This Week in Science

Science  29 Apr 2016:
Vol. 352, Issue 6285, pp. 546
  1. Reptile Sleep

    The dragon sleeps tonight

    1. Peter Stern

    Monitoring the brains of sleeping reptiles, like this bearded dragon, reveals the ancient origins of slow-wave and REM sleep.

    PHOTO: STEPHAN JUNEK/MAX PLANCK INSTITUTE FOR BRAIN RESEARCH

    Most animal species sleep, from invertebrates to primates. However, neuroscientists have until now only actively recorded the sleeping brains of birds and mammals. Shein-Idelson et al. now describe the electrophysiological hallmarks of sleep in reptiles. Recordings from the brains of Australian dragons revealed the typical features of slow-wave sleep and rapid eye movement (REM) sleep. These findings indicate that the brainstem circuits responsible for slow-wave and REM sleep are not only very ancient but were already involved in sleep dynamics in reptiles.

    Science, this issue p. 590

  2. Microbiome

    “Normal” for the gut microbiota

    1. Caroline Ash

    For the benefit of future clinical studies, it is critical to establish what constitutes a “normal” gut microbiome, if it exists at all. Through fecal samples and questionnaires, Falony et al. and Zhernakova et al. targeted general populations in Belgium and the Netherlands, respectively. Gut microbiota composition correlated with a range of factors including diet, use of medication, red blood cell counts, fecal chromogranin A, and stool consistency. The data give some hints for possible biomarkers of normal gut communities.

    Science, this issue pp. 560 and 565

  3. Coral Reefs

    Strengths that are now weaknesses

    1. Jeremy Jackson

    Acroporids have been the dominant reef-building corals over the past few million years. Unfortunately, they are also the most vulnerable species to human impacts. Renema et al. show that acroporids originated more than 50 million years ago but did not dominate reef communities until the intensification of fluctuations in sea level associated with the ice ages. This geologically recent success is attributable to their exceptionally rapid growth and their ability to spread across reefs by clonal fragmentation. These very features, however, have also made them vulnerable to heat stress and disease, as exemplified by the tragic mass bleaching and mortality of corals along the Australian Great Barrier Reef.

    Sci. Adv. 10.1126.sciadv.1500850 (2016).

  4. Microbiota

    Parasitic worms affect gut microbes

    1. Kristen L. Mueller

    Improved hygiene practices in high-income countries may come with an increased risk of developing inflammatory bowel disease (IBD) or other similar disorders. Ramanan et al. show that intestinal helminth infection, caused by parasitic worms, protects IBD-susceptible mice from developing the disease. The infection increases specific protective species and limits other inflammatory members of the microbiota. People from helminth-endemic regions harbored a similar protective microbiota, and their deworming led to an increase in inflammatory Bacteroidales species, similar to what the authors observed in the mice. Thus, a changing microbial environment may shape susceptibility to inflammatory disease.

    Science, this issue p. 608

  5. Geochemistry

    Iron isotopes constrain core chemistry

    1. Brent Grocholski

    The overall composition of Earth's core is an important constraint on the chemistry and evolution of our planet's interior. A longstanding problem has been determining the minor element contribution to its predominately iron-nickel alloy. Based on the iron isotope fractionation of various iron alloys with pressure, Shahar et al. find that carbon and hydrogen are probably not primary components of the core. The fractionation occurs at the high pressures of core formation, suggesting that the stable iron isotope ratios of Earth are a new and independent constraint on core composition.

    Science, this issue p. 580

  6. Chemistry

    Synthetic twists among lipids

    1. Jake Yeston

    Proteins embedded in cell membranes perform a wide variety of signaling and transport functions through conformational shifts. De Poli et al. examined how a much smaller, simpler construct might begin to achieve similar aims (see the Perspective by Thiele and Ulrich). Specifically, they designed an artificial peptide with a photosensitive group at one end and embedded it in a phospholipid bilayer akin to a membrane. Nuclear magnetic resonance spectroscopy revealed how light-induced isomerization influenced conformational dynamics at the other end. The results point the way toward development of small-molecule–based switches in membrane environments.

    Science, this issue p. 575; see also p. 520

  7. Infectious Disease

    Beyond antibiotics

    1. Angela Colmone

    Antibiotics are the cornerstone of antibacterial therapy, but resistant bacterial strains are increasingly prevalent. As an alternate approach, Puthia et al. targeted bacterial infection by boosting host innate immunity. A tight balance between the transcription factor IRF-7 and its heterodimeric partner IRF-3 is critical for an efficient and self-limiting innate immune response to bacterial infection. Dysregulation of this balance contributed to kidney disease in infected mice and children. Targeting IRF-7 protected mice against infection and renal tissue damage, suggesting that it could be a therapeutic target for protection against bacterial infection.

    Sci. Transl. Med. 8, 336ra59 (2016).

  8. Structural Biology

    Signaling at the synapse

    1. Valda Vinson

    Neurons signal to each other at synapses using neurotransmitters. Glutamate is a key neurotransmitter, and AMPA-type glutamate receptors (AMPARs) mediate rapid responses to glutamate release. These receptors mainly occur as heteromers comprising GluA1-4 subunits. Herguedas et al. used electron microscopy and x-ray crystallography to determine the structure of GluA2/3 and GluA2/4 heteromers. The structures differ from those determined previously for GluA2 homomers but emphasize how signals may be transmitted through these dynamic receptors.

