This Week in Science

Science  12 Sep 1997:
Vol. 277, Issue 5332, pp. 1581
  1. A long trip up the coast

    A large part of coastal British Columbia and Alaska has been suggested to have originated at low latitudes and migrated northward, but the primarily paleomagnetic evidence has been controversial because original inclinations (which give paleolatitudes of rocks) may have been altered or rotated. Ward et al. (p. 1642; see the news story by Kerr, p. 1608) identified a series of sedimentary rocks in Vancouver Island that are near horizontal and remarkably unaltered. Paleomagnetic data from these rocks indicate that the rocks were at the latitude of Baja California during the Cretaceous.

  2. Steadier light

    Convection in Earth's atmosphere refracts light and thus significantly reduces the resolution of astronomical observations. Max et al. (p. 1649) present a means to correct for this atmospheric distortion using observations of laser-produced sodium fluorescence in Earth's mesosphere. The approach improved two measures of resolution by about a factor of 2 and may allow ground-based telescopes to attain the diffraction limit.

  3. Smoke clouds

    The effects of aerosols and particles suspended in the atmosphere on the radiative properties of clouds have been difficult to quantitate; direct measurements are scarce, and the different effects involved are not readily isolated. Kaufman and Fraser (p. 1636) analyzed satellite data over South America to establish the dependence of climate forcing by smoke particles from biomass burning on the availability of water vapor. The results indicate that smoke increases cloud reflectance and allow an estimate of climate forcing by smoke clouds to be made.

  4. Playing several roles

    Human herpesvirus-8 is associated with Kaposi's sarcoma and appears to encode several proteins that resemble human cell signaling molecules. Kledal et al. (p. 1656) show that one of these proteins, vMIP-II, is unusual in its ability to act as a ligand—it can bind with high affinity to the human chemokine receptor CXCR4 and the structurally different receptors CCR5, CCR2, CCR1, and the cytomegalovirus-encoded receptor US28. In the presence of vMIP-II, the normal rapid movement of calcium from intracellular storage in response to chemokines did not occur and chemotaxis induced by RANTES was blocked. As CXCR4 and CCR5 are major co-receptors for entry of human immunodeficiency virus-type 1 into cells, vMIP-II may provide insight into new therapeutic candidates against AIDS.

  5. Life and lipids

    When cells are in the process of dying, their lipid metabolism changes. Some of the lipids, like ceramide, are thought to be intimately involved in the death pathway, which can be triggered by “death receptors” on the surface of cells or by radiation. De Maria et al. (p. 1652) show that GD3 gangliosides accumulate when death is induced, and that these lipids can also induce death if overproduced. When their synthesis is inhibited, the death program is prevented. These natural products can disrupt the transmembrane potential of the mitochondria, a critical event in the death pathway, thereby providing a link from initiation to execution.

  6. Leukemia virus structure

    The x-ray crystal structure to 2.0 angstrom resolution of a fragment of Friend murine leukemia virus containing the receptor-binding activity (RBD) has been determined by Fass et al. (p. 1662). The RBD is an L-shaped molecule that contains a conserved β-sheet core which acts as a scaffold to display helical variable regions that appear to determine receptor specificity. These findings have importance both for basic virology and in the design of vectors for gene therapy.

  7. Licking stress

    A warm and loving childhood is thought to have a greater likelihood of yielding well-adjusted offspring that can cope with stress. Liu et al. (p. 1659; see the Perspective by Sapolsky, p. 1620) examined the neuroendocrine responses in adult rats as a function of the mother-pup contact during the early postnatal life. Greater licking and grooming as a pup yielded an adult with a more effective glucocorticoid regulation of adrenalcorticotropin release; in brief, the response to stress was less severe and shorter lived.

  8. Older bird divergence

    The origin of the great variety of North American bird species has been thought to coincide with the glaciation of the Late Pleistocene. Individual populations of any given species that were isolated by encroaching barriers of inhospitable territory would each be allowed to follow their own genetic path and diverge into separate species. Klicka and Zink (p. 1666; see the Perspective by Rosenzweig, p. 1622) analyzed mitochondrial DNA of various bird species and now find that the evolutionary history of species divergence recorded in the DNA extends much further back than the Pleistocene. The divergence of North American bird species was more gradual than expected and well under way before this glacial cycle.

