First sequence-based map of large-scale structural variation across the human genome
May 9, 2008
Medical Science News
A nationwide team of researchers, funded in part by the National Human Genome Research Institute (NHGRI), part of the National Institutes of Health (NIH), has produced the first sequence-based map of large-scale structural variation across the human genome. The work, published today in the journal Nature, provides a starting point to examine how such DNA variation contributes to human health and disease.
Other recently created maps, such as the HapMap, have catalogued the patterns of small-scale variations in the genome that involve single DNA letters, or bases. However, the scientific community has been eagerly awaiting the creation of additional types of maps in light of findings that larger scale differences account for a great deal of the common genetic variation among individuals and between populations, and may account for a significant fraction of disease. While previous work has identified structural variation in the human genome, a sequence-based map provides much finer resolution and location information.
Large-scale structural variations are differences in the genome among people that range from a few thousand to a few million DNA bases. Some are gains or losses of stretches of genome sequence. Others appear as re-arrangements of stretches of sequence. Already, some structural variations have been linked to individual differences in susceptibility to the human immunodeficiency virus (HIV), risk of coronary heart disease, as well as to schizophrenia and autism. Researchers hope the new map will open the door to uncovering the functions of structural variants in even more conditions.
“It is important that we understand how changes in the human genome, both small and large, contribute to individual differences in susceptibility to diseases,” said Francis Collins, M.D., Ph.D. “This map is a valuable starting point for researchers studying the normal patterns of structural variation and how differences in those patterns affect human health.”
Researchers constructed the structural variation map by partially sequencing the genomes of eight people: four people of African descent, two of Asian descent and two of European descent. The samples were collected as part of the International HapMap Project. No medical or personal identifying information was obtained from the donors, but the samples were labeled by population group.
Sequence data were collected from each end of roughly 1 million random small pieces of DNA from each individual?s genome. These end sequences were compared to the reference sequence of the human genome completed in 2003. Where precise matches did not occur, the scientists inferred that there was a structural difference between the volunteer?s sample and the reference sequence of the human genome.
In addition to revealing new variations, the map also provides a more detailed look at the locations of nearly 1,700 structural variations - half of which had not been previously described. About half of the structural variations were found in at least two of the eight genomes analyzed. The work also uncovered 525 new regions of large-scale structural variation in the human genome. The large-scale differences came in many forms, including deletions and out-of-place insertions of long stretches of DNA. Almost half of the new variations consist of differences in how many copies individuals have of a certain gene, which researchers refer to as a copy number variant.
“The structural variation map will give us a much better picture of genetic variation between each individual, and help us better understand these areas of the genome that are prone to large-scale changes over time,” said Evan Eichler, Ph.D., of the University of Washington, who led the research.
Sequence data from the structural variation map are publicly available through the NIH?s National Center for Biotechnology Information Trace Archive, www.ncbi.nlm.nih.gov/Traces. Mapping data are also freely available from the University of Washington, http://hgsv.washington.edu.
In addition to Eichler and his colleagues at the University of Washington, the project included researchers at Agencourt Bioscience Corp., Beverly, Mass.; Agilent Technologies, Santa Clara, Calif.; Washington University School of Medicine, St. Louis; Division of Intramural Research, NHGRI, Bethesda, Md.; the University of Wisconsin, Madison; the Broad Institute of MIT and Harvard, Cambridge, Mass.; and Illumina, Inc., San Diego.
NHGRI is one of 27 institutes and centers at the NIH, an agency of the Department of Health and Human Services. The NHGRI Division of Extramural Research supports grants for research and for training and career development at sites nationwide. Additional information about NHGRI can be found at its Web site, www.genome.gov.
The National Institutes of Health (NIH) - The Nation’s Medical Research Agency - includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases.
http://www.nih.gov.
Binge eating and crash diets could shorten your life
April 30, 2008
Medical Science News
According to scientists in Britain binge eating and crash dieting may significantly reduce life expectancy.
The scientists from Glasgow University in Scotland arrived at this conclusion based on the results of an animal study.
The study which compared the growth rate, success of reproduction and life span of stickleback fish, found that fish given a “binge then diet” food regime had a reduced life span of up to 25%.
The scientists believe their findings could have implications for teenagers and children who follow extreme patterns of dieting while they are still growing.
