This Week in Science

Science  17 Jul 2015:
Vol. 349, Issue 6245, pp. 279
  1. Thermal Physiology

    Keeping cool

    1. Sacha Vignieri

    Saharan silver ant

    PHOTO: NORMAN NAN SHI AND NANFANG YU

    Silver ants inhabit one of the hottest and driest environments on Earth, the Saharan sands, where most insects shrivel and die moments after contact. Shi et al. show that the triangular shape of the silver hairs that cover their bodies enables this existence. The hairs both increase the reflection of near-infrared rays and dissipate heat from the ants' bodies, even under full sun conditions. Evolution's simple solution to intense heat management in this species could lead to better designs for passive cooling of human-produced objects.

    Science, this issue p. 298

  2. HIV-1 Vaccines

    To defeat SIV, add a protein boost

    1. Kristen L. Mueller

    Despite 30 years of effort, no HIV-1 vaccine exists. Barouch et al. evaluated one promising strategy in rhesus macaques, a preclinical model commonly used to test potential HIV-1 vaccine candidates. They immunized monkeys with adenovirus-36 vectors engineered to express SIV (simian immunodeficiency virus) genes and then boosted them with a recombinant gp120 envelope glycoprotein (Env) from SIV. This regimen afforded greater protection than a strategy that instead used a viral vector–based boost. A parallel trial using a SHIV (simian/human immunodeficiency virus)–based vaccine and challenge model produced similar results. Whether this particular approach will be equally successful in humans remains to be tested.

    Science, this issue p. 320

  3. Magnetism

    Skyrmions emerge in trilayers

    1. Jelena Stajic

    Skyrmions are tiny whirlpools of magnetic spin with potential to act as carriers of information in future devices. Skyrmions have been observed in multiple materials but usually at impractically low temperatures. Jiang et al. used a constriction in a trilayer system to create skyrmions at room temperature (see the Perspective by von Bergmann). The authors pushed elongated magnetic domains through the constriction using an in-plane current, causing individual skyrmion bubbles to form.

    Science, this issue p. 283; see also p. 234

  4. Nanoparticle Imaging

    Looking at teeny tiny platinum particles

    1. Marc S. Lavine

    Electron microscopy is a powerful technique for taking snapshots of particles or images at near-atomic resolution. Park et al. studied free-floating platinum nanoparticles using electron microscopy and liquid cells (see the Perspective by Colliex). Using analytical techniques developed to study biological molecules, they reconstructed the threedimensional features of the Pt particles at near-atomic resolution. This approach has the scope to study a mixed population of particles one at a time and to study their synthesis as it occurs in solution.

    Science, this issue p. 290; see also p. 232

  5. Plant Science

    Substrate channeling in morphine biosynthesis

    1. Pamela J. Hines

    Poppies are still the most economically viable source of the excellent painkiller morphine. Winzer et al. have now identified a key enzyme in the poppy's biosynthetic pathway for morphine. The enzyme turns out to be an unusual protein that contains both cytochrome P-450 and oxidoreductase modules. Together these modules process two subsequent steps in the biosynthetic pathway. The identification of this enzyme may enable alternate routes for morphine biosynthesis that are less dependent on poppy cultivation.

    Science, this issue p. 309

  6. Sex Determination

    How germ cells become sperm or egg

    1. Beverly A. Purnell

    During vertebrate development, germ cells switch from a sexually indifferent to a committed state for either egg or sperm. Signals from somatic gonadal cells are generally thought to influence the sexual differentiation of germ cells. However, Nishimura et al. demonstrate that germ cell–intrinsic sex determination cues are at play in the teleost fish medaka. The forkhead box transcriptional factor foxl3 represses the initiation of spermatogenesis. In the absence of foxl3 function, females develop ovaries filled with functional sperm. Thus, the male gonad environment is not required for spermatogenesis.

    Science, this issue p. 328

  7. Ice Sheets

    Movers and shakers

    1. H. Jesse Smith

    When the edge of an ice sheet breaks off and falls into the sea (calves), the remaining section of the ice sheet moves backward and down and can suffer a glacial earthquake. Murray et al. studied calving from Greenland's Helheim Glacier. The forces that cause the change in the motion of the ice sheet at its terminus also trigger the accompanying earthquakes. Because these seismic signals can be detected by instruments located all over the globe, it should be possible to use these glacial earthquakes as proxies for glacier calving.

    Icebergs near the terminus of Helheim Glacier

    PHOTO: MAGDALENA ANDRES/©Woods Hole Oceanographic Institution

    Science, this issue p. 305

  8. Drug Discovery

    Long-acting drug to treat resistant malaria

    1. Orla M. Smith

    Malaria kills 0.6 million people annually. Currently available drugs are no longer fully effective, because the malarial parasite has developed resistance. Now, Phillips et al. have identified a drug, DSM265, that kills both drug-sensitive and drug-resistant parasites by targeting their ability to synthesize precursors required for synthesis of DNA and RNA. DSM265 kills parasites in the blood and the liver and is sufficiently long-acting that it could potentially cure malaria after a single dose or provide effective chemo-prevention if given weekly.

    Sci. Transl. Med. 7, 296ra111 (2015).

  9. Infectious Disease

    GBS toxin activates mast cells for host defence

    1. Philip Yeagle

    Ascending Group B streptococcus (GBS) is a major cause of preterm birth. How the mother defends against GBS infections is not clear. Working in mice, Rajagopal et al. found that immune cells, called mast cells, are activated by a lipid toxin produced by GBS. This lipid toxin is an ornithine rhamno-polyene that stains the bacteria red. The toxin assists penetration of the placenta by the bacteria. The toxin also stimulates mast cell degranulation, an early step in host efforts to defeat the bacterial infection.

