This Week in Science

Science  25 May 2018:
Vol. 360, Issue 6391, pp. 870
  1. Neurodevelopment

    Evolution of the brain

    1. Pamela J. Hines

    A freshwater turtle known as the red-eared slider (Trachemys scripta elegans)

    CREDIT: STEPHAN JUNEK/MPI BRAIN RESEARCH

    Just how related are reptilian and mammalian brains? Tosches et al. used single-cell transcriptomics to study turtle, lizard, mouse, and human brain samples. They assessed how the mammalian six-layered cortex might be derived from the reptilian three-layered cortex. Despite a lack of correspondence between layers, mammalian astrocytes and adult neural stem cells shared evolutionary origins. General classes of interneuron types were represented across the evolutionary span, although subtypes were species-specific. Pieces of the much-folded mammalian hippocampus were represented as adjacent fields in the reptile brains.

    Science, this issue p. 881

  2. Paleoclimate

    Forcing the East Asian summer monsoon

    1. H. Jesse Smith

    What factors have controlled the intensity of the East Asian summer monsoon over the recent geological past? To answer this key question requires a robust proxy for rainfall amounts. Beck et al. measured the beryllium isotopic content of loess from China, from which they reconstructed a 550,000-year-long record of rainfall. Rainfall correlated with orbital precession and global variations in ice volume. This finding suggests that the monsoon is governed by low-latitude interhemispheric gradients in solar radiation levels, rather than by high-northern-latitude solar radiation levels as previously suggested.

    Science, this issue p. 877

  3. Valleytronics

    Tracking the spin-valley current

    1. Jelena Stajic

    Taking advantage of the electron's spin and valley degrees of freedom requires a method for generating currents of carriers that have a particular spin or come from a particular valley in the electronic structure. Jin et al. used a heterostructure made out of adjacent layers of WSe2 and WS2 to create a spin-valley diffusion current without applying an external electric field. Instead, they used circularly polarized laser light to initiate the diffusion and a second laser pulse to image the propagation of the carriers. With long lifetimes and diffusion lengths, the method may be of practical use in future valleytronic devices.

    Science, this issue p. 893

  4. Cold Molecule Physics

    Lighting the way to molecules, one by one

    1. Jake Yeston

    When chemists run reactions, what they are really doing is mixing up an enormous number of reacting partners and then hoping that they collide productively. It is possible to manipulate atoms more deliberately with a scanning tunneling microscope tip, but the process is then confined to a surface. Liu et al. directly manipulated individual atoms with light to form single molecules in isolation (see the Perspective by Narevicius). They used optical tweezers of two different colors to selectively steer ultracold sodium (Na) and cesium (Cs) atoms together. A subsequent optical excitation formed NaCs.

    Science, this issue p. 900; see also p. 855

  5. Synthetic Biology

    Using bugs in the gut to detect blood

    1. Steve Mao

    Bacteria are environmentally resilient and can be engineered to sense various biomolecules. Mimee et al. combined biosensor bacteria with a miniaturized wireless readout capsule to produce a minimally invasive device capable of in vivo biosensing in harsh, difficult-to-access environments (see the Perspective by Gibson and Burgell). The device successfully measured gastrointestinal bleeding in pigs.

    Science, this issue p. 915; see also p. 856

  6. Diabetes

    A stimulating therapy for diabetes

    1. Mattia Maroso

    In type 2 diabetes, insulin resistance leads to elevated blood glucose and increased risk of cardiovascular disorders. The brain participates in glucose metabolism, but whether and how modulation of brain activity affects systemic blood concentrations of glucose is poorly understood. In diabetic and nondiabetic patients, ter Horst et al. found that dopamine release induced by deep brain electrical stimulation of the nucleus accumbens decreased systemic glucose concentrations. Conversely, pharmacological systemic dopamine depletion reduced insulin-mediated blood glucose uptake.

    Sci. Transl. Med. 10, eaar3752 (2018).

