This Week in Science

Science  12 Apr 2002:
Vol. 296, Issue 5566, pp. 213
  1. In Brevia

    Using the fruit fly Drosophila, Clancy et al. (p. 319) show that slowing of aging by a mutation in an insulin/insulin growth factor-like signaling pathway and by dietary restriction occurs through overlapping but distinct mechanisms of life-span extension.

  2. Cleaning Up Chlorophenols

    Chlorophenols have been used in many product formulations and are by-products of wood-pulp bleaching. Although a number of biological and chemical approaches have been developed to clean up these toxic compounds from the environment, most are either slow, ineffective at high pollutant concentrations, or can, in some cases, create other more toxic products. Sen Gupta et al. (p. 326; see the Perspective by Meunier) show that activation of hydrogen peroxide by iron catalysts that bear a tetraamidomacrocyclic ligand (TAML) can completely convert two of the most common of these pollutants, trichlorophenol and pentachlorophenol, to inorganic species (CO, CO2, and Cl) or to less harmful organic species on time scales of minutes under ambient conditions.

  3. More Differentiated Bodies

    Basaltic meteorites are thought to be derived from a parent body that differentiated early in the solar system to form a dense core, a silicate mantle, and a basaltic crust. Most of these parent bodies are planets or our own Moon, but one group, the eucrites, derives from the only known differentiated asteroid, Vesta. Yamaguchi et al. (p. 334; see the Perspective by Palme) measured an anomalous oxygen isotopic concentration in the recently recovered basaltic meteorite, Northwest Africa 011 (NWA011), which shows that it arose in a different region of the early solar system than did the eucrites. Thus, there may be other differentiated bodies (Vesta-like asteroids) orbiting in our solar system.

  4. Algae Fouls a Thermometer

    The uptake of strontium (Sr) during the crystallization of coral skeleton aragonite (calcium carbonate) is controlled thermodynamically, and thus Sr/Ca ratios should provide a reliable measure of estimating past sea surface temperatures (SSTs). However, calibrations derived from different studies can give temperatures that can disagree by as much as 5°C or more. Cohen et al. (p. 331; see the Perspective by Schrag and Linsley), in an attempt to identify possible sources of error in these types of measurements, report that algal symbionts are responsible for as much as 65% of the variation of the Sr/Ca of Astrangia poculata coral growing in coastal waters of New England. This finding suggests that a reexamination of this method will require additional care in sampling.

  5. From Winds to Rings

    A supernova, the final uncontrolled explosion and death of a star, leaves behind a highly luminous remnant of gas and ejecta that traces the stellar dynamics. Tanaka and Washimi (p. 321) performed a magnetohydrodynamic simulation of the 1987A explosion and reproduced the distinctive three-ring structure of SN 1987A. A wind-wind interaction occurred between the slowly expanding red supergiant and the rapidly expanding blue supergiant phases that preceded the explosion. A magnetic pinch, the twisting of the magnetic field lines caused by the winds and stellar rotation, enhances the wind-wind interaction.

  6. Shake and Make

    Construction of an integrated semiconductor device, such as a display, requires the assembly and interconnection of a large number of components. Jacobs et al. (p. 323) show that assembly processes used to combine centimeter-scale objects can also be applied to much smaller objects (∼300 micrometers). Light-emitting diodes (LEDs), which were formed on a single gold-coated surface, were immersed in solution with a flexible substrate that was patterned with a solder array. Under gentle agitation, the LEDs attached to the solder. The few defects that formed during the initial assembly could be readily corrected through a more vigorous agitation and a repeat of the initial deposition cycle. The process was demonstrated for both a 113-element and a 1600-element substrate. Although for the latter case the assembly was not perfect, in both cases the entire process was complete within a few minutes, which suggests that with optimization this process can be scaled up to form large devices.

  7. Cattle Called

    Despite the central role of cattle pastoralism in many African cultures, its origins have remained largely unknown. Hanotte et al. (p. 336; see the news story by Stokstad) used molecular data from a comprehensive sampling of the African continent's cattle populations to unravel different strands of genetic variation. The initial dispersal of the earliest cattle from an indigenous domestication center was followed by a secondary influx from the Near East and Europe. Two phases of Asian zebu introgression into African cattle populations also occurred, and the recent introduction of pastoralism to southern Africa proceeded via an eastern rather than western migration corridor.

  8. Expression Making the Difference

    Chimpanzees and humans share more than 98% of their genetic material, yet differ strikingly in morphology and cognitive ability. Enard et al. (p. 340; see the news story by Pennisi) explore how differences in the expression patterns of shared genes might account for such differences between the species. Using microarrays carrying 18,000 human complementary DNAs, they compare gene expression patterns in the brains, liver, and blood of humans, chimpanzees, and macaques. The differences in the expression patterns in liver and blood corresponded to the evolutionary distance between the species. However, in the brain there was a much greater difference in expression patterns between chimp and human than between macaque and chimp. The divergence between the chimps and humans was accompanied by an accelerated evolution of expression patterns in human brain.

