This Week in Science

Science  12 Mar 2010:
Vol. 327, Issue 5971, pp. 1297
  1. Nanoparticles, Lightly Twisted


    The helical structures that are widespread in natural macromolecules result from well-coordinated bonding interactions and affect their physical properties in striking ways. To obtain helical nanoparticles, Srivastava et al. (p. 1355, published online 11 February) slowly oxidized cadmium-tellurium under visible light and assembled ribbons of nanostructure. The ribbons were persuaded to twist into helices because they were doped with cadmium sulfide nanoparticles, which underwent surface oxidation and caused localized stresses that could only be relieved by a conformational change. The pitch of the twisted ribbons that were produced could be controlled by the intensity of illumination applied. This behavior offers promise for application in the development of materials with interesting optical properties.

  2. Thalidomide Teratogenicity Target

    In the late 1950s and early 1960s, thalidomide was prescribed to pregnant women as a cure for morning sickness, but it was then found to have developmental defects, most obviously, stunted limbs in thousands of babies. Although its use was banned worldwide, thalidomide has since been found to be a valuable treatment for a range of cancers, inflammatory disorders, and leprosy. Several hypotheses have been proposed, but the mechanism of action of thalidomide is unknown. Using zebrafish and chicken as animal models, Ito et al. (p. 1345) show that the protein cereblon is a primary target of thalidomide. Thalidomide exerts teratogenic effects by binding to cereblon and inhibiting associated enzymatic activity important for limb development. Knowing the mechanism of action of thalidomide should encourage the search for thalidomide derivatives without teratogenic activity.

  3. Scattered and Coupled

    Cavity electrodynamics explores the coupling of light with matter—ideally, that of a single photon with a single atom. Typically, this requires that the photon and the atom be confined to increase the likelihood of interaction, but scattering of light is an unavoidable product of an engineered device and is usually considered to be detrimental because it leads to loss of the photons from the cavity. Sapienza et al. (p. 1352; see the Perspective by Wiersma) saw extreme light scattering as an opportunity for the spontaneous generation of localized modes of light that can be exploited to induce light-matter coupling. Thus, working with a process where scattering is considered a resource rather than a nuisance, as in this case, may prove useful for realizing robust quantum information devices.

  4. Slightly Cracked

    While there are detailed theories to explain the propagation of a crack in the bulk of a material, our understanding of cracking breaks down near the tip of the crack. Experimentally, it is very hard to observe the propagation of a crack at the tip region because it tends to move very quickly. Livne et al. (p. 1359) approached this problem by working with a polyacrylamide gel in which cracks progress slowly enough to monitor them. A hierarchy of linear and nonlinear regions was observed through which energy is transported before being dissipated by the growing crack. How stresses are distributed during cracking will determine whether the resulting failure will be brittle or ductile.

  5. Speak to Me, Mama

    Maternal effects are effects of the mother (for example, hormones) on her offspring that are independent of genetic inheritance, but related to the mother's phenotype and her environment. Despite their universal occurrence, little is known about the evolutionary influence of maternal effects. Hinde et al. (p. 1373; see the cover) modeled maternal effects in birds and showed that nestling begging, as well as provoking feeding, also provides parents with information about offspring vigor. Conversely, maternal effects provide information to the unborn offspring about parental quality. Experimental studies with canaries provided support for the theoretical predictions, and together these studies show that parent-offspring conflict (that is, the conflict between the offspring for its immediate needs and the need of the parent to conserve resources for any future offspring) is resolved by the reciprocal exchange of information before and after birth. Hormonal signaling ensures a match between parental capacity for resource provisioning and offspring behavior and development after hatching that meet the mother's capacity to provide resources.

  6. Dinosaur Plumage


    Coloration and appearance provide important behavioral and evolutionary information in animals. However, for the most part, we do not know the coloration of fossil terrestrial animals. Li et al. (p. 1369, published online 4 February) have reconstructed the appearance of a theropod dinosaur by mapping features of its well-preserved feathers and comparing them with modern samples from birds. Feather color is partly determined by melanosome density and shape, and this information is preserved in a recently discovered fossil from China. The dinosaur was gray with white limbs and had a reddish crest and a speckled face.

  7. Titan Through to the Core

    Gravity measurements acquired from orbiting spacecraft can provide useful information about the interior of planets and their moons. Iess et al. (p. 1367; see the Perspective by Sohl) used gravity data from four flybys of the Cassini spacecraft past Saturn's moon, Titan, to model the moon's gravity field and probe its deep interior structure. Their analysis implies that Titan is a partially differentiated body with a core consisting of a mix of ice and rock or hydrated silicates.

  8. Moving Signals

    Many types of human breast cancers overexpress a cell-surface receptor—EphA2—a tyrosine kinase activated by the ligand ephrin-A1 present on adjoining cells. Salaita et al. (p. 1380; see the Perspective by Paszek and Weaver) studied the regulation of mechanically stimulated EphA2 signaling by inducing intermembrane signaling between living EphA2-expressing human breast cancer cells and supported membranes displaying laterally mobile ephrin-A1. When the receptors engaged their ligands, they formed clusters that moved radially to the junction between the cells and the membranes. Physically impeding this movement altered the cellular response to ephrin-A1. Different breast cancer cell lines showed differences in receptor movement that correlated with their invasion potential, and might indicate their capacity for metastasis formation.

