This month in Science Roundup:
Dealing with Disasters
Rethinking Nuclear Power
Melting and Freezing
Silica under Pressure
Earth's Core Spins Faster
Accounting in Ancient Peru
Of Stones and Health
Soil Microbes Aplenty
Adaptable Insect Immunity?
Flowering Signals Revealed
Containing Influenza
Toward Cheaper Genomes
New Route to Stem Cells?
Dealing with Disasters
http://www.sciencemag.org/sciext/disasters/
Devastating disasters like the December 2004 Sumatran earthquake and tsunami remind us that societies today are facing increasingly diverse and costly natural and human-triggered threats. A special section of the 12 Aug 2005 Science surveyed some of the emerging approaches both for preparing for disasters before they happen and for dealing with them afterward. The lasting effects that disasters have on the mental health of affected populations pose a particularly challenging problem. A News story by G. Miller described the massive effort under way in villages around the Indian Ocean to gauge, and help alleviate, the psychological toll of the tsunami. Two Viewpoint articles emphasized steps that can be taken now that will increase security and help society even if a disaster does not strike. For example, preserving natural ecosystems such as reefs diversifies coastal economies, which can reduce vulnerability and enhance recovery from disasters. Two other Viewpoints discussed the need for the insurance industry to adapt in the face of climate change to ensure adequate affordability and availability for even the poorest areas. In a related set of features on Science Online, Next Wave ( http://nextwave.sciencemag.org/ ) explored career and funding opportunities in disaster science.
Rethinking Nuclear Power
http://www.sciencemag.org/cgi/content/summary/309/5738/1168
The threat of global warming and high fossil fuel prices have inspired talk of a revival of nuclear power, but skeptics say it is a poor investment and a worse security risk. A special News Focus in the 19 Aug 2005 Science explored nuclear power's global reach and the prospect of a nuclear renaissance. In the past half-century, nuclear fission has become a widely used source of commercial electricity. Despite the high construction costs and special risks, more than 30 nations now have nuclear power; 104 of the 441 currently working reactors are in the United States. Since the Chernobyl accident, reactor designs have been overhauled. Many now reflect smaller, simpler plants that incorporate so-called passive safety measures, but whether the new designs can overcome the concerns of utilities and the public remains to be seen. While Western governments debate the pros and cons of replacing old nuclear power plants, India, China, and Japan are facing increasing demand for electricity and are rapidly investing in new systems. A concrete plan for disposing of long-lived radioactive waste remains a major impediment to the rise of nuclear power, however. The few plans in the works involve digging deep geologic repositories and relying on robust storage containers to keep the waste from leaking into the biosphere. Not surprisingly, the first hurdle facing any plan is winning the support of the public.
Freezing and melting are among the most common processes in nature, but the detailed mechanisms underlying them are still not fully understood. Two studies in the 19 Aug 2005 Science provided new insight into what happens at the particle level when materials freeze and melt. Alsayed et al.( http://www.sciencemag.org/cgi/content/short/309/5738/1207 ) examined the melting of colloidal crystals composed of microgel particles that undergo large volume changes with small changes in temperature. Using real-time video microscopy, they showed that before a bulk material is warm enough to melt completely, particles "premelt" (move rapidly and show liquidlike diffusion) at grain boundaries and other defect sites where there is additional free energy. Meanwhile, de Villeneuve et al. ( http://www.sciencemag.org/cgi/content/short/309/5738/1231 ) investigated the effect of impurities on crystal structure and growth. The researchers found that small impurities distort and slow crystallization more so than larger ones, because of their greater curvature. They also found that the first particle layer around each crystal impurity remains fluid. An accompanying Perspective by P. N. Pusey ( http://www.sciencemag.org/cgi/content/short/309/5738/1198 ) highlighted the studies.
Two Reports in the 5 Aug 2005 Science described some intriguing properties displayed by silica subjected to high pressure and stress. Li et al. ( http://www.sciencemag.org/cgi/content/short/309/5736/909 ) found that during the fabrication of nanoparticles consisting of a silver core surrounded by a silica shell, controlling the cooling rate can induce stresses in the silica such that it forms predictable mathematical arrangements that happen to resemble the natural, highly ordered patterns found in plant buds. Such "stress engineering" could facilitate mass-production of biosensors and other micromachines.
In another study, Kuwayama et al. ( http://www.sciencemag.org/cgi/content/short/309/5736/923 ) confirmed a long-standing prediction that under extremely high pressure, silica can adopt a crystal structure like that of the mineral pyrite -- with each silicon atom coordinated to six nearby oxygens and two more distant ones. Although silica is the most abundant oxide component in the Earth's crust and mantle, it is unlikely that this crystal form plays a role because the pressures required to make it are greater than those found in Earth's core. Nevertheless, the new structure has implications for the existence of silica oxide in the deep planetary interiors of gas giants such as Uranus and Neptune.
