This Week in Science

Science  14 Dec 2007:
Vol. 318, Issue 5857, pp. 1691
  1. PIKing Oncogenic Mutations


    Phosphoinositide 3-kinases (PI3Ks) are lipid kinases that can initiate a variety of signaling events. Many human cancers involve mutations that activate PI3Kα, a heterodimer comprised of a catalytic subunit, p110α, and a regulatory subunit, p85α, both of which contain multiple domains. Huang et al. (p. 1744) describe the crystal structure of a complex between the full-length human p110α catalytic subunit and the binding and activation domains of the p85α regulatory subunit. The structure provides insight into how oncogenic mutations affect enzyme activity and could assist in the future design of isoform- or mutation-specific inhibitors.

  2. Deeper Understanding of the MJO

    The Madden-Julian Oscillation (MJO) is a large-scale (1000-kilometer) atmospheric disturbance that propagates slowly eastward through the tropics from the Indian Ocean to the western Pacific during the course of 30 to 60 days. The MJO affects precipitation over the tropical monsoon regions and has been implicated as a trigger of El Niño-Southern Oscillation events. It is coupled with the upper ocean through its effects on surface fluxes of solar radiation caused by changes in cloudiness, and on evaporation from the ocean surface caused by surface wind speed changes, which can heat or cool the ocean mixed layer by up to 1°C during a strong MJO event. Nonetheless, important aspects of the MJO still are unclear, such as how deep into the ocean its influence extends, in part because the range of scales of the processes it involves have made it difficult to simulate in models (see the Perspective by Hartmann and Hendon). Matthews et al. (p. 1765) used a data set of unprecedented size obtained from autonomous, free-drifting instruments, called Argo floats, to show that the surface wind stress associated with the MJO can force eastward-propagating oceanic Kelvin waves that extend to a depth of 1500 meters and that have amplitudes of as much as six times those of annual-cycle Kelvin waves. These amplitudes are significantly greater than those predicted by ocean models, so that the MJO could affect a much larger volume of the Pacific Ocean than just the ocean surface. Miura et al. (p. 1763) address one of the shortcomings of contemporary global meteorological models—cumulus cloud parameterization—by using a model that allows direct coupling of atmospheric circulation and clouds to simulate an MJO event. Their results show that MJO predictions extending 1 month into the future soon may be possible.

  3. Storing Light in Optic Fiber

    Communication with optical pulses is fast, but direct storage of optical signals for later processing is challenging. There are routes for stopping and storing light that make use of quantum gases, but the wavelengths that can be used are fixed by the excitation levels of the atoms or ions of the gas. Zhu et al. (p. 1748; see the news story by Cho) show that stimulated Brillouin scattering can be used to write a sequence of optical pulses as an acoustic signal in a fiber and retrieve the signal on demand with a read pulse. Thus, variable delays can be achieved with commonly used components. The induced time delays are limited by the lifetime of the acoustic signal, but can be on the order of several nanoseconds. The authors also show that a small number of pulses can be stored simultaneously within the optic fiber.

  4. Close-Ups of Phase Transitions

    The study of phase transitions is often done with macroscopic probes that can average out some underlying microscopic inhomogeneities. Qazilbash et al. (p. 1750) report on the development of a new spectroscopic method that combines the high accuracy and sensitivity of spectral ellipsometry with the high spatial resolution of near-field microscopy. They used this method to study the metal-insulator transition in VO2 and identified an inhomogeneous state with metallic and insulating regions near the transition regime. Within the metallic regions, they observed a divergent electron mass, an effect predicted by one of the competing scenarios of the transition in which correlation effects play a dominant role.

  5. A Magnesium(I) Dimer


    The partially reduced +1 state has rarely been observed for magnesium or any of its heavier alkaline-earth congeners, calcium, strontium, and barium. Green et al. (p. 1754, published online 8 November) used potassium metal to reduce a pair of Mg(II) compounds and thereby isolate and crystallographically characterize stable dimers in which two Mg(I) centers are connected by a single bond. Coordination of bulky bidentate nitrogen-based ligands helped stabilize these unusual complexes.

  6. Mud Formation on the Move

    Mudstones make up the majority of the geological record and have been thought to record the quies-cent conditions of offshore and deeper water environments. However, it is difficult to reconstruct the complex processes of mud deposition in the laboratory, such as the clumping of particles into floccules. Using flume experiments, Schieber et al. (p. 1760; see the Perspective by Macquaker and Bohacs) investigated the transport and deposition of clay floccules and find that this process occurs at flow velocities that transport and deposit sand. Floccules form and are deposited over a wide range of experimental conditions. The floccules form ripples that develop into mud beds and appear laminated after compaction. These results bear not only on interpretations of paleoenvironments that mudstones record, but also on current problems such as hydrocarbon exploration and the management of sediment accumulation.

