This Week in Science

Science  17 Jun 2016:
Vol. 352, Issue 6292, pp. 1421
  1. Forest Ecology

    A future for boreal forests

    1. Andrew M. Sugden

    Boreal forest and wetlands along the Labrador Coastal Drive, Canada

    PHOTO: © ALL CANADA PHOTOS/ALAMY STOCK PHOTO

    Conservation under climate change presents the challenge of predicting where will be suitable for particular organisms and ecological communities in the future. D'Orangeville et al. assess the probable future range for boreal forests in eastern North America, which are expected to be subject to large temperature increases in their natural range. Using tree-ring data from many thousands of forest stands, they delineate the geographical extent of the region where tree growth responds favorably to higher temperatures and where the forest should persist at least until 2070.

    Science, this issue p. 1452

  2. Aging

    A dietary supplement protects aging muscle

    1. L. Bryan Ray

    The oxidized form of cellular nicotinamide adenine dinucleotide (NAD+) is critical for mitochondrial function, and its supplementation can lead to increased longevity. Zhang et al. found that feeding the NAD+ precursor nicotinamide riboside (NR) to aging mice protected them from muscle degeneration (see the Perspective by Guarente). NR treatment enhanced muscle function and also protected mice from the loss of muscle stem cells. The treatment was similarly protective of neural and melanocyte stem cells, which may have contributed to the extended life span of the NR-treated animals.

    Science, this issue p. 1436; see also p. 1396

  3. Human Behavior

    Tackling the advance of online threats

    1. Barbara R. Jasny

    Online support for adversarial groups such as Islamic State (ISIS) can turn local into global threats and attract new recruits and funding. Johnson et al. analyzed data collected on ISIS-related websites involving 108,086 individual followers between 1 January 1 and 31 August 2015. They developed a statistical model aimed at identifying behavioral patterns among online supporters of ISIS and used this information to predict the onset of major violent events. Sudden escalation in the number of ISIS-supporting ad hoc web groups (“aggregates”) preceded the onset of violence in a way that would not have been detected by looking at social media references to ISIS alone. The model suggests how the development and evolution of such aggregates can be blocked.

    Science, this issue p. 1459

  4. Addiction Research

    Punishment doesn't work in cocaine addicts

    1. Peter Stern

    Addiction is extremely difficult to treat, particularly cocaine use disorder. Animal experiments have led to the concept of drug addiction as abnormal goal-directed learning and habit formation. Ersche et al. found that overtraining with positive reinforcement such as rewards made cocaine-addicted patients less sensitive to the outcome of their actions. In contrast, overtraining on a punishment paradigm had no effect. Thus, habits may determine the behavior of cocaine users.

    Science, this issue p. 1468

  5. Neuroscience

    Why stress makes epilepsy worse

    1. Wei Wong

    Seizures caused by uncontrolled neuronal activity often start in a part of the brain called the piriform cortex. The activity of the piriform cortex is normally suppressed by corticotropin-releasing factor (CRF), a neuropeptide that is released in response to stress. Narla et al. found that in rodents with experimentally induced epilepsy, CRF enhanced, rather than suppressed, neuronal activity in this part of the brain. This was because the receptor for CRF signaled through a different Gα protein, which may explain why stress and anxiety tend to increase the frequency of seizures in epileptics.

    Sci. Signal. 9, ra60 (2016).

  6. Applied Physics

    Organic solar cells tuned by blending

    1. Jake Yeston

    Electrical engineers can finetune the energetics of rigid photovoltaics and transistors by blending different semiconducting materials. However, it's hard to apply this tuning protocol to the flexible class of carbon-based semiconductors. Schwarze et al. now show that continuous band energy tuning is indeed possible by varying the blend ratios of certain organic phthalocyanines and their fluorinated or chlorinated derivatives (see the Perspective by Ueno). They demonstrated the effect, which they attribute to quadrupolar interactions, in model solar cells.

    Molecular structural properties of organic semiconductors.

