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HIV--No time for complacency
06/14/2018 05:40 PM
News at a glance
06/14/2018 05:40 PM
Seaweed masses assault Caribbean islands
06/14/2018 05:40 PM
Quantum physics could get big boost from U.S. Congress
06/14/2018 05:40 PM
Report details persistent hostility to women in science
06/14/2018 05:40 PM
Seafloor fiber optic cables can listen for earthquakes
06/14/2018 05:40 PM
Stricter Chinese student visas raise alarm
06/14/2018 05:40 PM
Far from over
06/14/2018 05:40 PM
The mother of all challenges
06/14/2018 05:40 PM
Building TRUST in an LGBTQ-hostile country
06/14/2018 05:40 PM
Babies who dodge HIV may not be unscathed
06/14/2018 05:40 PM
Dark nights, bright stars
06/14/2018 05:40 PM
Status symbol
06/14/2018 05:40 PM
Poster couple
06/14/2018 05:40 PM
The pill exchange
06/14/2018 05:40 PM
The loyal opposition
06/14/2018 05:40 PM
The Sunshine State's dark cloud
06/14/2018 05:40 PM
A tool for finding rare marine species
06/14/2018 05:40 PM
Crystallizing a memory
06/14/2018 05:40 PM
Scaling of human brain size
06/14/2018 05:40 PM
Animals feel safer from humans in the dark
06/14/2018 05:40 PM
Facing your fears
06/14/2018 05:40 PM
Understanding spatial environments from images
06/14/2018 05:40 PM
Preparing ocean governance for species on the move
06/14/2018 05:40 PM
Asperger's chilling complicity
06/14/2018 05:40 PM
Platforms of power
06/14/2018 05:40 PM
Conservation accord: Let countries govern
06/14/2018 05:40 PM
Conservation accord: Cash is not enough
06/14/2018 05:40 PM
Conservation accord: Corporate incentives
06/14/2018 05:40 PM
Response--Conservation accord
06/14/2018 05:40 PM
Nocturnal refuge
06/14/2018 05:40 PM
A scene-internalizing computer program
06/14/2018 05:40 PM
An intrinsic magnetic tunnel junction
06/14/2018 05:40 PM
Lower-energy photons do the work, too
06/14/2018 05:40 PM
Seeing ghosts
06/14/2018 05:40 PM
Mesoamerican turquoise locally sourced
06/14/2018 05:40 PM
Disentangling specific memories
06/14/2018 05:40 PM
Designer bugs as drugs
06/14/2018 05:40 PM
Modeling memory differentiation in T cells
06/14/2018 05:40 PM
Chronic stress as a survival tactic
06/14/2018 05:40 PM
Reconsidering resonator sensing
06/14/2018 05:40 PM
How to make bioactive alkaloids
06/14/2018 05:40 PM
The mechanisms of fear attenuation
06/14/2018 05:40 PM
Tackling microtubule-tau interactions
06/14/2018 05:40 PM
Shifts in brain regions with brain size
06/14/2018 05:40 PM
Environmental DNA tracks rare species
06/14/2018 05:40 PM
Letting thymocytes go
06/14/2018 05:40 PM
Spontaneous HIV controllers
06/14/2018 05:40 PM
In the company of top quarks
06/14/2018 05:40 PM
Salmon teleconnection disservice
06/14/2018 05:40 PM
Gut bacteria relieve epilepsy
06/14/2018 05:40 PM
RNA processing for metabolic control
06/14/2018 05:40 PM
Variants may affect disease heritability
06/14/2018 05:40 PM
A quantum enhancement for plasmonic sensors
06/14/2018 05:40 PM
Edge cases cause trouble
06/14/2018 05:40 PM
Neural scene representation and rendering

Scene representation—the process of converting visual sensory data into concise descriptions—is a requirement for intelligent behavior. Recent work has shown that neural networks excel at this task when provided with large, labeled datasets. However, removing the reliance on human labeling remains an important open problem. To this end, we introduce the Generative Query Network (GQN), a framework within which machines learn to represent scenes using only their own sensors. The GQN takes as input images of a scene taken from different viewpoints, constructs an internal representation, and uses this representation to predict the appearance of that scene from previously unobserved viewpoints. The GQN demonstrates representation learning without human labels or domain knowledge, paving the way toward machines that autonomously learn to understand the world around them.

