Science Roundup


Industrial Chemistry
Introduction to Special Issue

Fuels, pharmaceuticals, plastics, paints, and countless other components of modern life are prepared through chemical synthesis at the industrial scale. At the molecular level, chemical processes take place in much the same way whether the bulk material is being collected in fractions of a milligram or hundreds of kilograms. At the industrial scale, however, cost can be a concern, and factors such as waste disposal and reaction efficiencies require special consideration. A special section of the 7 Aug 2009 Science elaborated on the challenges and opportunities in industrial chemistry as the field embarks on its second century of development. Four Perspectives discussed the design of chemical reactors, the future of pharmaceutical process chemistry, reinventing the world's most common synthetic polymers, and efforts to replace petroleum with biofuels. News stories, meanwhile, explored efforts to reform the U.S. Toxic Substances Control Act, and the quest for faster, more effective toxicology tests (listen to the related podcast interview). In a Science Careers feature, young chemists offered impressions and advice to others planning to make the leap from academia to industry.


Stemming the Flu

The distribution of vaccines for infectious diseases like influenza is a complex issue lying at the intersection of public health, economics, and ethics. Mathematical modeling of disease transmission can be a valuable tool for guiding policy, and in a Report published online, ahead of print, in Science Express on 20 Aug 2009, Medlock and Galvani presented an analysis of how to distribute influenza vaccine among different age groups in a way that will minimize spread of the virus. The team used survey-based data and mortality data from historical influenza pandemics to determine optimal vaccine allocation based on five different measures: deaths, infections, years of life lost, contingent valuation, and economic costs. They found that optimal vaccination is achieved by prioritization of schoolchildren (ages 5 to 19) and adults aged 30 to 39 years. This is because schoolchildren are most responsible for transmission, and their parents serve as bridges to the rest of the population. The results suggest that the current recommendations for vaccine distribution from the U.S. Centers for Disease Control and Prevention, for both seasonal influenza and the more recent swine-origin HINI influenza, probably need to be revised to account for age-related patterns of transmission. Lead author Jan Medlock discussed the work in a related podcast interview.


The Gamma-Ray Sky

Pulsars are fast-spinning neutron stars that emit radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently, only seven were observed to pulse in gamma rays, and they were all discovered at other wavelengths. Results from the Fermi Gamma-ray Space Telescope, launched in 2008, are now helping to illuminate the gamma-ray sky (see the Perspective by J. P. Halpern). In a Research Article in the 14 Aug 2009 Science (published online 2 Jul), Abdo et al. reported the detection of 16 gamma-ray pulsars using the Large Area Telescope, the main instrument on Fermi. Thirteen of these pulsars coincide with previously unidentified gamma-ray sources, and many are associated with supernova remnants. With time, pulsars slow down and cease to radiate -- but they can live a second life in binary systems where they can acquire mass and spin momentum from their companions and radiate anew as millisecond pulsars. In a Report in the same issue, Abdo et al. reported the detection of pulsed gamma rays from eight millisecond pulsars rotating faster than 200 times per second. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars, suggesting that they share the same basic emission mechanism in which the gamma rays are produced in the outer magnetosphere of the neutron star. Finally, in another study, Abdo et al.  reported detection of gamma-ray emissions from the globular cluster 47 Tucanae. The data indicate that the emissions derive from as many as 60 millisecond pulsars within the cluster -- twice as many as predicted by radio observations.


Designer DNA Curves

DNA nanotechnology aims to use DNA as a molecular engineering material to create nanostructures with controlled geometries, topologies, and periodicities and to organize matter with nanometer precision. Now, in a Report in the 7 Aug 2009 Science, Dietz et al. describe an important step toward building sophisticated molecular machines: engineering complex DNA shapes that can twist and curve at the nanoscale. The principal building blocks of the novel structures are DNA bundles, arranged in honeycomb lattices. Targeted insertions and deletions of base pairs in some DNA helices but not others, creates stress in the DNA bundles and causes them to twist or bend in controllable ways. The researchers were able to produce curvatures as tight as 6 nanometers and combine multiple curved elements to build intricate nanostructures including a wireframe beach ball and square-toothed gears (listen to a related podcast interview with senior author William Shi). An accompanying Perspective by Y. Liu and H. Yan explained that although other groups have created DNA nanostructures with curved features, the new study is different in that the curvatures continuously connect different DNA nanostructure domains and can be quantitatively controlled.


