This Week in Science

Science  07 Apr 2017:
Vol. 356, Issue 6333, pp. 37
  1. Nonlinear Optics

    Probing the interaction of solitons

    1. Ian S. Osborne

    Internal dynamics of femtosecond soliton molecules


    As a pulse of light propagates through a medium, scattering and dispersion processes usually result in the pulse diffusing. However, under certain circumstances, the dispersion processes can be balanced by nonlinearities to produce localized structures known as solitons or optical bullets. Herink et al. used spectral interferometry to image and track the formation of soliton complexes as they propagated in a laser cavity. Real-time access to the formation processes and complex interaction dynamics could help in modeling other nonlinear systems.

    Science, this issue p. 50

  2. Celiac Disease

    Viruses compound dietary pathology

    1. Caroline Ash,
    2. Kristen L. Mueller

    Reoviruses commonly infect humans and mice asymptomatically. Bouziat et al. found that immune responses to two gut-infecting reoviruses take different paths in mice (see the Perspective by Verdu and Caminero). Both reoviruses invoked protective immune responses, but for one reovirus, when infection happened in the presence of a dietary antigen (such as gluten or ovalbumin), tolerance to the dietary antigen was lost. This was because this strain prevented the formation of tolerogenic T cells. Instead, it promoted T helper 1 immunity to the dietary antigen through interferon regulatory factor 1 signaling. Celiac disease patients also exhibited elevated levels of antibodies against reovirus.

    Science, this issue p. 44; see also p. 29

  3. Memory Research

    The network of memory consolidation

    1. Peter Stern

    Memories are thought to be formed in the hippocampus and later moved to the neocortex for long-term storage. However, little is known about the mechanisms that underlie the formation and maturation of neocortical memories and their interaction with the hippocampal network. Kitamura et al. discovered that at the onset of learning, neurons for contextual fear memory are quickly produced in the prefrontal cortex. This process depends on the activity of afferents from both the hippocampus and the amygdala. Over time, the prefrontal neurons consolidate their role in memory expression. In contrast, the hippocampal neurons slowly lose this function.

    Science, this issue p. 73

  4. Solar Cells

    Seeing hot carriers break the limit

    1. Phil Szuromi

    If charge carriers in solar cells can be harvested before they cool on their way to equilibrium, then the Shockley-Queisser limit of 33% for solar cell efficiency can potentially be beaten. Long carrier lifetimes (∼100 ps) have been reported for hybrid organic-inorganic metal halide perovskites. Guo et al. imaged charge transport in CH3NH3PbI3 thin films with transient absorption microscopy. Hot carriers could travel up to 600 nm, which suggests that devices that harvest hot carriers may be feasible.

    Science, this issue p. 59

  5. Polymers

    Processable cross-linked polymers

    1. Marc S. Lavine

    Thermoplastics can be made stiffer and more durable by cross-linking them, but this makes it more difficult to reprocess and recycle them. Röttger et al. show that the transesterification of boronic esters grafted onto common polymers such as polyethylene and polystyrene improves their shape stability and chemical resistance. However, unlike traditionally cross-linked materials, their polymers can still be extruded or injection-molded. This is because the covalent cross-links can undergo rapid exchange reactions, which allows the material to flow at high temperatures while still retaining a cross-linked structure.

    Science, this issue p. 62

  6. Research Economics

    Patents from papers both basic and applied

    1. Brad Wible

    Public funding for research depends on the idea that the resulting knowledge translates into socially valuable outcomes, such as medicines. Such linkages are easier to assert than to prove. Li et al. studied 27 years of grant-level funding by the U.S. National Institutes of Health. About 10% of grants are directly cited by patents, suggesting some technological application, and 30% of grants are cited in research articles that are then cited in patents. Five percent of grants result in papers cited by patents for successfully approved drugs, compared with less than 1% that are cited directly by such patents. These patterns hold regardless of whether the research is more basic or applied.

    Science, this issue p. 78

  7. Emerging Infections

    Fighting filoviruses with antibody therapy

    1. Lindsey Pujanandez

    Color-enhanced transmission electron micrograph of Marburg viruses


    Ravn and Marburg viruses cause hemorrhagic fever with high morbidity rates in humans. Mire et al. tested the ability of previously identified human monoclonal antibodies to protect guinea pigs from lethal infection. One candidate antibody was administered 5 days after otherwise lethal Marburg or Ravn infection in nonhuman primates and was able to reduce clinical symptoms and confer almost uniform protection. This antibody is a promising therapeutic that could be helpful in future filovirus outbreaks.

    Sci. Transl. Med. 9, eaai8711 (2017).