06/14/2018 05:40 PM
Photochemistry beyond the red limit in chlorophyll f-containing photosystems

Photosystems I and II convert solar energy into the chemical energy that powers life. Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal and is considered to define the energy "red limit" of oxygenic photosynthesis. We present biophysical studies on the photosystems from a cyanobacterium grown in far-red light (750 nm). The few long-wavelength chlorophylls present are well resolved from each other and from the majority pigment, chlorophyll a. Charge separation in photosystem I and II uses chlorophyll f at 745 nm and chlorophyll f (or d) at 727 nm, respectively. Each photosystem has a few even longer-wavelength chlorophylls f that collect light and pass excitation energy uphill to the photochemically active pigments. These photosystems function beyond the red limit using far-red pigments in only a few key positions.

06/14/2018 05:40 PM
Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance that is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI3. Our work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.

06/14/2018 05:40 PM
Probing magnetism in 2D van der Waals crystalline insulators via electron tunneling

Magnetic insulators are a key resource for next-generation spintronic and topological devices. The family of layered metal halides promises varied magnetic states, including ultrathin insulating multiferroics, spin liquids, and ferromagnets, but device-oriented characterization methods are needed to unlock their potential. Here, we report tunneling through the layered magnetic insulator CrI3 as a function of temperature and applied magnetic field. We electrically detect the magnetic ground state and interlayer coupling and observe a field-induced metamagnetic transition. The metamagnetic transition results in magnetoresistances of 95, 300, and 550% for bilayer, trilayer, and tetralayer CrI3 barriers, respectively. We further measure inelastic tunneling spectra for our junctions, unveiling a rich spectrum consistent with collective magnetic excitations (magnons) in CrI3.

06/14/2018 05:40 PM
Normative brain size variation and brain shape diversity in humans

Brain size variation over primate evolution and human development is associated with shifts in the proportions of different brain regions. Individual brain size can vary almost twofold among typically developing humans, but the consequences of this for brain organization remain poorly understood. Using in vivo neuroimaging data from more than 3000 individuals, we find that larger human brains show greater areal expansion in distributed frontoparietal cortical networks and related subcortical regions than in limbic, sensory, and motor systems. This areal redistribution recapitulates cortical remodeling across evolution, manifests by early childhood in humans, and is linked to multiple markers of heightened metabolic cost and neuronal connectivity. Thus, human brain shape is systematically coupled to naturally occurring variations in brain size through a scaling map that integrates spatiotemporally diverse aspects of neurobiology.

06/14/2018 05:40 PM
Synapse-specific representation of the identity of overlapping memory engrams

Memories are integrated into interconnected networks; nevertheless, each memory has its own identity. How the brain defines specific memory identity out of intermingled memories stored in a shared cell ensemble has remained elusive. We found that after complete retrograde amnesia of auditory fear conditioning in mice, optogenetic stimulation of the auditory inputs to the lateral amygdala failed to induce memory recall, implying that the memory engram no longer existed in that circuit. Complete amnesia of a given fear memory did not affect another linked fear memory encoded in the shared ensemble. Optogenetic potentiation or depotentiation of the plasticity at synapses specific to one memory affected the recall of only that memory. Thus, the sharing of engram cells underlies the linkage between memories, whereas synapse-specific plasticity guarantees the identity and storage of individual memories.

