Editors' Choice

Science  12 Jan 2007:
Vol. 315, Issue 5809, pp. 162

    Upheaval Down Under

    1. Brooks Hanson

    New Zealand sits astride a transition from a west-dipping subduction zone toward the north (responsible for the volcanism of the North Island) to an east-dipping subduction zone toward the south. The transition forms a system of right-lateral strike-slip faults that have produced the dramatic topography of the South Island, as well as several large earthquakes. One of these was the 1855 magnitude 8.2 temblor on the Wairarapa Fault just east of the city of Wellington. Rodgers and Little remeasured offsets produced by this earthquake and conclude that the ground slipped by as much as 18 m, an enormous amount for a strike-slip fault. For comparison, the devastating 1906 San Francisco earthquake produced a maximum of about 6 m of slip at the surface. Furthermore, the earthquake extended laterally only about 150 km (versus 480 km for the 1906 quake). An earlier quake may have produced surface slip of 14 m. The authors explain the paradox of a huge slip and short surface rupture by suggesting that the Wairarapa Fault extends deep into the crust, connecting with the northern-dipping subduction zone at depth. — BH

    J. Geophys. Res. 111, B12408 (2006).


    Adapting to the Blow

    1. Marc Lavine

    Designing equipment to protect an individual from a collision or impact often requires compromises between safety and comfort. For example, seat cushions, armrests, or headrests need to be fairly soft and compliant to be comfortable, but under these conditions they fail to absorb much energy in a collision. Deshmukh and McKinley have designed a series of adaptive energyabsorbing materials using polyurethane foams impregnated with a magnetorheological fluid (MRF). An MRF consists of a suspension of micometer-sized magnetizable particles, which flow like water under normal conditions. When subjected to a magnetic field, however, the particles align with the field to form columns or aggregates that must be deformed or broken under flow; thus the field confers considerable stiffness. This adaptability is in turn transferred to the foam when an MRF coats the struts of its open cells, offering a means of stiffening upon stress. Application of magnetic fields in the 0-to-0.2 tesla range effectively modulated the energy absorbed by these composite foams by up to a factor of 50. A scaling model allowed the authors to express all of the response data on a single curve governed by only three parameters, a convenient framework for tuning the properties of the composite. Furthermore, they envision making similar composites using a shear-thickening fluid, which responds in accordance with its rate of deformation and so would not require a magnetic field to adaptively alter its properties. — MSL

    Smart Mater. Struct. 16, 106 (2007).


    A Fluke Migration

    1. Caroline Ash

    Parasites in the trematode family, which includes liver flukes and schistosomes, have fantastically complicated life cycles that often involve snails and other aquatic hosts, as well as birds and mammals that prey on the intermediate hosts. Mud snails are small estuarine species that can harbor the intermediate stages of many species of trematode. A century ago on the coast of California, the Japanese mud snail was accidentally introduced when oysters were imported; it can outcompete the native snails partly because it is victimized by fewer trematodes parasites—only three.

    Miura et al. have studied the population genetics of these traveling trematodes and have found a different itinerary for each. The most common North American species is also the most common one in northeastern Japan, whereas the rarest one was found only at Elkhorn Slough and at the original oyster source in Matsushima Bay. The third showed a striking level of genetic diversity, rarely seen in introduced species and probably due to its repeated re-importation by migrating shore birds. Before the accidental entry of its preferred host (native mud snails simply won't do), this trematode was merely a passenger in transit. — CA

    Proc. Natl. Acad. Sci. U.S.A. 103, 19818 (2006).


    Pinned Propeller

    1. Jake Yeston

    Many coordination complexes have been prepared with threefold symmetry. However, exploiting chirality in such compounds tends to be challenging, in some cases because labile ligands scramble their orientation about the metal center, and in others because there is no feasible means of asymmetric induction in the synthesis, which therefore affords a racemic product mixture that must be laboriously resolved. Most chiral catalysts instead rely on a twofold symmetric motif.

