This Week in Science

Science  05 Dec 2003:
Vol. 302, Issue 5651, pp. 1621
  1. Fault Lines More Complex

    The surface trace of a fault is often displayed as a line, but the actual structure of the fault zone is more complex. Detailed structures can be used to determine the strength of the fault zone and to better estimate its ability to fail. Chavarria et al. (p. 1746) have determined the structure of the San Andreas fault near Parkfield using scattered body and surface waves from a vertical drill hole. Besides the San Andreas fault, there are four secondary faults with variable dips, and these structures may connect to a deeper and older part of the fault system. The fault zone is also composed of multiple cracks or possibly pockets of fluid.

  2. Inflammation Prevents Generation of New Neurons

    The birth of new neurons in the brain seems to be required for normal cognitive function, but in a manner that is not well understood. After cranial radiation therapy, cognitive function may be impaired, probably due to the inhibition of neurogenesis. Monje et al. (p. 1760; see the Perspective by Kempermann and Neumann) now show that neurogenesis in the hippocampal region of the brain can be inhibited by inflammation in the area surrounding the stem or progenitor cells. The inhibition occurred whether the inflammation resulted from local radiation-induced tissue damage or from the introduction of lipopolysaccharide. Inhibition of inflammation with the common nonsteroidal anti-inflammatory agent indomethacin could partially restore neurogenesis, possibly because of the local release of interleukin-6 from activated microglial cells.

  3. Protons That Wire Ahead

    Proton transfer reactions underlie acid-base chemistry, and in the biological environments of enzymes and ion channels, protons appear to be relayed along “wires.” The rapidity of proton transfer coupled to solvent motion has made fundamental studies of proton transfer difficult. Tanner et al. (p. 1736; see the Perspective by Domcke and Sobolewski) now present a combined experimental and theoretical study of photoinduced hydrogen-atom transfer along a tri-ammonia hydrogen-bonded “wire” that bridges an OH donor site and N acceptor sites on the molecule 7-hydroxyquinoline. These attachment sites provide directionality to proton transfer. Proton transfer required not only the excitation of the 7-hydroxyquinoline into its electronic excited state but also the small additional excitation of the ammonia wire's vibrational modes (about 200 wavenumbers) to drive the reaction over its first potential barrier and eventually convert the enol into the fluorescent keto isomer. Further studies should help elucidate the several intermediate steps in this model reaction pathway.

  4. A Nudge from Yarkovsky

    The Yarkovsky effect, a subtle nudge given to an asteroid by the uneven heating of its irregular surface, is often invoked in orbital dynamic models, particularly to push main-belt asteroids into near-Earth orbits. Chesley et al. (p. 1739) have detected this effect on near-Earth asteroid 6489 Golevka using precise radar ranging from Arecibo and Goldstone. Continued detections of this effect on Golevka and other asteroids will help refine their past, present, and future orbital paths and their characteristics, such as shape, density, and porosity.

  5. The Soft Side of Ancient Ostracods

    Ostracods, which include lobsters and crabs, are thought to have originated in the Cambrian, but fossils are sparse, particularly those showing soft parts. Siveter et al. (p. 1749; see the news story by Stokstad) now describe an exquisitely preserved ostracod from rocks dating to about 425 million years ago that confirms the presence of ostracods during the Paleozoic. They sectioned the fossil to create a detailed view of its anatomy. This fossil is remarkably similar to a family of ostracods that swims vigorously and hides within the sandy sea floor, and thus is an example of extreme evolutionary stasis.

  6. High and Dry

    The upper troposphere and lower stratosphere are extremely dry, and thus any changes in the amount of water in these regions of the atmosphere might affect ozone depletion and stratospheric cooling. The sources and sinks of water in cirrus cloud formations, a crucial component of this region's water budget, can be determined by analyzing the isotopic composition of the water they contain, but detailed determinations have not been made successfully in the past. Webster and Heymsfield (p. 1742; see the Perspective by Rosenlof) now report measurements of water isotopes made in and out of cirrus clouds in the subtropics in the region between the upper troposphere and the lower stratosphere. Their measurements allow them to discriminate between ice crystals lofted from below by convective processes and those ice crystals formed in situ, and also help resolve differences between two competing theories of dehydration, those of convection and gradual ascent.