Mapping Maize

Corn, or maize, is a staple food crop in much of the world, as well as a source of cooking oil, grain alcohol, livestock feed, and biofuel. Maize strains display tremendous variation in traits of agronomic importance -- such as yield and pest resistance -- due to genetic variation in multiple regions of DNA referred to as quantitative trait loci (QTL). In the 7 Aug 2009 Science, Buckler et al. and McMullen et al. described the genetic properties of a new resource for mapping quantitative traits in maize and used the resource to study the genetic architecture of flowering time. The researchers crossed a common reference strain to 25 diverse maize lines. Individuals resulting from each of the 25 crosses (families) were self-fertilized for four further generations to create a population of 5000 inbred lines, capturing ~136,000 recombination events. Variation in recombination was not attributable to QTLs with general effects on recombination, but rather to numerous and localized regions of variation in recombination specific to each family. Nearly a million plants were used to dissect variation in maize flowering time. Consistent with results from mice, flies, and humans for many different quantitative traits, the researchers found that differences in flowering time were not caused by a few genes with large effects, but by numerous QTL with small effects. An accompanying Perspective by T. F. C. Mackay highlighted the studies.


Friendly Fire

The controlled use of fire was a breakthrough development in human evolution, allowing for the production of warmth and light, cooking, and protection from predators. In the 14 Aug 2009 Science, Brown et al. offered evidence that early modern humans were using fire to improve the processing of raw materials about 72,000 years ago and possibly as early as 164,000 years ago in coastal South Africa. The find adds to the evidence that a wide range of sophisticated behaviors -- including jewelry making and symbolism -- were flourishing around the same time (see the ScienceNOW story by A. Curry). Experiments of heat-treating and analysis of artifacts from multiple archaeological sites indicate that stone materials, including tools crafted from silica-rich silcrete, were systematically manipulated with fire to improve their flaking properties. In an accompanying Perspective, J. Webb and M. Domanski explained how heat treatment can improve tool production, noting that "[b]y enabling the manufacture of more efficient tools, heat treatment may have played a key role in allowing early modern humans to spread rapidly from the relatively benign environments of southern Africa into the colder, more hostile environments of Europe."


Imitation and Affiliation

Imitation may be the sincerest form of flattery, but it's also a good way to make friends. When others mimic us -- often unconsciously and unintentionally -- we like them more, empathize with them more, and are more helpful and generous toward them. Some researchers suggest that imitation has played an important role in human evolution by helping to maintain harmonious relationships. According to a new Report in the 14 Aug 2009 Science, the social consequences of mimicry may have deeper evolutionary roots than previously thought. Paukner et al. showed that capuchin monkeys, a highly social primate species, prefer human imitators over non-imitators in a variety of ways: The monkeys look longer at imitators, spend more time in proximity to imitators, and choose to interact more frequently with them in a token exchange task (see the related ScienceNOW story by E. Pennisi). An accompanying Perspective by J. Call and M. Carpenter highlighted the study and commented that "[f]uture studies will be needed to ascertain precisely what type of social information nonhuman animals extract from social mimicry."


Chemosensory Cilia

Epithelial cells that line the human airway are constantly bombarded by environmental hazards, including toxins, viruses, and bacteria. The airway rids itself of these irritants by secreting mucus to "capture" harmful substances and by increasing the beat frequency of motile cilia on epithelia cells to sweep the mucus out of the system. It has been assumed that motile cilia serve a purely motor function, but in a Report in the 28 Aug 2009 Science (published online 23 Jul), Shah et al. show that these organelles are also chemosensory, expressing bitter taste receptors and their associated signaling machinery. The researchers found that when stimulated with bitter compounds, cultured human airway epithelial cells respond with an increase in intracellular calcium ion concentration and a concomitant increase in ciliary beat frequency. Thus, airway epithelia contain a cell-autonomous system in which motile cilia both sense noxious substances entering airways and initiate a defensive mechanical mechanism to help eliminate the offending compound. An accompanying Perspective by S.C. Kinnamon and S.D. Reynolds  highlighted the study.


