This Week in Science

Science  06 Dec 2013:
Vol. 342, Issue 6163, pp. 1143
  1. Oscillation Stabilizes the Progenitor State

    Transcription factors regulate fate choice between different neural lineages, but the same transcription factors are also expressed in neural progenitor cells. Imayoshi et al. (p. 1203, published online 31 October) analyzed the details of expression of several transcription factors in mouse neural cells. In neural progenitor cells, several different transcription factors were expressed in an oscillatory manner, whereas differentiated neurons stably expressed a single lineage-specific factor.

  2. Giant Solar Cells

    Convection motions within the Sun transport heat from its interior to its surface. The hot regions are seen as granular (∼1000 kilometers across) and supergranular (∼30,000 kilometers across) cells in the Sun. Using data from the Helioseismic Magnetic Imager on the Solar Dynamics Observatory, Hathaway et al. (p. 1217) found evidence for even larger cells that have long been predicted by theory but not unambiguously detected. The flows associated with these giant cells transport angular momentum toward the equator and are important for maintaining the Sun's equatorial rotation.

  3. Good Foundations, Poor Access

    CREDIT: BOETS ET AL.

    Dyslexia makes reading and spelling difficult. Boets et al. (p. 1251) analyzed whether for adult readers with dyslexia the internal references for word sounds are poorly constructed or whether accessing those references is abnormally difficult. Brain imaging during phonetic discrimination tasks suggested that the internal dictionary for word sounds was correct, but accessing the dictionary was more difficult than normal.

  4. Dissecting Chromosome Segregation

    During cell division, the centromere regions of chromosomes assemble multiprotein organelles called kinetochores that form attachments to spindle microtubules. Working in Caenorhabditis elegans, Cheerambathur et al. (p. 1239, published online 14 November) describe a mechanism controlling the formation of kinetochore-spindle microtubule attachments that is essential for accurate chromosome segregation. The findings suggest the existence of crosstalk between the two major protein complexes involved in forming spindle microtubule attachments: the kinetochore dynein module, which initially captures spindle microtubules, and the Ndc80 complex, which ultimately forms the dynamic end-coupled attachments that segregate chromosomes.

  5. Nonlinear Optics Made Easier

    Nonlinear optical materials can change their optical properties in the presence of light. The nonlinearity results from the constructive addition of interacting photons, but the amount of nonlinear light produced is crucially dependent on meeting strict phase-matching conditions of the interacting photon fields. Suchowski et al. (p. 1223; see the Perspective by Kauranen) now show that metamaterials can be designed with optical properties that relax the phase-matching requirements. At a specific wavelength where the metamaterial exhibits zero refractive index, the photons are found to interact nonlinearly with the phasematching done automatically.

  6. Toward a New Physics

    The search for physics beyond the Standard Model is carried out at accelerator facilities such as the Large Hadron Collider but also on a smaller scale in atomic and molecular physics experiments. One of the signatures of this “new physics” would be a nonvanishing electric dipole moment of the electron, but experiments designed to look for it need to distinguish between the signal and many potential artifacts. Loh et al. (p. 1220) introduce a method based on the spectroscopy of polarized molecular ions that avoids some of the sources of systematic error.

  7. Epithelial Stem Cells

    Much remains to be known about how epithelial stem cells are generated and maintained. Lim et al. (p. 1226; see the Perspective by Frede and Jones ) describe a mechanism of stem cell maintenance where epidermal stem cells generate their own self-renewing Wnt signals rather than being controlled by adjacent “niche” signals. These stem cells also express secreted Wnt inhibitors that become localized to more differentiated progeny cells. These autocrine Wnt signals and paracrine long-range Wnt inhibitors may balance stem cell self-renewal and differentiation.

  8. Hedgehog View to a Kill

    Hedgehog (Hh) signaling is best known for its role in development and is a key signaling component of primary cilia. Hh signaling plays a role in T cell development, but whether Hh signaling plays a role in the function of mature effector T cells is unclear. De la Roche et al. (p. 1247; see the Perspective by Le Borgne and Shaw) now show that T cell receptor signaling triggers Hh signaling. When Hh signaling is disrupted, centrosome polarization to the immunological synapse is reduced, and cytotoxic T cell–mediated killing is impaired.

