This Week in Science

Science  02 Jul 2010:
Vol. 329, Issue 5987, pp. 10
  1. Blissful Ignorance?

    Although recent research has established the remarkable ways in which cognitive processing can occur without our being aware of it—for instance, casual exposure to retiree-related words, such as “elderly,” induces us to walk more slowly—behavior that is directed toward goals still seems to be the product of conscious thought. Custers and Aarts (p. 47) review a set of findings that point toward the possibility that goals may, in fact, also be vulnerable to manipulation via avenues of which we remain blissfully unaware. They place these results within a framework that reveals how thoroughly unconscious processes permeate our everyday activities.

  2. Let There Be Life

    The DNA sequence information from thousands of genomes is stored digitally as ones and zeros in computer memory. Now, Gibson et al. (p. 52, published online 20 May; see the cover; see the Policy Forum by Cho and Relman) have brought together technologies from the past 15 years to start from digital information on the genome of Mycoplasma mycoides to chemically synthesize the genomic DNA as segments that could then be assembled in yeast and transplanted into the cytoplasm of another organism. A number of methods were also incorporated to facilitate testing and error correction of the synthetic genome segments. The transplanted genome became established in the recipient cell, replacing the recipient genome, which was lost from the cell. The reconstituted cells were able to replicate and form colonies, providing a proof-of-principle for future developments in synthetic biology.

  3. Planet Is Born

    CREDIT: LAGRANGE ET AL.

    The 10-million-year-old star β Pictoris, has long been suspected to host a planet. Through images obtained with the Very Large Telescope, an array of four telescopes located in Chile, Lagrange et al. (p. 57, published online 10 June) now confirm the presence of a young, giant planet, β Pictoris b, orbiting within the dusty disk that surrounds the star. β Pictoris b orbits closer to its star than Uranus and Neptune do to the Sun in our solar system. This orbital separation is consistent with the in situ formation of the planet via a core accretion mechanism. Thus, giant planets can form within a stellar dust disk in only a few million years.

  4. Maintaining the Supercurrent

    When a superconductor is placed in contact with a ferromagnet, the antiparallel spin pairs that form the supercurrent are expected to be broken almost immediately upon entering the ferromagnet, which tends to orient spins parallel to each other. If the supercurrent survives for more than a few nanometers, it is assumed that a change of pairing symmetry has taken place, with the spin-singlet pairs having been converted into spin-triplets. Magnetic inhomogeneity at the superconductor-ferromagnet interface is thought to account for this change. Robinson et al. (p. 59, published online 10 June) have now been able to observe long-ranged supercurrents in a symmetric junction consisting of a superconductor, a conical magnet, and a ferromagnet. The conical magnet layer provided the required inhomogeneity, and varying its thickness enabled control over the magnitude of the current.

  5. Quantum Anomalous Hall Effect

    In addition to the Hall effect, which appears as a voltage change in conductors in response to an external magnetic field, ferromagnets exhibit the anomalous Hall effect, which is often proportional to their magnetization and independent of the presence of the magnetic field. This effect, first observed more than a century ago, has not been realized in its quantized form. Yu et al. (p. 61, published online 3 June) propose a realization of a quantum anomalous Hall system by magnetically doping thin films of three-dimensional topological insulators and calculate the effects of various dopants and film thicknesses. The resulting insulators are predicted to have long-range ferromagnetic order, potentially joining dilute magnetic semiconductors as candidates for spintronic applications.

  6. Filling a Cavity

    Unlike liquid ammonia, water cannot sustain a steady concentration of isolated electrons. Nonetheless, high-energy irradiation can introduce a small number of free charges that engage in potent reductive chemistry and have clear spectroscopic signatures. The manner in which water solubilizes these hydrated electrons has remained uncertain, but the general consensus has been that repulsive interactions drive the nearest water molecules away, leaving the electron in a nearly spherical empty cavity. Larsen et al. (p. 65; see the Perspective by Jordan and Johnson) upend this consensus with simulations based on a more thorough potential function for modeling the competing attractions and repulsions between the electron and surrounding water. The calculations suggest that the hydrated electron actually draws water in, occupying a region denser than the pure bulk liquid. The model reproduces experimental spectral and dynamic observations as effectively as, and in some cases better than, the cavity framework.

