This Week in Science

Science  18 Jan 2002:
Vol. 295, Issue 5554, pp. 401
  1. In Brevia

    Simian immunodeficiency virus (SIV) has been detected in a wild chimpanzee by Santiago et al. (p. 465) using noninvasive methods, which extends the natural range of this virus to East Africa.

  2. Mud Energy

    We can harvest the remnants of once-living organisms (oil) for energy, but present-day organisms in mud may offer a new source. Using two-chambered “mud-water batteries,” Bond et al. (p. 483; see the news story by Pennisi) discovered that several species of Geobacteraceae, which normally use insoluble iron (III) oxide as an electron acceptor, preferentially grow on graphite anodes inserted in anoxic mud. The anodes are used directly by the bacteria as electron acceptors, without any other mediator, to generate an electrical current via an external circuit with a cathode in the aerobic surface water. Various species have been found that operate optimally under diverse conditions, for example, a freshwater species that can live in sewage and another that can oxidize aromatic pollutants.

  3. Science in Europe

    First aired 2 years ago by EU Commissioner for Research Philippe Busquin, the concept of a European Research Area to promote cross-border research projects and to help coordinate research across the continent has won acclaim. Now, four voices (see the Policy Forum section, p. 443) discuss its implementation. Banda describes ways in which a European Research Council can serve as a support structure and how the European Science Foundation can be involved. Wigzell believes that the Framework Programme itself needs to be split into a European Research Council and an Innovation Council to promote large projects. In counterpoint, Radda comments that scientific networking across Europe is proceeding well without the need for new administrative structures. Winnacker suggests strategies that will aid “small science” and provide a “bottom-up” approach.

  4. Optimizing Organic Pores

    Microporous materials such as zeolites offer a wide range of pore sizes, but even with sophisticated templating approaches, changes in pore size usually involve a change in framework connectivity. Eddaoudi et al. (p. 469) now report on a series of metal-organic framework compounds (16 in all) in which the pore size defined by octahedral Zn-O-C clusters and aromatic linking groups is increased systematically with the same topology from about 4 to 29 angstroms. They exploited these features to produce a material that shows an exceptionally high uptake of methane that may prove useful in fuel storage.

  5. Engineering Spider Silk

    The silk that spiders produce for their draglines has mechanical properties that rival the best aramid fibers and is much stronger than steel on a weight basis. Two challenges to making silk artificially are generating protein precursors with a high molecular weight and spinning the proteins from solution, preferably from a nontoxic solvent. Lazaris et al. (p. 472; see the news story by Service) used mammalian cells to express proteins similar in length to those found in a spider's silk glands. The proteins were then spun from aqueous solution into fibers that were stretched to improve their mechanical properties. The toughness and modulus values of these fibers were similar to those of native dragline silk, although the tenacity was somewhat lower.

  6. More Ice, Not Less

    Over the past several decades, a number of studies have reported evidence suggesting that the rapid collapse of the West Antarctic Ice Sheet, which would raise sea level by 5 to 6 meters, could occur within an interval as short as several centuries or as long as 4000 years. One piece of evidence used to support ice sheet collapse scenarios is the observation of ice discharge from the Ross Ice Streams. Using more and better data of ice movements, Joughin and Tulaczyk (p. 476; see the Perspective by Alley) find that the Ross Ice Streams are now accumulating, not losing, mass. This suggests that the ice sheet may be advancing after having retreated for the past several thousand years and that the chance of rapid collapse is lower than has been believed.

  7. Order in a Vortex

    The penetration of quantized magnetic flux lines, or vortices, into superconducting materials locally destroys the superconductivity. Understanding how this occurs may provide insight into how the superconducting state is formed, which remains a controversial issue for high-temperature superconducting cuprates. Using a scanning tunneling microscope to probe the electronic density of states surrounding a vortex core, Hoffman et al. (p. 466; see the Perspective by Sachdev and Zhang) seek out and identify a theoretically proposed feature that indicates that the vortex consists of an antiferromagnet ordered state, confirming recent neutron-scattering results that hinted at such an ordering.

  8. Coordinating Chromosome Segregation

    The centrosomes provide organizing centers for the formation of the mitotic spindle and are thus critical for proper chromosome segregation during cell division. Matsumoto and Maller (p. 499; see the Perspective by Arlot-Bonnemains and Prigent) studied the control of centrosome duplication in an in vitro system derived from Xenopus eggs. They find that increased concentrations of intracellular calcium and consequent activation of the calcium/calmodulin-dependent protein kinase II (CaMKII) are required, which is consistent with oscillations in the concentration of intracellular calcium that occur with each cell cycle.

  9. Coordinating Synaptic Development

    Two different mechanisms guide the development of the central nervous system. Molecular signals initially guide developing neurons to the correct position and, once neuronal activity begins, repeated stimulation helps synapses form and mature. Takasu et al. (p. 491; see the Perspective by Ghosh) describe a signaling mechanism that may integrate these two processes. Ephrins and their receptors are cell-surface proteins that participate in interactions of developing axons and dendrites that are largely independent of neuronal activity. However, the activation of the EphB subtype of ephrin receptors in rat neurons potentiated signaling by N-methyl-D-aspartate (NMDA)-type glutamate receptors, which mediate activity-dependent effects on developing neurons. Activated EphB proteins associated physically with NMDA receptors and caused the activation of the Src tyrosine kinase, which apparently phosphorylates the NMDA receptor and thus modulates activity-dependent control of neuronal gene expression.

