This Week in Science

Science  29 May 2009:
Vol. 324, Issue 5931, pp. 1115
  1. Arctic Energy Reserves

    CREDIT: DAVID W. HOUSEKNECHT/USGS

    The Arctic consists of approximately equal fractions of terrain above sea level, continental shelves with depths less than 500 meters, and deep ocean basins that have been mostly covered in ice. While the deep ocean regions probably have limited petroleum reserves, the shelf areas are likely to contain abundant ones. Based on the limited amount of exploration data available, Gautier et al. (p. 1175) have constructed a probabilistic, geology-based estimate of how much oil and gas may be found. Approximately 30% of the world's undiscovered gas, and 13% of its undiscovered oil, may be found north of the Arctic Circle. Advances in the technology of hydrocarbon recovery, as well as vanishing ice cover around the North Pole, make the Arctic an increasingly attractive region for energy source development, although the existing reserves are probably not large enough to shift current production patterns significantly.

  2. Quantum-Enhanced Measurement

    The single electron spin in a molecule, atom, or quantum dot precesses in a magnetic field and so can be used as a magnetic field sensor. As the number of spins in a sensor increases, so too does the sensitivity. Quantum mechanical entanglement of the spin ensemble should then allow the sensitivity to increase much more than would be expected from a simple increase in the number of individual spins in the ensemble. Using the highly symmetric molecule, trimethyl phosphite, a molecule containing a central P atom surrounded by nine hydrogen atoms, Jones et al. (p. 1166, published online 23 April) quantum mechanically entangled the 10 spins (or qubits) to generate a nearly 10-fold enhancement in the magnetic field sensitivity. The results pave the way for the further development of quantum sensors.

  3. The Power of Green

    CREDIT: WISE ET AL.

    Carbon dioxide is produced both by fossil fuel burning and by deforestation and other land-use changes. Limiting both sources of CO2 is necessary if we are to curb global warming. Wise et al. (p. 1183) use an integrated assessment model to explore the consequences of limiting atmospheric CO2 concentrations at levels between 450 and 550 parts per million through a combination of fossil-fuel emissions reductions and land-use modification. Land-use modification strategies reduce the cost of limiting atmospheric CO2 concentrations, but can make crop prices rise and transform human diets, for example, when people consume less beef and other carbon-intensive protein sources. The rate at which crop productivity is improved has a strong influence on emissions from land-use change. Thus, the technology used for growing crops is potentially as important for limiting atmospheric CO2 as are approaches like CO2 capture and storage.

  4. The Close and Personal Biome

    Fortunately, our skin is readily accessible for ecological studies of the microbial communities that influence health and disease states. Grice et al. (p. 1190) present a metagenomic survey of body sites from 10 healthy human individuals sampled over time. Although, altogether 18 phyla were discovered, only a few predominated. The most diverse communities were found on the forearm and the least behind the ear, but between people the microorganisms living behind the knees, in the elbow, and behind the ear were most similar. This finding might have some bearing on the common occurrence of atopic dermatitis in these zones, although no similar relationship was discerned between skin microbial flora and psoriasis.

  5. Tearing the Plate

    Recent seismic data show a widely variable geometry of subduction: Some plates penetrate deep into the mantle; others bend and become horizontal at 670 kilometers near a prominent phase boundary. Obayashi et al. (p. 1173; see the Perspective by Nolet) provide a detailed view of a situation where subduction of juxtaposed plates in the western Pacific, in somewhat different directions, seems to have ripped a gash in the plates starting at a depth of about 300 kilometers. The geometry of the gash provides information on the past evolution of this plate boundary.

  6. Middle Permian Extinction

    A major extinction in the Middle Permian 260 to 270 million years ago preceded the huge end-Permian extinction. Wignall et al. (p. 1179) present a detailed analysis of the Middle Permian event from rocks in southwest China. The extinction coincided with extensive nearby volcanic eruptions. A major drop in carbon isotope values followed the extinction event, implying massive disruption of the carbon cycle.

  7. Early Riser

    How glacial-interglacial cycles and the long-term variability of sea level depend on the amount of energy received by Earth from the Sun is unclear. Thomas et al. (p. 1186, published online 23 April; see the cover) report results from fossil corals found in Tahiti that indicate that sea level began to rise when insolation at 65° North latitude was near a minimum, not after it had begun to rise, as predicted by the Milankovitch theory. In contrast, the timing of the last deglaciation agrees well with the Milankovitch theory. Thus, glacial cycles do not behave as simply as the Milankovitch theory suggests.

  8. GLUT4, Clathrin, and Glucose

    In human muscle, the GLUT4 glucose transport pathway responds to insulin and is responsible for 70 to 90% of human glucose clearance. In the basal metabolic state, GLUT4 is sequestered away from the cell surface and is released from an intracellular membrane compartment in response to insulin. This GLUT4 membrane pathway is defective in type II diabetes. Vassilopoulos et al. (p. 1192; see the Perspective by Orme and Bogan) now describe a function for CHC22 clathrin, a second isoform of clathrin that is present in humans and not in mice. CHC22 participates in the biogenesis of the intracellular compartment that sequesters the GLUT4 glucose transporter for insulin-stimulated release. Because CHC22 is restricted to humans, mice differ in their pathways that control glucose metabolism, which may restrict the utility of the mouse as a model system in assessing glucose metabolism and diabetes.

