This Week in Science

Science  06 Aug 2010:
Vol. 329, Issue 5992, pp. 606
  1. The Storage of Emotions

    The neural mechanisms involved in emotional learning are well understood. However, how and where emotional memories are stored is still largely unclear. Sacco and Sacchetti (p. 649) now show that Pavlovian fear memories are stored in a modality-specific way in the secondary, but not primary, sensory cortices. The site of storage depended on whether the conditioned stimulus was visual, auditory, or olfactory. Only “old,” not new, memories were stored in this way, and lesions of secondary cortices, while disrupting the old memories, did not prevent the acquisition of new memories.

  2. Measuring Motion

    Within a solid, atoms vibrate about their mean position in a series of frequencies known as the normal modes, which relate to the thermal and mechanical transport properties of the material. D. Kaya et al. (p. 656) used video microscopy to observe the motion of colloidal crystals made from microgel particles. The colloidal particles varied slightly in their properties, allowing the behavior of disordered materials to be probed. Long-wavelength plane-wave modes were observed, characteristic of perfect crystals, and a conventional elastic behavior, modified by short-wavelength features, was also observed, in spite of the disorder of the colloidal crystals. The analysis method will allow studies on the effects of different types of disorder on the structure of the normal modes and the elasticity in a range of material systems.

  3. Threats to and from Bats

    Bats appear to be able to host an assortment of alarming pathogens, which, if they do not extirpate the bats, have implications for human health (see the Perspective by Daszak). For example, exposure to bats is the main source of human rabies in the Americas. But rabies is not generally transmitted among people; humans are a dead end for the virus. Streicker et al. (p. 676, see the cover) show that rabies virus lineages tend to be specific for bat lineages. It seems that although rabies viruses have the potential for rapid evolution, this property alone is not enough to overcome genetic barriers, which inhibit the onward transmission of rabies virus into a new species. White-nose syndrome, an exotic fungal infection of bats, has, over the past 3 years, spread from upstate New York to West Virginia, killing on average 70% of the animals in a hibernating colony. The infection makes bats restless over winter when they should be dormant, which makes them exhaust their fat reserves, resulting in the death of over a million bats. Frick et al. (p. 679) have analyzed population data collected on bats in the northeastern United States for the past 30 years and show that, mainly owing to white-nose syndrome, the once abundant little brown bat is heading for regional extinction in the next 16 years or so. This scale of loss of an insectivorous mammal is expected to have repercussions for ecosystem integrity and for the economic costs of agricultural pest control.

  4. Opening a Surface Gap

    Many properties of topological insulators are a consequence of their so-called gapless surface state, in which electrons are protected from back-scattering, thanks to time-reversal symmetry. Breaking the time-reversal symmetry and opening a surface gap offers prospects for studying phenomena relevant to particle physics, such as axion electrodynamics. To achieve this, Chen et al. (p. 659; see the Perspective by Franz) doped the three-dimensional topological insulator Bi2Se3 with magnetic dopants and observed the opening of a surface gap. Simultaneous doping with charge dopants was used to shift the Fermi energy to the inside of the surface gap, thus achieving an insulating gapped Dirac state. Both the size of the gap and the position of the Fermi energy level were tunable by varying the nature and the density of the dopants.

  5. Entanglement in a Twist

    The strong correlations observed in quantum mechanically entangled particles, such as photons, offer potential for secure communication and quantum information processing. Leach et al. (p. 662) now show such strong quantum correlations between the complementary variables—angular position and orbital angular momentum—of two photons created during the parametric down-conversion process in a nonlinear crystal. This demonstration of entanglement in an angular basis establishes that angles are genuine quantum observables and can therefore be considered a resource for quantum information processing, capable of secure, high-dimension, key distribution.

