Research articles

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  • Phenotypic robustness in the face of genetic and environmental perturbations — known as canalization — relies on buffering mechanisms. Hsp90 chaperone machinery has been proposed to be an evolutionarily conserved buffering mechanism of phenotypic variance. Here, an additional, perhaps alternative, mechanism whereby Hsp90 influences phenotypic variation is proposed; Hsp90 mutations can generate new variation by transposon-mediated mutagenesis.

    • Valeria Specchia
    • Lucia Piacentini
    • Maria P. Bozzetti
  • The earliest body fossils of tetrapods (vertebrates with limbs rather than paired fins) date to the Late Devonian period. There have been claims of tetrapod trackways predating these body fossils but the age and identity of the track makers have remained controversial. The discovery of well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian age, around 18 million years older than the earliest tetrapod body fossils, is now presented.

    • Grzegorz Niedźwiedzki
    • Piotr Szrek
    • Per E. Ahlberg
  • The amplitude of the magnetic field near the Galactic Centre has been uncertain by two orders of magnitude for several decades. A compilation of previous data now reveals a downward break in the region's non-thermal radio spectrum; this requires that the Galactic Centre field be at least ∼50 microgauss on 400 parsec scales, with evidence supporting a field of 100 microgauss. This would imply that over 10% of the Galaxy's magnetic energy is contained in only around 0.05% (or less) of its volume.

    • Roland M. Crocker
    • David I. Jones
    • Raymond J. Protheroe
  • From earthquakes to hard drives, frictional motion and its strength are involved in a wide range of phenomena. The strength of an interface that divides two sliding bodies is determined by both the real contact area and the contacts' shear strength. By continuous measurements of the concurrent local evolution of the real contact area and the corresponding interface motion from the first microseconds when contact detachment occurs, frictional strength is now characterized from short to long timescales.

    • Oded Ben-David
    • Shmuel M. Rubinstein
    • Jay Fineberg
  • Kinase regulatory pathways are used in eukaryotic DNA replication to facilitate coordination with other processes during cell division cycles and response to environmental cues. The Dbf4–Cdc7 kinase (DDK) is one of at least two cell-cycle-regulated protein kinase systems essential for initiation of DNA replication. DDK is now shown to relieve the inhibitory activity of the amino-terminal domain of the replicative helicase Mcm4, thus promoting S phase.

    • Yi-Jun Sheu
    • Bruce Stillman
  • The Dirac equation successfully merges quantum mechanics with special relativity. It predicts some peculiar effects such as 'Zitterbewegung', an unexpected quivering motion of a free relativistic quantum particle. This and other predicted phenomena are key fundamental examples for understanding relativistic quantum effects, but are difficult to observe in real particles. Here, using a single trapped ion set to behave as a free relativistic quantum particle, a quantum simulation of the one-dimensional Dirac equation is demonstrated.

    • R. Gerritsma
    • G. Kirchmair
    • C. F. Roos
  • Existing models of type Ia supernovae generally explain their observed properties, with the exception of the sub-luminous 1991bg-like supernovae. It has long been suspected that the merger of two white dwarfs could give rise to a type Ia event, but simulations so far have failed to produce an explosion. Here, a simulation of the merger of two equal-mass white dwarfs is presented that leads to a sub-luminous explosion; it requires a single common-envelope phase and component masses of about 0.9 solar masses.

    • Rüdiger Pakmor
    • Markus Kromer
    • Wolfgang Hillebrandt
  • If the activity of genetically specified neurons is silenced in a temporally precise fashion, the roles of different cell classes in neural processes can be studied. Members of the class of light-driven outward proton pumps are now shown to mediate powerful, safe, multiple-colour silencing of neural activity. The gene archaerhodopsin-3 (Arch) enables near 100% silencing of neurons in the awake brain when virally expressed in the mouse cortex and illuminated with yellow light.

    • Brian Y. Chow
    • Xue Han
    • Edward S. Boyden
  • The Southern Ocean is potentially a substantial sink of anthropogenic carbon dioxide; however, the regulation of this carbon sink by the wind-driven Ekman flow, mesoscale eddies and their interaction is under debate. Here, a high-resolution ocean circulation and carbon cycle model is used to study intra-annual variability in anthropogenic carbon dioxide over a two-year time period; the Ekman flow is found to be the primary mechanism of anthropogenic carbon dioxide transport across the Antarctic polar front.

    • T. Ito
    • M. Woloszyn
    • M. Mazloff
  • Until now, retroviruses have been the only group of viruses known to have left a fossil record, in the form of endogenous proviruses; those elements make up approximately 8% of the human genome. Elements homologous to the nucleoprotein gene of the non-retroviral bornavirus are now shown to exist in the genomes of several mammalian species; the results give insights into the role of bornavirus as a source of genetic novelty to its host.

    • Masayuki Horie
    • Tomoyuki Honda
    • Keizo Tomonaga
  • Although Archaea encode proteasomes highly related to those of eukaryotes, archaeal ubiquitin-like proteins are less conserved and not known to function in protein conjugation, complicating our understanding of the origins of ubiquitination. Two small archaeal modifier proteins, SAMP1 and SAMP2, structurally similar to ubiquitin, are now reported to form protein conjugates in the archaeon Haloferax volcanii.

    • Matthew A. Humbard
    • Hugo V. Miranda
    • Julie A. Maupin-Furlow
  • The role of B-cell-receptor (BCR) signalling in human B cell lymphomas has been a long-standing question, with genetic and functional evidence for its oncogenic role in human lymphomas lacking. Here, a form of 'chronic active' BCR signalling that is required for cell survival in the activated B-cell-like subtype of diffuse large B-cell lymphoma is described and analysed, with potential implications for future therapeutic strategies.

    • R. Eric Davis
    • Vu N. Ngo
    • Louis M. Staudt
  • G-protein-coupled receptors (GPCRs) mediate the majority of cellular responses to hormones and neurotransmitters and are the largest group of therapeutic targets for a range of diseases. The extracellular surface (ECS) of GPCRs is diverse and therefore an ideal target for the discovery of subtype-selective drugs. Here, NMR spectroscopy is used to investigate ligand-specific conformational changes around a central structural feature in the ECS of a GPCR.

    • Michael P. Bokoch
    • Yaozhong Zou
    • Brian K. Kobilka
  • Clear cell renal carcinoma, the most common form of adult kidney cancer, is often characterized by the presence of inactivating mutations in the VHL gene. A large survey for somatic mutations now identifies inactivating mutations in two genes encoding enzymes involved in histone modification, highlighting the role of mutations in components of the chromatin modification machinery in human cancer.

    • Gillian L. Dalgliesh
    • Kyle Furge
    • P. Andrew Futreal
  • After fertilization in mammals, the maternal and paternal genomes undergo epigenetic reprogramming to prepare for the transition from germ cell to somatic cell transcription programs. One of the events that takes place is the demethylation of the paternal genome. To identify the factors involved in this process, a live cell imaging system is now used to monitor the paternal DNA methylation state in zygotes; Elp3, a component of the elongator complex, is found to have an important role.

    • Yuki Okada
    • Kazuo Yamagata
    • Yi Zhang
  • The differentiation of an embryonic stem cell (ESC) requires both suppression of the self-renewal process and activation of the specific differentiation pathway. The let-7 family of microRNAs (miRNAs) are now shown to suppress the self-renewal program in cells that are normally unable to silence this program, whereas introduction of ESC cell cycle regulating miRNAs blocks the action of let-7. Thus, the interplay between these two groups of miRNAs dictates cell fate.

    • Collin Melton
    • Robert L. Judson
    • Robert Blelloch