Editors' Choice

Science  24 Jun 2011:
Vol. 332, Issue 6037, pp. 1483
  1. Psychology

    Channeling Euclid

    1. Brad Wible
    CREDIT: WIKIMEDIA COMMONS

    Behavioral research has explored how human and animal understanding of space reflects principles of Euclidean geometry. Though perception of the environment can affect many mental processes, Kant argued for an a priori, innate spatial intuition. Such intuition might underpin the ability to understand geometric concepts that are not observable in nature, such as an infinitely thin line or infinitely large plane. To address the universality of Euclidean concepts, Izard et al. tested a population indigenous to the Amazon, the Mundurucu, who have no formal training in geometry. This group of both children and adults was compared to mathematically educated U.S. adults, comparably aged French children, and younger U.S. children. Among other queries, people were shown dots and lines, representing villages and paths, projected on a plane or sphere, and asked whether a line could be drawn through a point and never cross another line. The Mundurucu responses were similar to those of U.S. adults and French children, reflecting strong application of Euclidean principles. The younger U.S. children responded similarly but were more error-prone. Across cultures, people were biased to erroneously apply Euclidean principles to spheres. The authors propose that new research explore whether understanding of abstract geometry is innate but only emergent at a certain time in development, or whether it is learned as a result of experiences so general that all humans are exposed to them.

    Proc. Natl. Acad. Sci. U.S.A. 108, 9782 (2011).

  2. Materials Science

    Nanoparticles Make the Cut

    1. Phil Szuromi

    It has long been known from ex situ studies that metal nanoparticles can catalyze reaction of oxygen with graphite surfaces and create grooves or channels. Such reactions could be used for patterning graphene sheets. Booth et al. have studied the dynamics of silver nanoparticles on suspended monolayer and bilayer graphene sheets in a transmission electron microscope. They imaged these samples at temperatures from 600 to 850 K and partial pressures of oxygen over the sample from about 30 to 100 millitorr. The nanoparticles cut channels along <100> crystallographic directions, but some fluctuations of motion normal to the channel direction were also observed. The nanoparticles did not move at a constant speed. Instead, their velocity profile was erratic, and the start-stop motion was better described by a Poisson distribution.

    Nano Lett. 11, 10.1021/nl200928k (2011).

  3. Biochemistry

    Breakdown Breakthrough

    1. Lisa D. Chong

    Lignin is an organic polymer that binds tightly to cellulose fibers in plant cell walls, imparting rigidity and strength. The conversion of plant biomass into biofuels has been a challenge, in part because lignin hinders the degradation of cellulose into sugars that can be fermented. One approach is to use enzymes that break down lignin. Although such enzymes have been characterized in fungi, these microorganisms have been difficult to exploit commercially. Some bacteria secrete lignin-degrading enzymes, but the details are not well understood. The identification of a bacterial lignin-degrading gene would allow large-scale production of the enzyme in an organism that is easy to genetically manipulate and grow. Ahmad et al. used a bioinformatics approach to identify a gene in the soil bacterium Rhodococcus jostii that encodes a lignin-degrading peroxidase (DypB). In the presence of manganese salts, recombinant DypB expressed and purified from Escherichia coli showed degradation activity toward lignin, lignocelluloses from wheat straw, and synthetic model compounds. It is not clear how DypB is secreted from R. jostii, but the dypB gene is adjacent to a gene that encodes encapsulin, a shell-forming protein. The authors speculate that the genes may be coupled, and that an encapulsin nanocompartment could facilitate secretion.

    Biochemistry 50, 5096 (2011).

  4. Immunology

    Viruses Are (I)FIT To Be Tied

    1. Kristen L. Mueller
    CREDIT: PICHLMAIR ET AL., NAT. IMMUNOL. 12, 10.1038/NI.2048 (2011)

    The immune system is constantly surveying the body for signs of infection, but how can it distinguish viruses from self? Viruses can be distinguished from self because their nucleic acids contain specific characteristics, such the triphosphorylated RNA (PPP-RNA), that are not found in the nucleic acids of host cells. The molecules that recognize these viral structures, however, are still being identified. Pichlmair et al. carried out a screen to identify proteins that interact with PPP-RNA and identified several members of the IFIT family of interferon-stimulated proteins. In response to antiviral interferons, IFIT proteins formed a molecular complex with other family members and RNA-binding proteins. Subsequent biochemical and genetic analysis focused on IFIT1 and found that, although it did not appear to be involved in the initial detection of the virus, it was highly induced in response to antiviral interferons and was required for keeping viral growth in check in cultured cells and in mice infected with vesicular stomatitis virus. Although IFITs have been previously associated with inhibition of protein translation, the authors presented data consistent with IFIT1 functioning by sequestering viral nucleic acids within the cell.

