Editors' Choice

Science  10 Sep 2010:
Vol. 329, Issue 5997, pp. 1259
  1. Biophysics

    Two Eyes in One

    1. Lisa D. Chong
    CREDIT: STOWASSER ET AL., CURR. BIOL. 20, 1482 (2010).

    Nearly 500 million years ago, schizochroal trilobites roamed the oceans, guided by compound eyes with bifocal lenses. In extant animals, the structures of the eye range from those with accommodating lenses (us) to those with multilayered retinas, such as the complex eyes of jumping spiders. Now, to add to these varieties, Stowasser et al. have described a bifocal lens in the larva of the sunburst diving beetle Thermonectus marmoratus. Of its six pairs of eyes, the E2 eyes are tubular and face directly forward. They contain two retinas that are positioned at unequal distances from the lens, with photoreceptors oriented either parallel or perpendicular to the light path. Using a microscope to observe images formed by isolated lenses, the authors measured optical performance and determined that two distinct and well-focused images are produced on the proximal and distal retinas, indicating a true bifocal lens. Moreover, the images are separated vertically, leading to an improved contrast for each of the focused images.

    Curr. Biol. 20, 1482 (2010).

  2. Genetics

    Daddy's Little Girl

    1. Laura M. Zahn

    Transgenerational genetic effects—in this context, genetic variation in one generation that affects the phenotype of an offspring that has not inherited the variant—have been invoked as a means by which non-Mendelian inheritance may account in part for the current difficulty in explaining the known heritability of traits (such as height) or of complex disease risk on the basis of known genetic variants. Nelson et al. constructed chromosome substitution strains (CSSs) of male mice by replacing the Y chromosome of a host strain with that from a donor. They examined the genetically identical female offspring from pairings of host strain females with either host strain males or CSS males. Surprisingly, just over a third of the physiological and behavioral traits examined showed significant differences between daughter mice who differed only on the basis of their father's Y chromosome, which is not, of course, passed on to female offpsring. Hence, the authors conclude that the frequency and magnitude of transgenerational effects may be nearly equal to those of inherited genetic variation.

    Epigenomics 2, 513 (2010).

  3. Physics

    Spinning Randomly in the Hall

    1. Jelena Stajic

    The Hall effect occurs when a current running through a conductor is deflected by a perpendicular magnetic field, causing a transverse voltage to develop. In certain semiconductor structures where the motion of the charge carriers is confined to two dimensions, this Hall voltage is quantized. When the parameter of quantization (the so-called filling factor ν) is an integer, the effect can be easily explained through the formation of Landau levels. Fractional filling factors may also occur, requiring a more involved explanation in terms of non-interacting composite fermions. Α state with ν = 5/2 is yet more exotic as it eludes the composite fermion description and was predicted to exhibit a complicated kind of quantum statistics known as non-Abelian, making it especially interesting for quantum computing. However, one of the assumptions of that prediction was that the state was also spin-polarized. Stern et al. test that assumption by measuring the photoluminescence of a GaAs-AlGaAs quantum well and find that the state appears to be spin-unpolarized. Their conclusions agree with those extracted from Raman and tilted-field measurements, prompting further theoretical research into whether a spin-unpolarized state can still support a non-Abelian theory for quantum computing applications.

    Phys. Rev. Lett. 105, 96801 (2010).

  4. Geophysics

    Constructing a Craton

    1. Nicholas S. Wigginton
    CREDIT: USGS

    The cores of continents, or cratons, make up the stable lithosphere. Their formation probably occurred billions of years ago, though the mechanisms responsible remain unclear. One way to seek further insight is to look below the present-day continents for clues, such as where the lithosphere ends and the asthenosphere begins. Miller and Eaton used receiver function seismic analysis to study a transect across the width of Canada, revealing the lithosphere-asthenosphere boundary in addition to tilted discontinuities in the mid-lithosphere. These discontinuities may be the scars of an ancient collision of several smaller microcontinents that ultimately fused together to form the North American craton. In a related study, Yuan and Romanowicz modeled the anisotropy of seismic waves across nearly the entire North American continent and observed not only a continuous lithosphere-asthenosphere boundary, but another shallower, laterally variable boundary within the middle of the lithosphere. Based on its thickness and a correlation with geochemical evidence, this new boundary may separate the older part of the craton from a relatively younger layer. Although the two studies present a contrasting view of the evolution of the lithosphere beneath North America, they suggest that accretion processes, and not hot mantle plumes, were primarily responsible for its formation.

