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Volume 458 Issue 7237, 26 March 2009

A fragment of asteroid 2008 TC3 as found in the desert in northern Sudan in March 2009. The asteroid disintegrated at an altitude of 37 km in October 2008 but, remarkably, 47 fragments with a total mass of 3.95 kg have been recovered, and Jenniskens et al. have identified the material as surface matter from a class ‘F’ asteroid, a type not previously represented in meteorite collections. [Credit: Peter Jenniskens/ SETI Institute.]

Authors

Editorial

  • Editorial |

    Now that the US federal funding ban on human embryonic stem cells is lifted, scientists must engage the public's concerns about embryo research.

  • Editorial |

    The granting of patents on human genes has so far not been the disaster it was predicted to be.

  • Editorial |

    UK researchers are rightly outraged at one funding council's decision to exclude certain applicants.

Research Highlights

Journal Club

News

News in Brief

News Feature

  • News Feature |

    The only way to meet the increasing demand for fish is through aquaculture. Daniel Cressey explores the challenges for fish farmers and what it means for dinner plates in 2030.

    • Daniel Cressey
  • News Feature |

    When an asteroid was spotted heading towards our planet last October, researchers rushed to document a cosmic impact from start to finish for the first time. Roberta Kwok tells the tale.

    • Roberta Kwok

Correspondence

Commentary

  • Commentary |

    In the first of two commentaries on intellectual property, Robert Cook-Deegan, Subhashini Chandrasekharan and Misha Angrist show how the United States can address glitches with exclusive licences.

    • Robert Cook-Deegan
    • Subhashini Chandrasekharan
    • Misha Angrist
  • Commentary |

    In this, the second of two Commentaries, Sibylle Gaisser, Michael M. Hopkins and colleagues discuss a survey demonstrating that European health-care systems are ill prepared for the commercial reality of gene patents.

    • Sibylle Gaisser
    • Michael M. Hopkins
    • Dolores Ibarreta

Books & Arts

  • Books & Arts |

    Election campaigns are increasingly being staged online, but digital innovation has brought few new voices into the political debate, explains former parliamentarian Richard Allan.

    • Richard Allan
  • Books & Arts |

    In his dynamic 1891 ceiling decoration for Paris's city hall, Paul-Albert Besnard depicts the unveiling of truth by the sciences and makes a statement as strong as that of the Impressionists, explains Martin Kemp.

    • Martin Kemp

News & Views

  • News & Views |

    Discovery of an unusually intact and ancient fossil fish provides further evidence that the search for modern vertebrate origins requires breaking out of the Devonian and into the preceding period.

    • Michael I. Coates
  • News & Views |

    Understanding the mechanisms by which matter flows into black-hole systems is pivotal to elucidating how such systems work. It seems that a 'quiet' mass outflow can play a hitherto-unknown part in the process.

    • Daniel Proga
  • News & Views |

    Various gene mutations contribute to the motor-neuron disease known as amyotrophic lateral sclerosis. Further mutations that have been identified could help to clarify the neurodegenerative mechanism in this disorder.

    • Kristel Sleegers
    • Christine Van Broeckhoven
  • News & Views |

    The marine geochemical budget of some solutes does not add up. A test case shows that at least part of the reason may lie in the timescale over which continental weathering recovers from glaciations.

    • Louis A. Derry
  • News & Views |

    The spliceosome enzyme binds to RNA transcripts at splice sites and removes intron sequences. The crystal structure of a spliceosome subunit shows how the enzyme recognizes one end of the intron.

    • Charles C. Query

Editorial

Review Article

Article

  • Article |

    This study presents an exceptionally well-preserved fossil fish from the Silurian period (more than 418 million years ago) from southern China. The new form shows a mix of derived and primitive features. It is the earliest known well-preserved bony fish, and is a basal member of the lobe-finned fishes (which includes, today, the lungfishes, coelacanth and all land vertebrates), meaning that the split between ray-finned and lobe-finned bony fishes must have happened at least 419 million years ago, suggesting a deep history for jawed vertebrates.

    • Min Zhu
    • Wenjin Zhao
    • Qingming Qu
  • Article |

    In eukaryotes, many genes contain one or more introns — sequences that are transcribed into mRNA, but which are then excised before the mRNA is translated into protein. Multiprotein–RNA complexes called snRNPs are the machinery that clips these introns out. This study presents the structure of the U1 snRNP, which assembles at the 5′ end of the intron; the subunit interactions suggest a model by which the snRNP is assembled and the 5′ splice site is recognized.

    • Daniel A. Pomeranz Krummel
    • Chris Oubridge
    • Kiyoshi Nagai

Letter

  • Letter |

    Stellar-mass black holes with relativistic jets (microquasars) mimic the behaviour of quasars and active galactic nuclei, but the mechanisms that trigger and suppress jet formation remain a mystery. Neilsen and Lee analyse the spectrum of microquasar GRS 1915+105 in two different states — faint, emitting hard X-rays, and bright, emitting soft X-rays — and conclude that a hot wind off the accretion disk halts the flow of matter into the jet.