  7. Epidemiology

    A faster way to detect Zika in mosquitoes

    1. Philippa J. Benson

    A major challenge in preventing mosquito-borne diseases is providing rapid and affordable tests to identify infected insects. Conventional techniques are often time-consuming and too expensive when analyzing large numbers of mosquitoes. Leveraging a technique known as near-infrared spectroscopy (NIRS), Fernandes et al. tested for Zika virus in female Aedes aegypti mosquitoes. NIRS distinguished infected from uninfected mosquitoes with up to 99% accuracy 7 days after infection. NIRS is faster by a factor of 18 and cheaper by a factor of 110 than RT-qPCR (quantitative reverse transcription polymerase chain reaction), a technique commonly used for pathogen screening in mosquitoes.

    Sci. Adv. 10.1126/sciadv.aat0496 (2018).

  8. Microbiome

    Bile acids and liver cancer

    1. Priscilla N. Kelly

    Liver cancer is a leading cause of cancer-related deaths in the United States. The composition of the gut microbiome influences many human diseases, including liver inflammatory disorders. Ma et al. found that commensal gut bacteria can recruit the immune system to control the growth of liver tumors in mice (see the Perspective by Hartmann and Kronenberg). Clostridium species modified bile acids to signal liver sinusoidal endothelial cells to produce the chemokine CXCL16. This recruited natural killer T (NKT) immune cells to perform antitumor surveillance of the liver. Growth of both primary and metastatic cancer was reduced by NKT cell–driven killing.

    Science, this issue p. eaan5931; see also p. 858

  9. Migratory Behavior

    Follow the leader

    1. Sacha Vignieri

    What role do social dynamics play in guiding collective migrations? Identifying such dynamics requires following individual animals across long migratory distances. Flack et al. used GPS tags to follow individual juvenile white storks on their southern migration (see the Perspective by Nevitt). Birds generally fell into two categories: leaders and followers. Leaders sought out areas of thermal uplift, flapped less in transit, and flew farther. Followers followed leaders into thermals but had different trajectories, exhibited greater flapping effort, and flew shorter total distances.

    Science, this issue p. 911; see also p. 852

  10. Inorganic Chemistry

    Transforming nitrogen without carbon

    1. Jake Yeston

    How much carbon does it take to make nitric acid? The counterintuitive answer nowadays is quite a lot. Nitric acid is manufactured by ammonia oxidation, and all the hydrogen to make ammonia via the Haber-Bosch process comes from methane. That's without even accounting for the fossil fuels burned to power the process. Chen et al. review research prospects for more sustainable routes to nitrogen commodity chemicals, considering developments in enzymatic, homogeneous, and heterogeneous catalysis, as well as electrochemical, photochemical, and plasma-based approaches.

    Science, this issue p. eaar6611

  11. Single-Cell Analysis

    Mapping the planarian transcriptome

    1. Beverly A. Purnell

    A cell type's transcriptome defines the active genes that control its biology. Two groups used single-cell RNA sequencing to define the transcriptomes for essentially all cell types of a complete animal, the regenerative planarian Schmidtea mediterranea. Because pluripotent stem cells constantly differentiate to rejuvenate any part of the body of this species, all developmental lineages are active in adult animals. Fincher et al. determined the transcriptomes for most, if not all, planarian cell types, including some that were previously unknown. They also identified transition states and genes governing positional information. Plass et al. used single-cell transcriptomics and computational algorithms to reconstruct a lineage tree capturing the developmental progressions from stem to differentiated cells. They could then predict gene programs that are specifically turned on and off along the tree, and they used this approach to study how the cell types behaved during regeneration. These whole-animal transcriptome “atlases” are a powerful way to study metazoan biology.

    Science, this issue p. eaaq1736, p. eaaq1723

  12. Catalysis

    Reduction can make cobalt act precious

    1. Jake Yeston

    Enzymes rely on abundant metals such as iron and nickel to manipulate hydrogen. Chemists, on the other hand, have largely had to rely on precious metals such as platinum and rhodium for the task. Friedfeld et al. now report a simple trick to make cobalt act more like rhodium. Reduction of Co(II) to Co(I) by zinc reinforced binding of phosphine ligands to the metal to facilitate its use in asymmetric hydrogenation of alkenes. The cobalt catalysts tolerated alcohol solvents, unlike their rhodium congeners, and could be applied to a 200-gram-scale reduction at 0.08% loading.

