This Week in Science

Science  22 Aug 2014:
Vol. 345, Issue 6199, pp. 886
  1. Massive Stars

    How huge early stars enriched the universe

    1. Margaret M. Moerchen

    Remnants of a supernova explosion

    CREDITS: (X-RAY) NASA/CXC/SAO/F. SEWARD ET AL.

    How big did the first generation of stars get? Knowing their size is critical to understanding how they enriched the chemistry of the universe through supernova explosions. According to numerical simulations, some of the earliest stars were more than 100 times the Sun's mass. However, no traces of these live-fast, die-young stars had been detected in any low-mass stars still extant from that era. Aoki et al. now show spectra of one such metal-poor star that may have recorded the activity of a very massive predecessor (see the Perspective by Bromm). This observational evidence will spur further supernova models, as none predicts this specific chemical signature.

    Science, this issue p. 912; see also p. 868

  2. Reef Ecology

    Corals and reef fish choose nice homes

    1. Sacha Vignieri

    Young animals tend to disperse into new habitats. Can we use populations in protected areas to colonize nearby recovering or overused habitats? It seems that for corals and reef fish, the answer may be no. Dixson et al. show that dispersing juvenile corals and reef fish were overwhelmingly attracted to healthy reefs but were repelled by seaweeds that colonize degraded reefs (see the Perspective by Bruno). Thus, even species that appear passive in their choice of habitat may have stronger preferences than we thought.

    Science, this issue p. 892; see also p. 879

  3. Quantum Optics

    Routing one photon with a few others

    1. Ian S. Osborne

    Single particles of light, photons, are ideal carriers of quantum information because they can travel far and fast and don't interact much with each other. However, this behavior has hampered attempts to control the propagation of single photons using all-optical setups. Shomroni et al. coupled a trapped atom to an optic fiber. That allowed them to control the polarization and propagation direction of a single photon in the fiber by controlling the atom's state (see the Perspective by Rempe). Because a faint pulse containing between 1.5 and 3 photons can switch the atom's state, the scheme provides a route to develop all-optical quantum networks.

    Science, this issue p. 903; see also p. 871

  4. Sensory Biology

    The makings of a powerful sweet tooth

    1. Sacha Vignieri

    The main attraction of nectar, a hummingbird favorite, is the sweet taste of sugar. Oddly, though, birds lack the main vertebrate receptor for sweet taste, TIR2. Baldwin et al. show that a related receptor, TIR1-T1R3, which generally controls savory taste in vertebrates, adapts in hummingbirds to detect sweet (see the Perspective by Jiang and Beauchamp). This repurposing probably allowed hummingbirds to specialize in nectar feeding and may have assisted the evolution of the many and varied hummingbird species seen today.

    Science, this issue p. 929; see also p. 878

  5. Bone Biology

    An inhibitor breaks RANK

    1. John F. Foley

    Osteoclasts are cells that break down bone; however, excessive bone loss leads to conditions such as osteoporosis. When three proteins called RANKL bind to three receptors called RANK on the osteoclasts' surfaces, the osteoclasts go to work. Warren et al. linked three mutant versions of RANKL protein together to generate an inhibitor of RANK (see the Perspective by Ou-Yang and Siegel). Two of the proteins bound more strongly to RANK, and the third protein could not bind to RANK. This engineered RANKL variant bound to RANK without activating the receptor, preventing osteoclasts from breaking down bone in mice.

    Sci. Signal. 7, ra80 and pe20 (2014).

  6. Polio Eradication

    Two vaccines together are better than one alone

    1. Caroline Ash

    Polio is proving difficult to eradicate. Making the choice between administering a live attenuated vaccine orally (Sabin) or an inactivated vaccine (Salk) by injection has been highly controversial. Patients prefer the Sabin vaccine, but it requires many doses to offer immunity. Jafari et al. tested the two vaccines together in northern India. The injected vaccine significantly reduced virus shedding and boosted intestinal mucosal immunity in children already given the oral vaccine. Thus, using both vaccines could help speed the eventual global demise of polio.

