This Week in Science

Science  29 Jul 2016:
Vol. 353, Issue 6298, pp. 458
  1. Human Genetics

    Near Eastern genomes from Iran

    1. Laura M. Zahn

    Genome sequencing of modern Iranian Zoroastrians reveals a previously uncharacterized ancient human population.

    PHOTO: ASSOCIATED PRESS

    The genetic composition of populations in Europe changed during the Neolithic transition from hunting and gathering to farming. To better understand the origin of modern populations, Broushaki et al. sequenced ancient DNA from four individuals from the Zagros region of present-day Iran, representing the early Neolithic Fertile Crescent. These individuals unexpectedly were not ancestral to early European farmers, and their genetic structures did not contribute significantly to those of present-day Europeans. These data indicate that a parallel Neolithic transition probably resulted from structured farming populations across southwest Asia.

    Science, this issue p. 499

  2. Education

    Signaling ability and grit to academia

    1. Gilbert Chin

    In many professions, getting ahead requires evidence of both effort and ability. This is especially true if one is not a member of the dominant group and thus surmounting social norms. Breda and Hillion show that oral examiners of candidates for teaching positions in the French education system reward such applicants. Specifically, women applying for high-level teaching positions in male-dominated fields, such as physics and philosophy, are favored, as are men who apply in female-dominated fields, such as literature and foreign languages.

    Science, this issue p. 474

  3. Optics

    Microlasers with a twist

    1. Ian S. Osborne

    Structured light, in the form of helical wavefronts, provides an additional degree of freedom to encode information for optical communications. Creating light beams with the desired amount of optical angular momentum, or twist, has usually been achieved with bulk optic devices. Miao et al. demonstrate a possible route for an integrated optics approach in which a twisted-light source with a controlled amount of optical angular momentum is generated internally to the designed device structure. These microlasers could find application in telecommunication and information technologies to increase the rate of information transmission.

    Science, this issue p. 464

  4. Electrochemistry

    Small and salty CO2 reduction scheme

    1. Jake Yeston

    Most artificial photosynthesis approaches focus on making hydrogen. Modifying CO2, as plants and microbes do, is more chemically complex. Asadi et al. report that fashioning WSe2 and related electrochemical catalysts into nanometer-scale flakes greatly improves their activity for the reduction of CO2 to CO. An ionic liquid reaction medium further enhances efficiency. An artificial leaf with WSe2 reduced CO2 on one side while a cobalt catalyst oxidized water on the other side.

    Science, this issue p. 467

  5. Plant Ecology

    Patchy landscapes select for invasiveness

    1. Andrew M. Sugden

    Invasive species are ubiquitous in human-dominated landscapes, yet we have only limited understanding of their ecological and evolutionary dynamics. Williams et al. used an experimental system with the model plant species Arabidopsis thaliana to examine how evolution affects the spread of plant populations through landscapes of varying patchiness. Plant height and dispersal ability evolved more rapidly in patchier experimental landscapes, suggesting that fragmentation can select for more rapid invasion velocity. Hence, evolution may need to be taken into account in predictions of future invasion rates.

    Science, this issue p. 482

  6. Plant Development

    Spring break

    1. Pamela J. Hines

    Some plants will only flower after a long exposure to cold temperatures, a response known as vernalization. When the floral repressor encoded by FLOWERING LOCUS C (FLC) is shut down, once the temperatures start to increase, the restriction of the flowering process is removed. The repressive epigenetic marks on FLC are initiated at a specific location within the gene. Qüesta et al. now find that a transcriptional repressor, VAL1, is responsible for finding the correct DNA sequence at which to nucleate the formation of repressive chromatin. VAL1 then recruits the machinery that silences the floral repressor.

    Science, this issue p. 485

  7. Infection

    Plasmid copy number promotes plague

    1. Caroline Ash

    The plague bacterium, Yersinia pestis

    PHOTO: DR. GARY GAUGLER/SCIENCE SOURCE

    The virulence of the plague bacterium, Yersinia pestis, is encoded on a plasmid. Normally, the bacterium only tolerates one copy of the plasmid, which provides the molecular machinery for injecting toxins into host cells. Wang et al. have found that Y. pestis can only be pathogenic if plasmid numbers are boosted and express enough protein components to assemble a functional virulence apparatus. Problematically, the synthetic activity of the plasmid has such a high metabolic cost that it can impede growth. Thus, the bacterium only allows the plasmid to replicate when it senses a potential host cell.