They say uneven growth, due to the fluctuation in the amount eaten per day, is responsible for the increase in the risk of sudden death.
The study was led by Professor Neil Metcalfe from the university’s faculty of biomedical and life sciences, who says the fish on the fluctuating diet put just as much effort into breeding - the males became brightly coloured as usual and the females produced the normal number of eggs - but their life span was three-quarters that of animals eating a constant amount every day.
Professor Metcalfe says the difference in life span was not a consequence of more rapid ageing but an increase in the risk of sudden death, possibly because the body tissues are more likely to have imperfections due to growth spurts.
Professor Metcalfe says similar results would most likely be seen in other animals with short life spans that grow throughout their lives and could also be applied to humans who follow extreme patterns of dieting which would only occur in children and teenagers.
The findings are published in the journal, Proceedings of the Royal Society B.
Miniscule closed containers for precise delivery of nano-quantities of drugs
April 30, 2008
Medical Science News
Researchers at the USC Information Sciences Institute have demonstrated a way to manufacture miniscule closed containers that might be used to deliver precise micro- or even nano-quantities of drugs.
According to ISI project leader Peter Will, who is also a research professor in the Viterbi School of Engineering, the new technique, described in a paper in the Journal of Micromechanics and Microengineering, is a two-step process.
Part alt=”Researchers at the USC Information Sciences Institute have demonstrated a way to manufacture miniscule closed containers that might be used to deliver precise micro- or even nano-quantities of drugs.” “border=”0″ align=”left” vspace=”0″ hspace=”0″ >Flat forms fabricated in polisilicon, ready for additional processing and subsequent folding. Credit: USC Information Sciences Institute
“Our experiments show” says the paper, that “the combination of partial folding of structures by magnetic actuation and liquid closure to bring the structures to their final closed state is an extremely promising technique for mass production of large arrays of micrometer size ?voxels. Furthermore, we believe that future optimization of the voxel hinge geometry and composition should allow for extensions of our work to” much smaller voxels.
The Voxel team - consisting of Will, professor of chemistry Bruce Koel (who has since gone to Lehigh University), former post-doctoral researcher Alejandro Bugacov and former grad student (now graduate) Rob Gagler folded a number of different shapes, including four- and five-sided pyramids, pentagonal ‘lotus’ shapes, and also simple square plates that folded over each other to make flat mini-envelopes.
Will has been pursuing the idea of creating voxels for many years, “way back to my days in HP labs, when I was working in Medical and Chemical applications.” The USC team designed the chips using MEMSPRO CAD software; the actual chip fabrication was done in France.
“The experimental work was done on campus,” said Will, “since ISI doesn’t have a wet lab.”
The National Science Foundation supported the research, under an exploratory research grant. The paper is “Voxels: volume-enclosing microstructures,” J. Micromech. Microeng. 18 (2008) 055025.
http://www.usc.edu/
Silver nanoparticles may kill beneficial bacteria
April 30, 2008
Medical Science News
Too much of a good thing could be harmful to the environment. For years, scientists have known about silver’s ability to kill harmful bacteria and, recently, have used this knowledge to create consumer products containing silver nanoparticles.
Now, a University of Missouri researcher has found that silver nanoparticles also may destroy benign bacteria that are used to remove ammonia from wastewater treatment systems. The study was funded by a grant from the National Science Foundation.
Several products containing silver nanoparticles already are on the market, including socks containing silver nanoparticles designed to inhibit odor-causing bacteria and high-tech, energy-efficient washing machines that disinfect clothes by generating the tiny particles. The positive effects of that technology may be overshadowed by the potential negative environmental impact.
“Because of the increasing use of silver nanoparticles in consumer products, the risk that this material will be released into sewage lines, wastewater treatment facilities, and, eventually, to rivers, streams and lakes is of concern,” said Zhiqiang Hu, assistant professor of civil and environmental engineering in MU’s College of Engineering. “We found that silver nanoparticles are extremely toxic. The nanoparticles destroy the benign species of bacteria that are used for wastewater treatment. It basically halts the reproduction activity of the good bacteria.”
