This Week in Science

Science  21 Oct 2005:
Vol. 310, Issue 5747, pp. 401
  1. Calcium Channel Regulation by Klotho


    Klotho, a membrane protein with β-glucuronidase activity, also occurs in a soluble form that has recently been implicated as a hormone that regulates longevity in mice. Chang et al. (p. 490) now show that its enzymatic activity is required to activate the Ca2+ channel, TRPV5. Upon cleavage of sugar residues on TRPV5 by klotho, the channel becomes activated and accumulates at the surface of cells, increasing the influx of Ca2+. This interaction may control Ca2+ homeostasis in tissues such as the kidney, where both proteins are abundantly expressed in the mouse.

  2. Ice Sheets and Sea Level

    Increases in population near coastlines have added to the potential impact of the flooding dangers posed by sea-level rises that accompany global warming. Accurate projections of changes in the Greenland and Antarctic ice sheets are critical in this regard. Alley et al. (p. 456) review recent observational and modeling advances in the understanding of the response of those ice sheets. Confident projections in ice sheets and sea level in the coming decades and centuries still require additional observations to characterize rapid dynamic changes in ice sheets, as well as improved models.

  3. Particle-Based Photovoltaics

    The ability of organic materials to serve as low-cost replacements for silicon in solar cells is hampered by their limited absorption range for light and the low mobility of the charge carriers that are generated. The addition of colloidal semiconductor nanoparticles can enhance electron transport in these polymers. Gur et al. (p. 462) now show that a solar cell can be realized with only inorganic nanoparticles. They spin-cast bilayers of rod-shaped CdSe or CdTe nanoparticles, which act as donor-acceptor pairs, on indium oxide glass, and then coat them with a metallic top electrode. The highest efficiency for simulated solar illumination was ~3% for a device in which the top contact was made from calcium and the carrier trapping was minimized by sintering the nanoparticles.

  4. Metals Distort into Insulators


    At room temperature, metals and insulators usually represent very different classes of materials, but a number of materials systems can undergo metal-to-insulator transitions at low temperatures. Wachowiak et al. (p. 468; see the Perspective by O'Shea) studied potassium-C60 monolayers at 7 K with scanning tunneling microscopy and spectroscopy and found that increasing the potassium to C60 ratio from 3 to 4 changed the films from metals into insulators. This charge-induced structural rearrangement was driven by distortions resulting from the Jahn-Teller effect, which helped enhance electron localization.

  5. Holey Snowball

    Snowball Earth episodes were periods during the Neoproterozoic when global glaciation persisted for time spans of millions of years. How much of the planet was actually covered by ice, and how thick it was, are topics that have been debated vigorously. Olcott et al. (p. 471, published online 29 September) report the discovery of a large body of black shales that was deposited in southeastern Brazil during one of the Neoproterozoic low-latitude glaciations, between 740 and 700 million years ago. These organic-rich deposits suggest that they were formed as a result of vigorous marine primary production, either in open waters or beneath relatively thin sea ice. Thus, in one area during one Snowball Earth glaciation, there existed spots with environmental conditions conducive to continued, intense biological activity.

  6. Creating Clouds on Titan

    Titan's atmosphere contains abundant methane that condenses to form clouds. The short lifetime of methane in the atmosphere, however, may require local sources on this moon. New observations from Cassini and ground-based telescopes are revealing the dynamics of these clouds and possible methane sources (see the news story by Kerr). Roe et al. (p. 477) describe observations from the Keck and Gemini telescopes which show that for several months, methane clouds were most abundant in one region in the southern hemisphere of Titan. Griffith et al. (p. 474), using Cassini observations over several days, show that typical mid-latitude clouds only persist for a few hours, and their dynamics reflect convective processes in Titan's atmosphere. Both results may be consistent with a local source of methane on this part of Titan.

  7. Deforestation by Stealth?

    For more than two decades, satellite imagery has been used to assess deforestation rates in the Brazilian Amazon, but this kind of remote sensing only detects large “clear-cuts” in tropical rainforests. Asner et al. (p. 480) developed an automated remote-sensing system for detection of forest disturbances down to the level of a few treefalls. They applied this system in the Brazilian Amazon to monitor selective logging, which is currently unaccounted for in most policy-making arenas. Selective logging doubles previous estimates of the amount of tropical rainforest that is degraded by humans each year; it occurs mostly in frontier areas, and via illegal operations on conservation and indigenous lands. The results lead to revised estimates of the amount of carbon removed from the region and the flux of carbon to the atmosphere.

