This Week in Science

Science  04 Mar 2016:
Vol. 351, Issue 6277, pp. 1038
  1. Electron Transport

    Electrons that flow like a fluid

    1. Jelena Stajic

    Artistic rendering of Dirac fluid experimentally observed in graphene

    CREDIT: SECOND BAY STUDIOS

    Electrons inside a conductor are often described as flowing in response to an electric field. This flow rarely resembles anything like the familiar flow of water through a pipe, but three groups describe counterexamples (see the Perspective by Zaanen). Moll et al. found that the viscosity of the electron fluid in thin wires of PdCoO2 had a major effect on the flow, much like what happens in regular fluids. Bandurin et al. found evidence in graphene of electron whirlpools similar to those formed by viscous fluid flowing through a small opening. Finally, Crossno et al. observed a huge increase of thermal transport in graphene, a signature of so-called Dirac fluids.

    Science, this issue p. 1061, 1055, 1058; see also p. 1026

  2. Superconductivity

    Resolving the thermoelectric paradox

    1. Zakya H. Kafafi

    The existence of thermoelectric effects in superconductors has posed a particularly difficult challenge for physicists. Not only have experiments and theory been in paradoxical discrepancy by orders of magnitude, but they often are in full disagreement with one another. Shelly et al. resolved this stalemate and developed an experimental method using highly sensitive quantum nanoscale interferometers. A theory that identifies these thermoelectric effects in superconductors supports the experimental measurements. This work may help lead to practical applications of superconductors.

    Sci. Adv. 2, 10.1126.sciadv.01250 (2016)

  3. Ebola Virus

    Profiling the antibody response to Ebola

    1. Kristen L. Mueller

    The recent Ebola virus outbreak in West Africa illustrates the need not only for a vaccine but for potential therapies, too. One promising therapy is monoclonal antibodies that target Ebola's membrane-anchored glycoprotein (GP). Bornholdt et al. isolated and characterized 349 antibodies from a survivor of the 2014 outbreak. A large fraction showed some neutralizing activity and several were quite potent. Structural analysis revealed an important site of vulnerability on the membrane stalk region of GP. Antibodies targeting this area were therapeutically effective in Ebola virus–infected mice.

    Science, this issue p. 1078

  4. Immunology

    Diversity reigns in antibody responses

    1. Kristen L. Mueller

    Multiple B cell clones can make up a single germinal center

    CREDIT: TAS ET AL.

    During the course of an immune response, B cells specific for an invading pathogen divide. The antibodies they produce increase in affinity via somatic mutation in specialized lymph node structures called germinal centers. Tas et al. used multiphoton microscopy and sequencing to determine how different B cell clones compete with one another within mouse germinal centers. Multiple B cell clones can seed individual germinal centers, and germinal centers lose diversity at disparate rates. Such heterogeneity suggests that manipulating minor clonal populations to gain an advantage during vaccination may one day be possible.

    Science, this issue p. 1048

  5. Gene Expression

    Doubling DNA but not expression

    1. Guy Riddihough

    As the genome replicates, and before the cell divides, the copy number of the replicated portions of the genome doubles. In bacteria and archaea, gene expression tracks with gene dosage, both of which increase after DNA replication. Voichek et al., however, show that an increase in DNA dosage after replication does not increase gene expression in budding yeast. This expression buffering is mediated by the acetylation of newly synthesized histone H3 deposited on the replicated DNA. This acetylation helps suppress transcription from the excess DNA.

    Science, this issue p. 1087

  6. Cell Biology

    Separating dividing cells into two

    1. Wei Wong

    By activating genes involved in cell growth and proliferation, the transcriptional coactivator YAP can act as a tumor promoter. Bui et al. uncovered a nontranscriptional role for YAP in separating dividing cells, a process called cytokinesis. In mitotic cells, YAP was localized to subcellular structures that mediate cytokinesis, which ensured the proper localization of other proteins necessary for cytokinesis. Cells deficient in YAP were more likely to have an abnormal number of chromosomes, a condition that can give rise to tumors.

    Sci. Signal. 9, ra23 (2016).

  7. Catalysis

    Small olefins from syngas

    1. Phil Szuromi

    The conversion of coal or natural gas to liquid fuels or chemicals often proceeds through the production of CO and H2. This mixture, known as syngas, is then converted to hydrocarbons with Fischer-Tropsch catalysts. For the light olefins (ethylene to butylenes) needed for chemical and polymer synthesis, conventional catalysts are mechanistically limited to <60% conversion and deactivate through carbon buildup. Jiao et al. developed a bifunctional catalyst that achieves higher conversions and avoids deactivation (see the Perspective by de Jong). A zinc-chromium oxide creates ketene intermediates that are then coupled over a zeolite.

    Science, this issue p. 1065, see also p. 1030

  8. Human Altruism

    Brain activity shows underlying motives

    1. Peter Stern

    In humans, two completely different motives may nevertheless lead to exactly the same behavior. Because we can't directly observe motives, modern economists often completely disregard them. However, Hein et al., using fMRI, show that different human motives can yield observable responses in the brain (see the Perspective by Gluth and Fontanesi). In empathy-based and reciprocity-based altruistic behavior, the direction and the strength of functional connectivity between specific brain regions were different for each motive. Moreover, the connectivity patterns were independent of the behavioral implications of the motives.

    Science, this issue p. 1074; see also p. 1028

  9. Flexible Electronics

    Make it stretch, make it glow

    1. Marc S. Lavine

    The skins of some cephalopods, such as the octopus, are highly flexible and contain color-changing cells. These cells are loaded with pigments that enable rapid and detailed camouflaging abilities. Larson et al. developed a stretchable electroluminescent actuator. The material could be highly stretched, could emit light, and could also sense internal and external pressure. A soft robot demonstrated these combined capabilities by stretching and emitting light as it moved.

