This Week in Science

Science  08 Oct 2004:
Vol. 306, Issue 5694, pp. 193
  1. Embryonic Stem Cells to the Rescue


    Mice carrying mutations in the Id genes are characterized by a variety of problems, including defects in the vasculature and the lymph nodes. Fraidenraich et al. (p. 247; see the Perspective by Chien et al.) show that Id mutant mice also have defective heart development indicative of problems with the myocardium and its signaling. Injection of nonmutant embryonic stem cells into Id-defective mouse blastocysts rescued the heart defects in the mutant mice, and injection of normal embryonic stem cells into the peritoneal cavity of pregnant mice rescued some of the heart defects in mutant offspring.

  2. Helping Cobalt Atoms Hop

    Many studies now have used the tips of the scanning tunneling microscope (STM) to manipulate atoms on surfaces. In most cases, the tip actually picks up the atom and physically moves it to a new location. Stroscio and Celotta (p. 242, published online 9 September 2004) have now used the tip interaction to influence the hopping of a cobalt atom adsorbed on the (111) face of a copper crystal between almost equivalent binding sites (the face-centered site, which has no copper atom directly below it, and the hexagonally close-packed site, which has a copper atom below it). At very low temperatures, the switching of a single cobalt atom between sites creates a periodic noise pattern in the tunneling current. Changing the probe tip height changes the potential between the two sites and hence the residence time of Co in the sites. The strong dependence of the transfer rate between sites at high tunneling voltages indicates that vibrational heating caused by scattered electrons plays a role in that regime.

  3. Gold on the Double


    Small gold clusters dispersed on transition metal oxides such as TiO2 can exhibit unusually high catalytic activity, but the origin of this enhancement has been up for debate—electronic, structural, and support effects have all been evoked. Chen and Goodman (p. 252, published online 26 August 2004; see the Perspective by Campbell) prepared a well-ordered titanium oxide that is unusual, in that gold completely wets its surface and allows adsorption of monolayer or bilayer gold films. The bilayer is about 45 times more catalytically active for CO oxidation than gold clusters supported on high-surface-area titanium oxide. Because the support is not in contact with the reactant and the gold is no longer in the form of nanoparticles, these results indicate that the distinctive chemical and electronic properties of the supported bilayer gold particles exert the main catalytic effect.

  4. Losing Fast

    Loss of ice from Antarctica is thought to be responsible for about 10% of contemporary sea level rise, but that estimate is still uncertain. Knowing the mass balance of the Antarctic Ice Sheet is of great importance because of its tremendous size, which is large enough to cause sea level to rise more than 70 meters were it to melt completely. Thomas et al. (p. 255, published online 23 September 2004; see the 24 September news story by Kerr) report results from aircraft and satellite surveys of the ice sheet in the Amundsen Sea sector of West Antarctica and find that glacial thinning rates near the coast have doubled since the 1990s. This region of the ice sheet alone, which contains enough ice to raise sea level by more than 1 meter were it to melt, may be contributing as much to sea level rise as all of Antarctica was thought to contribute a decade ago.

  5. Dissecting Mass Extinctions

    The extinctions at the close of the Paleozoic are thought to be characterized by an “instantaneous” event (in geological terms) at the Permian-Triassic boundary, along with a distinct mass extinction event 10 million years earlier. Villier and Korn (p. 264) studied the variety of forms of the conch-like ammonoids to further characterize these mass extinctions. The earlier Cambrian extinction was highly selective and consistent with background extinction driven by environmental change, whereas the mass extinction at the end of the Permian was nonselective and probably caused by a massive catastrophic event.

  6. Genesis Revealed?

    A key question in prebiotic chemistry is how amino acid or nucleotide monomers were condensed to form oligomers. Leman et al. (p 283) show that carbonyl sulfide (COS), a gas that is a product of volcanic eruptions, brings about the formation of peptides from amino acids under mild conditions in aqueous solution. Certain metal ions, alkylating agents, or oxidizing agents increase the yields of the reaction, in some cases dramatically. The authors suggest that COS may have functioned near its volcanic sources in a “polymerization on the rocks” scenario.

  7. Home on the Range

    Large animals seemingly defend larger territories or occupy larger home ranges than are required simply to meet their resource requirements. Jetz et al. (p. 266; see the Perspective by Buskirk) present a solution to this paradox. Their model predicts that with increasing body size and resource requirements, the inevitable dispersion of movements across the range results in reduced encounter rates with neighbors, decreased exclusive use of the range, and increased loss of resources to overlapping intruders. The model is supported by data for several hundred mammal species, and shows that, in large mammals, more than 90% of the available resources within the home range may be lost to neighbors.

