This Week in Science

Science  09 Apr 2004:
Vol. 304, Issue 5668, pp. 167
  1. Clue to Asthma Heritability


    Asthma is an increasingly prevalent condition with both environmental and genetic influences. Only a handful of candidate genes showing direct association have been identified, and even fewer have provided any clear insight into the pathophysiology. In a study of three independent patient cohorts presenting with asthma or allergy from Finland and Canada, Laitinen et al. (p. 300; see the news story by Couzin) identified inherited single nucleotide polymorphism (SNP) haplotypes in a region of chromosome 7p. Genotyping of these risk-associating haplotypes helped guide identification of a candidate gene encoding a G protein-coupled receptor, designated GPRA. This gene has coding SNPs that associate strongly with both asthma and the allergic phenotype, and apparently also cause alterations in expression, and possibly function, of the protein.

  2. Twisting Up Carbon Nanotube Fibers

    Many routes have been developed for synthesizing single- and multiwalled carbon nanotubes, but even under the best of conditions, the fibers are less than 1 meter in length. By adding a rotating wind-up rod and through careful selection of the reaction conditions, Li et al. (p. 276) have made continuous twisted ropes. The process worked with a variety of oxygen-containing carbon feedstocks, and the choice of single- or multiwalled nanotubes was controlled by the operating temperature and gas flow rates.

  3. Chirality at Multiple Size Scales

    Chirality can appear at the level of an individual molecule, and also in the construction of aggregates, which can be built up from achiral materials. De Jong et al. (p. 278) have constructed a molecular system in which the chiralities at these two size scales communicate with each other through a series of thermally or optically activated transitions. Both stable and metastable aggregates can be obtained in gel form, with photoinitiated switching between them.

  4. Improving Uncertainty

    The Heisenberg uncertainty principle sets limits on the accuracy with which an experimental parameter can be determined. With two orthogonal parameters, the accuracy of one can be improved upon, but only at the expense of losing information about the other. However, the extent to which such quantum state squeezing can be obtained has been generally passive. Geremia et al. (p. 270) present a real-time feedback technique to control the amount of squeezing, thus enabling the accuracy to be set deterministically by the observer.

  5. Membrane Effects on Ion Channel Function

    What is the effect of the membrane environment on ion channel function? Are ion channel subunits solely responsible for channel properties, or can lipids alter the gating of potassium channels? Oliver et al. (p. 265; see the Perspective by Hilgemann) demonstrate that membrane lipids can convert A-type potassium channels into delayed rectifiers, and vice versa. Phosphoinositides such as PIP2 immobilize the inactivation domain and thus remove N-type inactivation from A-type potassium channels. The other way around, the fatty acids arachidonic acid and anandamide equip delayed rectifier channels with rapid voltage-dependent inactivation.

  6. C60 Charges Ahead

    The fullerene C60 is a good electron acceptor, and fullerides can be formed by doping C60 crystals with alkali metals like potassium. Yamachika et al. (p. 281) have followed the alkali-metal doping of a C60 molecule that was adsorbed onto a silver surface that was partially covered with potassium atoms. The samples were kept at very low temperatures (7 Kelvin) to minimize thermal motion. The C60 molecule was moved with a scanning tunneling microscope tip over a potassium atom to create KC60; successive steps led to the synthesis of K4C60. They also observed the loss of a potassium atom from K4C60 to a surface impurity. The charging of the C60 molecule could be followed by scanning tunneling spectroscopy.

  7. Ozone from Above

    Ozone in the upper troposphere has a significant effect on climate; one important yet poorly constrained source of tropospheric ozone is the stratosphere. Marcy et al. (p. 261) present an analysis of HCl measurements made with aircraft in subtropical latitudes that quantifies the transport of ozone in air mixed from the stratosphere into the upper troposphere, a region where there are significant discrepancies in the ozone budget and associated radiative forcing. Their approach takes advantage of the fact that there are no significant sources of HCl in the upper troposphere, but the amount produced in the stratosphere is proportional to ozone production there. Hence, measurements of HCl concentrations in the upper troposphere can be used to calculate how much ozone was transported from above.

