This Week in Science

Science  29 Mar 2019:
Vol. 363, Issue 6434, pp. 1411
  1. Conservation Ecology

    Threats to the Serengeti

    1. Andrew M. Sugden

    A herd of blue wildebeest, Connochaetes taurinus, graze in the Maasai Mara National Reserve in Kenya.

    PHOTO: IMAGEBROKER/ALAMY STOCK PHOTO

    Protected areas are an important tool for conserving biodiversity and ecosystem functioning. But how well do these areas withstand pressure from human activity in surrounding landscapes? Veldhuis et al. studied long-term data from the Serengeti-Mara ecosystem in East Africa. Human activities at boundary regions cause animals to concentrate in the core of the protected area, which eventually reduces soil carbon storage and nitrogen fixation rates and increases vulnerability to extreme droughts. Similar patterns are likely for many, if not all, large protected areas.

    Science, this issue p. 1424

  2. Magnetism

    Magnetic building blocks in two dimensions

    1. Jelena Stajic

    Artificial magnetic structures can offer a variety of functionalities in spintronics devices. Luo et al. engineered magnetic domains in Pt/Co/AlOx trilayers that had alternating in-plane and out-of-plane magnetizations. The regions interacted laterally through the so-called Dzyaloshinskii-Moriya interaction, which determined the relative sign and orientation of the magnetization in adjacent domains. Using the coupling between the domains, the researchers were able to engineer more-complex magnetic structures such as skyrmions and frustrated magnets.

    Science, this issue p. 1435

  3. Wildlife Disease

    The demise of amphibians?

    1. Sacha Vignieri

    Rapid spread of disease is a hazard in our interconnected world. The chytrid fungus Batrachochytrium dendrobatidis was identified in amphibian populations about 20 years ago and has caused death and species extinction at a global scale. Scheele et al. found that the fungus has caused declines in amphibian populations everywhere except at its origin in Asia (see the Perspective by Greenberg and Palen). A majority of species and populations are still experiencing decline, but there is evidence of limited recovery in some species. The analysis also suggests some conditions that predict resilience.

    Science, this issue p. 1459; see also p. 1386

  4. Protein Design

    Precise packing for membrane proteins

    1. Valda Vinson

    Although nonpolar amino acid side chains pack efficiently in membrane proteins, it has been difficult to determine how much this contributes to membrane protein stability. Designed membrane proteins have largely relied on other stabilizing interactions such as metal-ligand interactions and hydrogen bonds. Mravic et al. uncovered a steric packing code underlying the folding of the natural protein phospholamban, which they used to design stable membrane proteins with nonpolar interfaces. They suggest that packing of nonpolar residues plays a role in the folding and stability of many membrane proteins.

    Science, this issue p. 1418

  5. Organic Chemistry

    Crowdsourcing a chromophore

    1. Jake Yeston

    Photoredox catalysis is widely used to accelerate chemical reactions by channeling the energy in visible light. However, most implementations rely on expensive chromophores to absorb light. Fu et al. now show that a pair of cheap components acting in concert can induce these reactions, despite not being strong visible absorbers individually. The combination of sodium iodide and triphenylphosphine allowed photoinduced electron transfer to catalyze a variety of alkylations.

    Science, this issue p. 1429

  6. Plant Science

    Speeding up stomatal responses

    1. Pamela J. Hines

    A plant's cellular metabolism rapidly adjusts to changes in light conditions, but its stomata—pores that allow gas exchange in leaves—are slower to respond. Because of the lagging response, photosynthesis is less efficient, and excess water is lost through the open pores. Papanatsiou et al. introduced a blue light–responsive ion channel into stomata of the small mustard plant Arabidopsis. The channel increased the rate of stomata opening and closing in response to light. The engineered plants produced more biomass, especially in the fluctuating light conditions typical of outdoor growth.

    Stomata on the leaf of an English yew, Taxus baccata, seen in a scanning electron micrograph

    CREDIT: EYE OF SCIENCE/SCIENCE SOURCE

    Science, this issue p. 1456

  7. RNA Sequencing

    Gene expression at fine scale

    1. Laura M. Zahn

    Mapping gene expression at the single-cell level within tissues remains a technical challenge. Rodriques et al. developed a method called Slide-seq, whereby RNA was spatially resolved from tissue sections by transfer onto a surface covered with DNA-barcoded beads. Applying Slide-seq to regions of a mouse brain revealed spatial gene expression patterns in the Purkinje layer of the cerebellum and axes of variation across Purkinje cell compartments. The authors used this method to dissect the temporal evolution of cell type–specific responses in a mouse model of traumatic brain injury.