  8. Viral Genomics

    The evolution of giant virus genomes

    1. Laura M. Zahn

    Some giant viruses encode a genome larger than that of some bacteria, but their evolutionary history is a mystery. Examining the genomes within a sample from a wastewater treatment plant in Austria, Schulz et al. assembled a previously undiscovered giant virus genome, which they used to mine genetic databases for related viruses. The authors thus identified a group of giant viruses with more genes encoding components of the protein translation machinery, including aminoacyl transfer RNA synthetases, than in other giant viruses. Phylogenetic analyses suggest that the genes were acquired in an evolutionarily recent time frame, likely from, and as an adaptation to, their hosts.

    Science, this issue p. 82

  9. Biomedical Engineering

    Nanoparticles for drug delivery in lungs

    1. Philip Yeagle

    Engineering drug-delivery nanoparticles for adhesion to mucus can increase their residence times in lungs. Schneider et al. alternatively developed mucus-penetrating nanoparticles that exhibit greater retention in the lung and enhanced drug-delivery capability. Retention was related to the size of the particles; those smaller than the average mesh spacing of airway mucus were able to penetrate it, thus defeating physiologic mucus clearance. The result was a more effective and uniform distribution of the particles within the mucus and greater efficacy in a mouse model of acute lung inflammation.

    Sci Adv. 10.1126.sciadv.1601556 (2017).

  10. Crispr Biology

    Variation in prokaryote adaptive immunity

    1. Caroline Ash

    To repel infection by phage and mobile genetic elements, prokaryotes have a form of adaptive immune response and memory invested in clustered regularly interspaced short palindromic repeats and associated proteins (CRISPR-Cas). This molecular machinery can recognize and remember foreign nucleic acids by capturing and retaining small nucleotide sequences. On subsequent encounters, the cognate CRISPR-Cas marshals enzymatic defenses to destroy infecting elements that contain the same sequences. Jackson et al. review the molecular mechanisms by which diverse CRISPR-Cas systems adapt and anticipate novel threats and evasive countermeasures from mobile genetic elements.

    Science, this issue p. eaal5056

  11. Epigenetics

    DNA sequence and inherited gene silencing

    1. Beverly A. Purnell

    Cell fate decisions require a gene's transcriptional status, whether on or off, to be stably and heritably maintained over multiple cell generations. For silenced genes, heterochromatin domains are associated with specific histone posttranslational modifications, and these histone marks are maintained during DNA replication and chromosome duplication (see the Perspective by De and Kassis). Laprell et al. show that parental methylated histone H3 lysine 27 (H3K27) nucleosomes in Drosophila are inherited in daughter cells after replication and can repress transcription, but that they are not sufficient to propagate the mark. Trimethylation of newly incorporated nucleosomes requires recruitment of the methyltransferase Polycomb repressive complex 2 (PRC2) to neighboring cis-regulatory DNA elements. Coleman and Struhl demonstrate that H3K27 trimethylated nucleosomes play a causal role in transmitting epigenetic memory at a Drosophila HOX gene through anchoring of PRC2 at the Polycomb response element binding site. Wang and Moazed examine fission yeast and show that both sequence-dependent and chromodomain sequence-independent mechanisms are required for stable epigenetic inheritance of histone modifications and the epigenetic maintenance of silencing. These studies highlight the crucial role of DNA binding for heritable gene silencing during growth and development.

    Science, this issue p. 85, p. eaai8236, p. 88; see also p. 28

  12. Device Technology

    Printing nanosheet-network transistors

    1. Phil Szuromi

    Two-dimensional (2D) materials such as graphene and metal chalcogenides such as tungsten diselenide (WSe2) are attractive for use in low-cost thin-film transistors (TFTs) because they have high charge-carrier mobility. Kelly et al. printed TFTs from networks of exfoliated dispersions of 2D materials with graphene contacts, WSe2 as the semiconductor, and a boron nitride separator. Electrolytic gating with ionic liquids enabled higher operating currents than achieved with comparable organic TFTs.

    Science, this issue p. 69

  13. Neuroscience

    A tailored look at behavioral pharmacology

    1. Stella M. Hurtley

    It is important to understand how animal behavior is mediated by molecular, cellular, and circuit components of the brain. However, it has been difficult to link the activity of specific molecules in defined cells to behavioral roles. Shields et al. developed an approach to deconstruct behavioral neuropharmacology with cellular specificity. The technique, termed DART (drugs acutely restricted by tethering), uses enzymatic capture to restrict standard drugs to the surface of genetically specified cells without prior modification of the native pharmacological target. The method provides cell-type specificity, endogenous-protein specificity, acute onset, and utility in behaving animals. This enables the activity of specific molecules in defined circuit elements to be causally linked to behavior.

