This Week in Science

Science  06 Jul 2012:
Vol. 337, Issue 6090, pp. 10
  1. A Long Collapse


    Coral reefs are threatened by global warming and ocean acidification, and so it is important to understand better how and why environmental changes have affected them in the past. Toth et al. (p. 81) present a 6000-year-long record of coral reefs off the coast of Panama, Central America. The reefs effectively stopped growing for approximately 2600 years, beginning around 4000 years ago. This collapse of the coral reef system was probably caused by increased variability of ENSO, the El Nino–Southern Oscillation. If the strength or frequency of ENSO were to increase, the viability of these and other reef systems in the Pacific could be put further at risk.

  2. Network, Network, Network

    The fact that our interactions with others influence many of our decisions has led to research on characterizing the networks to which we belong and, more recently, on interventions that can change networks thereby changing behavior. This can have a variety of purposes, including promoting information flow through an organization or finding vulnerable points in bioterrorist networks. Valente (p. 49) reviews a variety of strategies for affecting networks.

  3. Dissecting Wnt/Fz Interaction

    Wnt proteins activate the transmembrane receptor Frizzled (Fz) to initiate pathways central to vertebrate and invertebrate development. Wnts are palmitoylated, which has complicated structural and functional characterization. Janda et al. (p. 59, published online 31 May; see the Perspective by Bienz and He) achieved coexpression and purification of Xenopus Wnt8 (XWnt8) with mouse Fz8 cysteine rich domain (CRD) and determined a crystal structure of the complex. Wnt binds to the Fz8 CRD at two distinct sites with the lipid group playing a key role in the first interface. Both interfaces involve conserved amino acids, which may explain the known pleiotropy of the Wnt/Fz interaction.

  4. A Dwarf in the Making

    It is a mystery how brown dwarfs, which have masses in between those of planets and stars, form. Based on observations with the Institut de Radioastronomie Millimétrique Plateau de Bure Interferometer, located in the French Alps, André et al. (p. 69; see the Perspective by Basu) report the detection of a brown dwarf that is still in the process of forming. The results lend support to models that suggest that brown dwarfs form in the same way as nuclear-burning stars, like our Sun, but do not rule out other models.

  5. Early Bloom Trigger


    Springtime phytoplankton blooms occur when high nutrient concentrations are combined with abundant sunlight and a stratified upper ocean layer. It has been thought that stratification occurs because in the spring, seasonal warming causes the water to expand, making it less dense, which creates a layer resistant to mixing from below. Now, Mahadevan et al. (p. 54; see the Perspective by Martin) have combined observations of the upper water column from the subpolar North Atlantic with ocean model simulations, which demonstrate that the initial stratification can be triggered by the dynamic effects of passing ocean eddies. These eddies can advance the time of the bloom by 20 to 30 days.

  6. Entanglement On Cue

    Quantum entanglement between particles lies at the core of quantum mechanics. For practical applications such as long-distance quantum communications, cryptography, and quantum networks, entanglement must be heralded. That is, a signal flags the existence of the entangled state so that it can be manipulated and transferred. Hofmann et al. (p. 72; see the Perspective by Volz and Rauschenbeutel) excited trapped single atoms in different laboratory rooms 20 meters apart and were able to show that manipulation, interference, and detection of the photons from the excited atoms could signal when the atoms are entangled. The extent of the observed entanglement may be sufficient to start to probe fundamental questions relating to the entanglement process and thus address the foundations of quantum mechanics.

  7. Mr. Cool

    Laser cooling of atoms relies on the presence of electronic transitions of specific structure, making it practical for a limited number of atomic species at relatively low densities. Alternative methods include those involving optical cavities, where atom-cavity interaction enables cooling without the need for resonant transitions. Wolke et al. (p. 75) present such a cooling scheme that was used to heat and then cool a Bose-Einstein condensate of Rb atoms. The method should be applicable to hotter samples where a sequence of laser pulses of different frequencies would need to be used.

