This Week in Science

Science  24 Sep 2010:
Vol. 329, Issue 5999, pp. 1569
  1. Discriminating Dendrites

      CREDIT: TIAGO BRANCO/UNIVERSITY COLLEGE LONDON

      Can dendrites read out spatiotemporal input sequences? Combining two-photon glutamate uncaging and two-photon calcium imaging, electrophysiology, and computational modeling, Branco et al. (p. 1671, published online 12 August; see the Perspective by Destexhe) discovered that single dendrites were indeed sensitive to both the direction and velocity of synaptic inputs. This direction- and velocity-sensitivity was measurable with only a few inputs and should thus be engaged frequently during normal brain function.

    1. Substituting Salt for Cerium Oxide

        The water-gas shift reaction converts carbon monoxide and water to hydrogen and carbon dioxide. Catalysts that operate at lower temperatures will be useful in fuel cells. Nanoparticles of platinum adsorbed on reducible oxides, such as ceria, can stabilize catalytically active Ptoxygen species. Zhai et al. (p. 1633) now show that, when alkali atoms are added, atomically dispersed Pt can be an active catalyst for the water-gas shift reaction at ∼100°C, even on simple oxides such as alumina and silica.

      1. Self-Renewing T Cells

          The homeostasis of cell populations within an organism can be achieved through a variety of mechanisms, including the differentiation of precursor populations, self-renewal of terminally differentiated cells, or by programming cells to be extremely long-lived. Regulatory T cells that express the transcription factor Foxp3 are critical for maintaining immune tolerance by preventing excessive inflammation and autoimmunity. Rubtsov et al. (p. 1667) now use genetic fate mapping and cell transfer studies in vivo to demonstrate that Foxp3-expressing cells are remarkably stable under both basal and inflammatory conditions. Thus, regulatory T cells appear to be maintained through self-renewal and should maintain their identity if used in adoptive cell therapies for treatment of autoimmunity or other inflammatory disorders.

        1. Let Me See Your Supernova

            As the matter expelled from a supernova travels through and interacts with the interstellar medium, it creates a radiating structure called a supernova remnant. In 1987, astronomers detected a bright supernova in our galaxy, SN 1987A, the remains of which are now expanding into and interacting with a dense ring of gas and dust that surrounds the explosion site. France et al. (p. 1624, published online 2 September; see the Perspective by Laming) obtained spectroscopic data of the ring surrounding SN 1987A and compared it with similar data acquired in 2004. Because SN 1987A is so close to us, the explosion was visible to the naked eye and the results provide a glimpse into the hydro dynamics and kinetics of fast astrophysical shocks in a young supernova remnant.

          1. Turing Model Explained

              The reaction-diffusion (Turing) model is a theoretical model used to explain self-regulated pattern formation in biology. Although many biologists have heard of this model, a better understanding of the concept would aid its application to many research projects and developmental principles. Kondo and Miura (p. 1616) now review the reaction-diffusion model. Despite the associated mathematics, the basic idea of the Turing model is relatively easy to understand and relates to morphogen gradients. In addition, user-friendly software makes it easy to understand how a whole variety of patterns can be produced by this simple mechanism.

            1. Relativity Comes Down to Earth

                Over a century ago, Einstein presented the theory of relativity—where space and time are no longer fixed concepts, but are relative to an observer and their frame of reference. Tests of relativity have usually been confined to space-based measurements and/or with objects with velocities approaching the speed of light. Time-dilation and length-contraction have been confirmed and are used in satellite communication and global positioning systems. Using the precision of state-of-the-art optical clocks, Chou et al. (p. 1630) have confirmed that relativistic effects can now be measured at speeds attained by 100 meters sprinters (10 m/s) and gravitational effects due to just one meter height difference.

              1. Slippery When Squeezed

                  CREDIT: LOWELL MIYAJI

                  The behavior of seismic waves as they pass through Earth's interior depends on the physical properties of major mineral phases at depth. If such minerals are anisotropic—that is, they influence seismic waves preferentially depending on crystallographic orientation—interpreting the structure of a region becomes more challenging. In the lowermost mantle, near the boundary with the outer core, deformation of MgSiO3 post-perovskite may affect anisotropy. Miyagi et al. (p. 1639) solved previous experimental limitations to show that, when squeezed at high pressures, MgSiO3 post-perovskite weakens and breaks along its (001) lattice plane. When modeled, this deformation pattern produces anisotropic structures that are consistent with seismic data collected from this region.

                1. Extending the Capability of Supercapacitors

                    Supercapacitors have porous electrodes that can store more charge per volume in electrical double layers than conventional parallel plate capacitors. However, the porous electrodes cause poor performance in filter circuits that eliminate residual alternating current ripple from rectified direct current. Miller et al. (p. 1637) fabricated electrodes with a high surface area for ionic adsorption by growing graphene sheets in the vertical direction off a metal surface. Such capacitors may be able to perform the same filtering tasks as conventional capacitors but take up less space.

                  1. Return of the Florida Panther

                      The Florida panther is an endangered lineage that has been the target of extensive human management to maintain genetic diversity within a small population. Now, Johnson et al. (p. 1641; see the Perspective by Packer) provide comprehensive genetic and demographic analyses of a project to rescue the Florida panther from inbreeding, low genetic diversity, inbreeding depression, and demographic stochasticity by outcrossing it to Texas pumas. The genetics and reproductive fitness traits of different panther populations and their crosses reveal the benefits of outcrossing on survival, genetic diversity, male reproductive characteristics, and population demography.

