Editors' Choice

Science  13 Oct 2006:
Vol. 314, Issue 5797, pp. 224

    The Advantage of Keeping Quiet

    1. Andrew M. Sugden

    The Hawaiian Islands have long been known as a natural laboratory for studying evolution. Zuk et al. have assessed the effect of the selective pressure of parasitoid flies on Teleogryllus field crickets introduced to the island of Kauai. Female flies locate male crickets when they call to female crickets, and lay their eggs on the cricket; the larvae burrow into the host and consume it from within, eventually killing it. Over just 20 generations, the singing males dwindled in abundance owing to the selective pressure from the parasitoid, and a new, silent type of male—known as flatwings—became prevalent. Given that the song functions as a signal to potential mates, how do the flatwing males attract female partners? Field experiments suggest that the silent males congregate around the few remaining singers, increasing the chance of intercepting inquisitive females (who have possibly relaxed their requirement that the male keep singing up to the moment of mating). Thus, natural selection has not only had a rapid population genetic effect; there has been a behavioral response as well. It remains to be seen, however, if the singing males are now too rare to support the local parasitoid population, or if the singing males will disappear entirely (and, if so, whether the crickets will find a new solution to the problem of finding mates). — AMS

    Biol. Lett. 2, 10.1098/rsbl.2006.0539 (2006).


    Glimpsing a Magnetic Carpet

    1. Joanne Baker

    The surface of the Sun is covered in a granular network of convection cells that are created as ultrahot gas wells up from below. Intense stirring causes magnetic dipoles to grow continually within the cells before being shed into the Sun's atmosphere. By analogy with a woven textile, this distribution of magnetic loops that thread the surface has been dubbed the magnetic carpet. Despite strong theoretical underpinnings, the observational evidence for such a process has been mixed.

    McIntosh et al. have marshaled a variety of observations from the SOlar and Heliospheric Observatory (SOHO) satellite to support the magnetic carpet model. They used ultraviolet images of the Sun dispersed into several spectral lines, including ionized silicon, neon, and carbon emissions, to trace the motions of gases at temperatures of tens of thousands to nearly 1 million K across many different cells. The gas velocities were strongest near the edges of the convection cells, and different patterns were observed in quiet Sun regions and coronal holes, consistent with the different magnetic field configurations in those environments. As the magnetic dipoles leave the cells, they release their energy through annihilation. By calculating the amount of energy released, the authors substantiate the importance of the magnetic carpet process in heating the solar corona. — JB

    Astrophys. J. astro-ph/0609503 (2006).


    Films from Clusters

    1. Phil D. Szuromi

    In the “atom by atom” growth mode of inorganic films, strain induced by the substrate can largely control the final morphology, dictating outcomes ranging from a smooth film to island formation. Carlier et al. have explored the consequences of delivering material to a surface as clusters rather than individual atoms. Beams of antimony clusters were tuned to peak at different average sizes—either 88 atoms (Sb88) or 300 atoms (Sb300)—and then directed toward a graphite surface. Both types of cluster formed fractal structures on this weakly interacting substrate, but when they were deposited sequentially, distinct morphologies resulted depending on the order of addition. The large clusters, if added second, filled in the center of an Sb88 fractal network. In contrast, the small clusters filled out the ends of a preformed Sb300 network. In the latter case, further deposition of the small clusters created instability, causing the initially thick end groups to flatten out and spread along the graphite in two dimensions. The authors suggest that this transition is triggered because the strain accumulating in the compact end groups eventually exceeds the surface energy cost of producing a flatter but more crystalline structure. — PDS

    Nano Lett. 6, 1875 (2006).


    Preludes to an Eruption

    1. Brooks Hanson

    The cataclysmic 79 A.D. eruption of Vesuvius buried Pompeii and Herculaneum, and thanks to careful observation of the event by Pliny the Younger, marked the beginning of the science of volcanology. Several million people now live on volcanic deposits surrounding Vesuvius, and it is one of the world's most thoroughly monitored volcanoes. Thus, understanding the pre-eruptive behavior of this volcano is crucial. Morgan et al. have analyzed the concentration profiles of barium across crystals in the 79 A.D. ash; the profiles reflect the time during which diffusion occurred in the magma between an abrupt phase of crystal growth or dissolution and the eruption. Because of the strong temperature dependence of the diffusion rates, the profiles also constrain the magma temperature. The data suggest that the eruptive magma was recharged several times in the decades leading up to the cataclysmic eruption, most noticeably around 20 years before. Such recharge may explain the origin of a major earthquake in 62 A.D. A separate intrusion likely triggered the eruption. — BH

    Geology 34, 845 (2006).


