Editors' Choice

Science  01 Dec 2006:
Vol. 314, Issue 5804, pp. 1355

    Going to the Dingoes

    In the past 200 years, since the arrival of Europeans in Australia, 18 of the continent's mammal species have become extinct. These extinctions have been chiefly attributed to introduced, non-native predators, especially foxes and cats. Johnson et al. present evidence that the success of these medium-sized introduced predators has been the direct result of persecution by humans of Australia's native large predator, the dingo. In areas where dingoes have been left alone, foxes and cat populations are kept at bay, and the diversity and abundance of native marsupials are greater. Thus, top predators can maintain biodiversity at middle trophic levels and may help ecosystems to resist invasion by alien species. By allowing dingo populations to recover in regions where they have been persecuted, it might be possible to insure remaining small marsupials against further decline and extinction. — AMS

    Proc. R. Soc. London Ser. B 10.1098/rspb.2006.3711 (2006)


    Toward the Chaperome

    The expression of misfolded or aberrant proteins on the cell surface could wreak havoc with the immune system. Cells have therefore developed an efficient quality-control system, which diverts misfolded membrane and secretory proteins from the secretory pathway by retaining and degrading them at the entry portal to the secretory pathway, the endoplasmic reticulum (ER). One well-studied example of quality control involves the cystic fibrosis transmembrane conductance regulator (CFTR), misfolding of which is responsible for disease in a large proportion of sufferers. However, sometimes quality control is too stringent, and functional, though mutant, proteins are retained. Wang et al. used a systematic approach to examine the folding pathway and protein interaction partners of CFTR and the common disease variant CFTR ΔF508, which, even though functional, is retained in the ER. A variety of chaperone proteins, which help to promote protein folding, are present in the ER, and a chaperome of over 30 proteins involved in CFTR folding and transport was identified from among more than 200 interacting proteins. In particular, Aha1, a Hsp90 co-chaperone ATPase regulator, was found to be important in retaining mutant CFTR. When levels of Aha1 were reduced, mutant CFTR managed to escape from the ER and reached the plasma membrane. Interfering with CFTR-specific chaperone mechanisms may thus be a useful strategy to correct disease, and other protein misfolding diseases might be similarly amenable to equivalent interventions. — SMH

    Cell 127, 803 (2006).


    Sediment Sources

    The Nile River drains much of northeast Africa, and its sediments reflect erosion across the continent. Dams such as the Aswan have caused efficient collection of these sediments in the human-made lakes that form behind them. Garzanti et al. examined the mineralogy and amount of sand dumped by the Nile into these lakes and found that ∼200 million metric tons of sediment are transported per year, several times the quantities estimated previously. The sand is mainly composed of basaltic rock or feldspar and metamorphic minerals, indicative of the Ethiopian highlands, an area of abundant deforestation and farming that receives monsoon rainfall during summer. Thus, a relatively small area of the Nile drainage, greatly affected by humans, supplies most of the sediments carried by the river to artificial lakes. — BH

    Earth Planet. Sci. Lett. 10.1016/j.epsl.2006.10.001 (2006).


    Catalyst Compatibility

    The isolation and purification procedures that follow synthetic chemical reactions often produce substantial quantities of waste material. Research has thus increasingly focused on methods for carrying out multiple reaction steps in a single vessel. However, the mutual incompatibility of many catalysts, in particular Lewis acids and bases, presents a major challenge to this approach.

    Poe et al. present an encapsulation technique that allows the mixing of a polymeric amine catalyst with a nickel-centered Lewis acid while avoiding the complexation reaction that would deactivate both. The poly(ethyleneimine) base is treated with a cross-linking agent in a methanol/cyclohexane emulsion, yielding a microcapsule morphology that conserves catalytic activity in the condensation reaction of benzaldehyde and nitromethane. Addition of a bis(diamino)nickel catalyst to the reaction mixture promotes a Michael addition of dimethyl malonate to the dehydrated product in ∼80% yield. Moreover, the compatibility of the two catalysts is a boon to selectivity as well as efficiency; the nickel complex staves off a side pathway that would lead to a double nitromethane adduct. — JSY

    J. Am. Chem. Soc. 128, 10.1021/ja066476l (2006).


    Trekking Lymph Node Tracks

    Lymph nodes are crucial staging posts from which immune responses are launched throughout the body. To achieve this, naïve lymphocytes must locate and respond to their specific antigens, which are relatively scarce. The active migratory tendency of lymphocytes helps to achieve this, and the structural organization of the lymph node itself also improves the chances of antigen encounter. Bajenoff et al. now find that organized networks of stromal cells provide trackways for lymphocytes to travel around lymph nodes. With a combination of microscopy and real-time intravital imaging, T cells were seen to enter the lymph node paracortex by interacting with fibroblastic reticular cells (FRCs). Inside the lymph node, the FRC formed a three-dimensional network along which a large proportion of T cells could crawl. Antigen-presenting dendritic cells also associated with the FRC network, which is consistent with the idea that this would optimize the rate of encounter between the two types of cell. B cells were also seen to move along the FRC tracks within the paracortex, transferring to a similar network of dendritic cells once they had entered the lymph node follicle. It will now be interesting to elucidate the molecular cues that govern migration along these cellular highways and byways. — SJS

    Immunity 25 10.1016/j.immuni.2006.10.011 (2006).


    Fast Track for Fusion

    The search for controlled nuclear fusion for energy production has been hindered by substantial engineering and fundamental physical challenges. One approach has been to confine a hot plasma with magnetic fields in a device called a Tokamak and then to heat the plasma until nuclear reactions become self-sustaining. As the plasma is heated, however, the highest-velocity ions can drive wave motions and instabilities that disrupt its integrity. Worse yet, the fast ions can escape with their energy rather than contributing to the heating process. Bindslev et al. report a diagnostic technique in which beams of electromagnetic waves at frequencies of ∼110 GHz are scattered off the ions in the TEXTOR (Tokamak Experiment for Technology-Oriented Research) reactor in Germany. The energy spectrum of the scattered photons from this collective Thomson scattering process reveals the velocity distribution of the fast ions. By acquiring spectra at different times during the heating of the plasma, the authors can uncover the evolution of the fast ion dynamics. Diagnostic tools such as this are expected to be especially important when ITER (the International Thermonuclear Experimental Reactor) commences operation in 2016. — DV

    Phys. Rev. Lett. 97, 205005 (2006).