    Science, this issue p. 888

  13. Photovoltaics

    Poking a semiconductor

    1. Jelena Stajic

    Noncentrosymmetric crystal structure can lead to a peculiar kind of charge separation under illumination called the bulk photovoltaic (BPV) effect. Solar cells made of such materials, however, typically have low efficiency. Yang et al. expanded the class of materials capable of exhibiting the BPV effect by making ordinarily centrosymmetric materials, such as SrTiO3 and TiO2, lose their inversion symmetry. The authors accomplished this by applying a point force on the surface of the material. This induced a strain gradient and the loss of inversion symmetry, resulting in large photovoltaic currents under illumination. The mechanism, dubbed the flexo-photovoltaic effect, is expected to apply to most semiconductors.

    Science, this issue p. 904

  14. Organic Electronics

    A longer exciton pathway

    1. Marc S. Lavine

    Organic semiconductors typically exhibit exciton diffusion lengths on the order of tens of nanometers. Jin et al. prepared nanofibers from block polymers consisting of emissive polyfluorene cores surrounded by coronas of polyethylene glycol and polythiophene (see the Perspective by Holmes). Excitons generated in the polyfluorene cannot enter the polyethylene glycol layer and so diffuse more than 200 nm. This distance can be tuned by varying the length of the polyethylene glycol—a feature that could potentially be exploited in the development of organic devices such as photovoltaics.

    Science, this issue p. 897; see also p. 854

  15. Molecular Biology

    RNA and membraneless organelles

    1. Steve Mao

    Membraneless compartments can form in cells through liquid-liquid phase separation (see the Perspective by Polymenidou). But what prevents these cellular condensates from randomly fusing together? Using the RNA-binding protein (RBP) Whi3, Langdon et al. demonstrated that the secondary structure of different RNA components determines the distinct biophysical and biological properties of the two types of condensates that Whi3 forms. Several RBPs, such as FUS and TDP43, contain prion-like domains and are linked to neurodegenerative diseases. These RBPs are usually soluble in the nucleus but can form pathological aggregates in the cytoplasm. Maharana et al. showed that local RNA concentrations determine distinct phase separation behaviors in different subcellular locations. The higher RNA concentrations in the nucleus act as a buffer to prevent phase separation of RBPs; when mislocalized to the cytoplasm, lower RNA concentrations trigger aggregation.

    Science, this issue p. 922, p. 918; see also p. 859

  16. Cancer Immunology

    Killing without poking holes

    1. Anand Balasubramani

    Given the success of T cell–centric cancer immunotherapies, there is considerable interest in understanding exactly how tumors sometimes evade this form of treatment. Kearney et al. carried out a series of genome-wide CRISPR screens to identify mechanisms of tumor immune evasion from cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Interferon-γ signaling and antigen presentation were critical for CTL-mediated killing of cancer cells, and TNF (tumor necrosis factor) signaling was a key effector mechanism for both CTL and NK cell antitumor activity. The same immune evasion mechanisms arose upon screening with perforin-deficient CTLs, suggesting that tumors evade the immune system by dampening the effects of cytokines, rather than reducing direct killing via perforin.

    Sci. Immunol. 3, eaar3451 (2018).

  17. Evolution

    Multiple parasites speed host evolution

    1. Caroline Ash

    Virtually all organisms are parasitized by multiple species, but our current understanding of host-parasite interactions is based on pairwise species interactions. Betts et al. address this by using the bacterium Pseudomonas aeruginosa and five different phage virus parasites. Increasing parasite diversity accelerated the rate of host evolution, driving both faster genomic evolution within populations and greater divergence between populations. Thus, different parasite loads prompt different evolutionary dynamics and profoundly shape host evolution by different mechanisms.

    Science, this issue p. 907

  18. Car T Cell Signaling

    More ITAMs for more potent receptors

    1. Erin Williams

    A form of cancer immunotherapy uses the patient's own T cells, which are engineered to express a chimeric antigen receptor (CAR) that recognizes a cancer cell antigen. Increasing signal transduction efficiency in these CAR T cells would enhance treatment efficacy. James engineered synthetic T cell receptors with differing numbers of ITAMs, a protein motif involved in immune cell signaling. Increasing ITAM number enhanced the fraction of T cells that became activated by antigen, suggesting a strategy to improve the potency of CAR T cells.

    Sci. Signal. 11, eaan1088 (2018).