    Science, this issue p. 922

  7. Climate

    Deep-sea warming slows down global warming

    1. H. Jesse Smith

    Global warming seems to have paused over the past 15 years while the deep ocean takes the heat instead. The thermal capacity of the oceans far exceeds that of the atmosphere, so the oceans can store up to 90% of the heat buildup caused by increased concentrations of greenhouse gases such as carbon dioxide. Chen and Tung used observational data to trace the pathways of recent ocean heating. They conclude that the deep Atlantic and Southern Oceans, but not the Pacific, have absorbed the excess heat that would otherwise have fueled continued warming.

    Oceans stow recent heat excesses

    PHOTO: GETTY IMAGES/ISTOCKPHOTO

    Science, this issue p. 897

  8. Tuberculosis

    How immune cells fight TB and show it

    1. Angela Colmone

    Mycobacterium tuberculosis causes an infection that can sometimes kill, but it proceeds to disease in only about 10% of individuals. Now, Montoya et al. provide a clue to how most people keep this bacterium in check. They show that when people fight tuberculosis, their immune cells secrete the cytokine interleukin-32, which may work through an antimicrobial pathway that uses vitamin D. The researchers analyzed five different clinical data sets and found that interleukin-32 may indicate latent tuberculosis. Interleukin-32 therefore may both contribute directly to the host response to tuberculosis and reflect protection against the disease.

    Sci. Transl. Med. 6, 250ra114 (2014).

  9. Immunogenetics

    Opening and closing blood enhancers

    1. Laura M. Zahn

    As cells develop and differentiate into different types, the shape and accessibility of their DNA can change. Lara-Astiaso et al. studied this phenomenon in blood. They developed a technique that examines a relatively small number of cells to identify the changes that affect DNA during blood development. They found that the DNA of noncoding regions, called enhancers, is set in an open position when cells are undifferentiated and able to take on a variety of roles and gradually closes as cells mature into their final forms.

    Science, this issue p. 943

  10. Glaciers

    Putting the heat on Mother Nature

    1. H. Jesse Smith

    Humans are now the biggest cause of glacier melting. Until recently, that was not true. Glaciers take a long time—decades to centuries—to respond to the environmental changes that control their sizes. They have been retreating gradually from the peak levels they reached in the middle of the 19th century, at the end of a 500-year-long cold period called the Little Ice Age. Marzeion et al. show that that has recently changed though, as climate warming has continued: Over the past 20 or so years, the anthropogenic contribution to glacial mass loss has increased markedly (see the Perspective by Marshall).

    Science, this issue p. 919; see also p. 872

  11. Stem Cell Therapy

    Challenges for stem cell–based therapies

    1. Beverly A. Purnell

    Patient-derived pluripotent stem cells (PSCs) hold promise in the treatment of injury and disease. An ever-increasing number of specific cell types can be generated from PSCs, but technical challenges remain in applying these cells in the clinic. Fox et al. review the challenges in attaining this goal. These include gene modification, cell rejection, and delivery and localization issues involved in transplantation of cells for the treatment of diabetes and disorders of the blood, liver, heart, and brain.

    Science, this issue 10.1126/science.1247391

  12. Political Science

    Censorship of social media in China

    1. Gilbert Chin

    Figuring out how many and which social media comments are censored by governments is difficult because those comments, by definition, cannot be read. King et al. have posted comments to social media sites in China and then waited to see which of these never appeared, which appeared and were then removed, and which appeared and survived. About 40% of their submissions were reviewed by an army of censors, and more than half of these never appeared. By varying the content of posts across topics, they conclude that any mention of collective action is selectively suppressed.

    Science, this issue 10.1126/science.1251722

  13. Plant Development

    Removing the nucleus in sieve elements

    1. Pamela J. Hines

    Although a cell's nucleus performs critical command and control functions, some cell types, such as enucleated red blood cells, seem to do without. Sieve element cells in plants similarly carry out their function of transporting nutrients and signals from one end of the plant to the other without the guidance of a nucleus. Furuta et al. watched how the nucleus self-destructs during the development of sieve element cells (see the Perspective by Geldner). The process is regulated under the control of transcription factors, even as the entire nuclear edifice crumbles into nothingness.