    Science, this issue p. eaaj2161

  14. Organic Chemistry

    Picking structures out of a lineup

    1. Jake Yeston

    Pharmaceutical research relies critically on determining the correct structures of numerous complex molecules. When well-ordered crystals are not available for x-ray analysis, nuclear magnetic resonance (NMR) spectroscopy is the most common structure-elucidation method. However, sometimes it is hard to distinguish isomers with similar spectra. Liu et al. showcase a protocol that combines computer modeling with anisotropic NMR data acquired using gel-aligned samples. Because of its uniform sensitivity to relative bond orientations across the whole molecular framework, the method overcomes common pitfalls that can lead to invalid structure assignments.

    Science, this issue p. eaam5349

  15. Chemical Physics

    X-ray vision catches Woodward-Hoffmann

    1. Jake Yeston

    The celebrated Woodward-Hoffmann (W-H) rules rationalize a variety of rapid bond rearrangements in organic molecules. The key insight involved symmetry conservation in the electronic journey from reactant to product. Attar et al. now report femtosecond x-ray absorption spectra and accompanying simulation studies that track shifts in carbon electronic states during one such reaction: the photochemical ring opening of cyclohexadiene to hexatriene (see the Perspective by Sension). The smooth evolution that occurs in the vicinity of the pericyclic minimum provides direct affirmation of the W-H framework. Moreover, the use of a convenient tabletop apparatus bodes well for future x-ray studies of ultrafast electronic dynamics.

    Science, this issue p. 54; see also p. 31

  16. Geochemistry

    A mantle story told with metal and gas

    1. Brent Grocholski

    Differences in isotopic compositions of trace elements can help identify how regions of Earth's mantle have evolved over time. Mundl et al. identified several ancient domains that have been isolated from mantle homogenization and thus contain signatures of primordial material. Tungsten and helium isotope values indicate fractionation and isolation of these mantle domains just after Earth's formation. The findings help constrain ancient processes such as core formation, but also provide insight into unexplained structures in the lower mantle today.

    Science, this issue p. 66

  17. Genome Assembly

    Hi-C for mosquito genomes

    1. Laura M. Zahn

    Most genomes sequenced today are determined through the generation of short sequenced bits of DNA that are computationally pieced together like a jigsaw puzzle. This has resulted in the need for funds and additional data to fill in gaps in order to fully assemble the many chromosomes that make up a eukaryotic genome. Dudchenko et al. used the Hi-C method, which measures the distance between contact points within and between chromosomes for scaffold validation, together with correction and ordering to more completely determine the arrangement of short sequencing reads for genome mapping. They validated their approach through the de novo generation of a complete human genome. A comparative analysis of mosquito genomes was made possible by improving the Culex quinquefasciatus genome assembly and generating the genome of Aedes aegypti, the vector of Zika virus.

    Science, this issue p. 92

  18. Physiology

    An astrocyte call to arms after brain injury

    1. Leslie K. Ferrarelli

    Brain injury stimulates the infiltration of peripheral immune cells that may cause persistent secondary tissue damage, impairing patient recovery. Using a mouse model of inflammatory brain injury, Dickens et al. found that astrocytes at the site of inflammation released vesicles into the circulation. When these vesicles reached the liver, they stimulated the secretion of cytokines that mobilized peripheral immune cells to infiltrate the brain. Inhibiting this communication between the brain and liver might accelerate and improve recovery from brain injuries.

    Sci. Signal. 10, eaai7696 (2017).

  19. Hypothesis

    From learning to instinct

    1. Julia Fahrenkamp-Uppenbrink

    The molecular and cellular processes that govern animal learning are relatively well understood, but it is much less clear how animals acquire instincts. In a Perspective, Robinson and Barron argue that instincts evolve from learning and that the underlying processes are the same. Support for this idea comes, for example, from laboratory studies showing that when mice learn to fear an odor, their offspring learn to fear this odor faster than do their parents. Furthermore, in bees and flies, the same neural circuits govern instinctive and learned olfactory responses. Epigenetic changes that affect gene expression without changing the DNA sequence itself may be key to translating a learned response into an instinct that requires no external stimulus.

    Science, this issue p. 26

  20. Autoimmunity

    Regulating the regulators

    1. Anand Balasubramani

    Inhibitory receptors on T cells, including LAG3 (encoded by lymphocyte-activation gene 3), limit immune-mediated damage to the host. LAG3 is expressed by exhausted conventional T cells in the tumor microenvironment. The role of LAG3 in regulatory T cells (Tregs) has remained unclear. Zhang et al. studied a mouse model of autoimmune diabetes. Treg-specific deletion of LAG3 led to enhanced Treg proliferation and reduced the incidence of type 1 diabetes. The findings highlight the cell-type dependence and context specificity of LAG3 and call for a more holistic assessment of the functions of inhibitory receptors that are emerging as targets for tumor immunotherapies.

    Sci. Immunol. 2, eaah4569 (2017).