Editors' Choice

Science  06 Jul 2012:
Vol. 337, Issue 6090, pp. 14
  1. Ocean Science

    Going Up

    1. H. Jesse Smith
    CREDIT: ASSOCIATED PRESS

    Models of dynamic sea-level rise have demonstrated that sea-level increases caused by global warming will not be the same in all locations, because changes in ocean circulation, temperature, and salinity; the redistribution of mass owing to the melting of ice sheets; and the resulting changes in the shape and rotation of Earth all affect the regional expression of sea surface height. These models predict that one region in which sea level should rise most rapidly is along the northeast coast of the United States. Sallenger et al. examined tide gauge records from around the entire perimeter of the county, finding that such a hot spot already exists and that the rate at which sea level is rising there is three to four times the global average, consistent with model predictions. The rise is also correlated to the rate of melting of the Greenland ice sheet, in concert with a slowing of deep circulation in the Atlantic.

    Nat. Clim. Change 2, 10.1038/NCLIMATE1597 (2012).

  2. Ecology

    Don't Discount the Deep

    1. Sacha Vignieri

    The deep sea is one of the least-known regions on Earth. Its inaccessibility, however, should not be equated with a lack of biological relevance. Deep-sea corals, often referred to as cold-water corals (CWCs), are a case in point. Tropical coral habitats are known for their diversity, and they provide essential ecosystem functions for many marine taxa. As a result, they receive substantial conservation consideration. It has been suggested that CWC systems are also important biodiversity hot spots and may serve as essential fish nurseries, but without direct evidence, their protection is minimal. Baillon et al. searched marine research trawls conducted over 5 years off the eastern coast of Canada for evidence of a fish nursery role for CWCs. They found fish embryos associated with five species of sea pens and used genetic data to identify them as belonging to several species, including two species of redfish (Sebastes spp.), which are commercially important and listed as either endangered or threatened in Canada. Although much remains to be learned about CWC systems, these results confirm that they act as fish nurseries. Furthermore, they suggest that like tropical coral systems, CWCs deserve serious conservation and policy consideration.

    Front. Ecol. Environ. 10, 10.1890/120022 (2012).

  3. Cell Signaling

    Keeping a Lid on Signaling

    1. L. Bryan Ray

    Keeping growth factor receptors turned off when appropriate is just as important as proper activation by ligand binding. This is demonstrated by the developmental abnormalities and cancer-promoting effects ascribed to the uncontrolled activity of such receptors. Lin et al. propose a mechanism by which cells may be protected from unwanted phosphorylation of targets by the fibroblast growth factor receptor (FGFR), a receptor tyrosine kinase. The adaptor protein Grb2 is normally thought to promote receptor signaling by binding to phosphorylated residues on the receptors and interacting with other signaling proteins. In cultured human cells transfected with FGFR, however, Grb2 associated with unstimulated FGFR and was required for a basal amount of autophosphorylation of the receptor. Such basal phosphorylation appeared not to activate signaling, however, because the bound Grb2 sterically inhibited further receptor autophosphorylation. The authors propose that when the receptor becomes stimulated by its ligand, Grb2 itself is phosphorylated by the receptor, resulting in its release and relief of its inhibitory effect on receptor signaling.

    Cell 149, 1514 (2012).

  4. Astrophysics

    Textures in the Sky?

    1. Maria Cruz
    CREDIT: NASA/WMAP SCIENCE TEAM

    Theories of high-energy physics predict that topological defects formed in the early universe as a result of symmetry-breaking phase transitions. As the universe cooled and expanded, it underwent phase changes in which the different forces decoupled and the symmetries between elementary particles broke. These transitions did not happen in the same way everywhere in the universe, and as misalignments in the arrangement of atoms lead to defects in crystals, misalignments in symmetry breaking led to cosmic defects. Textures are one of the types of defects predicted by theory and should generate characteristic hot and cold spots in the oldest image we have of the universe—the cosmic microwave background, emitted when the first atoms formed 13.7 billion years ago. To test these predictions, Feeney et al. used state-of-the-art Bayesian methods to analyze full-sky microwave background data from the Wilkinson Microwave Anisotropy Probe. They show that these data are consistent with the absence of cosmic textures and rule out any theories that predict more than six detectable textures on the full sky. Data from the Planck satellite may soon provide better constraints. If detected, these features would probe physics at energies much higher than those that can be reached at the Large Hadron Collider.

