This Week in Science

Science  22 Jul 2016:
Vol. 353, Issue 6297, pp. 359
  1. Mitochondria

    Eliminating paternal mitochondria

    1. Beverly A. Purnell

    Midpiece of a possum sperm cell with closely packed mitochondria (purple)

    PHOTO: DAVID M. PHILLIPS/SCIENCE SOURCE

    During fertilization, the oocyte and sperm each bring their mitochondria to the union. Shortly afterward, the paternal mitochondria are degraded, and only the maternal mitochondria are conveyed to the progeny. Zhou et al. observed that the integrity of the inner membrane of paternal mitochondria is compromised, which apparently marks them for degradation (see the Perspective by van der Bliek). Autophagy commences by mitochondrial endonuclease G relocating from the intermembrane space into the matrix and subsequently degrading the paternal mitochondrial DNA. Any delay in this process increases embryonic lethality.

    Science, this issue p. 394; see also p. 351

  2. Metallurgy

    Lightweight shapeshifting alloys

    1. Brent Grocholski

    Shape memory alloys (SMAs) spring back into shape after they are deformed, a useful property for a variety of applications. Transition metal alloys, which are robust but dense, dominate the SMA landscape. Ogawa et al. report a new type of lightweight SMA made from magnesium and scandium, which has comparable properties to known SMAs but at significantly lower density. Although this magnesium-scandium alloy is limited to low-temperature applications, development of a new lightweight class of SMAs could be on the horizon.

    Science, this issue p. 368

  3. Neurology

    Seeing synapses misfiring

    1. Megan Frisk

    Nerve junctions (or synapses) electrically transmit (or fire) information from one neuron to another. Many diseases are characterized by misfiring synapses. Finnema et al. have developed a noninvasive imaging approach that targets the synaptic vesicle glycoprotein 2A. Now human synapses can be observed firing in the living brain. In the brains of patients with epilepsy, synaptic density was found to be asymmetric, which is consistent with damage to certain regions. Thus, this imaging method permits monitoring of synaptic loss in the brains of people with various neurological and psychiatric diseases, which could contribute prognostic information.

    Positron emission tomography image of a subject with epilepsy

    PHOTO: FINNEMA ET AL.

    Sci. Transl. Med. 8, 348ra96 (2016).

  4. Physics

    Imaging electromagnetic waveforms

    1. Ian S. Osborne

    Understanding the dynamics of electrons and the spatial and temporal evolution of electromagnetic fields within a material or device is often the key to optimizing performance. Ryabov and Baum show that electron microscopy can be used to measure collective carrier motion and electromagnetic fields with subcycle and subwavelength resolution. As an example, they used a train of compressed electron pulses to produce movies of the electromagnetic excitation in an optical excited metamaterial component.

    Science, this issue p. 374

  5. Water Resources

    Groundwater flow drives partitioning

    1. Nicholas S. Wigginton

    Soil evaporation and plant transpiration together contribute a substantial proportion of terrestrial freshwater fluxes. Land surface models are used to understand the partitioning of these fluxes on a continental scale; however, model outputs are often inconsistent with stable isotope observations. Maxwell and Condon incorporated dynamic groundwater flow into an integrated hydrologic model simulation for the entire United States. The model showed that water table depth and lateral flow strongly affect transpiration partitioning, thus explaining the inconsistencies between observations and models.

    Science, this issue p. 377

  6. Memory Research

    How to link and separate memories

    1. Peter Stern

    Engrams are the changes in brain tissue that store single memories. Neuroscientists can localize and manipulate them, but until now, little was known about how multiple engrams interact to influence memories. Rashid et al. examined how neural assemblies in an area called the lateral amygdala interact. If two frightening events occurred within 6 hours, the same set of neurons was used to express fear memories for both events. However, if the events were separated by 24 hours, distinct memory traces were formed.

    Science, this issue p. 383

  7. Behavioral Ecology

    Show me a sign of sweetness to come

    1. Sacha Vignieri

    Communication between humans and domesticated animals is common. Regular communication between humans and wild animals, however, is rare. African honey-guide birds are known to regularly lead human honey-hunters to bee colonies, and the humans, on opening up the nest, leave enough mess for the birds to feast on. Spottiswoode et al. show that when the honey-hunters make a specific call, honey-guides are both more likely to come to their aid and more likely to find them a bee's nest. This interaction suggests that the birds are able to attach a specific meaning of cooperation to the human's call—a rare case of mutualism between humans and a wild animal.

    Science, this issue p. 387

  8. Cancer Immunotherapy

    Cyclin suppresses antitumor immunity

    1. Kristen L. Mueller

    Despite the dramatic success of cancer immunotherapy, many types of cancer do not respond. Understanding why could help us to find ways to enhance the overall responsiveness of tumors to immunotherapies. Dorand et al. report that cyclin-dependent kinase 5 (Cdk5), an enzyme that is highly expressed by neurons in many brain cancers, may dampen the ability of T cells to reject tumors. In a mouse model of medulloblastoma, if tumors were Cdk5 deficient, T cells were able to remove them. This heightened antitumor immunity correlated with reduced expression of the inhibitory molecule programmed cell death ligand 1 (PD-L1), a target of current cancer immunotherapies.

