This Week in Science

Science  30 Jul 2010:
Vol. 329, Issue 5991, pp. 488
  1. Probed But Not Perturbed >>

    CREDIT: FEDOR JELEZKO AND JOHANNES BECK/(PHOTOS BY ELEMENT 6 LTD.)

    The processing and manipulation of quantum information holds great promise in terms of outperforming classical computers and secure communication. However, quantum information is delicate, and even reading the information is a destructive and probabilistic process requiring a number of measurements to home in on the information stored as a quantum state. For the nitrogen vacancy in diamond, Neumann et al. (p. 542, published online 1 July) show that these limitations can be eliminated. A measurement protocol was designed and implemented where the spin state of the nuclear spin of the vacancy could be mapped onto and read out from the surrounding electronic spins in a single-shot measurement nondestructively.

  2. Insight into Silks

    Silkworms have been cultivated for thousands of years and their silk has been used to make fabrics for clothing, bed sheets, shirts, dresses, and for other applications like sutures. Spider silk is harder to harvest, and thus has not found such widespread use, but its fantastic combination of properties has made it a tempting material to study in detail. Omenetto and Kaplan (p. 528) review our understanding of silk chemistry, the limitations in being able to reconstitute silks and to generate them synthetically, and a range of applications that have been developed using silk materials.

  3. Tilting Toward Reaction

    CREDIT: YODER ET AL.

    Collisions between molecules and metal surfaces underlie many of the catalytic pathways that transform natural feedstocks into fuels and commodity chemical compounds. One such reaction, in which nickel strips hydrogen from methane, depends on whether the methyl C-H bonds are vibrating just before the molecule strikes the surface. Yoder et al. (p. 553) now delve deeper into this system. By aligning incoming molecular samples using polarized infrared light, they show that the hydrocarbon reacts most readily when it is vibrating parallel, rather than perpendicular, to the surface.

  4. Devil in the Detail

    Genetically identical cells in the same environment can show variation in gene expression that may cause phenotypic variation at the single-cell level. But how noisy are most genes? Taniguchi et al. (p. 533; see the Perspective by Tyagi) now report single-cell global profiling of both messenger RNA (mRNA) and proteins in Escherichia coli using a yellow fluorescent protein fusion library. As well as a common extrinsic noise in high-abundance proteins, large fluctuations were observed in low-abundance proteins. Remarkably, in single-cell experiments, mRNA and protein levels for the same gene were uncorrelated.

  5. Waiting to Exhale

    Lung tissue does not regenerate, so, when it is damaged by disease and/or surgically removed, lung transplantation is often the only treatment option. Because donor tissue is in short supply, there has been a long-standing interest in engineering functional and transplantable lung tissue in the laboratory. Petersen et al. (p. 538, published online 24 June; see the Perspective by Wagner and Griffith) now report an important step in this direction. After gently removing the cellular constituents of rat lungs with detergent, the residual scaffold of extracellular matrix—which retained the compliance and mechanical properties of the original lung—was re-seeded with a mixture of lung epithelial and endothelial cells and cultured in a bioreactor. Within a few days, the engineered lung tissue contained alveoli, microvessels, and small airways that were repopulated with the appropriate cell types. When transplanted into a rat for short time periods, the engineered lung showed evidence of gas exchange.

  6. Straining Graphene's Electronic States

    The conduction electrons in graphene, single sheets of graphite, can have very high mobilities. Under the influence of an applied magnetic field, a series of energy steps, or Landau levels, can be observed that correspond to the conduction electrons traveling in cyclotron orbits. Recent theoretical work has indicated that if graphene layers are strained, the strain field creates a pseudomagnetic field that should also lead to observable Landau levels. Levy et al. (p. 544) used scanning tunneling microscopy to probe the energy levels of graphene grown on a platinum surface, which forms highly strained “nanobubbles.” The strain is equivalent to applying very high magnetic fields (in excess of 300 tesla). Thus, the electronic properties of graphene can indeed be modified using applied strain.

  7. Manufacturing Nanomaterials

    The exploration of many materials at the nanoscale has revealed properties that only emerge when working at these small dimensions. For device manufacture, materials need to be deposited or assembled in specific patterns. Schliehe et al. (p. 550; see the cover) show the oriented attachment of lead sulfide nanocrystals into two-dimensional sheets. The packing is driven by the choice of solvents that influence the interactions between the nanocrystals. The nanocrystals have excellent photoconductive properties and were incorporated into a photodetector without any additional chemical processing.