Hu said silver nanoparticles generate more unique chemicals, known as highly reactive oxygen species, than do larger forms of silver. These oxygen species chemicals likely inhibit bacterial growth. For example, the use of wastewater treatment “sludge” as land-application fertilizer is a common practice, according to Hu. If high levels of silver nanoparticles are present in the sludge, soil used to grow food crops may be harmed.
Hu is launching a second study to determine the levels at which the presence of silver nanoparticles become toxic. He will determine how silver nanoparticles affect wastewater treatment processes by introducing nanomaterial into wastewater and sludge. He will then measure microbial growth to determine the nanosilver levels that harm wastewater treatment and sludge digestion.
The Water Environment Research Foundation recently awarded Hu $150,000 to determine when silver nanoparticles start to impair wastewater treatment. Hu said nanoparticles in wastewater can be better managed and regulated. Work on the follow-up research should be completed by 2010.
http://www.missouri.edu/
CSIRO researchers open up new class of chemistry
April 30, 2008
Medical Science News
CSIRO Entomology business manager, Cameron Begley, said researchers believed the discovery opened up an entirely new class of chemistry.
“Some of these alpha-hydroxy polyacetylenic fatty acids act as indicators for a range of different conditions, such as mechanical stress or heat, and display self-assembling properties. Others display anti-microbial properties,” he said.
Australian scientists working within the Crop Biofactories Initiative (CBI) have also been developing applications for alpha-hydroxy unsaturated fatty acids (AHUs).
“Alpha-hydroxy fatty acids (AHA’s) are well known to industry, but we have found some interesting applications for AHUs. We have introduced them to a range of bio-based condensation polymer systems that have increased film flexibility. Using these AHUs we have also observed strong adhesion between polyolefins and a range of substrates.”
CBI researchers have also identified novel uses for hydroxy fatty acids and how these affect polymer properties.
The team will be outlining these discoveries on 28 April during the Fifth Annual World Congress on Industrial Biotechnology & Bioprocessing (WCIBB), being held in Chicago, Illinois, from 27-30 April 2008.
The CBI is a 12-year project which aims to add value to the Australian agricultural and chemical industries by developing technologies to produce novel industrial compounds from genetically modified oilseed crops. This Initiative is a joint venture between CSIRO and the Grains Research and Development Corporation.
The project focuses on three key areas; Industrial Oils, Complex Monomers and Protein Biopolymers. CBI project leaders will present the latest research findings in each of these three areas at the WCIBB in Chicago which will showcase innovation at the convergence of biotechnology, chemistry and agriculture.
http://www.csiro.au/
Scientists determine drug target for the most potent botulinum neurotoxin
April 30, 2008
Medical Science News
Botulinum neurotoxin - responsible for the deadly food poisoning disease botulism and for the beneficial effects of smoothing out facial wrinkles - can also be used as a dreaded biological weapon. When ingested or inhaled, less than a billionth of an ounce can cause muscle paralysis and eventual death. Although experimental vaccines administered prior to exposure can inhibit the destructive action of this neurotoxin - the most deadly protein known to humans - no effective pharmacological treatment exists.
Now, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) have taken the first step toward designing an effective antidote to the most potent form of the toxin. They have found that they can trick the toxin to bypass its normal binding protein, thereby blocking its deadly action. The results of their research are reported in the April 22, 2008 online issue of the Journal of Biological Chemistry.
“We have found a highly efficient inhibitor of botulinum neurotoxin type A - the most potent of seven neurotoxins produced by the bacterium Clostridium botulinum. This finding can lead to a very effective drug to stop the devastating effects of the toxin,” said Brookhaven Lab biologist Subramanyam Swaminathan, the study’s co-principal investigator. “We intend to do further research to tailor the inhibitor for the best results.”
“We are excited about the success of this work and the prospects it holds for future drug development,” said USAMRIID principal investigator S. Ashraf Ahmed, who initiated the structure-based inhibitor design as part of the Institute’s bio-defense research program.
To cause its deadly effects, the botulinum neurotoxin first binds to a nerve cell membrane, which curves inward, incorporating the toxin into a vesicle that drifts inside the cell. The toxin eventually travels from the vesicle to the cytosol, the internal fluid of the cell. The toxin then cleaves specific proteins in the cytosol, thereby blocking the release of neurotransmitters - chemicals nerve cells use to communicate with one another and with muscles. Blockage of this communication paralyzes muscles - including those that enable breathing.
