This Week in Science

Science  12 Dec 2014:
Vol. 346, Issue 6215, pp. 1338
  1. Pollinator Declines

    “Green” revolution not so great for pollinators

    1. Sacha Vignieri

    Bees pollinate lavender and other flowering plants

    CREDIT: SAGE_SOLAR/FLICKR

    It is increasingly recognized that many pollinator populations are declining. Ollerton et al. looked at British historical distribution records for bees and flower-visiting wasps across the past century. Though it is well known that agricultural intensification after World War II had a negative impact on many species, pollinator declines began in the decades preceding this time, when other changes were made to agricultural practices and policies.

    Science, this issue p. 1360

  2. Ultrafast Dynamics

    Watching electrons dart through silicon

    1. Jake Yeston

    The ultimate speed limit in electronic circuitry is set by the motion of the electrons themselves. Schultze et al. applied attosecond spectroscopy to glimpse this motion in a sample of silicon, the semiconducting building block of modern integrated circuits (see the Perspective by Spielmann). The technique distinguished the electron dynamics—which proceed faster than a quadrillionth of a second after laser excitation—from the comparatively slower lattice motion of the silicon atomic nuclei.

    Science, this issue p. 1348; see also p. 1293

  3. Separation Membranes

    Metal-organic framework material membranes

    1. Marc S. Lavine

    There continues to be a lot of interest in developing membranes for gas separations that go beyond the current polymer membranes used commercially for this purpose. Peng et al. took a porous metal-organic framework material with a layered structure and exfoliated it to give nanometer-thick molecular sieves. The membranes were exceptionally good at separating hydrogen gas from carbon dioxide both in terms of permeance and selectivity.

    Science, this issue p. 1356

  4. HIV Antibodies

    A fierce competition to attack HIV

    1. Kristen L. Mueller

    The Holy Grail in the HIV field is a protective vaccine. However, because HIV mutates rapidly, it can escape from vaccine-elicited antibodies. Nevertheless, some HIV-positive individuals harbor antibodies that HIV cannot escape from very easily, so-called broadly neutralizing antibodies (bNAbs). McGuire et al. asked why these bNAbs don't win out over their more narrow brethren (nNAbs) early after infection (see the Perspective by Ofek and Diskin). They compared the responses of B cells carrying germline versions of nNAbs and bNAbs—that is, versions of these Abs that HIV would initially encounter—to HIV's envelope glycoprotein (Env). The nNAbs could recognize Env from a more diverse array of viruses compared to bNAbs, which puts them at a competitive advantage.

    Science, this issue p. 1380; see also p. 1290

  5. Nutritional Immunity

    The frontline of host-pathogen coevolution

    1. Caroline Ash

    Pathogens have to subvert a host's innate defenses to avoid being killed. Barber and Elde now show that this principle extends to nutrient-transporting proteins, such as transferrin, which binds iron (see the Perspective by Armitage and Drakesmith). Without iron, invading pathogens cannot replicate, but iron is sequestered in transferrin, which stops pathogens using it. So pathogens have evolved a succession of transporters that can hijack transferrin's iron. Over time, the primate transferrin binding surface has coevolved to wrestle iron back from the grip of pathogens.

    Science, this issue p. 1362; see also p. 1299

  6. Political Science

    Dialogue opens the door to attitude change

    1. Gilbert Chin

    Personal contact between in-group and out-group individuals of equivalent status can reduce perceived differences and thus improve intergroup relations. LaCour and Green demonstrate that simply a 20-minute conversation with a gay canvasser produced a large and sustained shift in attitudes toward same-sex marriage for Los Angeles County residents. Surveys showed persistent change up to 9 months after the initial conversation. Indeed, the magnitude of the shift for the person who answered the door was as large as the difference between attitudes in Georgia and Massachusetts.

    Science, this issue p. 1366

  7. Nanolithography

    Laser shock imprinting for patterning metals

    1. Marc S. Lavine

    Silver fishnet structure from laser shock imprinting

    CREDIT: GAO ET AL.

    High-fidelity, small-scale patterning is often a tradeoff between full-pattern methods that may have limited resolution or flexiblity, and serial methods that can create high-resolution patterns but only by slow processes. Furthermore, metals have limited formability at very small scales. Gao et al. developed a method to create very smooth threedimensional crystalline metallic nanoscale structures using a laser to create shockwave impulses. The shockwave creates ultrahigh-strain-rate deformations that overcome the metal's normal strength and, thus, resistance to patterning.

    Science, this issue p. 1352

  8. Oncogene Regulation

    A super-enhancer in leukemia development

    1. Paula A. Kiberstis

    Human cancer genome projects have provided a wealth of information about mutations that reside within the coding regions of genes and drive tumor growth by functionally altering protein products. However, this mutational portrait of cancer is incomplete: A growing number of mutations are being found within gene regulatory regions. Mansour et al. present an intriguing example of this in a study of a childhood cancer, T-cell acute lymphoblastic leukemia (see the Perspective by Vähärautio and Taipale). An oncogene known to drive the growth of this cancer is expressed at high levels in the leukemic cells because the cells harbor mutations that create a powerful superenhancer (a DNA sequence that activates transcription) upstream of the oncogene.