  7. Reefs Run to Rubble

    With no immediate prospect of slowing anthropogenic climate change, the long-term outlook for the survival of coral reefs is bleak. Hoegh-Guldberg et al. (p. 1737; see the cover, the editorial by Kennedy, and the special News report) review three scenarios for the fate of coral reefs, none of which offer much solace for human societies dependent on their resources and protection. To maintain the status quo requires urgent implementation of conservation measures to reduce stress on corals, but even small further increases in atmospheric carbon dioxide could tip many reef systems into ecological and structural collapse.

  8. Invasion of the Whitefly

    Individuals of closely related but geographically isolated populations of organisms are often able to interbreed when brought together by human activities. Liu et al. (p. 1769, published online 8 November; see the Perspective by Reitz) report the behavioral mechanisms underlying the recent widespread, rapid invasion of the B biotype of the whitefly Bemisia tabaci in China and Australia. Biotype B is one of the top 100 invasive species in the world and is more harmful to crops than other biotypes. Asymmetric mating between closely related but previously geographically separated biotypes appears to drive the invasion of alien populations. Contrary to expectation, the indigenous individuals helped to increase the competitiveness of the invaders and accelerated the process of invasion and displacement.

  9. Human Impacts on Fish and Frogs


    Farmed fish are reared under conditions that promote transmission of pathogens among the stock, notably crustacean parasites called salmon lice. Salmon lice are highly damaging to juvenile salmon and can cause in excess of 90% mortality. Krkošek et al. (p. 1772; see the news story by Stokstad) now show that fish farms are a fatal source of salmon lice infestation to juvenile fish off the coast of Canada and are rapidly driving populations of wild fish to extinction in some rivers. A concerted decline in amphibian populations and species worldwide has been evident for at least a decade. Various causes have been implicated, including fungal disease, habitat loss, and pollution. Becker et al. (p. 1775) show that in the Brazilian Atlantic Forest, amphibian population loss is determined by the mismatch in the landscape between the location of aquatic breeding sites and the remnants of natural terrestrial vegetation across which they migrate. This result helps explain why population declines are biased toward amphibian species with aquatic larvae and suggests that conservation management of riverside vegetation could help to reduce the rate of amphibian decline.

  10. Serine and the CTD Code

    The carboxyl-terminal domain (CTD) of the large subunit of mammalian polymerase II (pol II) has a unique structure comprising 52 repeats of a consensus serine-rich heptapeptide. Phosphorylation of serine-2 and serine-5 is known to be critical for cotranscriptional RNA processing steps that are required for maturation of pol II transcripts (see the Perspective by Corden). Chapman et al. (p. 1780) use monoclonal antibodies to show that serine-7 is phosphorylated on transcribed genes, and Egloff et al. (p. 1777) show that this phosphorylation event plays a specific role in recruitment of the Integrator complex to genes for noncoding small nuclear RNAs. This gene type-specific requirement for a residue within the CTD heptapeptide reinforces the notion of a CTD code.

  11. Getting Gold the Help It Needs

    The relative roles in heterogeneous catalysts played by metal particles and oxide “supports” can be difficult to assign, in part because the catalyst as a whole often accelerates more than one elementary step. For example, for the water-gas shift reaction, in which CO and H2O are converted to CO2 and H2, pure gold, even in nanoparticle form, is inactive, but gold nanoparticles on supports such as ceria are good catalysts. Rodriguez et al. (p. 1757) found that gold surfaces on which islands of slightly reduced titanium or cerium oxide were good water-gas shift catalysts, despite the gold remaining in bulk form. They conclude that vacancy sites on the oxide particles catalyze water dissociation, a step for which gold is a poor catalyst, but that other steps, such as CO adsorption, occur on gold or at the gold-oxide interface.

  12. Carbon Bookkeeping

    We have a pressing need to understand all of the routes by which carbon is cycled through Earth systems, but our knowledge of the carbon budget is incomplete. Berg et al. (p. 1782; see the Perspective by Thauer) have discovered that a range of Archaea use an enzyme, 4-hydroxybutyrate-CoA dehydratase that can assimilate inorganic carbon from CO2 into organic molecules. The widespread occurrence of the sequence for the gene for 4-hydroxybutyrate-CoA dehydratase in marine microbial metagenomes signals the significance of this process in marine carbon budgets.

  13. Circadian Rhythm Methods

    Circadian rhythms in plants and animals appear to be coupled to periodic changes in activity of metabolic pathways (see the Perspective by Imaizumi et al., published online 15 November). Yin et al. (p. 1786; published online 15 November) describe a molecular mechanism that may contribute to the coordination of these biochemical processes. Rev-erbα controls transcription of the gene encoding the circadian clock component Bmal1. Rev-erbα binds to and is regulated by heme, which stabilizes Rev-erbα in a repressor complex, which in turn can block production of gluconeogenic enzymes. Thus, Rev-erbα acts as a heme sensor to coordinate the cellular clock, glucose homeostasis, and energy metabolism in human liver cells. Studying Arabidopsis, Dodd et al. (p. 1789) now show that a cytoplasmic signaling molecule, cyclic adenosine diphosphate ribose (cADPR), is also a component of the clock mechanism. Perturbations to the feedback loop including cADPR result in instabilities in the clock and disruptions in the daily oscillations of cytoplasmic Ca2+ release.