This Week in Science

Science  14 Oct 2005:
Vol. 310, Issue 5746, pp. 191
  1. Prions in Urine?

    CREDIT: SEEGER ET AL.

    The factors enabling horizontal prion spread for diseases, including sheep scrapie and chronic wasting disease in deer and elk, have been discussed for many years. Seeger et al. (p. 324) have found that infectious urinary prions are consistently shed by mice suffering from chronic inflammatory kidney conditions (nephritis) long before any clinical symptoms of scrapie are seen. In the absence of kidney inflammation, or if inflammation occurs in other organs (such as the liver in hepatitis), urinary prion infectivity was never observed, even in transgenic mice that overexpress the prion protein. Thus, inflammation of excretory organs may be one of the cofactors responsible for the spread of prion diseases, and it may be important to screen biopharmaceuticals derived from urine.

  2. Faraway Planets

    Since the mid-1990s, more than 150 planets have been discovered in orbit around stars outside the solar system. As a result of increased precision and power of planet-search surveys, a wide variety of these objects has been identified. Santos et al. (p. 251) review these findings and how they relate to theories of planet formation. As the database of exoplanets continues to grow, such observations should answer key questions about chemical and physical processes involved in formation of planetary systems.

  3. Quantum Criticality in a 2DES

    Experimental work on a variety of two-dimensional electron systems (2DESs) has shown that the observed metallic behavior is a robust phenomenon, contrary to the insulating behavior expected from scaling considerations. Punnoose and Finkel'stein (p. 289) now present a theoretical description of this behavior that includes electronelectron interactions and disorder in the vicinity of the metal-to-insulator transition (MIT). They used renormalization group theory to identify a quantum critical point that separates the metallic and insulating phases of the 2DES. This model can account for the observed anomalous transport and magnetic properties in the vicinity of the MIT.

  4. Carving a Steep Slope

    CREDIT: CHEN ET AL.

    Ion-beam irradiation is an important tool for the micro- and nanofabrication of steep sidewall features, but theoretical approaches to understanding the sputtering process are normally formulated as expansions in the opposite limit, that of very shallow slope. Chen et al. (p. 294) now present a theoretical model that allows for the control of slope during the sputtering process that has a mathematical form that resembles a shock equation. They demonstrate that features created by field-ion bombardment can be sharpened and increase in slope as they get smaller, rather than dissipate.

  5. Ups and Downs of Mantle Melting

    Much of the dynamics on Earth are driven by differences in density among liquids or gases, or between liquids and solids. In Earth's deep mantle, dynamics depends on how the density of solid silicate minerals compares with that of likely melt phases. Stixrude and Karki (p. 297) have used molecular dynamics simulations to infer the structure of the melt of MgSiO3 perovskite, the dominant mineral in Earth's lower mantle. Their simulations show that with increasing pressure, the coordination of Si in the melt changes from four to six (the solid is six-coordinated) and at pressures near the core, the melt with pure magnesium is nearly as dense as the solid.

  6. Filling an Anthropoid Gap

    Anthropoids, the clade that includes higher primates and humans, arose about 45 to 55 million years ago (Ma), but much of their history prior to about 35 Ma is poorly understood. Seiffert et al. (p. 300; see the Perspective by Jaeger and Marivaux) obtained two early anthropoid jaw fragments, with several teeth, from rocks in Egypt dating to about 37 million years ago. These specimens show derived features shared with the much earlier fossils dating to >45 Ma, as well as more abundant later fossils.

  7. The Flexible Bird Catches the Worm

    Climate change can lead to mismatches in the seasonal responses of predators and prey. During the last 30 years, the growing season for the caterpillar prey of Dutch great tits occurs earlier in the year, so that the peak of caterpillar abundance is reached before the predator chicks are at their most voracious. Nussey et al. (p. 304; see the news story by Pennisi) investigate whether the current mistiming could be restored. Phenotypic plasticity in egg-laying date would need to be both under selection and heritable, conditions that have not been demonstrated in the wild. The authors find that there is indeed heritable variation among females in their laying date plasticity, and that selection favors highly plastic females.

  8. Illuminating Quantitative Biology

    Efforts to model cell biological processes are hampered by a lack of quantitative information on reaction rates, concentration, and stoichiometry. Wu and Pollard (p. 310) measured protein concentrations directly in living cells using fluorescence microscopy. Global and local concentrations of 28 cytoskeletal and signaling proteins, fused to yellow fluorescent protein (YFP) in the fission yeast Schizosaccharomyces pombe, were tracked. Used with caution, this method provides a precision measuring tool for quantitative biology.

  9. Mitochondria and NO for Longer Life

    Calorie restriction extends life span in organisms ranging from yeast to mammals. Nisoli et al. (p. 314) find that when mice are subjected to calorie restriction, endothelial nitric oxide synthase (eNOS) expression and 3′,5′-cyclic guanosine monophosphate formation are increased. This change is accompanied by mitochondrial biogenesis, increased oxygen consumption, adenosine triphosphate production, and expression of sirtuin 1, a protein previously implicated in mediating the effects of calorie restriction on life span. These effects are strongly attenuated in mutant mice lacking eNOS. Thus, NO may play a role in the processes induced by calorie restriction and in life-span expansion in mammals.

