proteins, KPTN, ITFG2, C12orf66 and SZT2, and that is required for amino acid or glucose deprivation to inhibit mTORC1 in cultured human cells. In mice that lack SZT2, mTORC1 signalling is increased in several tissues, including in neurons in the brain. KICSTOR localizes to lysosomes; binds and recruits GATOR1, but not GATOR2, to the lysosomal surface; and is necessary for the interaction of GATOR1 with its substrates, the Rag GTPases, and with GATOR2. Notably, several KICSTOR components are mutated in neurological diseases associated with mutations that lead to hyperactive mTORC1 signalling. Thus, KICSTOR is a lysosome-associated negative regulator of mTORC1 signalling, which, like GATOR1, is mutated in human disease.



Arrays of horizontal carbon nanotubes of controlled chirality grown using designed catalysts

2017-02-15

The semiconductor industry is increasingly of the view that Moore’s law—which predicts the biennial doubling of the number of transistors per microprocessor chip—is nearing its end. Consequently, the pursuit of alternative semiconducting materials for nanoelectronic devices, including single-walled carbon nanotubes (SWNTs), continues. Arrays of horizontal nanotubes are particularly appealing for technological applications because they optimize current output. However, the direct growth of horizontal SWNT arrays with controlled chirality, that would enable the arrays to be adapted for a wider range of applications and ensure the uniformity of the fabricated devices, has not yet been achieved. Here we show that horizontal SWNT arrays with predicted chirality can be grown from the surfaces of solid carbide catalysts by controlling the symmetries of the active catalyst surface. We obtained horizontally aligned metallic SWNT arrays with an average density of more than 20 tubes per micrometre in which 90 per cent of the tubes had chiral indices of (12, 6), and semiconducting SWNT arrays with an average density of more than 10 tubes per micrometre in which 80 per cent of the nanotubes had chiral indices of (8, 4). The nanotubes were grown using uniform size Mo2C and WC solid catalysts. Thermodynamically, the SWNT was selectively nucleated by matching its structural symmetry and diameter with those of the catalyst. We grew nanotubes with chiral indices of (2m, m) (where m is a positive integer), the yield of which could be increased by raising the concentration of carbon to maximize the kinetic growth rate in the chemical vapour deposition process. Compared to previously reported methods, such as cloning, seeding and specific-structure-matching growth, our strategy of controlling the thermodynamics and kinetics offers more degrees of freedom, enabling the chirality of as-grown SWNTs in an array to be tuned, and can also be used to predict the growth conditions required to achieve the desired chiralities.









Extrachromosomal oncogene amplification drives tumour evolution and genetic heterogeneity

2017-02-08

Human cells have twenty-three pairs of chromosomes. In cancer, however, genes can be amplified in chromosomes or in circular extrachromosomal DNA (ecDNA), although the frequency and functional importance of ecDNA are not understood. We performed whole-genome sequencing, structural modelling and cytogenetic analyses of 17 different cancer types, including analysis of the structure and function of chromosomes during metaphase of 2,572 dividing cells, and developed a software package called ECdetect to conduct unbiased, integrated ecDNA detection and analysis. Here we show that ecDNA was found in nearly half of human cancers; its frequency varied by tumour type, but it was almost never found in normal cells. Driver oncogenes were amplified most commonly in ecDNA, thereby increasing transcript level. Mathematical modelling predicted that ecDNA amplification would increase oncogene copy number and intratumoural heterogeneity more effectively than chromosomal amplification. We validated these predictions by quantitative analyses of cancer samples. The results presented here suggest that ecDNA contributes to accelerated evolution in cancer.












Particle physics: Search for neutrinoless double-β decay

2016-09-21

Neutrinos are much lighter than the other constituents of matter. One explanation for this could be that neutrinos are their own antiparticles and belong to a new class of 'Majorana' particle. An experiment sets strong constraints on this scenario.



Human migration: Climate and the peopling of the world

2016-09-21

The human dispersal out of Africa that populated the world was probably paced by climate changes. This is the inference drawn from computer modelling of climate variability during the time of early human migration.



Cancer: Acidic shield puts a chink in p53's armour

2016-09-14

Underactivity of the transcription factor p53 can lead to tumour development. The discovery that the SET protein binds to and inhibits p53 points to a way to unleash the tumour suppressor's activity.



Evolutionary biology: To mimicry and back again

2016-05-25

Deadly coral snakes warn predators through striking red-black banding. New data confirm that many harmless snakes have evolved to resemble coral snakes, and suggest that the evolution of this Batesian mimicry is not always a one-way street.



Addendum

2015-06-17