This Week in Science

Science  01 Nov 1996:
Vol. 274, Issue 5288, pp. 697
  1. Ice age in California


    Nevada.

    During the last glaciation, North American ice sheets periodically became unstable and discharged numerous icebergs. These Heinrich events are associated with rapid (1000-year) changes in air and sea surface temperatures recorded in the Greenland ice cores. Benson et al. (p.746) and Phillips et al. (p.749) show that similar rapid oscillations in climate occurred in the western United States and were roughly coeval with the Heinrich events. They correlate a detailed record of climate changes and local glacial conditions inferred from cores from Owens Lake in eastern California with variations in the extent of mountain glaciers in the Sierra

  2. Times to relax

    When supercooled liquids or polymers are perturbed externally, the return to the original unperturbed state occurs over a spread of relaxation times. This effect could arise through a heterogeneous response, with local domains relaxing at different times, or to an intrinsic complexity in an overall homogeneous response. Schiener et al. (p.752) present direct evidence for a heterogeneous response in the relaxation of supercooled liquids. By selectively modifying the dielectric loss spectrum, they show that spectral holes can be created, leading to characteristic changes in the dielectric response.

  3. STM-induced phase change

    A scanning tunneling microscope (STM) study of the surface of the 2H phase of TaSe2, a material that exhibits weak charge density waves (CDWs), revealed a surprising result. Zhang et al. (p.757) found that at 4.8 kelvin a low-voltage pulse induced a phase transition that produced surface nanocrystals of the 1T phase, which exhibits strong CDWs. The phase change could extend more than 100 nanometers, a distance much greater than that localized by the tip. The authors suggest that correlated motions of the top layer of Se atoms shift the Ta coordination from trigonal prismatic to octahedral.

  4. NO blocker

    Nitric oxide is a critical messenger molecule in many biological processes, and its activity is regulated by the enzyme that makes it, nitric oxide synthase (NOS). Jaffrey and Snyder (p.774) have identified a 10-kilodalton protein that binds to the neuronal form of NOS and inhibits its activity, most likely through destabilization of the active NOS dimer. This protein, called PIN, is one of the most conserved in nature and conceivably could regulate many processes through its dampening effect on NOS.

  5. NF-kappaB and apoptosis

    Tumor necrosis factor-α (TNF-α) is a major cytokine present at sites of inflammation and can induce cell death through apoptosis. Three reports by Beg and Baltimore ((p.782), Wang et al. (p.784), and Van Antwerp et al. (p.787) show that certain cells are more resistant to the apoptotic signal because TNF-α also stimulates the production of nuclear factor-kappaB (NF-kappaB) (see the news story by Barinaga, (p.724). Cells that were made deficient in NF-kappaB lost their resistance and underwent cell death. Specific inactivation of NF-kappaB may prove helpful in the design of more effective strategies for the treatment of tumors and chronic inflammation.

  6. Stealing equipment

    How bacterial pathogens invade cells of their hosts is not well understood. Ireton et al.(p.780) found that the invasion of cells by Listeria monocytogenes, a bacterium that can cause food-borne infections in humans, requires the activity of the host enzyme phosphoinositide 3-kinase (PI 3-kinase). It is not clear how PI 3-kinase or its products contribute to the invasion process, but the enzyme is implicated in control of the cytoskeleton, phagocytosis, and endocytosis. The invading bacteria may commandeer the host cells' own apparatus that is normally used for endocytosis to gain transport into the cell.

  7. Coordinating day and season

    The early-flowering (elf) mutants in Arabidopsis cannot coordinate flowering with changes in the length of days. Hicks et al.(p.790) found that daily rhythms of the elf3 mutants are also disrupted. Analysis of leaf movements and gene transcription showed that circadian rhythms in elf3 mutants persist normally in constant darkness but fail in constant light. The elf3 mutation thus indicates a point in common between mechanisms sensing day length and circadian rhythms.

  8. Overactive B cells

    Antibody production by B cells is initiated by antigen interactions with the B cell antigen receptor, which then sets off a cascade of protein tyrosine phosphorylation events. One surface glycoprotein that undergoes phosphorylation, CD22, is critical for controlling antigen responsiveness. O'Keefe et al. (p.798) show that B cells from the spleen of mice lacking CD22 respond to lower than normal antigen concentrations. They suggest that CD22 is a negative regulator of B cells that helps them respond to foreign antigens and avoid autoimmune responses

  9. Color chart

    Red-green color blindness comes in a variety of shades-the ability to discriminate color in deuteranomalous individuals ranges from almost normal to severely limited. From a molecular analysis of individual genes encoding the visual pigments, Neitz et al.(p.801) find that a specific aspect of the genetics serves to predict the behavioral outcome. The key lies in the amount of divergence between spectral sensitivities of the pigments in any one person. As the divergence that results from shuffling of the specific available mutations increases, the ability to discriminate color approaches normal.