This Week in Science

Science  05 Sep 2014:
Vol. 345, Issue 6201, pp. 1131
  1. Nanomaterials

    Tuning the twisting in helical nanowires

    1. Phil Szuromi

    Assembly of inorganic nanoparticles into complex structures often requires a template. Researchers can now assemble helical nanowires out of cubic magnetite nanocrystals by tuning interactions that bind or separate them. Singh et al. floated the nanocrystals on a liquid and aligned them with a magnetic field. After the liquid evaporated, different twisted nanowires remained. The helices varied according to the concentration of nanocrystals, their shape, and the strength of the magnetic field. Competition between weak forces drives this self-assembly and can lead to arrays with the same twist direction.

    Science, this issue p. 1149

  2. Metal Alloys

    A metal alloy that is stronger when cold

    1. Marc S. Lavine

    Metal alloys normally consist of one dominant element, with others in small amounts to improve specific properties. For example, stainless steel is primarily iron with nickel and chromium but may contain trace amounts of other elements. Gludovatz et al. explored the properties of a high-entropy alloy made from equal amounts of chromium, manganese, iron, cobalt, and nickel. Not only does this alloy show excellent strength, ductility, and toughness, but these properties improve at cryogenic temperatures where most alloys change from ductile to brittle.

    Science, this issue p. 1153

  3. Development

    Bringing up baby

    1. Orla M. Smith

    Feeding methods matter to macaques

    CREDIT: KATHY WEST/UC DAVIS

    Diet influences microbes in the intestine, and for the immune system to develop normally, microbes must colonize the gut. It remains unclear how profoundly diet shapes the primate immune system or how durable the influence is. Ardeshir et al. demonstrate that breast-fed and bottle-fed infant macaques develop dramatically different immune systems, which remain different for at least six months after they begin receiving identical diets. These findings may explain the variation in people's susceptibility to conditions involving the immune system, as well as the variation in how well the immune system protects people against certain infectious diseases.

    Sci. Transl. Med. 6, 252ra121 (2014).

  4. Neurodegeneration

    Dipeptide repeat peptides on the attack

    1. Stella M. Hurtley

    Studying neurodegeneration in Drosophila

    CREDIT: TERESA NICCOLI/UCL INSTITUTE OF AGEING, LONDON, UK

    Certain neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), are associated with expanded dipeptides translated from RNA transcripts of disease-associated genes (see the Perspective by Paul and Gitler). Kwon et al. show that the peptides encoded by the expanded repeats in the C9orf72 gene interfere with the way cells make RNA and kill cells. These effects may account for how this genetic form of ALS causes disease. Working in Drosophila, Mizielinska et al. aimed to distinguish between the effects of repeat-containing RNAs and the dipeptide repeat peptides that they encode. The findings provide evidence that dipeptide repeat proteins can cause toxicity directly.

    Science, this issue p. 1139 and p. 1192; see also p. 1118

  5. Physiology

    Connecting DNA damage to fibrosis

    1. Leslie K. Ferrarelli

    In the autoimmune disease systemic sclerosis (SSc), high collagen production by fibroblasts causes “scarring” of the skin and internal organs. During this process, called fibrosis, the Wnt signaling pathway is frequently activated. Svegliati et al. found that antibodies in the serum from SSc patients stimulated a pathway that suppressed the expression of WIF-1, which encodes a Wnt inhibitor, and triggered collagen production in fibroblasts from normal individuals. Effects were similar when cells were treated with DNA-damaging agents. In fibroblasts from SSc patients, inhibiting this pathway caused the cells to express WIF-1 and produce less collagen. In a mouse model of fibrosis, inhibiting this pathway prevented fibrotic skin thickening.

    Sci. Signal. 7, ra84 (2014).

  6. Plant Genomics

    Coffee, tea, and chocolate converge

    1. Laura M. Zahn

    Caffeine has evolved multiple times among plant species, but no one knows whether these events involved similar genes. Denoeud et al. sequenced the Coffea canephora (coffee) genome and identified a conserved gene order (see the Perspective by Zamir). Although this species underwent fewer genome duplications than related species, the relevant caffeine genes experienced tandem duplications that expanded their numbers within this species. Scientists have seen similar but independent expansions in distantly related species of tea and cacao, suggesting that caffeine might have played an adaptive role in coffee evolution.

    Science, this issue p. 1181; see also p. 1124

  7. Paleoclimate

    Old and older, cold and colder

    1. H. Jesse Smith

    Greenland surface air temperatures changed dramatically during the last deglaciation. The exact amount is unknown, which makes it difficult to understand what caused those changes. Buizert et al. report temperature reconstructions for the period from 19,000 to 10,000 years before the present from three different locations in Greenland and interpret them with a climate model (see the Perspective by Sime). They provide the broad geographic pattern of temperature variability and infer the mechanisms of the changes and their seasonality, which differ in important ways from the traditional view.

    Science, this issue p. 1177; see also p. 1116

  8. Genome Editing

    Genome editing corrects a muscle disease

    1. Paula A. Kiberstis

    Patients with Duchenne muscular dystrophy find their muscles growing progressively weaker. Studies identified dystrophin as the culprit gene, which galvanized research into gene-targeted therapies. Long et al. apply genome editing to “correct” the disease-causing mutation in mice genetically destined to develop the disease. This germline editing strategy kept muscles from degenerating, even in mice harboring only a small percentage of corrected cells. Although not feasible for humans, this proof of concept sets the stage for applying genome editing to specific cell types involved in the disease.

