This Week in Science

Science  22 Nov 2013:
Vol. 342, Issue 6161, pp. 908
  1. Chromosome Conundrum

    CREDIT: IMAGES GENERATED BY MAXIM IMAKAEV WITH INPUT FROM GEOFF FUDENBERG AND NATALIA NAUMOVA

    The three-dimensional organization of chromosomal DNA within the cell nucleus plays an important role in gene regulation. Naumova et al. (p. 948, published online 7 November; see the Perspective by Kleckner et al.) used chromosome conformation capture-based methods in human tissue culture cells to analyze the higher order folding of human chromosomes across the cell cycle. During interphase the chromosomes showed locus-specific compart-mentalization. In mitotic cells, on the other hand, the chromosome organization was more linear, consistent with arrays of consecutive chromatin loops.

  2. Imaging Excitations

    Complex processes such as chemical reactions and photosynthesis involve the transport of energy. The mechanisms of how the energy migrates, the influence of the surrounding environment, or the extent to which quantum mechanics affects the process remain unclear. Günter et al. (p. 954, published online 7 November; see the Perspective by Donley) found that a cloud of cold atoms suitably prepared and decorated with “impurity” Rydberg atoms could be used to image the transport of excitations between excited Rydberg atoms directly. This ability to tune the influence of the background environment may help in the study of the coherent transport of energy in complex many-body systems.

  3. Fluorinating Pyridine

    Appending fluorine substituents to carbon centers is commonly used to tune small-molecule properties in pharmaceutical and agrochemical research. However, fluorinations often require the use of corrosive, hazardous reagents. Fier and Hartwig (p. 956) present an unusually mild and convenient protocol for fluorinating carbon sites adjacent to nitrogen in pyridines and related nitrogen-bearing arenes. The reaction entails treatment with silver difluoride and proceeds rapidly at room temperature.

  4. Bipolar Signature

    Atmospheric methane has increased approximately 2.5-fold since the start of the industrial revolution, a consequence of human activity. However, a smaller and more gradual rise began around 6000 years ago, near the time when human agriculture began to develop and expand. Mitchell et al. (p. 964) present two, high-resolution ice core methane records of the past 2500 years, one from each pole. Methane emissions were primarily from the tropics, with secondary contributions from the higher latitudes where most humans lived. Thus, both natural and human sources are needed to explain the late-Holocene atmospheric methane record.

  5. Building Vocalization

    The transcription factor FoxP2 (forkhead box P2) affects language acquisition in humans and regulates the protein SRPX2 (sushi repeat-containing protein X-linked 2), which itself also affects language. Sia et al. (p. 987, published online 31 October; see the Perspective by Lieberman) found that in the mouse brain, the FoxP2 transcription factor binds to the SRPX2 gene. In tissue culture experiments, FoxP2, but not SRPX2, affected dendritic morphology, while both FoxP2 and SRPX2 affected the formation of excitatory synapses. Overexpression of SRPX2 in the mouse brain equivalent of the human brain's language area affected synapse density and disrupted the ultrasonic vocalizations emitted by mouse pups in search of their mothers.

  6. The Microbiota Makes for Good Therapy

    The gut microbiota has been implicated in the development of some cancers, such as colorectal cancer, but—given the important role our intestinal habitants play in metabolism—they may also modulate the efficacy of certain cancer therapeutics. Iida et al. (p. 967) evaluated the impact of the microbiota on the efficacy of an immunotherapy [CpG (the cytosine, guanosine, phosphodiester link) oligonucleotides] and oxaliplatin, a platinum compound used as a chemotherapeutic. Both therapies were reduced in efficacy in tumor-bearing mice that lacked microbiota, with the microbiota important for activating the innate immune response against the tumors. Viaud et al. (p. 971) found a similar effect of the microbiota on tumor-bearing mice treated with cyclophosphamide, but in this case it appeared that the microbiota promoted an adaptive immune response against the tumors.