    Science, this issue p. 492

  8. Conservation

    Genomics sees wolves differently

    1. Shahid Naeem

    The taxonomy of America's wolves—including the red (Canis rufus), gray (C. lupus), and eastern (C. lycaon) species—is fraught with debate. Species identification, however, informs listing, delisting, and relisting under the Endangered Species Act. Von Holdt et al. analyzed the whole genomes of red, gray, and eastern wolves, along with those of coyotes (with which they can interbreed) and distant canid species, such as the golden jackal and Eurasian gray wolf. America's wolves consist of geographically complex sets of populations differing in degrees of past interbreeding. Wolf conservation may therefore need to be based on evolutionary history rather than taxonomic typologies.

    Sci. Adv. 2, e1501714 (2016).

  9. HIV

    Influencing the infant microbiome

    1. Orla M. Smith

    More than 1 million children are born to HIV-infected women each year. Most of these children do not acquire HIV infection, yet they experience twice the mortality of children who are born to HIV-negative mothers. Bender et al. show that HIV infection in mothers is associated with changes in the microbiome of their HIV-exposed, uninfected infants. Disruption of the HIV-exposed infant's microbiome, possibly mediated by breast milk, may affect development of the immune system and contribute to the increased mortality of these infants.

    Sci. Transl. Med. 8, 349ra100 (2016).

  10. Applied Physics

    The rise and rise of 2D materials

    1. Ian S. Osborne

    Since the discovery of graphene, the study of two-dimensional (2D) materials and their van der Waals heterostructures has attracted worldwide interest. These materials are important not just for fundamental research but also for many potential applications. Novoselov et al. review the state-of-the-art progress in the field of 2D materials, describing the recent developments in their growth and fabrication and in controlling and manipulating their optical and electronic properties for application in potential device structures.

    Science, this issue p. 461

  11. Cell Lineage Tracing

    Tracing cell history in zebrafish

    1. Beverly A. Purnell

    Following the pattern of cell divisions and specializations as a fertilized egg develops into a complex organism is essential to understanding organismal development. McKenna et al. developed a method termed GESTALT that introduces unique patterns of mutations into a genomic barcode during zebrafish development. The DNA sequence of mutated barcodes in different cells is then used to reconstruct cell lineage relationships. When applied to zebrafish, this cell lineage tracing method demonstrates that most adult organs are dominated by the progeny of a few ancestral cells. In future analyses, this method can be applied to other complex multicellular organisms to study cell lineage in normal development, as well as to identify the cellular origin of tumors and metastases.

    Science, this issue p. 462

  12. Ecology

    The creeping pace of plant extinctions

    1. Julia Fahrenkamp-Uppenbrink

    Predictions of plant extinctions far exceed those recorded in the UN Red List database. In a Perspective, Cronk explores the reasons for this discrepancy. It can be extremely difficult to prove that a species is fully extinct. Even if a few individuals persist, the species may be functionally extinct, that is, it can no longer regenerate in its natural environment. For woody plants, such “living dead” can persist for hundreds of years. The world may thus be facing creeping plant biodiversity loss over the course of this century.

    Science, this issue p. 446

  13. Pharmacology

    Drug combinations to prevent blindness

    1. Nancy R. Gough

    Light can damage the retina through processes that involve G protein-coupled receptors (GPCRs). In a mouse model of progressive retinal degeneration, Chen et al. explored combinations of drugs that activate or inhibit specific GPCRs to prevent light-induced retinal damage. This approach identified a photoreceptor-protecting combination of U.S. Food and Drug Administration-approved drugs that activated the dopamine receptors D2R and D4R, inhibited the dopamine receptor D1R, and inhibited the adrenergic receptor α1A. Similar approaches could lead to the discovery of new combinations of available drugs to promote therapeutic changes in signaling networks.

    Sci. Signal. 9, ra74 (2016).