  9. Diheme Conversion


    A dehydrogenase enzyme found in methylotrophic and autotrophic bacteria, which converts methylamine to ammonia and formaldehyde, must be posttranslationally modified to create a covalently bound cofactor. Synthesis of the cofactor is completed by a diheme enzyme, MauG, which oxidatively links two tryptophan residues to form tryptophan tryptophylquinone. Jensen et al. (p. 1392; see the Perspective by Bollinger and Matthews) describe the crystal structure of a catalytically competent complex of MauG bound to the methylamine dehydrogenase precursor. The reactive tryptophans are buried and well-separated from both heme irons. The heme closest to the nascent tryptophylquinone site is a 6-coordinate with an unusual His-Tyr axial link. The axial Tyr likely stabilizes a bis-Fe(IV) state involved in catalysis. Two other tyrosine residues are positioned to participate in long-range interprotein electron and radical transfer.

  10. Hair Today, Skin Tomorrow

    The epidermis of mammals contains hair follicles, sebaceous glands, and interfollicular epidermis, but it has not been clear how the development and repair of these structures is regulated. Snippert et al. (p. 1385) show that a stem-cell cluster in the hair follicle, characterized by the expression of Lgr6, a close homolog of the Lgr5 marker for stem cells in the small intestine and colon, resides directly above the hair bulge and gives rise to all cell lineages of the skin. Skin wounds in adult mice are repaired by Lgr6 stem cells in the hair follicles that flank the damage. After hair morphogenesis, Lgr6 stem cells give rise to epidermal and sebaceous gland lineages to generate fully differentiated new skin.

  11. Steady As She Blows

    A fundamental characteristic of many biological control networks is the capacity to maintain the concentration of a particular component at steady state within a narrow range, in spite of variations in the amounts of other network components that might change as a result of environmental variables in the state of a cell. In a mathematical analysis, Shinar and Feinberg (p. 1389) reveal the essential requirements of a network robust to perturbation. Using this method, the sources of robustness in two bacterial systems—one that functions in osmoregulation and another that controls carbon flux in metabolism—were explained.

  12. Spite and Altruism

    Many social animal species can exhibit altruism—the loss of their own individual fitness to help others. One of the most extreme examples is that of the social insects (bees and ants) where, in a colony of related individuals, only a few reproduce. The nonreproductive individuals contribute to the success of the young of these individuals thereby increasing their collective fitness. Spite occurs when an individual damages its own fitness to harm another's. This negative form of altruism can arise if the victim is less related to the perpetrator than an average member of the population. West and Gardner (p. 1341) review the current literature on the origins and maintenance of altruism and spite and the associated phenomenon of greenbeards. Greenbeards use a visible inherited character to signal relatedness and spur altruism. Greenbeard genes provide a mechanism to link the genes that encode cooperative behavior with those that cause cooperators to associate. These traits maybe an ornament or a type of behavior, and they may result in altruistic or spiteful behavior.

  13. Solar Meridional Flow

    The surface of the Sun is composed of plasma that exhibits observable flow patterns. The weakest flow pattern occurs along meridional lines from the equator toward the poles. Hathaway and Rightmire (p. 1350) measured the meridional flow using observations taken with the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory between 1996 and 2009 and found that meridional flow varied with the solar cycle, such that flow was faster during the 2004–2009 minimum than during the 1996–1997 minimum. This finding provides further evidence that the last solar minimum was peculiar by comparison with previous cycles.

  14. An Electrochemical Landscape

    Electrochemical detection is an analytical method that has been used for a wide range of purposes, including trace chemical analysis, glucose and neurotransmitter monitoring, DNA and protein detection, and electrocatalysis. Scanning electrochemical microscopy maps changes in the local electrochemical current along a surface in a serial way, but serial probing can disrupt the process under study. Shan et al. (p. 1363) show that optical measurements of surface plasmon resonances can be used as a less disruptive way of determining the concentration of electrochemically active species on gold-coated glass slides and their current density. This method can be used for a wide range of applications from analyzing DNA and protein microarrays and enzyme-amplified biosensors to probing the activities of cells.

  15. Theoretically Speedy Trees

    Phylogenetic tree construction often uses distance matrix methods, which offer promising scalable methods for rapid building of very large phylogenies. It has generally been assumed that trees constructed from distance matrices are intrinsically less accurate than those inferred from maximum likelihood methods, but the latter are slower to make. Roch (p. 1376; see the Perspective by Allman and Rhodes) theoretically examined this problem and showed that distance methods can achieve the same level of accuracy as likelihood methods. Thus, the generally assumed tradeoff between accuracy and speed in phylogenetic reconstruction can be overcome.