This Week in Science

Science  23 Jun 2017:
Vol. 356, Issue 6344, pp. 1243
  1. Solar Physics

    Understanding the formation of spicules

    1. Keith T. Smith

    Small jets, or spicules, in the solar atmosphere

    PHOTO: SST/ROYAL SWEDISH ACADEMY OF SCIENCES/LMSAL/WIKIMEDIA COMMONS

    Spicules are small jets lasting a few minutes that form in the solar atmosphere and propel hot plasma upward from the visible surface. The underlying physics of spicules is not well understood. Martínez-Sykora et al. developed radiation-magnetohydrodynamic simulations that can spontaneously produce numerous spicules with properties that match observations. Interactions between large-scale magnetic fields and the plasma, such as ambipolar diffusion, drive the formation process and subsequent evolution. Understanding how spicules form will help assess how much they heat the solar corona and how they relate to other solar phenomena.

    Science, this issue p. 1269

  2. Cardiac Fibrosis

    Lnc-ing fibroblasts to cardiac fibrosis

    1. Caitlin Czajka

    Therapies for cardiac injury typically focus on cardiomyocytes, the contractile cells of the heart. But cardiac fibroblasts can play a key role in the pathogenesis of heart failure by depositing extracellular matrix to compensate for reduced cardiac function. Micheletti et al. identified a long noncoding RNA (lncRNA), Wisper, that is enriched in cardiac fibroblasts and up-regulated in infarcted mouse heart tissue. They treated mice with anti-sense oligonucleotides to Wisper after infarction, when fibrosis was already initiated; treatment reduced the expression of matrix proteins, decreased tissue remodeling, and improved cardiac function and survival. WISPER expression was increased in tissue samples from patients with aortic stenosis and correlated with collagen volume fraction and severity of fibrosis. Fibroblast-specific lncRNAs may thus be useful targets for fibrosis therapies.

    Sci. Transl. Med. 9, eaai9118 (2017).

  3. Optomechanics

    Quantum effects in ambient conditions

    1. Jelena Stajic

    Quantum back action—the “reaction” of a quantum mechanical object to being measured—is normally observed at cryogenic temperatures, where it is easier to distinguish from thermal motion. Purdy et al. managed to tease out the effects of quantum back action at room temperature by using a mechanical oscillator and probing it with light (see the Perspective by Harris). The fluctuations of the force produced by the light probe caused correlated changes to the motion of the oscillator and the properties of the transmitted light. These correlations revealed the effects of the back action, which allows the system to be used as a quantum thermometer.

    Science, this issue p. 1265; see also p. 1232

  4. Microcompartments

    How to make a protein-based nanocontainer

    1. Stella M. Hurtley

    Bacterial microcompartments are to bacteria what membrane-bound organelles are to eukaryotic cells. They are specialized subcellular compartments for colocalizing enzymes to enhance reaction rates, protect sensitive proteins, and sequester toxic intermediates. Sutter et al. determined the atomic-resolution structure of a complete 6.5-megadalton bacterial microcompartment shell. The shell is composed of hundreds of copies of five distinct proteins that form hexamers, pentamers, and three types of trimers. The assembly principles revealed by the structure provide the basis to rationally manipulate self-assembly in native and engineered systems and could help, for example, in the design of subcellular nanoreactors.

    Science, this issue p. 1293

  5. Evolution

    The influence of flying

    1. Sacha Vignieri

    Although birds' eggs are generally ovoid in shape, there is considerable variation in the degree to which they are symmetrical, round, or bottom-heavy. Many hypotheses have been put forward to explain what has driven this variation, with many accepting life history or nesting explanations. Stoddard et al. looked at nearly 50,000 eggs from more than 1400 species from morphological, biophysical, and evolutionary perspectives and found little support for previous hypotheses (see the Perspective by Spottiswoode). Instead, their results suggest that selection for flight adaptations is most likely to be responsible for the variation.

    Science, this issue p. 1249; see also p. 1234

  6. Engineering

    Instant tough bonding of hydrogels

    1. Lynden A. Archer

    Tough cyanoacrylate hydrogels bond within minutes.

