This Week in Science

Science  12 Apr 2019:
Vol. 364, Issue 6436, pp. 141
  1. Trophic Cascades

    Ecosystems feel war's effects

    1. Sacha Vignieri

    A pack of African wild dogs (Lycaon pictus) takes advantage of a rural road in the Gorongosa National Park in Mozambique.

    PHOTO: BRETT KUXHAUSEN, GORONGOSA MEDIA

    War ravages human lives and landscapes, but nonhuman victims are no less affected. The Mozambican Civil War resulted in the rapid decline of predators in Gorongosa National Park and led to a trophic cascade that shifted prey behaviors and plant communities. Atkins et al. monitored this shift and found that the absence of wild dogs and leopards resulted in a change in habitat use and plant consumption by bushbuck, which are forest-dwelling antelopes. Experiments further showed that changes in prey behavior were reversible when signs of predator activity were introduced, supporting the impact of the predator loss. These results confirm patterns seen elsewhere and go further in providing mechanistic detail about the importance of the “landscape of fear” perceived by prey animals.

    Science, this issue p. 173

  2. Structural Biology

    Bone-cell regulation, fleshed out

    1. L. Bryan Ray

    One of many medically relevant G protein–coupled receptors, parathyroid hormone receptor-1 (PTH1R) functions in the control of calcium homeostasis and bone physiology. Zhao et al. used cryo–election microscopy to observe the structure of PTH1R in a complex with a modified form of parathyroid hormone and stimulatory G protein. The structural model helps explain how parathyroid hormone interacts with its receptor and the molecular basis for receptor activation.

    Science, this issue p. 148

  3. Graphene

    Electron hydrodynamics in graphene

    1. Jelena Stajic

    Electrons can move through graphene in a manner reminiscent of fluids, if the conditions are right. Two groups studied the nature of this hydrodynamic flow in different regimes (see the Perspective by Lucas). Gallagher et al. measured optical conductivity using a waveguide-based setup, revealing signatures of quantum criticality near the charge neutrality point. Berdyugin et al. focused on electron transport in the presence of a magnetic field and measured a counterintuitive contribution to the Hall response that stems from hydrodynamic flow.

    Science, this issue p. 158, p. 162; see also p. 125

  4. Thin Films

    Epitaxial films through spin coating

    1. Phil Szuromi

    A simple way to coat a surface with a uniform film is by spin coating. The substrate is spun at high speed, and a droplet of solution containing the coating is added at the center, spreads out, and evaporates. This method is used to make polycrystalline inorganic coatings and amorphous films, such as polymers used in lithography. Kelso et al. performed spin coating with single-crystal substrates, carefully controlling the thickness of the spreading solution on the basis of its viscosity and the rotation rate. In this way, they achieved epitaxial growth—in which the crystallites are oriented by the substrate—for perovskites, zinc oxide, and sodium chloride.

    Science, this issue p. 166

  5. Glacial Cycles

    Controlling cooling

    1. H. Jesse Smith

    On million-year time scales, Earth's climate state is determined by sources and sinks of carbon to the ocean-atmosphere system. But which specific mechanisms are important in controlling the timing of glacial intervals? Macdonald et al. identify arc-continent collisions in the tropics as a primary control (see the Perspective by Hartmann). They compiled a database of Phanerozoic arc-continent collisions and the latitudinal distribution of ice sheets, showing that ice coverage was greatest when those collisions were most widespread, maximizing global weatherability.

    Science, this issue p. 181; see also p. 126

  6. Heart Regeneration

    The price of staying warm

    1. Beverly A. Purnell

    Among vertebrates, zebrafish and salamanders can regenerate their hearts, whereas adult mice and humans cannot. Hirose et al. analyzed diploid cardiomyocyte frequency as a proxy for cardiac regenerative potential across 41 vertebrate species (see the Perspective by Marchianò and Murry). They observed an inverse correlation of these cells with thyroid hormone concentrations during the ectotherm-to-endotherm transition. Mice with defects in thyroid hormone signaling retained significant heart regenerative capacity, whereas zebrafish exposed to excessive thyroid hormones exhibit impaired cardiac repair. Loss of heart regenerative ability in mammals may represent a trade-off for increases in metabolism necessary for the development of endothermy.

    Science, this issue p. 184; see also p. 123

  7. Evolutionary Biology

    Adaptation by way of compromise

    1. Laura M. Zahn

    Many plants rely on animal pollinators to spread pollen and increase the genetic diversity of their offspring. However, there are trade-offs, because attracting pollinators may also attract herbivores and deterring predation may diminish floral displays. Ramos and Schiestl studied the interplay between mating system, flowers, and chemical defenses over several generations in Brassica rapa plants (see the Perspective by Ågren). Evolution driven by pollination and herbivory can be observed after only eight generations, suggesting that trade-offs have large evolutionary consequences.

