This Week in Science

Science  16 Aug 2019:
Vol. 365, Issue 6454, pp. 652
  1. Perovskites

    Strain-stabilized perovskites

    1. Phil Szuromi

    X-ray scattering images of a perovskite material (under) used in solar cells (overlay)


    The perovskite materials used for solar cells and light-emitting diodes (which are black in color) are generally less stable at room temperature than the electronically inactive nonperovskite phases (which are yellow in color). Steele et al. show that for CsPbI3, strain induced in a thin film after annealing the material to 330°C and then rapidly cooling it to room temperature kinetically trapped the black phase. Grazing-incidence wide-angle x-ray scattering revealed the crystal distortions and texture formation created by interfacial strain.

    Science, this issue p. 679

  2. Gravitation

    Gravitational redshift in the Galactic Center

    1. Keith T. Smith

    General relativity predicts that light emitted by an object in a strong gravitational field—for example, close to a black hole—should be shifted to longer wavelengths. This gravitational redshift does not exist in the Newtonian theory of gravity. Do et al. monitored the position and spectrum of the star S0-2 as it passed Sagittarius A*, the supermassive black hole at the center of the Milky Way. Around the closest part of S0-2's 16-year orbit, they detected the effect of gravitational redshift on its spectrum. These results are more consistent with general relativity than Newtonian gravity at the 5σ level.

    Science, this issue p. 664

  3. Optics

    Switching on quantum dot lasers

    1. Ian S. Osborne

    The optical properties of quantum dots can be tailored with alterations to their size and composition. Developing quantum dots as low-threshold laser sources requires overcoming problems associated with carrier recombination and stability. Kozlov et al. report success in this direction by demonstrating that a mix of processing and postsynthesis charging can overcome these problems. Synthesis of compositionally graded core-shell quantum dots followed by a carrier charging step provides stable, low-threshold lasing.

    Science, this issue p. 672

  4. Geochemistry

    Diamond window into the deep mantle

    1. Brent Grocholski

    Helium isotopes provide a window into the very deepest and oldest parts of Earth's voluminous mantle. However, several processes tend to obscure the helium isotope signal from reservoirs in basaltic lavas that have erupted at the surface. Timmerman et al. identified a set of diamonds that formed deep within Earth and were rapidly erupted, which have avoided near-surface contamination. They find evidence for a deep, primordial rock source along with mixing of sediments from old subducting plates. The signatures extracted from these diamonds have implications for chemical and dynamic models of Earth.

    Science, this issue p. 692

  5. Neuroscience

    Visualizing neuronal activity in vivo

    1. L. Bryan Ray

    Imaging the changes in fluorescence of voltage-sensitive reagents would enable monitoring of the activity of neurons in vivo. Abdelfattah et al. created such a voltage indicator by designing a protein that combines the voltage sensor domain from microbial rhodopsin with a domain that captures a dye molecule with exceptional brightness and photostability. When the protein was expressed in mice, flies, or zebrafish, they could monitor single action potentials in dozens of neurons simultaneously for many minutes.

    Science, this issue p. 699

  6. Metabolism

    Malleable muscle metabolism

    1. Wei Wong

    The effect of sex on physiological processes such as metabolism has not been sufficiently studied, despite signs that cellular-level processes can be sexually dimorphic. During fasting, skeletal muscles switch from using carbohydrates to fatty acids as a fuel source. Yang et al. found that fasting induced skeletal muscle in female mice to produce brain-derived neurotrophic factor (BDNF), a protein known for its role in synaptic plasticity and neuronal survival. Skeletal muscle deficiency of BDNF in female mice, but not in male mice, prevented this metabolic switch and resulted in myofiber necrosis and reduced muscle strength.

    Sci. Signal. 12, eaau1468 (2019).

  7. Engineering

    Decoding sweat to monitor health

    1. John Rogers

    Our sweat carries biomolecules, such as electrolytes, metabolites, and hormones, that can be used probe the state of our bodies at a chemical level. Nyein et al. developed a wearable microfluidic patch that captures sweat, which they used to predict whole-body fluid and electrolyte loss during exercise. Secretion rate and sodium levels show a positive correlation across regions of the body and among study subjects. Correlation between regional fluid loss and whole-body water loss could be used to track hydration status.

    Sci. Adv. 10.1126/sciadv.aaw9906 (2019).

