Editors' Choice

Science  16 Dec 2011:
Vol. 334, Issue 6062, pp. 1473
  1. Cell Signaling

    ProNGF is Anti Growth

    1. L. Bryan Ray
    CREDIT: DEINHARDT ET AL., SCI. SIG. 4, RA82 (2011)

    Nerve growth factor (NGF) can influence multiple activities of neurons including survival, differentiation, and migration. The broad array of effects results in part from interaction with multiple distinct receptors and receptor complexes. Adding further to the regulatory versatility, NGF peptides are made in a precursor form (proNGF) that is proteolytically processed to form mature NGF, and this proNGF form has distinct biological effects. In cultured rat or mouse hippocampal neurons, Deinhardt et al. show that although NGF promotes neurite extension, proNGF caused growth cone collapse. ProNGF acted through the p75 neurotrophin receptor complexed with the sortilin family member SorCS2. This caused inhibition of the small guanosine triphosphatase Rac and inactivation of the actin-binding protein fascin, thus leading to collapse of growth cones. Because proNGF and the p75 neurotrophin receptor accumulate after nerve injury, they may contribute to impaired neuronal recovery after injury or in neurodegenerative diseases.

    Sci. Sig. 4, ra82 (2011).

  2. Chemistry

    Pi Underwater

    1. Jake Yeston

    Hydrogen bonding among hydroxyl, carbonyl, and amine groups is a critical organizing force in the structure of proteins and nucleic acids. Over the past several decades, an analogous attraction of O-H groups to the pi-electron cloud of aromatic rings has drawn increasing study. Gierszal et al. have now probed the strength of such pi-hydrogen bonds in dilute aqueous solutions of benzene. Their experiment relied on an unusually sensitive combination of Raman scattering measurements and spectral deconvolution to tease out the vibrational signature of this motif from amid the thousandfold more-intense set of vibrations spanning water-water interactions. Selective deuteration of both solvent and solute bolstered the assignment. A temperature-dependent study of the relative energetics supported a picture of pi-H bonds enthalpically weaker than the OH-H variety, but entropically favored on account of the greater conformational freedom accorded the water molecule by a benzene partner.

    J. Phys. Chem. Lett. 2, 2930 (2011).

  3. Ocean Science

    Eyeing Ojos for Coral Clues

    1. H. Jesse Smith
    CREDIT: CROOK ET AL., CORAL REEFS 10.1007/S00338-011-0839-Y (2011)

    As the concentration of CO2 in the atmosphere rises, so too does the amount of CO2 that is dissolved in the surface ocean. This dissolution lowers the pH and the carbonate saturation state of those waters, which can affect the viability of calcifying marine organisms such as coral reefs. It is difficult to project how severe will be the consequences of this acidification on the physiology of susceptible species, because as the process has not been occurring for long enough to foster accurate projections, and laboratory studies have a number of weaknesses that preclude convincing detailed predictions. Crook et al. wade into this issue by studying the marine biology of locations with naturally low carbonate saturation and low pH (called ojos), formed by the discharge of groundwater at localized submarine springs. They find that only three scleractinian coral species occur in these environments, none of which are common in Caribbean reefs. The reef ecosystems that occur in ojos may provide insights into potential long-term responses of corals to the low saturation conditions that now are becoming more common and more extreme.

    Coral Reefs 10.1007/s00338-011-0839-y (2011).

  4. Immunology

    Autoimmune Shutdown

    1. Kristen L. Mueller

    Many people with autoimmune diseases experience disease flares in which disease symptoms worsen. These flares often subside for a while, only to return again. Rosenblum et al. sought to understand the immunological basis for this phenomenon using a mouse model of inducible T cell–driven autoimmunity in the skin that resolves spontaneously. Disease induction was accompanied by an initial expansion of effector T cells in the skin that was followed by an expansion of regulatory T cells (Tregs). Although Treg cells were present in the skin before disease induction, they proliferated in response to autoantigen expression and were more potent immune suppressors. Moreover, disease resolution was critically dependent on Treg cells. Treg cells persisted in the skin in high numbers after disease resolution and were better able to control autoimmune symptoms when autoantigens were reexpressed in the skin. These results demonstrate that Treg cells are important regulators of immune homeostasis and may be critical for containing disease flares often seen in autoimmune diseases.