    Science, this issue p. 1463

  8. T Cells

    Zooming in on the kiss of death

    1. Anand Balasubramani

    Cytotoxic T lymphocytes (CTLs) engage and kill antigen-specific target cells by injecting toxic proteins. The toxic proteins, including perforin and granzyme, are stored in lytic granules in the CTLs and are delivered via so-called immunological synapses between the CTLs and target cells. Tamzalit et al. used an in vitro system to generate and visualize three-dimensional immunological synapses. They examined actin dynamics and lytic granule fusion within these synapses and found that granule fusion was physically separated from regions of actin depletion. Their studies shed light on the microscopic details of CTL-driven killing.

    Sci. Immunol. 4, eaav5445 (2019).

  9. Computer Science

    Heart-function modeling for the masses

    1. Kollen Post,
    2. Aaron Clauset

    Modeling cardiac dynamics allows scientists to understand individual heart behaviors, such as arrhythmia. These models typically require supercomputers to solve an individualized network of differential equations that capture the fluid dynamics within a heart. Kaboudian et al. translated popular cardiac models to run on graphics processing units, or GPUs, that normally handle image and video processing. The result is a massively parallel simulation that can run quickly inside a web browser on a standard mobile phone. This technology may be broadly applicable to many other computationally expensive biomedical calculations.

    Sci. Adv. 10.1126/sciadv.aav6019 (2019).

  10. Earth System

    Nanomaterials in the Earth system

    1. Julia Fahrenkamp-Uppenbrink

    Nanomaterials have been part of the Earth system for billions of years, but human activities are changing the nature and amounts of these materials. Hochella Jr. et al. review sources and impacts of natural nanomaterials, which are not created directly through human actions; incidental nanomaterials, which form unintentionally during human activities; and engineered nanomaterials, which are created for specific applications. Knowledge of the properties of all three types as they cycle through the Earth system is essential for understanding and mitigating their long-term impacts on the environment and human health.

    Science, this issue p. eaau8299

  11. Synthetic Biology

    How to make an organelle in eukaryotes

    1. Stella M. Hurtley

    A key step in the evolution of complex organisms like eukaryotes was the organization of specific tasks into organelles. Reinkemeier et al. designed an artificial, membraneless organelle into mammalian cells to perform orthogonal translation. In response to a specific codon in a selected messenger RNA, ribosomes confined to this organelle were able to introduce chemical functionalities site-specifically, expanding the canonical set of amino acids. This approach opens possibilities in synthetic cell engineering and biomedical research.

    Science, this issue p. eaaw2644

  12. Immunology

    Phage subverts immune response

    1. Seth Thomas Scanlon

    Pseudomonas aeruginosa (Pa) is a multidrug-resistant Gramnegative bacterium commonly found in health care settings. Pa infections frequently result in considerable morbidity and mortality. Sweere et al. found that a type of temperate filamentous bacteriophage that infects and integrates into Pa is associated with chronic human wound infections. Likewise, wounds in mice colonized with phage-infected Pa were more severe and longer-lasting than those colonized by Pa alone. Immune cell uptake of phage-infected Pa resulted in phage RNA production and inappropriate antiviral immune responses, impeding bacterial clearance. Both phage vaccination and transfer of antiphage antibodies were protective against Pa infection.

    Science, this issue p. eaat9691

  13. Immunometabolism

    Stemness against adversity

    1. Priscilla N. Kelly

    T lymphocytes are powerful immune cells that can destroy tumors, but cancers have developed tricks to evade killing. Vodnala et al. found that potassium ions in the tumor microenvironment serve a dual role of influencing T cell effector function and stemness (see the Perspective by Baixauli Celda et al.). Increased potassium impairs T cell metabolism and nutrient uptake, resulting in a starvation state known as autophagy. The increased potassium can also preserve T cells in a stem-like state where they retain the capacity to divide. These seemingly divergent processes are linked to the cellular distribution of acetyl–coenzyme A, which, when manipulated, can restore the ability of human T cells to eliminate tumors in mice.