  7. Controlling When to Make Flowers

    Flowering time in plants is regulated in part by environmental cues, such as changes in day length, but plants may also begin to flower under direction from their autonomous regulatory pathway. He et al. (p. 1751; see the Perspective by Bastow and Dean) have now shown that one of the autonomous pathway genes, flowering locus D (FLD), is a homolog of a protein found in mammalian histone deacetylase complexes. FLD helps to regulate the acetylation status of the chromatin around the flowering locus C (FLC) gene, which encodes a transcription factor that blocks the floral transition. FLD-induced deacetylation of FLC increases its expression and leads to an extreme delay in flowering time.

  8. The Drosophila Protein Interaction Network

    Analyses of protein-protein interactions are vital to understanding gene function. Giot et al. (p. 1727; see the cover) now describe a protein-interaction map for the fruit fly Drosophila melanogaster. Algorithmic methods were used to look for false positives and to generate a high confidence set of 4679 proteins and their 4780 interactions. Protein-protein interaction maps were generated to look at human disease orthologs and to confirm and extend known metabolic pathways.

  9. The Right Amount of Needling

    Type III secretion is used by many animal, insect, and plant bacterial pathogens to inject effector proteins directly into the cytosol of their eukaryotic host cells. These effectors take control of the host cells and reprogram them to the benefit of the pathogen. The organelle responsible for the injection is called the injectisome or needle complex. Journet et al. (p. 1757) provide evidence that the length of the needle of the injectisome of Yersinia pestis is strictly proportional to the number of residues of the protein YscP, a protein which is itself secreted by the apparatus. In this way, the length of the needle is determined by a protein that acts as a molecular ruler.

  10. Reactive Oxygen Species in Development and Aging

    As human society gets older, there is great interest in understanding the molecular mechanisms of aging. One agent that has been linked to aging is reactive oxygen species (ROS). Shibata et al. (p. 1779) now show that reactive oxygen species also function in the normal development of the nematode, Caenorhabditis elegans. A specific role was observed in both germline development that involved lipoprotein oxidation and in vulval development that involved activation of the small GTP-binding protein, Ras. This in vivo model will be useful in studies of ROS signaling, and it provides a system to explore the biology of lipoproteins that are important in the development of atherosclerosis.

  11. Neurodegeneration in Yeast

    The study of neurodegenerative disorders like Parkinson's disease and Huntington's disease would be enhanced by the production of a genetically tractable model system in which to study the cellular mechanisms involved in the pathology. Outeiro and Lindquist (p. 1772) describe the phenotype of yeast cells expressing—synuclein, a protein implicated in the pathogenesis of Parkinson's disease. Willingham et al. (p. 1769) identify a group of yeast genes that enhance the toxicity of expressed α-synuclein, or a mutant huntingtin fragment implicated in the pathology of Huntington's disease. Together, these papers support the notion that yeast might be a suitable model in which to gain insight into the molecular pathology of these disorders.

  12. Smurfing Cell Polarity

    The Rho family of small guanosine triphosphatases (GTPases) is critical for controlling cell shape, motility, polarity, and behavior in development and tumor progression. However, little is known about how the activity of different Rho GTPases is spatially coordinated to control these processes. Wang et al. (p. 1775; see the Perspective by Jaffe and Hall) examined the role of Smurf1, a HECT domain E3 ubiquitin ligase that modulates Smad signaling. The localization of Smurf1 to lamellipodia and filopodia required the activity of atypical protein kinase zeta, an effector involved in establishing cell polarity. Smurf1 controls the local level of RhoA whose accumulation in cellular protrusions is linked to the suppression of the transformed phenotype induced by knocking down Smurf1 expression.

  13. Memory in Space and Time

    Expression of the rutabaga-encoded type I adenylyl cyclase in Drosophila mushroom bodies can rescue the short-term memory defect in rutabaga mutant flies. In order to differentiate between a potential developmental role of the adenylyl cyclase from its acute function in memory formation, McGuire et al. (p. 1765) developed a system to control both temporal and spatial expression of a transgene in Drosophila. Using this system, rutabaga expression in the mushroom bodies during adulthood allowed for normal memory acquisition by otherwise mutant rutabaga animals. This technique will be useful more generally to study when and where gene products are needed during the lifetime of an organism.

  14. Adaptation Leads to Speciation in Fruit Flies

    The interplay between molecular and ecological processes is key to understanding the process of speciation in organisms. Using molecular manipulation, Greenberg et al. (p. 1754) introduced an allele of a sexual isolation locus from one population of Drosophila melanogaster into another. The results indicate that this sexual isolation gene evolved for reasons of ecological adaptation, and that sexual isolation, an important prerequisite of speciation, is a secondary consequence of this adaptation.