  7. One Two T

    CREDIT: L. LI ET AL.

    T cells develop in the thymus, where they proceed through several developmental stages, losing alternative lineage potential as they progress. The molecular regulation of this developmental process, however, is not fully understood (see the Perspective by Di Santo). P. Li et al. (p. 85, published online 10 June), L. Li et al. (p. 89), and Ikawa et al. (p. 93) now identify expression of the zinc finger transcription factor Bcl11b as the earliest checkpoint in T cell development in mice. Genetic deletion of Bcl11b in developing T cells inhibited commitment to the T cell lineage. Under conditions that should have stimulated T lineage differentiation, Bcl11b-deficient T cell progenitors failed to up-regulate genes associated with lineage-committed T cells and maintained stem cell– and progenitor cell–associated gene expression. In both developing and committed T cells, loss of Bcl11b resulted in the generation of cells that resembled natural killer (NK) cells in both phenotype and function. These NK-like cells could be expanded easily in vitro and possessed antitumor cytotoxicity, but they did not exhibit cytotoxicity against normal cells and were not tumorigenic. Because T cells are much easier to obtain from human patients than NK cells, deletion of Bcl11b in T cells may thus provide a source of easy-to-grow NK cells for cell-based antitumor therapies.

  8. Erasing Markers

    CREDIT: HAJKOVA ET AL.
    CREDIT: HAJKOVA ET AL.

    Epigenetic reprogramming of the mammalian genome, which involves the removal and replacement of the various regulatory epigenetic marks such as DNA methylation, occurs during germ cell differentiation and during early zygotic development. This process is also critical during the experimental generation of stem cells, but the factors and pathways that control epigenetic reprogramming are not well understood. Hajkova et al. (p. 78) investigated the erasure of DNA methylation during germ cell differentiation and during early zygotic development in the developing mouse and found that factors involved in the base excision repair (BER) pathway, which helps repair damaged DNA, were involved. Furthermore, inhibitors of BER resulted in the retention of DNA methylation in the zygote.

  9. Early Rising Hydrogen

    Formation of molecular hydrogen through electron-expelling collisions of H atoms and H anions is regarded as a key step in the cooling process that led to assembly of the first stars in the early universe. Kreckel et al. (p. 69; see the Perspective by Bromm) performed highly precise laboratory measurements of the rate of this reaction at a range of different energies. The study required construction of a dedicated apparatus to carefully tune the relative velocity of merged atom and ion beams. The data validated prior theoretically calculated reaction cross sections, which were then extended for use in cosmological models.

  10. No Genetic Vertigo

    Peoples living in high altitudes have adapted to their situation (see the Perspective by Storz). To identify gene regions that might have contributed to high-altitude adaptation in Tibetans, Simonson et al. (p. 72, published online 13 May) conducted a genome scan of nucleotide polymorphism comparing Tibetans, Han Chinese, and Japanese, while Yi et al. (p. 75) performed comparable analyses on the coding regions of all genes—their exomes. Both studies converged on a gene, endothelial Per-Arnt-Sim domain protein 1 (also known as hypoxia-inducible factor 2α), which has been linked to the regulation of red blood cell production. Other genes identified that were potentially under selection included adult and fetal hemoglobin and two functional candidate loci that were correlated with low hemoglobin concentration in Tibetans. Future detailed functional studies will now be required to examine the mechanistic underpinnings of physiological adaptation to high altitudes.

  11. Dodgy Repair

    A double-strand break (DSB) in genomic DNA poses a serious threat to genome stability, and yet vertebrate cells may suffer 10 or more DSBs every time the genome is replicated. Pathways have thus evolved that can recognize and repair DSBs before they wreak havoc in the cell. Hicks et al. (p. 82) show that this repair can come at a price. DSBs were induced in the budding yeast genome. Repair of a break was accompanied by a massive increase in the rate of mutation in the vicinity of the break. The mutations generated displayed a specific “signature” that included the copying of divergent sequences from other chromosomes.

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