06/14/2018 05:40 PM
The influence of human disturbance on wildlife nocturnality

Rapid expansion of human activity has driven well-documented shifts in the spatial distribution of wildlife, but the cumulative effect of human disturbance on the temporal dynamics of animals has not been quantified. We examined anthropogenic effects on mammal diel activity patterns, conducting a meta-analysis of 76 studies of 62 species from six continents. Our global study revealed a strong effect of humans on daily patterns of wildlife activity. Animals increased their nocturnality by an average factor of 1.36 in response to human disturbance. This finding was consistent across continents, habitats, taxa, and human activities. As the global human footprint expands, temporal avoidance of humans may facilitate human-wildlife coexistence. However, such responses can result in marked shifts away from natural patterns of activity, with consequences for fitness, population persistence, community interactions, and evolution.

06/14/2018 05:40 PM
Missing enzymes in the biosynthesis of the anticancer drug vinblastine in Madagascar periwinkle

Vinblastine, a potent anticancer drug, is produced by Catharanthus roseus (Madagascar periwinkle) in small quantities, and heterologous reconstitution of vinblastine biosynthesis could provide an additional source of this drug. However, the chemistry underlying vinblastine synthesis makes identification of the biosynthetic genes challenging. Here we identify the two missing enzymes necessary for vinblastine biosynthesis in this plant: an oxidase and a reductase that isomerize stemmadenine acetate into dihydroprecondylocarpine acetate, which is then deacetoxylated and cyclized to either catharanthine or tabersonine via two hydrolases characterized herein. The pathways show how plants create chemical diversity and also enable development of heterologous platforms for generation of stemmadenine-derived bioactive compounds.

06/14/2018 05:40 PM
Reactivation of recall-induced neurons contributes to remote fear memory attenuation

Whether fear attenuation is mediated by inhibition of the original memory trace of fear with a new memory trace of safety or by updating of the original fear trace toward safety has been a long-standing question in neuroscience and psychology alike. In particular, which of the two scenarios underlies the attenuation of remote (month-old) fear memories is completely unknown, despite the impetus to better understand this process against the backdrop of enduring traumata. We found—chemogenetically and in an engram-specific manner—that effective remote fear attenuation is accompanied by the reactivation of memory recall–induced neurons in the dentate gyrus and that the continued activity of these neurons is critical for fear reduction. This suggests that the original memory trace of fear actively contributes to remote fear attenuation.

06/14/2018 05:40 PM
Near-atomic model of microtubule-tau interactions

Tau is a developmentally regulated axonal protein that stabilizes and bundles microtubules (MTs). Its hyperphosphorylation is thought to cause detachment from MTs and subsequent aggregation into fibrils implicated in Alzheimer’s disease. It is unclear which tau residues are crucial for tau-MT interactions, where tau binds on MTs, and how it stabilizes them. We used cryo–electron microscopy to visualize different tau constructs on MTs and computational approaches to generate atomic models of tau-tubulin interactions. The conserved tubulin-binding repeats within tau adopt similar extended structures along the crest of the protofilament, stabilizing the interface between tubulin dimers. Our structures explain the effect of phosphorylation on MT affinity and lead to a model of tau repeats binding in tandem along protofilaments, tethering together tubulin dimers and stabilizing polymerization interfaces.

06/14/2018 05:40 PM
Ghost cytometry

Ghost imaging is a technique used to produce an object’s image without using a spatially resolving detector. Here we develop a technique we term "ghost cytometry," an image-free ultrafast fluorescence "imaging" cytometry based on a single-pixel detector. Spatial information obtained from the motion of cells relative to a static randomly patterned optical structure is compressively converted into signals that arrive sequentially at a single-pixel detector. Combinatorial use of the temporal waveform with the intensity distribution of the random pattern allows us to computationally reconstruct cell morphology. More importantly, we show that applying machine-learning methods directly on the compressed waveforms without image reconstruction enables efficient image-free morphology-based cytometry. Despite a compact and inexpensive instrumentation, image-free ghost cytometry achieves accurate and high-throughput cell classification and selective sorting on the basis of cell morphology without a specific biomarker, both of which have been challenging to accomplish using conventional flow cytometers.

