Editors' Choice

Science  09 May 2003:
Vol. 300, Issue 5621, pp. 867

    Renewable Nylons

    Many efforts aimed at improving the environmental friendliness of a chemical process tend to focus on minimizing unwanted side products or solvent use, or on replacing a fossil fuel-based material with a different one based on a renewable feedstock. Thomas et al. now report on a catalytic method for producing a key intermediate that allows the same product, in this case nylon, to be made from renewable sources. Adipic acid is widely used in the production of nylon and is usually produced from fossil fuel-derived benzene. Thomas et al. used muconic acid, which can be derived from glucose, as the starting material. Their catalysts consisted of bimetallic clusters anchored in the pores of mesoporous silica. A Pt10Ru2 composition was more selective than several other bimetallic clusters and was also superior to monometallic Pt and Rh catalysts. Bimetallic catalysts of this kind may also be useful for other environmentally friendly hydrogenation reactions.—JFU

    Chem. Commun. 10.1039/b300203a (2003).


    Dropping the Voltage

    “Smart windows” that control the amount of light coming into a room are based on nematic liquid crystals dispersed in polymer matrices. With no applied electric field, the random orientation of the molecules scatters light and the display is dark. Turning on the field aligns the molecules, and in this state they match the refractive index of the matrix and transmit light. This same idea can be used to control the direction of the transmitted light in device applications, but even higher switching voltages are required. Rudhardt et al. found a way to disperse nematic liquid crystals that can lower the necessary voltage. They created droplets of a nematic by extruding the material through a capillary into a flowing stream of water that contained a small amount of poly(vinyl alcohol) (PVA). Because the droplets formed when the viscous drag exceeded the surface tension, they tended to be very uniform in size. The droplets were placed on a conducting glass slide (one coated with indium tin oxide) and allowed to dry. The droplets spontaneously ordered into a hexagonally close-packed monolayer, but the thin PVA layer prevented coalescence. The PVA also controlled the orientation of the nematic, which at rest is governed by two disclinations at the edges. The devices can be switched between an off state to an ordered one at 0.05 V per micrometer, but a transition between two ordered states which changes the diffracted intensity by 80% can be achieved at voltages as low as 0.03 V per micrometer.—MSL

    Appl. Phys. Lett. 82, 2611 (2003).


    Diabetic Voles

    Infection with specific strains of virus and autoimmunity are each implicated in the destruction of insulin-producing β cells of the pancreas that leads, eventually, to the development of type 1 diabetes.

    In a study of wild bank voles, Niklasson et al. found evidence for a direct association between type 1 diabetes and infection by a novel picorna virus. Although no diabetes could be detected in recently captured voles, one-third of those kept in captivity developed elevated blood glucose levels and showed destruction of β cells by 1 month. Diabetic animals developed elevated antibodies to the new virus, as well as to proteins familiar as potential autoimmune targets in human diabetes. Inoculation of nondiabetic voles with the virus correlated with the onset of varying degrees of β cell destruction and viral presence in the pancreatic islets, suggesting a direct role for the virus in the disease. A preliminary study of children with type 1 diabetes also revealed a modest increase in antibodies to the same picorna virus, suggesting that it might contribute to some cases of human type 1 diabetes, possibly as a result of zoonosis from this rodent reservoir.—SJS

    Exp. Diabesity Res. 4, 35 (2003).


    Not Your Typical Gallstone

    Vaterite is a CaCO3 polymorph that tends to form spherules and is most painfully familiar to some as gallstones. Inorganic vaterite is rarely found on Earth and has never been conclusively found to precipitate from natural waters.

    Grasby has found vaterite precipitating inorganically from supraglacial sulfur-rich natural spring waters in Borup Fiord Pass, Ellesmere Island, in the Canadian High Arctic. Vaterite precipitation is favored because the water is extremely cold (1° to 2°C) and highly alkaline (pH 7.3 to 9.5). Sulfate-reducing bacteria are active in these springs, making the competing process of methanogenesis, which might yield organic vaterite, unlikely. Understanding how vaterite forms in this extreme biogenic environment can help to explain carbonate precipitation under different conditions and provides clues about terrestrial extremophiles and their biomarkers, and perhaps useful analogs for other planetary environs. Groundwater discharges at Borup Fiord Pass are similar to suggestions of liquid water discharges on Mars and perhaps Europa. The carbonate spherules in the Martian meteorite ALH 84001, considered possible evidence for life, are similar in shape to the vaterite, although the Martian carbonates are rich in Mg and Fe, making any additional correlation inconclusive.—LR

    Geochim. Cosmochim. Acta 67, 1659 (2003).


