Editors' Choice

Science  07 Oct 2005:
Vol. 310, Issue 5745, pp. 19

    Of Sunlight, Water, and Trees

    Although many examples of environmental changes that are forced by variations in solar energy input have been documented, the solar influence on climate need not be a direct relationship. For example, climate variability can be caused by forcing from internal modes of ocean circulation, ice sheet growth and decay, solar effects induced in different regions and propagated across time and distance, or changes in the biosphere, all of which could recur at frequencies independent of solar input. And even if direct, solar forcing can be nonlinear, which may obscure the driving force of changes at any particular location.

    Turney et al. investigate the links between solar forcing and regional climate in the North Atlantic during the Holocene by comparing the solar component, recorded in the 14C record of tree rings, with surface moisture, derived from fluctuations in the populations of oaks and pines in Irish bogs. They find that climate change in the North Atlantic, on centennial to millennial time scales, is not a direct, linear response to changes in solar input. — HJS

    J. Quaternary Sci. 20, 511 (2005).


    Peptides Seeing Polymers

    The recognition of nonbiological material surfaces by peptides can be useful for controlling material growth or providing a scaffold for surface modification. Examples include mineral surfaces, and peptide motifs that recognize particular polymer compositions have been reported. Serizawa et al. investigated the binding of a large library (~109 members) of short peptides (seven amino acids) and found that a few sequences can selectively latch onto the stereochemistry of the backbone of poly(methyl methacrylate) (PMMA). One peptide, containing an -Arg-Pro-Thr-Arg-motif, had six times greater affinity for isotactic PMMA (with the side chains all on one side of the backbone) over the syndiotactic form (in which the side chains alternate). Modeling suggests that the basic ends of the extended peptide motif recognize a repeat of two to six units in the PMMA chain. — PDS

    J. Am. Chem. Soc. 10.1021/ja054402o (2005).


    Malaria Breaks Out

    The malaria parasite spends part of its life cycle growing and dividing within red blood cells. Infection involves a well-orchestrated invasion process that is followed by growth and division within the so-called parasitophorous vacuole. The parasite progeny, the merozoites, need to escape both the parasitophorous vacuole membrane and the erythrocyte plasma membrane to free themselves. Possible mechanisms of release include the coordinated rupture of both membranes, fusion of the parasitophorous vacuole membrane with the plasma membrane (releasing the merozoites into the blood stream), or release of the parasitophorous vacuole containing the merozoites and subsequent vacuole rupture.

    Glushakova et al. examined the fate of the host and vacuole membranes directly after labeling infected erythrocytes with fluorescent lipids. No erythrocyte ghosts were observed, suggesting that direct rupture of the erythrocyte membrane was unlikely; similarly, inhibition of membrane fusion did not block release. Instead, it appears that the erythrocytes suffer a two-stage release in which the infected erythrocyte membranes first fold and then rupture, releasing free merozoites and leaving behind plasma membrane and internal membrane fragments. How the parasite induces these changes to occur remains to be elucidated. — SMH

    Curr. Biol. 15, 1645 (2005).


    Cosmic Crashes

    Like cheese stirred into hot soup, the gravitational mixing of giant clusters of galaxies leaves behind faint tidal trails of stars and streamers of gas. These fossils give astronomers clues as to the past dynamical history of the cluster, including collisions and interactions between its members, but the streaks can be difficult to see because they are very faint and distorted by instrumental effects in telescope images.

    Mihos et al. have imaged the weak diffuse glow from intra-cluster light in the well-known and nearby Virgo cluster. At a distance of only 16 million parsecs, Virgo covers an area of several degrees on the sky, so obtaining deep and uniform images over such a wide area has been tricky. These images show a web of tidal tails and bridges between galaxies, as well as common envelopes of gas and stars circling galaxy groups. The clumpiness of the diffuse light shows that the cluster formed from many smaller galaxy groups crashing together—the process of hierarchical assembly—rather than growing smoothly from steady accretion. — JB

    Astrophys. J. 631, L41 (2005).


    Picky Inhibitors for PI3K

    Selective inhibition of signaling pathways that lead to inflammation represents a major goal of drug discovery. Because of their regulation of multiple signaling pathways, the phosphoinositide 3-kinase (PI3K) enzymes are particularly attractive targets, although so far the selectivity and efficacy of PI3K inhibitors have been modest.

    Using structure-based design, Camps et al. identify small molecules that inhibit the gamma isoform of PI3K and not PI3K α, β, or δ; AS-605240 displayed specificity and potency, preventing phosphorylation of the downstream mediator protein kinase B in vitro. Oral administration of this inhibitor impeded joint inflammation in two experimental rodent models of rheumatoid arthritis. The corresponding reduction in neutrophil infiltration seen in the inflamed joints was consistent with the inhibitory effects of AS-605240 on monocyte and neutrophil chemotaxis in vitro and in vivo. In another study, Barber et al. found that oral dosing of the same inhibitor diminished the severity of an experimental form of the autoimmune disease systemic lupus erythromatosis. Both studies suggest that treatment of inflammatory conditions in humans might be improved through the selective targeting of this and other PI3K pathways. — SJS

    Nature Med. 9, 936; 933 (2005).


    For or Of

    Unlike the title, which is equally valuable (or not) read backward or forward, beliefs acquire different values depending on whether we rely on them as explanations for why things happen or instead focus on figuring out explanations of how these beliefs evolved. In surveys of Boston train station patrons, Preston and Epley found that a statement describing human behavior—individuals prefer partners with similar characteristics—was regarded as being important and relevant when it was applied as a causal guide for organizing and predicting life's events. On the other hand, coming up with possible explanations as motivating this statement reduced its perceived value, perhaps as a consequence of relegating it to an intermediary in a chain of causes and effects. The authors go on to point out that this valuation hierarchy is consistent with the weighting of scientific disciplines providing mechanistic insights, such as neuroscience, over those that offer broader-scale analysis, such as social psychology. They also note that these two ways of interacting with beliefs—applying them as explanations for x and y versus seeking to uncover explanations of a and b—may bear upon discussions of religion and science. — GJC

    Psychol. Sci. 10, 826 (2005).

  7. STKE

    Nanotubular Communication

    Cells often use diffusible molecules to communicate with one another, but results from Watkins and Salter show that some cells are hard-wired. They explored how human monocyte-derived dendritic cells respond to soluble factors released from Escherichia coli. When the supernatant of a bacterial culture was applied near a dendritic cell with a micropipette, the stimulus appeared to spread not by diffusion, but rather by passing from one cell to another. High-resolution differential interference contrast microscopy revealed intercellular tubular structures up to 100 μm in length and 20 to 200 nm in diameter. When cells were labeled with a calcium-sensitive dye, an increase in the concentration of free intracellular calcium caused by mechanical stimulation of one cell could be seen to pass via the nanotubules. Furthermore, THP-1 monocytes, which themselves did not respond to the supernatant, displayed calcium responses within seconds after nearby dendritic cells had been pulsed with the bacterial products. The authors propose that immune cells may use such communication to distribute intracellular signals across large networks of cells. — LBR

    Immunity 23, 309 (2005).