This Week in Science

Science  20 Jun 2014:
Vol. 344, Issue 6190, pp. 1354
  1. Low-Density Materials

    Microlattices make marvelous materials

    1. Marc S. Lavine

    Macro scale octet lattice structure.

    PHOTO: RYAN CHEN/LAWRENCE LIVERMORE NATIONAL LABORATORY

    Framework or lattice structures can be remarkably strong despite their very low density. Using a very precise technique known as projection microstereolithography, Zheng et al. fabricated octet microlattices from polymers, metals, and ceramics. The design of the lattices meant that the individual struts making up the materials did not bend under pressure. The materials were therefore exceptionally stiff, strong, and lightweight.

    Science, this issue p. 1373

  2. Human Evolution

    Neandertal ancestors from Pleistocene Spain

    1. Andrew M. Sugden

    The Sima de los Huesos site in Atapuerca, northern Spain, is a rich source of fossil hominin specimens. The site has now yielded further skull specimens that illuminate patterns of human evolution in Europe nearly half a million years ago. Arsuaga et al. studied 17 crania, including 7 that are new specimens and 6 that are more complete than before (see the Perspective by Hublin). This assemblage of specimens reveals the cranial, facial, and dental features of the Atapuerca hominins, which allows more precise evolutionary positioning of these Neandertal ancestors.

    Science, this issue p. 1358; see also p. 1338

  3. Ecological Genomics

    Crows of a feather flock together

    1. Laura M. Zahn

    Closely related species with overlapping ranges typically evolve genetic barriers to prevent crossbreeding. Poelstra et al. sequenced genes from two species of central European crows: gray-bodied hooded crows and black carrion crows (see the Perspective by de Knijff). Although most of the genomes shared genes between the two species, one region that affected coat color and color vision differed. The authors suggest that black and gray-coated crows prefer to mate with birds like themselves.

    Science, this issue p. 1410; see also p. 1345

  4. HIV Latency

    Noisy genes flush HIV out of hiding

    1. L. Bryan Ray

    HIV can hide in the body, making it hard to kill with drugs. Increasing variation or “noise” in the virus's gene expression turns out to be an effective strategy for reactivating latent HIV. Once reawakened, the virus is more sensitive to antiviral drugs. Dar et al. screened for agents that increased variation in the expression of HIV genes. In a model system with HIV-infected human cells, the noise enhancers worked with existing compounds used to reactivate latent HIV and helped eradicate the virus.

    Science, this issue p. 1392

  5. Quantum Mechanics

    Creating and erasing quantum knowledge

    1. Jelena Stajic

    Particles in the quantum world can also assume wavelike properties. Researchers often use photons to illustrate this particle/wave duality, but electrons interact with each other, which might make them a better choice. Weisz et al. used electrons to create a “quantum eraser” (see the Perspective by Feldman). By taking advantage of the electrons' interaction, the researchers first acquired information about the electrons' path—a process that destroys their wavelike properties. Next, they deliberately erased this information in order to recover the electrons' wave nature.

    Science, this issue p. 1363; see also p. 1344

  6. Nanophotonics

    A controlled launch for plasmons

    1. Ian S. Osborne

    To create nanophotonic devices, engineers must combine large-scale optics with tiny nanoelectronics. Plasmons, the collective light-induced excitations of electrons at a metal's surface, can bridge that difference in size scales. Alonso-Gonzalez et al. placed structured gold “antennas” on top of a graphene layer to launch and propagate plasmonic excitations into the graphene. By carefully designing the antennas, the researchers could engineer the wavefronts of the plasmons and control the direction of propagation. This approach illustrates a versatile approach for the development of nanophotonics.

    Science, this issue p. 1369

  7. Toxin Mechanism

    Breaking through the epithelial barrier

    1. Valda Vinson

    Botulinum neurotoxin (BoNT) poisons its host when it crosses the intestinal epithelial barrier. To help it cross this barrier, the toxin forms a large complex with three bacterial proteins called hemagglutinins (HAs). To find out what happens when this complex binds to a cell-adhesion protein called E-cadherin, Lee et al. crystallized the bound complex and protein. Toxin binding disrupted the way E-cadherin maintains the epithelial barrier. When the researchers prevented the toxin complex from binding to E-cadherin, mice were protected from the toxin's deadly effects.

    Science, this issue p. 1405

  8. Cell Biology

    Cell proliferation in hard environments

    1. Wei Wong

    Cross-section of a mouse femoral artery undergoing repair.

    PHOTO: BAE ET AL.

    The extracellular matrix that surrounds cells in tissues and organs can be harder or softer. In damaged blood vessels, the extracellular matrix becomes stiffer around the site of damage. Smooth muscle cells that surround blood vessels then proliferate to repair the damage. Bae et al. found that stiff surfaces stimulated cell proliferation through a signaling pathway that included the enzyme Rac. Mice that lacked Rac in their smooth muscle cells were unable to repair damaged blood vessels efficiently.

    Sci. Signal. 7, ra57 (2014).