    Life, Death, and microRNA

    Tissue growth and patterning during development rely on coordinated control of cell proliferation and cell survival. Research from two independent groups now suggests that this relationship may involve microRNA (miRNA). These small regulatory RNAs (21 to 25 nucleotides) are posttranscriptional repressors of gene expression, but their specific functions across species are largely unknown.

    Brennecke et al. show that the bantam gene encodes a miRNA that controls the development of eye and wing imaginal disc structures in Drosophila by stimulating cell proliferation. In vivo bantam expression was spatially regulated during development. This may be controlled by the secreted protein Wingless, linking a signaling morphogen known to control spatial patterning to cell proliferation and tissue formation. Furthermore, bantam repressed the apoptosis-inducing gene hid, blocking hid-induced cell death.

    In a genetic screen for inhibitors of apoptosis in Drosophila, Xu et al. identified mir-14 as a miRNA that suppresses the cell death effects of several proapototic genes, including rpr, hid, and grim. A potential target site for mir-14 was identified in a transcript encoding Drice, an apoptotic effector caspase. Flies lacking mir-14 exhibited increased Drice expression and a reduced life-span.

    Thus, miRNAs may represent a general regulatory mechanism of cell death during development.—LDC

    Cell 113, 25 (2003); Curr. Biol. 13, 790 (2003).


    Calcium and the Nucleoplasmic Reticulum

    Calcium is used in multiple signal transduction events within cells to control multiple cellular activities involved in locomotion, morphogenesis, and secretion. In the nucleus, calcium signals regulate gene transcription and cell growth independently of their effects in the cytosol. In trying to visualize and understand nuclear calcium signals, Echevarria et al. revealed the presence of an intranucleoplasmic reticulum. This reticular network of calcium stores was physically connected to the nuclear envelope and to the endoplasmic reticulum. The nucleoplasmic reticulum was enriched in inositol 1,4,5-trisphophate (InsP3) receptors. Under limited localized stimulation, these InsP3 receptors generated local intra-nuclear calcium signals and stimulated nuclear protein kinase C to translocate to the same specific region of the nuclear envelope. Thus, the nucleoplasmic reticulum may represent a specialized cellular compartment involved in regulating in time and space specific intranuclear signalling events.—SMH

    Nature Cell Biol. 5, 440 (2003).

  7. STKE

    PPARδ: Burning off the Fat

    Energy consumption and fat metabolism are the keys to controlling weight gain. Peroxisome proliferator-activated receptors (PPARs) are essential regulators of lipid storage and metabolism. The three isoforms of PPARs—PPARα, PPARγ, and PPARδ—exhibit tissue-specific expression and functions. PPARγ stimulates adipogenesis and lipid storage, whereas PPARα stimulates lipid combustion in the liver. The role of PPARδ is unclear.

    Wang et al. used transgenic mice overexpressing PPARδ in adipose tissue to show that PPARδ inhibited weight gain and blocked fat storage. In adipose tissue from the transgenic mice, PPARδ promoted expression of β-oxidation enzymes, of triglyceride hydrolysis enzymes involved in lipid metabolism, and of proteins that uncouple mitochondria, allowing cellular energy stores to be converted to heat in a process known as thermogenesis. In cultured cells overexpressing PPARδ, β oxidation and triglyceride metabolism were increased in response to a PPARδ agonist. The effects of PPARδ were very similar to those of the transcriptional coactivator PGC-1α. In addition, PPARδ and PGC-1α could be coprecipitated, suggesting that the thermogenic effects of PGC-1α may be mediated through interaction with PPARδ. Thus, PPARδ agonists may provide another target in the war against obesity.—NG

    Cell 113, 159 (2003).