  9. Anti-Aging

    Several human neurodegenerative diseases, such as Alzheimer's and Huntington's, are caused by aberrant protein aggregation. These disorders typically develop after the fifth decade of life, suggesting a connection with the aging process. In a number of different species, life span can be extended by dietary restriction and reduced insulin and insulin-like growth factor–1 (IGF-1) signaling. These pathways can also decrease toxic protein aggregation, mechanistically linking aging with proteotoxic diseases. While searching for regulators of proteotoxicity in Caenorhabditis elegans, Mehta et al. (p. 1196, published online 16 April) found that reduction of the von Hippel–Lindau tumor suppressor homolog VHL-1 significantly increased life span and enhanced resistance to proteotoxicity. VHL-1 is an E3 ubiquitin ligase that negatively regulates the hypoxic response, and animals grown under hypoxic conditions lived longer. This alternative longevity pathway was distinct from both dietary restriction and insulin/IGF-1–like signaling.

  10. One, Two, Three

    CREDIT: FRIEDLAND ET AL.

    Synthetic biologists take much of their inspiration from computing and electrical engineering, attempting to gain programmability in cells using analogous genetic circuits. Friedland et al. (p. 1199; see the Perspective by Smolke) have constructed complementary Escherichia coli synthetic gene networks that keep track of prior molecular events to function as counters. These modular devices count up to three induction events over a range of frequencies and could be extended to higher numbers. Similar devices may find application in multi-event processes of cell biology, bioengineering, and, potentially, therapeutics.

  11. Stepping Back to Go Forward

    Insight into the mechanism of transcription has come from crystal structures of actively transcribing RNA polymerase II complexes in the pre- and posttranslocation states. RNA polymerase also backtracks on the DNA template. Backtracking by only a few residues is reversible, but longer backtracking leads to arrest that is relieved by cleavage of the transcript by the transcription elongation factor SII (TFIIS). Now Wang et al. (p. 1203) report x-ray structures of backtracked ternary complexes and of a backtracked complex bound to a noncleaving mutant of TFIIS. The structures show a defined one-residue, backtracked state supporting the idea that RNA polymerase oscillates between backward and forward motion during active transcription. Mismatched residues disfavor forward translocation, increasing the lifetime of the backtracked state and facilitating cleavage by TFIIS. Thus, TFIIS-induced cleavage is likely to provide an important proofreading function during transcription.

  12. Attention and Synchrony

    Neural activity in the visual cortex becomes synchronized with attention and other behavioral states. However, the source of this synchrony is still unknown. Gregoriou et al. (p. 1207) tested the hypothesis that synchronized activity from the frontal eye field is one of the causes of the synchrony in monkey visual cortical area V4 during attention. With attention, neural activity in area V4 synchronized with frontal eye field activity when a stimulus fell in a joint receptive field, but did not do so when the fields were not overlapping.

  13. Social Sciences Reviewed

    The social sciences focus on multibody problems within changing environments, where the intentions and actions of both actor and acted-upon vary over time. In such situations, it can be challenging, to say the least, to identify unambiguously and persuasively which behaviors are causes, which are effects, and which are epiphenomena. Behrens et al. (p. 1160) review the recent application of formal behavioral models in the area of social cognitive neuroscience.

  14. Seeing Double

    Whereas electrons roam free in a metal, their motion in a semiconductor often correlates with that of the positively charged holes their excitation has left behind. Various spectroscopic techniques have quantified the energetics associated with such electron-hole pairs, termed excitons. However, the higher-order correlations that ensue from exciton-exciton interactions are harder to probe. Now, Stone et al. (p. 1169) have characterized the dynamics of such exciton pairs, or biexcitons, directly in a gallium arsenide quantum well structure using a sequence of four ultrashort optical pulses with precisely controlled mutual phase relationships.

  15. Editing Expectations

    Although genetic information is stored in DNA, and faithfully copied into RNA, the cell can make the odd (and occasionally vitally important) change to the meaning of code during a process known as RNA editing. Thirteen edited genes are known in the nonrepetitive portion of the human genome, but the overall prevalence of RNA editing is unclear. Li et al. (p. 1210), used an unbiased genome-wide approach to identify 239 sites (in 207 target genes), with stringent criteria for editing. The sites identified included 10 of the 13 known edited genes. Fourteen out of 18 randomly chosen sites were validated by sequencing, and these putatively edited genes were enriched for synapse, cell trafficking, and membrane functions. Furthermore, lowering the search stringency suggested that many more human genes may be edited at lower frequencies.

  16. Genotype, Phenotype, and Variation

    Phenotypic evolution results from changes in coding sequences, as well as in regulatory regions of the genome. Vinces et al. (p. 1213) uncover an abundant source of gene expression variability in the promoters of Saccharomyces cerevisiae genes. Up to 25% of yeast promoter regions contain a highly variable tandem repeat sequence, which effect gene expression and local chromatin structure. The intrinsic instability of these repeats generates variability in gene expression levels and provides a mechanism for rapid evolution of phenotypic traits.