This Week in Science

Science  24 Oct 2014:
Vol. 346, Issue 6208, pp. 435
  1. Evolutionary Biology

    Making adjustments for a new neighborhood

    1. Sacha Vignieri

    Anolis carolinensis (green) moves up for Anolis sagrei (brown)

    PHOTO: © CHRIS MATTISON/ALAMY

    Competition between species drives the acquisition of diversity. Stuart et al. introduced a non-native anole lizard to natural experimental islands. In response, the original inhabitants adopted higher perches in the trees, where the larger invader was at a disadvantage. Within about 3 years—or 20 generations—the shift led to inherited morphological changes in the native lizards, including their growing larger toepads.

    Science, this issue p. 463

  2. Immunology

    Digital amplification of T cell receptor signals

    1. John F. Foley

    The kinase PKD2 is activated in T cells of the immune system when a peptide antigen binds to and stimulates the T cell receptor (TCR). Navarro et al. found that low concentrations of a peptide antigen activated PKD2 in a small proportion of T cells. In response to increased amounts of peptide antigen, a greater proportion of T cells exhibited maximal PKD2 activation. Thus, PKD2 may act as a digital amplifier of TCR signals, so that T cells mount an immune response tailored to the strength of the stimulus.

    Sci. Signal. 7, ra99 (2014).

  3. New World Archeology

    Mountain dwellers of the Pleistocene

    1. Andrew M. Sugden

    Humans colonized the inhospitable high Andes at least 11.5 thousand years ago. Rademaker et al. unearthed evidence of hunter-gatherer occupation at heights of almost 4500 m in Peru in two open-air sites. The sites contained more than 750 tools, including likely spearheads and scrapers. A nearby rockshelter with sooted ceilings and floor detritus may have been a campsite. The sites were probably used seasonally for hunting vicuña and other high-altitude prey.

    Science, this issue p. 466

    Stone artifacts from mountain camp

    PHOTO: ERICA COOPER
  4. Viral Cell Biology

    Flu mimics damaged proteins during entry

    1. Stella M. Hurtley

    Viruses are master manipulators. The early stages of how flu viruses enter cells are very well understood, but Banerjee et al. describe a new wrinkle (see the Perspective by Rajsbaum and García-Sastre). It seems that the virus carries with it into the cell ubiquitin: a molecule involved in marking proteins for destruction. The virus then exploits host cell machinery involved in recognizing and dealing with damaged proteins to uncoat its own RNA genome, ready to continue its path toward successful infection.

    Science, this issue p. 473; see also p. 427

  5. Valleytronics

    Making use of graphene's valleys

    1. Jelena Stajic

    Graphene has two distinct valleys in its electronic structure, in which the electrons have the same energy. Theorists have predicted that creating an asymmetry between the two valleys will coax graphene into exhibiting the so-called valley Hall effect (VHE). In this effect, electrons from the two valleys move across the sample in opposite directions when the experimenters run current along the sample. Gorbachev et al. achieved this asymmetry by aligning graphene with an underlying layer of hexagonalboron nitride (hBN) (see the Perspective by Lundeberg and Folk). The authors measured the transport characteristics of the sample, which were consistent with the theoretical predictions for the VHE. The method may in the future lead to information processing using graphene's valleys.

    Science, this issue p. 448; see also p. 422

  6. Solar Cells

    Layering on solar cell power and stability

    1. Jake Yeston

    Solar cells made from carbon-based polymers are helpfully flexible. However, there's been a frustrating tradeoff between cell stability and efficiency when converting solar power to electrical power. Page et al. offer a strategy to partially resolve this dilemma by inserting a layer of polar organic compound (a fullerene derivative) between the cathode (the positive pole in the circuit) and the rest of the cell. Aluminum is an efficient cathode material but is prone to oxidative degradation. The easily applied polar layer enables the use of more stable metals, such as silver and copper, for the cathode, while counteracting their tendencies to diminish power conversion efficiency.

    Science, this issue p. 441

  7. Protein Design

    Building with alphahelical coiled coils

    1. Valda Vinson

    Understanding how proteins fold into well-defined three-dimensional structures has been a longstanding challenge. Increased understanding has led to increased success at designing proteins that mimic existing protein folds. This raises the possibility of custom design of proteins with structures not seen in nature. Thomson et al. describe the design of channelcontaining α-helical barrels, and Huang et al. designed hyperstable helical bundles. Both groups used rational and computational design to make new protein structures based on α-helical coiled coils but took different routes to reach different target structures.

    Science, this issue p. 485, p. 481

  8. Cancer

    Anticancer drug coming out on TOPK

    1. Yevgeniya Nusinovich

    The TOPK protein is found in a wide range of human cancers and is believed to promote tumor growth. Matsuo et al. developed a drug that can inhibit TOPK and be delivered by multiple routes. The oral form of this drug was well tolerated by mice, which allowed convenient and effective treatment. An intravenous form was even more effective, and providing it as a liposomal formulation eliminated hematological side effects and promoted the complete regression of tumors. The inhibitor may thus be a viable anticancer agent, although human trials will be required before it can be used in the clinic.

    Sci. Transl. Med. 6, 259ra145 (2014).

  9. Metalloproteins

    How bacteria break down organohalides

    1. Nicholas S. Wigginton

    Anaerobic bacteria can break down a range of organohalide pollutants. To do so, they use unusual reductive dehalogenase enzymes that remove the halogen ion from the molecule, making the pollutants less toxic. Bommer et al. describe x-ray crystal structures of one such enzyme from Sulfurospirillum multivorans (see the Perspective by Edwards). Vitamin B12, present near the substrate binding site, catalyzes the reduction of trichloroethylene in concert with two iron-sulfur clusters. The structures provide mechanistic clues for how to engineer enzymes to recognize other pollutants.

