This Week in Science

Science  15 Feb 2002:
Vol. 295, Issue 5558, pp. 1189
  1. In Brevia

    Data from miniaturized Global Position Satellite tracking devices, attached to wandering albatrosses residing on an island in the southern Indian Ocean in a study by Weimerskirch et al. (p. 1259), reveal their flight patterns and foraging behavior.

  2. Shocking Images

    In most gasoline or diesel engines, fuel is pressurized and sprayed into the engine so it is rapidly dispersed with the oxidant. Optimizing this process is critical for fuel and engine efficiency, yet it has been difficult to examine the dynamics of such sprays in sufficient detail to optimize designs rationally. MacPhee et al. (p. 1261) now show that synchrotron x-radiography can reveal the high-speed dynamics of high-pressure sprays. Their analysis shows that for conditions typical of many engines, a shock wave develops and propagates in the spray.

  3. Early Rise of Human Behavior

    Anatomically modern human specimens have been found in sub-Saharan Africa as far back as 100,000 years. When behaviorally modern humans developed, as evidenced by abstract or symbolic art, has remained controversial. Some archaeologists have argued for a late and rapid development of behavior about 40,000 to 50,000 years ago in the European Upper Paleolithic and sub-Saharan African Late Stone Age, but others argue for an earlier and more gradual development starting in the African Middle Stone Age. Henshilwood et al. (p. 1278; see the news section on human evolution and the 11 January news story by Balter) discovered two pieces of ochre with geometric patterns, which they interpret as symbolic artwork, in Blombos Cave, South Africa. Thermoluminescence dating of the rock deposits and associated burnt lithic fragments indicates the ochre pieces are about 77,000 years old, belonging to the Middle Stone Age and supporting an earlier and gradual rise of human behavior in sub-Saharan Africa.

  4. Southern Warmth

    The Southern Ocean mixes water from the Pacific, Atlantic, and Indian Oceans in the fast-flowing Antarctic Circumpolar Current, and thus is considered to be a good integrator of conditions in the world's oceans. Gille (p. 1275) compared temperature measurements for Southern Ocean waters at depths of 700 to 1100 meters in the period between 1930 and 2000. They found that water temperatures in this region increased nearly twice as much as that of the average global ocean between 1950 and 1990. This increase is comparable to the amount atmospheric warming in the Southern Hemisphere during that period and is more precisely defined than average surface air temperature. Measurements of mid-depth of Southern Ocean water could be useful for tracking the progress of warming south of the equator.

    CREDIT: GILLE
  5. Mantle Flow: Old or New?

    The overall flow of mantle material in a preferred direction tends to align the olivine grains along one axis that can be revealed as an anisotropy in electrical conductivity. Bahr and Simpson (p. 1270) measured the anisotropy of electrical conductivity beneath Australia and the fast-moving Australian plate and beneath Fennoscandia and the slower-moving Eurasian plate. They found a greater degree of olivine grain alignment in the mantle beneath Fennoscandia, which indicates that the flow is dominated by mantle convection independent of plate motion or that the flow is a fossil remnant of older and faster Eurasian plate motion. Either mechanism provides useful estimates of mantle dynamics, such as relaxation times and convective flow patterns.

  6. High Humidity

    Increases in stratospheric water vapor may contribute to global temperature trends and also interfere with the recovery of polar ozone by strengthening destruction mechanisms. The concentration of water vapor in the stratosphere has approximately doubled in the last 50 years and the only known mechanism (the oxidation of methane) for producing water accounts for only half of this increase. Sherwood (p. 1272) examined nearly two decades of recent satellite data and found that stratospheric moisture variations can be traced back to relative humidity changes near or below the tropical tropopause. These changes appear to be influenced by the size distribution of ice crystals lofted in deep convective updrafts. A contributing factor could be the accelerating rates of tropical biomass burning, which produces the small aerosols required for this proposed mechanism.