    Science, this issue p. 10.1126/science.aad3873

  9. Microbiome

    Persistence of fecal transplants

    1. Caroline Ash

    Fecal microbiota transplantation is a successful way of treating the distressing symptoms of irritable bowel disease or Clostridium difficile infection. The procedure is done by administering a concentrate of colonic bacteria from a healthy donor. Li et al. used metagenomic data to look at single-nucleotide variants after transplants in humans. Donor and recipient strains coexisted for at least 3 months. Some donor strains replaced related strains of the same species, but totally novel species from a donor were unlikely to thrive in a recipient. Rational design of personalized fecal transplant “cocktails” will therefore rely on resolution beyond the species level.

    Science, this issue p. 586

  10. Organic Chemistry

    EZ catalyst control in olefin metathesis

    1. Jake Yeston

    A decade has passed since the partner-swapping chemical dance known as olefin metathesis garnered a Nobel Prize, and distinct routines continue to emerge. In general, olefins are most stable in an E configuration, with the two largest substituents diametrically opposed. However, chlorine and fluorine substituents often invert this trend, favoring the alternate Z geometry. Nguyen et al. report a molybdenum metathesis catalyst with ligands carefully optimized to produce Cl- and F-substituted E olefins more quickly than the more stable Z isomers.

    Science, this issue p. 569

  11. Signal Transduction

    Phase separation organizes signaling

    1. L. Bryan Ray

    In T cell receptors, signaling molecules reorganize into tiny phase-separated droplets—like oil in water. Su et al. used an in vitro system with artificial membranes and 12 components of the T cell receptor signaling system to closely monitor the role of these molecular clusters (see the Perspective by Dustin and Muller). The clusters formed through phosphorylation-dependent association of the linker protein LAT (linker for activation of T cells) with other proteins. These clusters also managed to exclude an inactivating phosphatase and increased the specific activity of enzymes controlling actin polymerization.

    Science, this issue p. 595; see also p. 516

  12. Human Genetics

    RNA splicing links genetics to disease

    1. Laura M. Zahn

    Many genetic variants associated with disease have no apparent effect on any specific protein coding sequence. Li et al. systematically analyzed the effects of DNA variants on the main steps of gene regulation, from the chromatin state through protein function. One-third of expression quantitative train loci (QTLs) are mediated through transcriptional processes, not chromatin. Splice QTLs and expression QTLs are about comparable in their complex disease risk. Posttranscriptional mechanisms therefore play a large role in translating genotype to phenotype.

    Science, this issue p. 600

  13. Biophysics

    Identifying nonequilibrium dynamics

    1. Valda Vinson

    Living systems clearly operate out of thermodynamic equilibrium at the molecular scale. How these activities are manifest at the cellular scale, however, has been unclear. Battle et al. use video microscopy together with statistical thermodynamics to unambiguously identify which random fluctuations at the cellular scale are out of equilibrium (see the Perspective by Rupprecht and Prost). Transitions between states obey a detailed balance in equilibrium, whereas imbalanced transitions point to nonequilibrium dynamics. For instance, nonequilibrium dynamics can be identified in the periodic beating of a flagellum and in the nonperiodic fluctuations of primary cilia.

    Science, this issue p. 604; see also p. 514

  14. Sleep Research

    Sleep induction through ion changes

    1. Peter Stern

    How do we switch from sleep to arousal and back? Ding et al. found that a combination of modulatory neurotransmitters influenced the levels of extracellular ions in the brain (see the Perspective by Landolt and Holst). This influence was not driven by changes in local neuronal firing, suggesting direct effects of the neuromodulators on extracellular ion composition. However, these changes in interstitial ion levels could switch a brain from wakefulness to sleep. Changes in extracellular ions may thus be a cause, rather than a consequence, of sleep/wake-dependent changes in neuronal activity.

    Science, this issue p. 550; see also p. 517

  15. Reproductive Biology

    Progesterone signaling in sperm

    1. Beverly A. Purnell

    Cumulus cells surrounding the ovulated egg release the female hormone progesterone, which is necessary for sperm activation in mammals. Miller et al. identified the human sperm progesterone receptor as the orphan enzyme ABHD2. When bound by progesterone, the ABHD2 receptor acts as a lipid hydrolase to deplete an endocannabinoid inhibitor of the plasma membrane's calcium channel. This allows the entry of calcium ions through the calcium channel to activate sperm that are then primed for fertilization.

    Science, this issue p. 555

  16. Neuroscience

    How sleep deprivation impairs memory

    1. Leslie K. Ferrarelli

    Nearly everyone has directly experienced that a bad night of sleep can impair learning and memory. But how? Tudor et al. found that sleep deprivation in mice suppressed activation of the kinase complex mTORC1 and consequently protein synthesis in hippocampal neurons (see also the Focus by Sweatt and Hawkins). Restoring protein synthesis by increasing the amount of phosphorylated 4EBP2 protein in the hippocampus, a function normally performed by mTORC1, protected mice from the memory impairment caused by sleep deprivation.

    Sci. Signal. 9, ra41 and fs7 (2016).

  17. Structural Biology

    Peering into a membrance oxidase

    1. Nicholas S. Wigginton

    Microorganisms have evolved a number of enzymes to reduce oxygen and prevent oxidative stress. Cytochrome bd oxidases serve this role and also protect pathogenic bacteria from nitric acid; however, this class of enzymes so far has eluded high-resolution crystallography. Safarian et al. were able to resolve the three-dimensional structure of cytochrome bd oxidase from a thermophilic bacterium (see the Perspective by Cook and Poole). The overall structure and triangular arrangement of its heme cofactors bear little structural resemblance to those of other membrane-spanning oxidases, despite serving a similar function.

    Science, this issue p. 583; see also p. 518