06/14/2018 05:40 PM
New Products
06/14/2018 05:40 PM
Technology Feature | Translating big data: The proteomics challenge
06/14/2018 05:40 PM
Hitting the wall
06/14/2018 05:40 PM
Induction of CD4 T cell memory by local cellular collectivity

Cell differentiation is directed by signals driving progenitors into specialized cell types. This process can involve collective decision-making, when differentiating cells determine their lineage choice by interacting with each other. We used live-cell imaging in microwell arrays to study collective processes affecting differentiation of naïve CD4+ T cells into memory precursors. We found that differentiation of precursor memory T cells sharply increases above a threshold number of locally interacting cells. These homotypic interactions involve the cytokines interleukin-2 (IL-2) and IL-6, which affect memory differentiation orthogonal to their effect on proliferation and survival. Mathematical modeling suggests that the differentiation rate is continuously modulated by the instantaneous number of locally interacting cells. This cellular collectivity can prioritize allocation of immune memory to stronger responses.

06/14/2018 05:40 PM
Unresolved endoplasmic reticulum stress engenders immune-resistant, latent pancreatic cancer metastases

The majority of patients with pancreatic ductal adenocarcinoma (PDA) develop metastatic disease after resection of their primary tumor. We found that livers from patients and mice with PDA harbor single disseminated cancer cells (DCCs) lacking expression of cytokeratin 19 (CK19) and major histocompatibility complex class I (MHCI). We created a mouse model to determine how these DCCs develop. Intraportal injection of immunogenic PDA cells into preimmunized mice seeded livers only with single, nonreplicating DCCs that were CK19 and MHCI. The DCCs exhibited an endoplasmic reticulum (ER) stress response but paradoxically lacked both inositol-requiring enzyme 1α activation and expression of the spliced form of transcription factor XBP1 (XBP1s). Inducible expression of XBP1s in DCCs, in combination with T cell depletion, stimulated the outgrowth of macrometastatic lesions that expressed CK19 and MHCI. Thus, unresolved ER stress enables DCCs to escape immunity and establish latent metastases.

06/14/2018 05:40 PM
Improving mechanical sensor performance through larger damping

Mechanical resonances are used in a wide variety of devices, from smartphone accelerometers to computer clocks and from wireless filters to atomic force microscopes. Frequency stability, a critical performance metric, is generally assumed to be tantamount to resonance quality factor (the inverse of the linewidth and of the damping). We show that the frequency stability of resonant nanomechanical sensors can be improved by lowering the quality factor. At high bandwidths, quality-factor reduction is completely mitigated by increases in signal-to-noise ratio. At low bandwidths, notably, increased damping leads to better stability and sensor resolution, with improvement proportional to damping. We confirm the findings by demonstrating temperature resolution of 60 microkelvin at 300-hertz bandwidth. These results open the door to high-performance ultrasensitive resonators in gaseous or liquid environments, single-cell nanocalorimetry, nanoscale gas chromatography, atmospheric-pressure nanoscale mass spectrometry, and new approaches in crystal oscillator stability.

06/14/2018 05:40 PM
Comment on "Satellites reveal contrasting responses of regional climate to the widespread greening of Earth"

Forzieri et al. (Reports, 16 June 2017, p. 1180) used satellite data to show that boreal greening caused regional warming. We show that this positive sensitivity of temperature to the greening can be derived from the positive response of vegetation to boreal warming, which indicates that results from a statistical regression with satellite data should be carefully interpreted.

06/14/2018 05:40 PM
Response to Comment on "Satellites reveal contrasting responses of regional climate to the widespread greening of Earth"

Li et al. contest the idea that vegetation greening has contributed to boreal warming and argue that the sensitivity of temperature to leaf area index (LAI) is instead likely driven by the climate impact on vegetation. We provide additional evidence that the LAI-climate interplay is indeed largely driven by the vegetation impact on temperature and not vice versa, thus corroborating our original conclusions.

06/14/2018 05:40 PM