  7. Conservation by Land and by Sea

    A quarter of the world's coral reefs are now seriously degraded by human activity, and many more are highly threatened. Using data on the distribution of 3235 reef species, Roberts et al. (p. 1280) pinpoint the hotspots of reef degradation and biodiversity and investigate how conservation action might be targeted to where it is most needed. A striking concordance is seen among terrestrial and marine biodiversity hotspots: Many marine hotspots are adjacent to or overlap terrestrial biodiversity hotspots, indicating an opportunity for developing integrated terrestrial and marine conservation strategies.

  8. Chirality Enhancement on Films

    A key question for those interested in the origins of life is whether a racemic mixture of molecules can react to form chiral polymers. Zepik et al. (p. 1266) studied three analogs of lysine and glutamic acid that were modified to give them an amphiphilic nature and then deposited as racemic monolayers onto a water surface. Disordered monolayers formed oligomers with random or binomial distributions. However, for ordered monolayers, a racemate in which nearest neighbors were of opposite configuration favored alternating oligomers, and racemates in which nearest neighbors were of the same configuration favored homochiral oligomers. This finding is somewhat surprising given the slow diffusion of molecules within the monolayer surface and the need for the growing oligomer to fit within the crystalline structure of the monolayer.

  9. Programmed or Plastic?

    In vertebrates, cranial neural crest cells specify the bone and connective tissues of the head. In classical experiments involving the chick embryo, portions of the chick hindbrain, which specified the first arch skeletal derivative, were transplanted to posterior locations in the hindbrain. This transplanted material continued to give rise to duplications of the first arch, despite its new location, which suggested that the neural crest is pre-programmed to make specific head structures. However, subsequent analyses have indicated that the neural crest is more plastic. Trainor et al. (p. 1288) now show that the inclusion of the midbrain/hindbrain junction in the grafts is sufficient to account for duplication of first arch structures and that fibroblast growth factor 8 from the isthmus results in this duplication.

    CREDIT: TRAINOR ET AL.
  10. Maintaining Even Distributions

    Distributing adhesive contacts evenly around the cell periphery may require a signaling pathway that depends on the small guanosine triphosphatase (GTPase) Rap1. Knox and Brown (p. 1285) reveal that loss of Rap1 function in Drosophila epithelial tissue caused unequal distribution of adherens junctions and disrupted normal cell migration. Rap1 was also enriched at the junction between newly divided sister cells. The GTPase may link junctional complex proteins to signaling pathways that regulate cell-cell contacts and possibly changes in cytoskeletal tension that are critical to cell mobility and division.

  11. Doing Double Duty

    Regulation of the cell cycle involves the nedd8 ubiquitin-like modification of key proteins. Kurz et al. (p. 1294) now find that these modifications are also important in controlling the cytoskeleton in Caenorhabditis elegans embryos. Nedd 8 conjugation inhibits microfilament contraction in the cell cortex during pronuclear migration and again during cytokinesis. In addition, katanin, a microtubule-severing complex, is degraded after neddylation at the end of meiosis.

  12. AIDing Immunological Diversity

    The phenomenal diversity of the antigen receptor genes arises in part from their assembly by V(D)J recombination, and three distinct processes generate still further diversity of the rearranged immunoglobulins. The rearranged V segments are subject to somatic hypermutation and gene conversion, and class switching changes the effector function of the immunoglobulins. Activation-induced deaminase (AID), a protein predicted to be involved in RNA editing, has been shown to regulate the activity of both somatic hypermutation and switch recombination. Arakawa et al. (p. 1301; see the Perspective by Fugmann and Schatz) now show that immunoglobulin gene conversion is also regulated by AID, indicating that somatic hypermutation and gene conversion are likely initiated by the same event. Thus, AID appears to be a master regulator of all three processes.