    Science, this issue p. 399

  9. Immunology

    Blocking ROCK2 to prevent autoimmunity

    1. John F. Foley

    T follicular helper (Tfh) cells assist in the production of antibodies. When activated, peripheral blood T cells from patients with the autoimmune disorder lupus can develop into Tfh cells. Weiss et al. found that a pharmacological inhibitor of the kinase, RO CK2, decreased the number and function of human Tfh cells that were generated in lupus cases. Unlike a general immunosuppressant, the ROCK2 inhibitor was specific and ameliorated disease severity in a mouse model of lupus without interfering with other immune cells.

    Sci. Signal. 9, ra73 (2016).

  10. HIV-1 Cure

    Next steps toward curing HIV-1

    1. Kristen L. Mueller

    Since the discovery of HIV-1 more than 30 years ago, prevention and treatment strategies have dominated the research agenda. More recently, however, scientists are also focusing their efforts toward finding a cure. Margolis et al. review an approach that involves HIV-1 latency reversal and viral clearance. The idea is to reactivate any dormant virus and coax it to produce viral proteins that the immune system can recognize. By combining a latency reversal strategy with immunotherapies, the body might be able to rid itself of all infected cells.

    Science, this issue p. 10.1126/science.aaf6517

  11. Synthetic Biology

    Building a computing system in bacteria

    1. L. Bryan Ray

    Finite state machines are logic circuits with a predetermined sequence of actions that are triggered depending on the starting conditions. They are used for a variety of devices and biological systems, from vending machines to neural circuits. Roquet et al. have taken a finite state machine approach to control the expression of integrases, or enzymes that insert or excise phage DNA into or out of bacterial chromosomes. The integrases altered the DNA sequence of a plasmid to record all five possible combinations of two inputs. Such circuits can be used to record the states that the cell experienced over time and can be deployed in state-dependent gene expression programs.

    Science, this issue p. 10.1126/science.aad8559

  12. Composites

    Stacking up the filler material

    1. Marc S. Lavine

    In composite materials, a strong or stiff filler is added to a softer matrix to create a combined material with better mechanical or electrical properties. To minimize the filler content, it needs to be uniformly distributed in the composite, which is particularly challenging for nanoscale materials. Liu et al. alternately stacked sheets of graphene and polycarbonate to make a base composite. By further cutting and stacking, up to 320 aligned layers were made with a very uniform filler distribution. Alternatively, the initial stack could be rolled into a rod. In both cases, the properties exceeded what might be expected from a simple combination of the two materials.

    Science, this issue p. 364

  13. Quantum Gases

    Steps to ultracold gas expansion

    1. Jelena Stajic

    Cold atomic gases are often studied while confined in parabolic traps, with the largest atomic density at the center of the trap. When the trap is made shallower, the gas radially expands as the energy cost for atoms that are farther from the trap center decreases. Deng et al. observed an interesting effect when they reduced the characteristic frequency of the parabolic trap so that it was at any moment inversely proportional to the elapsed time. Instead of expanding continuously, a strongly interacting Fermi gas held in such a trap stalled at certain time points. These time points formed a geometric progression, a consequence of scale invariance in the strongly interacting limit.

    Science, this issue p. 371

  14. Microbiome

    Human-microbiota coevolution

    1. Caroline Ash

    The bacteria that make their home in the intestines of modern apes and humans arose from ancient bacteria that colonized the guts of our common ancestors. Moeller et al. have developed a method to compare rapidly evolving gyrB gene sequences in fecal samples from humans and wild chimpanzees, bonobos, and gorillas (see the Perspective by Segre and Salafsky). Comparison of the gyrB phylogenies of major bacterial lineages reveals that they mostly match the apehominid phylogeny, except for some rare symbiont transfers between primate species. Gut bacteria therefore are not simply acquired from the environment, but have coevolved for millions of years with hominids to help shape our immune systems and development.

    Science, this issue p. 380; see also p. 350

  15. Microbiome

    Using antimicrobials with care

    1. Julia Fahrenkamp-Uppenbrink

    Many soaps and other household products contain the antimicrobial compound triclosan. In a Perspective, Yee and Gilbert highlight recent animal studies showing that triclosan can alter the composition of the microbiota of fish and rats. It remains unclear whether triclosan has a negative effect on the human microbiota at the concentrations that are used in domestic settings. Triclosan and other antimicrobial agents are used at high concentrations in hospital settings, where most children in developed countries are born. This may be of concern because infant microbiomes are particularly vulnerable to disturbance, with potentially long-term consequences for growth and development.

    Science, this issue p. 348

  16. Ecology

    Olive quick decline syndrome

    1. Julia Fahrenkamp-Uppenbrink

    For the past 3 years, the plant pathogen Xylella fastidiosa has been wreaking havoc in southern Italy, destroying centuries-old olive groves. In a Perspective, Almeida looks at the challenges of controlling the pathogen. European regulations require specific containment measures, including the destruction of affected plant material and susceptible hosts within 100 meters. But local opposition to destruction has been fierce because the trees play a central cultural role. If the pathogen spreads further, it may threaten other crops such as citrus and almond, as well as oak, elm, and sycamore trees.

    Science, this issue p. 346

  17. Protein Design

    Designed to assemble

    1. Valda Vinson

    Symmetric macromolecular structures that form cages, such as viral capsids, have inspired protein engineering. Bale et al. used pairwise combinations of dimeric, trimeric, or pentameric building blocks to design two-component, 120-subunit protein complexes with three distinct icosahedral architectures. The capsid-like nanostructures are large enough to hold nucleic acids or other proteins, and because they have two components, the assembly of cargoes such as drugs and vaccines can be done in a controlled way.

    Science, this issue p. 389

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