This Week in Science

Science  09 Apr 2010:
Vol. 328, Issue 5975, pp. 133
  1. Like Father, Like Mother, Like Child


    Transcriptional regulation is mediated by chromatin structure, which may affect the binding of transcription factors, but the extent of how individual-to-individual genetic variation affects such regulation is not well understood. Kasowski et al. (p. 232, published online 18 March) investigated the binding of two transcription factors across the genomes of human individuals and one chimpanzee. Transcription factor binding was associated with genomic features such as nucleotide variation, insertions and deletions, and copy number variation. Thus, genomic sequence variation affects transcription factor binding and may explain expression difference among individuals. McDaniell et al. (p. 235, published online 18 March) provide a genome-wide catalog of variation in chromatin and transcription factor binding in two parent-child trios of European and African ancestry. Up to 10% of active chromatin binding sites were specific to a set of individuals and were often inherited. Furthermore, variation in active chromatin sites showed heritable allele-specific correlation with variation in gene expression.

  2. Ultrafast Imaging

    Optical microscopy is generally limited in resolution by the wavelength of light incident on the substrate. Because these wavelengths, even in the ultraviolet, are on the order of hundreds of nanometers, electron beams have long been used instead to probe structural detail at the smallest scale. While offering exceptional spatial resolution, electrons repel one another and so cannot be compressed in time as easily as a pulse of light. Electron microscopy has thus traditionally been a comparatively static characterization method. Zewail (p. 187) reviews recent technological developments in stripping down the electron pulses used for imaging that have been able to introduce time resolution of trillionths of a second to this spatially precise technique. Local transformations ranging from graphite film oscillations to iron phase transitions have been tracked in this manner.

  3. From Australopithecus to Homo

    Our genus Homo is thought to have evolved a little more than 2 million years ago from the earlier hominid Australopithecus. But there are few fossils that provide detailed information on this transition. Berger et al. (p. 195; see the cover) now describe two partial skeletons, including most of the skull, pelvis, and ankle, of a new species of Australopithecus that are informative. The skeletons were found in a cave in South Africa encased in sediments dated by Dirks et al. (p. 205) to about 1.8 to 1.9 million years ago. The fossils share many derived features with the earliest Homo species, including in its pelvis and smaller teeth, and imply that the transition to Homo was in stages.

  4. It Pays to Be a Copy Cat

    Does it pay to copy what others do? Rendell et al. (p. 208) elected to copy Robert Axelrod's 1979 tournament in which strategies for playing the iterated prisoner's dilemma game were pitted against each other until an overall winner emerged—the tit-for-tat strategy. In the 2008 tournament, 100 social learning strategies designed to cope with a changing environment competed against each other; the winning strategy involved sampling the behaviors of other players periodically, rather than exploring the environment alone.

  5. Heat Flow in Graphene

    Unsupported graphene sheets show exceptional thermal transport properties, but are these properties maintained when a graphene sheet is in contact with a substrate? Seol et al. (p. 213; see the Perspective by Prasher) measured the thermal conductivity of graphene supported on silicon dioxide and found that, while the conductivity was considerably lower than that of free-standing graphene, it was still greater than that of metals such as copper. A theoretical model suggested that the out-of-plane flexing vibrations of the graphene play a key role in thermal transport. Thus, graphene may help in applications such as conducting heat away from electronic circuits.

  6. Mussel Fibers

    While it is possible to make strong fibers or threads from organic materials, most suffer from high wear abrasion. Marine mussels attach themselves to rocky seashores using a series of byssal threads. Despite the constant rubbing caused by the motion of the tides, the threads show high wear resistance. Harrington et al. (p. 216, published online 4 March; see the Perspective by Messersmith) now find that the threads are protected by a proteinaceous outer cuticle that is rich in the amino acid 3,4-dihydroxyphenylalanine (dopa), which is known to be a strong adhesive. The cuticle is also rich in metal ions, primarily Fe3+. The dopa-metal crosslinks helped to form the tough outer coating.