    Nat. Immunol. 12, 10.1038/ni.2048 (2011).

  5. Chemistry

    Phosphorus Ins and Outs

    1. Jake Yeston
    CREDIT: STOLLENZ ET AL., ANGEW. CHEM. INT. ED. 50, 10.1002/ANIE.201100893 (2011)

    Both amines and phosphines are shaped like pyramids. The difference is that amines rapidly undergo so-called umbrella inversions, whereby the three groups pushed downward by the electron lone pair at the nitrogen vertex suddenly point upward (or vice versa). In phosphines, the inversion is much slower: At room temperature, the three groups bound to P tend to stay put. Stollenz et al. were therefore initially puzzled by the behavior of a diphosphine in which three flexible (CH2)14 chains bridge two P atoms: Facile conversion was taking place between the isomer with both electron pairs facing in and the one with both pairs facing out. Some study of models convinced them of a rather distinct mechanism, in which one of the methylene chains was passing through the ring bounded by the other two, in effect turning the compound inside out. To bolster this hypothesis, they heated the compound to high enough temperature to induce the more common umbrella inversions and isolate in/out isomers, and then verified that these new isomers could not convert to the in/in and out/out variants at room temperature—a result in accord with the topological restrictions of the inside-out pathway.

    Angew. Chem. Int. Ed. 50, 10.1002/anie.201100893 (2011).

  6. Development

    It's Complicated

    1. Pamela J. Hines

    Puberty in humans responds to factors as varied as nutritional status and social interactions. But sooner or later, pulses of gonadotropin-releasing hormone begin and puberty ensues. Previous studies had implicated the neuropeptide kisspeptin in initiating puberty, but Mayer and Boehm now show that puberty initiation may be more complicated. Studying mice, the authors selectively ablated neurons that expressed kisspeptin, or its receptor, in young or mature mice. Although deletion of the genes encoding kisspeptin or its receptor result in infertility and deficient gonadal development, toxin-mediated ablation of neurons that express kisspeptin did not. If the ablation occurred in young mice, the mice went through puberty and reached fertility, although with smaller-than-normal gonads. If the ablation occurred in mature mice, these mice became infertile. The differential sensitivity of mice to kisspeptin gene deletion compared to deletion of kisspeptin-expressing neurons indicates that there are probably redundancies in the puberty-initiating machinery, which, given the importance of this process to the success of the species, may make sense.

    Nat. Neurosci. 14, 704 (2011).

  7. Immunology

    Estrogen Receptor's Two Faces

    1. Kristen L. Mueller

    Many autoimmune diseases, including multiple sclerosis (MS), are more prevalent in women. This, coupled with prior findings implicating a role for the estrogen receptor (ER) in MS, prompted Saijo et al. to uncover the underlying molecular mechanisms. After determining that microglia, resident myeloid cells in the brain, primarily express ERβ, the authors showed that depending on the ligand, signaling through ERβ could either induce or inhibit proinflammatory gene expression. 17β-estradiol, which is more prevalent in women, drove expression of proinflammatory genes, whereas 5-androsten-3β,17β-diol (ADIOL) inhibited them. This occurred because ADIOL, but not 17β-estradiol, led to the recruitment of CtBP corepressor complexes, which functioned with ERβ and the transcription factor AP-1 to shut down proinflammatory gene expression. In women, this pathway may be antagonized because of increased amounts of 17β-estradiol, which competes with ADIOL for binding to ERβ and does not induce the recruitment of CtBP. Synthetic ligands that signaled similarly to ADIOL were protective and therapeutic in a mouse model of MS, which suggests that this pathway may be a useful target for therapeutic intervention.

    Cell 13, 584 (2011).

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