This Week in Science

Science  28 Oct 2011:
Vol. 334, Issue 6055, pp. 430
  1. Snake Oil Revisited

    CREDIT: RIQUELME ET AL.

    The human heart can increase in size in two diverse settings. “Physiological” cardiac hypertrophy occurs in well-trained athletes and enhances heart function, whereas “pathological” hypertrophy occurs in response to heart attacks or hypertension and compromises heart function. To identify molecular factors that promote beneficial hypertrophy, Riquelme et al. (p. 528) studied Burmese pythons, which show a dramatic 40% increase in heart mass within 2 to 3 days after consumption of a large meal. This extreme physiological response was promoted by specific fatty acids in postprandial python plasma. In vitro and in vivo administration of these fatty acids stimulated signaling pathways associated with physiological hypertrophy in both python and mouse cardiac myocytes. Therapeutic interventions based on these fatty acids could potentially provide a way to enhance the heart's performance in patients.

  2. Aerosols and the Monsoon

    Most regions of India receive the majority of their rainfall from the summer monsoon, without which agriculture and the economy would fail. Annual precipitation has decreased since the middle of the last century over a wide area of the country. Bollasina et al. (p. 502, published online 29 September) used a climate model to simulate how the South Asian monsoon is affected by a variety of natural and anthropogenic influences and conclude that aerosols have caused most of the observed reductions in precipitation. The energy imbalance caused by the distribution of aerosols between the Northern Hemisphere (where pollution-derived aerosol concentrations are higher) and the Southern Hemisphere (where concentrations are lower) slows the atmospheric circulation that drives monsoonal rainfall.

  3. Watching the Action

    Experimental and theoretical studies have provided a framework for understanding protein folding, and computational advances have allowed millisecond-long simulations of specific folding pathways. However, experimental methods have not had the resolution to validate these pathways (see the Perspective by Sosnick and Hinshaw). Stigler et al. (p. 512) used ultra stable high-resolution optical tweezers to monitor at submillisecond resolution for tens of minutes the fluctuations of full-length calmodulin as it transitioned between unfolded and folded states. Lindorff-Larsen et al. (p. 517) used the supercomputer Anton and a single force field to simulate reversible folding and unfolding of 12 protein domains over periods ranging between 100 µs and 1 ms. The proteins, which represent the major structural classes (α helix, β sheet, and mixed αβ) folded to their experimentally determined structures by following a single dominant route in which the backbone adopted a native-like structure early in the folding process.

  4. Tiny Yarns

    While considerable progress has been made in the miniaturization of motors, pumps, and compressors, challenges arise in making very small devices. For linear motion, a range of actuating materials have been developed, depending on whether one needs a high actuating force or a large displacement, but far less progress has been made on rotational actuators. Foroughi et al. (p. 494, published online 13 October) show that carbon nanotube yarns can be used as torsional actuators. When the yarns were immersed in an electrolyte, the injection of charge caused reversible untwisting.

  5. Rosetta Flies by Lutetia

    Launched from Earth in 2004 and presently en route to a comet, the European Space Agency Rosetta spacecraft flew by the large, main-belt asteroid 21 Lutetia on 10 July 2010. Sierks et al. (p. 487) calculated the asteroid's volume based on images obtained during the fly by; Pätzold et al. (p. 491) used radio-tracking of the Rosetta spacecraft as it flew past 21 Lutetia to compute the asteroid's mass. In comparison to other asteroids, 21 Lutetia has a high bulk density—a parameter that provides clues to its origin and internal structure. 21 Lutetia is a highly cratered asteroid with a complex surface geology, suggesting a long and complex history. Coradini et al. (p. 492) examined 21 Lutetia's temperature and surface composition, which showed that its surface is very homogeneous, with no evidence of aqueous alteration or space weathering.

  6. Another Footprint of Man

    Human activities, particularly industrial and agricultural, have had significant impacts on the biogeochemical cycles of both nitrogen and phosphorous. Nitrogen and phosphorus are essential nutrients for marine fauna and are cycled in a roughly constant ratio. In the coastal and marginal seas of the northwestern Pacific Ocean, however, nitrogen concentrations have increased faster than those of phosphorus over the past 30 years. Kim et al. (p. 505, published online 22 September) present evidence that the discrepancy results from atmospheric nitrogen deposition. While air pollution is a source of nitrogen in lakes, its impact on the ocean has not been clear.