  13. Potent Antimalarial Agent

    Within human beings infected with malaria, the asexual stages of Plasmodium falciparum reside in red blood cells. Unlike their host cells, the parasites synthesize large amounts of membrane, probably to assist nutrient uptake. Wengelnik et al. (p. 1311; see the news story by Taubes) have been working on ways to inhibit parasite phospholipid biosynthesis that have focused on using structural mimics of choline. The lead compound, G25, was tested in monkeys with heavy infections of P. falciparum and P. vivax (5 to 14% parasitized erythrocytes). They were able to cure the monkeys after intramuscular treatment without recrudescence up to 60 days later. G25 cures monkeys of malaria at doses far below those used for current antimalarials and is effective in mice infected with parasites that are resistant to the drugs currently in use.

  14. Protons Through Ice

    Protons diffuse rapidly through liquid water, but in ice, molecular diffusion dominates at ambient pressures. Protonic diffusion processes could be of importance in planetary interiors where ice exists at high temperature and pressure. Katoh et al. (p. 1264) measured protonic diffusion coefficients for ice VII at 400 K and pressures of 10 to 63 gigapascals. They placed a block of D2O next to one of H2O and then measured changes in the O-D and O-H stretches. Oxygen isotope measurements confirmed that no molecular diffusion occurred under these conditions.

  15. Pull TAB1 to Activate

    Members of the mitogen-activated protein kinase (MAPK) family control a wide range of cellular processes and are regulated as part of a cascade of protein kinases that are activated by sequential phosphorylation. Thus, MAPK kinases phosphorylate MAPKs on specific threonine and tyrosine residues, which leads to activation of the MAPK. Ge et al. (p. 1291; see the Perspective by Johnson) now show that there is another way to activate the so-called stress-activated MAPK known as p38α. They isolated proteins that interacted in a yeast system with human p38α and found TAB1 [transforming growth factor β-activated protein kinase 1 (TAK1)-binding protein 1], a protein previously implicated in activating a different protein kinase, TAK1. TAB1 directly interacted with p38α and thereby enhanced autophosphorylation and activation of the p38α enzyme. Studies of signaling to p38α in cultured cells indicated that some stimuli activate p38α by the conventional kinase cascade, whereas others require the interaction with TAB1 and activation of p38α autophosporylation.

  16. Regulating Plant Steroids

    Plant hormones include small peptides, complex chemicals, and steroids known as brassinosteroids. Brassinosteroids regulate, among other aspects, the plant's response to light conditions, its growth habit, and flowering patterns. The signaling pathways controlled by brassinosteroids are likely to be complex and highly branched. Li and Nam (p. 1299) have cloned and analyzed the BIN2 gene, which encodes a protein that resembles the SHAGGY-type kinases well known for controlling a variety of metabolic pathways in Drosophila, yeast, and mammalian cells. The BIN2 protein product functions seemingly early in the brassinosteroid signaling response pathway, but just how closely linked its function is to the initial response of brassinosteroid and its receptor remains unclear.

  17. Tertiary Chromosome Structure

    Chromosome structure has been a topic of study ever since the early days of light microscopy, and the pattern of light and dark bands in Giemsa-stained preparations is familiar from introductory biology courses. In complementary fashion to these low-resolution observations, genome-sequencing projects have generated primary structural information, and crystallographic studies have provided views of the nucleosome, which may be equated with secondary or local structure. Dekker et al. (p. 1306) now describe a population-based method for global measurement of medium-range interactions within and between chromosomes. They apply this technique to yeast nuclei to follow chromosome movement during meiosis and to develop an averaged picture of chromosome III as a contorted horseshoe.

  18. Control Your Head

    Although there is substantial literature on the neurons and structures in the midbrain involved in the control of the eyes, little is known about the control of the head. Using electrical stimulation techniques and pharmacological deactivation, Klier et al. (p. 1314) show that the interstitial nucleus of Cajal in the midbrain controls not only torsional eye movements but also head movements. These results may also help to understand the etiology of disorders like torticollis.