  8. Preventing Fatal Arrythmias


    The precise mechanisms that cause cardiac arrythmias have been hard to pin down. Wehrens et al. (p. 292) describe the effects of the experimental drug JTV519, a derivative of 1,4-benzothiazepine, which causes increased binding of the protein calstabin2 to the ryanodine receptor. The ryanodine receptor is a calcium release channel that contributes to muscle contraction. When calstabin binds, the channel is held in its closed state and calcium is not released. Mice that have decreased amounts of calstabin2 are prone to arrythmias. Treatment with JTV519 protected such animals from fatal arrythmias, but the drug had no effect on animals that completely lacked the calstabin2 protein. Thus, JTV519 appears to prevent arrhythmias by increasing association of calstabin with ryanodine receptor channels, plugging the leak of calcium thought to initiate the life-threatening abnormal contractions.

  9. Fixing a Molluscan Shell

    Shell formation in molluscs is usually thought to be mediated by an extracellular organic matrix that is secreted from the mantle epithelium. Mount et al. (p. 297) report that a class of immune cells, granulocytic hemocytes, nucleate calcite crystals and deliver these crystals to the site of shell formation. After notching an oyster in the shell margin, calcium carbonate crystals could be observed in circulating granulocytes. After being released at the mineralization front, the crystals were remodeled to yield regenerated shell.

  10. Deleting Deformation Dislocations


    When the grain sizes of pure metals approach nanometer dimensions, metal strength can be increased because the normal mechanisms for the formation of new defects during deformation no longer apply. Budrovic et al. (p. 273; see the Perspective by Hemker p. 221) find that for nanocrystalline nickel, plastic deformation that occurs on straining the specimen is reversible and does not lead to the formation of new defects when removed. An in situ technique that they developed allowed them to look at deformed and undeformed specimens, thus eliminating the ambiguities that occur when postdeformation analysis techniques are used.

  11. Differences Beget Differences

    Ecologists have generally assumed that positive correlations between species diversity and the diversity of their resources are mainly the result of specialization by particular species on particular resources. Using twig-nesting ant species in a tropical agroecosystem, Armbrecht et al. (p. 284) found that, even with no apparent specialization, diversity of resources still promotes diversity of consumers or users of those resources. Thus, diversity at one level may promote diversity at another level independently of any niche specialization. Resource diversity seems to generate yet-to-be-determined emergent properties that act to diversify the users of those resources.

  12. Pinning Down Fusion Pores

    The fusion pore for exocytosis, which can be defined biophysically, can be modulated by synaptotagmin, a protein found on synaptic vesicles. However, the nature of the fusion pore itself remains unclear. It is not even clear if the fusion pore is composed of lipid or protein. Han et al. (p. 289) identify a specific plasma membrane protein, syntaxin, as a physical part of the fusion pore during Ca2+-dependent exocytosis from a rat neuroendocrine cell line. Mutations within the transmembrane segment of syntaxin altered both neurotransmitter flux through fusion pores and pore conductance.

  13. Motivation and Reward

    Is there a difference in neuronal firing patterns between “reward” and “motivation”? Differences in neuronal response could arise either because the cells represent the magnitude of reward (or modulate their activity according to reward value), or because they could reflect the increased motivation resulting from the reward. Roesch and Olson (p. 307) recorded from neurons in macaque monkeys and independently increased their motivation by increasing the punishment for failure. They found that orbital frontal neurons indeed represent reward value, increasing their response to increasing reward. But these cells do not increase their response with increasing threat of punishment, i.e., increased motivation. Premotor cells, by contrast, increase their response for both reward and motivation.

  14. Fungal Family History

    Two completely sequenced fungal genomes were compared that are sufficiently conserved to allow reconstruction of syntenies, but are sufficiently diverged to find multiple levels of sequence alterations. Although there was evidence that Saccharomyces cerevisiae evolved by a whole genome duplication, the newly sequenced Ashbya gossypii appears to resemble the ancestor predating that duplication. Through comparisons of the two genomes, Dietrich et al. (p. 304) were able to infer the history of changes that led from the ancient sequence to the modern ones.

  15. Maintaining One Way Traffic

    The communication between different membrane-bounded compartments in the cell is brought about by vesicles. Vesicles are generated from a donor compartment and travel to an acceptor organelle, where they will dock and fuse. Kamena and Spang (p. 286) show that an active mechanism exists in the cell that prevents back fusion of newly formed vesicles with the donor membrane. This mechanism provides directionality to vesicular transport. In Saccharomyces cerevisiae, the TIP20 protein prevents the back fusion of endoplasmic reticulum (ER)-derived vesicles and could thus act as a discriminator between incoming and outgoing vesicles at the ER.