Editors' Choice

Science  08 Jul 2005:
Vol. 309, Issue 5732, pp. 222
  1. EARTH SCIENCE

    Water Water Everywhere?

    1. Brooks Hanson

    Seasonally, the amount of water stored on and in the upper part of the various land areas and river basins varies greatly. These changes are enough to produce subtle differences in the distribution of mass over Earth, which produce slight effects in its local gravity. To detect these slight variations, the satellite mission GRACE flies twin satellites in formation, which communicate with each other, increasing sensitivity greatly. It has been recording global gravity since its launch in March 2002, producing essentially monthly data sets.

    Ramillien et al.present an analysis of Earth's terrestrial hydrosphere using the GRACE data for the past 2 years, and attempt to separate out water in snow, groundwater, surface water, and soil water. By inversion, and with precipitation data, this also provides information on net evapotranspiration, an important climate parameter. Although the data resolution is still undergoing improvement, large-scale monthly hydrologic changes are evident over Earth's major river basins, and evapotranspiration seems to be more seasonal in tropical basins than in purely equatorial ones. — BH

    Earth Planet. Sci. Lett. 235, 283 (2005).

  2. ECOLOGY/EVOLUTION

    Dolphin Culture

    1. Andrew M. Sugden

    Wild bottlenose dolphins in Shark Bay, Western Australia, have been shown to break off pieces of marine sponge, which they then wear over their closed snouts while probing for fish concealed in the seabed. It has been uncertain whether this “sponging” behavior, which is apparently confined almost entirely to a subset of females, is transmitted genetically or culturally, or whether it reflects ecological preferences of individuals for foraging in particular locations. It is difficult to make direct observations of social learning in wild animals (especially underwater); instead, attempts may be made to rule out alternative explanations. Krützen et al. show that ecological explanations for sponging are unlikely, as spongers and nonspongers (both male and female) forage in the same deep channels. Genetic data gathered from almost 200 individual dolphins, coupled with mating behavioral observations of the animals over a 14-year period, indicate that none of the plausible modes of single-locus inheritance could account for transmission of the behavior. Nevertheless, mitochondrial DNA data indicate that sponging is passed on through a single matriline and that all spongers are closely related. It seems possible that all spongers are descended from a recent, innovative “sponging Eve,” whose daughters and granddaughters have learned the behavior from their mothers. — AMS

    Proc. Natl. Acad. Sci. U.S.A. 102, 8939 (2005).

  3. NEUROSCIENCE

    Cannabis Use Impairs Brain Development

    1. Peter R. Stern

    During early brain development hippocampal activity is driven by two excitatory neurotransmitters, glutamate and GABA. Because GABA does not have the usual inhibitory function it has in the mature brain, other systems need to be in place to stabilize the activity of neuronal networks and prevent the potential danger of runaway excitation that may lead, for example, to epileptic activity. Potential candidates for such a system are the endocannabinoids: endogenously produced metabolites capable of activating the brain's cannabinoid (CB) receptors. Bernard et al. investigated endocannabinoid signaling during the first postnatal week in the rat hippocampus, an age that corresponds, in terms of brain development and physiological activity, to the last trimester of pregnancy in humans. Endocannabinoids were released by both interneurons and pyramidal cells in the CA1 region of the hippocampus, activating CB1 receptors and reducing GABA release. Interfering with endocannabinoid signaling during pregnancy either by smoking cannabis or by using recently developed CB1 receptor antagonists may thus affect the normal brain development of the fetus and the newborn child. — PRS

    Proc. Natl. Acad. Sci. U.S.A. 102, 9388 (2005).

  4. IMMUNOLOGY

    Fatty Obstacle to TB Immunity

    1. Stephen J. Simpson

    Immunopathology caused by the chronic production of inflammatory cytokines is normally avoided through a number of counterinflammatory pathways. Some of these depend on lipid mediators known as lipoxins, including lipoxase A4 (LXA4), which is derived via 5-lipoxygenase (5-LO)-mediated biosynthesis.

