This Week in Science

Science  22 Feb 2002:
Vol. 295, Issue 5559, pp. 1421
  1. In Brevia

    Extracellular DNA plays a critical role in the establishment of Pseudomonas aeruginosa biofilms, as demonstrated by Whitchurch et al. (p. 1487), who suggest that deoxyribonucleaseI may be useful as a prophylactic against chronic P. aeruginosa infection.

  2. Electrical DNA Detection

    One of the simplest ways to detect a molecule is devise an assay based on electrical conductivity. Park et al. (p. 1503; see the news story by Service) show that DNA can be detected electrically at concentrations as low as 500 femtomolar. Capture strands placed a substrate between two electrodes bind a longer target DNA strand. Probe strands capped with gold nanoparticles are then hybridized to the remainder of the target. When exposed to a silver solution, the nanoparticles nucleate silver deposition, and the time to develop a wire is inversely proportional to DNA concentration. Exposure to high salt concentration at room temperature provides a stringency wash that allows the elimination of thermal cycling.

  3. Modeled Instability

    During periods when the Northern Hemisphere continental ice sheets melted, the sudden addition of fresh water to the North Atlantic Ocean could have caused the slowing or cessation of North Atlantic deepwater formation and thermohaline circulation. Schmittner et al. (p. 1489) use a coupled model to examine interactions between the ocean, atmosphere, sea ice, and continental ice sheets during glacial periods. They find that the stability of the North Atlantic overturning was greatly reduced during glacial conditions, and that interactions between ice sheets, icebergs, and ocean circulation could produce the rapid warming events of millennial duration known as interstadials.

  4. An Ear to the Past

    It is thought that El Niño-Southern Oscillation (ENSO) events were less frequent in a generally warmer Pacific basin during the mid-Holocene, but a lack of sea surface temperature (SST) data had made this assertion difficult to prove. Andrus et al. (p. 1508) studied sagittal otoliths (ear stones) from Peruvian sea catfish that lived in the shallow waters of coastal Peru approximately 6500 to 6000 years before the present. These ear structures precipitated aragonite (CaCO3), and their oxygen isotopic compositions provide a record of ocean temperature. These high-resolution (sub-seasonal) measurements show that the eastern Pacific was indeed warmer during that interval than it is today, and that seasonal SST variability was greater then at 9°S latitude than at 5°S.

  5. Pressure? What Pressure?

    Two strains of bacteria can actually live at pressures above 1000 megapascals (Mpa), well beyond the currently known conditions for life on Earth (for example, the pressure in the deepest part of the ocean is about 100 MPa). Sharma et al. (p. 1514) conducted experiments observing such activity for Shwanella oneidensis, which is related to several other bacteria that live in deep, high-pressure environments. More surprisingly, even Escherichia coli can survive under these conditions. Bacteria were still viable under ambient conditions even after a stint in ice at 1200 to 1600 MPa.

  6. Sex, Mice, and Videotapes

    The vomeronasal organ (VNO) is a sensory organ at the base of the nasal cavity that allows mice to detect and respond to pheromones, the chemical cues emitted by other mice which provide information about their social and sexual identity. To investigate the specific behavioral responses that are mediated by the VNO, Stowers et al. (p. 1493; see the cover and the 1 February news story by Beckman) produced mice genetically deficient in TRP2, a putative ion channel of the transient receptor potential family that is expressed selectively in the VNO. Sensory activation of VNO neurons was completely abolished in mice lacking TRP2. The results of videotaped behavioral assays revealed that male mice lacking TRP2 failed to display aggression toward other males, and, surprisingly, they initiated sexual behavior toward both males and females. VNO activity, which had been previously thought to be required for the initiation of male-female mating, may actually confer on mice the ability to distinguish males and females.

  7. A Rational C60 Synthesis

    Recently, it was shown that a polycyclic aromatic hydrocarbon, C60H30, can lose hydrogen under laser irradiation to form gas-phase C60. Scott et al. (p. 1500) now show that a chlorinated derivative, C60H27Cl3, can produce C60 through a flash-vacuum pyrolysis step in sufficient quantities to be isolated. Although not yet competitive with graphite vaporization synthesis, this approach might allow fullerenes to be synthesized that are not major products by that route.

  8. The Plan for Partitioning Plant Parts

    A general model can now predict how biomass is partitioned among plant organs both within and across seed plants. Enquist and Niklas (p. 1517; see the Perspective by Zens et al.) have quantified the scaling of stem, leaf, and root mass and show how different plants may differ in their allometric constants. These “general allocation rules” were then tested on a large global compilation of inter- and intraspecific patterns of leaf, stem, and root biomass that covered more than nine orders of magnitude in plant size. Statistical analysis provides robust support for the model predictions and shows broad generalities in the scaling of plant biomass across functionally diverse communities and ecosystems.

  9. Two Steps Forward...

    Most conventional cancer drugs gradually lose their effectiveness because tumor cells are genetically unstable and can readily acquire mutations that confer drug resistance. It had been hoped that drug resistance would not be a problem for angiogenesis inhibitors because these drugs target endothelial cells in the tumor vasculature, which are genetically stable. However, Yu et al. (p. 1526; see the news story by Marx), found that mice bearing human colorectal tumors deficient in the tumor suppressor protein p53 were less responsive to anti-angiogenic therapy than those bearing tumors with normal p53 function. The most likely explanation is that p53 loss confers an improved capacity to grow in low-oxygen conditions on the tumor cells. Because p53 is mutated in most human cancers, these results could have important implications for the design and interpretation of clinical trials testing anti-angiogenic drugs.