  7. CO2 Lends a Hand


    Solvent plays a complex and multifaceted role in facilitating charge transfer events. One obstacle to understanding its influence is that solvent molecules are in constant motion; just teasing out their arrangement in space at the point in time when an electron hops from one substrate to another is often a great challenge. Sheps et al. (p. 220; published online 4 March) have studied a highly simplified prototype system, in which a single CO2 molecule coordinates, as a solvent might, to an IBr ion in the gas phase. A combination of ultrafast photoelectron spectroscopy and theoretical simulations was applied that suggests that even this solitary interaction is sufficient to induce electron transfer from iodide to bromine during a dissociation reaction. Energy channeled through CO2-bending vibrations promoted formation of I(CO2) and Br.

  8. Silver Cluster Catalysts for Propylene Oxide

    The formation of ethylene oxide—in which an oxygen atom bridges the double bond of ethylene—can be made directly and efficiently from ethylene and oxygen with the aid of silver catalysts (typically comprising a small silver cluster on aluminum oxide). Similar approaches are not so successful for making propylene oxide—an important starting material for polyurethane plastics, which are made from chlorinated intermediates. Lei et al. (p. 224) report that silver trimers, Ag3, deposited on alumina are active for direct propylene oxide formation at low temperatures with only a low level of formation of CO2 by-product, unlike larger particles that form from these clusters at higher temperatures. Density functional calculations suggest that the open-shell nature of the clusters accounts for the improved reactivity.

  9. Speedy TCR Transgenic Mouse Manufacture


    T cell receptor (TCR) transgenic mice are one of the most useful and ubiquitous tools of the immunologist. This is because the majority of T cells that develop in these mice express T cell receptors with known antigen specificity, and thus the mice can be used to study antigen-specific immune responses. The downside of TCR transgenic mice is that they can be difficult and time-consuming to generate and the antigen specificities of their T cells are often not physiologically relevant. Kirak et al. (p. 243) now describe the use of somatic cell nuclear transfer to create TCR transgenic mice with specificity for antigens known to be important in the immune response against the parasite Toxoplasma gondii. This method generates mice with greater ease and speed than conventional TCR transgenic mice and can be applied to generate mice with T cells specific to antigens from a variety of infectious diseases.

  10. Debugging Metabolic Disease

    Obesity, now officially recognized as an epidemic in many developed nations, is a key component of “metabolic syndrome,” an array of metabolic disturbances that increase an individual's risk of developing diabetes and heart disease. The rise in obesity rates has been largely attributed to the growing imbalance between food intake and energy expenditure, but recent provocative work has suggested a possible link between obesity and the composition of microbes residing within the gut. Vijay-Kumar et al. (p. 228, published online 4 March; see the Perspective by Sandoval and Seeley) now find that mutant mice deficient in a component of the innate immune system (which defends the body against microbial pathogens) develop hallmark features of metabolic syndrome, accompanied by changes in gut microbiota. Notably, transfer of gut microbiota from the mutant mice to wild-type mice conferred several features of metabolic syndrome to the recipients. Thus, the development of metabolic syndrome may indeed be influenced by gut microbes that are regulated by the innate immune system.

  11. Arsenic on the Fingers

    Arsenic, an ancient drug used in traditional Chinese medicine, has attracted wide interest because it has therapeutic activity in patients with acute promyelocytic leukemia (APL). The drug acts by promoting degradation of an oncogenic protein, PML-RARα, a fusion protein containing sequences from the PML zinc finger protein and retinoic acid receptor α, which is found specifically in APL cells and helps drive their growth. Zhang et al. (p. 240; see the Perspective by Kogan) now explain how arsenic initiates the molecular events leading to PML-RARα degradation. Arsenic was found to bind directly to cysteine residues within zinc finger domains of PML. Arsenic binding then induced oligomerization of PML, which in turn enhanced its association with an enzyme that helps catalyze SUMOylation, a posttranslational modification that can target proteins for degradation.

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