  9. Deep Drilling for Earthquake Clues

    CREDIT: JAMSTEC/IODP

    The 2011 Mw 9.0 Tohoku-Oki earthquake and tsunami were remarkable in many regards, including the rupturing of shallow trench sediments with huge associated slip (see the Perspective by Wang and Kinoshita). The Japan Trench Fast Drilling Project rapid response drilling expedition sought to sample and monitor the fault zone directly through a series of boreholes. Chester et al. (p. 1208) describe the structure and composition of the thin fault zone, which is predominately comprised of weak clay-rich sediments. Using these same fault-zone materials, Ujiie et al. (p. 1211) performed high-velocity frictional experiments to determine the physical controls on the large slip that occurred during the earthquake. Finally, Fulton et al. (p. 1214) measured in situ temperature anomalies across the fault zone for 9 months, establishing a baseline for frictional resistance and stress during and following the earthquake.

  10. Light Turns the Array

    CREDIT: LINDEBOOM ET AL.

    The organization of cortical microtubule arrays in higher plant cells is essential for organizing cell and tissue morphogenesis, but it is not clear how specific architectures are acquired and reconfigured in response to environmental cues. Lindeboom et al. (10.1126/science.1245533, published online 7 November; see the Perspective by Roll-Mecak) used live-cell imaging and genetic studies to show that the microtubule-severing protein, katanin, plays a crucial role in reorienting cortical arrays from transverse to longitudinal in Arabidopsis seedlings in response to blue light perception. Katanin localized to microtubule intersections where, stimulated by blue light receptors, it preferentially catalyzed the severing of the newer microtubule. The microtubule “plus” end created by severing were observed to grow preferentially, effectively building a new population of microtubules orthogonal to the initial array. The net effect of this process steers the growing seedling toward light.

  11. Avian Affinity for H7N9

    Structural analyses of the binding of avian origin H7N9 influenza viruses have revealed how the receptor-binding characteristics differentiate between birds and mammals, and studies involving the use of whole viruses have suggested that the virus is acquiring human-type receptor specificity. In contrast, Xu et al. (p. 1230) show that the H7 hemagglutinin strongly retains its specificity for avian-type receptors by using cocrystal structures with receptor analogs and glycan binding analysis with recombinant hemagglutinin against a library of receptor analogs. Thus, current human H7N9 viruses appear to remain poorly adapted to human receptors, and additional mutations will be required to achieve specificity for human-type receptors equivalent to those of human pandemic viruses.

  12. Dual-Duty Active Site

    O-linked N-acetylglucosamine transferase (OGT) catalyzes the addition of N-acetylglucosamine (GlcNac) to serine or threonine residues, influencing the localization and function of proteins. Because its activity is sensitive to the nutrient uridine diphosphate (UDP)–GlcNac, OGT has been proposed to regulate cellular responses to nutrient status. Recently, OGT in the presence of UDP-GlcNac was shown to cleave host cell factor–1 (HCF-1), a transcriptional coregulator of human cell-cycle progression. This cleavage is required for HCF-1 maturation. Through a combination of structural, biochemical, and mutagenesis studies, Lazarus et al. (p. 1235) show that both cleavage and glycosylation of HCF-1 occur in the OGT active site. Cleavage occurs between cysteine and glutamine and converts the glutamine into a serine which can then be glycosylated.

  13. Command and Control

    Innate lymphoid cells are vital for the development of gut-associated lymphoid tissues, maintenance of the epithelial barrier, and protection against intestinal microbes; their dysfunction can promote immune pathology. Immunoglobulin A (IgA) production is important for maintenance of the gut epithelial barrier and the composition of the gut microbiota. Through the generation of knockout mouse models, Kruglov et al. (p. 1243) were able to distinguish how soluble and membrane-bound lymphotoxins expressed by innate lymphoid cells in the gut specifically regulate IgA production and thereby control gut microbiota composition.

  14. Not Too Much, Not Too Little

    The microRNA miR128 is expressed in brain neurons of the mouse. Lek Tan et al. (p. 1254) now find that miR128 is crucial to stable brain function. Mice deficient in miR128 developed hyperactivity and were susceptible to fatal seizures, whereas overexpression of miR128 correlated with reduced motor activity and reduced susceptibility to proconvulsive drugs. Experiments using ex vivo–isolated adult brain tissues suggested that miR-128 controlled motor activity by governing the signaling network that determines the intrinsic excitability and signal responsiveness of neurons.

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