    Science, this issue p. 193; see also p. 122

  8. Bacterial Infections

    Friend turned foe

    1. Orla M. Smith

    Enterococci are commensal bacteria found in the gut of most humans, but strains adapted to survival in the bloodstream can be deadly. Because these bacteria spread patient-to-patient in hospitals, their adaptation can be tracked. Van Tyne et al. analyzed the genomes of enterococcal strains from an outbreak of bloodstream infection in a hospital in the mid-1980s. Genetic changes gradually accumulated in the enterococci to allow evasion of the host innate immune system and harden them against antibiotic therapy.

    Sci. Transl. Med. 11, eaat8418 (2019).

  9. Engineering

    Pulling water from air

    1. Lynden Archer,
    2. Kollen Post

    The scarcity of fresh water is a global problem in need of energy-efficient solutions. Sadeghpour et al. developed a dehumidifier that takes advantage of capillary instabilities produced by water's high surface tension to create water beads flowing down an array of cotton threads. The high surface area of the beads and the intrinsic low resistance to air flow yields devices that are very efficient in condensing water vapor carried in humid air.

    Sci. Adv. 10.1126/sciadv.aav7662 (2019).

  10. Human Physiology

    What to expect after a year in space

    1. Laura M. Zahn

    Space is the final frontier for understanding how extreme environments affect human physiology. Following twin astronauts, one of which spent a year-long mission on the International Space Station, Garrett-Bakelman et al. examined molecular and physiological traits that may be affected by time in space (see the Perspective by Löbrich and Jeggo). Sequencing the components of whole blood revealed that the length of telomeres, which is important to maintain in dividing cells and may be related to human aging, changed substantially during space flight and again upon return to Earth. Coupled with changes in DNA methylation in immune cells and cardiovascular and cognitive effects, this study provides a basis to assess the hazards of long-term space habitation.

    Science, this issue p. eaau8650; see also p. 127

  11. Plant Science

    Glycosylation goes back and forth

    1. Pamela J. Hines

    Plants produce receptors that recognize fragments of microbial flagellin, thus monitoring for infection by bacteria. Buscaill et al. studied how a flagellin fragment is made accessible for recognition by host glycosidases, which degrade the glycosylations shielding the peptide that triggers the immune response. The pathogen, in turn, evades detection by altering flagellin glycosylation and inhibiting the host glycosidase. This aspect of plant defense against infection plays out in the apoplast, the extracellular space within plant tissues.

    Science, this issue p. eaav0748

  12. Neuroscience

    Improved agonists for chemogenetics

    1. Peter Stern

    Targeting ligand-responsive receptors to specific groups of cells, a strategy known as chemogenetics, is a powerful tool in many neurological applications. There is increasing interest in extending these tools for human treatment. Magnus et al. designed chemogenetic ion channels that improve currently available systems and are activated by the clinically used antismoking drug varenicline. They engineered a ligand-binding domain less responsive to endogenous signals and identified agonists that function at nanomolar concentrations. The combination of drug and introduced channels transiently silenced neurons, with slow but effective washout, and induced behavioral changes in animal models after brain administration.

    Science, this issue p. eaav5282

  13. Neuroscience

    Why is ketamine an antidepressant?

    1. Peter Stern

    A better understanding of the mechanisms underlying the action of antidepressants is urgently needed. Moda-Sava et al. explored a possible mode of action for the drug ketamine, which has recently been shown to help patients recover from depression (see the Perspective by Beyeler). Ketamine rescued behavior in mice that was associated with depression-like phenotypes by selectively reversing stress-induced spine loss and restoring coordinated multicellular ensemble activity in prefrontal microcircuits. The initial induction of ketamine's antidepressant effect on mouse behavior occurred independently of effects on spine formation. Instead, synaptogenesis in the prefrontal region played a critical role in nourishing these effects over time. Interventions aimed at enhancing the survival of restored synapses may thus be useful for sustaining the behavioral effects of fast-acting antidepressants.

    Science, this issue p. eaat8078; see also p. 129

  14. Physics

    Graphene: Driven to emission

    1. Ian S. Osborne

    Studying the electronic properties of graphene under extreme nonequilibrium conditions has provided a productive testbed to probe and monitor exotic transport phenomena. Andersen et al. report measurements of electron transport in ultraclean graphene devices where the electron drift velocity is extremely high. They found that direct current at high drift velocities generates a large increase in the noise at gigahertz frequencies and that the noise grows exponentially in the direction of the current. The authors attribute the emission mechanism to amplification of acoustic phonons through the Cerenkov effect.