  7. Since the Time of the Dinosaurs

    The timing of mammalian diversification and the relationships between the major mammalian lineages have long been debated. Meredith et al. (p. 521, published online 22 September; see the Perspective by Helgen) present a phylogenetic analysis of a molecular supermatrix of 164 mammals from 26 gene fragments calibrated with multiple fossils. The findings support the “long fuse” model of mammalian evolution, which suggests that the majority of mammalian orders originated at the end of the Cretaceous period and then further diversified after the Cretaceous-Paleogene Mass Extinction when the dinosaurs became extinct, approximately 65 million years ago.

  8. Together We Can

    Mobilizing groups of unrelated people requires incentives. Recently, a competition was held by the U.S. Defense Advanced Research Projects Agency, in which teams attempted to mobilize large numbers of individuals to solve a shared task. Pickard et al. (p. 509) describe the winning strategy, in which participants were not only encouraged to solve part of a task but also rewarded if they passed on the information to others who were successful.

  9. Toward a Malaria Vaccine

    CREDIT: SUMANA CHAKRAVARTY/SANARIA, INC.

    Despite malaria being a major global public health threat, there is still no effective malaria vaccine. The only highly protective immunogen is the delivery of sporozoites by mosquito bite, but approximately 1000 bites may be required. A viable vaccine strategy this is not, but it does suggest that an attenuated sporozoite vaccine may provide protection. Epstein et al. (p. 475, published online 8 September; see the Perspective by Kappe and Mikolajczak) tested this hypothesis by creating a vaccine composed of purified, irradiated Plasmodium falciparum sporozoites. The vaccine was administered subcutaneously or intradermally to volunteers. Although the vaccine was suboptimally immunogenic and protective, the vaccine was safe. In animal models, intravenous delivery of the vaccine, rather than inoculation of the skin, produced sporozoite-specific responses in monkeys and conferred protection in mice. Thus, intravenous delivery of the vaccine might confer greater protection in humans.

  10. Where Do Interneurons Come From?

    Interneurons shape the output of functional circuits in the brain. Proper functioning of the neocortex critically depends on the production of a correct number of excitatory and inhibitory neurons, which largely occurs during the embryonic stages. However, our knowledge of neocortical interneuron neurogenesis remains sparse. Brown et al. (p. 480) performed clonal analysis of the production and organization of inhibitory interneurons in the mouse neocortex and discovered that neocortical interneurons are produced as spatially organized clonal units. The lineage relationship seems to play a critical role in organizing neocortical interneurons.

  11. Toward Heparin in a Hurry

    The heparin class of anticoagulant drugs—widely used for more than half a century—comprises a range of saccharide chains with a particular pattern of sulfate substitution. Because this pattern is hard to produce artificially, most heparins are sourced from farm animals that biosynthesize them, but a recent contamination scandal has focused attention on finding more readily controllable synthetic routes. The one commercially applied purely chemical synthesis requires ∼50 steps to produce an appropriately functionalized pentasaccharide. Xu et al. (p. 498; see the Perspective by Turnball) now show that application of a cocktail of carefully chosen enzymes to a simple precursor produces two different heptasaccharides with the proper sulfation pattern in 10 to 12 steps and ∼40% yield. In preliminary in vitro and rabbit model assays, the product possessed promising anticoagulant activities.

  12. Unraveling Tumor Suppression

    The BRCA1 tumor suppressor was identified in 1994 as a target of germline mutations that confer hereditary breast and ovarian cancer. Although various cellular functions of BRCA1 have been defined, including its biochemical activity as an E3 ubiquitin ligase, their relevance in tumor suppression is unclear. Shakya et al. (p. 525; see the Perspective by Greenberg) used a mouse model of hereditary breast cancer to define which BRCA1 domains are required to prevent mammary carcinogenesis. The BRCT phospho-recognition domain was critical for BRCA1 tumor suppression, whereas the ubiquitin ligase activity was not, challenging current assumptions on the mechanistic role of BRCA1 in tumor suppression.

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