Research articles

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  • An exotic two-dimensional electron gas (2DEG) forms at oxide interfaces based on SrTiO3, but the precise nature of the 2DEG has remained elusive. In a systematic study using angle-resolved photoemission spectroscopy (ARPES), new insights into the electronic structure of the 2DEG are obtained. The findings shed light on previous observations in SrTiO3-based heterostructures and suggest that different forms of electron confinement at the surface of SrTiO3 lead to essentially the same 2DEG.

    • A. F. Santander-Syro
    • O. Copie
    • M. J. Rozenberg
    Letter
  • Many biomineralized tissues (such as teeth and bone) are hybrid inorganic–organic materials whose properties are determined by their convoluted internal structures. Now, using a chiton tooth as an example, this study shows how the internal structural and chemical complexity of such biomaterials and their synthetic analogues can be elucidated using pulsed-laser atom-probe tomography.

    • Lyle M. Gordon
    • Derk Joester
    Letter
  • The X-ray crystal structure of the human β2 adrenergic receptor, a G-protein-coupled receptor (GPCR), covalently bound to a small-molecule agonist is solved. Comparison of this structure with structures of this GPCR in an inactive state and in an antibody-stabilized active state reveals how binding events at both the extracellular and intracellular surfaces stabilize the active conformation of the receptor. Molecular dynamics simulations suggest that the agonist-bound active state spontaneously relaxes to an inactive-like state in the absence of a G protein.

    • Daniel M. Rosenbaum
    • Cheng Zhang
    • Brian K. Kobilka
    Letter
  • This study provides molecular insights into barriers to gene flow during the formation of species. The study identifies cis-regulatory mutations in two genes that cause a flower-colour change in the Texas wildflower Phlox drummondii and are part of the anthocyanin biosynthetic pathway. Flowers of plants that carry one of each mutation are of intermediate colour and therefore less frequently pollinated by insects, contributing to prezygotic as well as postzygotic isolation.

    • Robin Hopkins
    • Mark D. Rausher
    Letter
  • Henize 2-10 is a nearby dwarf starburst galaxy that may be similar to galaxies in the infant Universe. It is reported that Henize 2-10 contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source, from which it is concluded that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. The results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and by implication so can their primordial counterparts.

    • Amy E. Reines
    • Gregory R. Sivakoff
    • Crystal L. Brogan
    Letter
  • Templates are widely used to arrange molecular components so they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods. But, as larger structures are targeted, the synthesis of the templates themselves becomes challenging. It is now shown that 'molecular Verniers' can solve this problem: using a template with six binding sites and molecular building blocks with four porphyrins acting as binding sites, a 12-porphyrin nano-ring with a diameter of 4.7 nm is created. The ease and efficiency of this synthesis establishes Vernier templating as a powerful new strategy for producing large monodisperse macromolecules.

    • Melanie C. O’Sullivan
    • Johannes K. Sprafke
    • Harry L. Anderson
    Letter
  • One approach to sustainable fisheries is that of co-management, in which fishers and managers take joint responsibility for regulation. The evidence that this works is largely anecdotal, so this study systematically examined 130 co-managed fisheries. Several attributes of co-management were required for success, with leadership being the most important. A total of 8 attributes of co-management were required for a successful fishery, and above this number there was a linear relationship between the extent of co-management and success.

    • Nicolás L. Gutiérrez
    • Ray Hilborn
    • Omar Defeo
    Letter
  • The anomeric effect is a chemical phenomenon that refers to an observed stabilization of six-membered carbohydrate rings when they contain an electronegative substituent at the C1 position of the ring. This stereoelectronic effect influences the three-dimensional shapes of many biological molecules, but the underlying physical origin is unclear. Here it is shown that complexes formed between a truncated peptide motif and an isolated sugar in the gas phase are nearly identical structurally; however, the strength of the polarization of their interactions with the peptide differs greatly. It will be important to re-evaluate the influence, and biological effects, of substituents at position C2 of the six-membered carbohydrate rings.