  10. Moving in Concert

    Dynamical effects can play a role in enzyme function and link the movement of amino acid residues with steps in the catalytic pathway. Eisenmesser et al. (p. 1520; see the Perspective by Falke) have now used nuclear magnetic resonance relaxation methods to characterize motions of the enzyme cyclophilin A as it isomerizes a proline residue of its substrate. Apart from detecting motion associated with substrate binding at nine residues, they identify one residue where the movement appears to be linked to transition-state rearrangement.

  11. Interferon with Nuclear Export

    A variety of proteins and RNAs are trafficked across the nuclear membrane via nuclear pores in a signal-mediated process. Enninga et al. (p. 1523) examined the control of messenger RNA (mRNA) export by the antiviral agents, interferons. Two of the protein constituents of the nuclear pore that are targeted by a viral protein and that lead to an inhibition of host-cell mRNA export were specifically up-regulated in the presence of interferons. These findings delineate an antiviral strategy that can reverse virally induced changes in host-cell gene expression.

  12. Neuron Survival Without Retrograde Transport

    Some neurons depend on signals from their environment for their survival. In particular, sympathetic neurons are supported by nerve growth factor (NGF) that is secreted by their targets. Previous observations have indicated that NGF was internalized and transported back to the neuronal cell body. Using NGF anchored to beads, MacInnis and Campenot (p. 1536; see the Perspective by Miller and Kaplan) now show that although sympathetic rat neurons in compartmentalized culture do require NGF for survival, their survival does not require that NGF be internalized and transported.

  13. After the Signal's Gone, What's Left?

    T cells are stimulated into action when they associate with other immune cells that present them with specific antigens. An intercellular synapse facilitates this intimate encounter and a prolonged engagement is thought to be required for T cell activation. Lee et al. (p. 1539; see the Perspective by van der Merwe and Davis) in fact show that signaling through the T cell receptor has abated by the time a mature immunological synapse has formed. The center of the mature synapse may not function as a supramolecular signaling complex as previously thought, which raises new questions about the function of this specialized and dynamic structure.

  14. Polymers Plus Nanocrystals Yield Near-IR Light

    Pushing the emission from polymer-based light-emitting diodes (LEDs) into the near-infrared region, which includes the short-wavelength telecommunications bands, is difficult because few polymers are optically active at such long wavelengths. Tessler et al. (p. 1506) report that by adding nanoparticles with InAs cores surrounded by ZnSe shells to films of conjugated polymers, electroluminescence could be observed at wavelengths between 1.0 and 1.3 micrometers. The emission feature can be tuned by changing the nanoparticle core radius.

  15. Warmer, But Not All Over

    Several global paleotemperature reconstructions show that the 20th century was clearly warmer than the previous three centuries, but more regional records are needed to determine how uniform this warming was and to allow climate models to be tested. Hendy et al. (p. 1511) present coral paleotemperature records from seven sites within the Great Barrier Reef, Australia, which give the surprising result that the tropical Western Pacific was not unusually warm in the 20th century compared to the last 420 years. They also find that salinity was higher there in the 18th century than in the 20th century, and that an abrupt freshening after 1870 AD occurred simultaneously throughout the Western Pacific. The authors suggest that these variations are best explained by a combination of advection and wind-induced evaporation caused by a strong latitudinal temperature gradient and intensified circulation. Also, the global glacial expansion of the Little Ice Age (roughly from 1400 to 1900) may have been due in part by greater poleward transport of water vapor from the tropical Pacific.

  16. Comparing Monkey and Human Brains

    Monkeys have been investigated in brain research for many years, mainly in morphological, electrophysiological, and lesion studies. Humans, on the other hand, have been mainly investigated in brain imaging or neuropsychological studies. Nakahara et al. (p. 1532) used functional magnetic resonance imaging to directly compare awake, behaving monkeys with human subjects performing an identical high-level cognitive task (a modified Wisconsin Card Sorting Test). Homologous brain regions in both species are involved in cognitive set shifting. This result demonstrates the similarity of human and monkey brains at the functional level even for high executive tasks.

  17. Layer by Layer

    During development, neurons of the mammalian cerebral cortex are generated at distant sites and must migrate to their final location. The signaling mechanisms that are involved in these migrations are now being elucidated. McEvilly et al. (p. 1528) examined the role of two POU-domain transcription factors, Brn-1 and Brn-2, in neuronal migration. When Brn-1 and Brn-2 were eliminated in mice, defects were seen in cortical layers II-V. Brn-1 and Brn-2 directly contribute to the transcription of p35 and p39, two regulatory subunits of Cdk5, a molecule which is known to regulate neuronal migration. Hence, Brn-1 and Brn-2 regulate the Cdk5 pathway and are necessary for the proper radial migration of neurons within specific cortical layers.

  18. The Problematic Rise of Archean Oxygen

    Catling et al. (Reports, 3 Aug. 2001, p. 839) offered an explanation for why Earth's atmospheric oxygen suddenly increased between 2.4 and 2.2 billion years ago (Ga), hundreds of millions of years after the onset of bacterial photosynthesis: In the early, reducing atmosphere, hydrogen from photosynthetic splitting of water was first incorporated into methane (CH4) as an intermediate product. Subsequent upper atmospheric photolytic decomposition of CH4 into carbon and hydrogen, they suggested, allowed hydrogen to escape to space, and the permanent loss of that reductant led, over time, to irreversible oxidation of Earth. Towe comments that “the fate of the photosynthetic free oxygen produced each year… presents a serious problem for this proposal": One result of the rapid buildup of such oxygen, he suggests, would be oxidation of the methane itself, reducing the rate of atmospheric methane accumulation and, thus, hydrogen escape. Catling et al. respond that “kinetic losses of O2 operated at a greater rate than [Towe] allows,” sufficient to allow the buildup of CH4 that they envisage—and that such a buildup “may help explain several major issues in Earth history.” The full text of these comments can be seen at