This Week in Science

Science  23 Apr 2004:
Vol. 304, Issue 5670, pp. 485
  1. Spinning Down


    Climate models commonly predict that global warming could slow ocean circulation. If true, heat transport from low to high latitudes would decrease, and the communication of climate changes between high and low latitudes by ocean currents would be affected. Häkkinen and Rhines (p. 555; see the 16 April issue for the News story by Kerr, the Perspective by Weaver, and the Letter by Broecker) present a suite of satellite altimeter data and current meter measurements that shows that circulation in the subpolar gyre of the North Atlantic Ocean has slowed during the past decade. The satellite data reveal that sea surface height there has increased since the early 1990s, a conclusion supported by current meter measurements from the Labrador Sea and consistent with other hydrographic data. Whether this slowdown is a consequence of climate change or part of a periodic variation related to climate cycles like the North Atlantic Oscillation remains an open question.

  2. Remote Spin Control

    The conductance of electrons through a quantum dot depends on whether there is an odd or even number of electrons on the dot. With two quantum dots some distance apart, but connected by a small reservoir of electrons, Craig et al. (p. 565; see the Perspective by Glazman and Ashoori) show that the conductance through one of the dots can be controlled by changing the number of electrons on the other dot. Such remote spin control should be useful for quantum information processing, spintronics, and quantum nondemolition measurements.

  3. Chinese Climate Change

    Polar ice cores provide detailed records of high-latitude precipitation, but for lower latitudes, other natural proxies must be sought out. Stalagmites can provide an excellent archive of past climate variability because their oxygen isotopic compositions reflect the isotopic composition of the precipitation from which they formed, and their ages can be determined precisely by 230Th dating techniques. Yuan et al. (p. 575) report oxygen isotopic values of a stalagmite from western China, which they interpret as a record of Asian Monsoon precipitation for the last 160,000 years. From the timing of the observed variations, they conclude that changes in tropical and subtropical precipitation were driven by insolation and millennial-scale reorganization of atmospheric and oceanic circulation.

  4. Making and Breaking Peptides

    The proteasome is a cytosolic protein degradation machine that acts on a variety of intracellular substrates. Recognition of a peptide by cytolytic T lymphocytes (CTLs) resulting from protein splicing was recently reported, but the origin of this splicing was not identified. Vigneron et al. (p. 587; see the Perspective by Cresswell) found that human melanoma cells could present a spliced antigenic peptide to autologous CTLs. Generation of the spliced peptide resulted from a newly identified activity of the proteasome via a transpeptidation reaction. This mechanism is likely to be useful in increasing the diversity of antigenic peptides presented to T cells.

  5. Ancient Lava Life

    Microbes colonize ocean crust, both the newly erupted basalts and deeper rocks, soon after the crust forms and cools to a tolerable temperature. Microbes can bore into the outer surfaces of volcanic glass and leave behind characteristic pits as well as organic (and even genetic) material. Such processes have been reproduced in the lab. Furnes et al. (p. 578; see the news story by Kerr) have now identified similar features, including relic organic material in micrometer-sized pits, in oceanic crust that is 3.5 billion years old. The rocks are from the Barberton Greenstone belt in South Africa. The microbial alteration is overprinted by younger metamorphic minerals (dating to 3.4 billion years ago) and thus likely occurred soon after the basalts were erupted.

  6. Recordings from Synfire Chains

    The idea that the nervous system plays out highly specific patterns of network activity may be a key step in closing the gap between neural network models and experimental neurophysiology. Theoreticians have long proposed that cortical activity takes the form of sequences of synchronous activity, the so-called synfire chains. Ikegaya et al. (p. 559; see the Perspective by Abeles) used brain slice intracellular recordings to show patterns of postsynaptic currents, optical recordings of slice, and in vivo multicellular recordings to demonstrate the existence of these chains. Blocking NMDA or dopamine D1 receptors also reduced the chains.

  7. Petroleum Fossil Tree

    Diatoms store oil within their silicaceous skeletons for food and flotation. Over geological time, they have become a major source of fossil fuel, and characteristic fossil diatom species are used to date and map the distribution of petroleum-bearing strata. However, diatom phylogeny and history are controversial because of gaps in the fossil record. Diatoms synthesize distinctive isoprenoid alkenes with “T-junctions” in their carbon chains. Sinninghe-Damste et al. (p. 584) have plugged the gaps in the fossil record by combining data on the occurrence of the T-junction-containing alkane derivatives from dated sediment cores and petroleum samples to calibrate the “molecular clock” of the ribosomal DNA record. The origins of the isoprenoid producers can now be precisely timed to 91.5 million years ago—important news for petroleum prospecting, for biochemists, and for taxonomists.