    • Joseph Neilsen
    • Julia C. Lee
  • Letter |

    On 6 October 2008, a small asteroid designated 2008 TC3 hit the Earth in northern Sudan. Jenniskens et al. searched along the approach trajectory and luckily found 47 bits of a meteorite named Almahata Sitta. Analysis reveals it to be a porous achondrite and a polymict ureilite, and so the asteroid was F-class (dark carbon-rich anomalous ureilites).

    • P. Jenniskens
    • M. H. Shaddad
    • S. P. Worden
  • Letter |

    A static magnetic field should generate no e.m.f. in a closed electrical circuit: but there is the possibility of generating an e.m.f. of purely spin origin in a static magnetic field. Pham Nam Hai and colleagues have now realised such an effect using magnetic tunnel junctions containing nanoscale magnetic particles; the resulting conversion of magnetic to electrical energy gives rise to a huge magnetoresistance (as high as 100,000 per cent), and might also form the basis of a 'spin battery'.

    • Pham Nam Hai
    • Shinobu Ohya
    • Sadamichi Maekawa
  • Letter |

    Rivers are the dominant source of many elements and isotopes in the ocean, but the fluxes vary with time. Derek Vance and colleagues suggest that the pulse of rapid chemical weathering initiated at the last deglaciation has not yet decayed away, and that weathering rates remain about two to three times the average for an entire late Quaternary glacial cycle. Consideration of such variability largely ameliorates long-standing problems with chemical and isotopic mass balances in the ocean.

    • Derek Vance
    • Damon A. H. Teagle
    • Gavin L. Foster
  • Letter |

    In this paper the authors demonstrate that events such as the massive Mount Pinatubo eruption are associated with the formation of volcanic mesocycles, in which the eruption plume begins to rotate and spreads into an asymmetric lobate umbrella. The work outlines a new conceptual framework for the behaviour of volcanic plumes and presents a clear avenue for future high-resolution remote sensing campaigns.

    • Pinaki Chakraborty
    • Gustavo Gioia
    • Susan W. Kieffer
  • Letter |

    This study reveals that cells originating from the same mother cell (ontogenetic radial clones) were more likely to be connected to each other within the developing neocortex. These specific microcircuits may underlie or contribute to the establishment of interconnected local neuronal ensembles that define functional cortical columns.

    • Yong-Chun Yu
    • Ronald S. Bultje
    • Song-Hai Shi
  • Letter |

    Using crosses between two strains of mice, one of which is susceptible and the other resistant to tumour development, these authors mapped genetic variants that contribute to skin cancer susceptibility. By combining these data with gene expression in normal skin they generated a network view of the gene expression architecture of mouse skin and identify expression motifs that contribute to tissue organization and various biological functions.

    • David A. Quigley
    • Minh D. To
    • Allan Balmain
  • Letter |

    This paper provides evidence for a role of caspase 8 in skin homeostasis. Loss of epidermal caspase 8 promotes epidermal cell proliferation and inflammation, and authors propose that caspase 8 expression by keratinocytes in the granular layer limits the release of preformed IL1α.

    • Pedro Lee
    • Dai-Jen Lee
    • Colin Jamora
  • Letter |

    Osteoclasts resorb bone and their precursor cells express sphingosine-1-phosphate (S1P) receptors. Too much S1P, and too many osteoclast precursors move into the blood; too little S1P results in increased attachment to bone and osteoporosis. Furthermore, S1P receptor stimulation in live mice diminishes bone loss in a mouse model of postmenopausal osteoporosis.

    • Masaru Ishii
    • Jackson G. Egen
    • Ronald N. Germain
  • Letter |

    Trithorax group (trxG) and Polycomb group (PcG) gene products are part of a chromatin remodelling system that activates or silences gene expression, respectively. This paper shows that show that Mll1 (mixed-lineage leukemia 1), a trxG member, is required for neurogenesis in the postnatal brain. They show that, in Mll1-deficient cells, expression of proneural and gliogenic regulatory genes are preserved, but Dlx2, a key downstream regulator of subventricular zone neurogenesis, is not expressed.

    • Daniel A. Lim
    • Yin-Cheng Huang
    • Arturo Alvarez-Buylla
  • Letter |

    This paper investigates why nicotine selectively activates neuronal and not muscular acetylcholine receptors, finding that a strong cation–π interaction, and also a hydrogen bond, form between nicotine and a specific tryptophan residue in receptors composed of α4 and β2 subunits — the subunit combination thought to underlie nicotine addiction. Muscle-type receptors also contain this tryptophan residue, but the cation–π interaction does not exist and the hydrogen bond is weaker, apparently due to the overall shape of the binding pocket.

    • Xinan Xiu
    • Nyssa L. Puskar
    • Dennis A. Dougherty

Corrigendum

Prospects

  • Prospects |

    Naturejobs gets a facelift in print.

    • Gene Russo

Movers

Networks and Support

Career View

  • Career View |

    I'm in serious postdoc limbo. Hopefully I won't fall flat on my face.

    • Julia Boughner

Futures

Insight

  • Insight |

    The ubiquitin system

    The central role of ubiquitin in cell-cycle regulation, DNA repair, cell growth, signalling and immune function is starting to become clear right down to the molecular level. Identifying irregularities in the system has opened up opportunities in drug discovery, and in diagnostics and treatment for a range of disorders, from cancer to neurodegeneration.

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