Several studies during the past 10 years have suggested that Earth's inner core is rotating faster than the rest of the planet, but other studies have challenged these interpretations. In a Report in the 26 Aug 2005 Science, Zhang et al. ( http://www.sciencemag.org/cgi/content/short/309/5739/1357 ) presented new evidence confirming this so-called superrotation. The researchers analyzed 18 seismic doublets -- nearly identical earthquakes that occur in the same place but years or decades apart -- near the South Sandwich Islands in the South Atlantic Ocean. If Earth's core rotates faster than the mantle, quakes striking the same place, but separated in time, will send out waves that take slightly different paths through the core and arrive in Alaska a bit sooner than they did the time before. The researchers found that this was indeed the case. Their measurements indicate the core is rotating faster by about 0.009 second per year and that it takes about 900 years for the inner core to gain one full revolution on the rest of the planet. As noted in an accompanying News story by R. A. Kerr ( http://www.sciencemag.org/cgi/content/short/309/5739/1313a ), "researchers can now consider what the observed superrotation says about Earth's interior or changes in the length of a day."
The Inka Empire was the largest pre-Columbian empire in the New World, yet it apparently lacked a written language. The empire was not lacking in communicative power, however. Sets of intricately knotted and colored strings called khipu were used for record keeping, but deciphering their meaning and significance has proven to be a major challenge. In a Report in the 12 Aug 2005 Science, Urton and Brezine ( http://www.sciencemag.org/cgi/content/short/309/5737/1065 ) help unravel the story behind these enigmatic strings. Through a computer-aided analysis of seven khipu that appear to comprise a "set," the researchers identified one way that data and instructions were passed through the Inka bureaucracy. Most khipu consist of a main horizontal cord from which as many as a thousand smaller knotted strings dangle. The team found that successive khipu record summations of other ones and may thus represent demands for labor or goods that were passed down the administrative hierarchy or reports of taxes that were passed up to high-ranking officials. An accompanying News Focus by C. C. Mann ( http://www.sciencemag.org/cgi/content/short/309/5737/1008 ) noted that "[t]he increased belief that the khipu were a complex means of communication is coupled with growing recognition of the extraordinary role of textiles in the precolonial Andes."
Chandra Dissanayake, senior professor of geology in Sri Lanka and author of this month's "Global Voices of Science Essay" essay ( 5 Aug 2005; http://www.sciencemag.org/cgi/content/full/309/5736/883 ), has dedicated his career to studying the influence of geologic factors on human and animal health -- a discipline that has come to be known as medical geology. Indeed too much or too little of key elements can mean the difference between sickness and health. In his essay, Dr. Dissanayake reviewed some of the ways that local or regional geology can affect our well-being, including the presence of fluoride in drinking water, iodine deficiencies caused by materials that trap the mineral in the soil, and the connection between hard water and reduced heart disease. He also described a curious paradox, by which people affected by high levels of background radiation often do not appear to suffer any harmful health effects. An online slideshow ( http://www.sciencemag.org/sciext/globalvoices/ ) accompanied the essay.
Measuring species diversity is essential for understanding ecological dynamics as well as evaluating the effects of factors such as pollution, climate change, and foreign species encroachment. Unfortunately, traditional methods of calculating diversity by identifying and counting organisms fail for microbes owing to the overwhelming complexity of bacterial communities. In a Report in the 26 Aug 2005 Science, Gans et al. ( http://www.sciencemag.org/cgi/content/short/309/5739/1387 ) apply a new method based on historical data for DNA reassociation kinetics, which involves measuring the amount of time it takes for separated strands of DNA to find their other halves in a pool of sequences. The researchers estimate that pristine soils contain more than one million different bacteria, most of them rare. That's at least 100 times more species than previously thought. The new work also highlights the dramatic effects of pollution on diversity: the presence of toxic metals destroys rare microbial species leading to loss of 99% of the original diversity. An accompanying Perspective by T. P. Curtis and W. T. Sloan ( http://www.sciencemag.org/cgi/content/short/309/5739/1331 ) highlighted the study as an example of how, in field of microbial ecology, "our powers of observation can be vastly enhanced by sensible mathematical techniques."
The ability to produce millions of distinct antibodies that can bind to and thwart pathogens is considered a hallmark of higher vertebrates. Now a Report published online Science Express on 18 Aug 2005 suggests that insects have their own version of a complex, adaptive immune system. Watson et al. ( http://www.sciencemag.org/cgi/content/abstract/1116887 ) described a mechanism of alternative splicing of the insect gene Dscam, that has the potential to generate an exceptional level of protein diversity. Previously known for its role in neuronal development, Dscam is a member of the immunoglobulin superfamily -- a diverse group of immune proteins. The gene contains 116 coding regions that can mix to encode as many as 19,000 protein isoforms. The researchers identified a number of these proteins in fruit fly hemolymph -- the insect equivalent of blood serum -- and on the surfaces of fat body cells and immune cells called hemocytes. Further functional studies suggest that some isotypes of Dscam could assist in the phagocytosis of bacteria (by which cells ingest and destroy the microbe), pointing to a direct and adaptable form of insect immunity. An accompanying News story by E. Pennisi ( http://www.sciencemag.org/cgi/content/short/309/5738/1166a ) highlighted the report.
