Editors' Choice

Science  02 Mar 2012:
Vol. 335, Issue 6072, pp. 1020
  1. Immunology

    Skin Surveyors

    1. Kristen L. Mueller

    A specialized population of T cells that reside in the skin are important for responding to stress, such as that caused by wounding or malignancy. In mice, most of these cells express the γδ T cell receptor (TCR), and it is thought that they recognize stress when the TCR itself engages stress-induced ligands. Whether the TCR of skin γδ T cells is engaged in the steady state, however, is not well understood. Chodaczek et al. used a combination of intravital microscopy and immunohistochemistry of recently imaged mouse skin fragments to obtain a better picture of the actions of epidermal γδ T cells in the steady state. They found that these cells had specific orientations: They were positioned along squamous keratinocyte tight junctions and had multiple dendrites that extended toward the apical epidermis. The γδ TCR as well as other TCR signaling molecules localized to the tips of the dendrites in a TCR-specific manner. Epidermal stress caused γδ T cells to reorient toward the basal epidermis and Langerhans cells, but did not substantially alter the strength of the TCR signals. These results suggest that active TCR signaling in the basal state may help to prime γδ T cells to respond to a secondary stress signal.

    Nat. Immunol. 13, 272 (2012).

  2. Chemistry

    The Ends Control the Means

    1. Phil Szuromi

    Changing the balance of weak intermolecular forces can change the types of phases that molecules form. Cortese et al. explored the ordering of polypropylene (PPO) oligomers (either 460 or 2200 g/mol) bearing either thymine (Thy) or diaminotriazine (DAT) end groups, as well as mixtures of these molecules. The better-defined hydrogen bonding complementarity of Thy caused those associated oligomers to arrange in both a crystalline phase and a lamellar phase, in which the Thy groups formed an ordered two-dimensional crystal but the PPO chains were disordered. In contrast, DAT-terminated oligomers formed only glasses; the stronger affinity of PPO for DAT than Thy and the multiple hydrogen bonding motifs provided less driving force for microphase separation. In mixtures of the oligomers, the stronger Thy-DAT versus Thy-Thy interactions actually disrupted the lamellar ordering. In these systems, the ability of the end groups to crystallize appeared to be the main driver of mesoscopic ordering.

    J. Am. Chem. Soc. 134, 10.1021/ja2119496 (2012).

  3. Engineering

    Lightening the Load

    1. Jake Yeston

    One clear-cut method of raising the fuel efficiency of a car is to reduce its weight. Of course, that's easier said than done, given competing constraints such as safety and performance. Alonso et al. focus on a more subtle aspect of the problem. In principle, an overall reduction in gross vehicle mass (GVM) enables an associated reduction in the masses of many individual components that now bear and act on a lighter load. In practice, such secondary mass savings (SMS) may go unrealized because the subsystems are designed and manufactured separately—and in some cases are used in a range of car models that vary in GVM. The authors therefore empirically analyze the subsystems in a set of 77 vehicles (representing 13 different manufacturers) currently marketed in North America and Europe to pinpoint sources and scope of SMS, with the ultimate goal of facilitating consideration of these factors earlier in the overall design process. Their statistics indicate prospective mean SMS as high as 0.95 kg per kg of primary mass reduction.

    Environ. Sci. Technol. 46, 10.1021/es202938m (2012).

  4. Climate Science

    Soon It's Gonna Rain

    1. Brooks Hanson

    As climate warms, the atmosphere holds more moisture, and increased global precipitation is expected even while deserts may expand or move as areas receiving precipitation shift. This physics is captured in global climate models, and their results show changes even for warming over the 20th century. However, observational data seem to show an even greater increase in precipitation. Noake et al. take a closer look, comparing three data sets of on-land precipitation covering the latter half of the 20th century with the output from 54 climate model runs. Their analysis shows that precipitation increased most noticeably at higher latitudes in the Northern Hemisphere from December through May and over a wider belt in the fall; summer precipitation decreased slightly at lower latitudes. The model results are consistent with the pattern seen, but underestimate the spring increases seen at higher latitudes. Most useful for planning are estimates of the likely extremes in precipitation, as these affect flood forecasts and mitigation contingencies. Mishra et al. conduct an analysis comparing regional climate models and observations of urban extreme precipitation events across the United States. Their comparison similarly implies that regional models generally underestimate short-lived precipitation extremes but do somewhat better (about 25% success) with daily averages.