  10. Vigorous Immigrants

    Fragmented populations have become an important topic in ecology, evolution, and conservation biology. Inbreeding and inbreeding depression have been linked to population survival and to the ability to adapt to local conditions. In an experimental study of water fleas in Finnish lakes, Ebert et al. (p. 485; see the Perspective by Ives and Whitlock) test the hypothesis that gene flow plays an important role in maintaining high fitness in subdivided populations where inbreeding is common. They find that hybrid vigor resulting from hybridization between residents and immigrants leads to an increase in the effective rate of gene flow. This is the first test of the phenomenon called “genetic rescue,” which has been predicted to occur when local populations suffer from the consequences of genetic bottlenecks.

  11. Keeping Blood Pressure Low

    Estrogens are steroid hormones best known for their effects in female reproductive tissues. However, estrogens also have physiologically important roles in both sexes. Zhu et al. (p. 505) examined vascular function in mice lacking the β form of the estrogen receptor (ERβ); instead of the relaxing effect normally seen, they observed an estrogen-induced constriction of blood vessel walls. In the ERβ-knockout animals, estrogen increased expression of nitric oxide synthase, which produces the contractile agent nitric oxide. These animals also developed hypertension as they aged, which may yield new insights into the treatment of hypertension, particularly that associated with menopause.

  12. Emergence of New Properties

    Neurons in the visual cortex are highly selective for the orientation of a stimulus, a property that does not yet exist at the level of their input neurons. How does this orientation selectivity arise? Sharon and Grinvald (p. 512) addressed this question by using fast optical imaging of voltage changes in large populations of neurons in the cat visual cortex. They compared the dynamics of the response of selected cortical regions to their preferred versus their nonpreferred orientation. They found that the tuning curve widths stay constant, thus indicating that they are dominated by thalamic inputs, while the modulation depth shows a characteristic temporal evolution. Two models, feedforward and cortical recurrent information flow, previously introduced to explain orientation selectivity, need to be integrated to explain the emergence of this phenomenon.

  13. Trauma, Stress, and Consequences

    Traumatic stress often causes long-term pathological changes. To elucidate the molecular basis of these stress-induced changes, Meshorer et al. (p. 508) analyzed the regulation of expression of acetylcholinesterase (AChE) splice variants at cholinergic synapses in the central nervous system. They saw a change from the dominant membrane-bound AChE-S form to the rare soluble AChE-R form. This switch could be triggered by various stresses, occurred very rapidly, and could last for many weeks.

  14. Catching Molecular Chain Gangs

    Elements such as carbon, silicon, and sulfur readily form long chains within stable molecules, but for oxygen and nitrogen, small neutral molecules with three or more atoms in a chain tend to be unstable and difficult to create or observe experimentally. Two reports show how experimental obstacles have been overcome for N4 and H2O3. Cacace et al. (p. 480) synthesized N4 in the gas phase from N4+ via neutralization reionization mass spectrometry and show that a linear species was produced in which two closely bonded N2 units are joined by a longer bond. Engdahl and Nelander (p. 482) observed all of the fundamental vibrations of H2O3 isolated in an argon matrix. Their results not only definitively identify this species but also provide a spectroscopic signature (an O-O stretch at 776 wavenumbers) that could prove useful in identifying H2O3 in chemical reactions.

  15. Cardiac Action Potentials

    Efficient intracellular signal transduction requires proper localization of signaling components. Neurotransmitters bind to β adrenergic receptors in the heart and control action potential duration by altering ion current through K+ channels composed of hKCNQ1 and hKCNE1 subunits. Marx et al. (p. 496) show that the adenosine 3', 5'-monophosphate-dependent protein kinase is physically yoked to these proteins via a targeting protein known as yotiao and is required for the enhancement of current through the K+ channel in response to adrenergic signaling. Furthermore, one of the genetic abnormalities associated with a potentially deadly hereditary form of cardiac arrhythmia in humans (long QT syndrome) turns out to be a mutation in a K+ channel subunit that disrupts interaction with yotiao.

  16. Progeny or Longevity

    Devoting resources to reproduction logically might shorten an organism's life-span. Indeed, in the nematode Caenorhabditis elegans, removal of part of the reproductive system from young worms does increase their life-span. By genetically ablating various cell types in the lineage of the progenitor cells (oocytes, sperm, germ cells) at different times in the animal's life, Arantes-Oliveira et al. (p. 502) show that germ-line stem cells are responsible for this effect. Even in the adult animal, these proliferating stem cells act to shorten life; their removal from the adult, as well as the larvae, prolongs life. Exactly what feature of these cells is responsible is still not known, but the authors speculate that it may be a hormone secreted during proliferation.

  17. Limiting Flux

    Protein transport from the cytoplasm to the nucleus is regulated by the guanosine triphosphatase Ran, which mediates release of cargo proteins from carriers that ferry the cargo in and out of the nucleus; because at least one molecule of Ran is moved along with each cargo protein, measuring transport of Ran itself gives the minimum flux across the nuclear membrane. Smith et al. (p. 488) use a model that takes into account compartmentalization of the cytosol and nucleus along with experimental analysis of fluorescently labeled Ran molecules to show that transport flux—about 520 molecules per nuclear pore complex per second—is limited by the amount of the guanine nucleotide exchange factor RCC1.

Log in to view full text

Via your Institution

Log in through your institution

Log in through your institution