Editors' Choice

Science  05 Nov 2010:
Vol. 330, Issue 6005, pp. 732
  1. Evolution

    How the Leopard Got Its Spots

    1. Sacha Vignieri

    The evolution of color patterns in animal coats has long been of interest to evolutionary biologists. From stripes on tigers to leopard spots and even the lion's plain coat, members of the cat family (Felidae) display some of the most striking patterns and variation in the degree of patterning across species. Camouflaging may be especially important in felids due to their stalking predatory behavior; however, the degree to which this shapes patterning across the family is unresolved. Allen et al. now compare mathematical model–generated categories of pattern complexity and variation to the phylogenetic history of the family and find that coat patterning is a highly changeable trait, which is largely related to felids' ecology. For instance, spots occur in species that live in closed environments, such as forests, and particularly complex patterns are found in arboreal and nocturnal species. In contrast, most species that live in open habitats, such as savannahs and mountains, have plain coats. These findings imply that spots provide camouflage in the spotted light found in forest canopies, whereas nonpatterned animals do better in the flat light of an open habitat. Thus, strong selection for background matching has rapidly generated tremendous diversity in coat patterning among felids.

    Proc. R. Soc. London Ser. B 10.1098/rspb.2010.1734 (2010).

  2. Cell Biology

    A BACE-is for Therapy

    1. Lisa D. Chong

    Amyloid beta (Aβ) peptides aggregate in the brains of patients with Alzheimer's disease (AD), forming the hallmark plaques associated with neurodegeneration. β-site APP-cleaving enzyme 1 (BACE1) cleaves the amyloid precursor protein (APP) to generate Aβ. Blocking BACE1 activity is an attractive therapeutic approach, but so far, no such inhibitors have been identified. BACE1 is naturally degraded by the neuron's ubiquitinproteasome machinery, which suggests that the proteins that prepare BACE1 for degradation may also be potential therapeutic targets. Gong et al. now report that the protein Fbx2 in mice, as part of the SCFFbx2-E3-ligase complex, targets BACE1 for proteasomal degradation by tagging it with ubiquitin. In a mouse model of AD, Fbx2 overexpression not only promoted BACE1 degradation and reduced Aβ production but also improved synaptic activity.

    The authors further determined that the transcriptional coactivator PGC-1α increases the expression of Fbx2 in neurons and thus also proteosomal degradation of BACE1. Indeed, AD mouse model brains and postmortem brain samples from humans with AD showed reduced amounts of PGC-1α that correlated with a decrease in Fbx2 and an increase BACE1 expression. Thus, controlling BACE1 activity by manipulating Fbx2 expression in the brain may be an effective strategy for treating AD.

    Aging Cell 9, 10.1111/j.1474-9726.2010.00632.x (2010).

  3. Climate Science

    Pine Island Losses

    1. H. Jesse Smith

    Mass loss from the Antarctic ice sheet is responsible for much of the observed rise in global sea level. No part of the Antarctic ice sheet is losing mass more quickly than the Pine Island Glacier, whose flow velocity has nearly doubled since the mid-1970s, although it has been unclear exactly how much mass it is losing and which factors are most responsible. Joughin et al. have developed a basin-scale glaciological model to examine the sensitivity of the Pine Island Glacier to various environmental forcings. They find that the factor most responsible for mass loss by the glacier is melting due to exposure of the ice shelf to warm ocean currents, which causes ice shelf thinning, retreat of the grounding line, and a resulting increase in the speed of ice stream flow to the sea. Their model indicates that mass loss there may continue throughout the 21st century at rates similar to, or even slightly greater than, that of the present. They suggest that the rise in sea level by the year 2100 due purely to mass loss by Pine Island Glacier will probably lie between 1.1 and 1.8 cm, perhaps inching up to 2.7 cm—a large increase but still substantially less than the theoretical maximum of between 11 and 39 cm.

    Geophys. Res. Lett. 37, L20502 (2010).