To block the toxin’s action, the researchers designed four “decoy” protein fragments that mimic the structure of the protein to which the toxin ordinarily binds. The toxin then attaches itself to the decoy fragments instead of to the cell’s protein. This re-routing of the toxin allows neurotransmitters to keep functioning, thus stopping the toxin’s pathological effects.
The scientists used x-ray techniques at Brookhaven’s National Synchrotron Light Source (NSLS) to see how the toxin binds to the protein inhibitors. They found that all four decoy proteins are efficient at inhibiting the toxin’s binding to the cell’s protein, but one of them in particular is by far the best of any known inhibitors. The scientists’ next step in this process is to transform the most effective of the four protein fragments into a drug-like molecule before clinical testing is done.
“This study represents an impressive collaboration in identifying potential inhibitors of the toxin for therapeutic use,” said Colonel George W. Korch, Jr., USAMRIID’s commander. “It builds upon the successes we have realized in developing effective next-generation vaccines to protect our citizens against the toxin’s deadly effects prior to exposure.”
The scientists did not work with intact Clostridium botulinum bacteria. Instead, they produced a functional fragment of the neurotoxin protein, which is not toxic. The research is performed in strict compliance with Brookhaven’s Institutional Biosafety Committee regulations according to standards set by the U.S. Centers for Disease Control and Prevention. Only authorized scientists have access to the laboratory.
This research was funded by the Defense Threat Reduction Agency of the U.S. Department of Defense. The NSLS is supported by the U.S. Department of Energy’s Office of Basic Energy Sciences, Office of Science.
http://www.bnl.gov
Tomato paste helps fight sunburn and wrinkles
April 29, 2008
Medical Science News
Scientists in Britain are suggesting that a tomato product may help fight sunburn and wrinkles.
A study by researchers at Manchester and Newcastle Universities has found that adding five tablespoons of tomato paste to the daily diet of 10 volunteers, their skin’s ability to protect against harmful UV rays improved.
Damage from UV rays can lead to premature ageing and even skin cancer and the scientists say it is the antioxidant lycopene found in tomatoes which provided the benefit.
The lycopene in tomatoes is at its highest concentration when the vegetable has been cooked - a link has already been established between lycopene and a reduction in the risk of prostate cancer.
The researchers gave 10 volunteers around 55g of standard tomato paste which contains high levels of cooked tomatoes and 10g of olive oil daily while another 10 participants received just the olive oil.
Tests after three months using UV lamps showed the tomato-eaters were a third better protected against sunburn at the end of the study than at the start, and other tests suggested the tomato-based diet had boosted the production of collagen the protein that keeps skin supple.
The skin samples from the tomato group showed they had 33% more protection against sunburn, the equivalent of a very low factor sun cream and much higher levels of pro-collagen, a molecule which gives the skin its structure and keeps its firm.
Professor Lesley Rhodes, a dermatologist at the University of Manchester says the tomato diet boosted the level of pro-collagen in the skin significantly which suggests a potential for the reversal of the skin ageing process.
The team warn however that tomatoes should be viewed as a “helpful addition” rather than an alternative to suncream and are now conducting research into the benefits of lycopene for the skin.
Other research has shown lycopene may protect against prostate cancer, as well as the lung, bladder, cervical and pancreatic forms of the disease; it may also boost heart health by combating artery-clogging cholesterol.
The study was presented at the British Society for Investigative Dermatology.
Making GNA for nanotechnology
April 29, 2008
Medical Science News
In the rapid and fast-growing world of nanotechnology, researchers are continually alt=”In the rapid and fast-growing world of nanotechnology, researchers are continually align=”left” vspace=”0″ hspace=”0″ >The only chemical difference between DNA and a synthetic cousin, GNA, is in the sugar molecule. GNA uses a three-carbon sugar called glycerol rather than the five-carbon deoxyribose used in DNA. The sugar provides the chemical backbone for nucleic acid polymers, anchoring a phosphate molecule and nitrogenous base (B). Credit: Biodesign Institute at Arizona State University
“Making GNA is not tricky, it’s just three steps, and with three carbon atoms, only one stereo center,” said Chaput. “It allows us to make these right and left-handed biomolecules. People have actually made left-handed DNA, but it is a synthetic nightmare. To use it for DNA nanotechnology could never work. It’s too high of a cost to make, so one could never get enough material.”
