This Week in Science

Science  11 Feb 2005:
Vol. 307, Issue 5711, pp. 811
  1. Cuprates in Real- and Momentum-Space

    CREDIT: SHEN ET AL.

    Recent real-space imaging experiments on the high-temperature cuprate superconductors have revealed the existence of a “checkerboard” charge-ordering pattern on the surface. This structure has received much attention in terms of its relation to understanding the mechanism underlying superconductivity in these materials. To strengthen the case, what is now needed are samples that allow direct comparison between real-space and momentum-space data. Working with the sodium-doped oxychloride superconductor, Shen et al. (p. 901) present angle-resolved photoemission data that provides complementary data in momentum space. Interpreting the similarities and differences found in the real-space and momentum-space experiments may provide some guidance in revealing the underlying mechanism.

  2. Stuffed with Pulsars

    Globular clusters contain thousands to millions of stars and are among the oldest objects in the universe. Ransom et al. (p. 892; see the Perspective by Lorimer) studied the globular cluster, Terzan 5, with the Green Bank radio telescope and discovered 21 new millisecond pulsars, about half in binary systems (two with close enough orbits to allow repeated eclipses and others with unusually wide orbits or odd companions), several with some of the highest rates of rotation, and two with masses that exceed the theoretical limits for neutron stars. This menagerie of extraordinary pulsars has much to tell us about pulsar physics, general relativity, and globular cluster evolution.

  3. Through a Glass, Darkly

    Most carbon nanotubes are grown with the aid of catalyst particles that reside at the tips of the growing tubes. However, how do nanotubes grow during the catalyst-free process in which an arc is struck between two graphite rods? De Heer et al. (p. 907) studied this process in detail and found the formation of amorphous carbon beads on a small number of the multiwalled tubes, which suggests that the tubes grow in a manner similar to other crystal-growth processes.

  4. Shifting Reference Frames

    CREDIT: KOPPERS AND STAUDIGEL

    There are several chains of volcanoes and seamounts within the Pacific plate that have been used to track its motion, given the assumption that there is a fixed hot spot that can serve as a reference frame. The Hawaiian-Emperor chain shows a sharp bend which indicates that a change in growth direction occurred at about 47 million years ago. Koppers and Staudigel (p. 904) dated a similar bend in two volcanic chains in the southern Pacific plate and found that the chains changed directions at different times. The lack of synchronicity among the three bends in the three volcanic chains means that the hot spot must have been moving or the plate properties were different in different regions. These results indicate that a fixed hot-spot reference frame cannot be used to track plate motions and that some revisions of plate tectonic histories may be needed.

  5. Ear Origins

    All living mammals have a distinctive ear containing three bones (hammer, anvil, and stirrup) and a single jaw bone. These structures evolved from four or more bones that made up the jaw of their reptilian ancestor in the Mesozoic. It has been thought that this evolution occurred in a basal mammal, prior to the split of monotremes (the few extant mammals that lay eggs) from marsupials and placentals. Rich et al. (p. 910; see the Perspective by Martin and Luo) now show that the ear of the earliest known monotreme, from the Early Cretaceous, has only one bone. Thus, the complex ears of mammals arose separately and converged in different mammalian lineages.

  6. Decisions, Decisions...

    What makes an individual decide to choose one set of activities over another? Briggman et al. (p. 896) tried to unravel the mechanisms underlying behavioral choice in the relatively simple nervous system of the medicinal leech. They presented an animal with a constant stimulus that repeatedly produced two different, mutually exclusive behaviors with roughly equal probabilities. This approach allowed the authors to focus on neurons involved in decision-making rather than the neural effects of sensory input, which was invariant. Neurons exhibiting decisive roles in the choice between swimming and crawling were identified by combining high-resolution voltage-sensitive dye imaging with the sophisticated mathematical methods of principal component analysis and linear discriminant analysis. A candidate key neuron highlighted by these analyses (neuron 208) could selectively bias the decision to swim or crawl.

  7. Bt Receptor Defines Specificity

    The Bt toxin, a crystalline protein produced by the soil-borne bacterium Bacillus thuringiensis, is used to control insect pests in agriculture. After the toxin is ingested by insect larvae, the toxin damages the gut of susceptible insects. Griffitts et al. (p. 922) examined the mode of action of Bt. Several genes known to control resistance to the Bt toxin encode enzymes that synthesize a set of glycolipids found in nematodes and insects. These glycolipids function as the receptor for the Bt toxin explaining why the toxic effects of Bt are limited to nematodes and insects.