Although plants respond to environmental conditions such as day length, temperature, and nutrient availability by signaling mechanisms in their leaves, they coordinate this response to the production of flowers in their shoots. Three studies reported in Science this month investigated the molecular and genetic details of this coordinated signaling effort and further identified the elusive signal that travels from leaf to shoot. In two Research Articles in the 12 Aug 2005 Science, Abe et al. ( http://www.sciencemag.org/cgi/content/short/309/5737/1052 ) and Wigge et al. ( http://www.sciencemag.org/cgi/content/short/309/5737/1056 ) showed that in the model plant Arabidopsis thaliana two nuclear genes, one activated in the leaf and one in the shoot, work together to determine the time and location of flowering. Flowering Locus T (FT) is expressed in leaves in response to daylight conditions conducive for flowering. FD is a transcription factor expressed only in the shoot apex (where new flowers develop). Together, the FT and FD proteins activate key genes required for flower development. In a related Report published online Science Express on 11 Aug 2005, Huang et al. ( http://www.sciencemag.org/cgi/content/abstract/1117768v1 ) showed how the two factors meet: the FT messenger RNA transcript travels from the leaf through the plant vascular tissue to the shoot, where the FT protein is then made. An accompanying Perspective by M. A. Blázquez ( http://www.sciencemag.org/cgi/content/full/309/5737/1024 ) highlighted the studies.
Given influenza's history, most experts agree that the world is sure to be hit by another pandemic. The question is when it will occur and how bad it will be. The widespread outbreaks of avian flu in Southeast Asia currently pose the most obvious source and threat -- a simple mutation or reassortment of the avian virus could result in a strain that is devastating to humans. In a study reported in the 12 Aug 2005 Science (published online 4 Aug 2005), Longini et al. ( http://www.sciencemag.org/cgi/content/short/309/5737/1083 ) used an epidemic simulation model to investigate how the disease, starting with a single case, would spread through a rural Southeast Asian population in a variety of different scenarios. Their analysis indicates that there is a good chance of preventing the spread of any emergent influenza strain at the source through proper surveillance and the aggressive use of influenza antiviral agents, quarantine, and vaccines. According to the model, the success of these measures would depend on the infectiousness of the pandemic virus, but in all cases, early intervention was essential. An accompanying News story by M. Enserink in the 5 Aug issue ( http://www.sciencemag.org/cgi/content/short/309/5736/870 ) highlighted the Report.
Given the high cost of deciphering genomes, most labs have left that job to big sequencing centers. Now, a Report published online Science Express on 4 Aug 2004 describes a new DNA sequencing technology that may give small labs a chance to do more of their own sequencing. Using off-the-shelf instruments and reagents, Shendure et al. ( http://www.sciencemag.org/cgi/content/abstract/1117389 ) sequenced an E. coli genome at a fraction of the cost of conventional sequencing -- roughly ninefold cheaper and with greater accuracy and speed. The researchers used a non-electrophoretic approach based on amplification of DNA fragments followed by ligase-based sequencing on immobilized beads and imaging using an epifluorescence microscope. A related News story by E. Pennisi in the 5 Aug issue ( http://www.sciencemag.org/cgi/content/short/309/5736/862a ) notes that the new technique is one of several new low-cost sequencing approaches that may eventually realize the goal of sequencing individual human genomes for under $1000.
Researchers have shown that they can derive human embryonic stem cells (hES) by a process called somatic cell nuclear transfer, which involves replacing the nucleus of a human oocyte with one from a different cell, and then stimulating development of the egg. In a Report in the 26 Aug 2005 Science, Cowan et al. ( http://www.sciencemag.org/cgi/content/full/309/5739/1369 ) described an alternative method for deriving hES that may ultimately circumvent the need for human oocytes ( see the related News story by G. Vogel in the 8 Jul 2005 issue; http://www.sciencemag.org/cgi/content/short/309/5732/240 ). By fusing adult skin cells with ES cells, the team was able to create hybrid cells that have twice the normal amount of DNA but and share ES cells' talent for differentiating into different cell types. The gene expression profile of the hybrid cells was almost identical to that of normal ES cells. If future experiments indicate that this reprogrammed state is retained after removing the embryonic stem cell DNA -- currently a formidable technical hurdle -- the hybrid cells could theoretically be used to make stem cells genetically matched to individual patients without using oocytes or embryos.