    Science, this issue p. 1071

  10. Structural Biology

    A more complete look at the HIV-1 envelope

    1. Kristen L. Mueller

    HIV-1 uses its envelope protein (Env), a large glycoprotein present on the viral surface, to enter target cells. Env forms trimers on the viral surface. Structural studies of solubilized Env trimers have provided important insights into viral entry and antibody binding, but soluble trimers lack several important insoluble regions of the native protein. Lee et al. used cryo–electron microscopy to solve the structure of a trimeric Env protein of HIV-1, missing only its cytoplasmic tail, in complex with broadly neutralizing antibodies. A more complete understanding of Env's structure may aid in vaccine design efforts.

    Science, this issue p. 1043

  11. Immunogenomics

    Regulatory use of endogenous retroviruses

    1. Laura M. Zahn

    Mammalian genomes contain many endogenous retroviruses (ERVs), which have a range of evolutionary ages. The propagation and maintenance of these genetic elements have been attributed to their ability to contribute to gene regulation. Chuong et al. demonstrate that some ERV families are enriched in regulatory elements, so that they act as independently evolved enhancers for immune genes in both humans and mice (see the Perspective by Lynch). The analysis revealed a primate-specific element that orchestrates the transcriptional response to interferons. Selection can therefore act on selfish genetic elements to generate novel gene networks.

    Science, this issue p. 1083 see also p. 1029

  12. Fibrosis

    SRC shows it stripes

    1. Angela Colmone

    The nonreceptor tyrosine kinase SRC is a proto-oncogene that has been associated with cancer progression. Turro et al. found a gain-of-function mutation in SRC in nine patients with myelofibrosis, bleeding, and bone disorders. This mutation prevented SRC from inhibiting itself. The overactive enzyme also enhanced tyrosine phosphorylation in a zebrafish model and in patient-derived cells. In patients with myelofibrosis, this SRC mutation was associated with increased outgrowth of myeloid and megakaryocytic colonies and abnormal platelet production, which could be rescued by SRC kinase inhibition. These findings provide a possible explanation for the severe bleeding seen in cancer patients treated with inhibitors of Src family kinases.

    Sci. Transl. Med. 8, 328ra30 (2016).

  13. Neural Computation

    Credit assignment in the brain

    1. Peter Stern

    To discover relevant clues for survival, an organism must bridge the gap between the short time periods when a clue occurs and the potentially long waiting times after which feedback arrives. This so-called temporal credit-assignment problem is also a major challenge in machine learning. Gütig developed a representation of the responses of spiking neurons, whose derivative defines the direction along which a neuron's response changes most rapidly. By using a learning rule that follows this development, the temporal credit-assignment problem can be solved by training a neuron to match its number of output spikes to the number of clues. The same learning rule endows unsupervised neural networks with powerful learning capabilities.

    Science, this issue p. 10.1126/science.aab4113

  14. DNA Repair

    To have or have not determines DNA repair

    1. L. Bryan Ray

    Cells presumably try to protect DNA from damage at all costs. But Uphoff et al. show that they do not, because the cost is too high. Single-molecule and single-cell measurements show that the DNA repair enzyme Ada, which also regulates its own expression, was present in such low amounts in E. coli that stochastic variation led to some cells having none of the protein at all. Such cells undergo increased mutagenesis, which could be beneficial in circumstances in which increased genetic heterogeneity is required for adaptation. The expression of large amounts of such a DNA-altering protein was also toxic.

    Science, this issue p. 1094

  15. Transcription

    Choosing where to start transcription

    1. Guy Riddihough

    The RNA polymerase enzyme complex binds to the promoter of a gene and separates the two DNA strands. The subsequently formed “transcription bubble” is required for RNA synthesis to begin. How RNA polymerase chooses the exact DNA base at which it will start transcription has been unclear. Winkelman et al. show that a control element upstream of the start site is involved in helping RNA polymerase make this choice in bacteria. Start site selection involves promoter scrunching, where a stationary RNA polymerase unwinds and pulls DNA through the active site, scrunching the DNA of the transcription bubble.

    Science, this issue p. 1090

  16. Quantum Computing

    Reducing quantum overhead

    1. Ian S. Osborne

    A quantum computer is expected to outperform its classical counterpart in certain tasks. One such task is the factorization of large integers, the technology that underpins the security of bank cards and online privacy. Using a small-scale quantum computer comprising five trapped calcium ions, Monz et al. implement a scalable version of Shor's factorization algorithm. With the function of ions being recycled and the architecture scalable, the process is more efficient than previous implementations. The approach thus provides the potential for designing a powerful quantum computer, but with fewer resources.

    Science, this issue p. 1068

  17. Cancer Biology

    Have cancer stem cells MET their match?

    1. Paula A. Kiberstis

    Solid tumors have been hypothesized to contain a subset of highly aggressive cells that fuel tumor growth and metastasis. The search is on for drugs that selectively kill or diminish the malignant properties of these tumor-initiating cells (TICs; previously called “cancer stem cells”). Pattabiraman et al. hypothesized that compounds that induce TICs to undergo a phenotypic change called the mesenchymal-to-epithelial transition (MET) would therefore cause TICs to lose their tumor-initiating ability. Indeed, drugs activating the protein kinase A signaling pathway triggered an epigenetic reprogramming of TICs that resulted in the cells acquiring a more benign epithelial-like phenotype.

    Science, this issue p. 10.1126/science.aad3680