This Week in Science

Science  03 May 2013:
Vol. 340, Issue 6132, pp. 523
  1. Lord of the Robotic Flies


    While small-scale flying objects are ubiquitous in nature, they are quite hard to engineer. As sizes get smaller, fixed-winged flight becomes less efficient because of increased drag resistance. Ma et al. (p. 603) developed a tethered robotic fly with wings that flap through the use of piezo-electric materials. Control of the flight motion involved a feedback process, which allowed the tethered robotic fly to hover and make controlled flight maneuvers.

  2. Magnetic Frustration

    The study of magnetic frustration has a long history in solid-state physics, but cold-atom systems now offer the possibility of simulating the problem with exquisite control. Islam et al. (p. 583) study a system of 16 trapped ions, using the Coulomb interactions between the ions to simulate exchange interactions present in magnetic systems. The measured spin correlations provide a window into the behavior of the system, as the effective magnetic field and the range of the interactions are tuned.

  3. Closing the Cycle

    Cyclic hydrocarbons that incorporate nitrogen in the ring are among the most heavily investigated compounds in medicinal chemistry. Hennessy and Betley (p. 591) demonstrate an iron catalyst that forms a range of such cyclic compounds by inducing linear alkyl azides to curl back on themselves, inserting the nitrogen at one end into a carbon-hydrogen bond further down the chain. The reaction furthers a trend of C-H bond activation chemistry that forms elaborate products from relatively simple precursors, without the need to install activating groups at unreactive sites.

  4. Seeing Below the Surface

    Marte Vallis represents the largest of the young outflow channels on Mars. Thought to be the result of an ancient megaflood that occurred during a period that is otherwise known to be cold and dry, this channel system extends more than approximately 1000 kilometers in length and 100 kilometers in width. The channels' depths are unknown, however, because they have been covered by lava flows. By using the SHARAD radar sounder on the Mars Reconnaissance Orbiter, Morgan et al. (p. 607, published online 7 March) produced a three-dimensional reconstruction of the subsurface channels. The channels are twice as deep as previously thought and the floodwaters came from the Cerberus Fossae extensional fracture system.

  5. Dissecting Serotonin Receptors


    Serotonin receptors are the targets for many widely used drugs prescribed to treat ailments from depression to obesity and migraine headaches (see the Perspective by Palczewski and Kiser). C. Wang et al. (p. 610, published online 21 March) and Wacker et al. (p. 615, published online 21 March) describe crystal structures of two members of the serotonin family of receptors bound to antimigraine medications or to a precursor of the hallucinogenic drug LSD. Subtle differences in the way particular ligands bind to the receptors cause substantial differences in the signals generated by the receptor and the consequent biological responses. The structures reveal how the same ligand can activate one or both of the two main serotonin receptor signaling mechanisms, depending on which particular receptor it binds.

  6. IDHology

    Among the most exciting drug targets to emerge from cancer genome sequencing projects are two related metabolic enzymes, isocitrate dehydrogenases 1 and 2 (IDH1, IDH2). Mutations in the IDH1 and IDH2 genes are common in certain types of human cancer. Whether inhibition of mutant IDH activity might offer therapeutic benefits is unclear (see the Perspective by Kim and DeBerardinis). F. Wang et al. (p. 622, published online 4 April) isolated a small molecule that selectively inhibits mutant IDH2, describe the structural details of its binding to the mutant enzyme, and show that this compound suppresses the growth of patient-derived leukemia cells harboring the IDH2 mutation. Rohle et al. (p. 626, published online 4 April) show that a small molecule inhibitor of IDH1 selectively slows the growth of patient-derived brain tumor cells with the IDH1 mutation.

  7. Dynamic Protection

    During an immune response, CD8+ T cells are recruited to provide protection. Most cells differentiate into short-lived effectors that help to clear the pathogen, whereas others form long-lived memory cells to protect against reinfection. Gerlach et al. (p. 635, published online 14 March) and Buchholz et al. (p. 630, published online 14 March) used in vivo fate mapping of mouse T cells with a defined specificity during a bacterial infection to show that the dynamics of the single-cell response are not uniform. The response of a particular T cell population is the average of a small number of clones that expand greatly (“large clones”) and many clones that only proliferate at low amounts (“small clones”). The memory pool arises largely from small clones whereas effectors are primarily made up of large clones.

  8. Reading Dreams

    How specific visual dream contents are represented by brain activity is unclear. Machine-learning–based analyses can decode the stimulus- and task-induced brain activity patterns that represent specific visual contents. Horikawa et al. (p. 639, published online 4 April) examined patterns of brain activity during dreaming and compared these to waking responses to visual stimuli. The findings suggest that the visual content of dreams is represented by the same neural substrate as observed during awake perception.

  9. Two Small Habitable Planets

    NASA's Kepler space telescope was launched in 2009 with the goal of detecting planets the size of Earth in the habitable zone of Sun-like stars and determining the frequency of these planets. Using data from Kepler, Borucki et al. (p. 587, published online 18 April) report the detection of a five-planet system where all the planets are smaller than twice the size of Earth and where the two outermost planets orbit in the habitable zone of their star, defined as the region where a rocky planet can host liquid water on its solid surface. The star, Kepler-62, is smaller and cooler than the Sun.

  10. Biological Transistor

    A transistor is a device that amplifies and switches electronic signals. Bonnet et al. (p. 599, published online 28 March; see the Perspective by Benenson) engineered a genetic circuit to behave like a transistor in individual living cells. Instead of regulating messenger RNA levels, which has been used previously in designing such systems, the approach relied on changing the state of double-stranded DNA. Six basic logic gates were designed and constructed that were based on the activity of two serine recombinases.

  11. From Coils to Cages


    Self-assembly strategies that mimic protein assembly, such as the formation of viral coats, often begin with simpler peptide assemblies. Fletcher et al. (p. 595, published online 11 April; see the Perspective by Ardejani and Orner) designed two coiled-coil peptide motifs, a heterodimer, and a homotrimer. Both peptides contained cysteine residues and could link through disulfide bonds, so that the trimer could form the vertices of a hexagonal network and the dimer its edges. However, these components are flexible and, rather than form extended sheets, they closed to form particles ∼100 nanometers in diameter.

  12. Making Antisense of Flowering

    The recent discovery of biological roles for long noncoding RNAs raises important questions as to how they are themselves regulated. Sun et al. (p. 619) adopted a genetic approach to identify regulators of COOLAIR—a set of antisense transcripts from the locus encoding the major Arabidopsis floral repressor, FLC. Analysis of a mutant misregulating COOLAIR revealed a homeodomain protein that repressed COOLAIR expression via an R-loop covering the COOLAIR promoter. Thus, R-loop stabilization is an integral part of COOLAIR regulation, FLC expression, and flowering time.