Bacterial Genes That Improve Plant Growth by 40% Identified

You might think bacteria that "invade" trees are there to cause certain destruction. But like the helpful bacteria that live within our guts, some microbes help plants thrive. To find out what makes these microbe-plant interactions "tick," scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory decoded the genome of a plant-dwelling microbe they'd previously shown could increase plant growth by 40 percent. Their studies, described online in PLoS Genetics, identified a wide range of genes that help explain this symbiotic success story. The work could move the approach of using bacteria as growth-promoting agents one step closer to implementation for improved agriculture and biofuel production.

"To fuel and feed the planet for the future, we need new approaches," said Brookhaven scientist Safiyh Taghavi, the study's lead author. "Biofuels derived from plants are an attractive alternative energy source, but many biofuel feedstock crops are in direct competition with food crops for agricultural resources such as land, water, and fertilizers. Our research is looking for ways to improve the growth of biofuel feedstock plants on land that cannot be economically used for food production. What we learn might also be put to use to increase the productivity of food crops," she added.

The Brookhaven team has been studying a species of bacteria isolated from the roots of poplar trees. "Poplar is a model species for biofuel production, in part because of its ability to grow on marginal soils unsuitable for food crops," said scientist Daniel (Niels) van der Lelie, who leads the research program. Previous studies by the van der Lelie-Taghavi group have shown that the bacterium Enterobacter (sp. 638) increases poplar growth by as much as 40 percent.

In the current study -- through genome sequencing performed at DOE's Joint Genome Institute, manual genome annotation in collaboration with Brookhaven biologist Sebastien Monchy, and metabolic analyses performed at the University of South Carolina in collaboration with Brookhaven plant scientist Lee Newman -- the scientists identified an extended set of genes that help Enterobacter (sp. 638) establish itself in this niche. The studies also revealed remarkable interactions between the microbe and its host that help the plant survive and thrive.

Among the bacterial genes identified are ones that code for proteins that: help the microbe survive and compete with other species for resources in the soil; take up nutrients released by plant roots; and move toward, adhere to, and colonize poplar root tissues. The microbes also have genes that provide benefits for the plant, including: genes that may help confer drought resistance and the ability to coexist with toxic metals; genes that produce antimicrobial agents that protect plants from fungal and bacterial infections; and genes that produce plant-growth enhancing "phytohormones" and precursors that poplar cannot produce on its own.

"One of the most remarkable things about this association, which we confirmed with our metabolic assays, is that the production of these plant-growth-promoting phytohormones is directly dependent on the presence of plant-synthesized sugars, such as sucrose, in the growth medium. In addition, one metabolite (meso-2,3 butanediol) is known to elicit the induction of systemic tolerance to drought and induced systemic resistance against plant diseases," Taghavi said. So the plant makes sugar that helps the bacteria grow and make phytohormones and other compounds that help the plants grow better and healthier.

"Interestingly, the genes that allow the bacteria to metabolize sucrose and the genes that produce the phytohormones are located on a genomic island, suggesting they may have been acquired together via natural horizontal gene transfer," Taghavi said.

The scientists plan to continue their work by studying how these various genes are expressed during different stages of bacterial colonization of poplar. These detailed studies will further advance the scientists' understanding of the complex interactions, including the role of signaling compounds and other secondary metabolites that play a role in colonization and plant-growth promotion.

"These basic findings can eventually be translated into comprehensive strategies to exploit the use of these naturally occurring bacteria-plant relationships to improve plant establishment and biomass production. This approach can be applied to improve plant productivity for sustainable agriculture, bioenergy feedstock production on marginal lands, or to fight desertification of arid areas," van der Lelie said.

This research was funded by the DOE Office of Science. The DOE Joint Genome Institute unites the expertise of five national laboratories -- Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge, and Pacific Northwest -- along with the Hudson Alpha Institute for Biotechnology to advance genomics in support of the DOE missions related to clean energy generation and environmental characterization and cleanup. JGI is operated for DOE by the University of California.

Journal Reference:

1. Safiyh Taghavi, Daniel van der Lelie, Adam Hoffman, Yian-Biao Zhang, Michael D. Walla, Jaco Vangronsveld, Lee Newman, Sébastien Monchy. Genome Sequence of the Plant Growth Promoting Endophytic Bacterium Enterobacter sp. 638. PLoS Genetics, 13 May 2010 DOI: 10.1371/journal.pgen.1000943

Courtesy: ScienceDaily

How Spiders Create Silk Threads: Lowering pH Regulates Spider’s Silk Production, Researchers Find

How can a tiny spider body contain material for several decimeters of gossamer silk, and what governs the conversion to thread? Researchers at the Swedish University of Agricultural Sciences (SLU) in Sweden can now explain this process.