  8. Marking Up T Cell Memory

    After clearing pathogens from the host, most T cells die and leave a small band of memory cells to fight another day. What intrinsic and extrinsic factors determine the fate and the identity of memory precursors within the larger population of cells? Madakamutil et al. (p. 590; see the Perspective by Kim and Flavell) describe a population of CD8+ T cells that transiently express a homotypic form of the CD8α coreceptor after stimulation with antigen. These CD8αα T cells distinguished themselves from their CD8αβcounterparts by a resistance to activation-induced cell death and an ability to persist after viral infection. T cells from animals lacking enhancer elements for the CD8αgene, which are unable to induce sufficient CD8αexpression to form homodimers, generated deficient memory responses. CD8αα displays a particularly high affinity for the major histocompatibilty complex class I-like thymic leukemia antigen, which suggests that memory precursors might be singled-out by specific interaction with this ligand during an immune response.

  9. Nanoparticle Arrays in 3D

    The encapsulation of nanoparticles in thicker films can lead to nanoparticle aggregation, but for many applications, it is advantageous to form well-ordered nanoparticles arrays. Fan et al. (p. 567) present a method in which a microemulsion of surfactant-stabilized gold particles is added to an aqueous solution for the sol-gel synthesis of silica films. The gold particles form a well-ordered array reminiscent of mesoporous silica. The authors show that the arrays have electronic transport properties distinct from two-dimensional nanoparticle arrays.

  10. Defining Dangerous


    The United Nations Framework Convention on Climate Change adopted the goal that climate-related policy should be formulated to avoid “dangerous anthropogenic interference” in the climate system. Mastrandrea and Schneider (p. 571) present a method to evaluate quantitatively the probability of exceeding a “dangerous” threshold that considers the uncertainties involved in projecting future climate change. By using current knowledge of key parameters of climate and economics in a simple integrated assessment model, they show that the risk of exceeding these thresholds can be reduced from 45%, in cases with minimal climate policies, to near zero when conventional climate policy levers like a carbon tax are employed. This work, and work of this type, should help policy-makers and others better understand the benefits and risks associated with various climate-related policies.

  11. Spicing Up Cystic Fibrosis

    Cystic fibrosis, a common and lethal genetic disease is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, which functions as a chloride ion channel in the cells of secretory epithelia. The ΔF508 CFTR mutation, which is carried by ∼90% of CF patients, results in the production of a misfolded but functionally active CFTR protein that is retained in the endoplasmic reticulum and targeted for degradation. Egan et al. (p. 600) found that in tissue culture cells, curcumin, a major constituent of the spice turmeric, released the ΔF508 CFTR protein from interactions with chaperones in the endoplasmic reticulum, allowing it to transit to the cell surface. Treatment with oral curcumin corrected the principal physiological defects associated with the mouse model of ΔF508 cystic fibrosis and prevented the gastrointestinal manifestations of the disease.

  12. Mapping Recombinational Hotspots

    The nature and scale of recombination rate variation are largely unknown for most species. McVean et al. (p. 581) describe an algorithmic method to examine genetic variation that generates high- and low-resolution pictures of recombination rates. A complex picture was observed in regions of the human genome, with considerable rate variation. Although recombinational hotspots could be defined and mapped, a significant amount of recombination also occurs in other regions of the genome.

  13. MicroRNA in HOX

    Homeobox (HOX) genes are highly conserved transcriptional regulators that play a central role in development and pattern formation of higher eukaryotes. Genes encoding microRNAs (miRNAs), tiny 22-nucleotide RNAs involved in gene silencing, are found in almost all eukaryotes and have been implicated in a number of important cell and developmental pathways. Yekta at al. (p. 594) now show that an evolutionarily conserved and essentially complementary binding site for the miRNA miR-196 is found in the HOX gene HOXB8. miR-196 directs the cleavage of HOXB8 messenger RNA during mouse development, and other evidence suggests that miR-196 can regulate the translation of other HOX genes in the mouse HOX cluster.

  14. Peroxide Signaling and Antioxidant Defense

    Cells have robust antioxidant defense systems to protect them against reactive oxygen and nitrogen species. However, in eukaryotes, hydrogen peroxide is also a signaling molecule, and the enzymes that reduce peroxides, the peroxiredoxins (Prxs), can be inactivated by overoxidation of the catalytic center to allow signaling. Budanov et al. (p. 596) show that the sestrins, a family of proteins whose expression is modulated by p53, are required for regeneration of active Prxs. Sestrins contain a predicted redox active domain that is homologous to AhpD, the enzyme that catalyzes reduction of bacterial Prx. However, whereas AhpD is a disulfide reductase, sestrins are cysteine sulfinyl reductases.