    Geophys. Res. Lett. 10.1029/2010GL044366 (2010); Nature 466, 1063 (2010).

  5. Microbiology

    Menacing Methicillin

    1. Caroline Ash

    Almost since methicillin was first introduced as an antibiotic in the 1960s, resistant bacteria were detected, but no one has been quite sure where this form of defense originated. Resistance is encoded by mec on a transmissible cassette chromosome that spreads among staphylococcal bacteria, including the sometime hospital resident, Staphylococcus aureus. Tsubakishita et al. investigated, by genetic means, the wild relatives of S. aureus. They found in S. fleurettii (a commensal bacterium of domesticated animals) the original chromosomal locus that served as the template for the cassette; it appears that the cassette was formed by the combination of mec with the mobile element. mec genes comprise four classes, with mecA in S. fleurettii being the prototype and sharing almost complete nucleotide identity with mecA of methicillin-resistant S. aureus. Two scenarios are posited: that new resistant cassettes are continuously generated in staphylococci or that animal commensals act as a reservoir for human resistance.

    Antimicrob. Agents Chemother. 54, 10.1128/AAC.00356-10 (2010).

  6. Immunology

    Feeding a Fever

    1. L. Bryan Ray

    Starvation or poor nutrition weakens the immune system and makes organisms more susceptible to disease. This reflects in part the need for adequate energy stores. But Mieulet et al. provide evidence that sufficient uptake of the amino acid arginine is required for mouse macrophages to respond to bacterial lipopolysaccharide, which binds to Toll-like receptors that initiate innate immune responses. Macrophages deprived of arginine appeared to have a deficit in the activation of mitogen-activated protein kinases (MAPKs) that mediate the immune response. In cultured cells deprived of arginine, the protein kinase TPL-2 (tumor-promoting locus 2, a MAPK kinase kinase) was associated to a greater extent with protein phosphatase 2A, leading to dephosphorylation and inactivation of TPL-2. In mice, deprivation of arginine also reduced MAPK activation and the consequent production of tumor necrosis factor–α. Arginine thus appears to have multiple important roles in the innate immune response: It serves as a substrate for the synthesis of nitric oxide as part of cellular response to bacterial infection, and it maintains a key signaling pathway that allows macrophages to fight infection effectively.

    Sci. Signal. 3, ra61 (2010).

  7. Plant Science

    Staying Low to the Ground

    1. Pamela J. Hines

    Too much transferase leads to highly branched shoots.

    CREDIT: TOGNETTI ET AL., PLANT CELL 22, 10.1105/TPC.109.071316 (2010)

    As summer temperatures peak, air conditioning keeps indoor plants from wilting, but those outside need other strategies to cope with the heat. Hormone systems forge a link between environmental stresses and physiological responses. IBA (indole-3-butyric acid), a naturally occurring variant of the plant hormone auxin, accounts for about a quarter of the free auxin in Arabidopsis seedlings. Auxins have a variety of effects, including modulating the pattern of root and shoot development. How much hormone is made and where it is located are regulated by biosynthesis, degradation, transport, and metabolic interconversion.

    Tognetti et al. have identified a glucosyl transferase in Arabidopsis that adds a glucose to IBA preferentially. This transferase is induced in response to increases in reactive oxygen species, which are produced by environmental stress, and overexpressing it altered normal flowering time, leaf shape, apical dominance, and chlorophyll accumulation. Plants with excess transferase were unusually tolerant of drought and high salinity, and the expression pattern in younger tissues suggests that this enzyme may be part of a signaling pathway that alters plant shape in response to environmental stress.

    Plant Cell 22, 10.1105/tpc.109. 071316 (2010).