    Sci. Adv. 10.1126/sciadv.1400225 (2015).

  10. Chromosomes

    Protein partners for chromosome silencing

    1. Guy Riddihough

    Female mammals have two X chromosomes, one of which is almost completely shut down during development. The long noncoding Xist RNA plays a role in this process. To understand how a whole chromosome can be stably inactivated, Minajigi et al. identified many of the proteins that bind to the Xist RNA, which include cohesins. Paradoxically, the interaction between Xist and cohesin subunits resulted in repulsion of cohesin complexes from the inactive X chromosome, changing the three-dimensional shape of the whole chromosome.

    Science, this issue 10.1126/science.aab2276

  11. Plant Ecology

    Grassland diversity and ecosystem productivity

    1. Andrew M. Sugden

    The relationship between plant species diversity and ecosystem productivity is controversial. The debate concerns whether diversity peaks at intermediate levels of productivity—the so-called humped-back model—or whether there is no clear predictable relationship. Fraser et al. used a large, standardized, and geographically diverse sample of grasslands from six continents to confirm the validity and generality of the humped-back model. Their findings pave the way for a more mechanistic understanding of the factors controlling species diversity.

    Science, this issue p. 302

  12. Heavy Fermions

    Probing the insulating state of SmB6

    1. Jelena Stajic

    When a metal is subjected to a strong magnetic field, its electrons start rearranging into new energy levels, causing its electronic properties to oscillate as a function of the field. Unexpectedly, Tan et al. observed this phenomenon, called quantum oscillations, in the Kondo insulator samarium hexaboride (SmB6), which does not conduct electricity. They measured the magnetic torque and detected quantum oscillations originating from the bulk of this heavy fermion compound. These oscillations had an unusual temperature dependence, which presents another puzzle to theorists seeking to understand the nature of the insulating state of SmB6.

    Science, this issue p. 287

  13. Animal Physiology

    Not that unusual after all

    1. Sacha Vignieri

    As polar ice recedes, polar bears are facing a changed habitat with reduced summer foraging opportunities. It has been hypothesized that they might be able to resist summer food shortages by reducing their metabolic needs in a sort of “walking hibernation.” Whiteman et al. monitored energy expenditure in polar bears both on and off the ice and found energy reductions, but that these were more akin to normal mammalian fasting levels. Thus, it appears that polar bears have no energetic protections against reduced summer food supplies and will face increasing starvation threats if summer foraging habitats continue to decline.

    Science, this issue p. 295

  14. Circadian Rhythms

    Biochemical basis of a 24-hour clock

    1. L. Bryan Ray

    Circadian clocks keep organisms in synch with such daily cycles as illumination, activity, and food availability. The circadian clock in cyanobacteria has the necessary 24-hour period despite its three component proteins having biochemical activities that occur on a much faster time scale. Abe et al. focused on the cyanobacterial clock component KaiC, an adenosine triphosphatase (ATPase) that can autophosphorylate and autodephosphorylate. The slow ATPase activity of KaiC, which is linked to a peptide isomerisation, provided the slow kinetics that set the speed of the 24-hour clock. Chang et al. found that another clock component, KaiB, also has slow changes in its protein conformation that help to set the oscillation period of the clock and its signaling output.

    Science, this issue pp. 312 and 324

  15. Ecology

    The benefits of diversity

    1. Julia Fahrenkamp-Uppenbrink

    Pathogens and parasites are an integral part of all ecosystems. But the likelihood of them causing disease depends on environmental factors. In a Perspective, Keesing and Ostfeld highlight recent studies on disease prevalence as a function of diversity. In humans, other animals, and plants, disease prevalence is lower when diversity is high. This is the case even though pathogen diversity is higher in more-diverse systems. As biodiversity is lost from ecosystems, they become more vulnerable to infections.

    Science, this issue p. 235

  16. Inflammation

    Neutrophil NETs drive atherosclerosis

    1. Kristen L. Mueller

    The buildup of fats, cholesterol, and other substances in arteries causes atherosclerosis, which restricts blood flow and can lead to heart attacks and stroke. Inflammation contributes to the pathogenesis of atherosclerosis, but exactly how is not fully understood. Warnatsch et al. now show that immune cells called neutrophils release NETs (neutrophil extracellular traps) (see the Perspective by Nahrendorf and Swirski). These NETs are composed of DNA and antimicrobial proteins, and in the setting of atherosclerosis they activate innate immune signaling pathways in macrophages. This causes the macrophages to secrete proinflammatory cytokines, exacerbating the disease. Indirectly, NETS also attract a specialized subset of T cells that further amplify the proinflammatory response.

    Science, this issue p. 316; see also p. 237

  17. Immunology

    Fine-tuning the inflammatory response

    1. John F. Foley

    The binding of the bacterial product lipopolysaccharide (LPS) to the receptor TLR4 on macrophages triggers inflammatory responses that require the transcription factor NF-κB. TLR4 recruits the adaptor protein MyD88 when the receptor is at the plasma membrane and a different adaptor protein, TRIF, after internalization into endosomes. Cheng et al. found that MyD88 was required for the initial peak of transient NF-κB activation in all LPS-stimulated cells (see also the Focus by Williams et al.). In contrast, TRIF was required for more sustained NF-κB activation in a subset of cells. Thus, macrophages use both adaptor proteins to fine-tune NF-κB activation to induce an appropriate inflammatory response.

    Sci. Signal. 8, ra69 and fs13 (2014).

Navigate This Article