This Week in Science

Science  14 Nov 1997:
Vol. 278, Issue 5341, pp. 1201
  1. Observing climate oscillations

    The climate system during the last glaciation was disrupted by abrupt events in which ice sheets discharged many icebergs that rafted sediment across the Atlantic. Bond et al. (p. 1257; see the Perspective by Oppo, p. 1244) have now recognized the same events throughout the Holocene, which has been thought to have been climatically stable. The pacing of the events in the Holocene is the same as during glacial times and indicate that the mechanism driving these climate oscillations is robust through the major climate change.

  2. Lung lineage

    Reptiles and birds both possess bellowslike septate lungs, although the avian lung is highly modified to allow high rates of exchange of oxygen and carbon dioxide. Ruben et al. (p. 1267; see the cover and the news story by Gibbons, p. 1229) analyze lung geometry of theropods, thought by many to be the ancestors of birds, using several recently discovered fossils. The theropods possessed lungs analogous to those in crocodiles with a diaphragm driving the bellows, in contrast to those of most modern and early birds.

  3. The proof is in the proofs

    Albert Einstein and David Hilbert published the central elements of the general theory of relativity at almost the same time, and Hilbert in fact beat Einstein by 5 days in the submission dates of the manuscripts. Corry et al. (p. 1270) now provide archival evidence consisting of the proofs of Hilbert's paper, which show that at the time of submission, the manuscript did not in fact contain crucial parts of the theory, which were added later at proof stage. The evidence suggests that Einstein was the first to fully develop the theory, whereas Hilbert changed the proofs of his paper after seeing a copy of Einstein's paper.

  4. Icy clouds, warm Mars

    Images of the martian surface show evidence for flowing water about 4 billion years ago. Unfortunately, no simple mechanism has been found to warm the surface of Mars enough to allow liquid water on the surface. Forget and Pierrehumbert (p. 1273; see the Perspective by Kasting, p. 1245) added the effects of icy carbon dioxide clouds to a one-dimensional climate model and found that they can warm the martian surface enough to allow the flow of water. The importance of including icy clouds to warm the surface of any planet may extend the habitable zone (region where liquid water, considered a primary constituent for life, exists) aroun a sunlike star from about 1.3 to more than 2.4 times the distance of Earth to the sun.

  5. Covering the spread

    The nature of faulting and magmatism along the mid-ocean ridges and their geometry changes dramatically with spreading rate. A geophysical survey by Géli et al. (p. 1281) of a region of the Pacific-Antarctic Ridge system, where the spreading rate varies greatly over a short distance, reveals how changes in plate motion over the last 30 million years produced a V-shaped structure on the sea floor and led to reorganization of the local spreading system.

  6. Making a muscle

    Growth factors inhibit differentiation of myoblasts into muscle cells, but the intracellular signaling pathways by which they do so have not been established. Bennett and Tonks (p. 1288) found that activation of mitogen-activated protein kinases (MAPKs) was required in order for mitogens to inhibit transcription of muscle-specific genes. However, the role of MAPKs did not end there. Later in myogenesis (when muscle cells fuse to form multinucleated myotubes), the activation of MAPKs was required for myotube formation even if normal transcription of muscle-specific genes had occurred. Thus, MAPK signaling pathways appear to mediate both negative and positive control of distinct stages during muscle cell differentiation.

  7. Staying young

    In times of stress—when there is little food or water—the nematode Caenorhabditis elegans becomes a dauer, a metabolically inactive state akin to mammalian hibernation. Lin et al. (p. 1319) have now cloned daf-16, one member of the signal transduction pathway that acts continually to keep the animal from becoming a dauer. DAF-16 is a member of the HNF-3/forkhead family, another member of which participates in insulin's signal transduction pathway in mammals. When mutated, daf-16 prolongs the life of C. elegans, suggesting a link between longevity and insulin signaling.

  8. HIV persistence

    Highly active antiretroviral therapy (HAART), a cocktail of protease inhibitors and reverse transcriptase inhibitors, has been successful in some patients infected with the human immunodeficiency (HIV) virus in reducing the viral burden in the blood to undetectable levels. However, viral reservoirs could allow very low levels of ongoing viral replication or be a source of new problems once therapy is ended. In separate studies, Finzi et al. (p. 1295) and Wong et al. (p. 1291; see the news story by Balter, p. 1227) determined that latently infected, quiescent T cells from patients on HAART for as long as 30 months contain virus that could be induced in vitro to an actively replicating state. The viruses recovered showed little to no molecular evidence of evolution to drug resistance.