  8. Robotics

    Lowering locomotion's metabolic cost

    1. Marc S. Lavine

    Walking and running require different gaits, with each type of motion putting a greater bias on different muscles and joints. Kim et al. developed a soft, fully portable, lightweight exosuit that is able to reduce the metabolic rate for both running and walking by assisting each motion via the hip extension (see the Perspective by Pons). A waist belt holds most of the mass, thus reducing the cost of carrying the suit. By tracking the motion of the user, the suit is able to switch modes between the two types of motion automatically.

    Science, this issue p. 668; see also p. 636

  9. Plant Science

    Less space but greater maize yield

    1. Pamela J. Hines

    To meet increasing demands for food, modern agriculture works with increasingly dense plantings. Tian et al. identified a gene in teosinte, the wild ancestor of maize, and used it to alter maize such that the plant has a narrower architecture that nonetheless allows leaves access to sunlight (see the Perspective by Hake and Richardson). The yield advantage only becomes evident with the high-density plantings characteristic of modern agriculture, perhaps explaining why this gene was not brought into the fold during the previous millennia of maize domestication.

    Science, this issue p. 658; see also p. 640

  10. Mitochondria

    Putting a price on the powerhouse

    1. Stella M. Hurtley

    Mitochondria—the so-called powerhouse of the cell—are derived from bacterial endosymbionts. This history provides opportunities and challenges for their host cells, particularly metazoans, including humans. Youle reviews the interplay between host and mitochondrial biology and highlights how mitochondrial ancestry has influenced innate immune responses. Keeping mitochondria both healthy and in check is key to organismal health and, when perturbed, leads to a variety of pathologies, including Parkinson's disease and inflammation.

    Science, this issue p. eaaw9855

  11. Astrochemistry

    Enhanced abundance of primordial HeH+

    1. Yury Suleymanov

    Though only recently detected in space, the helium hydride ion (HeH+) is thought to be the first molecule ever to have formed in the early Universe. Novotný et al. report state-specific rate coefficients for the dissociative reaction of HeH+ with electrons, obtained using a cryogenic ion storage ring combined with a merged electron beam (see the Perspective by Bovino and Galli). They detect substantial rotational dependence and a decrease of the rates for the lowest states of HeH+, far below the values listed in astrochemistry databases and those previously applied in early-Universe models. These results suggest high abundance of this important primordial molecule at redshifts of first star and galaxy formation.

    Science, this issue p. 676; see also p. 639

  12. Superconductivity

    An unusual superconductor

    1. Jelena Stajic

    In conventional, and in many unconventional, superconductors, the electrons that form Cooper pairs have spins pointing in opposite directions. An applied magnetic field can easily “break” such pairs—and destroy superconductivity—by aligning both spins in the same direction. In contrast, spin-triplet superconductors are much more resilient to magnetic fields. Very few candidates for such materials have been discovered. Ran et al. add to this select group by observing signatures of spin-triplet superconductivity, including a very large and anisotropic upper critical magnetic field, in the material UTe2. Because spin-triplet superconductors may naturally exhibit topological superconductivity, this material may also be of interest in quantum computing.

    Science, this issue p. 684

  13. Solar Cells

    Strong perovskite interfaces

    1. Phil Szuromi

    The weak bonding in the crystal lattice of hybrid perovskites used in solar cells promotes surface decomposition and interferes with the formation of stable heterostructures with the charge carrier layers. Y. Wang et al. show that strong bonds are formed between lead and both chlorine and oxygen atoms in a film with a lead-rich surface and a chlorinated graphene oxide layer. This interface was used with common hole-transporting materials to fabricate solar cells that maintained 90% of their initial efficiency of 21% after operation at 60°C for 1000 hours.

    Science, this issue p. 687

  14. Neuroscience

    A newly discovered cell type for pain perception

    1. Peter Stern

    Pain has been thought to be initiated by activation of free nerve endings without end organs in the skin. In contrast to this paradigm, Abdo et al. discovered a previously unknown meshlike organ covering the skin that senses dangerous environmental stimuli (see the Perspective by Doan and Monk). This organ is built from specialized glial cells located in the epidermal-dermal border and is sufficient and required for initiation of mechanical pain transduction.

