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Volume 468 Issue 7326, 16 December 2010

Polar bears live only in marine regions of the Northern Hemisphere where sea-ice cover persists for long enough to allow them sufficient opportunity to access their marine mammal prey. Recent declines in summer Arctic sea ice have coincided with declines in some polar bear populations, and a US Geological Survey report in 2007 projected that with business as usual emissions, polar bears could be extinct throughout their range by the end of the century. Some observers have suggested that summer Arctic sea ice might already have crossed a tipping point from beyond which habitats might not recover. But a new analysis suggests that it is not too late to save the polar bear. The rapid summer ice losses seen of late may represent increased volatility of a thinning sea-ice cover, rather than a tipping point. Greenhouse-gas mitigation could yet halt sea-ice loss and preserve the Arctic ecosystem. The cover shows a bear working its way through an area of marginal ice near the Svalbard Archipelago in the summer of 2009. Picture credit: Daniel J. Cox/NaturalExposures.com.

Editorial

  • Editorial |

    Blogs and online comments can provide valuable feedback on newly published research. Scientists need to adjust their mindsets to embrace and respond to these new forums for debate.

  • Editorial |

    If Europe's new states are to follow the research roadmap, capacity is as essential as funding.

  • Editorial |

    Irresponsible policies could cause an epidemic of malignant lung disease.

World View

Research Highlights

Seven Days

Correction

News

News Q&A

News

Correction

News Feature

  • News Feature |

    Cancer epidemics in Turkey could hold the secret to staving off a public health disaster in North Dakota.

    • Brendan Maher
  • News Feature |

    To learn the chemical language of plants, Ian Baldwin has built up a German research empire that engineers seeds — and a field station in the Utah wilderness to grow them.

    • Alison Abbott

Comment

  • Comment |

    Biologists and engineers should work together: synthetic biology reveals how organisms develop and function, argue Michael Elowitz and Wendell A. Lim.

    • Michael Elowitz
    • Wendell A. Lim
  • Comment |

    Hybridization in polar species could hit biodiversity hard, say Brendan Kelly, Andrew Whiteley and David Tallmon.

    • Brendan P. Kelly
    • Andrew Whiteley
    • David Tallmon

Books & Arts

Correspondence

Obituary

News & Views

  • News & Views |

    How is light perceived? The answer that might immediately come to mind is, through the eyes. Fly larvae, however, can 'feel' light using specialized neurons embedded under the cuticle encasing their bodies. See Article p.921

    • Paul A. Garrity
  • News & Views |

    The two Magellanic Clouds may have joined our Milky Way quite recently. It turns out that this trio of galaxies is remarkably unlike most other galaxy systems — both in the luminosity of the clouds and in their proximity to the Milky Way.

    • Sidney van den Bergh
  • News & Views |

    The promise of an exciting new drug that inhibits the mutant B-RAF protein in skin cancer is marred by the fact that most patients relapse within a year. Fresh data hint at how such resistance emerges. See Letters p.968 & p.973

    • David Solit
    • Charles L. Sawyers
  • News & Views |

    Simulations show that the still-mysterious origin of Saturn's vast, icy rings could be explained by the 'peeling' by Saturn's tides of the icy mantle of a large satellite migrating towards the planet. See Letter p.943

    • Aurélien Crida
    • Sébastien Charnoz
  • News & Views |

    Is the polar bear doomed to extinction? Maybe not, according to models of the future extent of Arctic sea ice if greenhouse-gas emissions are curbed. The outlook depends on the ability of policy-makers to act. See Letter p.955

    • Andrew E. Derocher
  • News & Views |

    A neat study that involves placing colloidal particles on curved oil-glycerol interfaces reveals a new form of crystal defect. The defect is called a pleat, by analogy to the age-old type of fabric fold. See Letter p.947

    • Francesco Stellacci
    • Andreas Mortensen
  • News & Views |

    Neuronal networks in the brain that develop early in life underlie our ability to learn, remember and communicate. Genetic defects that perturb the fine-tuning of such neuronal connectivity can cause disease.

