This Week in Science

Science  03 Mar 2006:
Vol. 311, Issue 5765, pp. 1209
  1. Freeze and Squeeze


    Ice is a major component of the upper mantles of medium-to large-sized moons of the outer solar system, and in order to model heat flows in these bodies, it is necessary to understand how ice phases that form at higher pressures respond to stress. Kubo et al. (p. 1267; see the Perspective by Sammonds) perform cold-temperature experiments to address the microstructure deformation mechanism that dominates microcrystalline ice II, which was formed by overpressurizing normal ice to 300 megapascals at temperatures below 220 K. At low strain rates, the authors find that the creep mechanism becomes sensitive to grain size; smaller grains (6 versus 40 micrometers) created a weaker ice.

  2. Synaptic Stargazin

    The family of AMPA subtype glutamate receptors plays an important part in normal excitatory synaptic transmission and is also heavily involved in plastic synaptic changes. Recently, a family of homologous small transmembrane AMPA receptor regulatory proteins (TARPs), exemplified by the protein stargazin, have been discovered that regulate AMPA receptor trafficking and determine native AMPA receptor gating. Nicoll et al. (p. 1253) review how TARPs control AMPA receptors during normal synaptic transmission and during the induction of synaptic plasticity.

  3. Two Ways to Make the Fat

    The biosynthesis of fatty acids is a central metabolic pathway in which long hydrocarbon chains are built by adding two-carbon units in a repetitive sequence of reactions (see the cover and the Perspective by Smith). Maier et al. (p. 1258) and Jenni et al. (p. 1263) present the detailed views of the mammalian and fungal fatty acid synthase complexes by fitting the homologous catalytic domains from the corresponding bacterial enzymes into 4.5 or 5.0 angstrom electron density maps. Amazingly, the seven functional domains are arranged in completely different ways. The mammalian complex resembles an “X” in which the arms flex upward and downward during each round of addition. The fungal enzyme looks like an “egg” with separate reaction chambers in the top and bottom halves.

  4. Giant Electrocaloric Effect

    One route to improved energy efficiency is to put waste heat to use, and electrocaloric materials could in principle use waste heat to power refrigeration. The application of a electric field across an electrocaloric material has been known for several decades to reduce its temperature, but the effect was too small in these materials to allow commercial applications. Mischenko et al. (p. 1270) now show that a perovskite thin-film material exhibits an electrocaloric effect about two orders of magnitude larger than previously found in other materials.

  5. Order Out of Misfits


    The origins of the stability of a self-ordered array of defects have been determined by an analysis of the thermal fluctuations of their positions. Thürmer et al. (p. 1272) reexamined hexagonal arrays of sulfur-induced vacancy islands in a partial silver monolayer on the Ru(0001) surface by taking time-series scanning tunneling microscopy images at different temperatures. An analysis of how neighboring islands fluctuate parallel and perpendicular to the line connecting two islands allowed the stiffness and restoring forces operating on island-island bonds to be determined. The stability of this array is determined by the arrangement of misfit dislocations within the film, which themselves arose during the self-assembly processes.

  6. Hard Noble Nitrides

    Recently, a platinum nitride was synthesized under high pressure and temperature and shown to possess a large bulk modulus, but the structure of the compound was unknown. Crowhurst et al. (p. 1275) report that this material has a stoichiometry of PtN2 and that the structure is similar to that of pyrite. Under similar conditions, they could synthesize a recoverable nitride of iridium. Despite the similar stoichiometry of this compound, it has a much lower structural symmetry.

  7. Early Writing on the Walls

    Writing has been thought to have emerged in the New World in the Olmec culture, or more broadly near Oaxaca; clear evidence is seen in these regions by about 300 B.C., and some finds suggest an origin one to three centuries earlier. Aside from a few hints, clear writing in Maya ruins was enigmatically found only for much later dates. Saturno et al. (p. 1281, published online 5 January; see the Perspective by Houston) now describe a series of hieroglyphs from a deep room in a Maya temple that was built between 200 and 300 B.C. Writing appeared to emerge in the Maya region near the time when it appeared widely elsewhere in Mesoamerica.