  10. Genetic Clue to Tourette's Syndrome

    Tourette's syndrome (TS) is a common psychiatric disorder that is associated with a complex array of behavioral disturbances, most notably motor and vocal tics, and considerable evidence suggests a role for genetic factors. Abelson et al. (p. 317; see the news story by Olsen) show that a small number of patients with TS carry sequence alterations in SLITRK1, a gene that is expressed in the brain and that encodes a poorly characterized protein that enhances neuronal differentiation in vitro. Intriguingly, the location of one of these sequence alterations suggests that the SLITRK1 gene is regulated by microRNAs.

  11. Artificial Transfer of Wolbachia

    Some species of mosquito harbor the commensal rickettsia-like bacterium Wolbachia, which causes cytoplasmic incompatibility—fertile mating only occurs for infected female mosquitoes. Uninfected mosquitoes are eventually replaced by Wolbachia-infected mosquitoes within a population, an effect that could be exploited to facilitate control measures. Unfortunately, natural populations of Aedes aegypti, the vector for dengue and dengue hemorrhagic fevers, do not harbor Wolbachia. Xi et al. (p. 326) show that A. aegypti can be artificially infected in cage experiments with the bacterium obtained from A. albopictus and that such infections confer cytoplasmic incompatibility. The infections required an initial 20% infection frequency to obtain saturation after seven generations, with no evidence of maternal inheritance failure.

  12. Extending the Reach of Mirror Neurons

    CREDIT: NELISSEN ET AL.

    A subset of neurons, the mirror neurons, is active both when an individual performs an action and when the individual observes another individual performing the same action. These findings were made in monkey cortical area F5 in single-neuron recordings. Nelissen et al. (p. 322), using functional magnetic resonance imaging in awake monkeys, show that such action representation in the frontal lobe is only a small part of the story. They found activity in area F5c that was responsive to full-body images involving grasping movements; diminished responses were seen in this region in response to more abstract images. However, there were responses to more abstract images of grasping movements in more rostral regions of area F5. They also observed responses to action observation as well as to images of objects in area 45B of prefrontal cortex. The authors speculate that monkey areas F5 and 45B, which are thought to be the homologs of human areas BA44 and BA45, may represent ancestral precursors of these speech-related areas in humans.

  13. Suitably Spaced

    The underlying causes for the enhancement of a metal's catalytic activity by alloying with a second metal are often unclear. One such case is enhancement of the palladium (Pd)-catalyzed acetoxylation of ethylene to vinyl acetate (VA) by addition of gold (Au), which has been thought to involve larger ensembles of Pd atoms. Chen et al. (p. 291) examined the rate of VA formation for low Pd coverages relative to high Pd coverages on Au single-crystal surfaces and found that the critical reaction site consists of two Pd atoms spaced at critical distances, based on greater reactivity for the Au(100) surface compared to the Au(111) surface. These nearby Pd sites help couple critical surface species to products and also appear to inhibit the formation of undesirable by-products, such as CO, CO2, or surface carbon.

  14. Akt-ing on Regulated Gene Transcription

    Methylation of histone residues in chromatin plays a crucial role in the regulation of gene expression and other chromatin-dependent processes: for example, the methyltransferase enhancer of Zeste homolog 2 (EZH2), a Polycomb group protein, methylates lysine 27 in histone H3 and generally represses transcription. Cell signaling pathways are also critical for many cellular processes: for example, the phosphoinositide 3-kinase-Akt (PI3K-Akt) pathway is also implicated in oncogenesis and promotes cell proliferation and represses apoptosis. Cha et al. (p. 306) now link these signaling and gene regulation pathways by showing that the Akt kinase interacts with and down-regulates the H3 K27 methyltransferase activity of EZH2. A highly conserved serine residue is phosphorylated, which reduces the affinity of the protein for chromatin and up-regulates the target genes.

  15. Mapping Human Genetic Hotspots

    Genetic maps, which document the way in which recombination rates vary over a genome, are an essential tool for diverse genetic analyses, including fine-scale mapping and evolutionary inference. Myers et al. (p. 321; see the Perspective by Przeworski) have provided a genome-wide analysis of the frequency of hotspots in the human genome by analyzing linkage disequilibrium patterns in a 1.5-million single-nucleotide polymorphism data set. Their analysis characterized more than 25,000 novel hotspots. No substantial “deserts” devoid of recombination were observed. Recombination rate variation over large scales was caused by changes in the density and strength of hotspots. Male and female recombination processes and hotspots appeared to be similar.

  16. Central Expression of Peripheral Cannabinoid Receptors

    The discovery of endocannabinoids, which act as retrograde messengers in the brain, changed the way we think about the flow of information across the synapse. Are the endogenous actions of endocannabinoids in the brain solely accounted for by activation of CB1 receptors? Although there are hints for the presence of another receptor type, there have been no reports of an alternative CB receptor in the brain. Using reverse transcription polymerase chain reaction studies and pharmacological and behavioral evidence, Van Sickle et al. (p. 329) show that functional cannabinoid CB2 receptors, a receptor subtype traditionally considered to be expressed in immune tissues and circulating immune cells, are also present in brainstem neurons. This finding could lead to new therapies without the usual drawbacks of addiction and mind alteration traditionally associated with the consumption of cannabis derivatives.