This Week in Science

Science  01 Mar 2013:
Vol. 339, Issue 6123, pp. 1009
  1. Interfering Single Electrons


    Quantum information processing requires the generation of indistinguishable and coherent particles. While these have been demonstrated for photons, carrying it over for electrons and the possibility of quantum electronic implementations has been challenging. Using two independent single-electron sources patterned into a two-dimensional electron gas, Bocquillon et al. (p. 1054, published online 24 January; see the Perspective by Schönenberger) performed single-electron interference experiments. The results demonstrate that the generated electrons can possess the desired properties for potential quantum applications.

  2. Prevention or Repair

    Neural tube defects, such as spina bifida, remain remarkably common, despite widespread efforts to prevent them through supplementing maternal diets with folic acid. Surgery early in development has seen some success, but problems often remain. Wallingford et al. (10.1126/science.1222002) review normal and abnormal neural tube development and suggest that discovering the genetic risk factors for these serious birth defects could provide ways to prevent and treat neural tube defects.

  3. A Hidden Black Hole?

    Black holes with masses comparable to that of the Sun are often associated with variable x-ray sources. Corral-Santana et al. (p. 1048) report optical observations of a faint and variable x-ray source detected in our galaxy with the Swift Burst Alert Telescope. The optical data reveal a black hole with a mass greater than three times that of the Sun in a 2.8-hour period around a low-mass donor star. Unusual for this type of system, the black hole binary is seen at a very high inclination.

  4. Controlling Magnetic Noise

    Ferromagnetic materials contain a number of magnetic domains, with individual domains switching stochastically as the field strength is increased. As magnetic memory elements shrink in size, it is important to understand, and ultimately control, this magnetic noise. Using a magnetic vortex core integrated with a nanomechanical torsion balance, Burgess et al. (p. 1051, published online 17 January) created a two-dimensional map of the magnetic potential within the sample with nanoscale resolution. Moreover, introducing geometric defects (dimples) in the sample allowed the magnetization to be stabilized.

  5. How Migraine Develops

    Migraine is a common medical disorder. Unfortunately, how and why migraine headache is initiated is unclear. Karatas et al. (p. 1092) now describe a signaling pathway between stressed neurons and meningeal trigeminal afferents, which may explain how migraine headaches can be generated.

  6. No Leader to Follow

    Changes in the concentration of atmospheric CO2 and surface air temperature are closely related. However, temperature can influence atmospheric CO2 as well as be influenced by it. Studies of polar ice cores have concluded that temperature increases during periods of rapid warming have preceded increases in CO2 by hundreds of years. Parrenin et al. (p. 1060; see the Perspective by Brook) present a revised age scale for the atmospheric component of Antarctic ice cores, based on the isotopic composition of the N2 that they contain, and suggest that temperature and CO2 changed synchronously over four intervals of rapid warming during the last deglaciation.

  7. Mastering Meiosis

    Two conserved kinases (Ipl1/Aurora B and Mps1) are known to be critical for correct chromosome orientation on the spindle during meiosis, but their roles and relationships in controlling chromosome segregation are unclear. Working in yeast, Meyer et al. (p. 1071, published online 31 January) monitored chromosomes as they go through the steps of properly attaching to the spindle microtubules and dissected the roles of the two kinases in chromosome pairing, orientation, and segregation.

  8. Genetic Clues to Meningioma

    Meningiomas are the most common primary brain tumors in adults. Located within the layer of tissue covering the brain, these tumors are usually slow-growing and benign but can cause serious neurological complications. About half of these tumors have mutations in the neurofibromin 2 gene (NF2). To identify other genes that contribute to meningioma pathogenesis, Clark et al. (p. 1077, published online 24 January) performed genome sequence analysis on 300 tumors. Meningiomas fell into two general classes: benign tumors located at the skull base—which tend to harbor mutations in the TRAF7, KLF4, AKT1, and SMO genes—and higher-grade tumors located in the cerebral and cerebellar hemispheres harbor mutations in NF2.

  9. A Role for IFN-ɛ

    Type I interferons (IFNs) are critical cytokines involved in host defense against pathogens, particularly viruses. IFN-ɛ is an IFN-like gene encoded within the type I IFN locus in mice and humans whose function has not been characterized. Fung et al. (p. 1088) created mice with a genetic deletion in Ifn-ɛ and found that, like other type I IFNs, IFN-ɛ signals through the IFN-α receptors 1 and 2. However, unlike these other cytokines, which are primarily expressed by immune cells and are induced upon immune cell triggering, IFN-ɛ was expressed exclusively by epithelial cells of the female reproductive tract in both mice and humans and its expression was hormonally regulated. IFN-ɛ–deficient mice were more susceptible to infection with herpes simplex virus 2 and Chlamydia muridarum, two common sexually transmitted pathogens.