    • Peter Scheiffele
    • Asim A. Beg
  • News & Views |

    The structure of a mineral has been validated, ending the controversy about its potential usefulness as a model of an unusual magnetic lattice. This model might provide insight into superconductivity.

    • Mark A. de Vries
    • Andrew Harrison

Review Article

Article

  • Article |

    Light sensing outside the eyes is common in many animals but is usually confined to specialized organs. Here, the entire body wall of the fruitfly larva is found to be tiled with blue- and ultraviolet-light sensing neuronal dendrites, which are essential for the larva's innate light-avoidance behaviour. The phototransduction machinery used by these neurons is distinct from other Drosophila photoreceptor molecules but similar to a system recently identified in nematode neurons.

    • Yang Xiang
    • Quan Yuan
    • Yuh Nung Jan
  • Article |

    A crystal structure of the tandem PHD and bromodomain regions of the transcription and chromatin regulator TRIM24 reveals combinatorial recognition of dual marks on the histone H3 tail. TRIM24 is involved in activation of oestrogen-dependent genes and is aberrantly expressed in breast cancer.

    • Wen-Wei Tsai
    • Zhanxin Wang
    • Michelle Craig Barton
  • Article |

    β-adrenergic receptor signalling in adipocytes stimulates energy expenditure via cAMP-dependent increases in lipolysis and fatty-acid oxidation, and this signalling mechanism is thought to be disrupted in obesity. Here, the cAMP-responsive CREB coactivator Crtc3 is shown to promote obesity in mice by attenuating β adrenergic receptor signalling in adipose tissue.

    • Youngsup Song
    • Judith Altarejos
    • Marc Montminy

Letter

  • Letter |

    The stellar initial mass function describes the mass distribution of stars at the time of their formation. This study reports observations of the Na I doublet and the Wing-Ford molecular FeH band in the spectra of elliptical galaxies. These lines are strong in stars with masses <0.3 solar masses and weak or absent in all other types of stars. The direct detection of the light of low-mass stars implies that they are very abundant in elliptical galaxies, making up >80% of the total number of stars and contributing >60% of the total stellar mass.

    • Pieter G. van Dokkum
    • Charlie Conroy
  • Letter |

    Saturn's rings are more than 90–95% water ice, which implies that initially they were almost pure ice because they are continually polluted by rocky meteoroids. Saturn has only one large satellite, Titan, whereas Jupiter has four large satellites; additional large satellites probably existed originally but were lost as they spiralled into Saturn. Now, numerical simulations of the tidal removal of mass from a differentiated, Titan sized satellite as it migrates inward towards Saturn are reported. Planetary tidal forces preferentially strip material from the satellite's outer icy layers, while its rocky core remains intact and is lost to collision with the planet. The result is a pure ice ring.

    • Robin M. Canup
  • Letter |

    Hexagons can easily tile a flat surface, but not a curved one. Defects with topological charge (such as heptagons and pentagons) make it easier to tile curved surfaces, such as soccer balls. Here, a new type of defect is reported that accommodates curvature in the same way as fabric pleats. The appearance of such defects on the negatively curved surfaces of stretched colloidal crystals are observed. The results will facilitate the exploration of general theories of defects in curved spaces, the engineering of curved structures and novel methods for soft lithography and directed self-assembly.

    • William T. M. Irvine
    • Vincenzo Vitelli
    • Paul M. Chaikin
  • Letter |

    Here, an indirect estimate for the magnetic field strength within the Earth's core from measurements of tidal dissipation is presented. Previously reported evidence of anomalous dissipation in the Earth's nutations can be explained with a core-averaged field of 2.5 mT, eliminating the need for high fluid viscosity or a stronger magnetic field at the inner-core boundary.

