Editors' Choice

Science  30 Mar 2012:
Vol. 335, Issue 6076, pp. 1546
  1. Climate Science

    Extreme Melting

    1. H. Jesse Smith
    CREDIT: ISTOCKPHOTO.COM

    Climate models have predicted that extreme weather events will increase in frequency and intensity as greenhouse gases continue to accumulate in the atmosphere and the consequent global warming intensifies. Such a change could have tremendous practical impacts on our environment and our lives. It is of interest, therefore, to understand the mechanisms that may cause this phenomenon. One obvious part of the world toward which to look for evidence is the Arctic, where the rate of warming has been faster than anywhere else on Earth. Francis and Vavrus examined atmospheric data from the mid- and high-latitude Northern Hemisphere and identified two mechanisms that seem to contribute to the trend toward extremes, both of which have the effect of slowing down the west-to-east progression of weather systems in the northern mid-latitudes, thereby intensifying their impacts. These changes seem to be the result of growing Arctic sea-ice loss, which causes the transfer of additional energy from the ocean into the high-latitude atmosphere, and of earlier continental snow melt and drying of the soil, which increase the tendency toward high-amplitude weather patterns in summer.

    Geophys. Res. Lett. 39, L06801 (2012).

  2. Chemistry

    Golden Proteins

    1. Phil Szuromi

    Gold nanoparticles (Au NPs) have long been used as an aid in biological imaging, in part because of their low chemical reactivity. Malay et al. studied the effect of covalent attachment of Au NPs to TRAP (trp RNA-binding attenuation protein), which plays a feedback role in tryptophan biosynthesis in Bacillus, by mutating a Lys residue to Cys. The TRAP protein normally forms a ring of 11 monomers and has been of interest for the delivery of nanoscale objects. However, the incubation of the Cys-bearing protein with 1.4-nm Au NPs created two types of structures similar to viral capsids: hollow shells either 15 to 16 or 21 to 22 nm in diameter. These structures did not form when the native protein was simply mixed with Au NPs, and their formation depended on pH conditions and the concentration of Au NPs. Cryoelectron microscopy also revealed that not all of the capsids retained the Au NPs, which suggests that their role may be to catalyze the rearrangement from the toroidal structure.

    Nano Lett. 10.1021/nl3002155 (2012).

  3. Biomedicine

    Ovarian Cancer Origins

    1. Beverly A. Purnell

    One to 2% of women will be diagnosed with ovarian cancer in their lifetimes. As a result, there is great interest in better understanding the molecular and cellular events that drive the development of this cancer. In fact, whether the ovary or fallopian tube gives rise to serous ovarian cancer, the subtype that causes 70% of ovarian cancer deaths, is still unknown. To investigate this question, Kim et al. generated mice with reproductive tract–specific deletions in Dicer, the enzyme that converts pre-microRNAs to mature microRNAs, and Pten, a tumor suppressor. They found that serous ovarian carcinomas developed from the fallopian tube and then metastasized elsewhere, killing all double knockout mice by 6 to 12 months of age. Mice singly deficient in these proteins, however, did not show tumor development in the reproductive system. Histological analysis revealed that abnormal cell proliferation started in the stromal compartment of the fallopian tube rather than the epithelial layer, with the cells undergoing a stromal-to-epithelial transition. The phenotypic, histological, and molecular characteristics of the cancers that developed in the double knockout mice were similar to those seen in humans. These mice may therefore provide a useful model system for studying serous ovarian cancer.

    Proc. Natl. Acad. Sci. U.S.A. 109, 3921 (2012).