The new research findings are presented in an article in the scientific journal Nature.

"We have seen how the first part of the spider silk protein has a very special and important function. It quite simply controls when the protein is to be converted into gossamer," says My Hedhammar, one of the researchers at SLU.

By rapidly lowering the pH, a spider can initiate the conversion to silk. Before this, the protein needed to form the silk is stored in a gland in the spider's body.

When it is time to spin a thread, the protein passes through a canal where it is converted to gossamer. Along the canal, the conditions change: among other things, the pH is lowered from a neutral (pH 7) to a somewhat more acidic level, pH 6.

"The spider gossamer protein consists of three parts. At SLU, this time we have primarily studied the first part, named NT, and have seen that it has very special properties that are important to the spider. At neutral pH, NT helps the protein to remain in liquid form. When the pH goes down, NT sees to it that threads are formed rapidly and also in an orderly manner," says My Hedhammar.

It has long been a dream of researchers to be able to produce artificial spider silk, since it is one of the strongest materials known. There are therefore great hopes about what spider gossamer could be used for in the future, everything from surgical sutures to bullet-proof vests. Spider silk is a strong and elastic material, and it is moreover biodegradable. It could be of great importance in medical technology, for example.

To be able to produce artificial gossamer, basic research about how spiders go about it is a key piece of the puzzle. Numerous researchers around the world are trying to map this process.

At SLU several scientists are involved in this work, which is largely done with classical biochemical methods. These researchers have primarily conducted their studies using the spider Euprosthenops australis, a species that makes one of the strongest threads and that is moreover large enough to be dissected in a simple way. But the new findings about gossamer protein seems to apply to all spider silk, regardless of species.

The SLU researchers behind the research now presented in the new issue of the journal Nature are Glareh Askarieh, My Hedhammar, Kerstin Nordling, Anna Rising, Jan Johansson, and Stefan D. Knight.

Journal Reference:

1. Glareh Askarieh, My Hedhammar, Kerstin Nordling, Alejandra Saenz, Cristina Casals, Anna Rising, Jan Johansson, Stefan D. Knight. Self-assembly of spider silk proteins is controlled by a pH-sensitive relay. Nature, 2010; 465 (7295): 236 DOI: 10.1038/nature08962

Courtesy: ScienceDaily

Mobile Phone Use and Brain Cancer Risk: Inconclusive Results from International Study

A large international study of the risk of brain cancer from cell phone use has yielded inconclusive results. Although the study provides no definitive evidence of increased risk of brain cancer from mobile phones, observations at the highest level of cumulative call time and the changing patterns of mobile phone use, particularly among young people, warrant further investigation, researchers said.

The Interphone Study Group has published their results in the International Journal of Epidemiology. The paper presents the results of analyses of brain tumor (glioma and meningioma) risk in relation to mobile phone use in all Interphone study centers combined.

This interview-based case-control study, which included 2708 glioma and 2409 meningioma cases and matched controls was conducted in 13 countries using a common protocol. Analyses of brain tumors in relation to mobile phone use have been reported from a number of cohort and case-control studies, including several of the national components of Interphone. No studies, however, have included as many exposed cases, particularly long-term and heavy users of mobile phones, as this study.

Background

Mobile phone use has increased dramatically since its introduction in the early-to-mid 1980's. The expanding use of this technology has been accompanied by concerns about health. In the late 1990s, several expert groups critically reviewed the evidence on health effects of low-level exposure to radiofrequency (RF) electromagnetic fields, and recommended research into the possible adverse health effects of mobile telephone use.

IARC coordination of a multinational effort in cancer research

As a result, the International Agency for Research on Cancer (IARC) coordinated a feasibility study in 1998 and 1999, which concluded that an international study of the relationship between mobile phone use and brain tumor risk would be feasible and informative.

Scope of the Interphone study

Interphone was therefore initiated in 2000 as an international set of case-control studies in 13 countries around the world (Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Sweden and the UK) focusing on four types of tumors in tissues that most absorb RF energy emitted by mobile phones:

• tumors of the brain:
  • glioma, a cancer of the brain that begins in the glial cells that surround and support nerve cells; and
  • meningioma, a type of slow-growing tumor that forms in the meninges, the thin layers of tissue that cover and protect the brain and spinal cord;
• tumors of the acoustic nerve: schwannoma, a tumor of the peripheral nervous system that arises in the nerve sheath; and
• tumours of the parotid gland: tumors that form in a parotid gland, the largest of the salivary glands, which make saliva and release it into the mouth.