  14. Parasitic Plants

    Resistance is not, after all, futile

    1. Pamela J. Hines

    The parasitic plant known as dodder attaches to its hosts and sucks the life out of them. Oddly, the common tomato stands tall when under attack. Hegenauer et al. have leveraged that difference to identify part of the molecular defense system that protects tomato plants (see the Perspective by Ntoukakis and Gimenez-Ibanez). In a process analogous to defenses mounted against microbial infection, the host plant perceives a small-peptide signal from the parasitic plant and initiates defense responses. The candidate receptor isolated from the tomato plant provided partial protection when transferred to two other susceptible plant species.

    Science, this issue p. 478; see also p. 442

  15. Synthetic Biology

    Making bacterial cells into a memory device

    1. L. Bryan Ray

    The adaptation of the CRISPR-Cas integrase system has greatly facilitated gene editing. Shipman et al. explored how the system can be used to insert defined DNA sequences into bacterial genomes to serve as a form of memory (see the Perspective by Borkowski et al.). The order in which DNA was inserted into genomes could be determined from DNA sequencing of a population of bacterial cells. The approach may lead to recording mechanisms that could track the history of cellular events during development or other biological processes.

    Science, this issue p. 463; see also p. 444

  16. Paleooceanography

    An ocean of climate impacts

    1. H. Jesse Smith

    Large decreases in Atlantic meridional overturning circulation accompanied every one of the cold Northern Hemispheric stadial events that occurred during the heart of the last glacial period. These events, lasting on average around 1000 years each, have long been thought to result from changes in deep ocean circulation. Henry et al. used a suite of geochemical proxies from marine sediments to show that reductions in the export of northern deep waters occurred before and during stadial periods (see the Perspective by Schmittner). This observation firmly establishes the role of ocean circulation as a cause of abrupt glacial climate change during that interval.

    Science, this issue p. 470; see also p. 445

  17. Symbiosis

    Lichens assemble in three parts

    1. Caroline Ash

    Lichen growth forms cannot be recapitulated in the laboratory by culturing the plant and fungal partners together. Spribille et al. have discovered that the classical binary view of lichens is too simple. Instead, North American beard-like lichens are constituted of not two but three symbiotic partners: an ascomycetous fungus, a photosynthetic alga, and, unexpectedly, a basidiomycetous yeast. The yeast cells form the characteristic cortex of the lichen thallus and may be important for its shape. The yeasts are ubiquitous and essential partners for most lichens and not the result of lichens being colonized or parasitized by other organisms.

    Science, this issue p. 488

  18. Structural Biology

    Maturation and inhibition of HIV-1

    1. Stella M. Hurtley

    HIV-1 undergoes a two-step assembly process controlled largely by a single region of its Gag protein. Schur et al. determined a complete atomic model for this region within an assembled Gag protein lattice using cryo-electron tomography together with subtomogram averaging. Amino acids from different parts of multiple Gag molecules come together to form an intricate network of interactions that drive HIV-1 assembly. The final step of maturation into the infectious HIV-1 virus is controlled by structural changes in Gag that alter the accessibility of the final cleavage site to the viral protease.

    Science, this issue p. 506

  19. Epigenetics

    Mom's diet affects growth

    1. Beverly A. Purnell

    Nutrition is important during development. This appears to be true even in utero, with potential long-lasting effects on adult phenotype and disease. Epigenetic factors are prime suspects in identifying the corresponding molecular mechanism because they can be maintained throughout cell division. Holland et al. show in mice that in utero nutritional deficits influence offspring growth through epigenetic states at multicopy ribosomal DNA elements. This effect is influenced by the genetic variation that naturally exists within the ribosomal RNA.

    Science, this issue p. 495

  20. Structural Biology

    Zooming in on the Zika virus protease

    1. Kristen L. Mueller

    The lack of a vaccine or antiviral drugs to combat the Zika virus has scientists scrambling to identify and better characterize potential drug targets. One attractive candidate is the NS2B/NS3 viral protease, which, together with host cell proteases, cleaves the viral polyprotein into the individual proteins required for viral replication. Lei et al. report the crystal structure of this protease bound to a peptido-mimetic inhibitor. The structure reveals key interactions that probably contribute to the high catalytic efficiency of this enzyme relative to other flaviviruses, indicating promising starting points for drug design.

    Science, this issue p. 503

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