  8. Indirect Injection

    Aerosols in the stratosphere, especially submicron-hydrated sulfuric acid droplets, are an important factor influencing climate variability. Stratospheric sulfate aerosols can form from sulfur dioxide that has been transported from the underlying troposphere. Large volcanic eruptions can inject sulfur dioxide and other material into the stratosphere, but smaller volcanoes have been thought not to be energetic enough to do so. Bourassa et al. (p. 78) used satellite data to show that sulfur dioxide from the 2011 eruption of the Nabro stratovolcano in Eritrea was lofted into the stratosphere by deep convection associated with the Asian summer monsoon.

  9. Twin Tales of Two Toxins

    The luminescent bacterium, Photorhabdus luminescens, is carried in the gut of an insect-parasitic nematode as a stealth weapon. By using an allele swapping technique, Somvanshi et al. (p. 88) investigated the promoter-switching mechanism that flips the bacterium from the almost dormant M forms, which stick to the adult nematode's posterior gut, into the motile, luminous P forms, which are armed with the toxic virulence factors needed to overcome the insect prey of the nematode. Similar switches may operate in bacteria that flip between harmless commensals and lethal pathogens. The bio-control agent Bacillus thuringiensis also kills insects by means of a crystal toxin, which allows the bacteria to penetrate the host gut and access nutrients. Release of nutrients also allows bacterial cheats that do not make toxin, to grow and outcompete the toxin-producing colonizers. In field experiments, Raymond et al. (p. 85) found that, consequently, the bacterial population becomes less virulent. Because these type of virulence factors are secreted from the cell and are widespread in pathogens, such social interactions may affect the fitness and constrain the virulence of many toxin-producing bacteria.

  10. Letting Pyruvate In

    Transport of pyruvate is an important event in metabolism whereby the pyruvate formed in glycolysis is transported into mitochondria to feed into the tricarboxylic acid cycle (see the Perspective by Murphy and Divakaruni). Two groups have now identified proteins that are components of the mitochondrial pyruvate transporter. Bricker et al. (p. 96, published online 24 May) found that the proteins mitochondrial pyruvate carrier 1 and 2 (MPC1 and MPC2) are required for full pyruvate transport in yeast and Drosophila cells and that humans with mutations in MPC1 have metabolic defects consistent with loss of the transporter. Herzig et al. (p. 93, published online 24 May) identified the same proteins as components of the carrier in yeast. Furthermore, expression of the mouse proteins in bacteria conferred increased transport of pyruvate into bacterial cells.

  11. A Deep Look Into Our Genes


    Recent debates have focused on the degree of genetic variation and its impact upon health at the genomic level in humans (see the Perspective by Casals and Bertranpetit). Tennessen et al. (p. 64, published online 17 May), looking at all of the protein-coding genes in the human genome, and Nelson et al. (p. 100, published online 17 May), looking at genes that encode drug targets, address this question through deep sequencing efforts on samples from multiple individuals. The findings suggest that most human variation is rare, not shared between populations, and that rare variants are likely to play a role in human health.

  12. Cancer Gene Islands

    Human tumors are riddled with genomic alterations that rearrange, remove, amplify, or otherwise disrupt a wide spectrum of genes, and a key challenge is identifying which of these alterations are causally involved in tumorigenesis. The role of recurrent hemizygous focal deletions is especially puzzling because these deletions preferentially affect certain chromosomal regions and result in the loss of one copy of a whole cluster of adjacent genes. Solimini et al. (p. 104, published online 24 May; see the Perspective by Greenman) found that these deletions span genomic regions that are enriched in genes that negatively regulate cell proliferation. The cumulative reduction in dosage and tumor suppressive function of the genes within these “cancer gene islands” may represent a critical factor driving tumor growth.

  13. You Must Be Human

    Are there specific brain structures associated with social cognition or with aspects of information processing that frequently occur together with social cognition? Carter et al. (p. 109) invited subjects to play a simplified virtual poker game against either a human or a computer and examined brain scans collected during the game. The brains scans when the cards shown were used to predict the participant's decision 6 seconds later. Activity in one region, the temporal-parietal junction, was one of the best predictors of future decisions against a human opponent, but the single worst predictor against a computer opponent.