This Week in Science

Science  17 Feb 2017:
Vol. 355, Issue 6326, pp. 706
  1. Planetary Science

    Organic compounds detected on Ceres

    1. Keith T. Smith

    Image of Ceres taken by NASA's Dawn spacecraft, April 2015

    CREDITS (TOP TO BOTTOM): PLIKUS ET AL.; NASA/JPL-CALTECH/UCLA/MPS/DLR/IDA

    Water and organic molecules were delivered to the early Earth by the impacts of comets and asteroids. De Sanctis et al. examined infrared spectra taken by the Dawn spacecraft as it orbited Ceres, the largest object in the asteroid belt (see the Perspective by Küppers). In some small patches on the surface, they detected absorption bands characteristic of aliphatic organic compounds. The authors ruled out an external origin, such as an impact, suggesting that the material must have formed on Ceres. Together with other compounds detected previously, this supports the existence of a complex prebiotic chemistry at some point in Ceres' history.

    Science, this issue p. 719; see also p. 692

  2. Infectious Disease

    Hypoxic conditioning of immune cells

    1. Angela Colmone

    Oxygen deficiency, or hypoxia, alters immune cell function. How these hypoxia-induced immune cell changes affect the host response to bacterial infection has been unclear. Thompson et al. report that although acute hypoxia accentuated morbidity and mortality resulting from bacterial infection in mice, chronic hypoxia before infection actually prevented these pathological responses. This hypoxic preconditioning reduced neutrophil glucose use, decreasing the related pathology. Immune targeting thus might aid patients with systemic hypoxia and chronic infections resulting from adult respiratory distress syndrome or chronic obstructive pulmonary disease.

    Sci. Immunol. 2, eaal2861 (2017).

  3. Bacterial Division

    Coordinating cell wall synthesis and cell division

    1. Stella M. Hurtley

    Most bacteria are protected by peptidoglycan cell walls, which must be remodeled to split the cell. Cell division requires the tubulin homolog FtsZ, a highly conserved cytoskeletal polymer that specifies the future site of division. Bisson-Filho et al. and Yang et al. found that the dynamic treadmilling of FtsZ filaments controls both the location and activity of the associated cell wall synthetic enzymes. This creates discrete sites of cell wall synthesis that circle around the division plane to divide the cell.

    Science, this issue p. 739, p. 744

  4. High-Pressure Physics

    Stamping hydrogen into metal

    1. Brent Grocholski

    In 1935, Wigner and Huntington predicted that molecular hydrogen would become an atomic metal at a pressure of 25 GPa. Eighty years and more than 400 GPa later, Dias and Silvera have finally produced metallic hydrogen at low temperature. The metallization occurred between 465 and nearly 500 GPa at 5.5 K. Spectroscopic measurements verified that hydrogen was in the atomic state. The observation completes an unexpectedly long quest to find the metallic hydrogen that Wigner and Huntington predicted so long ago.

    Science, this issue p. 715

  5. Physiology

    Sugar rush

    1. Sacha Vignieri

    Flying requires high levels of energy production, which causes muscular oxidative damage. Food-derived antioxidants can protect against such damage; however, nectar is devoid of these compounds. Levin et al. found that nectar-feeding hawkmoths fed high concentrations of sugar had lower levels of damage than unfed moths. Sugar-fed moths generated antioxidant compounds by shunting glucose through a pentose phosphate pathway. This mechanism may have allowed for the evolution of energy-intensive flying nectarivores.

    Science, this issue p. 733

  6. Mutation Detection

    When is a mutation a true genetic variant?

    1. Laura M. Zahn

    Large-scale sequencing studies have set out to determine the low-frequency pathogenic genetic variants in individu als and populations. However, Chen et al. demonstrate that many so-called low-frequency genetic variants in large public databases may be due to DNA damage. They scored libraries sequenced with and without a DNA damage-repairing enzymatic mix to assess the proportion of true rare variants. It remains to be seen how best to repair DNA before sequencing to provide more accurate assessments of mutation.

    Science, this issue p. 752

  7. Glaucoma

    Vitamin B3 protects mice from glaucoma

    1. Priscilla Kelly

    Glaucoma is the most common cause of age-related blindness in the United States. There is currently no cure, and once vision is lost, the condition is irreversible. Williams et al. now report that vitamin B3 (also known as niacin) prevents eye degeneration in glaucoma-prone mice (see the Perspective by Crowston and Trounce). Supplementing the diets of young mice with vitamin B3 averted early signs of glaucoma. Vitamin B3 also halted further glaucoma development in aged mice that already showed signs of the disease. Thus, healthy intake of vitamin B3 may protect eyesight.

    Science, this issue p. 756; see also p. 688

  8. Infection

    Touchdown for gut pathogen virulence

    1. Caroline Ash

    Escherichia coli is transformed from a commensal organism into a pathogen by acquisition of genetic elements called pathogenicity islands (PAIs). Katsowich et al. investigated how the PAI virulence genes of enteropathogenic E. coli (EPEC) respond when the bacterium attaches to a host gut cell. EPEC first sticks to the host by means of pili and then uses a PAI-encoded type 3 secretion system (T3SS) to inject multiple effectors into the host cell. But not all virulence mediators are injected. For example, CesT, a bacterial chaperone, delivers virulence effectors into the T3SS apparatus. Then, within the bacterial cytoplasm, it interacts with a gene repressor called CsrA, which reprograms bacterial gene expression to help the bacteria to adapt to epithelial cell–associated life.