  7. From Yeast to Therapeutic?

    Yeast has shown some promise as a model system to generate lead compounds that could have therapeutic potential for the cellular problems associated with neurodegenerative diseases. Along these lines, Tardiff et al. (p. 979, published online 24 October) and Chung et al. (p. 983, published online 24 October) describe the results of multiple screens in yeast that lead to the identification of a potential therapeutic compound to combat the cytotoxic affect of α-synuclein accumulation. The compound was able to reverse the pathological hallmarks of Parkinson's disease in cultured neurons derived from patients with α-synuclein–induced Parkinson's disease dementia.

  8. Venus' Orbit in STEREO

    CREDIT: JONES ET AL.

    Around Earth's orbit there is a circumsolar dust ring composed of particles of cometary and asteroidal origin. Tenuous dust rings are believed to be commonly associated with planets, but—other than around Earth—have not been detected. Now, Jones et al. (p. 960) have used observations from the solar terrestrial relations observatory (STEREO) to map a dust ring associated with the orbit of Venus.

  9. Limiting Tumor Initiation

    What is the competitive advantage of cells with frequently occurring mutations during tumor development? Vermeulen et al. (p. 995; see the Perspective by Bozic and Nowak) quantified the advantages of Apc-loss, Kras activation, and P53 mutation during tumor initiation in the mouse intestine. The mutations conferred only a limited clonal advantage. Indeed, many mutated stem cells were stochastically replaced by wild-type stem cells, helping to limit tumor initiation.

  10. Macrophage Makeover

    Macrophages are important immune cells that function in tissue repair during homeostasis and in the innate immune response. Inflammation, which can be triggered by infection, is accompanied by a massive expansion of macrophages in affected tissues. The major source of this increase in resident macrophages has been thought to be hematopoietic stem cells in the bone marrow. However, recent results have shown that the mature differentiated macrophages residing in the affected tissues can themselves proliferate to boost cell numbers. Sieweke and Allen (10.1126/science.1242974) review what we know about the origin of macrophages and outline the consequences of local macrophage proliferation for the immune response and tissue homeostasis.

  11. Extraterrestrial Neutrinos

    Neutrinos are thought to be produced in astrophysical sources outside our solar system but, up until recently, they had only been observed from one supernova in 1987. Aartsen et al. (10.1126/science.1242856; see the cover) report data obtained between 2010 and 2012 with the IceCube neutrino detector that reveal the presence of a high-energy neutrino flux containing the most energetic neutrinos ever observed, including 28 events at energies between 30 and 1200 TeV. Although the origin of this flux is unknown, the findings are consistent with expectations for a neutrino population with origins outside the solar system.

  12. Flu Drift Limited

    CREDIT: KOEL ET AL.

    Five antigenic sites in the virus surface hemagglutinin protein, which together comprise 131 amino acid positions, are thought to determine the full scope of antigenic drift of influenza A virus. Koel et al. (p. 976) show that major antigenic change can be caused by single amino acid substitutions. These single substitutions substantially skew the way the immune system “sees” the virus. All substitutions of importance are located next to the receptor-binding site in the hemagglutinin. Because there are few positions of importance for antigenic drift, there are strict biophysical limitations to the substitutions at these positions, which restricts the number of new antigenic drift variants at any point in time. Thus, the evolution of influenza virus may be more predictable than previously thought.

  13. Just Add Peroxide

    The HppE enzyme uses iron to catalyze oxidation of an alcohol to an epoxide ring in the biosynthesis of the antibiotic fosfomycin. Because this process is a two-electron oxidation, it has been unclear how the enzyme reduces its presumed oxidative partner O2 all the way to water. Where do the two extra electrons come from? Wang et al. (p. 991, published 10 October; see the Perspective by Raushel) now show that HppE is actually a peroxidase, and thus reduces H2O2, for which just two electrons are sufficient. The result expands the structural scope of iron-bearing peroxidase enzymes beyond heme motifs.

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