This Week in Science

Science  04 Oct 2019:
Vol. 366, Issue 6461, pp. 68
  1. Wildlife Trade

    A heavy toll

    1. Sacha Vignieri

    The Sunda pangolin, Manis javanica, is critically endangered owing to poaching and illegal trade.

    PHOTO: SUZI ESZTERHAS/MINDEN PICTURES

    Trade in wildlife, and their parts, is well recognized for a few key species, such as elephants and rhinos, but it occurs globally, across a wide array of species. Scheffers et al. looked across tens of thousands of vertebrate species and found that one in every five species is affected by trade of some sort. The impacts of trade tend to be concentrated in certain phylogenetic groups, thus the potential for long-term impact on certain lineages is substantial. This analysis allows for prediction of potential for trade where it does not yet occur, facilitating proactive prevention.

    Science, this issue p. 71

  2. Atomic Physics

    Building up an optical clock

    1. Jelena Stajic

    Arrays of optical tweezers can be used to trap atoms, which can then be manipulated individually. Such arrays have shown promise in quantum simulation of many-body systems. Norcia et al. now demonstrate that they can also be used as a platform for optical clocks. The researchers lined up 10 optical tweezers in a one-dimensional array, where each tweezer held either one or zero atoms of strontium. The atoms were subjected to laser light whose frequency was tuned to a clock transition in strontium. By monitoring the number of atoms in each tweezer, the researchers measured a long coherence time of a few seconds. Increasing the number of tweezers should improve the figures of merit of this platform.

    Science, this issue p. 93

  3. Star Formation

    Gas flows and disks in a young binary

    1. Keith T. Smith

    Many stars are in binary systems, pairs of stars gravitationally bound to each other, often with the two components having similar masses. It remains unclear how these systems assemble and accrete material. Alves et al. made high-resolution observations of a young binary star that is still in the process of forming. A large disk surrounds both stars, and each component also has its own smaller circumstellar disk. Spiral filaments of dust and gas connect the small disks to the larger one. Material is accreting preferentially onto the star that currently has a lower mass, driving the masses toward similar values.

    Science, this issue p. 90

  4. Neuroprosthetics

    Good vibrations

    1. Mattia Maroso

    The lack of sensory feedback from the leg prosthesis in lower limb amputees is associated with risk of falls, low mobility, and perception of the prosthesis as an external object. Petrini et al. tested a leg neuroprosthesis, which provided real-time on-demand tactile sensory feedback through nerve stimulation in three transfemoral amputees. Stimulation improved mobility, decreased falling episodes, and increased the perception of the prosthesis as part of the body. Active complex tasks were accomplished with reduced effort when nerve stimulation was turned on.

    Sci. Transl. Med. 11, eaav8939 (2019).

  5. Biodiversity Loss

    Staggering decline of bird populations

    1. Andrew M. Sugden

    Because birds are conspicuous and easy to identify and count, reliable records of their occurrence have been gathered over many decades in many parts of the world. Drawing on such data for North America, Rosenberg et al. report wide-spread population declines of birds over the past half-century, resulting in the cumulative loss of billions of breeding individuals across a wide range of species and habitats. They show that declines are not restricted to rare and threatened species—those once considered common and wide-spread are also diminished. These results have major implications for ecosystem integrity, the conservation of wildlife more broadly, and policies associated with the protection of birds and native ecosystems on which they depend.

    Science, this issue p. 120

  6. 3D Printing

    Speeding up submicrometer printing

    1. Brent Grocholski

    3D printed pillars with submicrometer features

    PHOTO: VU NGUYEN AND SOURABH SAHA

    Using light to build three-dimensional structures with photopolymerization is the basis for two-photon lithography. However, there has been a trade-off between speed and resolution for fabricating structures with this method. Saha et al. optimize a new parallel printing methodology that relies on ultrafast lasers. They show the ability to dramatically increase the speed of printing while maintaining submicrometer resolution.

    Science, this issue p. 105

  7. Structural Biology

    The yin and yang of Raf inhibition

    1. Valda Vinson

    Many human melanomas contain an overactive form of Raf kinase (B-Raf). Inhibitors are effective against the mutant B-Raf, but, paradoxically, they activate wild-type B-Raf, limiting their therapeutic potential. Kondo et al. determined the structure of a phosphorylated B-Raf dimer in complex with the scaffold protein 14-3-3 by cryo–electron microscopy. Although both kinases are in the active conformation, one is blocked by the C-terminal tail of the other. This configuration inhibits one active site but also stabilizes the dimer in the active conformation. Understanding this mechanism provides a framework for development of inhibitors that do not activate wild-type Raf.