The objective was to determine whether mobile phone use increases the risk of these tumors. Interphone is the largest case-control study of mobile phone use and brain tumors yet and includes the largest numbers of users with at least 10 years of exposure.

Scientific direction of Interphone

The Interphone International Study Group, made up of 21 scientists, was responsible for the progress of the study, the choice of analyses to be conducted, and the interpretation and publication of results. All the decisions about the study were made exclusively and collectively by the Interphone International Study Group. In the course of the study, the IARC Principal Investigator, Dr. Elisabeth Cardis, moved to the Centre for Research in Environmental Epidemiology (CREAL) in Barcelona, Spain, where she continues her role as Interphone Principal Investigator, although the 13-country dataset remains at IARC.

Funding of Interphone

The Interphone study was undertaken as a collaborative effort between a number of partner institutions, coordinated by IARC. To date, the overall funding assigned to the Interphone study amounts to approx. 19.2 million euros (€). Of this amount 5.5 million € were contributed by industry sources.

Of these 5.5 million €, 3.5 million € were contributed by the Mobile Manufacturers' Forum (MMF) and the GSM Association, each contributing half of that amount, through a firewall mechanism provided by the UICC (International Union against Cancer) to guarantee the independence of the scientists. Most of the rest of the 5.5 million € came indirectly to individual centers from mobile phone operators and manufacturers, for example, through taxes and fees collected by government agencies. Only 0.5 million € (2.5%) of the overall study costs were provided directly by the industry, in Canada and France, under contracts which preserved the independence of the study.

Other funding was provided by the European Commission (3.74 million €) and national and local funding sources (9.9 million € in total) in participating countries.

Additional funding for the extension of the research to younger and older age groups was received directly from mobile phone operators in the UK under contracts which preserved the independence of the study.

Results

The Interphone Study Group summarized its findings as follows:

"A reduced odds ratio (OR) related to ever having been a regular mobile phone user was seen for glioma [OR 0.81; 95% confidence interval (CI) 0.70-0.94] and meningioma (OR 0.79; 95% CI 0.68-0.91), possibly reflecting participation bias or other methodological limitations. No elevated OR was observed ≥ 10 years after first phone use (glioma: OR 0.98; 95% CI 0.76-1.26; meningioma: OR 0.83; 95% CI 0.61-1.14). ORs were <>

(Note: the odds ratio (OR) is a measure of relative risk. In other terms, an OR of x is taken as meaning that people exposed have x times the risk of non-exposed people.)

Conclusions

The Interphone Study Group concluded with the following key message: A reduced OR for glioma and meningioma related to ever having been a regular mobile phone user possibly reflects participation bias or other methodological limitations. No elevated OR for glioma or meningioma was observed ≥10 years after first phone use. There were suggestions of an increased risk of glioma, and much less so meningioma, in the highest decile of cumulative call time, in subjects who reported usual phone use on the same side of the head as their tumor and, for glioma, for tumors in the temporal lobe. Biases and errors limit the strength of the conclusions that can be drawn from these analyses and prevent a causal interpretation.

Change in pattern of use

The majority of subjects were not heavy mobile phone users by today's standards. The median lifetime cumulative call time was around 100 hours, with a median of 2 to 21⁄2 hours of reported use per month. The cut-point for the heaviest 10% of users (1640 hours lifetime), spread out over 10 years, corresponds to about a half-hour per day.

Today, mobile phone use has become much more prevalent and it is not unusual for young people to use mobile phones for an hour or more a day. This increasing use is tempered, however, by the lower emissions, on average, from newer technology phones, and the increasing use of texting and hands-free operations that keep the phone away from the head.

What's next?

Dr. Christopher Wild, Director of IARC said: "An increased risk of brain cancer is not established from the data from Interphone. However, observations at the highest level of cumulative call time and the changing patterns of mobile phone use since the period studied by Interphone, particularly in young people, mean that further investigation of mobile phone use and brain cancer risk is merited."

Professor Elisabeth Cardis said that "the Interphone study will continue with additional analyses of mobile phone use and tumors of the acoustic nerve and parotid gland." She added:,"Because of concerns about the rapid increase in mobile phone use in young people, who were not covered by Interphone, CREAL is coordinating a new project, MobiKids, funded by the European Union, to investigate the risk of brain tumors from mobile phone use in childhood and adolescence."

