This Week in Science

Science  05 Jul 2013:
Vol. 341, Issue 6141, pp. 9
  1. Genetic Mosaicism in Brain Development

    With the increased power now available in sequencing and genomic technologies has come the realization that within an organism, individual cellular genomes can diverge from one another. Poduri et al. (10.1126/science.1237758) review how de novo mutations, which arise in the parental germ line, or during development of the child, are the cause of a variety of neurodevelopmental disorders.

  2. Cool Accretion

    Numerical models predict that in order to keep forming stars, galaxies should be continuously replenished with gas from the intergalactic medium. Using data from the Very Large Telescope in Chile, Bouché et al. (p. 50) report observations that are consistent with accretion of cold, chemically pristine gas onto a star-forming galaxy at a time when the cosmic star-formation activity was at its peak.

  3. Distorted Nanoparticle

    CREDIT: CLARK ET AL.

    Nanoparticles have found many applications in modern technology; however, the full characterization of individual particles is challenging. One of the most interesting mechanical properties is the particle's response to lattice distortion. This property has been probed for ensembles of nanoparticles, but the required averaging may distort the results. Clark et al. (p. 56, published online 23 May; see the Perspective by Hartland and Lo) were able to image the generation and subsequent evolution of coherent acoustic phonons from an individual perturbed gold nanocrystal on the picosecond time scale.

  4. Quantum Handedness

    When a rotating object is placed in circulating fluid, an imbalance of pressures on either side of it causes a deflecting force called the Magnus force. The quantum analog of this effect has been predicted to appear in the low-temperature A phase of 3He, where the Cooper pairs forming the superfluid have a specific handedness. An impurity traveling through such a superfluid would experience a deflecting force in the direction determined by the chirality of the pairs. Ikegami et al. (p. 59) trapped impurities beneath the free surface of 3He, set them in motion, and demonstrated the existence of this deflecting force by measuring the differential transverse current. The sign of the deflection varied over different cooling runs, indicating that the system was choosing one or the other chirality upon entering the superfluid phase—a signature of spontaneous symmetry breaking.

  5. A Nonclassical Conclusion

    The concept of valence, which underlies the Periodic Table, originated in studies of reactivity rather than structure. Nonetheless, when studies in the mid-20th century suggested that the transient norbornyl cation (C7H11+) reacted as though a carbon center had adopted a formally pentacoordinate motif, this nonclassical structural hypothesis engendered tremendous controversy. Scholz et al. (p. 62) have now succeeded in characterizing the norbornyl cation by x-ray crystallography and confirm the symmetrical fivefold motif.

  6. Inheritance Guts

    We know little about the stability of the constituent microbiota in the human gut or the extent to which the gut microbiota are a potential target for long-term health interventions. Faith et al. (10.1126/science.1237439) analyzed the fecal microbiota of 37 individuals and found that, on average, 60% of bacterial strains remained stable for up to 5 years and many were estimated to remain stable for decades.

  7. Female Infertility

    Anovulation, the failure of a woman's ovary to release an oocyte, is a major cause of female infertility. The mechanisms of ovulation have been studied extensively, with the hypothalamicpituitary axis serving as a key player in its regulation. Hasuwa et al. (p. 71, published online 13 June) describe a mechanism by which anovulation can be caused by the disruption of two microRNAs that are expressed in the pituitary gland.

  8. This Is the Place

    Bats, bees, seals, and many seabirds practice central-place foraging, leaving a central home site, such as a hive or a rookery, to forage in a specific territory. Such species also share the challenge of competing for local resources with individuals from separate colonies. Using satellite tags, Wakefield et al. (p. 68, published online 6 June; see the Perspective by Weimerskirch) followed over 180 northern gannets to determine potential drivers of foraging territory division. Boundaries among colonial territories arose as a result of competition with individuals from other territories. Individuals from the same colony appeared to share information about foraging sites, presumably contributing to the establishment and maintenance of specific, long-term colonial territories.

  9. Immunotherapy Packs a One-Two Punch

    CREDIT: IMAGE CONCEIVED AND CREATED BY CHRIS GARCIA AND ERIC SMITH

    Despite the immune system's best efforts, cancer always seems to be one step ahead. One example of this is that tumor cells express CD47 on their cell surface. CD47 acts as a “don't eat me” signal to phagocytic macrophages. A potential therapeutic strategy could thus be to block this signal. Weiskopf et al. (p. 88, published online 30 May; see the Perspective by Kershaw and Smyth) created variants of the CD47 receptor, SIRPα, that could act as high-affinity antagonists of CD47. Although the antagonists blocked CD47 effectively in tumor-bearing mice, on their own they did not induce macrophages to phagocytose the tumor cells. When paired with a variety of therapeutic antitumor antibodies, however, the CD47 antagonists were very effective in treating several mouse tumor models.