    Science, this issue p. 695; see also p. 641

  15. Cell Biology

    Active migration renews gut epithelia

    1. Stella M. Hurtley

    Epithelial tissues are continuously renewed throughout adult life, and the gut epithelium is the fastest self-renewing tissue in mammals. Over 3 days or so, epithelial cells migrate from the crypts, where they are born, to the tips of the villi, where they die. It is commonly believed that migration is strictly passive, driven by mitotic pressure in crypts—as cells divide, they push their neighbors upward. Krndija et al. now challenge this concept and show that cells migrate actively, using actin-rich basal protrusions oriented in the direction of migration (see the Perspective by Jansen).

    Science, this issue p. 705; see also p. 642

  16. Immune Signaling

    A nuclear sensor of viral DNA?

    1. Seth Thomas Scanlon

    A signaling pathway in eukaryotes known as cGAS–STING recognizes the presence of cytosolic DNA, which alerts the immune system to viral infection or cellular damage. However, the majority of DNA viruses direct their genomic DNA into nuclei, suggesting that nuclear-specific sensing is also needed. L. Wang et al. find that during herpes simplex virus–1 infection, heterogeneous nuclear ribonucleoprotein A2B1 forms a complex with viral DNA, homodimerizes, and is demethylated. These events result in translocation of the complex to the cytosol and activation of the immune system through type I interferon signaling. Additionally, the complex promotes N6-methyladenosine modification and translocation of cGAS–STING–related mRNAs after DNA virus infection, further amplifying the immune response.

    Science, this issue p. eaav0758

  17. Environment

    Watch out for river nutrient imbalances

    1. Julia Fahrenkamp-Uppenbrink

    Input of excess nutrients, such as nitrogen and phosphorus, into a body of water can cause excessive growth of algae. This eutrophication has occurred in fresh waters all around the world as a result of human activities. Efforts to reduce nutrient inputs have been effective, but as Ibáñez and Peñuelas explain in a Perspective, greater reductions in phosphorus than in nitrogen are leading to nutrient imbalances that can also have negative ecological impacts. Most studies have focused on lakes or smaller streams, but recent work is beginning to explore the profound effects of these changes in rivers.

    Science, this issue p. 637

  18. Cancer Immunology

    Enhanced inhibitor

    1. Christiana N. Fogg

    Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) block oncogenic receptor signaling and are used as a first-line treatment for EGFR-mutated non–small cell lung cancer. Resistance to EGFR TKIs, including the standard hyperfractionated EGFR TKI treatment (HyperTKI), is a problem that has driven the development of next-generation inhibitors. Liu et al. describe the improved efficacy of hypofractionated EGFR TKI treatment (HypoTKI) relative to HyperTKI in triggering antitumor T cell responses and preventing relapse in a TKI-sensitive syngeneic murine tumor model through a mechanism involving immune signaling pathways. Coadministration of HypoTKI with an immunotherapy antibody further improved antitumor responses and reduced tumor relapse, thus suggesting that this combined therapy may be a potential alternative to existing treatment regimens.

    Sci. Immunol. 4, eaav6473 (2019).

  19. Alzheimer's Disease

    An appetite for memory

    1. Mattia Maroso

    The hippocampus serves a critical role in memory formation and cognition. Hippocampal lesions are among the earliest changes in Alzheimer's disease (AD); however, the molecular mechanisms responsible for these alterations remain unclear. Using autoptic brain samples from patients with AD and a mouse model of AD, Tian et al. show that in the hippocampus, pathologic β-amyloid directly binds and inhibits the receptor for the “hunger hormone” ghrelin (GHSR1α). In the animal model, the binding blocked the GHSR1α-mediated dopamine receptor D1 (DRD1) activation, leading to synaptic plasticity impairments and memory loss. Simultaneous pharmacological activation of GHSR1α and DRD1 rescued synaptic plasticity and spatial memory in AD mice.

    Sci. Transl. Med. 11, eaav6278 (2019).

  20. Neuroscience

    Sharp-wave ripples in the hippocampus

    1. Peter Stern

    What are the brain mechanisms responsible for episodic memory retrieval? Norman et al. investigated epilepsy patients who had electrodes implanted in the hippocampus and a variety of cortical areas. Using a visual learning paradigm, they examined the temporal relationship between the incidence of hippocampal sharp-wave ripples and recall. Effective encoding of visual information was associated with higher incidence of ripples. Successful recall was preceded by an increased probability of ripples, which were also associated with transient reemergence of activation patterns in higher visual cortical areas. Hippocampal ripples may thus boost recollections during episodic memory retrieval.

    Science, this issue p. eaax1030