This Week in Science

Science  23 Sep 2005:
Vol. 309, Issue 5743, pp. 1961
  1. Calling in the Bodyguards

    CREDIT: KOPPERT BIOLOGICAL SYSTEMS

    Plants attacked by herbivorous insect pests can bring out their own chemical defenses, but can also call in “bodyguards,” predators that prey on the first round of pests. Volatile compounds are important in this signaling triangle. Kappers et al. (p. 2070; see the news story by Pennisi) have now engineered Arabidopsis to produce the volatile compounds necessary to call in such bodyguards by targeting terpenoid metabolism.

  2. Keeping the Guests Apart

    Many proteins form remarkably intricate pocket structures to orient and direct molecular reagents. Simpler nanometer-scale enclosures can also be formed by self-assembly from molecules in solution through hydrogen bonding or coordination to metal centers. Dalgarno et al. (p. 2037) show that one such structure can encapsulate two polyaromatic dye molecules but keep them rigidly apart, as evidenced by x-ray diffraction in the solid state and fluorescence-quenching studies in solution. The rigidity seems to arise from π-stacking and CHπ interactions between the guest molecules and the capsule walls.

  3. Roomy Solids

    Metal-organic framework compounds, which can have high surface area and useful gas storage capabilities, are normally held together by coordination to single metal centers. Recently, it was shown that hydrothermal synthesis of Cr ions, organic dicarboxylates, and fluorhydric acid produced porous frameworks anchored by inorganic trimers that are linked into large supertetrahedrons. Férey et al. (p. 2040; see the Perspective by Hupp and Poeppelmeier) now report the computational design and synthesis of a related compound based on Cr ions and terephthalate that is stable up to 275°C and adopts a zeotype cubic structure with a giant cell volume (~702,000 cubic angstroms), as determined from an analysis of x-ray powder diffraction data. The network of extra-large pore sizes (diameters of 30 to 34 angstroms) leads to a very high nitrogen sorption capacity of nearly 6000 square meters per gram, and allows even large Keggin polyanions to be incorporated into the cages.

  4. A Very Long Wave

    The recent Sumatra tsunami that produced devastation around the Indian Ocean traveled several times around the globe before dissipating. This history is recorded in a global tide-gauge network, and Titov et al. (p. 2045, published online 25 August 2005) have used an ocean model to understand the global propagation of this tsunami. Large waves were recorded in places such as the coast of Peru, locally in Antarctica, and at Halifax, Nova Scotia, far from the earthquake, and with a very indirect path. The modeling suggests that the waves were in part guided by Earth's mid-ocean ridge system.

  5. Out of a Wetter Africa

    Between 3 million and 1 million years ago, the modern human genus Homo arose, Homo erectus appeared, and our ancestors migrated out of Africa. During this sequence of events, the general trend of African climate has been thought to be one of increasing aridity. Trauth et al. (p. 2051, published online 18 August 2005) now present a record of lake development and disappearance in rift basins from East Africa, the region from which most of the human fossils from that time comes. Three separate periods, each roughly 200,000 years in duration, were apparently wetter and caused the rift lakes to be deep and extensive.

  6. Carry-on Chromosome

    One approach to dissecting human diseases with multiple interacting loci has been to try and express large numbers of genes on human transchromosomal fragments or constructed artificial chromosomes in mice. Down syndrome (DS) depends on trisomy in chromosome 21, and several attempts have been made at recapitulating the disease through a transchromosomal approach. O'Doherty et al. (p. 2033; see the news story by Miller) report the germline transmission of a transchromosomal fragment carrying 91% of chromosome 21 genes. At least 58 of these were transcriptionally active and, although the fragment was not expressed uniformly in all somatic cells, the transchromosomal animals displayed a phenotype sharing similarities with DS, including behavioral and physiological abnormalities. The ability to transmit such a large human chromosomal fragment in mice should also allow the exploration of other complex genetic diseases.

  7. Ready to Jump

    CREDIT: HABENICHT ET AL.

    Many studies have followed the rebound of droplets hitting a solid surface, but Habenicht et al. (p. 2043) have isolated just the second half of this process. They used a laser to melt irregularly shaped gold nanoparticles. Formation of the melted droplet causes the center of mass of the particle to move away from the surface, and for sufficiently high fluences, the process is rapid enough to desorb the droplet with speeds on the order of 10 meters per second.

  8. Carotenoid and Retinal United

    Carotenoids provide antenna molecules that increase the spectral range over which light energy can be absorbed and subsequently transferred to chlorophylls for use in photosynthesis. Retinal is the light-absorbing chromophore in a family of proton pumps—the archaeal and bacterial rhodopsins. Balashov et al. (p. 2061) describe the intermingling of these two phototransduction pathways within the bacterium Salinibacter rubber. They find a 1:1 complex of the carotenoid salinixanthin and the retinal-containing protein xanthorhodopsin and show that light absorbed via the carotenoid is transferred to the retinal and used as an energy source for pumping protons across the cell membrane.