IARC has scheduled a comprehensive review of the carcinogenic potential of mobile phone use under the auspices of its Monographs Programme. The review, scheduled for 24-31 May 2011, will consider all published epidemiological and experimental evidence, including the new data from the Interphone study.

Journal Reference:

1. The INTERPHONE Study Group. Brain tumour risk in relation to mobile telephone use: results of the INTERPHONE international case-control study. International Journal of Epidemiology, 2010; 1-20 DOI: 10.1093/ije/dyq079

Courtesy: ScienceDaily

BP Says One Oil Leak of Three Is Shut Off

BATON ROUGE, La. — A four-story containment dome is on its way to the site of the leaking oil well and when the structure is installed on Monday, BP officials hope the experimental procedure will help stem the flow of crude oil spewing into the Gulf of Mexico since an explosion rocked a drilling rig there 15 days ago.

For the first time in several days, due to light winds, crews were able to conduct a controlled burn in two of the most concentrated areas of oil. This effort came as officials started the day with some encouraging, albeit small news: engineers had succeeded in shutting off one of the three leaks from the damaged well late Tuesday night, BP said.

Though by itself the move will not reduce the amount of oil being released — estimated at 210,000 gallons a day — “it is from two locations now,” Doug Suttles, the chief operating officer of BP said at a news conference Wednesday afternoon in Robert, La.

Submersible robots, controlled remotely from a ship on the surface, were able to place a specially designed valve over the end of a leaking drill pipe lying on the sea floor in water about 5,000 feet deep, and stop oil from escaping at that point.

With one valve shut, BP turned its attention to capping the worst of the remaining leaks, but cautioned that it was hard to determine whether the containment dome would be effective.

“This hasn’t been done before, it’s very complex and it will very likely have challenges along the way,” Mr. Suttles said.

The structure, 98 tons, was loaded onto the barge that departed at noon for what is to be a 12-hour trip to the site.

The plan is to lower the dome to the sea floor and place it over the leak, capturing the gushing oil and funneling it up to a rig waiting at the surface. Because the other leak is too far away to fit inside the same dome, crews are building a second containment dome, which could be implemented if the first dome is successful, a BP spokesman. John Curry said.

Weather conditions allowed recovery crews to move forward on several fronts to control the spread of the oil slick.

Skimming boats were out in other areas to corral the thick oil from the surface of the water. Aircraft dropped dispersants onto the oil from overhead.

The Coast Guard Rear Admiral Mary Landry said officials could not accurately measure the size of the oil spill because it was constantly changing. “It’s a pretty wide swath of coverage with a rainbow sheen at the leading edge,” she said at the news conference.

“The leading edge is very close to the Chandeleur Islands, but the heavy concentrations are farther offshore,” she added.

The report of progress in containing the leak came as BP, which is responsible for cleaning up the vast oil spill resulting from the fatal explosion and fire that destroyed the rig it was leasing, acknowledged that the flow of oil could become vastly larger than initially estimated.

In a closed-door briefing for members of Congress, a senior BP executive conceded Tuesday that the ruptured oil well could conceivably spill as much as 60,000 barrels a day of oil, more than 10 times the estimate of the current flow. A barrel of crude oil contains roughly 42 gallons.

“The rate could go up to that,” Mr. Suttles of BP said, when asked to verify a report in The Times. “It’s not the situation we have at this moment, but it’s not impossible.”

The scope of the problem has grown drastically since the rig, the Deepwater Horizon, sank into the gulf. Now, the discussion with BP on Capitol Hill is certain to intensify pressure on the company, which is facing a crisis similar to what the Toyota Motor Company had with uncontrolled acceleration — despite its efforts to control the damage to its reputation as a corporate citizen, the problem may be worsening.

Amid growing uncertainty about the extent of the leak, and when it might be stanched, pressure on BP intensified on multiple fronts, from increasingly frustrated residents of the Gulf Coast to federal, state and local officials demanding more from the company.

Mississippi’s Attorney General, Jim Hood, along with attorneys general from the other Gulf Coast states of Louisiana, Alabama, Texas and Florida, sent a letter to BP officials on Wednesday asking them to clarify how they would pay for the cleanup of the spill.

BP has dispatched executives to hold town meetings in the affected region, and it has turned to lower-profile social media outlets to trumpet its cleanup efforts and moves to organize volunteers.

The Senate energy committee has summoned executives from BP and Transocean Ltd., the rig operator, as well as a number of oil industry technical experts to a hearing next week. The next day, the oversight and investigations subcommittee of the House Energy and Commerce Committee will hold a hearing, to which top executives of BP, Transocean and Halliburton have been asked to appear, a committee spokeswoman said.

