This Week in Science

Science  28 Sep 2012:
Vol. 337, Issue 6102, pp. 1580
  1. Making the Change


    The Apocynaceae plant family produces toxic cardenolids. However, many insects have managed to escape the deleterious effects of these chemicals and even, in some cases, use them in their own defense. Zhen et al. (p. 1634) investigated a broad range of taxa and found several examples of parallel changes, as well as duplications, in members of the ATPα family that likely explain the shift to allow insects to avoid the toxic effects of these plants. Thus, natural selection can harness a combination of gene duplication, protein evolution, and regulatory evolution to allow distantly related species to adapt to specific niches.

  2. Kindergarten Scientists

    Becoming a scientist takes many years of training … or so it seems. It requires learning how to acquire data, to incorporate it into hypotheses, and then to test those hypotheses against newly acquired data; it requires learning how to think critically and to apply statistical analysis. Gopnik (p. 1623) reviews recent cognitive development findings that demonstrate how preschoolers act as young scientists in refining their intuitive representations of the world as they explore reality.

  3. Changing Rains

    The water cycle of the western United States has varied dramatically across the glacial cycles of the Pleistocene, possibly because of changes in the tracks of the storms that deliver moisture to the region. Lyle et al. (p. 1629) present evidence from a collection of Great Basin lakes which show that water levels rose over the last 20,000 years because of moisture transported from the tropical Pacific, not from a southward diversion of the westerly storm track. Furthermore, the timing of the lake level highs in the Great Basin shows a progression from south to north that does not coincide with the northward progression of wet intervals.

  4. Our Constant Sun

    The exact shape of the Sun provides information on its internal structure. Based on data obtained by the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory, Kuhn et al. (p. 1638, published online 16 August; see the Perspective by Gough) measured the solar shape during a 2-year period in which the Sun evolved from a minimum to a maximum of sunspot activity. Against expectations, the Sun's oblate shape was found to be constant and not to vary with the 11-year solar cycle.

  5. Solid View of a Sigma Complex


    For decades, it has been clear from kinetic studies that saturated hydrocarbons can also act as weak ligands, often just prior to bond cleavage reactions. These short-lived intermediates—termed “σ complexes” because the donated electrons reside in single (sigma symmetry) C-H bonds—have been glimpsed spectroscopically but have largely eluded full structural characterization. Pike et al. (p. 1648, published online 23 August) now present the crystallographic characterization of an alkane bound to rhodium, which they captured by direct hydrogenation of a more stable crystalline precursor incorporating an alkene.

  6. Reversible Implants

    Silicon electronics are generally designed to be stable and robust—it would be counterproductive if the key parts of your computer or cell phone slowly dissolved away while you were using it. In order to develop transient electronics for use as medical implants, Hwang et al. (p. 1640, see the cover) produced a complete set of tools and materials that would be needed to make standard devices. Devices were designed to have a specific lifetime, after which the component materials, such as porous silicon and silk, would be resorbed by the body.

  7. Gently Coupled

    Linked aryl rings are found in a broad range of commercial chemical products. Currently, the most versatile synthetic route to this motif involves cross-coupling of one ring with a halide substituent to another ring with a boron or metal-based substituent. Recent research has focused on eliminating the need for one or both of these activating substituents, but for the most part, the emerging methods have required high temperatures and high concentrations of one coupling partner. Ball et al. (p. 1644) now present a gold catalyst that can couple silyl-activated arenes to unactivated arenes in comparable concentrations at room temperature.

  8. Beyond Youthful Aggression

    Two decades ago, the combination of a demographic bulge of young males in Enga Province of Papua New Guinea and more deadly armaments triggered a series of intertribal wars and a surge in war-related fatalities; more recently, both wars and deaths have dropped. Drawing upon 20 years of conflict data, as well as historical records of the local social institutions, Wiessner and Pupu (p. 1651) analyzed the impact of youth-driven violence upon the traditional hierarchies and the subsequent evolution of the indigenous institutions into political structures capable of controlling conflict and reducing bloodshed.

  9. You Snooze, You Lose

    Sleep serves restorative and memory functions, but it does not always operate analogously across species. Deferral of sleep may be possible when selection strongly favors the awake. Lesku et al. (p. 1654; see the Perspective by Siegel) show that sleep may be deferred without cost or impairment in pectoral sandpipers. These birds breed collectively in the high Arctic, and male competition is intense. Competing for, and displaying to, females are both physically and cognitively demanding, yet birds who slept the least showed no decrease in their ability to perform these activities. Indeed, those males who slept the least obtained the most matings and sired the most offspring.

  10. Limiting Your Options

    Many species are dependent on specific resources that may limit their range of hosts to that of a few or even a single species. The restriction of the fly Drosophila pachea to senita cactus is a classic case of an ecological specialization. Lang et al. (p. 1658) reveal how multiple amino acid substitutions in the neverland gene have rendered D. pachea dependent upon the lathosterol of the senita cactus. Thus, relatively few genetic changes can play a large role in determining a species' ecological niche.