  8. Finding Branches of the Tree of Life

    In order to understand how evolution occurred, from the development of molecular networks to organ systems and the relationships of organisms, it is necessary to have a framework. Ciccarelli et al. (p. 1283) used genomic information to construct a tree that can be easily automated and updated. They started with 36 genes universally present in 191 species for which orthologs could be unambiguously identified. An important component was a procedure for identifying and removing apparent lateral gene transfer effects. Using this open-source resource, the authors confirmed phylogenetic relationships and put forward hypotheses about the ancestor to modern bacteria.

  9. MAPK Signaling 1: Development


    Cardio-facio-cutaneous (CFC) syndrome is a rare disorder characterized by a distinctive facial appearance, skin abnormalities, heart defects, and growth delays. Rodriguez-Viciana et al. (p. 1287, published online 26 January) show that the disorder is caused by acquired mutations in genes encoding components of the mitogen-activated protein kinase (MAPK) signaling pathway. About 90% of the 23 patients studied carried missense mutations in the BRAF, MEK1, or MEK2 genes that functionally altered the corresponding proteins. This discovery highlights the critical role of the MAPK pathway in human development and provides a tool for molecular diagnosis of CFC syndrome.

  10. MAPK Signaling 2: Reversible Rescue

    Chemical rescue of catalytically defective mutant enzymes has been a productive approach to studying enzyme function in vitro, but applications of the technique in vivo have so far met with limited success. Qiao et al. (p. 1293) have achieved rapid and reversible rescue of the protein tyrosine kinase Src in live cells using the small molecule imidazole. The work provides insight into the MAP kinase signaling pathway, including identifying several new Src substrates. Besides being a useful tool for studying cell signaling, small molecules that rescue disease-related mutant enzymes may have therapeutic potential.

  11. Analog Axonal Signaling

    Traditional accounts of intraneuronal electric signal transmission have distinguished between digital signals (action potentials) and analog (graded) signals. In mammals, analog signals are thought to occur only in primary sensory systems, like photoreceptors or bipolar cells. The brain has been thought to use digital action potentials to mediate dendritic input to the axon terminal. Alle and Geiger (p. 1290) suggest that this may be wrong: analog signaling is used by axons even in the middle of the brain. These recordings demonstrate passive transmission of dendritic potentials all the way up to the axonal terminal in a brain neuron and show the modulation of excitatory postsynaptic signals by analog presynaptic signals.

  12. Do As You Would Be Done By

    Lending assistance to relatives fits easily into evolutionary theory. Behaving in similar fashion with regard to unrelated individuals is harder to explain but undoubtedly occurs, at least amongst humans (see the Perspective by Silk). How, then, do you decide whether to cooperate with a potential partner? Melis et al. (p. 1297) asked whether cooperation is uniquely human. In two situations, they found that chimpanzees recruited a partner to help them to solve a difficult task and that they prefer partners who are more adept. Warneken and Tomasello (p. 1301) tested matched situations on human infants and young chimpanzees, in which subjects were given the opportunity to commit a helpful action without reward. Infants were quite ready to help a stranger with a task, such as stacking books in a pile or placing them onto a cabinet shelf, and chimpanzees also displayed to a limited degree a similar capacity for altruism.

  13. Peroxy Pentagon

    The hydroperoxy radical (HO2) is a short-lived intermediate implicated in a wide range of atmospheric and combustion processes. Given the abundance of water in the atmosphere, HO2-water complexes have been postulated in reaction models, but they have eluded definitive detection. Suma et al. (p. 1278) characterized the HO2-H2O complex using microwave rotational spectroscopy. The data support a pentagonal geometry in which a water OH group is hydrogen bonded to coplanar OOH and provide a spectroscopic signature for probing the atmosphere for the presence of the complex. Comparison with theoretical modeling suggests that, despite a binding energy approaching 10 kilocalories per mole, the unpaired electron remains localized on the peroxy fragment.