This Week in Science

Science  10 Jun 2011:
Vol. 332, Issue 6035, pp. 1237
  1. Endotoxin Revealed


    Nematic liquid crystals are composed of rigid rod molecules that try to orient in the same direction on a local scale. When confined in certain geometries, the molecular ordering cannot satisfy the boundary conditions of the system. Instead, regions of low order in the form of point defects will form, which are easily observed using optical microscopy. I.-H. Lin et al. (p. 1297, published online 19 May) show that lipid A will interact with the defects in a liquid crystal droplet, allowing for the extremely sensitive detection of this glycophospholipid, an essential component of a bacterially produced endotoxin.

  2. Understanding Change

    As a result of human activities, ecological communities are losing functionally irreplaceable species and gaining functionally novel ones, but research into the two processes has developed largely independently. Wardle et al. (p. 1273) review these two topics, explore how the species interchange may transform ecosystems through altering aboveground and belowground processes, and search for generalizations and unifying principles needed to understand how the Earth system may respond to global change.

  3. Macrophages Expand in Place

    Macrophages play an important role in pathogen clearance during infections. Macrophages increase in number in infected tissues through the recruitment of monocytes from the blood, which then differentiate into macrophages. Although this is the case for inflammatory macrophages participating in classical “type 1” responses, Jenkins et al. (p. 1284, published online 12 May; see the cover; see the Perspective by Randolph) report a different mechanism for macrophage accumulation in tissues during “type 2” responses, which often occur in response to parasitic infection. Tissue resident macrophages proliferated in situ in response to infection with a filarial nematode. Proliferating macrophages had an “alternatively activated” phenotype and required the type 2 cytokine interleukin-4 for their expansion. This mechanism of macrophage expansion may promote parasite sequestration and tissue repair in the absence of the immune pathology typically associated with the recruitment of inflammatory cells.

  4. Microcredit in the Philippines

    One of the aims of microcredit—the granting of small loans to groups or individuals with limited access to traditional formal lending sources—is to spur the start or growth of small-scale businesses, especially those run by women. Karlan and Zinman (p. 1278) developed a randomized methodology for assigning microloans to individuals in the Philippines. The availability of microloans increased the amount of borrowing that individuals undertook, but their businesses did not grow and could actually shrink. However, microcredit fostered ties between these individuals and their communities, making risk more manageable and increasing access to informal lending.

  5. Graphene Transformation and Integrated Circuits

    Metamaterials and transformation optics allow for the design of circuits and devices with functionalities beyond those of natural materials. Vakil and Engheta (p. 1291) show numerically that the optoelectronic properties of graphene offer the possibility of realizing such designer circuitry in a two-dimensional landscape only a single atom thick. The high mobility of charge carriers in graphene makes it an ideal candidate for the high-frequency devices used in radio-frequency applications. High-frequency, field-effect transistors have been demonstrated, but devices such as mixers, which create the sum and difference combination frequencies from two input frequencies, require other components. Y.-M. Lin et al. (p. 1294) used electron-beam lithography to define the components of a mixer for graphene grown in silicon carbide.

  6. Superfluids in a Stir


    Stirring a liquid can result in the formation of vortices or a change in the properties of the liquid, where a phase transition can be induced. If the liquid is a superfluid, quantum mechanical considerations restrict the angular momentum of the vortices so that they take quantized values and the liquid can become “normal.” Using somewhat phenomenological descriptions, how the vortices develop for a given condition is well understood, as are the different states that can arise, but a general theory describing the full evolution has been lacking. Bulgac et al. (p. 1288) describe a time-dependent density functional theory that provides a generalized description of the dynamics and phase transitions associated with the complex interactions of Fermi superfluids, which should prove a powerful tool in describing such systems.

