This Week in Science

Science  31 May 2013:
Vol. 340, Issue 6136, pp. 1013
  1. Going to Mars


    The Mars Science Laboratory spacecraft containing the Curiosity rover, was launched from Earth in November 2011 and arrived at Gale crater on Mars in August 2012. Zeitlin et al. (p. 1080) report measurements of the energetic particle radiation environment inside the spacecraft during its cruise to Mars, confirming the hazard likely to be posed by this radiation to astronauts on a future potential trip to Mars. Williams et al. (p. 1068, see the Perspective by Jerolmack) report the detection of sedimentary conglomerates (pebbles mixed with sand and turned to rock) at Gale crater. The rounding of the rocks suggests abrasion of the pebbles as they were transported by flowing water several kilometers or more from their source.

  2. Building Better Vaccines

    Vaccines are one of the most effective tools to protect against infectious diseases. Unfortunately, vaccines for diseases with the highest global health burdens, such as HIV, malaria, and tuberculosis, are not yet available. Koff et al. (1232910) review the latest advances in vaccine development and why these particular diseases remain such a challenge. Respiratory syncytial virus (RSV) is a serious cause of morbidity and mortality in infants and young children worldwide. Although a prophylactic antibody is available for children at high risk, a vaccine is much needed. As a potential step toward this goal, McLellan et al. (p. 1113, published online 25 April) solved the cocrystal structure of a neutralizing antibody (D25) bound to the prefusion F protein of RSV. Knowledge of the structure of the prefusion protein should help to guide vaccine design and the development of additional therapeutics.

  3. Independent Chiral Catalysts

    Synthetic catalysts can be prepared in their mirror-image form and thereby furnish the mirror-image (enantiomer) of the reaction product. In practice, however, this versatility is largely limited to products featuring a single stereocenter that accounts for the dissymmetry. Krautwald et al. (p. 1065; see the Perspective by Schindler and Jacobsen) now report a pair of chiral catalysts—an iridium complex and an amine—that operate in concert to facilitate carbon-carbon bond formation, while retaining independent stereoselectivity toward their respective sides of the bond.

  4. Multiple Inputs to Flowering

    Perennial plants need to cycle through an extended vegetative phase, in a process known as vernalization, before they initiate flowering. Bergonzi et al. (p. 1094) and Zhou et al. (p. 1097) studied how molecular signals translate environmental information—such as exposure to a winter season or changes in daylength and physiological information, such as age of the plant—into signals that promote flowering. In both Arabis alpina and Cardamine flexuosa, age and vernalization pathways are integrated through the regulation of microRNAs miR156 and miR172.

  5. It's an Ant's Life

    Eusocial insects live in highly organized societies where groups of individuals carry out specific tasks; for example, caring for the eggs, cleaning the nest, or foraging, which might suggest the presence of an advanced form of organization, similar to what might be expected from more cognitively advanced species. Mersch et al. (p. 1090, published online 18 April) tracked individual ant movements and interactions to show that their precise social organization results from temporal changes in the spatial location of workers. As they aged, ants largely progressed from being nurses located near the queen, to nest cleaners who move throughout the colony, and finally to foragers moving in and out at the colony edges.

  6. Graphene Staying Strong

    Although exfoliated graphene can be extremely strong, it is produced on too small a scale for materials application. Graphene can be produced on a more practical scale by chemical vapor deposition, but the presence of grain boundaries between crystallites apparently weakens the material. Lee et al. (p. 1073) show that postprocessing steps during the removal of the graphene sheets can oxidize the grain boundaries and weaken them. If these steps are avoided, the material is comparable in strength to exfoliated graphene.

  7. The Birds and the Seeds


    When species are lost from ecosystems through local extinction, the pattern of ecological interactions changes. Galetti et al. (p. 1086) show how the loss of large fruit-eating birds from tropical forest fragments in Brazil affects the reduction of seed size in a palm species. A data set was compiled that consisted of >9000 seeds measured in 22 populations over a large area of Atlantic rainforest, including seven areas where large-seed dispersers (toucans, cracids, and large cotingas) were extinct and 15 areas where they are still common.

  8. Hedgehogs, Whirls, and Zippers

    Topologically ordered materials at certain ranges of temperature and magnetic field can form a regular lattice of magnetic whirls called skyrmions. Milde et al. (p. 1076) studied the destruction of a skyrmion lattice with varying magnetic fields by imaging the surface magnetic structure. Magnetic force microscopy revealed a pairwise merging of skyrmions on the surface. Furthermore, in the bulk, a hedgehog-like spin structure with the properties of the elusive magnetic monopole was needed to "zip" together the corresponding skyrmion lines.

  9. Choice in Changing Environments

    Animals, including humans, generally tend to judge the world on relative, rather than absolute, terms. For example, the value of a particular object or reward is generally determined based on comparison to other rewards we have received in the past or to those that others have received. Such contrast effects can have negative or positive impacts on our behavior. McNamara et al. (p. 1084) used an optimality model to show that contrast effects could evolve as an adaptive response to environmental instability and unpredictability.

  10. Limiting mTORC1

    The mTORC1 protein kinase complex has important functions linking metabolism to cell growth and its functions are disrupted in common diseases, including cancer and diabetes. Bar-Peled et al. (p. 1100; see the Perspective by Shaw) discovered regulatory components that help turn down signaling by mTORC1 when cells are deprived of amino acids. Two complexes of proteins, GATOR1 and GATOR2, have opposite effects on activity and cellular localization of mTORC1. Components of the GATOR1 complex negatively regulate mTORC1 and appear to function as tumor supressors. Cancers with loss of GATOR1 function may be particularly amenable to therapeutic strategies that limit activity of mTORC1.

  11. Kinetochore Targeting

    Chromosomes must be segregated accurately during cell division. This is facilitated by the attachment of mitotic spindle microtubules to the kinetochore at the chromosomal centromere. The centromere is marked with the histone H3 variant CenH3 (CENP-A in human), and CENP-C forms part of the inner kinetochore. Kato et al. (p. 1110) used structural biology, biochemistry, and mutagenesis to show that CENP-C recognizes CENP-A chromatin via several different interactions. The CENP-C "central domain" makes close contact with the acidic patch of histones H2A/H2B, and the highly conserved "CENP-C motif" senses both the acidic patch and recognizes the hydrophobicity of the otherwise nonconserved CenH3 tail, supporting a conserved mechanism of centromere targeting by the kinetochore.

  12. Vitamin E Out

    Familial vitamin E deficiency is caused by mutations in the α-tocopherol transfer protein (α-TTP) gene. Kono et al. (p. 1106, published online 18 April; see the Perspective by Mesmin and Antonny) studied natural mutations in α-TTP. α-TTP bound phosphatidylinositol polyphosphates (PIPs), especially PI(4,5)P2, and a disease-related missense mutation abolished PIP binding but not α-tocopherol binding. The x-ray crystal structure of the α-TTP–PIP complex suggested that PIP binding opens the lid of the α-tocopherol–binding pocket to facilitate the release of α-tocopherol. Thus, PIP binding to α-TTP at the target membrane may facilitate the release of α-tocopherol in the hydrophobic pocket of α-TTP to the lipid bilayer of the target membrane, providing a mechanism for the transfer of lipids from the lipid-transfer protein to the target membrane.