  8. A Sophisticated Riboswitch

    RNA gene control elements, or “riboswitches,” can regulate gene expression in ways that were once thought to be the domain of proteins. Mandal et al. (p. 275; see the Perspective by Famulok) now show that adjacent RNA motifs cooperatively bind two molecules of glycine in Bacillus subtilis and turn on an operon involved in glycine cleavage. The level of cooperativity per binding site produces a switch that is sensitive to very small changes in glycine concentration. The riboswitch controls genes responsible for shunting the carbon from excess glycine into the citric acid cycle.

  9. Stressing Out Before an Earthquake


    If seismologists could determine the state of stress in the crust right before an earthquake, they might be able to better understand what causes a rupture to begin. Yamashita et al. (p. 261) have reconstructed the state of stress before the moment magnitude 6.9 Kobe earthquake in 1995 using postearthquake measurements of hydrofracturing in four nearby boreholes and a kinematic model. Significant shear stress built up in the center of the fault, but the edges of the fault did not show any changes. The coefficient of friction was about 0.6, which is consistent with Byerlee's law. These findings indicate that the shear stress of the upper crust did not depend on rock type, but rather on the normal stress of the system.

  10. Of Insects, Wasps, and Viruses

    Almost a third of insect pest populations worldwide are naturally controlled by parasitoid wasps. One of the most astonishing strategies used by some of these wasps to modulate the prey caterpillars' physiology is the injection of a “symbiotic” polydnavirus along with the wasp's eggs. Genome analysis of polydnavirus undertaken by Espagne et al. (p. 286) shows that, unlike that of typical parasitic viruses, the genome is sparsely coded and resembles those of eukaryotes. Viral gene products inhibit the caterpillar's immune defenses and development, thereby guaranteeing the development and the emergence of adult parasitoid wasps. The viruses are not transmitted by infection, but are “inherited” as an endogenous provirus integrated in the wasp's genome. The virus genome seems to have evolved in partnership with the wasp's to play the role of a natural biological insecticide, to both partners' ultimate benefit.

  11. Another Notch for Targeted Therapy?

    T cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer that typically affects children and adolescents. Although the current cure rate is high, T-ALL patients must endure intensive regimens of highly cytotoxic chemotherapy, so there is great interest in developing targeted therapies with fewer side effects. Weng et al. (p. 269) now report that about 50% of T-ALLs have activating mutations in the gene encoding NOTCH1, a transmembrane receptor that regulates T cell differentiation. Together with previous evidence implicating NOTCH1 in cancer development, these results raise the possibility that inhibitors of NOTCH signaling, including the γ-secretase inhibitors, a group of drugs currently being developed for Alzheimer's disease, may merit investigation as anticancer agents.

  12. Mantle Flow in All Directions

    Shear waves at the base of the mantle tend to be split into a fast mode and a slow mode leading to seismic anisotropy. Garnero et al. (p. 259) have determined that the different modes travel in a range of azimuthal directions beneath the Caribbean. This azimuthal anisotropy may be caused by small-scale convection cells at the base of the mantle and provides information about the dynamics of the mantle.

  13. Regulatory Paradigm Revealed

    A well-established mechanism for the controlled degradation of proteins involves phosphorylation of the target protein, which marks the protein as a target for ubiquitin E3 ligases. Ubiquitination then leads to proteasomal degradation of the protein. Gao et al. (p. 271, published online 9 September 2004) show that controlled degradation of the transcription factor c-Jun is regulated not by Jun phosphorylation per se, but by the phosphorylation-dependent activation of the ubiquitin E3 ligase Itch. The c-Jun N-terminal kinase (JNK), which phosphorylates and activates Jun, also phosphorylates and activates Itch, which then mediates enhanced degradation of Jun. This feedback mechanism appears to attenuate the signaling pathway that leads to the production of T helper 2-type cytokines and may help to control T cell activation.

  14. Removing Epigenetic Marks

    Enzymes that covalently modify histones generally come in pairs that have opposing effects on gene expression, such as acetylases and deacetylases or kinases and phosphatases. One notable exception are the enzymes that methylate histones on lysine or arginine residues. No enzymes had been identified that remove these potent and very stable epigenetic marks, until now. Wang et al. (p. 279, published online 2 September 2004) show that the enzyme peptidylarginine deiminase 4 (PAD4), which converts unmodified arginine residues to citulline in histones, can also convert methylated arginine residues in histones to citrulline, thereby removing the methyl mark (“demethylimination”). PAD4 can modulate the expression of genes known to be regulated by arginine histone methylases, which suggests that at least one of the elusive histone demethylases may have been identified.