This Week in Science

Science  26 Sep 2014:
Vol. 345, Issue 6204, pp. 1574
  1. Plant Development

    A complex network makes simple pores

    1. Pamela J. Hines

    Microscopic view of plant stomata

    PHOTO: DE AGOSTINI PICTURE LIBRARY/SCIENCE SOURCE

    Stomata, the pores found on the surface of plant leaves, form at intervals from stem cells. Development of stomata is controlled by the SPEECHLESS transcription factor. Lau et al. surveyed the genes that SPEECHLESS itself controls. Targets include genes involved in hormone signaling, control of cell proliferation, and the specification of asymmetric cell fates. Despite the apparent simplicity of a single pore, the genetic network that generates that pore is anything but simple.

    Science, this issue p. 1605

  2. Remote Hydrology

    Crustal rebound from water drawdown

    1. Brent Grocholski

    The ongoing drought across the western United States has taken a toll on underground water storage. Borsa et al. use almost imperceptible crustal uplift to estimate the regional water depletion from the drought. Inverting GPS data maps the impact of the drought on local aquifers over the past few years. The deficit so far in the western United States adds up to 240 gigatons of water, the equivalent of a 10-cm layer across the region. Certain areas of California have fared much worse, with local depletions up to five times the regional average.

    Science, this issue p. 1587

  3. Paleontology

    Mysterious dinosaur a swimmer?

    1. Sacha Vignieri

    Dinosaurs are often appreciated for their size and oddity. In this regard, the North African carnivorous theropod Spinosaurus, with its huge dorsal sail and a body larger than Tyrannosaurus rex, has long stood out. This species also stands out because of its history. The unfortunate loss of the type specimen during World War II left much of what we know about Spinosaurus to be divined through speculation and reconstruction. Ibrahim et al. now describe new fossils of this unusual species. They conclude it was, at least partly, aquatic, a first for dinosaurs.

    Science, this issue p. 1613

  4. Catalysis

    Easier oxidation over gold with added water

    1. Phil Szuromi

    Gold adsorbed on metal oxides is an excellent catalyst for the room-temperature oxidation of CO to CO2. However, there has been continuing disagreement between different studies on the key aspects of this catalyst. Saveeda et al. now show through kinetics and infrared spectroscopy that the presence of water can lower the reaction activation barrier by enabling OOH groups to form from adsorbed oxygen (see the Perspective by Mullen and Mullins). The OOH then reacts readily with CO. It thus seems that the main role of oxide support and its interface with the metal is in activating water, but that the steps of the reaction that involve CO occur on gold.

    Science, this issue p. 1599; see also p. 1564

  5. Immunogenetics

    Beware of T cells that don't know how to stop

    1. Kristen L. Mueller

    During an infection, T cells divide extensively and secrete proteins that can severely damage tissues. But T cells know when to stop—they express proteins on their surface such as CTLA4, which put on the brakes. Kuehn et al. now report genetic evidence of the importance of CTLA4 in humans (see the Perspective by Rieux-Laucat and Casanova). They identified six patients with mutations in one copy of CTLA4. Patients presented with symptoms of an overzealous immune response, with immune cells infiltrating their organs. The findings support the idea that CTLA4 tells the immune system when enough is enough.

    Science, this issue p. 1623; see also p. 1560

  6. Neurotechnology

    Closing the loop on neuroprosthetic control

    1. Megan L. Frisk

    Patients paralyzed from a spinal cord injury may soon be able to move their legs more naturally. Current neuromodulation devices cause leg movement by electrically stimulating the spinal cord, but they require constant monitoring and adjustment. Wenger et al. created a closed-loop system that auto-tunes the device. The authors stimulated the spinal cords of paralyzed rats and then mapped their leg movements while they walked or climbed stairs, creating integrated feedback and feed-forward models for continuous stepping control.

    Sci. Transl. Med. 6, 255ra133 (2014).