  8. Sinking in Slowly

    As the Arctic warms and its sea ice continues to melt, more of the ocean surface will be exposed, creating the potential for greater uptake of carbon dioxide from the atmosphere. Cai et al. (p. 556, published online 22 July) present results from a series of Arctic Ocean transects that show that the amount of CO2 in the surface waters has increased greatly recently. This will act as a barrier to future CO2 uptake and suggests that the Arctic Ocean will not become the large CO2 sink that some have predicted.

  9. Epithelial Cleft Formation

    The internal architecture of many embryonic organs is established by repetitive branching of epithelia. Epithelial clefts and outgrowths generate this internal branching of glands and other organs. Onodera et al. (p. 562) identify a gene, Btbd7, as a regulator of epithelial dynamics and cleft formation, linking the extracellular matrix with morphogenesis. Btbd7 is induced by a matrix protein at sites of cleft progression and induces a transcription factor and suppresses cell adhesion. The resulting local cell separation and motility contribute to transient tissue gaps that contribute to clefts that help form branched organs.

  10. Toward Alkane Synthesis

    CREDIT: SCHIRMER ET AL.

    Alkanes are major components of fossil fuels, and synthesis of alkanes remains a challenge in the conversion of renewable raw materials to fuels. Even though diverse organisms synthesize alkanes, synthesis pathways have remained elusive. Now Schirmer et al. (p. 559) describe an alkane biosynthesis pathway in cyanobacteria that converts intermediates of fatty acid metabolism to alkanes and alkenes. Heterologous expression of the biosynthetic genes resulted in production of alkanes in Escherichia coli. This pathway is likely to be a valuable tool in the production of biofuels.

  11. Building the Heart

    The multichambered heart of birds and mammals develops through addition of second heart field (SHF)–derived precursor cells to a primary heart tube. Stolfi et al. (p. 565) show that, in the simple chordate Ciona intestinalis, the heart and atrial siphon muscle (ASM) precursors arise from common progenitors following asymmetric cell divisions and that the transcription factor COE (Collier/Olf1/EBF) is involved in this fate choice. The ASM precursors express molecular markers of the vertebrate pharyngeal mesoderm that gives rise to the SHF and lower jaw muscles, suggesting that the origins of both can be traced back to the last common ancestor of tunicates and vertebrates.

  12. Another Cell Culprit in Prostate Cancer

    A recent controversial hypothesis about the cellular origins of human cancer, the so-called “cancer stem cell hypothesis,” has fueled interest in identifying the specific cell types that give rise to common epithelial cancers. A single, well-defined cell of origin could, in principle, lead to more effective targeted therapies. Based on histological evidence and/or studies of mouse tumors, luminal cells are believed to be the cell of origin in prostate cancer. Now, using functional assays of cells derived from benign human prostate tissue, Goldstein et al. (p. 568) find that a different cell type, basal cells, can give rise in mice to prostate tumors that closely resemble human prostate tumors. Thus, the cellular origin of prostate cancer may be more complex than anticipated.

  13. Astrocytes, ATP, Brainstem, and Breathing

    Astrocytes (or glial cells), previously assumed to be passive players in brain physiology, may play a functional role in a number of complex behaviors. The central chemosensory control of breathing involves highly specialized neuronal populations in the brainstem, but what about astrocytes? Gourine et al. (p. 571, published online 15 July) now present evidence that glial cells may help to control breathing. A number of techniques were used to reveal glial calcium rises in vitro that elicit a depolarization of neurons in the primary locus for central respiratory chemosensitivity. The depolarization in these neurons is evoked by vesicular release of ATP in neighboring astrocytes in response to the fall in extracellular pH. Thus, brainstem astrocytes have the ability to sense changes in blood and brain CO2, and pH directly, and may control the activity of the respiratory neuronal networks to regulate breathing.

  14. From Superfluid to Mott Insulator

    One of the most attractive characteristics of cold atomic gases in optical lattices is their ability to simulate condensed-matter systems. The results of these quantum simulations are usually averaged over the atomic ensemble, or course-grained over several lattice sites. Now, Bakr et al. (p. 547, published online 17 June; see the Perspective by DeMarco) provide a single lattice site view onto the transition of a Bose gas of Rb-87 from the superfluid to the Mott-insulating state. Characteristic concentric shells of uniform number density were observed deep in the Mott insulator regime, and probing the local quantum dynamics revealed unexpectedly short time scales. The low-defect Mott structures identified may provide a starting point for quantum magnetism experiments.