    PHOTO: SCHWARZE ET AL.

    Science, this issue p. 1446; see also p. 1395

  7. Tissue Engineering

    Saving face

    1. Megan Frisk

    Bone grafts from the patient are currently used to correct facial deformities, but a biomaterials-based approach would be useful. Bhumiratana et al. designed a facial reconstructive strategy based on stem cells, decellularized bone, and a custom-designed perfusion bioreactor. First, bone was shaped to a defect in miniature pigs, and then stem cells were cultured on the bone. To mimic the manufacturing and transport chain for human facial bone reconstruction, the bioreactor containing living bone was shipped to the site of surgery. The implanted scaffold material integrated successfully with host tissue, formed new bone, and was vascularized.

    Sci. Transl. Med. 8, 343ra83 (2016).

  8. Molecular Junctions

    Stable molecular switches

    1. Phil Szuromi

    Many single-molecule current switches have been reported, but most show poor stability because of weak contacts to metal electrodes. Jia et al. covalently bonded a diarylethene molecule to graphene electrodes and achieved stable photoswitching at room temperature (see the Perspective by Frisbie). The incorporation of short bridging alkyl chains between the molecule and graphene decoupled their pielectron systems and allowed fast conversion of the open and closed ring states.

    Science, this issue p. 1443; see also p. 1394

  9. Stem Cells

    Tracking stem cell fate in time and space

    1. Beverly A. Purnell

    After injury and during homeostasis, tissues rely on the balance of cell loss and renewal. Rompolas et al. visualized individual stem cells over their lifetime in the epidermis of live mice. Tracking stem cells over multiple generations revealed that tissue homeostasis in the mouse epidermis is not maintained by asymmetric cell division as previously thought, but through the coordination of sibling cell fate and lifetimes. Furthermore, differentiating stem cells reused the existing spatial organization of the epidermis.

    Science, this issue p. 1471

  10. Immune Regulation

    Innate immune crosstalk in T cells

    1. Kristen L. Mueller

    The classical view of immune activation is that innate immune cells, such as macrophages and dendritic cells, recognize invading microbes and then alert adaptive immune cells, such as T cells, to respond. Arbore et al. now show that innate and adaptive immunity converge in human and mouse T cells. Activated T cells express components of the complement cascade, which in turn leads to the assembly of NLRP3 inflammasomes—both critical components of innate immunity that help hosts detect and eliminate microbes. In T cells, complement and inflammasomes work together to push T cells to differentiate into a specialized subset of T cells important for eliminating intracellular bacteria.

    Science, this issue p. 1424

  11. Translation

    The when, where, and how of translation

    1. Beverly A. Purnell

    High-resolution single-molecule imaging shows the spatial and temporal dynamics of molecular events (see the Perspective by Iwasaki and Ingolia). Wu et al. and Morisaki et al. developed an approach to study the translation of single messenger RNAs (mRNAs) in live cells. Nascent polypeptides containing multimerized epitopes were imaged with fluorescent antibody fragments, while simultaneously detecting the single mRNAs using a different fluorescent tag. The approach enabled a direct readout of initiation and elongation, as well as revealing the spatial distribution of translation and allowing the correlation of polysome motility with translation dynamics. Membrane-targeted mRNAs could be distinguished from cytoplasmic mRNAs, as could single polysomes from higher-order polysomal complexes. Furthermore, the work reveals the stochasticity of translation, which can occur constitutively or in bursts, much like transcription, and the spatial regulation of translation in neuronal dendrites.

    Science, this issue p. 1430, p. 1425; see also p. 1391

  12. Ecosystem Services

    China's national ecosystem assessment

    1. Andrew M. Sugden

    China recently completed its first National Ecosystem Assessment covering the period 2000–2010. Ouyang et al. present the main findings of the assessment. Investment in the restoration and preservation of natural capital has resulted in improvements at the national level in most of the major ecosystem services measured. In particular, food production, carbon sequestration, and soil retention showed strong gains; on the other hand, habitat provision for biodiversity showed a gradual decline. Regional differences remain nonetheless, and there are serious environmental challenges still to be met in areas such as air quality and the wider global footprint of raw material imports.