  9. Arrested growth

    The stages of metazoan development, from early cleavage to hatched young adults, have been identified in fossils. Bengtson and Zhao (p. 1645; see the cover) report the discovery of many fossilized embryos of metazoans from the Lower Cambrian about 550 million years ago. The authors suggest that such fossils might be quite common but have been previously overlooked because of their small size and nondescript morphology.

  10. Providing oxygen

    The placenta forms as embryonic cells invade the maternal uterine wall. Genbacev et al. (p. 1669) show how specific cellular responses to the microenvironment regulate this process. Cytotrophoblasts of the placenta respond to the lack of oxygen by proliferating, unlike most other cells of the developing embryo. Early in gestation, when the embryo has yet to establish good connections with the uterus, the embryo develops slowly while the placenta proliferates and invades the uterine wall. Once a robust utero-placental blood circulation is established, oxygen levels rise and the embryo develops more rapidly while the placental cells cease to proliferate.

  11. Comets and x-rays

    A surprising result from observations of comet Hyakutake was that it was emitting x-rays. Dennerl et al. review archival satellie (ROSAT) images of other comets and found that these were also emitting x-rays. Together, the data imply that the x-rays are produced from the interaction of the solar wind with comet particles.

  12. What's up with STATs

    Many extracellular polypeptides that produce changes in cells do so by way of STATs, signal transducers and activators of transcription. STATs are cytoplasmic proteins that are activated by cell surface receptors that interact with these extracellular polypeptides. After phosphorylation on tyrosine, STATs dimerize and enter the nucleus, where they regulate the transcription of many genes. Darnell reviews our current understanding of STAT function and evolution and discusses some of the unanswered questions that are the topic of current research.

  13. Volcanic styles

    Most explosive volcanic eruptions are from magmas with a high content of silica and water; eruptions of basaltic material with low silica content tend to be more effusive. Roggensack et al. examined two recent basaltic eruptions from the Cerro Negro Volcano in Mexico. One was quite explosive and produced an ash column 7 kilometers high. Data from melt inclusions imply that in the explosive eruption, water and carbon dioxide were retained in the magma to drive the eruption because the melt collected at a depth of 6 to 15 kilometers before erupting. In the more effusive eruption, the magma degassed first at shallower levels. One implication is that interpretations of magma composition based on eruptive style on other planets may not be accurate.

  14. Once and only once

    Progression of yeast through the cell division cycle from the G1 phase to the DNA synthesis (S) phase requires the activity of Cdc34, a ubiquitin-conjugating enzyme, and ubiquitin-mediated protein degradation of an inhibitor of cyclin-dependent kinase activity. Yew Sand Kirschner explored the role of Cdc34 in control of initiation of DNA synthesis in the frog Xenopus leavis and found both similarities and differences with the control mechanisms described in yeast. In Xenopus, Cdc34, in a large complex with other proteins, appears to be required for initiation of DNA replication and to act through destruction of a cyclin-dependent kinase inhibitor (Xic1). Destruction of Xic1 apparently requires the presence of the cell nucleus. The results begin to reveal the biochemical mechanisms by which DNA replication in higher eukaryotes is coordinated with cell division to assure that the DNA is replicated once, but only once, per cell cycle.

  15. Bacteriorhodopsin structure

    Shining light on certain cells moves protons from the inside to the outside. Bacteriorhodopsin, the protein that stores the energy of a photon in an electrochemical gradient, has served as the model for many of the basic explorations of transport through biological membranes. Pebay-Peyroula et al. present the high-resolution x-ray structure of this protein crystallized in a lipid matrix. Even so, not all of the mysteries are solved, such as the location of eight water molecules in the pathway of proton movement. [See the news story by Moffat.]

  16. Maintaining redox during secretion

    Secreted proteins are initially translocated into the endoplasmic reticulum (ER), where they are folded and assembled, ready for transport through the secretory pathway. Part of the folding process for many proteins involves the formation of disulfide bonds between cysteine residues, which requires an oxidizing environment. Carelli et al. have now shown that cells secrete small thiols—cysteine and glutathione—into the surrounding medium in amounts that correlate with the levels of disulfide-containing secretory proteins. The findings support a role for thiols and redox state in the regulation of export from the ER.

  17. Glial cells for better connections

    Although the main action of the central nervous system is carried out by neurons, there are a variety of other specialized cells that contribute each in their Pfrieger and Barres. frieger and Barres have found that certain types of glial cells are critical for the formation of effective neuronal synapses. When cultured without glia, rat neurons survived normally but formed synapses that transmitted only weakly. The synaptic connections were much more robust when the neurons were cultured in the presence of glial cells.

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