    Science, this issue p. 1373; see also p. 1291

  9. Systems Biology

    Dynamic signals enhance information transfer

    1. L. Bryan Ray

    Cells need to process information about their external environment reliably to survive. However, variation, or noise, in biochemical reactions, or in the states of individual cells, make it hard for a cell to detect concentration, rather than just the presence or absence of an activating ligand. Selimkhanov et al. show that cellular signaling circuits get around this problem by continually monitoring signals over time. Such dynamic responses in cultured human cells more effectively distinguish signals from noise and thus avoid loss of information transmitted to the cell from external signals.

    Science, this issue p. 1370

  10. Avian Evolution

    Bird evolution: How birds took to the air

    1. Valda Vignieri

    Research on the origin and evolution of birds has gathered pace in recent years, aided by a continuous stream of new fossil finds as well as molecular phylogenies. Bird origins, in particular, are now better understood than those of mammals, for which the early fossil record is relatively poor compared with that of birds. Xu et al. review progress in tracing the origins of birds from theropod dinosaurs, focusing especially on recent fossil finds of feathered dinosaurs of northeastern China. They integrate current research on developmental biology and functional anatomy with the paleontological record, to show how key features of birds—feathers, wings, and flight—originated and evolved, and radiated from their dinosaur forebears.

    Science, this issue 10.1126/science.1253293

  11. Solid-State Theory

    Predicting an exotic state of matter

    1. Jelena Stajic

    Much like graphene, twodimensional flakes of transition metal dichalcogenides have appealing electronic properties. Qian et al. now find that certain structures of these materials may also exhibit the so-called spin Hall effect. The spin Hall effect represents an exotic state of matter in which a 2D material conducts electricity along its edge in a way that drastically reduces dissipation. To show this, the researchers used first-principle calculations and found that the materials also feature a large band gap, which reduces undesirable conduction through the bulk. Their proposed device could be switched on and off quickly using an electric field.

    Science, this issue p. 1344

  12. Planetary Science

    Chemistry and physics of extraterrestrial life

    1. Julia Fahrenkamp-Uppenbrink

    Is there life on other planets? To answer this question, scientists must first determine what makes a planet habitable. Mars provides a natural laboratory to explore this question. In a Perspective, Conrad explains that, starting with the Viking landers in 1976, numerous missions to Mars have attempted to determine whether the planet could support life—or was able to do so in the past. Mobile rovers have explored the surface, aided by orbiters and, most recently, have been equipped with the tools to dig below the surface. By interrogating the chemical and physical conditions both now and in the past, these missions may soon be able to provide a more definitive answer.

    Science, this issue p. 1288

  13. Rock Mechanics

    Nanofibers involved in fault rupture

    1. Brent Grocholski

    Changing fault properties during rupture dictates the size and extent of an earthquake. Faulting leads to well-known microstructures that may play a role in how natural faults slip during rupture. Verberne et al. investigated tiny, nanogranular fibers found in microstructures generated on simulated carbonate faults. A microphysical model was able to account for how the small and aligned fiber produced runaway fault slip, similar to that seen in natural faults. These small structures play a role in carbonate faulting and similar microstructures could control fault rupture in other types of rocks.

    Science, this issue p. 1342

  14. Ophthalmology

    All eyes on human limbal stem cells

    1. Megan Frisk

    Our corneas—the transparent structures that allow us to see—are easily damaged by trauma and infection, which can cause scarring or blindness. Although corneas can be transplanted, transplants are limited by immune responses and by a shortage of cornea donors. Basu et al. devised a cell-based approach to prevent corneal scarring. They obtained stem cells from the human limbus (the region between cornea and sclera), which could be differentiated into keratocytes (corneal cells). The stem cells actively regenerated new corneal tissue when encased in a fibrin gel and applied to the wounded surface of the eye in mice. Such cells could potentially be obtained directly from a patient to treat scarring and prevent blindness.

    Sci. Transl. Med. 6, 266ra172 (2014).

  15. Electron Microscopy

    A golden era for electron microscopy

    1. Valda Vinson

    Electron microscopy (EM) is an attractive method for determining structures of protein complexes that are difficult to crystallize. Exciting recent developments in electron detectors allow EM structure determination to near atomic resolution. A key impediment to further improvement is that single specimens move during irradiation. Russo and Passmore designed a gold support that moves much less during irradiation than the current support and as a result prevents movement of the protein sample. Using the support they determined the structure of apo-ferritin which, as a spherical shell of α-helices, is particularly challenging to solve by EM.

    Science, this issue p. 1377

  16. Cancer

    A receptor tyrosine kinase signals to YAP

    1. Leslie K. Ferrarelli

    The Hippo pathway limits cell proliferation by inhibiting the activity of the transcriptional coactivator YAP. In contrast, cell proliferation is stimulated by the binding of growth factors to tyrosine receptor kinases, such as the binding of neuregulin to ERBB4. Neuregulin binding also triggers the cleavage of ERBB4. Haskins et al. found that a fragment containing the intracellular domain of ERBB4 interacted with and activated YAP (see the Perspective by Sudol). Breast cancer cell migration induced by neuregulin was blocked by knocking down YAP. Thus, ERBB4 could promote tumor aggressiveness both through receptor tyrosine kinase signaling and by stimulating YAP.

    Sci. Signal. 7, ra116 and pe29 (2014).