This Week in Science

Science  25 Aug 2017:
Vol. 357, Issue 6353, pp. 768
  1. Environmental Health

    Arsenic-contaminated drinking water

    1. Kip Hodges

    A drinking-water well in Pakistan


    In many parts of the world, the contamination of groundwater by the natural leaching of arsenic from surrounding rocks poses an important public health threat. Podgorski et al. generated systematic hazard and risk maps for arsenic contamination of groundwater in Pakistan. Much of the drinking water in the vast Indus River plain is likely contaminated with unsafe levels of arsenic, placing roughly 50 to 60 million people at risk of arsenic poisoning. Comprehensive testing of drinking water wells in the Indus River plain is thus required, and changes are needed to mitigate unsafe conditions.

    Sci. Adv. 10.1126/sciadv.1700935 (2017).

  2. Energy Harvesting

    Making the most of twists and turns

    1. Marc S. Lavine

    The rise of small-scale, portable electronics and wearable devices has boosted the desire for ways to harvest energy from mechanical motion. Such approaches could be used to provide battery-free power with a small footprint. Kim et al. present an energy harvester made from carbon nanotube yarn that converts mechanical energy into electrical energy from both torsional and tensile motion. Their findings reveal how the extent of yarn twisting and the combination of homochiral and heterochiral coiled yarns can maximize energy generation.

    Science, this issue p. 773

  3. Immunology

    Tolerogenic T cells need probiotics

    1. Seth Thomas Scanlon

    CD4+CD8αα+ double-positive intraepithelial lymphocytes (DP IELs) are a recently discovered class of intestinal T cells believed to take part in a variety of immune responses, including oral tolerance. These cells are absent in germ-free mice, but the mechanisms driving their development are unclear. Cervantes-Barragan et al. found that a particular species of probiotic bacteria, Lactobacillus reuteri, induces DP IELs. This does not occur by stimulating the immune system directly. Instead, L. reuteri generates a specific derivative of dietary tryptophan that promotes differentiation of DP IEL precursors. These findings underscore the delicate interplay between benign bacteria, diet, and gut health.

    Science, this issue p. 806

  4. Surface Science

    Imaging surfaces with water

    1. Phil Szuromi

    The surfaces of real materials are often highly chemically heterogeneous, and the reported values of even simple properties such as surface acidity can vary widely in many cases. Macias-Romero et al. developed a microscope that images surfaces on the basis of second-harmonic generation from the orientation of interfacial water (see the Perspective by Hunger and Parekh). They followed the deprotonation of silica along glass micropipettes by changing solution pH and found many regions where the surface acidity deviated strongly from the average for the entire micropipette.

    Science, this issue p. 784; see also p. 755

  5. Development

    Mechanics of follicle patterning in skin

    1. Beverly A. Purnell

    Studies of skin organogenesis have presupposed that a periodic molecular prepattern is responsible for the initiation of a periodic pattern of hair or feathers. To date, however, these initiating molecules have remained elusive. Using chicken skin as a model system, Shyer et al. found that the periodic spacing of feathers is triggered by mechanical rather than molecular events (see the Perspective by Grill). Furthermore, these mechanical events shape both the structure of prefeathers and their molecular identity.

    Science, this issue p. 811; see also p. 750

  6. Structural Biology

    Adapting to the right light

    1. Valda Vinson

    In plants, photosystem II is the first protein complex in the machinery that converts sunlight into chemical energy. It comprises antennae complexes (LHCIIs), which collect the light energy, and a dimeric core that contains the reaction center where water is split into oxygen and protons. Su et al. report cryo-electron microscopy structures of a supercomplex consisting of the dimeric core, two strongly bound LHCIIs, and two moderately bound LHCIIs (see the Perspective by Croce and van Amerongen). Under high-light conditions, the moderately bound LHCIIs might detach to down-regulate the efficiency of light harvesting and prevent damage.

    Science, this issue p. 815; see also p. 752

  7. Infectious Disease

    For Zika virus, experience counts

    1. Angela Colmone

    For the immune system, practice makes perfect. Previous exposure to an infection elicits a stronger, faster memory response. But how does the immune system respond to a similar but not identical infection? Rogers et al. tracked the neutralizing antibody response to Zika virus infection in individuals with and without previous exposure to the closely related dengue viruses. Zika virus infection primed the preexisting dengue virus response, but this cross-reactive response was poorly neutralizing. In contrast, de novo Zika virus responses were potently neutralizing. Thus, Zika virus vaccines should target epitopes that dengue virus subtypes lack.

    Sci. Immunol. 2, eaan6809 (2017).

  8. Microbiota

    Seasonal diets, seasonal microbiota

    1. Caroline Ash

    Among the Hadza of western Tanzania, a few hundred people still live in small groups as hunter-gatherers, reliant solely on the wild environment for food. Smits et al. found that the microbiota of these people reflects the seasonal availability of different types of food (see the Perspective by Peddada). Between seasons, striking differences were observed in their gut microbial communities, with some taxa apparently disappearing, only to reappear when the seasons turned. Further comparison of the Hadza microbiota with that of diverse urbanized peoples revealed distinctly different patterns of microbial community composition.

    Science, this issue p. 802; see also p. 754

  9. Neuroscience

    Brain mechanisms of pitch perception

    1. Peter Stern

    To emphasize a word, we briefly raise our pitch; this alone can change the meaning of a sentence. Tang et al. performed high-density brain recordings on clinically monitored neurosurgical patients. They discovered that intonational pitch is represented by a highly specialized and dedicated neural population in the auditory cortex. Discrete cortical sites extracted intonational information in real time from the speech signal. These sites were overlapping with, but functionally independent from, sites that encode other critical aspects of speech, such as the phonemes and information about the speaker.

