This Week in Science

Science  08 May 2009:
Vol. 324, Issue 5928, pp. 687
  1. Fine-Tuning Fisheries

      CREDIT: DEPARTMENT OF FISHERIES AND OCEANS CANADA

      The past decade has seen a tremendous increase in our understanding of how climate anomalies affect hydrographic properties in North Atlantic Shelf ecosystems, but less about how these events impact organisms. Koeller et al. (p. 791, see the Perspective by Greene et al.) measured the egg incubation and hatching times of an important fisheries resource, the pink North Atlantic shrimp, at a variety of locations and compared them to the timing of the local spring phytoplankton bloom. Shrimp reproduction was determined locally by bottom-water temperatures and was not directly coupled with the spring bloom. While the local bottom temperatures and bloom timing are well-matched in general, and match egg hatching to food availability, this evolved relationship can be decoupled by interannual variability and climate change.

    1. Mars Matters

        Several decades of exploration by orbiting and in situ spacecraft, together with analysis of martian meteorites, have resulted in a wealth of data on the chemical composition of Mars' crust. McSween et al. (p. 736) review these data, which help infer the planet's geological history, discrediting previous ideas suggesting Mars had a wet mantle—similar to that of Earth—and cautioning that martian meteorites are not representative of the planet's crust.

      1. Negatively Doped Graphene Nanoribbons

          The potential applications in electronic devices of graphene (single atom, thick layers of graphite) would be even greater if it can be accessed in both p- and n-doped forms. Graphene nanoribbons (long strips only tens of nanometers in width) are readily p-doped by adsorbates from the ambient atmosphere. Wang et al. (p. 768) show that when graphene nano-ribbons are electrically heated in an ammonia atmosphere, nitrogen is incorporated mainly at the edges of the ribbon and creates an n-type material. Field-effect transistors that operate at room temperature can be made from this material.

        1. Decisive Monkeys

            Decision-making is a central theme in current research in cognitive neuroscience. Behavioral protocols have provided an entry into explorations of the neural processes that underlie decision-making. Empirical studies have provided support for a diffusion model in which information accumulates over time until a threshold is reached, with noisiness in the inputs related to decision errors. Kiani and Shadlen (p. 759) developed a behavioral task to study choice certainty and identified the corresponding neuronal representations in monkeys. The monkeys were allowed to choose to opt out of an uncertain, higher reward choice in favor of a certain, lower payoff. The same neurons that encoded the information used to make a choice also encoded the extent of certainty, which in humans would be described as the degree of confidence in one's decision.

          1. Adding a Turing Pattern Reaction

              CREDIT: HORVÁTH ET AL.

              Two chemical-reaction systems can form sustained stationary patterns (Turing patterns) in solution as the result of the movement of a diffusible species and the formation of negative feedback loops—the chlorite-iodide–malonic acid reaction and the ferrocyanide-iodate-sulfite reaction. Horváth et al. (p. 772) set out to find other examples based on three criteria—that the reaction can develop spatial bistability, that independent control of the negative feedback reaction can be achieved, and the activating and inhibiting processes can be decoupled by slowing down the diffusing species with a complexing agent. The thiourea-iodate-sulfite (TuIS) reaction could be developed into a system that produced different stationary patterns, including stripes and hexagonal arrays of spots. Thus, such Turing pattern–generating reactions are not necessarily uncommon.

            1. Chorus Hissing

                Plasmaspheric hiss, a type of unstructured broadband, low-frequency radio emission, has long been known to exist in Earth's plasmasphere, but its origin has been uncertain. The source of hiss could be a different type of radio wave, called chorus, which originates outside the plasmasphere during geomagnetic storms. Both types of radio wave influence the behavior of energetic electrons in the near-Earth space environment, with implications for spacecraft and astronaut safety, but a correlation between the two has been difficult to establish experimentally. Recently, two of the five satellites of the THEMIS constellation were fortuitously able to record 4 minutes of electromagnetic wave data at high resolution during geomagnetically active conditions, detecting both chorus and hiss. An analysis of the data by Bortnik et al. (p. 775; see the Perspective by Santolik and Chum) revealed that the two sets of waves were well correlated, with hiss lagging behind chorus as expected, implying that one indeed evolved into the other.