  6. MESSENGER's Third Set of Messages


    MESSENGER, the spacecraft en route to insertion into orbit about Mercury in March 2011, completed its third flyby of the planet on 29 September 2009. Prockter et al. (p. 668, published online 15 July) present imaging data acquired during this flyby, showing that volcanism on Mercury has extended to much more recent times than previously assumed. The temporal extent of volcanic activity and, in particular, the timing of most recent activity had been missing ingredients in the understanding of Mercury's global thermal evolution. Slavin et al. (p. 665, published online 15 July) report on magnetic field measurements made during the 29 September flyby, when Mercury's magnetosphere underwent extremely strong coupling with the solar wind. The planet's tail magnetic field increased and then decreased by factors of 2 to 3.5 during periods lasting 2 to 3 minutes. These observations suggest that magnetic open flux loads the magnetosphere, which is subsequently unloaded by substorms—magnetic disturbances during which energy is rapidly released in the magnetotail. At Earth, changes in tail magnetic field intensity during the loading/unloading cycle are much smaller and occur on much longer time scales. Vervack et al. (p. 672, published online 15 July) used the Mercury Atmospheric and Surface Composition Spectrometer onboard MESSENGER to make measurements of Mercury's neutral and ion exospheres. Differences in the altitude profiles of magnesium, calcium, and sodium over the north and south poles of Mercury indicate that multiple processes are at play to create and maintain the exosphere.

  7. Measuring Single Myosins at Work

    In the past 15 years, the molecular mechanism of muscle contraction has been investigated at the single-molecule level; however, results have varied between laboratories because of the nonprocessive properties of skeletal myosin. Now, Kaya and Higuchi (p. 686) have measured the nonlinear elasticity and working stroke size of single skeletal myosins by combining optical trapping and fluorescence imaging with subnanometer accuracy. The data suggest that it is important to relate myosin's internal structural changes to physiological force generation and filament sliding.

  8. A Lot of HOTAIR

    The roles of several classes of small (<50 nucleotides) noncoding RNAs are beginning to be defined in molecular detail, whereas the function of most of the long (∼200+ nucleotides), intergenic noncoding (linc)RNAs found in most eukaryotic genomes remains something of a mystery. The HOTAIR lincRNA, which is transcribed from the mouse HOXC locus, binds to the Polycomb Repressive Complex 2 (PRC2) and recruits it to HOXD and other genes, where its histone methylase activity acts to repress gene transcription. Tsai et al. (p. 689, published online 8 July) now show that HOTAIR also binds to a histone demethylase enzyme, LSD1, part of the CoREST/REST repressor complex. LSD1 acts to remove transcription-activating histone marks, reinforcing the repressive activity of the PRC2 complex. HOTAIR thus functions as a platform for the coordinated binding of PRC2 and LSD1-containing complexes to genes, as revealed in a genome-wide analysis of PRC1/CoREST/REST co-regulated genes.

  9. Parental Influences


    Genomic imprinting results in the preferential expression of either the paternally or the maternally inherited allele of certain genes. Two papers by Gregg et al. (p. 643, published online 8 July; and p. 682, published online 8 July; see the Perspective by Wilkinson) use a genome-wide approach to characterize the repertoire of genes with parent-of-origin allelic effects in the mouse embryonic and adult brain. The studies uncovered over 1300 loci with maternal or paternal allelic bias. Comparison of the parent-of-origin allelic expression bias in the adult hypothalamus and cortex, and in the developing brain, revealed spatiotemporal, sex-specific, and isoform-specific regulation. Parent-of-origin effects thus represent a major and dynamic mode of epigenetic regulation of gene expression in the brain.

  10. Fanconi Anemia Protein in DNA Binding

    Fanconi anemia patients suffer a number of symptoms, including increased sensitivity to chemicals that cross-link DNA strands of the double helix together. Such aberrations can lead to genome instability. Mutations in 13 different genes implicated in repairing damaged DNA are known to be involved in the disease. Liu et al. (p. 693, published online 29 July) have identified a new factor, FAN1 (Fanconi anemia–associated nuclease 1), which they find to be associated with a complex of two of the FANC proteins, FANCI and FANCD2 (the ID complex). The mono-ubiquitylated ID complex locates to sites of DNA damage to which it recruits FAN1, a mono-ubiquitin–binding protein. FAN1 has a DNA branch–specific nuclease activity that is required for the removal and subsequent repair of the interstrand DNA cross-links.