  8. Natural Brominated Bioaccumulators

    Halogenated organic compounds can accumulate in animal tissues, in some cases with potentially toxic consequences. Some of these, such as the polybrominated diphenyl ethers (PBDEs) used as flame retardants, have industrial origins. The origins of some classes of bioaccumulating compounds, such as methoxylated polybrominated diphenyl ethers (MeO-BDEs), have been uncertain. Teuten et al. (p. 917) extracted more than 10 kilograms of blubber from a fatally stranded True's beaked whale, and isolated MeO-BDEs at 99% purity for radiocarbon analysis, which reliably distinguishes carbon of ancient and recent origin. The carbon content of MeO-BDEs was overwhelmingly recent, indicative of a natural rather than industrial origin for these compounds.

  9. Endangered Ginseng?

    Ginseng is a highly valued understory forest plant that is widespread in eastern North America, although at low population density. It has many uses in traditional Asian medicine and strong cultural ties to Appalachian communities. Population viability analyses carried out by McGraw and Furedi (p. 920; see the news story by Stokstad) suggest that high rates of browsing by burgeoning populations of white-tailed deer threaten to cause extinction of most, if not all, wild American ginseng populations within a century. The white-tailed deer represents a keystone species, with large and cascading effects on the natural community. Loss of the wild populations of ginseng and other potentially valuable understory herbs would have significant economic and cultural consequences.

  10. Earliest Influences

    The two main lineages of T cells to emerge from the thymus are distinguished by the T cell receptors that they carry, either αβ or γδ, which confer distinctive functional properties on each cell type. Within the thymus, the development of the two lineages has been thought to occur independently. Silva-Santos et al. (p. 925, published online 9 December 2004; see the Perspective by Rothenberg) now show that the features peculiar to γδT cells are not generated autonomously but are conferred directly on the cells by their immature αβ thymic counterparts. This process required signaling via a pathway already known to be essential for lymphoid organogenesis and generating effective immune responses. Thus, the developmental interaction between two lineages of T cell imparts fundamental features on one of the cell types.

  11. SADly Promoting Neuronal Polarity

    CREDIT: KISHI ET AL.

    As neurons wire together networks of communication, they need to know not only which other neurons to connect to, but in which direction they should send signals. Such polarity within a single neuron is reflected by its morphology: multiple short dendrites receive signals, and the single longer axon sends signals. Kishi et al. (p. 929) examined the role of SAD kinases, relatives of nematode synaptic differentiation regulators, in establishing neuronal polarity. Neurons lacking SAD kinases did not polarize to produce morphologically and functionally distinct axons and dendrites.

  12. Overcoming Stress

    Diverse human diseases such as viral infections, diabetes, and neurodegeneration are characterized at the cellular level by an inability of the endoplasmic reticulum (ER) to fold proteins properly, resulting in the onset of “ER stress.” Uncorrected ER stress activates apoptotic cell death pathways, and it has been hypothesized that these pathways might be manipulated for therapeutic benefit. In a chemical screen, Boyce et al. (p. 935) identified a small molecule (salubrinal) that protects cells from ER stress-induced apoptosis. Salubrinal selectively inhibited the dephosphorylation of eukaryotic translation initiation factor α (eIF2α), and inhibited herpesvirus replication. Thus, eIF2α may be a valuable drug target for diseases involving ER stress.

  13. Putting the Methyl in Plant MicroRNAs

    MicroRNAs (miRNAs), ∼22 nucleotide RNAs encoded in the genomes of both plants and animals, have the potential to regulate the expression of a diverse array of genes. Numerous factors modulate miRNA function, for example, Arabidopsis mutants of HEN1 show reduced miRNA abundance, as well as miRNA size heterogeneity. Yu et al. (p. 932) now show that HEN1 methylates miRNAs on the ribose of their last nucleotide. Methylation plays an important role in ribosomal RNA function and stabilizes exogenously introduced small interfering RNAs. It is likely that many, and possibly all, plant miRNAs are similarly methylated, whereas present evidence suggests that animal miRNAs are not methylated.

  14. Preserving the Hard Bits

    The evolution of hard body parts during the Cambrian Period vastly improved the preservation of organisms in the fossil record. However, calcite skeletal elements are thought to be better preserved than their more reactive aragonite counterparts—and such bias would affect the interpretation of the history of the biosphere from rocks. Kidwell(p. 914) addressed the question of this potential “calcite bias” by analyzing the preservation of the various calcite and aragonite forms of bivalve mollusk shells through evolutionary time. Unexpectedly, aragonite shell types show trends in abundance contrary to the anticipated biases when looked at as a group, in singleton taxa, or in the duration of genera with such shells. Thus, the fossil record is potentially a faithful representation of the evolutionary patterns for skeletonized organisms.

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