    Science, this issue p. 109

  8. Atmospheric Science

    Consequences of nuclear war

    1. Kip Hodges

    The likely catastrophic environmental effects of global nuclear war are well-described in the scientific literature, but the effects of a more limited, regional nuclear war are also staggering. Toon et al. combined a realistic war scenario involving the neighboring, nuclear-capable nations of India and Pakistan with established climate models to explore plausible global effects of such conflict. These models suggest that, in addition to human casualties, an India-Pakistan nuclear war would start fires releasing tens of trillions of grams of black carbon into the stratosphere. Distributed globally, this soot would limit the amount of sunlight that reaches Earth's surface, drastically reducing surface temperatures and thus potentially limiting food supplies globally for more than a decade.

    Sci. Adv. 10.1126/sciadv.aay5478 (2019).

  9. Prebiotic Chemistry

    Conditions right for making nucleosides

    1. Michael A. Funk

    In the absence of biological catalysts and metabolism, can atmospheric and geochemical processes provide the substrates and conditions required for production of biological molecules? Becker et al. devised an abiotic synthetic scheme that allows for accumulation of both purine and pyrimidine nucleoside mono- and diphosphates (see the Perspective by Hud and Fialho). A key starting material for this chemistry, hydroxylamine and/or hydroxylamine disulfonate, can form under plausible early atmospheric conditions. Cycles between wet and dry conditions provide the environments necessary to complete formation of purine and pyrimidine bases essentially in one pot.

    Science, this issue p. 76; see also p. 32

  10. Song Learning

    An imitation circuit

    1. Sacha Vignieri

    Animals, including humans, rely heavily on imitation and social learning, yet we know little about how this process operates in the brain. Zhao et al. used optogenetic manipulation of a synaptic pathway connecting auditory and vocal motor circuits to implant song memories sufficient to guide song learning into young zebra finches (see the Perspective by Clayton). Activation of this circuit overrode learning from live tutors. These experiments define circuits essential for social learning of songs from tutors and show that such memories can be localized.

    Science, this issue p. 83; see also p. 33

  11. Intergalactic Medium

    Glowing filaments of the cosmic web

    1. Keith T. Smith

    Most gas in the Universe lies in the intergalactic medium, where it forms into sheets and filaments of the cosmic web. Clusters of galaxies form at the intersection of these filaments, fed by gas pulled along them by gravity. Although this picture is well established by cosmological simulations, it has been difficult to demonstrate observationally. Umehata et al. mapped emission from the intergalactic medium in an area around galaxies that are starting to form a cluster (see the Perspective by Hamden). They found that the gas is arranged into filaments, whose position and velocity correlate with star-forming galaxies, supporting the theoretical picture.

    Science, this issue p. 97; see also p. 31

  12. Quantum Physics

    A test of quantum gravity

    1. Ian S. Osborne

    Quantum mechanics and the general theory of relativity represent two pillars of modern physics, but unification of the two theories remains an open problem. Theories of quantum gravity abound, but they tend to lack an experimental foundation. One such proposed theory, event formalism, predicts that a pair of entangled particles decorrelate as they pass through different regions of the gravitational well of a planetary object. Xu et al. present results of a quantum optical test of this proposal using the quantum satellite Micius. Using entangled photon pairs, one sent to the satellite and the other retained on Earth, they find no evidence for the predicted decorrelation effects. The results may help shed light on the interplay between quantum theory and gravity.

    Science, this issue p. 132

  13. Forest Ecology

    Fungal influence on density dependence

    1. Andrew M. Sugden

    Tree species in highly diverse tropical forests tend to exhibit conspecific negative density dependence, a phenomenon whereby individuals of the same species tend to grow at a distance from one another. This is understood to be a key driver of species coexistence. The strength of negative density dependence varies between species, but the mechanisms driving this variation are unknown. Chen et al. studied tree species in a subtropical forest in China and found an important role for soil-dwelling fungi in this variation. Elevated accumulation of pathogenic fungi leads to stronger negative density dependence, whereas elevated accumulation of mutualistic fungi leads to weaker negative density dependence.