The ability to make mirror image structures opens up new possibilities for making nanostructures. The research team also found a number of physical and chemical properties that were unique to GNA, including having a higher tolerance to heat than DNA nanostructures. Now, with a new material in hand, which Chaput dubs ‘unnatural nucleic acid nanostructures,’ the group hopes to explore the limits on the topology and types of structure they can make.
“We think we can take this as a basic building block and begin to build more elaborate structures in 2-D and see them in atomic force microscopy images,” said Chaput. “I think it will be interesting to see where it will all go. Researchers come up with all of these clever designs now.”
http://www.asu.edu/
New research suggests hypertonic, hyperviscous fluids may be better treatment for severe blood loss
April 29, 2008
Medical Science News
Intravenous administration of isotonic fluids is the standard emergency treatment in the U.S. for patients with severe blood loss, but UC San Diego bioengineering researchers have reported improved resuscitation with a radically different approach. Building alt=”Intravenous administration of isotonic fluids is the standard emergency treatment in the U.S. for patients with severe blood loss, but UC San Diego bioengineering researchers have reported improved resuscitation with a radically different approach. Building align=”left” vspace=”0″ hspace=”0″ >Arterioles constrict and relax in response to a variety of factors, including viscosity enhancers. Credit: UC San Diego, Jacobs School of Engineering
Over several decades, studies involving humans and animals have evaluated hypertonic saline (up to 7.5 percent sodium chloride) versus isotonic saline (0.9 percent sodium chloride). Given intravenously, hypertonic solutions act like magnets, drawing fluid from tissues into the bloodstream, thereby increasing blood volume. Such hypertonic saline has not received the approval of the Food and Drug Administration for clinical use in the United States. Therefore, it is not part of ATLS guidelines.
However, several medical research teams, including one led by Dr. Raul Coimbra, professor of surgery and chief, Division of Trauma, Surgical Critical Care and Burns at UC San Diego Medical Center, have investigated the effects of hypertonic saline for almost 20 years. “Our level-1 trauma center at UC San Diego is participating in a study of hypertonic saline as part of a multicenter trial sponsored by the National Institutes of Health,” said Coimbra. “Unfortunately, it will take us two to three more years to finish the trial and determine whether hypertonic saline is superior to conventional isotonic resuscitation.”
In Intaglietta’s study with hamsters in the Jacobs School of Engineering’s Department of Bioengineering, 90 minutes after hypertonic saline was given to blood-depleted hamsters about 30 percent of normal flow was reconstituted through skin arterioles, tiny branches of arteries that lead to the even smaller capillaries. The bioengineering researchers quantified blood flow with special microscopic procedures.
In blood-depleted hamsters given both hypertonic saline and a small volume of a commercially available viscosity enhancer called Hextend?, blood flow through arterioles improved to 40 percent of normal. When the hypertonic saline, Hextend?, and a small volume of another viscosity enhancer called alginate were given, arteriole blood flow improved to 55 percent of normal. Hextend? and alginate are plasma volume expanders, substances transfused to maintain the fluid volume of blood.
“Our findings suggest that elevating the viscosity of blood after severe blood loss is beneficial in resuscitation,” said Intaglietta. “In fact, our studies indicate that Hextend and similar plasma extenders could produce even greater benefit if they were formulated with higher viscosities.”
Arterioles regulate blood flow by constricting and dilating. A variety of factors in the body influence the process, including the viscosity of plasma, the fluid portion of blood. For example, higher viscosity plasma causes arterioles to dilate.
“For centuries, dating back to the time of the early Greeks, the idea has always been that blood is thick, so the sick should be treated by bleeding in order to thin the blood,” said Intaglietta. “Even as late as World War II and the Vietnam Way, it was thought that adding isotonic fluids to replace blood lost on the battlefield would be good because it lowered blood viscosity, making it easier for the heart to pump.”
Intaglietta said that while more research is needed, “Our findings and others suggest that the ATLS guidelines need to be modified.”