    PHOTO: SOFT ELECTRONICS LABORATORY/LINZ INSTITUTE OF TECHNOLOGY

    Soft electronic devices, including electronic skin, adaptive lenses, and stretchable batteries, are made possible through the use of tough, water-laden hydrogels that instantly bond to plastics, metals, and bone. Wirthl et al. blended cyanoacrylate-based adhesives that are dispersed in alkanes with either conventional or newer types of hydrogels. They used these to produce materials that form heavy-duty bonds with hard or soft materials in a matter of minutes. The materials take advantage of fast interdiffusion of cyanoacrylate-alkane mixtures and hydrogels and facile hydrogen bond formation between cyanoacrylates and hard or soft substrates. Potential applications range from robotics to wearable electronics to energy-harvesting technology.

    Sci. Adv. 10.1126/sciadv.1700053 (2017).

  7. Signal Transduction

    PKA-activation mechanism revised

    1. L. Bryan Ray

    Many hormone receptors stimulate production of cyclic AMP (adenosine monophosphate), which activates PKA (protein kinase A). The textbook view suggests that activation releases the catalytic subunit of the enzyme from its complex with the regulatory subunit. Smith et al. closely monitored activation of PKA in cultured human cells and found that dissociation of the holoenzyme was not necessary for activation. The kinase, which binds anchoring proteins that localize it in the cell, appears to be restricted to acting within about 200 Å of such anchoring proteins. Thus, PKA activity is more precisely targeted within the cell than previously anticipated.

    Science, this issue p. 1288

  8. Robotics

    Optimum human input

    1. Marc S. Lavine

    Exoskeletons can be used to augment human abilities—for example, to lift very heavy loads or to provide greater endurance. For each user, though, a device will need to be adjusted for optimum effect, which can be time-consuming. Zhang et al. show that the human can be included in the optimization process, with real-time adaptation of an ankle exoskeleton (see the Perspective by Malcolm et al.). By using indirect calorimetry to measure metabolic rates, the authors were able to adjust the torque provided by the device while users were walking, running, and carrying a load.

    Science, this issue p. 1280; see also p. 1230

  9. Microbiota

    One person's meat is another's poison

    1. Caroline Ash

    The human gut is packed with actively metabolizing microorganisms. These have a transformative effect on what we ingest—whether food, drugs, or pollutants. Koppel et al. review the distinguishing features of microbial xenobiotic metabolism, its interaction with somatic metabolism, and interindividual variation. Depending on the functional composition of microorganisms in the gut, the subsequent products may have nutritionally beneficial effects, modify pharmaceuticals, or be toxic. All of these consequences of our companion microbes can have important impacts on human health and well-being.

    Science, this issue p. eaag2770

  10. Infectious Disease

    Broadening the immune spectrum

    1. Angela Colmone

    Traditionally, the immune system has been thought to have two branches—a rapid antigen-independent innate response and a more specific antigen-dependent variable response. Kawabe et al. now add to the view that the immune response covers a broader spectrum. They found that memory-phenotype CD4+ T cells are generated from naïve T cells independently of infection, aided by environmental interleukin-12 (IL-12). These cells rapidly produced interferon-γ in response to IL-12 in the absence of pathogen recognition and provided both nonspecific defense and an adaptive immune boost against the pathogen Toxoplasma gondii. These memory-phenotype CD4+ T cells provide an early innate response, bridging innate and adaptive immunity.

    Sci. Immunol. 2, eaam9304 (2017).

  11. Neuroscience

    Neuronal basis of lethargy in worms

    1. Barbara R. Jasny

    How does the brain switch between wakefulness and sleep? Nichols et al. studied this question using brain-wide Ca2+ imaging at single-neuron resolution in nematodes. By changing O2 concentrations, they could rapidly switch the worms between behaviorally quiescent and active states. They observed a global quiescence brain state characterized by the systemic down-regulation of neuronal network dynamics. Signaling from O2 sensory neurons rapidly evoked and maintained active network dynamics. Conversely, in the absence of such arousing cues, network dynamics converged into the quiescent mode.

    Science, this issue p. eaam6851

  12. Chromosomes

    Packaging without nucleosomes

    1. Stella M. Hurtley

    The fundamental compaction of DNA in chromosomes is thought to start with the wrapping of DNA around nucleosomes, but is nucleosome wrapping required for the condensation of mitotic chromosomes? Shintomi et al. combined Xenopus egg extracts and mouse sperm nuclei and found that chromosome-like structures could be assembled in the near-complete absence of nucleosomes (see the Perspective by Kakui and Uhlmann). These “nucleosome-depleted” chromosomes were composed of condensin-enriched discrete axes and poorly organized chromatin loops. This finding challenges the textbook view of mitotic chromosome organization.