    Phys. Rev. Lett. 108, 241301 (2012).

  5. Chemistry

    Four Different Corners

    1. Jake Yeston

    Photochemical dimerization of olefins can yield a wide variety of symmetrically substituted cyclobutane derivatives. The bigger challenge is generating a carbon square with a different substituent at each corner. Two different olefins can pair up with each other in multiple distinct combinations and orientations, risking a messy mixture. Yet nature appeared to have overcome the obstacles in a class of compounds isolated recently from the plants that produce black pepper. Two studies demonstrate complementary synthetic routes to these tetrasubstituted cyclobutanes. Gutekunst et al. used photochemistry at the outset, but in an intramolecular context, to bias the relative olefin orientations and set two distinct opposing corners. This left unsubstituted CH2 centers at the remaining corners, and the authors applied direct palladium-catalyzed vinyl and aryl iodide additions to establish the basic skeleton before functional elaborations. Liu et al. skirted photochemistry altogether, setting three corners by expanding a triangular cyclopropane precursor outward to a pendant carbene center. This yielded a cyclobutene poised for rhodium-catalyzed conjugate addition of an arylboronic acid to set the final corner. Close comparison of these products to the natural isolate revealed that the pepper plant was actually synthesizing an isomer with a six-membered (rather than four-membered) ring.

    Angew. Chem. Int. Ed. 51, 10.1002/anie.201203897; 10.1002/anie.201203379 (2012).

  6. Ecology

    Drivers of Diversity

    1. Andrew M. Sugden
    CREDIT: ISTOCKPHOTO

    Large-scale biogeographic patterns of species diversity are generally attributed to the effects of regional climate, climatic history, and other physical factors such as topography. Greve et al. now report a case where continental-scale diversity patterns appear to also be influenced by biotic factors. In Africa, the diversity of acacia trees reaches its highest levels in East Africa and the Limpopo Basin, and the species richness of browsing herbivores (herbivores that use acacias as a food source) is the best explanatory driver of this pattern. The mechanism behind this association remains uncertain; however, one possibility is that decreased fitness and decreased competition of trees under heavier pressure from browsers could lead to greater opportunities for the coexistence of multiple tree species. If consumer diversity has indeed contributed to acacia diversity, the conservation and retention of large herbivores in the African landscape may ultimately be important to the persistence of a diverse tree community.

    J. Ecol. 100, 10.1111/j.1365-2745.2012.01994.x (2012).

  7. Molecular Biology

    Mighty Miniscule RNAs

    1. Guy Riddihough

    An ever-increasing number of small RNAs—ranging in size from ∼20 to 400 nucleotides (nt) in length—are being found that regulate gene expression in both prokaryotes and eukaryotes. A class of tiny RNAs, known as nanoRNAs because of their minuscule size (∼2 to 4 nt), have previously been shown to prime transcription initiation in vitro by being directly incorporated into a target transcript.

    By overexpressing the “nanoRNases” oligoribonuclease (Orn) and NrnB, Vvedenskaya et al. were able to reduce the levels of nanoRNAs in Escherichia coli to demonstrate that for specific genes, the tiny RNAs can influence transcription start-site selection during stationary phase growth. The nanoRNAs were also able to regulate some of these genes (tomB and bhsA), stimulating their levels during stationary-phase growth. Genome-wide analysis indicated that the promoters of many of the genes sensitive to growth phase–dependent nanoRNA-mediated start-site control have a specific sequence element that determines, in part, whether the promoter will be targeted by nanoRNA-mediated priming. NanoRNAs might stimulate de novo transcription initiation, or they could increase RNA stability through the addition of a U and/or a hydroxyl (both characteristic of nano RNAs) to the 5′ end of the RNA.

    Gene. Dev. 26, 10.1101/gad.192732.112 (2012).

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