  4. Cell Biology

    Knocking on Cilia's Door

    1. Stella M. Hurtley

    Primary cilia are hairlike projections found at the surface of differentiated cells that play a role in development and signalling. Defects in ciliary protein localization and function are linked to human diseases, including retinal degeneration, polycystic kidney diseases, skeletal defects, and obesity. Microtubules provide cilia with their fundamental structural integrity, but cilia contain a multitude of specific proteins and are ensheathed by a specialized membrane. The entry of proteins from the cytosol into the cilium appears to be restricted at its base, and there is evidence that components of the nuclear import machinery may play a role. Kee et al. exploited the potential similarities between nuclear import and ciliary protein import to try to dissect the molecular mechanisms involved. Like the nuclear pore, the base of the cilium in mammalian tissue culture cells excluded microinjected proteins larger than ∼40 kD, whereas smaller proteins freely diffused into the cilium. This diffusion barrier appeared to be related to the presence of nucleoporins, some of which could be localized at the base of the cilium. Indeed, microinjection of nucleoporin function–blocking agents restricted the entry of a ciliary motor protein. Thus, the base of the cilium appears to play a role similar to that of the nuclear pore in restricting access. How ciliary proteins are then specifically allowed to enter, however, remains unclear.

    CREDIT: NAT. CELL BIOL. 14, 10.1038/NCB2450 (2012)

    Nat. Cell Biol. 14, 10.1038/ncb2450 (2012).

  5. Economics

    Not So Committed?

    1. Barbara R. Jasny

    What factors influence the willingness of companies to engage in acts of social responsibility, and when does it represent a real commitment rather than window dressing? To study this question, Lim and Tsutsui looked at two global initiatives. The United Nations Global Compact encourages businesses to use sustainable practices and focuses on human rights, labor, the environment, and anticorruption. Governments can formally endorse the program, and corporations who participate are expected to submit annual Communications of Progress. The Global Reporting Initiative, which provides standards and Sustainability Reporting Guidelines, requires an even more substantial commitment. Using data from 99 countries spanning 2000–2007, the authors found that nongovernmental organization linkages encouraged the adoption of corporate social responsibility policies. In developing countries, this was associated with substantial commitment; however, in developed countries, commitment was more ceremonial. Liberal economic policies in the developed world were also associated with ceremonial commitment, suggesting to the authors a “pattern of organized hypocrisy” in which costly norms are imposed by the developed world on others.

    Am. Sociol. Rev. 77, 69 (2012).

  6. Chemistry

    More Oomph for OPH

    1. Jake Yeston

    Enzymes are remarkably adept at accelerating complex chemical reactions, but they tend to work best in the milieu where they evolved. It is therefore often challenging to apply them at high temperature or in the midst of interfering factors. El-Boubbou et al. sought to optimize the use of organophosphorus hydrolase (OPH) in the service of degrading the highly toxic organophosphorus compounds present in certain pesticides and nerve agents. They found that immobilization of the enzyme in mesoporous silica prefunctionalized with ammonium ions conferred substantial thermal stability without compromising the flexibility necessary for catalytic activity. Phosphorus-31 nuclear magnetic resonance spectroscopy was applied to monitor rates for hydrolysis of the model compound paraoxon, and revealed enhanced specific activity of the immobilized enzyme relative to the native enzyme in solution. The silica-bound enzyme remained active after being heated (either dry or in suspension) to temperatures as high as 65°C for extended periods—as long as a month at 45°C.

    Adv. Healthcare Mater. 1, 183 (2012).

  7. Microbiology

    In Need of Nutrients

    1. Kristen L. Mueller

    Gut pathogens such as E. coli and Salmonella are faced with several hurdles when trying to establish an infection: the recruitment of immune cells, the secretion of antimicrobial factors, and competition in the form of the billions of commensal bacteria that normally reside in our guts. As a result, the pathogens need to have a few tricks up their sleeve. Liu et al. now report on one such example, used by Salmonella enterica serovar Typhimurium, a pathogen that causes severe gastroenteritis in humans. In response to S. Typhimurium infection, neutrophils are recruited to the gut in mice and produce the antimicrobial protein calprotectin. Calprotectin functions by sequestering essential metals, such as zinc, thus limiting an important nutrient source for the invading pathogen. S. Typhimurium can overcome this, and compete with the commensal flora, however, because it expresses a high-affinity zinc transporter. Strains that lacked this transporter did not grow as well in the inflamed gut but were not at a disadvantage in the absence of inflammation. These results suggest that nutrient availability is a key factor in the establishment of gastrointestinal infections.

    CREDIT: ROCKY MOUNTAIN LABORATORIES, NIAID, NIH

    Cell Host Microbe 11, 227 (2012).

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