    Geophys. Res. Lett. 39, L03706; L03407 (2012).

  5. Ecology

    Behold My Triumph

    1. Sacha Vignieri

    Triumph displays are something we regularly associate with professional athletes, who often celebrate their victories in sometimes quite memorable ways. Such displays also occur widely among animals—for example, as loud calls that follow a victory over a competitor for territory or a mate. The functions of these displays, however, are not well understood. This is because understanding a display's function requires knowing something about how it influences its potential receivers, and characterizing a receiver's impression of a display is challenging. Mouterde et al. use a clever approach to try to characterize the internal response of nesting little blue penguins to the call of a triumphant male. They briefly replaced the eggs of nesting birds (both males and females) with egg-shaped heart monitors and then experimentally exposed them to calls simulated to represent winners and losers. When later exposed to the same calls, the heart rates of males rose significantly in the presence of winners, but not losers. The heart rates of females rose in response to both types of calls. These results suggest that triumph calls operate to establish a dominance reputation for individuals, particularly among males, and may help animals avoid conflict. This may be especially important in animals like little blue penguins whose contact with other individuals is relatively infrequent.

    Anim. Behav. 83, 605 (2012).

  6. Immunology

    Biased for the Better

    1. L. Bryan Ray

    Bacterial infections can turn deadly when components of the bacterial membrane, such as lipopolysaccharide (LPS), cause runaway activation of the host immune system. LPS binds to Toll-like receptor 4 (TLR4) on the surface of host cells and activates two major signaling pathways. One, which acts through an adaptor protein known as TRIF, leads to production of interferon and chemokines that beneficially stimulate the adaptive immune system. The problematic side is mediated by the adaptor known as MyD88, which stimulates inflammatory responses that can lead to toxicity. Bowen et al. report that a very small structural change in a mimetic molecule that acts like LPS, analogous to changing just one phosphate group on the lipid A portion of LPS, effectively separates the two signaling pathways. Binding of the mimetic to TLR4 activated TRIF-mediated signals but caused little or no activation of the MyD88-mediated pathway. The results confirm that it may be possible to design therapeutic agents that can harness beneficial signaling from the TLR4—for example, to promote a strong response to vaccination, but avoid the normally concomitant, potentially toxic inflammatory response.

    Sci. Signal. 5, ra13 (2012).

  7. Cell Biology

    A Forced Opening

    1. Valda Vinson

    Mechanical forces on bone stimulate intracellular signaling pathways in osteocytes that promote remodeling. Signaling molecules that drive such remodeling are likely transmitted between cells through the connexin 43 (Cx43) hemichannel (HC). Integrins are focal adhesion proteins that provide support to the cell by connecting the cytoskeleton to extracellular matrix (ECM) components like fibronectin. Integrins have also been proposed to be mechanosensors in bone cells. Batra et al. now show that the cytoplasmic domain of the α subunit of integrin α5β1 interacts with the cytoplasmic domain of Cx43, that the interaction is strengthened by fluid flow, and that this interaction is required for HC opening. The opening required osteocyte attachment to the ECM but was independent of integrin α5β1 binding to its ligand, fibronectin. Direct forces applied to integrin α5β1 by magnetic beads induced the opening of the HC, and such mechanical stress–induced opening required phosphatidylinositol 3-kinase (PI3K), which has been implicated in fluid-flow–induced activation of integrins in epithelial cells. It is likely that PI3K is responsive to fluid flow and transmits this to integrins, leading to opening of the HC and bone remodeling.

    Proc. Natl. Acad. Sci. U.S.A. 109, 10.1073/pnas.1115967109 (2012).