Editors' Choice

Science  11 Feb 2011:
Vol. 331, Issue 6018, pp. 650
  1. Biomedicine

    Taking Cancer Up (and Down) a Notch

    1. Paula A. Kiberstis
    CREDIT: SONOSHITA ET AL., CANCER CELL 19, 125 (2011)

    The Notch signaling pathway is aberrantly activated in several forms of human cancer, an observation that has triggered interest in the development of Notch inhibitors as possible cancer therapies. A new study reveals that in a mouse model of colon cancer, Notch signaling contributes to cancer development by promoting tumor invasion and metastasis. Sonoshita et al. investigated the function of a gene called Aes, whose expression is greatly reduced in liver metastases versus primary tumors, and found that its protein product, a transcriptional regulator, represses Notch signaling. Aes-deficient, tumor-prone mice showed more evidence of local tumor invasion than control mice, and in vitro assays indicated that loss of this gene enhances the ability of tumor cells to migrate across the endothelial lining of blood vessels—a key step in metastasis. Consistent with these findings, administration of a compound that inhibits Notch signaling to mice bearing primary colon tumors suppressed the formation of liver metastases. As is true for all therapies that target signaling pathways with complex functional roles, translation to the clinic will require careful preclinical studies to assess side effects. Highlighting the need for caution is a recent independent study by Liu et al., who found that genetic inactivation of one copy of the Notch1 receptor gene resulted in the formation of benign vascular tumors, which in some cases caused fatal hemorrhaging.

    Cancer Cell 19, 125 (2011); J. Clin. Invest. 10.1172/JCI43114 (2011).

  2. Geophysics

    Shaken While Stirred

    1. Nicholas S. Wigginton

    When oceanic plates are driven deep beneath continents at subduction zones, massive slabs of the lithosphere slowly get reincorporated by convection processes into the mantle (the large reservoir from which the seafloor originated long ago). The top and bottom boundaries of sinking slabs are roughly marked by two parallel planes of earthquake activity at depths of ∼50 to 200 km below Earth's surface. The upper seismic zone likely results from transformations of minerals in the wet crust as they are heated and squeezed; this process releases water and causes seismic activity. Based on low seismic wave anomalies in tomographic images of subduction zones in Japan, Reynard et al. conclude that the lower seismic zone is caused not by dehydration reactions but by deformation of anhydrous minerals as the slab accumulates stress and bends. Because no appreciable quantities of water are needed to explain these observations, recycling of water into the mantle from oceanic lithosphere may be limited to just the first few kilometers of descent.

    Geophys. Res. Lett. 37, L24309 (2010).

  3. Cell Biology

    RNA Builders

    1. Guy Riddihough

    The organization of the various—and often transient—compartments within the eukaryotic cell nucleus remains an underexplored area of cell biology. RNAs are suggested to be important in the morphogenesis of the nucleolus, the histone locus body (HLB), and splicing speckles, for example, all of which form in the vicinity of actively transcribed gene loci. To explore this idea further, Shevtsov and Dundr localized specific RNAs to a particular region of chromatin in HeLa cells and asked if they could initiate the formation of nuclear bodies. They found that histone H2b RNA drove the formation of HLBs with similar kinetics, composition, and structure as wild-type HLBs. Similarly, a tethered RNA polymerase II transcript from the β-globin gene was able to nucleate the formation of splicing speckles. Noncoding RNAs were able to initiate the formation of paraspeckles and nuclear stress bodies. The function of RNA in the nucleation step of nuclear body formation may be to act as a scaffold to localize diffusible proteins in the nucleoplasm, which in turn can recruit additional components of the structure.

    Nat. Cell Biol. 12, 167 (2011).

  4. Ecology

    Conservation and Migration

    1. Andrew M. Sugden
    CREDIT: NAVINDER J. SINGH

    Effective conservation, whether of whole habitats, ecosystem services, or individual species, is a challenge at the best of times. Under climate change, it becomes a moving target. Add migratory species to the mix, and the challenge can seem even more daunting, not least because it requires detailed knowledge of the migration patterns over wide geographical areas over many years and predictions of how these patterns might change in the future as climate and habitat change.