  9. Multiple Sclerosis

    A surprising culprit attacks the brain

    1. Angela Colmone

    The brain deterioration in mice with a multiple sclerosis (MS)–like disease is exacerbated by a signaling molecule called interleukin-17 (IL-17), raising hopes that MS patients could be treated with drugs that target this cytokine. In an unexpected twist, however, Noster et al. find that in humans the culprit is a different cytokine, GM-CSF, a small molecule that promotes inflammation in many autoimmune diseases. What's more, in human patients IL-17 blocked GM-CSF production, a striking contrast to its effect in mice. These data suggest a new rationale for a therapeutic approach in MS patients: decreasing GM-CSF.

    Sci. Transl. Med. 6, 241ra80 (2014).

  10. Nanomaterials

    Nanoparticle lattices and surfaces

    1. Phil Szuromi

    The challenge of resolving the details of the surfaces or assemblies of colloidal semiconductor nanoparticles can be overcome if several characterization methods are used (see the Perspective by Boles and Talapin). Boneschanscher et al. examined honeycomb superlattices of lead selenide nanocrystals formed by the bonding of crystal faces using several methods, including high-resolution electron microscopy and tomography. The structure had octahedral symmetry with the nanocrystals distorted through “necking”: the expansion of the contact points between the nanocrystals. Zherebetskyy et al. used a combination of theoretical calculations and spectroscopic methods to study the surface layer of lead sulfide nanocrystals synthesized in water. In addition to the oleic acid groups that capped the nanocrystals, hydroxyl groups were present as well.

    Science, this issue p. 1377, p. 1380; see also p. 1340

  11. Social Cognition

    Learning to read minds starts early

    1. Gilbert Chin

    No parent needs reminding that children are born with a surprising set of abilities. But children still need many hours of guidance and instruction. Heyes and Frith review one particular social cognitive skill: reading the minds of others (or at least working out what other people are thinking and feeling). An unrefined capacity for “mind reading” is present in infants, but teaching is necessary to develop the full-blown capacity seen in adults. The authors draw parallels between learning to read and learning to read minds.

    Science, this issue p. 10.1126/science.1243091

  12. Nanomagnetism

    Observing jumping domain walls

    1. Jelena Stajic

    Domain walls, which separate regions of opposite magnetization in a ferromagnet, have rich dynamics that are difficult to characterize in small samples. Tetienne et al. imaged the magnetization of a thin ferromagnetic wire and observed the jumping of a domain wall between different positions along the wire. They used a scanning magnetic microscope based on a defect in diamond. The laser light needed to operate the microscope also enabled the control of the domain wall motion by causing local heating, which made the illuminated position more likely to contain a domain wall.

    Science, this issue p. 1366

  13. Aging Cell Biology

    Yeast metacaspase: Grim Reaper or savior?

    1. Stella M. Hurtley

    Yeast metacaspases are structural and possibly functional homologs of caspases that execute apoptosis—programmed cell death—in higher organisms. Malmgren Hill et al. tested whether yeast metacaspase Mca1 acts as an executioner or beneficial protein during replicative aging of yeast (see the Perspective by Kampinga). Boosting metacaspase levels caused a substantial and robust extension of life span. This lifespan extension was only partly dependent on the caspase activity of Mca1 but required the presence of the protein disaggregase Hsp104. Consistent with a role in proteostasis, Mca1 was recruited to chaperone-enriched aggregates during aging. Mca1 increased aggregate asymmetry during yeast cytokinesis and counteracted the age-associated accumulation of inclusions.

    Science, this issue p. 1389; see also p. 1341

  14. Cancer Genomics

    Cancer at single-cell resolution

    1. Laura M. Zahn

    Single-cell sequencing can illuminate the genetic properties of brain cancers and reveal heterogeneity within a tumor. Patel et al. examined the genome sequence of single cells isolated from brain glioblastomas. The findings revealed shared chromosomal changes but also extensive transcription variation, including genes related to signaling, which represent potential therapeutic targets. The authors suggest that the variation in tumor cells reflects neural development and that such variation among cancer cells may prove to have clinical significance.

    Science, this issue p. 1396

  15. HIV Pathogenesis

    Adapting HIV-1 to infect monkeys, too

    1. Kristen L. Mueller

    HIV-1 replicates well in humans but not in monkeys or mice. On the up side, this reduces the risk of cross-species transmissions, but it makes the study of HIV-1 and AIDS more difficult. Hatziioannou et al. overcame this hurdle by serially passaging HIV-1 in pigtailed macaques. Over time, the HIV-1 acquired mutations that allowed it to adapt to the monkeys. Depleting CD8+ T cells during acute infection resulted in a subset of animals developing an AIDS-like disease by the fourth passage. HIV-1 envelope protein gene selection and the acquisition of mutations in the HIV protein Vpu, which allowed HIV-1 to overcome host restriction by the macaque protein tetherin, accompanied the viral adaptation to the monkeys.

    Science, this issue p. 1401

  16. Computational Biology

    Cell fate control—a numbers game

    1. L. Bryan Ray

    Precursor cells in adult mammalian tissues differentiate at very low rates; for example, only 10% of fat cells are replaced per year. If all precursor cells responded to the same threshold of stimulus, these low rates would not be possible. Noise in the system (variability in the abundance of key proteins in different cells) could allow only a few cells to differentiate, but then such variability would allow dedifferentiation as well, which is not observed. Ahrends et al. used computational modeling and protein measurements in single cells to show that multiple feedback loops in the regulatory circuits, along with noise, can allow both stable and infrequent differentiation.

    Science, this issue p. 1384