  9. Understanding Noise in Gene Expression

    Extensive variation among populations can be largely attributed to genetic differences. However, even when genetics are the same (as with identical twins or clonal populations of cells), variability still exists. Raser and O'Shea (p. 2010) review the level of variation in gene expression among cells measured as “noise” in gene expression and summarize the current understanding of the sources and consequences of noise as well as its regulation.

  10. Polypyrimidine-Tract Binding Protein Structures Revealed

    CREDIT: OBERSTRASS ET AL.

    Polypyrimidine-tract binding protein (PTB) is a eukaryotic protein that binds to UC-rich RNA substrates through four RNA binding domains (RBDs) and plays a key role in messenger RNA splicing. Oberstrass et al. (p. 2054) have determined the solution structures of the four RBDs each bound to a pyrimidine tract. Each domain has a distinct specificity, and the third and fourth domains interact so that their bound RNAs are antiparallel. Thus, RBD34 can bind two pyrimidine tracts in the same RNA only if they are separated by a linker sequence and can induce RNA looping to regulate alternative splicing.

  11. Manipulating Muscle Satellite Cells

    Satellite cells of muscle are thought to provide progenitors for muscle repair and regeneration, but are rare and difficult to isolate. Montarras et al. (p. 2064, published online 1 September 2005) successfully isolated muscle satellite cells from a mouse line that expresses green fluorescent protein using flow cytometry. When satellite cells isolated from the diaphragm were grafted into muscles of the mdx mouse, a model for muscular dystrophy, the cells effectively supported repair of the muscle and establishment of resident satellite cells. However, in vitro culture of the satellite cells to expand their numbers did not improve efficiency of engraftment.

  12. A Toothy Problem

    In mammalian tooth development, epithelial enamel knots appear where cusps will develop in a species-specific manner, but the question remains whether enamel knots really exert a causal effect on cusp patterns. Kassai et al. (p. 2067) show how regulation of enamel knots has dramatic effects on cusp patterning. Ectodin, a recently identified bone morphogenic protein antagonist in tooth development, appears to provide a “negative” image of genes expressed in the enamel knots that give rise to cusps and integrates the induction and inhibition of enamel knots. The enamel knots of ectodin null-mutant mice were enlarged and altered cusp patterns so extensively that they resembled the teeth of the black rhinoceros.

  13. Ancient Linguistics

    Studying the relationship of languages has traditionally depended on recognizing “cognate sets” of word pairs matched across languages and reconstructing the changes in their sounds and meaning. However, because of linguistic erosion, this method is limited to a time depth of only 8000 to 10,000 years, but much human migration occurred before then. Dunn (p. 2072; see the Perspective by Gray) develop a method that uses the language structure, rather than vocabulary, to construct language phylogenies, and allows a much deeper sampling of linguistic time. Using features such as the ordering of sentence elements or the grammatical elements of gender or tense, they constructed phylogenies of Papuan languages in Island Melanesia that may have been separated since the late Pleistocene.

  14. Caught in the Flow

    Origination, release, and flow of fluids in sedimentary basins are responsible for oil and mineral deposits, and such processes can deposit mineral cements that form rocks from sediments. Dating these processes has been difficult because small samples are needed and because whole minerals need to be associated with specific fluids. Mark et al. (p. 2048) obtained Ar-Ar laser dates from zoned feldspar cements that contain sequences of fluid inclusions which recorded the temperature and composition of fluids in an oil basin north of Scotland. Migration of fluids preceded charging of oil into the basin by about 30 million years.

  15. Tweezing Out Protein Folding and Unfolding

    Many proteins populate partially structured intermediates early in their folding process, but are these “on-pathway” intermediates or do they represent distinct thermodynamic states? Cecconi et al. (p. 2057) have used optical tweezers to map the mechanical unfolding and refolding trajectories of individual ribonuclease H molecules. This 155-residue, single-domain protein unfolds in a two-state manner, but refolds through a thermodynamically distinct molten globule-like intermediate. A similar intermediate has been observed in bulk studies, which suggests that solution folding also proceeds through an obligatory and thermodynamically distinct intermediate.

  16. Two Ways to Skin a Cat

    Many bacteria sense environmental change (and change some phenotypic traits accordingly), but such sensing has a cost. Kussell and Leibler (p. 2075, published online 25 August 2005; see the Perspective by Jansen and Stumpf) suggest an alternative strategy that may be used when environmental change is infrequent to switch phenotypic traits at random. As the rate of environmental change increases, the cost of bearing variable phenotypes within a population (some of which may be slow growers) becomes too high to tolerate, and it becomes relatively cheaper to maintain a sensory apparatus and a variety of phenotypic options in all individuals of a population.

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