  9. Going Against the Flow

    The mechanism of action of a drug already used for immunosuppression reveals a new level of regulation of lymphocyte migration. Mandala et al. (p. 346) show that the active form of the drug FTY720 becomes phosphorylated once administered and resembles sphingosine 1-phosphate, a lipid whose activation of cognate receptors has been implicated in modulating the immune response. The drug and lipid achieve immunosuppressive effects by inhibiting the circulation of lymphocytes in the body.

  10. Powering Up Muscle

    Endurance training enhances the oxidative capacity of skeletal muscle by stimulating the production of mitochondria, the organelles that supply fuel to cells. The molecular signals that mediate this adaptive process are not well understood. Through a study of transgenic mice that express a hyperactive form of calcium, calmodulin-dependent protein kinase IV (CaMKIV*) in their skeletal muscle, Wu et al. (p. 349) establish that calcium-regulated signaling pathways play a key in controlling mitochondrial biogenesis in muscle.

  11. Making Way for a Cluster

    The metalloenzyme nitrogenase catalyzes the reduction of unreactive atmospheric nitrogen into bioavailable ammonia. Nitrogen binds to the FeMo cofactor (FeMoco) cluster, which contains one Mo atom, seven Fe atoms, and nine S atoms. This cluster is synthesized in vivo and incorporated into the tetrameric MoFe protein. Schmid et al. (p. 352) describe the crystal structure of the MoFe protein isolated from an Azotobacter strain deficient in producing FeMoco. They observe a positively charged funnel of a size that would allow insertion of the negatively charged FeMoco, the last step in assembling a catalytically competent nitrogenase.

  12. Vaccine-Derived Polio in Hispaniola

    From July 2000 to July 2001, there were 21 cases of paralytic poliomyelitis, with two fatalities, in Haiti and the Dominican Republic. Kew et al. (p. 356; see the Perspective by Nathanson and Fine) show that these cases appear to have arisen from a type 1 virus shed by a vaccine about 3 years ago in Haiti, which then recombined with wild enteroviruses to regain virulence. Poor maintenance of vaccine coverage in these countries over the past several years (there were cases among teenagers) led to the epidemiological circumstances that allowed the recombinant virus to circulate among poorly immunized children. This outbreak sounds a warning for the careful development of immunization strategies and comprehensive monitoring of paralysis cases in the last stages of the global polio eradication scheme.

  13. Microbial Defense in Flies

    Two branches of innate immune response have evolved in Drosophila to recognize molecular patterns encoded either in fungi or in the cell walls of bacteria. Each activates distinct sets of genes encoding peptides with specific antimicrobial activity. Choe et al. (p. 359; see the Perspective by Khush et al.) investigated two mutant alleles (ird71 and ird72) that inhibited genes normally activated by the imd pathway by preventing the cleavage and nuclear translocation of the transcription factor Relish. The ird7 alleles mapped to a region of chromosome 3 containing peptidoglycan recognition protein (PGRP) genes and encoded truncations in PGRP-LC that could account for disruption of its function in each of the mutants. Phenotype rescue by transgenic overexpression of wild-type PGRP-LC in ird7 mutant flies and RNA interference analyses in cell lines confirmed that PGRP-LC is a critical component of the antimicrobial response of Drosophila.

  14. Molecular Moving Crew

    At the surface of a crystal, atoms will rearrange to form lower energy structures if there is sufficient thermal energy to overcome activation barriers. At low temperatures, the Cu(110) surface shows stable terraces or step edges, which at elevated temperature fluctuate in shape as the Cu atoms race across the surface. Rosei et al. (p. 328) show that using an organic “Lander” molecule, which is designed to have four legs and an elevated surface, the motion of the Cu atoms can be controlled. The Lander adsorbs Cu atoms to its surface and shuffles them from one step edge to another, thus forming atomic interconnects.

  15. The Roots of Ripening

    The gaseous hormone ethylene effects the ripening of certain climacteric fruits, such as tomatoes and bananas. Vrebalov et al. (p. 343; see the Perspective by Causier et al.) now provide insight into the regulatory steps that precede ethylene's involvement in ripening. It turns out that the long-known rin mutant of tomato, in which fruits fail to ripen, is the result of a chromosomal deletion that disrupts two neighboring genes and generates a chimeric transcriptional unit. Both genes contain a MADS-box, suggesting that the proteins they encode are transcription factors that share a familial resemblance. In their nonmutated state, one gene encodes an inhibitor of fruit ripening, and the other encodes a regulator of sepal and inflorescence development.

  16. Questioning the Evidence for Genetic Recombination in the 1918 "Spanish Flu" Virus

    In a molecular and phylogenetic analysis of the virus that caused the 1918 influenza pandemic, Gibbs et al. (Reports, 7 Sep. 2001, p. 1842) found evidence for a recombinant origin for the virus's hemagglutinin (HA) gene, and suggested that the recombination event, “which probably changed the virulence of the virus,” may have triggered the pandemic. Worobey et al., in a comment, conclude from an alternative phylogenetic analysis that “there is no evidence that the HA gene … had a recombinant origin” in this virus, and argue that the “apparent recombination” observed by Gibbs et al. actually stemmed from “a difference in the rate of evolution” between the globular domain and the stalk region of the HA gene. Gibbs et al. respond that the alternative proposal of Worobey et al., although interesting, is “not yet proven,” and offer several arguments in defense of the techniques and conclusions of the original study. The full text of these comments can be seen at