    Science, this issue p. 797

  10. Vascular Biology

    Dynamic vascular surfaces

    1. Beverly A. Purnell,
    2. Caroline Ash

    Blood vessels have long been considered as passive conduits for blood and circulating cells that, at best, respond to exogenous cytokines. However, recent work has shown that blood vessels serve as a highly dynamic interface between the circulation and tissues. Augustin and Koh review molecular mechanisms of vascular development and function in different organs. Differentiated endothelial cells develop as a sort of cobblestone monolayer to form one of the largest surfaces within the body. Vascular control of the tissue microenvironment is vital, not only for normal tissue development and homeostasis, but also for disease states ranging from inflammation to cancer.

    Science, this issue p. eaal2379

  11. Cell Biology

    Actin helps chromosome segregation in eggs

    1. Stella M. Hurtley

    Spindle microtubules are well known to orchestrate the segregation of chromosomes during egg development. But the other major cytoskeletal component, actin, has not been thought to play a role in this process. Mogessie and Schuh examined how chromosomes are segregated in mammalian cells (see the Perspective by Maiato and Ferrás). Instead of using an entirely microtubule-dependent mechanism, mammalian oocytes use a second spindle that is made of F-actin to segregate their chromosomes correctly. Actin associated with the spindle bundles microtubules into functional kinetochore fibers, the key structures that drive chromosome segregation. Increasing or decreasing the number of actin filaments in the spindle causes an imbalance in kinetochore fiber bundling, which results in chromosome segregation errors and aneuploidy, a frequent cause of miscarriage and Down syndrome in humans.

    Science, this issue p. eaal1647; see also p. 756

  12. Cancer

    A virus and its reinforcement

    1. Yevgeniya Nusinovich

    Oncolytic viruses can be effective against a variety of cancers, including hepatocellular carcinoma, for which a viral treatment is showing evidence of efficacy in people. Zhang et al. performed a high-throughput drug screen to search for compounds to pair with an oncolytic virus called M1 to further increase its effectiveness against hepatocellular carcinoma. They identified inhibitors of valosin-containing protein, then used them together with M1 and demonstrated the efficacy of this regimen in mouse models of cancer. Furthermore, the combination was well tolerated in primates, suggesting that the drug and virus combination may translate to human patients.

    Sci. Transl. Med. 9, eaam7996 (2017).

  13. Membranes

    Go with the flow

    1. Marc S. Lavine

    Enhanced water transport occurs in a number of narrow pore channels, such as biological aquaporins. Tunuguntla et al. thoroughly characterized molecular transport through narrow carbon nanotubes (CNTs) (see the Perspective by Siwy and Fornasiero). In contrast to previous studies, the authors focused on water and ion transport through relatively short (∼10-nm) fragments of CNTs embedded in lipid bilayer membranes. Strong confinement generated highly accelerated water flow compared with that observed in biological water transporters. A key factor in the transport rate was the tunable rearrangement of intermolecular hydrogen bonding. Furthermore, by changing the charges at the mouth of the nanotube, the authors were able to alter the ion selectivity.

    Science, this issue p. 792; see also p. 753

  14. Fluid Mechanics

    Tackling the life and death of whirls

    1. Brent Grocholski

    Energy in a turbulent system moves from large eddies to smaller ones until it is dissipated by viscous motion. The details of exactly how this works have remained obscure, in part because of the challenge of simulating fluids across many length scales in three dimensions over time. Cardesa et al. present a large numeric simulation of a water-like fluid that shows characteristic length scales for the birth and death of turbulent whirls. The approach can be extended to understand energy transfer in the atmosphere, plasmas, and other complex systems.

    Science, this issue p. 782

  15. Nanomaterials

    Cycling 2D crystal growth

    1. Phil Szuromi

    The electronic and optical properties of two-dimensional (2D) transitional metal dichalcogenides such as MoS2 and WSe2 could be modulated by creating in-plane superlattices and heterostructures from these materials. However, single layers of these materials are fragile and often do not withstand the processing conditions needed during subsequent growth steps. Zhang et al. developed a reverse-flow reactor that avoids thermal degradation and unwanted crystal nucleation. They demonstrate several examples of block-by-block epitaxial growth, such as 2D heterostructures where MoS2 surrounds a WS2 core and superlattices where the composition alternates between WS2 and WSe2.

    Science, this issue p. 788

  16. Neuroscience

    YAP supports dopaminergic neurons

    1. Leslie K. Ferrarelli

    Patients with Parkinson's disease experience progressive loss of dopaminergic neurons and motor control. Zhang et al. found that the transcriptional cofactor YAP promoted dopaminergic neuronal survival in mice. YAP was activated upon binding of the extracellular matrix protein laminin-511 to an integrin. YAP then transcriptionally activated differentiation factors and a microRNA that decreased the levels of the apoptotic protein PTEN. These findings uncover a previously unknown role for YAP in neurons and a pathway that could promote dopaminergic neuronal survival in patients with Parkinson's disease.

    Sci. Signal. 10, eaal4165 (2017).

  17. Organic Chemistry

    Slicing through both C-C and C-H bonds

    1. Jake Yeston

    A variety of catalysts can cleave the strained bonds in four-membered carbon rings and then link the ends to a reactive partner. Bender et al. found that after prying the ring open, a double-duty ruthenium catalyst could forge bonds to a traditionally unreactive partner. They used the reaction to couple cyclobutenones to adjacent saturated carbon centers in diols. This approach efficiently yielded a motif common in polyketide natural products. The reaction proceeds through dehydrogenation and is also amenable to coupling the opened rings to ketol or dione reagents.

    Science, this issue p. 779