  4. Physiology

    Stressing Sex Differences

    1. L. Bryan Ray

    Males and females show differences in susceptibility to many diseases, particularly those with inflammatory components. Duma et al. therefore investigated whether differential responses to glucocorticoid hormones may contribute to this disparity because of their known anti-inflammatory properties. When rats were treated with a synthetic glucocorticoid, sex-specific differences in gene expression in the rat liver, as measured by microarray analysis, were elevated. Nearly 2000 more hormone-responsive genes were detected in females than in males. Moreover, about 70 genes showed opposite changes in expression, going up in females and down in males, or vice versa. When genes implicated in inflammatory disorders were specifically analyzed, gene expression was more affected in males, and generally glucocorticoid treatment suppressed the expression of these genes.

    The authors then tested the physiological significance of their results by measuring the protective effects of glucocorticoid treatment in a deadly inflammatory response in rats. The hormone was more effective in promoting survival of the male rats. Thus, differences in response to anti-inflammatory hormones may explain, at least in part, the differential susceptibility of men and women to diseases associated with inflammation.

    Sci. Signal. 3, ra74 (2010).

  5. Chemistry

    Coloring with Intensity

    1. Marc S. Lavine

    Photoswitching of molecules between two isomeric states has been directed toward a range of applications, including data storage, drug delivery, and actuation. One shortcoming of most systems is that they require two distinct wavelengths to toggle between the two states, and thus two light sources. Further, the light sources may not be compatible for use with biological tissues. Boyer et al. devised a clever way to bypass this problem by using lanthanide-doped up-converting nanoparticles. On exposure of the particles to high-intensity near-infrared (NIR) light, emission due to Tm3+ dopant ions dominates, and the output spectrum has strong ultraviolet and blue peaks. At low NIR intensity, emission from Er3+ dopant ions in the green and red region dominates. When the nanoparticles are mixed with dithienylethene photoswitches, a single monochromatic light source can then be used to drive both ring-closing and -opening reactions, with the switching controlled by the source's intensity.

    J. Am. Chem. Soc. 132, 10.1021/ja107184z (2010).

  6. Biochemistry

    Actin's Many Modes

    1. Valda Vinson
    CREDIT: GALKIN ET AL., NAT. STRUCT. MOL. BIOL. 10.1038/NSMB.1930 (2010)

    Actin is one of the most abundant eukaryotic proteins. It polymerizes to form filamentous actin (F-actin), which plays a key role in regulating cell shape, polarity, and force generation. The sequence of eukaryotic actin is highly conserved over evolution. One explanation for this is that the many functions of actin require a large degree of biochemical and structural plasticity and heterogeneity. Such a large variety of states puts pressure on the majority of amino acid residues. To better understand the structural polymorphism of F-actin, Galkin et al. used electron microscopy of unmodified, frozen-hydrated actin filaments. They observed multiple structural states in the same filament (below), which requires that filaments form cooperative units. These states reveal allosteric coupling between certain structural features that contribute to plasticity both within and between actin subunits. A number of disease-causing mutations in the human ACTA1 gene that encodes skeletal muscle actin affect residues in the most dynamic structural elements of the protein. Actin plasticity is probably required to accommodate its multiple interactions and functions. The authors suggest that the allosteric coupling associated with this plasticity has played an important role in preventing sequence divergence.

    Nat. Struct. Mol. Biol. 10.1038/nsmb.1930 (2010).

  7. Chemistry

    Eight COs for U

    1. Phil Szuromi

    Although many transition metals readily form stable complexes with multiple carbonyl (CO) groups, uranium carbonyls have proven to be exceptionally difficult to synthesize and characterize. Ricks et al. studied the coordination of CO to U+ and UO2+ cations generated in the gas phase by laser-induced vaporization. The vibrational spectra of mass-selected clusters were determined by exciting the complexes in the infrared and measuring photodissociation yields. Although larger clusters with weakly bound CO molecules were observed, the core coordination complexes were U(CO)8+ and UO2(CO)5+. Aided by quantum chemical calculations, the authors assigned the former complex as a square antiprism with appreciable back-donation of metal electrons to CO and the latter as a pentagonal bipyramid with little back-donation. These results extend the range of metal complexes exclusively binding CO to coordination number 8.

    J. Am. Chem. Soc. 132, 10.1021/ja1077365 (2010).

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