    Bafica et al.explored whether the 5-LO pathway might influence the course of experimental M. tuberculosis infection, and found that LXA4 was indeed generated at significant levels in the sera of infected mice. Genetic deficiency in 5-LO increased the ability of animals to control infection, with a reduction in bacterial counts and increase in survival of animals after infection. This was accompanied by amplification of hallmark inflammatory cytokines, including IFN-γ and IL-12, as well as nitric oxide synthase 2, which is an important factor in host resistance to M. tuberculosis. Treatment of 5-LO-deficient mice with a lipoxin analog reversed resistance. 5-LO is already being assessed as a therapeutic target in asthma, and this study suggests that 5-LO inhibition may also help to control chronic infectious diseases. — SJS

    J. Clin. Invest. 115, 1601 (2005).

  5. PROTEIN CHEMISTRY

    An Easy Switch

    1. Julia Fahrenkamp-Uppenbrink

    Protein secondary structure changes from α helices to β sheets appear to play a key role in diseases such as Alzheimer's disease. Metal ions such as Cu2+ and Zn2+ may be partly responsible for these conformational changes. Pagel et al. have now developed a simple peptide model to investigate the influence of metal ions on secondary structure changes.

    The authors have designed a peptide that, depending on the solvent, can form either a two-helix dimer or a β-sheet structure. In a modified version of the peptide, histidine residues are incorporated to encourage metal complexation in the β-sheet configuration. The peptides were exposed to Cu or Zn ions, under conditions that normally favor α-helix formation. Whereas the original peptide did not change structure, the histidine- substituted peptide converted to a β-sheet structure. This process could be reversed by introducing a metal scavenger, proving that metal complexation was responsible for the structural change. The system will be useful for systematic studies of the impact of metals on peptide secondary structure. — JFU

    Org. Biomol. Chem. 10.1039/b505979h (2005).

  6. CHEMISTRY

    Catalysts Taking Turns

    1. Jake Y. Yeston

    Enzymes can be highly selective in promoting reactions of just one enantiomer from a racemic mixture. In dynamic kinetic resolution, a second catalyst is added to rapidly interconvert the starting enantiomers, so that eventually the chiral catalyst guides every molecule in the mixture to a single enantiomer of product. Now van As et al.have adapted this technique to form chirally pure oligoesters from racemic monomers. They use a lipase enzyme to catalyze ring-opening polymerization of 6-methyl-ϵ-caprolactone. The ring-opening liberates an alcohol center that can open another lactone; however, the enzyme selects for attack of an (R)-alcohol on an (S)-lactone. A ruthenium catalyst then racemizes the ring-opened alcohol so that, as the reaction proceeds, the enzyme adds an (S)-center to the end of the growing chain, and the metal swaps the configuration of this center to enable further chain growth. Decomposition of the pentamer and chromatographic analysis revealed 92% selectivity for (R)-configurations in the backbone. The results are an important contribution toward generating a novel route toward enantiopure polyesters. — JSY

    J. Am. Chem. Soc. 10.1021/ja052347d (2005).

  7. STKE

    Before the Rods and Cones

    1. Elizabeth M. Adler

    Rods and cones in the mouse retina, which are necessary for image formation, become responsive to light on the 10th day after birth (P10). The intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin and can detect brightness. By assaying the responses of retinas loaded with a fluorescent calcium indicator, Sekaran et al.examined the early postnatal development of light responses. About 5.4% of cells in the ganglion cell layer responded to 470-nm light at P4 to P5, whereas about 13.7% responded at P0 to P1. The response to light was not affected by pharmacological blockade of glutamate receptors but was absent in retinas from mice that lacked melanopsin. The fraction of light-responsive cells at birth and at P4 to P5 was greater than found in adults. The density of melanopsin-expressing cells was lower at P14 and in adults than earlier in development, peaking at about P4 to P5. ipRGCs project to the suprachiasmatic nucleus of the hypothalamus (SCN), and functional connections from ipRGCs to the SCN were present at P0. Thus, in mice, the ability to detect light substantially predates the ability to form images. — EMA

    Curr. Biol. 15, 1099 (2005).

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