This Week in Science

Science  08 Sep 2006:
Vol. 313, Issue 5792, pp. 1360
  1. Where's Which Whisker?


    Passing through several relay stations in the brain, sensory signals from the face are received in the somatosensory cortex of the brain in a spatial organization roughly reflecting that of the signal's origins. Oury et al. (p. 1408, published online 10 August) now show that in one of the relay stations in mice, the PrV nucleus, expression of Hox genes during development helps maintain the map and allows, for example, the discrimination of signals from the whiskers, upper jaw, and lower jaw.

  2. Water on Terrestrial Planets

    The Mars Exploration Rover Opportunity recently traveled 8 kilometers across Meridiani Planum, and an analysis by Squyres et al. (p. 1403; see the cover) of the features that it discovered has revealed information about ancient environmental conditions. These features include cross-laminations that formed in flowing liquid water, strata with hematite-rich concretions, weathered rock rinds, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical alteration of basalt can explain the composition of a 7-meter stratigraphic section. Observations from microscopic to orbital scales reinforce the conclusion that ancient Meridiani was characterized by abundant acidic ground-water, arid and oxidizing surface conditions, and occasional liquid flow on the surface. Beyond our solar system, some of the giant gas planets that have been observed have orbits that are much closer to their central stars compared to that of Jupiter in our own solar system. As gas giants should form from leftover gas in a protoplanetary disk more readily at large radii, they must gradually spiral inward, but this process would disrupt any other planets in that system. Raymond et al. (p. 1413) have simulated the behavior and formation of Earthlike planets in systems where a gas giant migrates inward and show that terrestrial planets can still form both interior and exterior to the migrating jovian planet. Outside the giant planet's orbit, very water-rich earth-mass planets could form within the habitable zone.

  3. High and Dry

    The vegetation of Eastern Africa shifted progressively from forest to grassland between 8 and 2 million years ago, and this change has been ascribed to the influence of decreasing concentrations of atmospheric CO2 (which favors grasses over trees), recurring periods of aridity caused by changing sea surface temperatures, and the beginning of glacial cycles. Sepulchre et al. (p. 1419) suggest that another contributing factor could have been increasing aridity caused by tectonic uplift along the East African Rift System, which would have led to a dramatic reorganization of atmospheric circulation and a strong drying trend. They examine the climatological and biological effects of uplift through numerical modeling, and conclude that it must have been a dominant factor in determining late Neogene African climate.

  4. Ionic Electroluminescence


    In a classic pn-junction between n-type and p-type semiconductors, the transfer of an electron through the junction can cause emission of light, as in a light emitting diode, or conversely, the absorption of light can lead to an electric current, as in a solar cell. Bernards et al. (p. 1416) used soft-contact lamination to fabricate an ionic junction between two organic semiconductors with mobile anions and cations. Similar to the classic pn-junction in which electrons are the mobile species, ionic charges can be successfully used to control the direction of electronic current flow in these semiconductor devices, which show electroluminescence under forward bias and produce a photovoltage upon illumination with visible light.

  5. Solid-State Entanglement

    Entanglement between qubits is a necessary requirement for any proposed quantum computer architectures, and solid-state implementations, particularly superconducting qubits, have the added advantage of being compatible with existing fabrication techniques. To date, the behavior and manipulation of single superconductor-based qubits have shown promising results. Steffen et al. (p. 1423; see the Perspective by Siddiqi and Clarke) use state tomography to demonstrate that entanglement between two superconducting phase qubits is possible. These new results put solid-state qubits on the roadmap as a basis for a scalable quantum computer.

  6. Volcanic Cracks in the Ocean Floor

    Volcanism on Earth occurs at plate boundaries (such as mid-ocean ridges and island arcs) and within plates above mantle plume hot spots. Hirano et al. (p. 1426, published online 27 July; see the Perspective by McNutt) report finding another type of volcano that is far from any of these primary sources. In submersible dives in the western Pacific Ocean, far from the plate edge, they saw the tops of small volcanoes that were partly buried in sediment and surrounded by pillow lavas and exploded shards. Geochemical analysis suggests the resulting basalts are young and formed at depths greater than 100 kilometers in the asthenosphere, which would imply that this layer contains a few percent melt. The authors argue that these “petit spot” volcanoes have grown along cracks where the asthenosphere has flexed and squeezed out its melt.