Early Solar System Chronometer

Models of the evolution of the early solar system rely on knowledge of the precise time scales for the physical and chemical processes that occurred in the early accretion disk. The short-lived radioactive aluminum isotope 26-Al has long been used as a relative chronometer of these early solar system processes, but its accuracy rests on the assumption that it was uniformly distributed in the initial solar accretion disk. In a Report in the 21 Aug 2009 Science, Villeneuve et al. validated this assumption on the basis of high-precision isotopic analyses of materials from primitive meteorites. The researchers used secondary ion mass spectrometry to measure magnesium isotopic compositions (26-Al decays to 26-Mg) and Mg/Al ratios in chondrules, the basic building blocks of primitive meteorites, and then calculated the 26-Al/27-Al ratio at the time of crystallization of each chondrule. Their results confirm that 26-Al was indeed uniform in the early solar system to about the 10% level and also show that chondrules formed in discrete events over a time period of more than 1 million years. An accompanying Perspective by A.M. Davis discussed the findings and the new questions they raise about early solar system processes.


Major Ozone Threat

Stratospheric ozone is depleted by many different chemicals, the most recognized being the chlorofluorocarbons (CFCs) responsible for causing the Antarctic ozone hole. Now, in a Report published online, ahead of print, in Science Express, Ravishankara et al. report that another chemical, nitrous oxide, is the single greatest ozone-depleting substance in the atmosphere today -- and is expected to remain the dominant ozone-depleting chemical throughout the 21st century, if emissions are not controlled. Global anthropogenic emission of nitrous oxide now -- produced mainly as a byproduct of fertilization, fossil fuel combustion and industrial processes, and biomass and biofuel burning -- is roughly 10 million tonnes per year compared to slightly more than a million tonnes from all CFCs at the peak of their emissions. Unlike CFCs, nitrous oxide has both natural and human-made sources. Moreover, its use and emissions are not regulated by the Montreal Protocol, an international treaty that has been successful in helping to stem emissions of ozone-depleting substances and in reversing the growth rate of the ozone hole. The researchers note that limiting future nitrous oxide emissions would enhance the recovery of the ozone layer from its depleted state, and -- because nitrous oxide is also a potent greenhouse gas -- would also reduce the anthropogenic forcing of the climate system. Lead author A. R. Ravishankara discussed the work in a related podcast interview.


Clues to Coat Variation

Two studies reported in Science this month investigated the molecular mechanisms that underlie variation in coat color and type in mice and dogs.
 
-- Linnen et al. (28 Aug 2009) investigated the molecular mechanisms underlying color variation in deer mice living on the Nebraska Sand Hills. The mice that live on the sand are much lighter in color than mice living nearby on darker soils. The researchers found that the paler color is due to changes at the Agouti coat color locus that arose de novo after the formation of the Sand Hills. Their findings demonstrate that rapid adaptive change does not always rely on preexisting genetic variation.
 
-- Cadieu et al. (published online 27 Aug 2009) examined the genetic basis of coat growth pattern, length, and curl in domestic dog breeds. The team performed genome-wide association studies of more than 1000 dogs from 80 domestic breeds and found that distinct mutations in just three genes together account for the majority of coat phenotypes in purebred dogs in the United States.




In Science Signaling

How Worms Learn with PKD

UUpon activation by various hormones and neurotransmitters, phospholipase C (PLC) catalyzes the production of the membrane-associated second messenger diacylglycerol (DAG), which is known for its role in recruiting and activating various isoforms of protein kinase C (PKC). DAG also recruits and, along with PKC, activates protein kinase D (PKD). PKD phosphorylates substrates distinct from those targeted by PKC, and studies in cultured cells have suggested that PKD may regulate numerous cellular processes, but its specific in vivo functions have remained unclear. In a Research Article in the 11 Aug 2009 issue, Fu et al. reported that two isoforms of PKD are found in the nematode Caenorhabditis elegans -- one in the intestine and the other in the nervous system. C. elegans learns to avoid sodium ions, normally a strong attractant, after being exposed to sodium-containing solutions in the absence of food. Experiments with various mutant and transgenic animals revealed that activation of neuronal and intestinal PKDs through the PLC-DAG-PKC signaling pathway was critical to this salt taste–induced learning.

Also in Science Signaling this month:
-- Bader highlighted computational and experimental techniques for analyzing signaling networks (4 Aug 2009)
-- Yasukawa et al. demonstrated that a protein that mediates mitochondrial fusion also suppresses innate immune responses to viral infection (18 Aug 2009)
-- Grillet et al. presented a slideshow on mechanotransduction in the mammalian inner ear (25 Aug 2009)


Image credits (in order of appearance): I. W. Davies and C. J. Welch; Hendrik Dietz; Wei Ming/La Trobe University; Tom Moninger (epithelia generated by Phil Karp); Emily Kay.