  7. Jovian Atmosphere

    Hot electron plasma moves in from Io

    1. Margaret M. Moerchen

    Volcanoes on Jupiter's moon Io

    PHOTO: NASA/JPL

    Scientists have known that solar radiation ionizes the gases from Io's volcanoes to create a torus of plasma around Jupiter, but how that plasma moves is unclear. To investigate this, Yoshioka et al. monitored the temperature of the hot electron plasma as a function of distance from the planet with the Hisaki Earth-orbiting satellite. The fraction of hot electrons decreases only gradually with distance from Jupiter, which implies a rapid resupply of these electrons from outside Io's orbit.

    Science, this issue p. 1581

  8. Physiology

    Preventing vascular scarring after surgery

    1. Wei Wong

    The endothelium that lines blood vessels can undergo a change called the endothelial-to-mesenchymal transition (EndMT), which can cause vessel “scarring.” Such scarring limits the success of surgical procedures that require blood vessel grafting, including, for example, heart transplantation or coronary bypass surgery. Chen et al. found that mice lacking FGFR1 in endothelial cells showed increased EndMT after blood vessel grafting. Moreover, arteries from patients who had rejected heart transplants had lower levels of FGFR1 than those from normal individuals. Thus, enhancing FGFR1 activity could limit vascular scarring in heart disease patients undergoing surgery.

    Sci. Signal. 7, ra90 (2014).

  9. Neural Development

    Differentiation rates regulate pool sizes

    1. Pamela J. Hines

    Even though a basketball player is bigger than a gymnast, their neural tubes are organized in the same way. Studying chick and mouse embryos, Kicheva et al. show that rates of cell differentiation are key (see the Perspective by Pourquie). In a two-phase process, signaling sweeps through the neural tube early on to establish some aspects of cell fate, but later, pools of progenitor cells take on their own regulation. A progenitor that differentiates is no longer a progenitor, and thus the rate of differentiation determines the size of the progenitor pool. The relative sizes of progenitor pools shift as development progresses, to build the spinal cord so that everyone, large or small, has the right proportion of each component.

    Science, this issue 10.1126/science.1254927; see also p. 1565

  10. Interstellar Chemistry

    Carbon chains branch out on space dust

    1. Margaret M. Moerchen

    Meteorites found on Earth contain a wide range of complex constituent molecules, including amino acids. Astrochemists proposed the existence of these molecules in interstellar space in the 1980s, but detections have been elusive. Belloche et al. used the ALMA telescope array in Chile to observe the massive star-forming region Sgr B2. There, the vast quantities of gas enabled detection of even sparsely distributed species such as iso-propyl cyanide. Despite being difficult to detect, such nonlinear organic molecules may be common. The formation of branched molecules is important, given the analogous structure of familiar amino acids — some of the building blocks for life.

    Science, this issue p. 1584

  11. Early Solar System

    Nature or nurture for solar system ices?

    1. Margaret M. Moerchen

    We know that life's favorite molecule, water, exists throughout the solar system. What we don't know is whether present water levels reflect the chemical conditions of our parent nebula or whether they result from later reprocessing in the young system. The levels of deuterium and hydrogen in solar system water ice offer a tracer for chemical history, and Cleeves et al. model the processes at play. The analysis suggests that all nascent planetary systems may have the same water resources that we did.

    Science, this issue p. 1590

  12. Immunogenetics

    A BLUEPRINT of immune cell development

    1. Laura M. Zahn

    To determine the epigenetic mechanisms that direct blood cells to develop into the many components of our immune system, the BLUEPRINT consortium examined the regulation of DNA and RNA transcription to dissect the molecular traits that govern blood cell differentiation. By inducing immune responses, Saeed et al. document the epigenetic changes in the genome that underlie immune cell differentiation. Cheng et al. demonstrate that trained monocytes are highly dependent on the breakdown of sugars in the presence of oxygen, which allows cells to produce the energy needed to mount an immune response. Chen et al. examine RNA transcripts and find that specific cell lineages use RNA transcripts of different length and composition (isoforms) to form proteins. Together, the studies reveal how epigenetic effects can drive the development of blood cells involved in the immune system.