    Science, this issue p. 154

  15. Physics

    Making heat stand still

    1. Ian S. Osborne

    Dissipative oscillating systems (waves) can be described mathematically in terms of non-Hermitian physics. When parity-time symmetric systems have dissipative components, the interplay between gain and loss can lead to unusual and exotic behavior. Li et al. show theoretically and demonstrate experimentally that such behavior need not be limited to wave systems. Looking at the diffusion of heat, they devised an experimental setup comprising two thermally coupled disks rotating in opposite directions. The thermal energy transported by each disk is strongly coupled to the disk rotating in the opposite direction, providing a return path for the heat wave. For a particular rotation rate, there is an exceptional point where thermal coupling and counterrotating motion balance, resulting in the thermal energy profile being stationary over time.

    Science, this issue p. 170

  16. Plant Science

    A fatty acid triggers immune responses

    1. Pamela J. Hines

    Plants and animals respond to the microbial communities around them, whether in antagonistic or mutualistic ways. Some of these interactions are mediated by lipopolysaccharide—a large, complex, and irregular molecule on the surface of most Gram-negative bacteria. Studying the small mustard plant Arabidopsis, Kutschera et al. identified a 3-hydroxydecanoyl chain as the structural element sensed by the plant's lectin receptor kinase. Indeed, synthetic 3-hydroxydecanoic acid alone was sufficient to produce a response. A small microbial metabolite may thus suffice to trigger immune responses.

    Science, this issue p. 178

  17. Signal Transduction

    Deubiquitinase fine-tunes Notch signaling

    1. L. Bryan Ray

    The branching of blood vessels is controlled in part by signaling through Notch receptor proteins. When NOTCH1 binds its ligand DLL4, the intracellular domain (NICD1) is cleaved from the receptor and works with other proteins to regulate gene transcription. In a screen for proteins that interacted with NICD1 in human cells in culture, Lim et al. identified the deubiquitinase USP10. NICD1 is rapidly ubiquitinated and degraded in cells, but interaction of NICD1 with USP10 counteracts ubiquitination of NICD1 and stimulates Notch signaling. Genetic experiments in mice support a role for USP10 in fine-tuning Notch signaling during vascular morphogenesis.

    Science, this issue p. 188

  18. Immunotherapy

    Refocusing to target neurodegeneration

    1. Gemma Alderton

    Given the success of immune checkpoint blockade in treating certain types of cancer and preclinical data connecting immune responses and neurodegeneration, might neurodegenerative disease be a viable future target of immunotherapy? In a Perspective, Liu and Aguzzi express words of caution about this approach, asserting that we do not yet know whether immune checkpoint blockade improves cognitive impairment that results from neurodegeneration. Instead, they suggest targeting inflammatory immune responses in the brain as a more promising approach consistent with preclinical data.

    Science, this issue p. 130

  19. Autoimmunity

    Superagonist diabetogenic peptides

    1. Ifor Williams

    Type 1 diabetes is an autoimmune disease triggered in part by activation of CD4+ T cells specific for insulin-derived autoantigens. Wang et al. prepared ternary complexes of a diabetogenic T cell receptor with insulin B-peptides and major histocompatibility complex class II proteins known to be associated with genetic susceptibility to diabetes. Fusion peptides with a covalent linkage of the carboxyl terminus of an insulin B-chain peptide to specific fragments of insulin C-peptide were highly potent ligands, enabling avid binding of both mouse and human T cell receptors. Transpeptidation reactions in lysosomes may therefore be a potential source of superagonist chimeric insulin peptides and play an important driver role in autoimmune diabetes.

    Sci. Immunol. 4, eaav7517 (2019).

  20. Calcium Sensing

    STIMulating basophils

    1. Erin Williams

    The endoplasmic reticulum–resident calcium sensors STIM1 and STIM2 promote store-operated calcium entry, which is required for immune cell function. Using conditional knockout mice, Yoshikawa et al. found that the development of antigen-dependent allergic inflammation required STIM1 expression in basophils, but the response to a combination of the cytokines interleukin-3 and -33 required basophil expression of STIM2 (see the Focus by Alansary and Niemeyer). These results suggest that the STIM proteins in basophils have distinct roles in mediating responses to antigens or cytokines.

    Sci. Signal. 12, eaav2060, eaax0210 (2019).

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