This Week in Science

Science  30 Nov 2001:
Vol. 294, Issue 5548, pp. 1785
  1. In Brevia ...

    The highly endangered North Pacific right whale (Eubalaena japonica) has changed both its habitat and prey during the last 50 years, according to Tynan et al. (p. 1894), and remains posed on the brink of extinction.

    Careful records kept on cloned cattle by Lanza et al. (p. 1893) reveal that the 24 adult cattle that survived from 110 pregnancies appear to be completely healthy, in spite of a higher-than-usual mortality rate during gestation and at birth.

  2. Photogenerating Triangular Silver Nanoprisms

    An important challenge in the solution-phase synthesis of nanoparticles is to control particle size and shape while maintaining a high overall yield of product. Jin et al. (p. 1901) show that spherical silver particles can be almost completely converted by visible light into thin triangular prisms with edge lengths of 100 ± 15 nanometers. The triangular shape of these nanoparticles leads to unusual optical properties, such as the presence of two distinct quadrupole plasmon resonances and Rayleigh scattering in the red, rather than in the blue as is typical for spherical particles.

  3. Rigidity in the Liquid Core

    Earth's outer core is composed of an iron-rich liquid, but differences in its chemistry and structure could have effects on core convection and nutation (the slight nodding of Earth toward the Sun as the Earth precesses on its axis). Rost and Revenaugh (p. 1911) have detected thin (about 0.2 kilometer) rigid zones at the top of the outer core and infer that these zones are mixtures of liquid iron alloys and solid grains of iron alloys and iron oxides.

  4. Tackling Ciguatoxin Synthesis

    Many marine fish are vectors for ciguatera neurotoxins produced by the dinoflagellate Gambierdiscus toxicus, which produce more than 20,000 cases of seafood poisoning in subtropical and tropical regions. The development of antibodies to these toxins has been hampered by the extremely low content of these poisons in fish. Hirama et al. (p. 1904; see the Perspective by Markó) now report the total synthesis of one ciguatoxin, CTX3C, through the convergent assembly of two comparably complex fragments.

  5. Polarizing Organic Frameworks

    Polar crystals, in which molecular dipoles align in one direction, should exhibit useful properties such as ferroelectricity and frequency doubling of light. Organic crystals offer the opportunity for the more rational design of bonding in the solid, but the dipoles of organic molecules tend to cancel in crystals and create nonpolar structures. Holman et al. (p. 1907) show that an organic host structure for the inclusion of guest molecules can be modified by using achiral banana-shaped bridging molecules to create a structure with an overall polarity. By properly choosing guest molecules, they can create crystals that exhibit second-harmonic generation of light.

  6. Hydrogen on Mars

    Molecular hydrogen on Mars, although a relatively minor species in the CO2-dominated atmosphere, stabilizes the chemistry of the atmosphere and soil and provides estimates of past water abundance. Krasnopolsky and Feldman (p. 1914; see the Perspective by Hunten) measured the H2 abundance of Mars' upper atmosphere using the Far Ultraviolet Spectroscopic Explorer (FUSE). They found that there is enough H2 to prevent the buildup of CO and O2 in the atmosphere, to explain the presence of hydrogen-based oxidants in the soil, and to suggest that Mars may have initially had more water (as a proportion of the planet's mass) than Earth.

  7. Revising CD8 Function

    Intestinal intraepithelial lymphocytes (IELs) reside at epithelial surface along the gut, and many members of this class of T cells express a homotypic form of the CD8α molecule whose role had been unexplained in the context of IEL biology. Leishman et al. (p. 1936; see the Perspective by Lambolez and Rocha) show that CD8αα homodimers interact specifically with a major histocompatibility complex-like molecule, termed TL, expressed on intestinal epithelial cells. When CD8αα engaged TL, cell division and cytokine production of antigen-specific IEL were increased, and other effector functions, such as cytotoxic activity, were inhibited. Thus, CD8αα may not act as a typical coreceptor but rather as a regulatory molecule that modulates that activity of intestinal T cells

  8. Managing Messenger RNA Traffic

    Two classes of proteins, receptors and adapters, recognize properly processed messenger RNAs (mRNAs), and facilitate their export through pores in the nuclear membrane in the cytoplasm. The adapters bind directly to the mRNAs, and the receptors interact with the nuclear pore complex (NPC) and the adapters. The multiplicity of potential protein-protein interactions has hindered efforts at assigning pairwise combinations of adapters and receptors, both of which must also be recycled through the NPC for repeated use (see the Perspective by Moore and Rosbash). Gallouzi and Steitz (p. 1895) have now developed cell-permeable peptides that inhibit pair-wise interactions between receptors and adapters selectively without perturbing the overall movement of mRNAs into the cell.

  9. Losses Coming from the Top Down

    Fragmentation of a natural habitat has been shown to create a community-level trophic cascade caused by the absence of predators. Terborgh et al. (p. 1923; see the Perspective by Diamond) show that for fragments of tropical forest created by the Guri dam project in central Venezuela, predator populations become unsustainable. Herbivores then become hyperabundant and severely suppress the recruitment of canopy trees, presaging wholesale degradation of the vegetation and loss of species diversity.

  10. Controlling Air Intake During Flight

    The tiny fruit fly, which has a diffusion-based respiratory system, must avoid excessive water loss during flight while maintaining sufficient gas exchange to fuel intense respiration. Is the opening of spiracles, which mediate gas exchange, tuned to match the intensity of force generation? To find out, Lehmann (p. 1926) glued individual female Drosophila to a support in a gas-tight chamber and indirectly measured spiracle opening by monitoring the release of water and CO2. The author interprets the results to indicate that the flies do not hold their spiracles open during flight as previously suggested, but somehow adjust the size of the spiracle opening to correspond to the fly's metabolic requirements.