    Science, this issue p. 124

  14. Lipid Metabolism

    Distant cousin helps spot animal enzyme

    1. Michael A. Funk

    In addition to forming the membranes that enclose cells, lipids are important signaling molecules. Plasmalogens, which contain a vinyl ether linkage, are an abundant group of lipids in animals. How these lipids are synthesized from precursors with an alkyl ether linkage has been a mystery. Gallego-García et al. found an enzyme, CarF, in the social bacterium Myxococcus xanthus that produces plasmalogens used in a signaling pathway for singlet oxygen, a marker of photooxidative stress. They then showed that the animal homolog could catalyze the final step in plasmalogen synthesis in bacterial and human cells, thus resolving a source for plasmalogens in animals.

    Science, this issue p. 128

  15. Respiratory Enzymes

    Hemes switch spots in a terminal oxidase

    1. Michael A. Funk

    Reduction of molecular oxygen to water is the driving force for respiration in aerobic organisms and is catalyzed by several distinct integral membrane complexes. These include an exclusively prokaryotic enzyme, cytochrome bd–type quinol oxidase, which is a potential antimicrobial target. Safarian et al. determined a high-resolution cryo–electron microscopy structure of this enzyme from the enteric bacterium Escherichia coli. Comparison to a homolog reveals a complete relocation of the site of oxygen binding and reduction caused by a change in the arrangement of heme cofactors and channels in the protein scaffold. This switch illustrates the diversity of structure and function in this family of enzymes and might reflect different biochemical roles of these homologs.

    Science, this issue p. 100

  16. Chromatin Biology

    Twisting DNA to move it

    1. Gemma Alderton

    A key regulatory aspect of DNA is how tightly it is wrapped around nucleosomes, the histone cylinders that help package DNA. The exposure of DNA determines accessibility of proteins, such as transcription factors and DNA methyltransferases, which in turn regulate gene expression and cell identity. How can DNA be unwound from nucleosomes to modulate gene expression? In a Perspective, Bowman and Deindl discuss recent advances in understanding the mechanism by which DNA movement around nucleosomes occurs. Nucleosome remodelers pull on the DNA strands to influence how the helix is twisted, which allows the strands to move around the nucleosome. Similar mechanisms might also exist for other protein complexes that move along DNA.

    Science, this issue p. 35

  17. Systems Biology

    Protein competition drives cell fate

    1. L. Bryan Ray

    Cell survival can require switching mechanisms that are flexible enough to accommodate environmental changes but also stable for the required duration. Lord et al. created a switching system in bacteria based on stochastic competition between two proteins: one is a transcriptional repressor, and the other is an antagonist that binds the repressor and locks it in an inactive state. They show that this system controls switching of the bacterium Bacillus subtilis from a motile, unicellular state to an immobile, multicellular state, and that the control system is transferable to another distantly related bacterium. Similar mechanisms could be more widely operable in biological systems than previously recognized.

    Science, this issue p. 116

  18. Cancer Therapy

    Targeting a kidney cancer

    1. Leslie K. Ferrarelli

    People with von Hippel-Lindau syndrome, caused by loss of the gene VHL, are at an increased risk of developing clear cell renal cell carcinoma (ccRCC). Currently, drugs that inhibit the transcription factor HIF-2α show some efficacy but not in all patients. Nicholson et al. performed a screen to identify targets that limited tumor growth in a VHL double-knockout fly model. They discovered that inhibiting the cyclin-dependent kinases CDK4 and CDK6 together impaired tumor growth in this model regardless of HIF-2α dependency, and they confirmed these results in human ccRCC cells and patient-derived xenografts in mice.

    Sci. Signal. 12, eaay0482 (2019).

  19. Lymphocytes

    Sending B cells back in time

    1. Anand Balasubramani

    B-1 cells are a subset of self-reactive B cells that arise in early life. Precisely how and why the immune system permits the development of self-reactive B cells in neonates remains a mystery. By studying B cell development in neonatal mice, Vanhee et al. uncovered the importance of RNA binding protein Lin28b in facilitating positive selection of self-reactive B-1 cells in neonates. They also found that ectopic expression of Lin28b was sufficient to promote selection of self-reactive B-1 cells in adult mice. The authors propose that Lin28b functions as a cell-intrinsic switch that jumpstarts the generation of B cells in early life.

    Sci. Immunol. 4, eaax4453 (2019).

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