    Science, this issue 10.1126/science.1251086, 10.1126/science.1250684, 10.1126/science.1251033

  13. Nitrogen Fixation

    Making nitrogen available for biosynthesis

    1. Valda Vinson

    Nitrogen gas (N2) is abundant in Earth's atmosphere; however, it must be converted into a bioavailable form before it can be incorporated into biomolecules. The enzyme nitrogenase, which is made up of two metalloproteins, converts N2 into bioavailable ammonia. One of these, the MoFe-protein, contains a complex metal center, the FeMo cofactor, where the triple N2 bond is reduced. Understanding how nitrogenase achieves the reduction of N2 has been a long-term goal. Spatzal et al. present the structure of MoFe-protein bound to carbon monoxide (see the Perspective by Hogbom). Although this is an inhibitor rather than the natural substrate, the structure gives insight into how the FeMo metallocluster rearranges to achieve substrate reduction.

    Science, this issue p. 1620

  14. Water Splitting

    The power of a pair of perovskites

    1. Jake Yeston

    In the past several years, perovskite solar cells have emerged as a low-cost experimental alternative to more traditional silicon devices. Luo et al. now show that a pair of perovskite cells connected in series can power the electrochemical breakdown of water into hydrogen and oxygen efficiently (see the Perspective by Hamann). Hydrogen generation from water is being actively studied as a supplement in solar power generation to smooth out the fluctuations due to variations in sunlight.

    Science, this issue p. 1593; see also p. 1566

  15. Atmospheric Chemistry

    Breaking down a Criegee intermediate

    1. Jake Yeston

    Ozone's damaging role in the upper atmosphere is well known, but ozone is also quite active closer down to where we live. In particular, ozone's run-ins with airborne unsaturated hydrocarbons, from natural or anthropogenic sources, produce even more-reactive OH radicals. Liu et al. used vibrational spectroscopy to study how OH emerges from a so-called Criegee intermediate formed when ozone attacks 2-butene. The results suggest that OH production is easier than current theory predicts.

    Science, this issue p. 1596

  16. Paleolithic Tools

    An early assemblage of obsidian artifacts

    1. Andrew M. Sugden

    Levallois technology is the name for the stone knapping technique used to create tools thousands of years ago. The technique appeared in the archeological record across Eurasia 200 to 300 thousand years ago (ka) and appeared earlier in Africa. Adler et al. challenge the hypothesis that the technique's appearance in Eurasia was the result of the expansion of hominins from Africa. Levallois obsidian artifacts in the southern Caucasus, dated at 335 to 325 ka, are the oldest in Eurasia. This suggests that Levallois technology may have evolved independently in different hominin populations. Stone technology cannot thus be used as a reliable indicator of Paleolithic human population change and expansion.

    Science, this issue p. 1609

  17. Plant Ecology

    How plant species diversity is shaped

    1. Andrew M. Sugden

    Factors controlling plant species diversity have been teased apart in an ancient dune ecosystem in western Australia. Laliberté et al. surveyed plants in the ancient dune, where variation in soil properties is associated with changes in plant diversity. Local plant diversity was mostly determined by environmental filtering from the regional species pool. This process is driven by acidification during long-term soil formation. The findings challenge the prevailing view that resource competition controls local plant diversity.

    Science, this issue p. 1602

  18. Neuroscience

    Animal behavior follows rewards

    1. Melissa McCartney

    Animal behavior is learned and reinforced by rewards. On a molecular level, the reward comes in the form of the neurotransmitter, dopamine, which modulates synapses. The exact timing and mechanism of this process remain unknown. Using optical stimulation, Yagishita et al. found that dopaminergic modulation involved dendritic spine enlargement only during an extremely narrow time window. Known as reinforcement plasticity, this cellular basis for learning could provide insight into psychiatric disorders involving dopaminergic regulation, such as depression, drug addiction, and schizophrenia.

    Science, this issue p. 1616

  19. Ecology

    Views of nature, views of conservation

    1. Julia Fahrenkamp-Uppenbrink

    When we think of nature conservation, some of us may imagine wilderness protected in a natural park. Others may think of species closer to home, such as birds and butterflies helped to recovery by the reintroduction of hedges. Mace traces the changes in conversation thinking in the past 50 years. She identifies four different views of nature as emphasis has shifted from individual species to ecosystems, and from viewing nature as separate from humans to considering direct benefits to humans from nature. The different views have important implications for how scientists can measure conservation success and how policy-makers value and manage nature.

    Science, this issue p. 1558

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