    Singh and Milner-Gulland studied the Saiga antelope, Saiga tatarica, a migratory ungulate found in Kazakhstan. The antelope has suffered a 95% population reduction in recent decades but is now the focus of conservation efforts. Aerial monitoring data of antelope movement over the past 25 years and rainfall, temperature, and vegetation data were used to understand the factors influencing antelope spring distribution patterns (the period when calving takes place and which is therefore critical for population viability). This knowledge is then applied to predict the location of future suitable spring habitats under scenarios of further climate change and to suggest likely locations for future protected areas for the antelope.

    J. Appl. Ecol. 48, 35 (2011).

  5. Physics

    Filling in Gaps

    1. Jelena Stajic

    Since the discovery of iron-pnictide superconductors 3 years ago, considerable progress has been made in understanding their properties, but the basic mechanism of pairing responsible for superconductivity has yet to be agreed on. The momentum-space structure of the superconducting gap has the potential to shed light on this important question, and one of the most reliable ways to extract it is angle-resolved photoemission spectroscopy (ARPES). So far, ARPES has been used to map the superconducting gap in the momentum plane corresponding to the parallel layers of FeAs in these compounds; now, Xu et al. use variable-energy ARPES to probe the three-dimensional gap function in a representative compound Ba0.6 K0.4Fe2As2. On all five Fermi surfaces, they find a nodeless gap function that disperses in the c-axis direction and is characterized by a single pair of energy scales, one corresponding to intra- and the other to interlayer coupling. Intriguingly, the ratio of these energy scales (the gap anisotropy) is similar to the ratio of magnetic exchange couplings in the corresponding directions, suggesting that antiferromagnetic fluctuations may be driving the pairing in this compound.

    Nat. Phys. 7, 10.1038/nphys1879 (2011).

  6. Climate Science

    Seasonal Sink

    1. H. Jesse Smith

    It is widely understood that the Southern Ocean (all of the ocean south of about 30°S latitude) is a net sink for atmospheric CO2, but estimates of how much CO2 it removes from the atmosphere vary widely, mostly due to a lack of sufficient observational constraints, particularly in the Southern Pacific. In order to quantify and characterize CO2 uptake in that region, Barbero et al. measured CO2 partial pressure and a variety of other parameters related to CO2 dynamics in the surface ocean of the Pacific Subantarctic Zone (approximately 40°S to 55°S) on four cruises conducted between 2004 and 2006 and with instruments on surface drifters. From these measurements, they were able to describe the variability in air-sea CO2 exchange on a basin-wide scale, as well as the relationships observed between CO2 parameters, ocean mixed-layer depth, and temperature—information that helped them construct a better dynamical picture of the CO2 exchange occurring there. They found that the Pacific Subantarctic Zone is a CO2 sink during spring and summer and is close to equilibrium or is a weak source during the winter. On an annual basis, the Pacific Subantarctic Zone is a sink for atmospheric CO2 but a weaker one than previously suggested. More of this type of work is needed to determine the finer-scale details of CO2 uptake by the Southern Ocean.

    Global Biogeochem. CyC. 25, 10.1029/2010GB003818 (2011).

  7. Development

    Anther Development Dissected

    1. Laura M. Zahn
    CREDIT: THINKSTOCK.COM

    Anthers are the male reproductive organ of flowering plants. Unlike in animals, they originate from somatic tissue, of which a small subset of cells undergoes meiosis and develops into pollen. Kelliher and Walbot used confocal microscopy to dissect the developmental stages of the maize anther (located in the tassel at the top of the plant) to provide a timeline of anther development and maturation, from organ initiation to pollen release. They found that cell growth was regulated by neighboring tissues and that cells within the same tissue grew at different rates and within different dimensions. Of interest, although cell sizes differed, cells of similar size clustered together. This indicates that cells of the same genetic origin may undergo synchronous division. These observations are in contrast to existing models, which suggest that anthers develop through growth waves. Future studies are needed to determine the mechanisms that regulate the asymmetrical growth in neighboring cells of the same tissue, and what its function may be.

    Dev. Biol. 350, 32 (2011).

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