                    1. Nervous Disposition

                        CREDIT: MATTHEW P. HOFFMAN

                        Organ development requires the differentiation and coordination of nerves and blood vessels with multiple cell types. The peripheral parasympathetic nervous system innervates many organs during embryogenesis; however, the function of this interaction during organogenesis is unclear. By exploiting the close association during development of the parasympathetic ganglion with the mouse embryonic salivary gland epithelium, Knox et al. (p. 1645; see the Perspective by Rock and Hogan) found that neuronal innervation preserves an epithelial progenitor cell population via muscarinic receptor and epidermal growth factor receptor signaling. These progenitor cells are then maintained in the adult salivary gland. A similar system was observed in the developing prostate gland. Peripheral innervation is thus necessary for organogenesis and may also be involved in organ repair or regeneration.

                      1. Enzymes for Sunscreen Synthesis

                          Many fungi, cyanobacteria, algae, and other marine organisms can biosynthesize small molecules termed mycosporine and mycosporine-like amino acids (MAAs) that, among other functions, protect them from harmful UV exposure. A formulation containing MAAs is used as a sunscreen in skin care and cosmetic products. Balskus and Walsh (p. 1653, published online 2 September) have now identified the gene cluster in a cyanobacterium that is responsible for MAA production. They expressed the cluster in Escherichia coli and characterized the four biosynthetic enzymes bio chemically. Two are adenosine triphosphate.dependent peptide bond.forming enzymes that catalyze imine bond formation through unusual mechanisms.

                        1. Mr. Blebby

                            Vibrio parahaemolyticus, an important cause of contaminated fish-associated food poisoning, kills infected host cells within hours, using three sequential mechanisms: autophagy, cell rounding, and cell lysis. Broberg et al. (p. 1660, published online 19 August) now describe a molecular mechanism of a bacterial effector protein that facilitates cell lysis by disrupting a target involved in regulating membrane dynamics and the actin cytoskeleton. The Vibrio effector, VPA0450, causes target cell membrane blebbing. The protein acts as an inositol polyphosphate 5-phosphatase and disrupts cytoskeletal binding sites on the inner surface of the plasma membrane of infected cells by hydrolyzing phosphatidylinositol 4,5-bisphosphate.

                          1. α-Synuclein and Aging

                              Transgenic α-synuclein can reverse the otherwise lethal neurodegeneration of cysteine string protein-α knockout mice via changes in SNARE proteins, which mediate synaptic vesicle release. Using experiments with purified recombinant proteins, triple αβγ-synuclein knockout mice, and studies of mouse aging, Burré et al. (p. 1663, published online 26 August) now demonstrate that α-synuclein directly interacts with the SNARE protein synaptobrevin and functions as a catalyst for SNARE-complex assembly. The role of synucleins is fully dispensable in young animals, but becomes essential late in life, which suggests that α-synuclein maintains normal synaptic function during aging.

                            1. Dust to Dust

                                Recently, the so-called coreshine effect was identified in a nearby interstellar cloud. The coreshine effect refers to the scattering of mid-infrared light by micron-sized dust grains in the densest regions of molecular clouds, the places where stars and planets are known to form. Using data from the Spitzer telescope, Pagani et al. (p. 1622) now show that, rather than being limited to one single molecular cloud, the coreshine effect is common all over our galaxy, but is not universal and could be used to learn about the properties of star-forming cores and the dust therein.

                              1. In a Spin

                                  The relaxation dynamics of electron spins in solid-state systems is of crucial importance for their usage in quantum computation and information storage. The interaction of the spin with its local environment results in lifetimes in the pico- to microsecond range. Thus, high temporal and spatial resolutions are needed to measure the relaxation time with atomic precision. Loth et al. (p. 1628, see the cover; see the Perspective by Morgenstern) used a scanning tunneling microscope with a spin-polarized tip to monitor the electron spin relaxation times of individual atoms adsorbed on a surface. A spin was excited by a pump signal, and its state read out after a variable time delay with a weak probe pulse that produced a spin-sensitive tunneling current. This general technique may be applicable to other systems with fast dynamics.

                                1. Too Close for Comfort

                                    Pheromones are often used for sexual communications in animals, but they can also serve as a measure of population density. Now, Yamada et al. (p. 1647) have found that population density in the nematode worm Caenorhabditis elegans regulates plasticity of olfactory behavior, in which attraction to an odorant decreases after prolonged exposure. Using two rounds of genetic screens, a peptide named SNET-1 and a homolog of a mammalian transmembrane peptidase neprilysin were found to mediate pheromonal regulation. This regulation of olfactory behavior may serve to coordinate the behavior of individual animals in relation to the status of the whole population.

                                  1. Addition by Contraction

                                      Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common hereditary neuromuscular disorders in Western populations, affecting about 1 in 20,000 people. In most patients, the disorder is associated with contraction of a D4Z4 microsatellite repeat array on chromosome 4q, but this contraction can also occur in the absence of disease, so the underlying genetic mechanisms have remained elusive. Lemmers et al. (p. 1650, published online 19 August; see the Perspective by Mahadevan) now show that FSHD patients carry sequence variants that create a canonical polyadenylation signal for transcripts derived from DUX4, a homeobox gene straddling the last D4Z4 repeat unit and the adjacent sequence. Addition of poly(A) stabilizes the DUX4 transcript, which is likely to be a contributing factor in the disease.

                                    1. Invariant in the Face of Change

                                        The number of copies of a gene network in a cell, or network dosage, is altered in a variety of situations, including switching between haploid and diploid states, and during cell cycle progression. Combining experimental and computational approaches, Acar et al. (p. 1656) explore how the activity of a gene network can be invariant despite alterations in network dosage. A two-component genetic circuit with elements of opposite regulatory activity (that is, an activator and an inhibitor) was revealed as a minimal requirement. Specific network topologies and a 1-to-1 interaction stoichiometry between the activating and inhibiting agents also represented essential elements for network-dosage compensation.

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