    Science, this issue p. 455; see also p. 424

  10. Microbe Analysis

    Experimental platforms for probing bacteria

    1. Phil Szuromi

    Bacteria respond to a host of changing cues provided by their environment. Hol and Dekker review how microfluidic and nanofabricated devices can provide a platform to deliver different stimuli in a variety of environments. Bacterial quorum sensing and electron transport are among the problems that can be studied in this way.

    Science, this issue 10.1126/science.1251821

  11. Advanced Imaging

    From single molecules to embryos in living color

    1. Stella M. Hurtley

    Animation defines life, and the three-dimensional (3D) imaging of dynamic biological processes occurring within living specimens is essential to understand life. However, in vivo imaging, especially in 3D, involves inevitable tradeoffs of resolution, speed, and phototoxicity. Chen et al. describe a microscope that can address these concerns. They used a class of nondiffracting beams, known as 2D optical lattices, which spread the excitation energy across the entire field of view while simultaneously eliminating out-of-focus excitation. Lattice light sheets increase the speed of image acquisition and reduce phototoxicity, which expands the range of biological problems that can be investigated. The authors illustrate the power of their approach using 20 distinct biological systems ranging from single-molecule binding kinetics to cell migration and division, immunology, and embryonic development.

    Science, this issue 10.1126/science.1257998

  12. DNA Replication

    How to stop after copying the genome

    1. Guy Riddihough

    Replication is highly regulated: Failure to copy any part of the genome or copying parts of it more than once can cause genome instability with potentially disastrous consequences. Maric et al. and Priego Moreno et al. show that the DNA replication machinery, which stably encircles DNA during the duplication process, is actively disassembled once replication is complete (see the Perspective by Bell). The protein ring encircling the DNA is covalently modified, which allows it to be opened and the whole replication complex to be removed from DNA by a special disassembly complex.

    Science, this issue 10.1126/science.1253596, p. 477; see also p. 418

  13. Ultrafast Dynamics

    How to make vanadium dioxide metallic

    1. Jelena Stajic

    At about 70°C, the material vanadium dioxide (VO2) switches from being a semiconductor to a metal. The switch happens so fast that it may be useful in electronic devices, but it is not clear whether the switch is primarily caused by enhanced interactions between electrons or by a change in the crystal structure. Morrison et al. shone laser light on a sample of VO2, initially in a semiconducting state. They used electron diffraction to monitor the changes in the material's crystal structure and simultaneously measured its optical properties to monitor the electronic state. For certain laser powers, VO2 switched to a long-lived metallic state even though it preserved its initial crystal structure.

    Science, this issue p. 445

  14. Asymmetric Catalysis

    Ensuring handedness when breaking C-H bonds

    1. Jake Yeston

    Many organic compounds are chiral: They manifest two distinct mirror-image variants, or enantiomers. Kinetic resolution can transform one enantiomer to a desired product while leaving its mirror image unmodified. Chu et al. applied this strategy to a reaction that replaces aryl carbon–hydrogen bonds with carbon-iodine bonds. They used a chiral palladium catalyst that reacts selectively with just one of two enantiomers of various benzylamine derivatives. In medicinal chemistry, such selective synthesis of individual enantiomers is essential for screening interactions with chiral biomolecules such as proteins.

    Science, this issue p. 451

  15. Working Memory

    Identifying the workhorse of working memory

    1. Peter Stern

    Working memory allows us to keep behaviorally relevant information in mind over a short period of time. Liu et al. trained mice to remember a smell for a short period after it had been removed. Manipulating nerve cell activity in the mouse medial prefrontal cortex during this period interfered with the mice's performance when learning what they were supposed to do when they then smelled the same or a different odor. Once the animals were well trained on the task, the same manipulations did not affect performance.

    Science, this issue p. 458

  16. Plant Science

    Sex determination driven by community cooperation

    1. Pamela J. Hines

    An optimized ratio of male and females in a sexually reproducing population helps to generate the genetic diversity useful to a species in a changing world. Tanaka et al. studied a fern in which the sex ratio is adjusted not by individual identity, but by signaling between individual plants (see the Perspective by Sun). Early-maturing individual ferns express some of the biosynthetic genes needed to make a precursor of the plant hormone gibberellin, which they secrete into the environment. Younger ferns, which express the enzymes needed to finalize synthesis of gibberellin, take up the signal and in response develop the organs that produce male gametes.

    Science, this issue p. 469; see also p. 423

  17. Marine Conservation

    Addressing fishing threats to ocean wildlife

    1. Julia Fahrenkamp-Uppenbrink

    Marine ecosystems are under pressure. In a Perspective, Vincent and Harris highlight the particular problems of illegal, unregulated, and unreported fishing. In coastal areas worldwide, millions of people fish without controls or records, including many women who gather marine species from intertidal areas or shallow waters. Deep-sea habitats and species are also under threat from bottom trawlers that may legally trawl for target species but capture much other marine life incidentally. Marine protected areas, comanagement, and other policy measures can help to reduce these pressures on ocean wildlife.

    Science, this issue p. 420

  18. Evolution

    Dinosaur color vision and the evolution of feathers

    1. Julia Fahrenkamp-Uppenbrink

    The first feathers that evolved in early dinosaurs had a simple hairlike structure and probably served to insulate the body. How did these simple protofeathers evolve into the more complex feathers found in today's birds? In a Perspective, Koschowitz et al. argue that dinosaur color vision played a key role in this evolution. Dinosaur color vision, like that of birds, is likely to have been superior to that of humans. The evolution of complex feathers would have enabled color signaling; for example, during sexual selection.

    Science, this issue p. 416