  7. Through a Topsy-Turvy Tunnel

    One of the counterintuitive consequences of quantum mechanics is that chemical reactions can sometimes proceed in systems that lack the energy needed to power the associated atomic rearrangements. This phenomenon is termed tunneling: The molecules pass through, instead of over, an energy barrier to products. Schreiner et al. (p. 1300; see the Perspective by Carpenter) describe a system in which tunneling completely upends the expected course of a molecular rearrangement. In an unstable carbene compound with OH and CH3 groups bonded to a low-valency central carbon, an H atom shifted to the central carbon to form a more stable isomer. However, the H atom came from the OH group, despite facing a higher barrier than would a competing H shift from CH3.

  8. The Organic Who Fell to Earth

    Carbonaceous chondrites are primitive meteorites that provide samples of the materials from which Earth and the other planets in the solar system formed. They contain organic matter, which, while it is thought to have formed in the solar protoplanetary disk or in the interstellar medium prior to the Sun's formation, could have suffered alteration inside the meteorite's parent asteroid. Herd et al. (p. 1304) studied the organic compounds present in four pieces of a well-preserved carbonaceous chondrite meteorite, the Tagish Lake meteorite. The data suggest that parent body hydrothermal alteration played a role in the preservation and creation of organic molecules.

  9. Seeing the Heat

    Dim-light vision requires a visual system that has high sensitivity to light but a low probability of thermal activation. Nevertheless, thermal pigment noise does occur. Luo et al. (p. 1307) used single-cell recordings to measure photoisomerization activation energies and noise rates for diverse rod and cone pigments. A quantitative relationship was observed between a pigment's photoactivation energy and its peak absorption wavelength. A statistical-mechanical analysis using this relationship and modeling thermal activation was able to predict pigment noise rates.

  10. Smoking and Body Weight


    Smokers are on average thinner than nonsmokers, and many smokers gain weight when they quit. However, the specific cellular mechanisms of nicotinic receptors responsible for the effects of nicotinic agents on feeding are unclear. Now, Mineur et al. (p. 1330) show that nicotine acts through α3β4-containing nicotinic acetylcholine receptors to increase hypothalamic pro-opiomelanocortin neuron activity, which then decrease feeding and body weight. Thus, nicotinic agonists may be useful for limiting weight gain after smoking cessation, and nicotinic drugs could also help control obesity and related metabolic disorders.

  11. Mammalian DNA Damage Response

    To identify previously unrecognized components of a mammalian DNA damage response system, Cotta-Ramusino et al. (p. 1313) used a large-scale screen of small interfering RNAs in a human tumor cell line. A group of about 100 genes were identified that were necessary to keep cells with damaged DNA from proceeding into mitosis. Two of the proteins that localized at sites of DNA damage were CLOCK and RHINO. CLOCK is a transcription factor that functions as part of the circadian clock, and RHINO is a component of a complex of proteins that act together to stimulate activity of the protein kinase ATR, which propagates the signal to arrest the cell cycle and allow DNA repair.

  12. mTOR Substrates Revealed

    The protein kinase mTOR functions in protein complexes (mTORC1 and mTORC2) that are activated in response to agents such as growth factors and insulin and has important roles in regulating many physiological responses, including cell growth, proliferation, metabolism, and cell survival (see the Perspective by Yea and Fruman). Hsu et al. (p. 1317) and Yu et al. (p. 1322) conducted proteomic screens to identify substrates of mTORC1 and mTORC2 kinases. Numerous proteins that appear to be direct substrates were identified, including a new mTOR substrate, Grb10. Grb10 is an adaptor molecule that functions in the formation of signaling complexes associated with growth factor receptor tyrosine kinases.

  13. The Climes, They Are a-Changing

    In the light of climate change, how will species adapt to changes in their current habitats and ranges? Using an ensemble of yeast populations across a gradient of salt to simulate different degrees of change across the environment, Bell and Gonzalez (p. 1327) explored the role of dispersal and evolution in explaining adaptation following environment deterioration in spatially structured populations. Adaptation was higher when there was local dispersal, and environmental degradation was gradual, and when previous adaptation to degradation had occurred relative to populations that had not previously experienced stressful conditions.

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