              1. Dust in the Wind

                  The temperature of North Atlantic surface waters has a major effect on climate in a variety of ways, not least because its heat content helps to control hurricane formation and strength. The North Atlantic surface has warmed considerably in recent decades, a trend generally associated with global or regional air temperature increases, or with changes in ocean circulation. Evan et al. (p. 778, published online 26 March) use nearly 30 years of satellite data to examine another source of ocean temperature variability, the radiative effects of atmospheric aerosols. Low frequency changes in local tropical North Atlantic surface temperatures seem mostly to be caused by variability in mineral and stratospheric aerosol abundances. Thus, to provide more accurate projections of these temperatures, general circulation models will need to account for long-term changes in dust loadings.

                1. A Second Act for Antiandrogens

                    Men with advanced prostate cancer are often treated with antiandrogens; drugs that inhibit the activity of male hormones, such as testosterone, that help drive tumor growth. Many of these drugs act by functionally disrupting the androgen receptor (AR), a transcriptional regulator of cell proliferation, but tumors eventually become resistant to the drugs by expressing higher levels of the AR. Tran et al. (p. 787, published online 9 April) have developed a “second-generation” antiandrogen, a thiohydantoin called MDV3100, which binds the AR with high affinity. MDV3100 retains its anticancer activity in cell culture and in mouse models even when AR levels are elevated. The drug appears to act both by inhibiting translocation of the AR into the nucleus and by reducing its transcriptional activity. MDV3100 is being tested in patients with advanced prostate cancer, the first group of which have shown a decline in blood levels of a marker of cancer growth, prostate-specific antigen.

                  1. Consciousness and Intention

                      CREDIT: DESMURGET ET AL.

                      Where in the brain are our intentions formed and how do we become aware of these intentions? Desmurget et al. (p. 811; see the Perspective by Haggard) investigated the effect of direct cortical stimulation of parietal and premotor regions in patients undergoing brain surgery for tumor removal. Stimulation of the parietal lobe provoked the conscious experience of wanting to move the upper limb, lips, or tongue without any concomitant motor activity. When stimulation intensity was increased, patients believed that they had actually moved or talked, but again no muscle activity was detected. When, however, the premotor region of the frontal lobes was stimulated, real complex multijoint movements were induced. However, patients did not experience these movements as produced by a conscious internal act of will. Indeed, they were not even aware that they had moved. Increasing stimulation intensity increased the amplitude or complexity of the movement but never made it reach consciousness.

                    1. Let Me Out

                        Apicomplexan parasites like Plasmodium falciparum, which causes malaria, and Toxoplasma gondii, which cause toxoplasmosis, replicate inside animal host cells. In order for infections to spread successfully within the host from cell to cell, daughter parasites after replication need to be able to escape from their incubator cell. In the course of studies intended to elucidate the functions of proteases during parasite infection, Chandramohanadas et al. (p. 794, published online 2 April) noted that host cell calpain is the only protease present at the right time and place to facilitate the egress of malaria parasites from infected red blood cells. Parasite egress from infected resealed erythrocytes was prevented when calpain was removed. Moreover, T. gondii was unable to escape efficiently from murine fibroblast knockouts lacking a calpain regulatory subunit.

                      1. Infrared Vision

                          Proteins from jellyfish and corals that fluoresce in the visible wavelength range have revolutionized optical imaging of cells. However, these wavelengths are absorbed by hemoglobin, water, and lipids and the proteins are thus not appropriate for deep-tissue imaging. Now Shu et al. (p. 804) have engineered a bacteriophytochrome from Deinococcus radiodurans that incorporates biliverdin as the chromophore, to fluoresce with excitation and emission spectra of 648 and 708 nanometers, respectively. These infrared fluorescent proteins are expressed well in mammalian cells and mice, and can be used for whole-body imaging.