    Science, this issue p. 735

  9. HIV

    Peak HIV viremia pushes CD8+ T cells

    1. Lindsey Pujanandez

    HIV induces widespread immune dysfunction. Animal studies with simian immunodeficiency virus have suggested that early CD8+ T cell responses may reduce viral burden. Takata et al. examined a large cohort of HIV patients given antiretroviral therapy (ART). They evaluated T cell activation and HIV viral load over time, which allowed them to parse out immune function on the basis of acute stages of infection. CD8+ T cell responses were a little slow to ramp up, but activated CD8+ T cells present after ART initiation reduced the viral reservoir. Thus, targeting CD8+ T cells early in infection could lead to viral eradication.

    Sci. Transl. Med. 9, eaag1809 (2017).

  10. Cell Biology

    Understanding insulin release

    1. Stella M. Hurtley

    Insulin release takes place in two phases: a first rapid burst followed by a series of small exocytic bursts that coincide with pulsatile spikes in cytosolic Ca2+ levels. The second phase is impaired in patients with type II diabetes, underscoring the importance of understanding its molecular basis. Lees et al. report a mechanism through which TMEM24, a lipid transport protein that concentrates at endoplasmic reticulum-plasma membrane contact sites, regulates the pulsatility of cytosolic Ca2+ and phosphoinositide signaling. This process in turn regulates pulsatile insulin secretion during the slow insulin release phase.

    Science, this issue p. eaah6171

  11. Plant Science

    Host-pathogen point-counterpoint

    1. Pamela J. Hines

    The arms race between pathogen and host is a well-known phenomenon. Ma et al. have now identified how an enzymatically inactive protein can abet a pathogen's infectivity. The pathogenic oomycete Phytophthora sojae secretes xyloglucanase that damages soybean cell walls. Soybean, in turn, secretes a defense protein that binds to and inactivates the xyloglucanase. To counteract this plant defense, the oomycete deploys a product of its own gene duplication: an inactive enzyme that binds the plant's defense protein. With the defense protein unproductively bound to the decoy, the oomycete can successfully invade the soybean cells.

    Science, this issue p. 710

  12. Photochemistry

    Hydroamination gets a light push uphill

    1. Jake Yeston

    Hydroamination of olefins is a broadly useful method for making carbon-nitrogen bonds. However, when both the amine and the olefin have multiple alkyl substituents, the reaction can become energetically unfavorable. Musacchio et al. used the energy in blue light to surmount this obstacle (see the Perspective by Buchanan and Hull). A photo-excited iridium complex oxidized the amine, which in turn bonded efficiently to the olefin, after which a thiophenol cocatalyst shuttled the electron back. The reaction could operate across a wide range of amine and olefin partners.

    Science, this issue p. 727; see also p. 690

  13. Regeneration

    Hair follicles: Secret to prevent scars?

    1. Beverly A. Purnell

    Although some animals easily regenerate limbs and heal broken flesh, mammals are generally not so gifted. Wounding can leave scars, which are characterized by a lack of hair follicles and cutaneous fat. Plikus et al. now show that hair follicles in both mice and humans can convert myofibroblasts, the predominant dermal cell in a wound, into adipocytes (see the Perspective by Chan and Longaker). The hair follicles activated the bone morphogenetic protein (BMP) signaling pathway and adipocyte transcription factors in the myofibroblast. Thus, it may be possible to reduce scar formation after wounding by adding BMP.

    Science, this issue p. 748; see also p. 693

  14. Solar Cells

    Passivating traps in perovskites

    1. Phil Szuromi

    Low-temperature processing of planar organic-inorganic perovskite solar cells made through solution processing would allow for simpler manufacturing and the use of flexible substrates. However, materials currently in use form interfaces with charge carrier trap states that limit performance. Tan et al. used chlorine-capped TiO2 colloidal nanocrystal films as an electron-selective layer, which limited interface recombination in solution-processed solar cells. Such cells achieved certified efficiencies of 19.5% for active areas of 1.1 cm2.

    Science, this issue p. 722

  15. Infectious Diseases

    Being selective in fighting infection

    1. Julia Fahrenkamp-Uppenbrink

    Antibiotic-resistant bacterial strains are increasingly found in healthy people who show no symptoms. As a result, they are more vulnerable to invasive infections that can be lethal. In a Perspective, Tacconelli et al. argue that existing, mostly broad-spectrum antibiotics are not sufficient for countering this threat and that a new strategy is needed to control the spread of these strains. They call for the development of drugs that selectively target specific pathogens in the human gut while leaving other bacteria unharmed. Together with improved surveillance and reduced use of antibiotics, such selective decolonization agents could help halt the rise in antibiotic-resistant infections.

    Science, this issue p. 689

  16. Antiviral Immunity

    An encephalitis-boosting microRNA

    1. John F. Foley

    Japanese encephalitis virus (JEV), which is related to the Zika and West Nile viruses, targets the central nervous system. The encephalitis induced by JEV inflicts neurological damage and can be fatal. Hazra et al. found that JEV infection of mouse and human neuronal cells reduced the production of antiviral cytokines through the microRNA miR-301a. Treating JEV-infected mice with a miR-301a inhibitor increased antiviral cytokine production, decreased viral replication, and improved survival. Thus, targeting miR-301a may be an effective therapy against JEV infection.

    Sci. Signal. 10, eaaf5185 (2017).

  17. Coastal Ecosystems

    Missing meadows fail to mop up microbes

    1. Caroline Ash

    Seagrass meadows, a prominent feature of most healthy coastal ecosystems, are often also associated with shallow coral reefs. Many plants have bioremediation qualities, and seagrasses, of which there are 60 or so species, produce natural biocides. Lamb et al. found that the seagrass meadows of inhabited atolls near Sulawesi, Indonesia, ameliorated seawater pollution from humano-riginating bacteria. This effect extended to potential pathogens of marine invertebrates and fish: Reefs fringing the seagrass meadows showed significantly less impact from coral and fish disease.

    Science, this issue p. 731