This Week in Science

Science  24 Jan 1997:
Vol. 275, Issue 5299, pp. 453
  1. What's next in climate models

    Successful weather forecasting and climate simulation depend on the parameterization of land-atmosphere interactions in atmospheric general circulation models. In recent years, much progress has been made toward a realistic representation of the energy, water, and carbon exchange between biosphere and atmosphere, aided by improved data from field experiments and satellite studies. Sellerset al. (p. 502) review the progress from the early, first-generation models to modern, sophisticated third-generation models, and present an outlook on the future of climate modeling and especially modeling climate change.

  2. Mantle duet

    Two reports probe the dynamics of the phase transition at a depth of about 660 kilometers separating the upper and lower mantle. Wang et al. (p. 510) suggest that the transformation of olivine in the upper mantle to magnesiowüstite and perovskite, which characterize the lower mantle, is blocked at temperatures below about 1000 kelvin. This result may provide estimates of temperatures in subducted slabs. Funamori et al. (p. 513) examined the transformation of garnet, which is the host of most of the aluminum in the upper mantle, to perovskite. Their data suggest that perovskite is also the host for aluminum in the lower mantle.

  3. Iron oxide core

    While chemists try to find more economical ways to convert natural gas to liquid fuels, the bacterial enzyme methane mono-oxygenase converts 1 billion tons of this greenhouse gas to methanol each year. Shu et al. (p. 515) present spectroscopic evidence that the key oxidizing species is an Fe2.(μ-O)2 core that forms a diamond structure.

  4. Tracing early crust

    When continental crust forms from the mantle, the composition of the remaining mantle changes. One key trace element ratio for inferring the amount of crust that has formed is the niobium/uranium ratio because continental crust sequesters U more strongly than it does Nb. Sylvester et al. (p. 521) measured this ratio in 2.7-billion-year-old volcanic rocks in Australia to infer the amount of crust that formed early in Earth's history. One interpretation of the data is that large amounts of crust had formed by this time, as also discussed by Hofmann in a Perspective on p. 498.

  5. Control of cell division

    The transcription factor NF-κB regulates genes that participate in the cellular response to stress and infection, generation of certain cancers, and control of HIV gene expression. Perkins et al.(p. 523) show how activation of NF-κB may be coupled to control of the cell division cycle. NF-κB associates with a transcriptional co-activator called p300; p300 in turn interacts with cyclin-cyclin-dependent kinase (CDK) complexes that regulate progression through the cell cycle. Inhibition of cyclin-CDK activity increased NF-kappaB-dependent gene expression. The interactions of proteins in these complexes apparently provides coupling of transcriptional regulation to control of the cell cycle.

  6. Tumor therapy: The clot thickens

    Tumors must have an adequate blood supply to sustain their growth, and strategies aimed at interrupting this blood supply are being explored as possible cancer therapies. Huang et al. (p. 547; see News story on p. 482) have used antibody technology to target a shortened form of tissue factor, a protein that helps initiate blood clot formation, to tumor blood vessels. Treatment of tumor-bearing mice with the targeted tissue factor produced clots in the tumor blood vessels, and the resultant blockage caused complete regression of the tumors in over one-third of the mice.

  7. A beneficial infection

    The symbiotic interaction between rhizobia and legumes begins with an infection of plant by bacterium. Some of those infections go on to develop into the nodules that are critical for nitrogen fixation. Penmetsa and Cook (p. 527) have identified a mutation that limits the ability of a plant to control the persistence of rhizobial infections but evidently does not affect susceptibility to initial infection. Plants carrying the mutation, sickle, are defective in the perception of ethylene and generate an excessive number of nodules.

  8. Impotent immunocytes

    Mittrücker et al. (p. 540) show that mice deficient in the transcription factor IRF4 (formerly known as LSIRF) have difficulty in mounting both humoral and cell-mediated immune responses: serum immunoglobulin levels are low and antitumor responses are lacking. The precise nature of the defect is unclear but it affects both T and B cells. Lymphocytes appear to develop normally in young animals but continue to accumulate in lymphoid organs, causing lymphadenopathy, while failing to be activated upon challenge. These findings, which would not have been predicted from previous studies of IRF4, may provide a new opportunity to study the thorny problem of lymphocyte homeostasis.

  9. Still life in action

    During development, axons extend from the neuronal cell body to the target, where the axon terminal changes to form synapses. Sone et al.(p. 543) screened Drosophila for mutations in which this process is defective. Mutations of the Still life protein showed abnormal motor activity, as well as defects, in both axon extension and synapse development. The still life gene encodes a guanine nucleotide exchange factor that is localized in the synaptic terminals, where it affects the actin cytoskeleton.

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