    Patterning at a Distance

    1. Ian S. Osborne

    Recent experimental work has shown that a metallic, quasi-two-dimensional electron gas (q2-DEG) can be formed at the interface region of two insulators such as LaAlO3 and SrTiO3 when the thickness of the upper LaAlO3 layer reaches a critical value of four unit cells. Because other high-mobility two-dimensional electron gases can be engineered to display a range of functional characteristics such as superconductivity, magnetism, and ferroelectric and multiferroic behavior at low temperature, there is interest in developing these oxide interfaces with the expectation of pushing such effects to higher temperature. However, because of the thinness of the upper oxide layer, conventional lithographic patterning techniques have proved detrimental to the interface properties.

    Schneider et al. achieve the critical thickness by lithographically patterning the q2-DEG without exposing or damaging the interface region during the process. They begin by depositing a LaAlO3 layer thinner than the critical threshold onto a SrTiO3 substrate, creating a temporarily insulating interface. Next they use a liftoff technique to add a thick patterned amorphous overlayer. LaAlO3 height in the gaps of the amorphous layer is then increased above the critical thickness to produce a patterned, high-quality metallic q2-DEG at the buried interface. — ISO

    Appl. Phys. Lett. 89, 122101 (2006).


    Cancer Stem Cells Lose Support

    1. Paula A. Kiberstis

    Acute and chronic myeloid leukemia (AML and CML, respectively) are maintained by populations of rare cancer stem cells that divide infrequently and therefore escape the effects of conventional chemotherapies that are designed to destroy rapidly dividing cells. Defining the properties of cancer stem cells and, in particular, identifying which of these might render the cells selectively vulnerable to therapy, are topics of great current interest.

    The normal stem cells that repopulate the hematopoietic system depend on interactions with stromal elements in their bone marrow microenvironment (niche) for survival and function. To explore whether cancer stem cells are similarly dependent, Jin et al. treated mice carrying human AML cells with an antibody to CD44, an adhesion molecule that is overexpressed on AML cells and that is involved in cell trafficking. Disruption of CD44 function markedly reduced the growth of leukemic cells in the mice, in part because the cells failed to migrate effectively to their bone marrow niche. Independent analysis of human CML stem cells by Krause et al. revealed a similar dependence on CD44. Importantly, in both studies, CD44 blockade had a preferential effect on cancer stem cells versus normal hematopoietic stem cells. These results suggest that certain leukemias may respond to treatments that disrupt the interaction of cancer stem cells with their supportive surroundings. — PAK

    Nature Med. 12, 10.138/nm1483 (2006); 10.138/nm1489 (2006).


    Developmental Fusogen

    1. Stella M. Hurtley

    Occasionally during development, two cells must fuse; for example, during the formation of muscle, myoblasts fuse with one another to form myotubes. This fusion of neighboring plasma membranes to form syncytia containing multiple nuclei must be very carefully regulated. The nematode Caenorhabditis elegans contains a number of syncytial tissues, and a protein termed EFF-1 is known to be a part of this fusion machinery. Podbilewicz et al. find by expression in heterologous cell lines that the EFF-1 transmembrane protein can drive the fusion of a variety of cells. The mechanism of fusion promoted by EFF-1 involves the formation of a hemifusion intermediate wherein the outer leaflets of the two plasma membranes merge before mixing of cytosolic components has occurred. For productive fusion to occur, the EFF-1 protein needs to be expressed at the surface of both partner cells, both in vitro and in intact worms. This homotypic interaction between proteins in two fusing membrane partners is a variant on the established themes in membrane fusion: In intracellular membrane fusion events, different proteins are needed in each membrane for successful fusion, whereas in virally mediated fusion, only one of the membranes needs to carry the fusogen. — SMH

    Dev. Cell 11, 471 (2006).

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