  8. Addressing Nanowire Circuits


    A number of methods have been developed for patterning nanowires into small circuits, but connecting these wires to electrical leads is still a challenge, as lithographic methods create patterns on much larger length scales. One possible method for integrating nanowires with larger-scale features is through a demultiplexer architecture. Beckman et al. (p. 465, published online 29 September) show that this architecture works for a series of circuits on various length scales. Unlike other designs, their configuration does not require precise doping of the nanowires, and it is reasonably fault tolerant with respect to the initial deposition of the nanowires.

  9. Faster Testing for Prion Infection

    In vitro tests are needed that replicate the in vivo infection characteristics of so-called prion diseases, such as scrapie in sheep and Creutzfeldt-Jakob disease (CJD) in humans. Nishida et al. (p. 493) now present an assay system using cultured neural cells that can replicate the mutual interference characteristics observed previously in mice between different strains responsible for CJD and scrapie. The coculture system reduces the time required to test agent interference characteristics from months to days.

  10. A Model of Regulation

    It is becoming possible to recognize basic principles of regulatory circuits that control biological processes. Brandman et al. (p. 496; see the Perspective by Bornholdt) compared three distinct biological regulatory systems and note that all contain multiple positive feedback loops with fast and slow time courses. They used mathematical models of the systems to show that these characteristics allow the systems to be relatively insensitive to fluctuations in signal input and allow for the kinetics of activation and inactivation to be adjusted independently to best fit the physiological requirements of the system.

  11. Optimal Enzyme Landscape

    Epistatic mutations, which have a nonadditive effect on phenotype, may be important in evolution because they could generate rugged adaptive landscapes. Alternatively, epistasis may be relatively unimportant in natural selection. Lunzer et al. (p. 499; see the Perspective by Ellington and Bull) construct a biochemical adaptive landscape for cofactor use by the Escherchia coli enzyme isopropylmalate dehydrogenase (IMDH). The enzyme normally uses nicotinamide adenine dinucleotide (NAD) as a coenzyme, but can be engineered through five amino acid changes to use nicotinamide adenine dinucleotide phosphate (NADP). More than 150 single and double intermediate mutants were assayed for performance and coenzyme preference, and mutant bacteria were assayed for fitness. Each amino acid change contributes additively to enzyme function, whereas they show epistatic contributions to fitness. All natural IMDHs use NAD, which suggests that an ancient adaptive landscape has been conserved.

  12. Each to Their Own

    In recent decades, the migration patterns of the European blackcap have diversified to include the British Isles in their overwintering habitat. This newly evolved habit has a genetic basis. However, birds using different locations to overwinter often share the same summer breeding territory, and this situation could allow for interbreeding. Bearhop et al. (p. 502; see the news story by Pennisi) show that birds in their breeding grounds mate with birds that have overwintered in the same location. Thus, divergence and ultimately speciation could occur despite overlapping territories. These studies may also reveal one way in which migratory species have responded to climate change.

  13. Flu from Horse to Dog

    Influenza virus can cross species barriers at any time in any place, and birds or swine are not the only sources of influenza virus for human beings. Crawford et al. (p. 482, published online 29 September; see the 30 September news story by Enserink) report a rare event, the transfer of an entire influenza virus, H3N8, between unrelated mammalian species (horse to dog) and its sustained transmission. The virus is phylogenetically related to an equine influenza that circulated in the 1990s. A serological and postmortem survey across the United States of recent outbreaks of respiratory disease and death among greyhounds from racing tracks revealed enzootic influenza virus was the cause. This virus is now spreading into the pet dog population.

  14. RNA Parking Spot

    Messenger RNAs (mRNAs) destined for degradation are removed from the translation machinery and gathered in cytoplasmic organelles called P-bodies, where they can be broken apart. Brengues et al. (p. 486, published online 1 September) have shown that not all of the mRNAs entering the P-bodies are necessarily degraded. These organelles can act both as junk yards and as storage depots for nontranslating mRNAs, and mRNAs can be released back, fully functional, to the translation machinery. An mRNA cycle may thus exist between polysomes and P-bodies and play a role in the ability of yeast to resume growth from a quiescent state.