    Nature 10.1038/nature10664 (2011).

  5. Applied Physics

    Reflecting Atoms off Graphene

    1. Ian S. Osborne

    Electron and ion microscopes can provide exquisite structural detail on the nano- and subnanometer scale. However, achieving such resolution requires that the charged particles be accelerated to high energy, which can lead to structural damage induced by the scattering particles. There is also a requirement that the sample surface be conducting so that charging effects can be avoided. The scattering of low-energy neutral atoms or molecules can also be used to obtain structural information at high resolution, obviating the restrictions of sample conductivity and induced damage. The neutral beams of particles can in principle be guided by mirrors, but the problem is then being able to identify and fabricate high-quality atom mirrors. Sutter et al. report that terminating a typical atom mirror (consisting of a ruthenium layer deposited on sapphire) with a single layer of graphene considerably improves the reflectivity of helium atoms and hydrogen molecules from the surface. The flexibility of graphene facilitates self-molding of the material to any surface contours and corrugations and should enable the fabrication of complex, perhaps even reconfigurable, atom optic elements that would allow the operation of a scanning helium atom or hydrogen molecule microscope.

    Appl. Phys. Lett. 99, 211907 (2011).

  6. Economics

    Fair and Balanced?

    1. Gilbert Chin

    Has easy access to information via the Internet altered the exchange of goods in the marketplace of ideas? That is, when faced with virtually limitless choice, have consumers sampled more widely? Or have they gravitated toward news stories that confirm their worldviews? Gentzkow and Shapiro have computed the conservative/liberal composition of consumers of print, broadcast, and online media and also of those consumers' social networks. They find that segregation (in essence, the difference in goods chosen by conservatives versus liberals) is higher for online media than print or broadcast, but much lower than in one's social networks. They suggest that much of the discussion, in the media, about the consumption of media has focused on the tails of the distribution of goods offered for sale (e.g., foxnews.com or nytimes.com), whereas consumers are by and large more mainstream in their purchases. Furthermore, the consumers who do populate the online sites in those tails are in fact more avid readers of opposing views than the centrist user. In other words, most visitors to a strongly conservative site get their news from sites that are considerably less conservative, and the converse applies to liberal sites. One point to keep in mind, however, is that these findings refer to information consumed, which is not quite the same as beliefs held.

    Quart. J. Econ. 126, 10.1093/qje/qjr044 (2011).

  7. Biomedicine

    Rebuilding Muscle

    1. Lisa D. Chong

    Skeletal muscle injury can be debilitating and potentially lethal. Factors released by the damaged muscle can stimulate local skeletal muscle stem cells (satellite cells) to become motile, proliferate, and differentiate into replenishing myofibers. Stark et al. now suggest that even satellite cells distant from a site of injury could be recruited to help. The authors found that satellite cell motility was controlled by cell surface proteins called Ephrins that are expressed by healthy and regenerating muscle cells. Ephrins and their Eph receptors function as a guidance system in a variety of developmental processes. Ephrins elicited a repulsive signal that caused satellite cells to alter their migratory course. Mouse satellite cells grafted into either the developing hindbrain or limb bud of quail embryos respected Ephrin-defined boundaries as they migrated in vivo. The authors propose that Eph-Ephrin interactions may modulate satellite cell migration and patterning during muscle fiber development.

    Page et al. have used microthreads of fibrin to restore muscle function in mice with substantial leg muscle injury. When placed into the damaged area, the microthread scaffolds, seeded with adult human muscle cells that were coaxed into a stem cell–like state, restored healthy muscle fibers. Suprisingly, most of the new muscle was generated from recruited mouse satellite cells. Together, these studies point to potential therapies for treating major muscle injuries.

    Development 138, 5279 (2011); Tissue Eng. Part A 17, 2629 (2011).