    Science, this issue p. 1455

  13. Brain Research

    Coding abstract concepts in the brain

    1. Peter Stern

    Grid cells are thought to provide the neuronal code that underlies spatial knowledge in the brain. Grid cells have mostly been studied in the context of path integration. However, recent theoretical studies have suggested that they may have a broader role in the organization of general knowledge. Constantinescu et al. investigated whether the neural representation of concepts follows a structure similar to the representation of space in the entorhinal cortex. Several brain regions, including the entorhinal cortex and the ventromedial prefrontal cortex, showed gridlike neural representation of conceptual space.

    Science, this issue p. 1464

  14. Metabolism

    A fluorescent sensor for NAD+ in living cells

    1. L. Bryan Ray

    Roles of cellular nicotinamide adenine dinucleotide (NAD+) in metabolism, aging, and disease have garnered much interest, but methods have been lacking to measure the amounts of NAD+ in living cells. Cambronne et al. developed a genetically encoded biosensor that can be used to monitor concentrations of free NAD+ in various compartments of a cell (see the Perspective by Guarente). Such concentrations of NAD+ appear to be important in regulating the activity of NAD+-consuming enzymes such as sirtuins and ADP-ribosyltransferases. The authors used the sensor to demonstrate that NAD+ concentrations in mitochondria of cultured human cells can be controlled by multiple mechanisms.

    Science, this issue p. 1474; see also p. 1396

  15. Marine Environment

    PCB threats continue despite ban

    1. Julia Fahrenkamp-Uppenbrink

    Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are banned under the Stockholm Convention. In recent decades, their concentrations in many wildlife species have gone down. In a Perspective, Jepson and Law explain that marine predators such as orcas can still have very high PCB concentrations. The pollutants affect reproduction, particularly in mammals, in which PCBs are transferred to the offspring through milk. Although data on PCB concentrations are limited, many marine predators are threatened with extinction. Safe disposal or destruction of remaining PCB stocks and PCB-containing materials is thus a priority.

    Science, this issue p. 1388

  16. Ecology

    Soils to the rescue

    1. Julia Fahrenkamp-Uppenbrink

    Today's farming methods tend to rely on pesticides for controlling plant diseases. In a Perspective, Raaijmakers and Mazzola describe how soils can also help plants defeat pathogens. Disease suppression by soils can be specific to particular pathogens and can be transferred between soils. However, attempts to harness disease-suppressive properties of soils by isolating individual species have shown limited success. Because soil-microbe-plant interactions are complex, sustainable disease management approaches should be based not on individual species but on the soil microbial community.

    Science, this issue p. 1392

  17. Astrochemistry

    Chiral molecule discovered in space

    1. Keith T. Smith

    A chiral molecule is one that has two forms that are mirror images of each other: enantiomers. Biological systems overwhelmingly use one enantiomer over another, and some meteorites show an excess of one type. The two forms are almost identical chemically, so how this excess first arose is unknown. McGuire et al. used radio astronomy to detect the first known chiral molecule in space: propylene oxide. The work raises the prospect of measuring the enantiomer excess in various astronomical objects, including regions where planets are being formed, to discover how and why the excess first appeared.

    Science, this issue p. 1449

  18. Light Pollution

    Star light, star bright?

    1. Philippa J. Benson

    More than 80% of the world's population lives under skies polluted by the luminescent glow of artificial lights. Falchi et al. present an atlas that shows how increasing light pollution has obscured our night skies, hiding celestial attractions like the Milky Way from more than one-third of the planet's population. The atlas sets a precise point against which researchers can compare future changes in global light pollution and provides a tool for studying the impact of artificial light on our planet.

    Sci. Adv. 2, 10.1126.sciadv.1600377 (2016).