  10. Improving Nanowire Photovoltaics

    In principle, solar cells based on arrays of nanowires made from compound inorganic semiconductors, such as indium phosphide (InP), should decrease materials and fabrication costs compared with planar junctions. In practice, device efficiencies tend to be low because of poor light absorption and increased rates of unproductive charge recombination in the surface region. Wallentin et al. (p. 1057, published online 17 January) now report that arrays of p-i-n InP nanowires (that switch from positive to negative doping), grown to millimeter lengths, can be optimized by varying the nanowire diameter and length of the n-doped segment. Efficiencies as high as 13.8% were achieved, which are comparable to the best planar InP photovoltaics.

  11. Coo Coo

    Charles Darwin was fascinated by the domestic rock pigeon and used this dramatic example of diversity within a species to communicate his ideas about natural selection. Many derived traits in domestic pigeons converge on ecologically and evolutionarily relevant traits in wild species. Shapiro et al. (p. 1063, published online 31 January; see the cover) sequenced the genome of the domestic rock pigeon (Columba livia), along with those of 36 breeds and two feral accessions and its sister species, the hill pigeon (C. rupestris). The results reveal the underlying genetics of the head crest and suggest that all crested breeds may have originated from a single mutational event.

  12. A Mossy Veil

    Land plants have two distinct generations: a haploid gametophyte responsible for producing the gametes, and a diploid sporophyte, that in most land plants is the dominant form observed. However, in mosses, a basal land plant, the primary biomass is composed of the haploid gametophyte. Sakakibara et al. (p. 1067; see the Perspective by Friedman) analyzed loss-of-function mutants of KNOX2 (class 2 KNOTTED1-LIKE HOMEOBOX) genes in the moss Physcomitrella patens. Mutant plants exhibit apospory, where fertilization apparently occurs, but the normal sporophyte phase is bypassed and instead a diploid structure resembling a haploid gametophyte is produced. The results suggest that KNOX2 regulates the alternation of generations by suppressing the haploid body plan in the diploid phase.

  13. The Regulatory Genome

    Multicellular organisms contain a variety of cell types that are morphologically and functionally distinct even though they typically contain the same genomic DNA. Differences stem from differential gene expression. Gene regulatory genomic regions (enhancers) are well studied, yet despite major efforts, such as Encode and modEncode, the number of enhancers in animal genomes and their genomic positions, cell-type specificity, and strengths are largely unknown. Arnold et al. (p. 1074, published online 17 January) report a method, termed STARR-seq, that measures the strength of enhancers genome-wide, giving insight into the organization of the regulatory genome.

  14. Dissecting Disaggregation

    The excessive accumulation of misfolded protein aggregates can overwhelm the cell's "quality control" machinery, leading to cell death. The yeast Hsp104 protein and its bacterial homolog ClpB are molecular chaperones that can "rescue" aggregated proteins by coupling the force generated from adenosine triphosphate hydrolysis to the progressive unfolding and threading of extended polypeptide segments through axial channels in these large molecular machines. Unfolded polypeptides emerging from the channel are refolded with the aid of a second chaperone system, DnaK/DnaJ/GrpE. DnaK also plays an important role in bringing regions of polypeptides within aggregates to ClpB to begin the solubilization process. Rosenzweig et al. (p. 1080, published online 7 February; see the Perspective by Saibil) describe a nuclear magnetic resonance–derived structure of the ClpB-DnaK complex, and verified it through mutagenesis and functional assays. The work clarifies the roles of each of the molecular players in the disaggregation reaction and provides a structural basis for the DnaK-ClpB interaction.

  15. Mighty Male Microbes

    Both genetic and environmental factors contribute to an individual's susceptibility to autoimmune disease, but the specific environmental influences are not well characterized. Markle et al. (p. 1084, published online 17 January; see the Perspective by Flak et al.) explored how microbial factors, in particular the gut microbiota, influence susceptibility to type 1 diabetes in mice. In the non-obese diabetic (NOD) mouse model of type 1 diabetes, female mice are significantly more susceptible to disease than males; however, this difference was not apparent under germ-free conditions. Transfer of cecal contents from male NOD mice to female NOD mice prior to disease onset protected against pancreatic islet inflammation, autoantibody production, and the development of diabetes and was associated with increased testosterone in female mice. Blocking androgen receptor activity abrogated protection. Thus, the microbiota may be able to regulate sex hormones and influence an individual's susceptibility to autoimmunity.

  16. Double Whammy

    Psychopathologies that cannot be explained by simple genetic or environmental circumstances may sometimes result from complex interplay between multiple inputs. Giovanoli et al. (p. 1095) analyzed the interactions between prenatal and postnatal stressors in mice to see what synergies give rise to psychopathologies in the adult mice. The results suggest that susceptibilities arise when mice are exposed to prenatal infection and also exposed to stressors around puberty. Stressors delivered later in adolescence did not seem to produce the same susceptibility. Although the mechanisms that impose the delay between stressors and psychopathology remain obscure, the timing and sequence of the triggers hint at possible cellular causes.