This Week in Science

Science  11 Mar 2005:
Vol. 307, Issue 5715, pp. 1529
  1. Mapping Magnetic Galaxies


    Many galaxies in the universe show signs of complex magnetic structures that are difficult to measure and are not well understood. One way to map out the magnetism is by means of the Faraday effect, in which the plane of polarization in an electromagnetic wave is rotated by a magnetic field. Gaensler et al. (p. 1610) report their measurement of polarized radio emissions from distant sources behind the Large Magellanic Cloud (LMC). The survey of 291 radio sources showed that the LMC has an axisymmetric spiral magnetic field that exhibits noticeable fluctuations. This analysis suggests that the field is produced by a cosmic-ray-driven dynamo mechanism that can create ordered magnetic structures even in the presence of star-forming and supernova disruptions.

  2. Thin But Tough Networks

    Additives that can form thin protective films on surfaces are typically added to lubricants in order to reduce the wear between moving parts. For steel engines, the primary ones are the zinc phosphates, but their breakdown by-products poison catalytic converters and they do not work well in aluminum engines. Using simulations, Mosey et al. (p. 1612) show that at the high pressures that occur during a compressing cycle in the engine, the zinc changes coordination number and forms chemically connected networks. Their results explain why other divalent cations, such as calcium, cannot be substituted for zinc, and why these additives do not work well in aluminum engines, where the strength of the alloys is such that the pressures do not get high enough to form the antiwear films.

  3. Prolonging Antigen Presentation

    It has been assumed that antigen-presenting cells must have exceptionally well developed capacities for proteolysis because they must degrade protein antigens to perform their function. However, Delamarre et al. (p. 1630) now find that the most efficient of the antigen-presenting cells (dendritic cells and B cells) harbor exceptionally low concentrations of lysosomal proteases when these levels are compared to those of macrophages. Dendritic cells also contain endogenous protease inhibitors that further attenuate their proteolytic potential. Remarkably, the levels of other lysosomal hydrolases in dendritic cells are similar to those found in macrophages. Thus, whereas macrophages rapidly degrade the antigens they encounter, dendritic cells may protect the very same antigens, facilitating their dissemination to and survival in secondary lymphoid organs.

  4. Sex and Smell


    In the antennae of the insect olfactory system, there exist two distinct chemical perception mechanisms. The so-called “generalist” system recognizes odorants from foods and plants and is made up of the olfactory receptor family with many different genes. The second perception mechanism, the “specialist” system, detects pheromones from insects of the same species. Nakagawa et al. (p. 1638, published online 3 February 2005) report that in the silk moth, coexpression of pheromone receptors with a receptor from the generalist insect olfactory receptor subfamily promotes the functional expression of pheromone receptors and confers ligand-stimulated nonselective cation channel activity.

  5. Domesticating Pigs Seven Times Over

    DNA sequencing has revolutionized the study of the domestication patterns of animals and plants by humans. Archaeological evidence suggests that domestication of wild boar took place principally in Asia. Larson et al. (p. 1618) focus on the origins and spread of the domesticated pig by examining mitochondrial DNA sequences from 687 wild, feral, and domestic pigs (across the entire natural range of wild boar) and combining these data with phylogenetic analyses. Pig domestication took place at least seven times in areas across Eurasia, including in previously unknown centers in India, Burma-Thailand, Central Italy, and Wallacea-New Guinea.

  6. Good Noise

    Ambient seismic noise from the atmosphere and ocean collected by seismic arrays is usually discarded by seismologists before they perform the inversion routines that yield crustal structure. Shapiro et al. (p. 1615; see the Perspective by Weaver) show that cross-correlation of the noise after periods of one or more months can be used to construct higher spatial resolution, three-dimensional images of shear wave speeds. Using data from 60 stations in southern California, the authors produce detailed images of the crustal structure that delineated sedimentary basins from igneous complexes, and even fault lines that offset different rock types. The use of noise has significant advantages for modeling crustal structure and related seismic hazards because it is not necessary to wait for an earthquake to produce seismic waves.

  7. Estrogen Barges In

    The steroid hormone estrogen acts both through nuclear receptors that control transcription of target genes, as well as through signaling pathways outside the nucleus. Revankar et al. (p. 1625, published online 11 February 2005; see the Perspective by Hewitt et al.) report that a G protein-coupled receptor located in the membrane of the endoplasmic reticulum mediates estrogen signaling in various cell types. Upon binding to estrogen, the receptor stimulates mobilization of intracellular calcium and synthesis of nuclear phosphatidylinositol 3,4,5-trisphosphate, both of which trigger further signaling events. Estrogen is a membrane-permeable molecule, and it is likely that its access to intracellular membrane receptors can facilitate some of the rapid nongenomic signaling initiated by the hormone.

  8. Helping Notch on Its Way

    Notch proteins act as receptors for a conserved signaling pathway affecting numerous cell fate decisions, and fucosylation of the glycans on Notch are thought to be important for its function. Okajima et al. (p. 1599, published online 3 February 2005; see the Perspective by Lowe) find that the fucosyltransferase, OFUT1, in addition to promoting fucosylation of a variety of substrates, including Notch, has a separable Notch-specific chaperone activity. It appears that OFUT1 binds to newly synthesized Notch receptors in the endoplasmic reticulum, where it promotes folding and thereby secretion of the Notch receptor. It is this chaperone function, not the ability to fucosylate the receptor, that is important in maintaining Notch function. It is possible that other glycosyl transferases may play similar roles in the quality control of other membrane and secretory proteins.

  9. Unraveling Signaling Networks


    Understanding complex signaling networks is a difficult task that requires new and improved technology. Barrios-Rodiles et al. (p. 1621) describe a method of tagging proteins that allows comprehensive mapping of interactions of suspected signaling proteins. High-throughput execution of more than 10,000 experiments yielded a signaling network activated by transforming growth factor β (TGFβ) with more than 900 interactions. The dynamic nature of the network involved connections being both lost and gained as cells respond to TGFβ, which regulates the epithelial to mesenchymal transition that occurs during development and also contributes to invasive properties of carcinomas. Ozdamar et al. (p. 1603) explored the regulation of tight junctions by TGFβ and the role of the polarity protein, Par6. Phosphorylation of Par6 by the TGFβ receptor was required for epithelial to mesenchymal transition of mammary gland cells. The function of Par6 appears to be recruitment of an E3 ubiquitin ligase (Smurf1), which leads to degradation of the small guanosine triphosphatase RhoA and dissolution of tight junctions.

  10. Brassinosteroid Signaling Pathway

    Plants lacking a type of steroid—brassinosteroid—are likely to be dwarfed with curled leaves and exhibit an ineffective growth pattern in the dark. Brassinosteroids bind to receptors at the plant cell surface and initiate a signaling cascade that involves nuclear factors including BZR1 and BZR2. He et al. (p. 1634, published online 27 January 2005; see the Perspective by Sablowski and Harberd) have now characterized aspects of the signaling pathway for brassinosteroids in detail and find that BZR1 is a DNA binding protein that functions as a transcriptional repressor.

  11. Linking Responses to Reward

    If the size and probability of rewards are variable, efficient neural coding would argue that our responses would be adjusted to center somewhere in the mid-range of possible reward magnitudes and that the response would be modulated to take into account how wide the range of probable rewards is. Tobler et al. (p. 1642) present data that suggest these adjusted responses are in fact encoded within the patterns of activity of dopamine neurons in monkeys as the animals adapted to a schedule of varying rewards.

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