  11. A Tight Squeeze


    During intracellular transport, the export of procollagen from the endoplasmic reticulum is intriguing because procollagen is too large to fit into conventional coat protein complex II (COPII)–coated transport vesicles. Recent work has implicated the receptor TANGO1 in procollagen export. Now, Venditti et al. (p. 1668) report that TANGO1 recruits Sedlin—also known as TRAPPC2, a homolog of the yeast TRAPP subunit Trs20—and helps to allow COPII-coated carriers to grow large enough to incorporate procollagen.

  12. A Radical Mechanism

    The bacterial enzyme nitrogenase plays a key role in the global nitrogen cycle by catalyzing the reduction of N2 to ammonia. At the heart of the enzyme is a metal-sulfur cluster that contains an interstitial light atom recently identified as a carbide. The identification raised questions concerning the role of the carbide in the enzyme mechanism and how it is inserted into the metal cluster. Wiig et al. (p. 1672; see the Perspective by Boal and Rosenzweig) now show that the carbide derives from S-adenosylmethionine (SAM) and is inserted into the core by the radical SAM enzyme NifB.

  13. No More Junk DNA

    The majority of the human genome is transcribed at some level, but the function and evolutionary constraint among regions that do not regulate gene expression or code for genes are generally unknown. Examining data from the 1000 Genomes Project and ENCODE, Ward and Kellis (p. 1675, published online 5 September) examined regions of the human genome that did not show conservation among mammals and found evidence for a human lineage-specific constraint spanning approximately 4% of the genome that is biochemically active but not directly associated with genes. Interestingly, these regions showed lower numbers of single-nucleotide polymorphisms, heterozygosity, and derived allele frequencies, suggesting that they are under constraint and may be functional.

  14. Keeping Cancer Cells At Bay

    Cancer cells are often aneuploid; that is, they have an abnormal number of chromosomes. But to what extent this contributes to the tumorigenic phenotype is not clear. Senovilla et al. (p. 1678; see the Perspective by Zanetti and Mahadevan) found that tetraploidization of cancer cells can cause them to become immunogenic and thus aid in their clearance from the body by the immune system. Cells with excess chromosomes put stress on the endoplasmic reticulum, which leads to movement of the protein calreticulin to the cell surface. Calreticulin exposure in turn caused recognition of cancer cells in mice by the host immune system. Thus, the immune system appears to serve a protective role in eliminating hyperploid cells that must be overcome to allow unrestricted growth of cancer cells.

  15. Tuberculosis Vaccine Conundrum

    Some children experience severe clinical disease when they are vaccinated against tuberculosis, an attenuated live vaccine that is normally innocuous in humans. Several germline mutations have been identified that account for this susceptibility, and now Bogunovic et al. (p. 1684, published online 2 August) add another to the list—ISG15. Uncovering this mutation, which is inherited in an autosomal recessive manner, was a surprise because studies with mice deficient in ISG15 showed enhanced susceptibility to some viral, but not bacterial, infections. Nevertheless, patients lacking ISG15 were not able to produce adequate amounts of interferon-γ, a cytokine critical for clearance of the bacteria.

  16. Get Ready, Assemble, Fold

    The outer membrane protein complex LptD/E is responsible for lipopolysaccharide export to the cell surface of Escherichia coli. LptD is an essential β-barrel protein that contains two disulfide bonds between nonconsecutive cysteines. Chng et al. (p. 1665, published online 30 August) describe the characterization of the oxidative folding and assembly pathway of LptD/E in living cells. A combination of steady-state and pulse-chase measurements was used to identify seven intermediates with different disulfide-bonded states, along the oxidative folding pathway. During folding and assembly, a non-native disulfide-bonded LptD intermediate accumulated and, triggered by β-barrel assembly and association with the lipoprotein LptE, rearranged to the native disulfide-bonded state required for lipopolysaccharide export. Thus, disulfide bond–dependent protein folding can involve the proper assembly of a two-protein complex in order to promote disulfide bond rearrangement.

  17. Bacterial PERegrinations

    Many branches of the bacterial domain of life are only known from sequences that turn up in metagenomic analyses and are still only named by acronym—for example, the phylum-level groups BD1-5, OP11, OD1, and the PERs. The parent organisms are probably widespread, but they have not been cultured, and very little is known about their metabolisms or their contributions and functions in the natural environment. Wrighton et al. (p. 1661) pumped acetate into an aquifer in Colorado to prompt the naturally occurring bacteria into action and then, from the runoff, filtered out the smaller microbial cells for further analysis. Mass-spectrometry–based proteomics was used to test for functional activity, and 49 distinct genomes were recovered, many with surprising functional attributes. All of the recovered organisms appeared to be strict anaerobes with a full glycolytic pathway that were capable of augmenting energy production by coupling proton-pumping activity to adenosine triphosphate synthase. Several hydrogenases were found that seemed to be able to switch between hydrogen production and polysulfide reduction, depending on the substrate available. Notably, carbon dioxide assimilation was a common feature, with many genes having similarity to those of archaea.