    • Bruce A. Buffett
  • Letter |

    The dramatic loss of Arctic sea ice with climate change has led to the prediction of a tipping point beyond which ice loss is irreversible and polar bear habitat will be catastrophically lost. By contrast, this study shows a linear relationship between temperature and sea-ice coverage that overcomes the albedo effect that would cause a tipping point. As a result, reducing greenhouse gas emissions can have a positive effect on polar bear populations.

    • Steven C. Amstrup
    • Eric T. DeWeaver
    • David A. Bailey
  • Letter |

    How new phenotypes can be introduced during evolution without losses of fitness remains largely unexplained at the molecular level. By comparing the molecular details of a well known process — mating type determination — across a large diversity of yeast species, the network rewiring event of the intercalation of a new level of gene transcription control into an ancient regulatory circuit is shown, which allowed for the creation of a new phenotype — taking food availability into account when deciding to mate.

    • Lauren N. Booth
    • Brian B. Tuch
    • Alexander D. Johnson
  • Letter |

    This study introduces a novel recording technique for simultaneously measuring excitatory and inhibitory conductances of retinal ganglion cells to show that excitatory and inhibitory inputs are strongly correlated, thereby cancelling each other. Furthermore, dynamic clamp is used to introduce these conductance changes into the cell with or without correlations, and it is found that, as predicted by theoretical work, correlations significantly increase reliability of the spiking response.

    • Jon Cafaro
    • Fred Rieke
  • Letter |

    Recent data from early clinical trials in melanoma patients carrying mutations in the B-RAF gene have shown promising results with the B-RAF kinase inhibitor PLX4032; however, many patients eventually develop resistance to this treatment. Two papers now uncover possible mechanisms of resistance to PLX4032. One paper shows that upregulation of MAP3K8 (which encodes COT) can confer resistance of melanoma cells to B-RAF inhibitors, whereas another paper found that melanomas can acquire resistance due to mutations of N-RAS or increased expression of PDGFRβ. Each of these resistance mechanisms seems to apply to at least some patients on recent PLX4032 trial, whereas, surprisingly, so far no secondary B-RAF mutations have been observed.

    • Cory M. Johannessen
    • Jesse S. Boehm
    • Levi A. Garraway
  • Letter |

    Recent data from early clinical trials in melanoma patients carrying mutations in the B-RAF gene have shown promising results with the B-RAF kinase inhibitor PLX4032; however, many patients eventually develop resistance to this treatment. Two papers now uncover possible mechanisms of resistance to PLX4032. One paper shows that upregulation of MAP3K8 (which encodes COT) can confer resistance of melanoma cells to B-RAF inhibitors, whereas another paper found that melanomas can acquire resistance due to mutations of N-RAS or increased expression of PDGFRβ. Each of these resistance mechanisms seems to apply to at least some patients on recent PLX4032 trial, whereas, surprisingly, so far no secondary B-RAF mutations have been observed.

    • Ramin Nazarian
    • Hubing Shi
    • Roger S. Lo
  • Letter |

    Protein machineries that move along the DNA, such as DNA polymerases and helicases, will necessarily encounter other bound proteins interacting with specific sites. Using 'curtains' of labelled DNA, this study measured whether such bound proteins interfere with the activity of the bacterial DNA translocase RecBCD. The translocase is able to push the proteins over nonspecific sites for thousands of base pairs before they are displaced.

    • Ilya J. Finkelstein
    • Mari-Liis Visnapuu
    • Eric C. Greene
  • Letter |

    Here, a comprehensive study of the sodium/galactose transporter (vSGLT) is presented, consisting of molecular dynamics simulations, biochemical characterization and a new crystal structure of the 'inward-open' conformation. These experiments show that sodium exit causes a reorientation of transmembrane helix 1, opening an inner gate required for substrate exit, while also triggering minor rigid-body movements in two sets of transmembrane helical bundles. This cascade of conformational changes is responsible for the proper timing of ion and substrate release.

    • Akira Watanabe
    • Seungho Choe
    • Jeff Abramson

News

Q&A

Futures

  • Futures |

    Turn on, tune out.

    • John Frizell

Brief Communications Arising

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