  11. Watch a Virus Make Its Moves

    For many of us, early instruction in microbiology included watching a movie of Paramecia engulfing their prey. Seisenberger et al. (p. 1929; see the news story by Beckman) now provide us with a real-time fluorescence video recording of a single virus particle adhering to a cell, being taken inward via endocytosis, breaking through into the cytoplasm, and reaching the nucleus where the wholesale takeover of host functions begins. The unexpectedly rapid transit time is of special interest because this invader, adeno-associated virus, is a prime candidate for virus-based gene therapy approaches.

  12. G Proteins and Vesicle Trafficking

    Attenuating a cellular signal is just as critical as inducing it. For example, regulator of G protein signaling (RGS) proteins modulate the signaling output from receptor-coupled heterotrimeric G proteins. Zheng et al. (p. 1939; see the Perspective by von Zastrow and Mostov) have identified what has been an elusive RGS for the Gαs class of G proteins. Named RGS-PX1, it also contains a membrane-interacting PhoX domain whose presence suggests a link between G protein signaling and vesicle trafficking in cells.

  13. Lipids and Immunosuppression

    Mitogens and other stimuli to cells cause generation of the lipid phosphatidic acid (PA), which acts as a second messenger to promote various cellular responses. Fang et al. (p. 1942) identify a new target regulated by PA binding that appears to account for the mitogenic effects of the lipid. In cells treated with PA, the mTOR protein (so named because it is mammalian target of the immunosuppressant rapimycin), which is a phosphatidylinositol kinase-like enzyme, becomes activated. Stimulation of human cells with mitogens increased accumulation of PA and inhibitors of PA production inhibited signaling through mTOR. The results indicate that PA mediates the effects of mitogens to activate mTOR and that rapimycin may interfere with mTOR function by blocking binding of PA.

  14. How to Catch a Smell

    Lobsters capture odors with small hairy arrays in their antennules. Does the movement of these antennules disrupt the spatial pattern of odors? Koehl et al. (p. 1948) used laser light and high-speed video imaging to visualize fluorescent dye flow through these antennules and found that small spatial patterns of dye enter the receptor area with little initial disturbance during the fast downstroke of the antennule. The spatial patterns only get blurred during the return stroke and the subsequent pause.

  15. Surface Aging

    Planktonic foraminifera record both a “true” radiocarbon age and a “reservoir age” of the surface water, which contains a mixture of younger carbon acquired from the atmosphere and older carbon acquired from deeper water. Siani et al. (p. 1917; see the Perspective by Adkins) have determined reservoir ages of Mediterranean Sea surface water for the past 16,000 years by measuring the radiocarbon ages of planktonic forams contained in independently dated volcanic ash layers. Reservoir ages nearly doubled at about 14,000 years ago, which the authors relate changes in North Atlantic Ocean circulation that occurred at the beginning of the last deglaciation.

  16. Greater Circulation of Stem Cells

    Hematopioetic stem cells and the related progenitor cells are thought to reside largely in the bone marrow, although occasionally cells have been spotted in the circulating blood. Using surgically conjoined mice that share their blood circulation, Wright et al. (p. 1933) now show that hematopoietic stem cells and progentior cells move with remarkable agility between the bone marrow and the circulating blood. The results suggest that the number of stem cells in circulation might be greater than previously thought.

  17. Not Waiting for the Cut

    Some polypeptide growth factors are synthesized as precursors that are enzymatically cleaved before secretion. Lee et al. (p. 1945) report that certain neurotrophin precursors can be secreted and are biologically active. Secreted proneurotrophins stimulated distinct cellular responses through receptors that bind to mature forms of the factors as well. Proneurotrophins could also be cleaved extracellulary to generate mature forms. These observations may prompt a re-evaluation of the potential actions of other precursor proteins.

  18. Reserves Pay Dividends

    Marine reserves protected from fishing are usually not popular locally, but Roberts et al. now show (p. 1920) that reserves can have a beneficial effect on adjacent fisheries. Substantial increases in biomass, quantity, and size of fish were found in two reserves and in neighboring zones despite major differences between the two locations. In St. Lucia, reserves were designed to enhance artisanal, subsistence fisheries. They protect coral reef habitat and relatively sedentary fish species. In Florida, they have protected estuarine habitat, relatively mobile fish species, and supplied recreational fisheries with record-size fish.

  19. Role of Apoptosis in Pseudomonas aeruginosa Pneumonia

    Grassmé et al. (Reports, 20 Oct. 2000, p. 527) found that P. aeruginosa, a bacterium responsible for pneumonia and sepsis in susceptible individuals, induces extensive apoptosis of lung epithelial cells through interaction with the CD95/CD95 ligand system—and that the epithelial cell death conferred a survival benefit on infected mice. Hotchkiss et al. comment that the TUNEL method used in the study to demonstrate epithelial cell apoptosis “may yield false positives,” and that they were unable to confirm epithelial cell apoptosis in pneumonia using alternative methods. They also found that “extensive lymphocyte apoptosis … occurred in lung, spleen, and thymus during pneumonia”—a pattern that suggests, according to Hotchkiss et al., that “extensive lymphocyte apoptosis may … contribute to the accompanying immune suppression and mortality” of bacterial sepsis, irrespective of infection site. Grassmé et al. respond with results of additional, non-TUNEL tests that “confirm induction of apoptosis in lung epithelial cells by P. aeruginosa.” The difference between their results and those of Hotchkiss et al., they suggest, may lie in the fact that the two groups used bacteria in different growth phases. The full text of these comments can be seen at