    Axe et al. have used an embedded ligand stereocenter to direct and enforce the threefold helical chirality of a tris(phenolate) titanium complex. Their tetradentate ligand consists of a central nitrogen atom bound through benzylic carbons to three alkyl-substituted phenol rings. One of these benzylic carbons also bears a methyl group in an enantiopure configuration. When the ligand reacts with a Ti(IV) precursor, the phenyl rings fan out in a propeller arrangement around the metal, and the methyl group induces a specific helical cant. Nuclear magnetic resonance spectroscopy confirmed exclusive formation of a single diastereomer in solution. The structure was likewise characterized in the solid state by x-ray crystallography. — JSY

    Org. Lett. 10.1021/ol062655w (2006).


    A Microbial Mystery

    1. Gilbert Chin

    One consequence of the widespread access to DNA sequencing machines and the accompanying proliferation of genomes and genes is a renewed focus on RNA. As the most labile and hard-to-handle biological polymer, it had been valued primarily as a carrier (messenger RNA and transfer RNA) of information or as a structural, and occasionally functional, macromolecule (ribosomal RNA). Noncoding RNAs of the micro and small interfering kinds have taken center stage recently, along with riboswitches, which exhibit small molecule-induced conformational changes that regulate gene expression.

    Puerta-Fernandez et al. have identified a large noncoding RNA (approximately 600 nucleotides in length) on the basis of a sequence that is highly conserved across 15 microbes that inhabit harsh environments (defined as extremes of pH, salt, or temperature). A consensus model of secondary structure reveals conserved regions within loops and bulges, suggesting that there are likely to be functional constraints on its tertiary structure, though what this function might be is a mystery. Nearby genes do not fall into a single type of metabolic pathway, but immediately downstream in 14 out of the 15 bacterial genomes is a putative membrane protein that may form a complex with this enigmatic RNA. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 103, 19490 (2006).


    Growing Old and Falling to Pieces

    1. Stella Hurtley

    Mitochondria are the powerhouses of the cell, yet experience a remarkably tumultuous life, repeatedly fusing with each other and then parting in a fissional process. This lifestyle seems to take its toll, and in aged cells, mitochondria are often found in pieces.

    Scheckhuber et al. examined mitochondrial morphology in yeast and in cells of a filamentous fungus as they aged. Young cells flaunted a filamentous network of mitochondria, whereas discrete mitochondria populated older cells. When mitochondrial fission was blocked, by deleting the mitochondrial fission protein dynamin-related protein 1, cells stayed younger longer and did not suffer the loss of fitness when compared to normally aging cells in other long-lived strains. It seems that reductions in mitochondrial fission can actually extend the life span of a cell, possibly by diminishing its susceptibility to mitochondria-induced apoptosis. Because similar mitochondrial dynamics are observed elsewhere, it will be interesting to see if reductions in mitochondrial fission can increase the healthy life span of other organisms. — SMH

    Nat. Cell Biol. 10.1038/ncb1524 (2006).


    Unstable Neighbors

    1. Paula Kiberstis

    Solid tumors may be conceptualized as a malignant mass of epithelial cells, but in fact they contain normal cells such as fibroblasts and the endothelial and smooth muscle cells that compose tumor blood vessels. The molecular conversations between malignant cells and these stromal cells can profoundly influence tumor growth; thus, stromal cells have become possible targets for cancer therapy. In contrast to tumor cells, stromal cells are widely believed to be genetically stable and hence would not be expected to develop resistance to therapy.

    Pelham et al. have investigated the possibility that tumor-associated stromal cells, like their malignant neighbors, acquire genetic alterations during tumor progression. They used high-resolution DNA copy-number analysis to study human breast and colorectal tumors that had grown in mice for 30 to 150 days, an experimental design that allowed the stromal components to be readily identified by virtue of their mouse origin. Surprisingly, the stromal cells had undergone amplification or deletion of several genes, some of which can plausibly be linked to tumorigenesis. The magnitude of the genetic changes suggests that clones of mutant host cells had been selected for during tumor establishment or progression. Whether these changes reflect a selective pressure placed on stromal cells by the tumor in order to invoke a favorable microenvironment or, conversely, a host-initiated selection of mutant stromal cells designed to suppress tumor progression is not yet clear. — PAK

    Proc. Natl. Acad. Sci. U.S.A. 103, 19848 (2006).