    Science, this issue p. 933; see also p. 875

  14. Riboswitches

    A dual-action RNA switch for expression

    1. Guy Riddihough

    Riboswitches are short segments of RNA that bind small molecules and switch between two different conformations, thereby regulating gene expression (see the Perspective by Chen and Gottesman). DebRoy et al. and Mellin et al. find a new class of riboswitches—in two different species of bacteria—that are both part of and regulate the production of a noncoding RNA. Each riboswitch ensures that a particular metabolic pathway is only activated in the presence of an essential small-molecule cofactor. In the absence of the cofactor, the full-length non-coding RNA is made and binds a regulator protein, preventing the regulator protein from inappropriately activating the metabolic pathway.

    Science, this issue p. 937 and p. 940; see also p. 876

  15. Nanoparticle Growth

    Watching platinum nanocube growth

    1. Marc S. Lavine

    Size and shape drive the properties of metal nanoparticles. Understanding the factors that affect their growth is central to making use of the particles in a range of applications. Liao et al. tracked the growth of platinum nanoparticle shapes at high resolution using state-of-the-art liquid cells for in situ monitoring inside an electron microscope. The authors tracked changes in the growth rates at different crystal facets caused by differences in the mobility of the capping ligand.

    Science, this issue p. 916

  16. Nanoparticle Imaging

    Detailed structure of a gold nanoparticle

    1. Marc S. Lavine

    Adding only a few atoms or changing the capping ligand can dramatically change the structure of individual metal nanoparticles. Azubel et al. used aberration-corrected transmission electron microscopy to derive a three-dimensional reconstruction of water-soluble gold nanoparticles. Small-angle x-ray scattering and other techniques have also corroborated this model. They used this to determine the atomic structure, which compared favorably with density functional theory calculations, without assuming any a priori structural knowledge or the use of model fitting.

    Science, this issue p. 909

  17. Helium Superfluidity

    X-raying superfluid helium droplets

    1. Jelena Stajic

    When physicists rotate the superfluid 4He, it develops a regular array of tiny whirlpools, called vortices. The same phenomenon should occur in helium droplets half a micrometer in size, but studying individual droplets is tricky. Gomez et al. used x-ray diffraction to deduce the shape of individual rotating droplets and image the resulting vortex patterns, which confirmed the superfluidity of the droplets. They found that superfluid droplets can host a surprising number of vortices and can rotate faster than normal droplets without disintegrating.

    Science, this issue p. 906

  18. Plant Genetics

    The genomic origins of rape oilseed

    1. Laura M. Zahn

    Many domesticated plants arose through the meeting of multiple genomes through hybridization and genome doubling, known as polyploidy. Chalhoub et al. sequenced the polyploid genome of Brassica napus, which originated from a recent combination of two distinct genomes approximately 7500 years ago and gave rise to the crops of rape oilseed (canola), kale, and rutabaga. B. napus has undergone multiple events affecting differently sized genetic regions where a gene from one progenitor species has been converted to the copy from a second progenitor species. Some of these gene conversion events appear to have been selected by humans as part of the process of domestication and crop improvement.

    Science, this issue p. 950

  19. Carbon Cycle

    Illuminating the pathway to destruction

    1. H. Jesse Smith

    Arctic lakes are an important source of atmospheric CO2 and therefore play a role in climate change. It is thus vital to know how the rapid Arctic warming will affect them. Cory et al. now show that light is the biggest culprit in the breakdown of carbon from thawing permafrost soils (see the Perspective by Tranvik). This carbon then moves out into Arctic lakes and streams. Contrary to previous expectations, these photochemical processes cause much more destruction of the organic molecules in fresh water than bacterial respiration does.

    Science, this issue p. 925; see also p. 870

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