    Science, this issue p. 1284; see also p. 1233

  13. Optics

    Resonant systems with high bandwidth

    1. Ian S. Osborne

    The performance of an active system, whether it is optical, electrical, or mechanical, is often described by its quality (Q) factor. Typically, one learns the rule that the higher the Q factor, the sharper the resonance—that is, the bandwidth of the device is reduced. Tsakmakidis et al. show that this is indeed the case, but only for symmetric systems. However, for the case of asymmetric (or nonreciprocal) systems, the rule need not be obeyed. They show theoretically that the more asymmetric a system with high Q is, the wider the bandwidth can be. The effect raises the prospect of designing high-Q devices operating over large bandwidths.

    Science, this issue p. 1260

  14. Biochemistry

    Sulfur's balancing act in cytochrome c

    1. Jake Yeston

    Cytochrome c enzymes have two distinct functions that depend on the position of a methionine residue. When the sulfur in the methionine side chain coordinates with iron in the enzyme's active site, the protein is optimized for electron transfer; otherwise, it is poised for peroxidase activity. Mara et al. used ultrafast x-ray absorption and emission spectroscopy to probe the energetics of this Fe–S bond (see the Perspective by Bren and Raven). By breaking the bond transiently with light and then timing its reformation, they determined that the surrounding protein environment boosts the bond strength by 4 kilocalories per mole—just enough to toggle between each functional state at a practical rate.

    Science, this issue p. 1276; see also p. 1236

  15. Solid-State Chemistry

    Lithium gets a new ground state

    1. Brent Grocholski

    For the past 70 years, the lowest-energy crystal structure of lithium was believed to be a relatively complex one called the 9R structure. Ackland et al. show that this is incorrect. The actual lowest-energy structure for lithium is the much simpler closest-packed face-centered cubic form. In addition, 6Li and 7Li isotopes have crystal phase transitions at slightly different pressures and temperatures. This difference is chalked up to large quantum mechanical effects between the isotopes. Lithium is the only metal that shows this type of quantum effect and presents a challenge for theoreticians to explain.

    Science, this issue p. 1254

  16. Neuroscience

    Kiss-and-run or a full commitment?

    1. Leslie K. Ferrarelli

    Communication between sensory neurons underlies our sense of touch and temperature and is mediated by the release of neuropeptides from exocytic vesicles in response to Ca2+ influx. Wang et al. discovered that the release mode was determined by the type of Ca2+ channel that was activated. The greater Ca2+ influx generated by voltage-gated Ca2+ channels inhibited a protein that limits fusion pore size, leading to complete vesicular fusion and complete release of vesicular contents. Activation of ligand-gated TRPV1 calcium channels resulted in transient vesicular fusion, generating a kiss-and-run release that was partial but pulsed and more prolonged.

    Sci. Signal. 10, eaal1683 (2017).

  17. Neurogenomics

    Of mice and men's microglia

    1. Laura M. Zahn

    Microglia are immune system cells that function in protecting and maintaining the brain. Gosselin et al. examined the epigenetics and RNA transcripts from single microglial cells and observed consistent profiles among samples despite differences in age, sex, and diagnosis. Mouse and human microglia demonstrated similar microglia-specific gene expression profiles, as well as a shared environmental response among microglia collected either immediately after surgery (ex vivo) or after culturing (in vitro). Interestingly, those genes exhibiting differences in expression between humans and mice or after culturing were often implicated in neurodegenerative diseases.

    Science, this issue p. eaal3222

  18. Chemistry

    Trifluoromethylation via broken C–F bonds

    1. Jake Yeston

    Trifluoromethyl substituents are widely used in pharmaceutical research to tune the properties of drug candidates. Generally, they are introduced intact through the formation of carbon-carbon bonds. Levin et al. discovered an unusual alternative mechanism, in which borane abstracts fluoride from the CF3 group in a gold complex. The activated CF2 fragment can then bond to a wide variety of other carbon substituents added to the same gold center. Return of the fluoride liberates a trifluoromethylated compound from the metal. This mechanism could be useful for the introduction of radioactive fluoride substituents for positron emission tomography applications.

    Science, this issue p. 1272