    Science, this issue p. 1184

  9. The Ribosome

    Caught in the act of making protein

    1. Guy Riddihough

    The ribosome is a large RNA-protein complex that converts the genetic code stored in messenger RNA (mRNA) into proteins. Zhou et al. have determined the structure of a bacterial ribosome caught in the act of decoding an mRNA. Transfer RNAs (tRNAs) decipher the genetic code in the mRNA to ensure that the ribosome uses the correct amino acids. The structure shows tRNAs in the process of being moved between successive protein-building binding pockets as the ribosome reads the mRNA like a piece of old-fashion computer tape.

    Science, this issue p. 1188

  10. Supernovae

    Surprise found by γ-ray metal detector

    1. Margaret M. Moerchen

    Gamma rays reveal an unusual event

    ILLUSTRION: ESO

    Astronomers commonly use type-Ia supernovae as standard distance measurement tools, though the physics of these bright sources are not fully understood. One product of the thermonuclear explosion is 56Ni, which probably lies at the heart of the supernova cloud. Diehl et al. detected the gamma-ray emission from 56Ni in SN2014J much earlier than expected, only about 20 days after the initial explosion. This early exposure suggests both an asymmetric event and the production of 56Ni farther out in the ejecta than predicted. These sources will help astronomers measure distances far beyond where supernovae have been studied.

    Science, this issue p. 1162

  11. Earthquake Dynamics

    The earthquake that rocked northern Chile

    1. Nicholas S. Wigginton

    Subduction zones often produce the largest earthquakes on Earth. A magnitude 8.2 earthquake (Iquique) occurred in one such zone off the coast of northern Chile on 1 April 2014, in a seismic gap that had not experienced a large earthquake since the 9.0 one in 1877. Ruiz et al. analyzed continuous GPS data to monitor the movement of plates over time in this region, including before and after major earthquakes. The most recent large quake was preceded by an extended series of smaller earthquakes and creeping westward movement of the coastline.

    Science, this issue p. 1165

  12. Superconductivity

    Optically manipulating superconductors

    1. Jelena Stajic

    In superconductors, electrons of opposite momenta pair to form a highly correlated state that manages to flow without encountering any resistance. Matsunaga et al. manipulated the wavefunction of these pairs in the superconductor NbN with an electromagnetic pulse that they transmitted through a thin layer of the material (see the Perspective by Pashkin and Leitenstorfer). The superconducting gap, which is the energy needed to break the pairs apart, oscillated at twice the frequency of the pulse's electric field. When they matched this frequency to half the gap, the authors excited a collective mode in the superconductor called the Higgs mode, a relative of the Higgs boson in particle physics.

    Science, this issue p. 1145; see also p. 1121

  13. Metalloproteins

    Cofactors linked to nutrient limitation

    1. Nicholas S. Wigginton

    Microbes require inventive ways to acquire scarce nutrients from the environment. Enzymes that catalyze the acquisition of phosphorus from dissolved organic matter, for example, rely on complex metal cofactors in the active site. Yong et al. determined the crystal structure of the PhoX alkaline phosphatase from Pseudomonas fluorescens (see the Perspective by Moore). The metal centers arrange themselves in a triangular structure of two iron atoms and one calcium atom, bridged together by an oxide ion. The presence of iron, which itself is a trace nutrient in most environments, suggests that it limits phosphorus acquisition.

    Science, this issue p. 1170; see also p. 1120

  14. Crystal Nucleation

    Watching nucleation pathways in calcite

    1. Marc S. Lavine

    The initial stage of crystallization, the formation of nuclei, is a critical process, but because of the length and time scales involved, is hard to observe. Nielsen et al. explored the crystallization of calcium carbonate, a well-studied material but one with multiple nucleation theories. Different calcium and carbonate solutions were mixed inside a fluid cell and imaged using a liquid cell inside a transmission electron microscope. Competing pathways operated during nucleation, with both the direct association of ions into nuclei from solution and the transformation of amorphous calcium carbonate into and between different crystalline polymorphs.

    Science, this issue p. 1158

  15. Innate Immunity

    Bringing in the agent of your own destruction

    1. Stella M. Hurtley

    Cells need mechanisms to detect and disable pathogens that infect them. Tam et al. now show that complement C3, a protein that binds to pathogens in the blood, can enter target cells together with the pathogen. Once inside the cell, the presence of C3 triggers both immune signaling and degradation of the internalized pathogen. The discovery of this pathway reveals that cells possess an early warning system of invasion that works against a diverse array of pathogens and does not require recognition of any specific pathogen molecules.

    Science, this issue 10.1126/science.1256070

  16. Dynamic Ordering

    Liquid crystals on a deformable substrate

    1. Marc S. Lavine

    The orientation of the molecules in a liquid crystalline material will change in response to either changes in the substrate or an external field. This is the basis for liquid crystalline devices. Vesicles, which are fluid pockets surrounded by lipid bilayers, will change size or shape in response to solvent conditions or pressure. Keber et al. report on the rich interactions between nematic liquid crystals placed on the surface of a vesicle. Changes to the vesicle size, for example, can “tune” the liquid crystal molecules. But conversely, the shape of the vesicles can also change in response to the activity of the nematic molecules.

    Science, this issue p. 1135

  17. Marine Microbes

    Protein markers of cyanobacterial stress

    1. Nicholas S. Wigginton

    Nutrients including iron, nitrogen, and phosphorus limit primary productivity in the oceans. Determining how abundant cyanobacteria such as Prochlorococcus adapt to nutrient stress across marine settings requires accurate molecular assays. Saito et al. developed a proteomic and metaproteomic approach capable of targeting specific metabolic biomarkers from mixed communities in seawater (see the Perspective by Moore). Prochlorococcus proteins are indicative of a major limiting nutrient across a wide transect in the Pacific Ocean; however, they also show that the limitation of multiple nutrients at overlapping biomes is an additional source of stress.

    Science, this issue p. 1173; see also p. 1120