    Science, this issue p. eaau0135; see also p. 1395

  14. Polymers

    The right hand lines up vinyl ethers

    1. Jake Yeston

    Well-optimized catalysts produce vast quantities of isotactic polypropylene, in which the side chains all face the same way. Add an oxygen into the monomer, though, and that degree of uniformity becomes harder to enforce. Teator and Leibfarth report a general protocol to polymerize a variety of such vinyl ethers isotactically (see the Perspective by Foster and O'Reilly). They rely on a chiral phosphoric acid in combination with a titanium Lewis acid to bias the monomer orientation during cationic polymerization. The resulting polymers show promising adhesive properties.

    Science, this issue p. 1439; see also p. 1394

  15. Neuroscience

    Reward and the map in the brain

    1. Peter Stern

    Recent findings suggest a more complex role of grid cells in the brain than simply coding for space. The grid map in the entorhinal cortex, which is responsible for encoding spatial information, is not as rigid as originally thought and can be distorted by environmental modifications (see the Perspective by Quian Quiroga). Butler et al. compared grid cell coding during a free-foraging task and a spatial memory task in rats. They discovered that entorhinal spatial maps restructure to incorporate the location of a learned reward. Boccara et al. tested the influence of behaviorally relevant information on the cognitive map that emerges from grid cell firing in the rat medial entorhinal cortex. They found that grid cells participate in neural coding of the goal locality, not the whole environment.

    Science, this issue p. 1447, p. 1443; see also p. 1388

  16. Conservation

    More than just numbers

    1. Sacha Vignieri

    We often frame negative human impacts on animal species in terms of numbers of individuals reduced or numbers of regions from which species are absent. However, human activities are likely affecting species in more complex ways than these figures can capture. Kühl et al. studied behavioral and cultural diversity in our closest relative, the chimpanzee. They found that human-mediated disturbance is reducing these complex traits. Human influence thus goes well beyond simple loss of populations or species, leading to behavioral change even where populations persist.

    Science, this issue p. 1453

  17. Biotechnology

    Endogenous gene editing

    1. Gemma Alderton

    Genetically modified crops have supporters and opponents, but how can these views be reconciled to improve food security? This problem is particularly acute for middle-income countries that need to export crops to maintain their economy as well as provide for their expanding population. In a Perspective, Zaidi et al. discuss the promise of new plant breeding technologies to edit endogenous genes in crop plants. These innovations will ideally improve food security and avoid barriers to use and implementation that face traditional genetically modified crops.

    Science, this issue p. 1390

  18. Law

    Recognizing rights to protect nature

    1. Julia Fahrenkamp-Uppenbrink

    Laws aimed at preventing harm to the environment appear to be insufficient to halt or reverse environmental destruction. In a Perspective, Chapron et al. highlight recent efforts to recognize intrinsic rights of nature. Going beyond the rights for individuals supported by animal rights advocates, the rights-of-nature proponents focus on natural communities, ecosystems, and other natural entities. These rights provide a means to protect natural entities when their needs conflict with those of humans. Successful expansion and implementation of this concept will depend on the ability of legal systems to integrate ecological knowledge and balance the rights of nature with those of humans or corporations.

    Science, this issue p. 1392

  19. Cystic Fibrosis

    Tackling cystic fibrosis in the womb

    1. Mattia Maroso

    Cystic fibrosis (CF) is a multiorgan disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). Abnormalities in the lungs, pancreas, and gastrointestinal tract develop even before birth. Sun et al. reasoned that early intervention using the approved drug VX-770 (ivacaftor), a CFTR modulator, could prevent the development of such abnormalities. They tested the effect of in utero and early postnatal VX-770 administration in a ferret model of CF. Organ pathologies were partially prevented in treated ferrets, suggesting that prenatal treatment might increase the efficacy of CFTR-correcting therapies.

    Sci. Transl. Med. 11, eaau7531 (2019).

  20. Fertility

    Protamine modification for fertility

    1. John F. Foley

    During the final stage of spermatogenesis, small, positively charged proteins known as protamines tightly package DNA in the mature sperm. Itoh et al. found that mice deficient in the heat shock protein Hspa4l, which is implicated in spermatogenesis, produced sperm with malformed heads and were sterile. Hspa4l kept protamine 2 dephosphorylated at a specific serine residue. Expression of an unphosphorylatable protamine 2 mutant reversed the infertility of Hspa4l-deficient mice, suggesting a pathway that could be targeted for fertility or contraceptive purposes.

    Sci. Signal. 12, eaao7232 (2019).