  10. Monitoring Land Use

    Land-use decisions are based largely on agricultural market values. However, such decisions can lead to losses of ecosystem services, such as the provision of wildlife habitat or recreational space, the magnitude of which may overwhelm any market agricultural benefits. In a research project forming part of the UK National Ecosystem Assessment, Bateman et al. (p. 45) estimate the value of these net losses. Policies that recognize the diversity and complexity of the natural environment can target changes to different areas so as to radically improve land use in terms of agriculture and greenhouse gas emissions, recreation, and wild species habitat and diversity.

  11. Mysterious Radio Bursts

    It has been uncertain whether single, short, and bright bursts of radio emission that have been observed are celestial or terrestrial in origin. Thornton et al. (p. 53; see the Perspective by Cordes) report the detection of four nonrepeating radio transient events with millisecond duration in data from the 64-meter Parkes radio telescope in Australia. The properties of these radio bursts indicate that they had their origin outside our galaxy, but it is not possible to tell what caused them. Because the intergalactic medium affects the characteristics of the bursts, it will be possible to use them to study its properties.

  12. Early Farmers?

    What was the role of the eastern Fertile Crescent (which includes southeastern Turkey, northeastern Iraq, and western Iran) in the transition from foraging to farming? Riehl et al. (p. 65; see the Perspective by Willcox) investigated an archaeobotanical assemblage from Chogha Golan, in modern Iran over an apparently continuous occupation of the site over 2000 years, which captures the transition from foraging to farming. The rich archaeobotanical remains suggest the use of a wide array of plant species, including the progenitors of key crop plants (wheat, barley, and large-seeded legumes). Residents of the eastern Fertile Crescent thus appear to have been involved in plant management and possibly in the domestication of wild crop plants.

  13. RGM Proteins

    CREDIT: BELL ET AL.

    Members of the repulsive guidance molecule (RGM) family of proteins can be secreted or reside on the surface of cells where they bind to the cell surface receptor, neogenin. The RGM proteins are named for their role in axon guidance for developing neurons, but their function is also linked to a range of human diseases, including inflammation, multiple sclerosis, and cancer. Bell et al. (p. 77) solved the crystal structures of the external portions of the RGMB protein with portions of neogenin. The structures revealed interactions of dimers of RGMB with neogenin in which ligand binding induced conformational changes that may initiate intracellular signaling from the receptor. RGM proteins contain a site of autocatalytic cleavage that affects secretion of the proteins, and some disease-associated mutations in RGM proteins were clustered at this site.

  14. Form and Function

    The contribution of disulfide bonding to oxidative protein folding and assembly, quality control, and stress responses in the endoplasmic reticulum (ER) are widely recognized. In contrast, catalysis of disulfide bond formation downstream of the ER is uncharted territory. QSOX, a Golgi-localized or secreted disulfide catalyst, was identified in the 1970s and was more recently shown to be upregulated in many cancers. However, the physiological importance of QSOX catalytic activity has been unclear. Ilani et al. (p. 74, published online 23 May) found that human QSOX1 is essential for incorporation of laminin into the extracellular matrix, with profound effects on the capability of the matrix to support integrin-mediated cell adhesion and migration.

  15. Spliceosome Helicase

    Introns are removed from eukaryotic premessenger RNA by the spliceosome. The spliceosome is assembled and disassembled during the course of each splicing reaction, and the RNA-protein remodeling involved is carried out by RNA helicases, whose activities must be closely regulated. Mozaffari-Jovin et al. (p. 80, published online 23 May) determined the crystal structure of the human Brr helicase in complex with the Jab1 domain of the Prp1 spliceosomal protein. The C-terminal tail of the Prp8 Jab1 domain inserts into the RNA-binding tunnel of Brr2, disrupting interaction of the RNA with the conserved helicase motifs inside tunnel. The temporal regulation of Brr2 RNA-binding and adenosine triphosphatase activity likely avoids premature disassembly of structures required during the splicing reaction.

  16. Drug Targeting

    Drug efficacy depends on the extent of binding to a cellular target (often a protein) with adverse effects caused by excessive target binding or by off-target binding. Engagement of a target protein inside cells is influenced by the effective drug concentration and by factors that regulate the protein conformation, making it difficult to predict efficacy based on in vitro affinity studies. Martinez Molina et al. (p. 84) took advantage of the shift in protein thermal stability caused by drug binding to directly monitor target protein-drug interactions in cells. The method was used to monitor drug target engagement in cancer cells and in mouse livers and kidneys.

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