  7. Of Mice and Men and Immunity

    The immunity-related p47 guanosine triphosphatases are a class of innate immunity effectors found in murine cells where they play a role in defense against intracellular pathogens. However, the role of similar proteins in humans has been less clear. Now Singh et al. (p. 1438, published online 3 August) demonstrate that in mouse cells one of these receptors acts via autophagy, inducing large autolysosomal organelles to destroy intracellular Mycobacterium tuberculosis bacilli. Furthermore, the sole human counterpart, IRGM, also works via autophagy to control intracellular mycobacteria.

  8. The Humanization of Yeast

    The ability to produce proteins modified with humanlike carbohydrates is important in therapeutics and structural studies. Hamilton et al. (p. 1441) describe the genetic engineering of the secretory pathway of the yeast Pichia pastoris to produce structurally homogeneous complex, terminally sialylated human-type N-glycans on therapeutically efficacious erythropoietin. The engineered cell lines contain a total of four gene knockouts and 14 heterologous genes, the majority of which had not been identified in nature and had to be discovered through an extensive screening effort.

  9. Dissecting Chloroplast Division Machinery


    Chloroplasts arose from an endosymbiotic cyanobacterial ancestor and have their own genomes that have been maintained by division. Yoshida et al. (p. 1435) isolated intact circular chloroplast division machineries containing dynamin and FtsZ from the red alga Cyanidioschyzon merolae. Rings isolated at the early phase of division formed supertwisted (or spiral) structures that could be reversibly stretched to four times their original length with optical tweezers. As the contraction of the rings progressed, small compact circles were produced, and the dynamin pinched off the narrow bridge between daughter chloroplasts. Thus, dynamin may function both as a mediator of filament sliding and as a pin-chase during chloroplast division.

  10. Making Even More Diversity

    Recently, a role for the proteasome was discovered in splicing together noncontiguous peptides into effective antigens. Warren et al. (p. 1444; see the Perspective by Shastri) identified an antigenic peptide that corresponds to a minor histocompatibility antigen that is expressed on leukemic cells. The antigen was also created in the proteasome by splicing of two noncontiguous fragments of the parental protein, but the two fragments were spliced in the reverse order to that in which they occur in the parent protein. Splicing of these reordered peptide fragments occurred by transpeptidation involving an acyl-enzyme intermediate. This mode of production of antigenic peptides expands the diversity of antigenic peptides presented on class I molecules and is potentially relevant for T cell recognition of tumors and pathogens.

  11. Clean Bodies, Clean Minds

    Cleanliness is regarded as a desirable state, not only in the physical sense of personal hygiene but also in the moral sense of feeling virtuous. Zhong and Liljenquist (p. 1451) describe a sequence of studies that make the connection between physically washing one's hands and feelings of virtue. Ethically compromised individuals experienced an increased desire to cleanse themselves, but physical cleansing alleviated the psychological consequences of unethical behavior, both assuaging moral emotions and reducing moral-compensatory behavior.

  12. Deep Dark Seeps

    Oceanic cold seeps support specialized fauna dominated by tube worms, clams, and mussels, and show similarities to hydrothermal vent and whale-fall communities. Kiel and Little (p. 1429) use the mollusk fossil record to analyze the evolutionary history of seeps and show that seep genera are old, but not relic fauna and have undergone continuous immigration, and thus have evolutionary patterns similar to that of deep-sea biota.

  13. Monkey See, One, Two, Three

    Humans and animals can nonverbally enumerate visual items across time in a sequence, or rapidly estimate the number of dots in a pattern. Nieder et al. (p. 1431) recorded neuronal activity in the intraparietal sulcus of monkeys trained to estimate the number of dots in a pattern, or to count items that appeared one after the other. Throughout the ongoing enumeration process, neurons were encoding quantity either in spatially or in temporally arranged sets, but not in both. Because both set types carry numerical information, quantity information should converge at a downstream processing stage. This convergence was found in a third population of neurons that represented the number of items most abstractly in a memory period, irrespective of whether quantity had been cued in dot patterns or dot sequences.

  14. Speciation Without Sequence Evolution

    Hybrid sterility has been well studied for more than a century by many prominent scientists, including Darwin, but the molecular underpinnings have remained unidentified. Masly et al. (p. 1448) have identified a gene involved in sperm motility, JYAlpha, responsible for F2 hybrid sterility resulting from crosses of Drosophila melanogaster and D. simulans. During speciation gene translocation had placed the gene on two different chromosomes, leading to sterile F2 males lacking any copies of the gene. Thus, reproductive isolation can occur without sequence evolution.