    • Emilio J. Cocinero
    • Pierre Carcabal
    • Benjamin G. Davis
    Letter
  • It has been suggested that the Cambrian ocean was oxygen deficient, but physical evidence for widespread anoxia has been lacking. Now, sulphur isotope data from Cambrian rocks at six different locations around the world is presented, with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation at the time. With the help of a box model, these isotope shifts support the idea of large-scale anoxic and sulphidic conditions in the later Cambrian ocean.

    • Benjamin C. Gill
    • Timothy W. Lyons
    • Matthew R. Saltzman
    Letter
  • Müllerian mimics have convergently evolved similar warning colouration because of the advantage of strength in numbers. However, it is not clear if this effect is sufficient to maintain coexistence when competitive exclusion would be expected to favour one mimic at the expense of the others. Here, Müllerian mimicry in catfish is characterized, and it is shown through morphometric and stable isotope analysis that mimics do not occupy identical niches, so are not in direct competition, thus explaining their coexistence.

    • Markos A. Alexandrou
    • Claudio Oliveira
    • Martin I. Taylor
    Letter
  • Single-atom-thick graphene sheets can be produced at metre scales, bringing large-area applications in electronics and photovoltaics closer. However, such large pieces can be expected to be polycrystalline, so that it is important to determine the nature and size of grains in large-area graphene. This paper uses a combination of old and new transmission electron microscope techniques to carry out atomic-resolution imaging at grain boundaries as well as mapping of the location, orientation and shape of several hundred grains and boundaries with diffraction-filtered imaging. By correlating grain imaging with scanned probe and transport measurements, it is shown that the grain boundaries dramatically weaken the mechanical strength of graphene membranes, but do not as dramatically alter their electrical properties.

    • Pinshane Y. Huang
    • Carlos S. Ruiz-Vargas
    • David A. Muller
    Letter
  • Nitrogen-fixing rhizobia use lipochitooligosaccharide (LCO) signal molecules to initiate a symbiotic relationship with plant roots. Although it has been suggested that mycorrhizal fungi also secrete chemical signals for this process, the identity of these molecules was unknown. It is now shown that like rhizobia, mycorrhizal fungi produce LCOs and that these molecules are important for the establishment of the symbiotic relationship between plant root and fungus.

    • Fabienne Maillet
    • Véréna Poinsot
    • Jean Dénarié
    Article
  • Tunicates are the closest living relatives of the vertebrates. Many aspects of their lives and development are, however, poorly understood. It is generally thought that among ascidian tunicates such as Ciona, the superficially vertebrate-like central nervous system of the motile 'tadpole' larva degenerates and is completely replaced by an adult nervous system that develops from scratch. Here, state-of-the-art transgenesis and imaging techniques are used to show that this is not the case. There is continuity between the larval and adult nervous systems, with the adult nervous system developing from stem-cell-like ependymal cells found in the larva.

    • Takeo Horie
    • Ryoko Shinki
    • Yasunori Sasakura
    Letter
  • During mitosis, adherent cells change from a flattened to a rounded morphology, and this is thought to be necessary for the geometric requirements of cell division. Here, the forces that drive this shape change are studied. Mitotic rounding force depends both on the actomyosin cytoskeleton and the cell's ability to regulate osmolarity. The rounding force is generated by osmotic pressure and the actomyosin cortex maintains this rounding pressure against external forces. These results support the idea that in animal cells, the actomyosin cortex behaves like an internal cell wall that directs osmotic expansion to control cell shape.

    • Martin P. Stewart
    • Jonne Helenius
    • Anthony A. Hyman
    Letter
  • The kinase JNK is known to stimulate c-Jun transcriptional activity, but the molecular mechanism has been unclear. Here, N-terminal phosphorylation of c-Jun is shown to antagonize the interaction of c-Jun with Mbd3, a component of the repressor complex NuRD. The interaction between c-Jun and Mbd3 is shown to be important in regulating the proliferation of intestinal progenitor cells in mice.

    • Cristina Aguilera
    • Kentaro Nakagawa
    • Axel Behrens
    Letter