                        1. Entanglement Sharing

                            Quantum information processing relies on the ability to generate quantum states, to entangle them, and to send and receive those quantum states reliably across networks. With quantum two-level systems, or qubits, if you want to have a large system (and solve complex problems), there is a fear that the ancillary equipment required to control the system will increase rapidly, perhaps too quickly. The use of multipartite systems, where several quantum states can be accessed in a single component, has been proposed as a solution. Papp et al. (p. 764) work with a multipartite system consisting of a single photon shared between four optical modes and show that the degree of entanglement can be controllably tuned. The ability to work with, and control, such entangled multipartite systems should help the development of quantum information processing.

                          1. Cl in the Sunlight

                              A major assumption in the long-standing mechanistic model for halogen-induced degradation of stratospheric ozone is the steady generation of Cl atoms by photolysis of molecules such as ClOOCl by sunlight. Recently, however, laboratory data raised uncertainties in the ClOOCl absorption cross sections underlying this assumption. Chen et al. (p. 781) undertook precise mass-sensitive cross-section measurements to explore the discrepancy. Molecules were directly quantified before and after ultraviolet photolysis, avoiding interference from impurity or by-product absorptions that can plague more traditional detection schemes that measure attenuation of a light beam. The measured cross sections at two different ultraviolet wavelengths proved well within the margin necessary to support standard models of ozone degradation.

                            1. Infections and Defense

                                Bacteria secrete effectors to suppress immunity in plant and animal hosts resulting in an evolutionary arms race between bacteria and their eukaryotic hosts. One important aspect of plant immunity against bacteria is based on disease resistance protein complexes, which recognize specific bacterial effectors and activate signal transduction. A strain of the bacteria Pseudomonas that infects tomato and Arabidopsis plants injects its effector protein, AvrPtoB, into plant cells. Two plant protein kinases, Fen and Pto, then stimulate disease defense responses that may restrain or halt the infection. Ntoukakis et al. (p. 784) show that the balance between resistance and susceptibility triggered by AvrPtoB is determined by the kinase activity Pto within a disease resistance complex.

                              1. Designer Stem Cells

                                  Despite their promise for use as disease models and in regenerative medicine, the generation of human-induced pluripotent stem (iPS) cells has been hindered by the integration of vector and transgenes in the host cell genome. Recent studies using the Cre/LoxP recombination strategy and the piggyBac transposon approach have approached this objective. However, Yu et al. (p. 797, published online 26 March) now show the derivation of human iPS cells from postnatal foreskin fibroblasts using the nonintegrating oriP/EBNA1-based episomal vectors. The resultant iPS cells show characteristics of human embryonic stem cells and are free of vector and transgenes.

                                1. Ammunition for the TB Wars

                                    Tuberculosis is a major human disease of global importance resulting from infection with the air-borne pathogen Mycobacterium tuberculosis, which is becoming increasingly resistant to all available drugs. An antituberculosis benzothiazinone compound kills mycobacterium in infected cells and in mice. Makarov et al. (p. 801) have identified a sulfur atom and nitro residues important for benzothiazinone's activity and used genetic methods and biochemical analysis to identify its target in blocking arabinogalactan biosynthesis during cell-wall synthesis. The compound affects the same pathway as ethambutol, and thus a benzothiazinone drug has the potential to become an important part of treatment of drug-resistant disease and, possibly, replace the less effective ethambutol in the primary treatment of tuberculosis.

                                  1. Antibody Repertoire Revealed

                                      Antibodies produced by B cells protect us against infection by a wide array of pathogens. Such wide-ranging responses are possible because the specific domain of the antibody that binds to the invader is highly variable owing to the somatic recombination of an inherited set of gene segments that encode the antibody molecule. Although antibody diversity within an individual organism is well-established, the specific antibody repertoire of an individual organism has not been characterized. Using high-throughput sequencing technology, Weinstein et al. (p. 807) characterized the diversity of the antigen-binding domain of the antibody heavy chain in zebrafish. The antibody repertoire of individual fish covered at least 50% of the possible gene combinations. Although the specific gene combinations differed between fish, a similar frequency distribution of the repertoire was observed. Unexpected examples of evolutionary conversion were also seen, with the same antibody observed in different animals.

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