  9. Deafness gene

    A study of an extended family in Costa Rica who suffer from a nonsyndromic form of deafness that begins at about age 10 by Lynch et al. (p. 1315; see the news story by Pennisi, p. 1223) indicates an association of this form of deafness with the presence of a truncation in a gene, DFNA1, that is a member of a family of genes found in the fruit fly and yeast. In these other organisms, the gene is involved in cytokinesis and the establishment of cell polarity. The normal form of the protein in humans may be involved in actin polymerization in hair cells of the cochlea of the human ear.

  10. Staff of life

    The beginnings of agriculture lie in the Fertile Crescent. Heun et al. (p. 1312; see the Perspective by Diamond, p. 1243) have used DNA fingerprinting to identify which of the wild relatives of einhorn wheat were most likely to have been the first domesticated. The results point to wild populations in the mountains of what is now southeastern Turkey. The site may yield clues into the earliest agricultural settlements.

  11. Accounting for the green airglow

    Excited oxygen is dissociated by electrons into atomic oxygen in the ionospheres of Earth, Mars, and Venus. The green airglow from atomic oxygen on Earth has been known for some time, but the mechanism for its production has still been unclear. Observations and experiments have shown that the yield of atomic oxygen is greater than that predicted by theory. Guberman added the effect of spin-orbit coupling (interaction of the electron's spin with its orbital motion) to the dissociative recombination calculations and produced a yield of atomic oxygen within the measurements.

  12. Fluids from the San Andreas

    Fluids emanating from the mantle are recognized in many volcanic systems, notably the mid-ocean ridges and Hawaii. Kennedy et al. now report that mantle fluids are emanating generally along the San Andreas fault system. They measured high helium-3/helium-4 ratios, a diagnostic of mantle fluids, in several springs located near and along the fault. They suggest that the presence of these fluids may act to weaken the fault.

  13. A few bumps in core rotation

    Recent seismic analysis showed that the inner core was rotating faster than the mantle by 1° to 3° per year. Creager analyzed the times and paths of seismic waves from south Atlantic earthquakes that propagate through the deep interior and resurface at station COL in Alaska over a 30-year period. Small-scale heterogeneities account for some of the arrival delays of the waves to COL, and this finding leads to a lower estimate of the rotation rate, with a maximum of 0.3° per year. This slower rotation rate helps define and explain some of the inner core's lateral velocity heterogeneity. It also allows for a larger viscosity of the inner core that fits better with gravitational coupling of the core to the mantle.

  14. A telling fusion

    The Janus kinase (JAK) family of protein-tyrosine kinases couple cytokine receptors to intracellular signaling pathways that control cell survival, proliferation, and differentiation. Lacronique et al. show that dysregulation of JAK kinases can play a causal role in human cancer. They describe a chromosomal translocation in an acute lymphoblastic leukemia that creates a fusion protein containing the catalytic domain of JAK2 and the oligomerization domain of the transcription factor TEL. The fusion protein has constitutive kinase activity and confers cytokine-independent growth on a hematopoietic cell line.

  15. Mediating death sentences

    The protein product of the proto-oncogene c-myc is not only involved in tumorigenesis but can also induce cell death. How c-Myc-activated death intersects with the standard cell death pathways, exemplified by the ligation of the Fas (CD95) death receptor, has not been clear. Hueber et al. show that c-Myc requires CD95 ligand to bind to CD95 in an autocrine fashion in order for c-Myc to induce death. Growth factors that give survival signals can overcome that induced death. An implication of these results is that in some cells the receipt of a death signal (such as binding of CD95L to CD95) is not an automatic death signal. c-Myc sensitizes a cell toward death, but survival signals still can intervene to save the cell. [See the Perspective by Green.]

  16. Making the tag

    Many peptides that function as neurotransmitters or hormones are amidated at their carboxyl end. This terminal amino group is not added to the peptide but instead derives from a supernumerary glycine residue, most of which is removed by the enzyme peptidylglycine α-amidating monooxygenase. The first step involves hydroxylation of the glycine with the aid of dioxygen, ascorbic acid, and two copper atoms. Prigge et al. present the high-resolution structure of the monooxygenase domain and discuss how the copper atoms, separated by 11 Å, each contribute one of the two electrons required in the hydroxylation.

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