“Studies such as Intaglietta’s are important because it uses not only hypertonic saline,” said Coimbra, “but also other adjuncts which may increase the effects of hypertonic saline in treating those patients and in advancing our knowledge about shock resuscitation.”
http://www.ucsd.edu/
Scientists find distinct kind of stem cells in the pituitary gland
April 29, 2008
Medical Science News
A team of researchers led by scientists at Cold Spring Harbor Laboratory have for the first time identified stem cells that allow the pituitary glands of mice to grow even after birth.
They found that, in contrast to most adult stem cells, these cells are distinct from those that fuel the initial growth of this important organ. The results suggest a novel way that the hormone-secreting gland may adapt, even in adolescents and adults, to traumatic stress or to normal life changes like pregnancy.
Maturity, in some respects, brings diminished possibilities. As a fertilized egg cell repeatedly divides to grow into a mature animal, most of the resulting cells become ever more specialized. But a small number of cells, known as stem cells, remain uncommitted even as they spawn more specialized progeny. The most versatile stem cells, taken from days-old embryos, are able to form any cell type - but studying them in people is controversial. Even in adults, however, other types of stem cell persist that have a more limited repertoire. Some replace specific cells as they wear out; others help to rebuild damaged tissues. Still other stem cells are suspected by some scientists of starting or maintaining cancers.
In spite of their importance, stem cells are hard to spot among the multitude of cells in complex tissue. Several years ago, neuroscientist Grigori Enikolopov, Ph.D., an associate professor at Cold Spring Harbor Laboratory (CSHL), and his colleagues developed a tool to look for stem cells that give rise to new adult brain cells. Researchers had known that a gene called Nestin was active in these neural stem cells. The CSHL team genetically engineered mice so that the same conditions that activate Nestin in a particular cell also make it glow green under ultraviolet light.
Using these mice gives researchers an important pointer to cells that may be adult stem cells. Almost 100 research teams around the world have now used these special mice to help find adult stem cells in hair follicles, liver, muscle, and other tissues.
One place where stem cells had been suspected - but never found - is the pituitary gland. This organ, which in people is about the size of a pea, sits at the base of the brain, where it secretes hormones that regulate various processes throughout the body. In mice, the gland develops in the embryo, but then has a second growth spurt. “A few weeks after they are born,” says Dr. Enikolopov, “the pituitary undergoes massive expansion” that suggests a role for adult stem cells.
Anatoli Gleiberman, Ph.D., a researcher in the lab of pituitary expert M. Geoff Rosenfeld at the University of California, San Diego, initiated a collaboration between the two labs to look for pituitary stem cells. The researchers used the Nestin-tracking mice to identify candidate cells in the anterior pituitary, the section of the organ that secretes hormones. They then used other techniques to show that these are true stem cells. “There are six main lineages in the adult pituitary,” says Dr. Enikolopov, “and we can demonstrate that one adult stem cell can generate all six lineages,” with each cell type secreting a different hormone.
These cells differ from most adult stem cells, however. “In most cases that we know,” says Dr. Enikolopov, “cells that become stem cells of the adult have been also contributing to embryonic development and continue to serve as stem cells in the adult.” The research team demonstrated that adult stem cells in the pituitary did not help construct the embryonic organ.
Their research, the scientists suggest, indicates that the adult mouse pituitary includes two similar - but not identical - types of hormone-producing cells: some that grew in the developing embryo, and some that appeared later. They speculate that having two sets of cells may let the organ respond differently to changing body conditions. Dr. Enikolopov notes that hormones strongly influence human neuropsychiatric phenomena, including stress and depression that are his main research focus. “All are mediated through the pituitary,” he said, so changes that happen during the later growth of the gland could have lasting effects.
“Genetic approaches identify adult pituitary stem cells” appears in the April 29, 2008 edition of the Proceedings of the National Academy of Sciences. Along with Dr. Enikolopov, Dr. Michael Geoff Rosenfeld, who is a Howard Hughes Medical Institute Investigator at the University of California at San Diego School of Medicine, is a corresponding author of the paper. The complete citation is as follows: Anatoli S. Gleiberman, Tatyana Michurina, Juan M. Encinas, Jose L. Roig, Peter Krasnov, Francesca Balordi, Gord Fishell, Michael G. Rosenfeld, and Grigori Enikolopov.
The paper is available online at http://www.pnas.org/cgi/doi/10.1073/pnas.0801644105.
http://www.cshl.org/