The White House released on Wednesday morning a detailed timeline of the federal government’s response to the oil spill on its Web site, even as President Obama’s administration has come under fire for not responding quick enough to the crisis in the Gulf of Mexico.

“We have compiled this chronology in the spirit of transparency so the American people can have a clear understanding of what their government has been and is doing to respond to the massive and potentially unprecedented environmental disaster,” Heidi Avery, White House Deputy Homeland Security Advisor wrote on the site.

Sam Dolnick reported from Baton Rouge, La., and Liz Robbins reported from New York. Campbell Robertson contributed reporting from New Orleans, John M. Broder from Washington, and Clifford Krauss from Houston. Sewell Chan contributed reporting from Washington.

Courtesy: Newyorktimes

New Tool Enables Wider Analyses of Genome 'Deep Sequencing'

Life is almost unbearably complex. Humans and mice, frogs and flies toggle genes on and off in dizzying combinations and sequences during their relentless march from embryo to death. Now scientists seeking to understand the machinations of the proteins behind the genomic wizard's screen have a powerful new tool at their disposal, courtesy of researchers at the Stanford University School of Medicine.

Until now, researchers have relied on outdated methods of analysis to identify those DNA sequences involved in controlling when and how individual genes are expressed. Most often, those methods -- capable of probing only specific, limited regions of the genome arising from a type of experiment called DNA microarrays -- led to the exclusive scrutiny of regions called promoters nestled near the start of the gene.

In contrast, the new Stanford-developed, web-based algorithm allows scientists to plumb the unprecedented depths of the data provided by new "deep-sequencing" techniques to reveal a pantheon of control regions for nearly any gene. The effect is like expanding a researcher's field of vision from a pencil-thin beam of light trained mainly on the regions near coding sequences to a sweeping spotlight illuminating the contributions of distant genomic regions.

"It used to be that people thought only the regions near the gene were important in controlling its function -- in part because they had no way of assessing the impact of regions further away," said Gill Bejerano, PhD, assistant professor of developmental biology and of computer science at the medical school and Stanford's School of Engineering.

As a result, said Bejerano, researchers often cherry-picked nearby regions for further analysis based on their proximity or interest. "But when you're being that conservative with current sequencing capabilities, you're typically throwing away at least half of the data you so laboriously worked to obtain," he said.

Typically that data exists in the form of DNA binding sites for regulatory proteins called transcription factors that dictate the activity of genes. And, with the advent of new, deep-sequencing techniques, it's being generated at rates that are both unimaginable and unmanageable.

Bejerano is the senior author of the research, which will be published online May 2 in Nature Biotechnology. The researchers coined the name "GREAT" for their algorithm, an acronym for "Genomic Regions Enrichment of Annotations Tool," and the website will be available for anyone to use after May 2 at http://great.stanford.edu

There are hundreds of known transcription factors. Each controls the expression of numerous genes by binding to specific regions in the genome. This makes it difficult for scientists to know exactly how any one transcription factor is acting, particularly if it works over long stretches of DNA. Usually they'll figure out where in the DNA the protein is binding and then look for interesting genes nearby. Or, conversely, they'll find an interesting gene and look for nearby transcription-factor binding sites. But recent research has shown that sections of DNA far away can also play an important role.

It works a bit like this: Think of your kitchen. Notice all the black things. Those are your transcription-factor binding sites. But what do they do? You might figure out that sliding the lever on the toaster makes the toast pop up. And plugging it into the wall makes it get hot. But you're likely to overlook that vitally important black breaker switch on the wall behind you, or to dismiss it as inconsequential among all the other black items in the room that don't, in fact, control the toaster. That is, unless you use this new analysis.

In contrast, users of the GREAT algorithm, developed by graduate students Cory McLean and Aaron Wenger and software engineer Dave Bristor, will simply enter a list of all the binding sites they've found throughout the genome for their transcription factor of interest. No prescreening is necessary, and the list can be hundreds or thousands of items long. Some will be biologically meaningful, and some will be experimental flukes. The software program will then provide an analysis revealing not only which genes that transcription factor is likely to moderate, both near and far, but also in which developmental or molecular pathways it is likely to function.

"The analysis gets pushed back into the hands of the person who did the experiment," said Bejerano. "Now you will start to see the kinds of results that we had expected with this much data." He and his collaborators found that test runs with well-known transcription factors verified the factors' association with the expression of particular genes, but also identified new, previously unsuspected alliances between binding sites and genes separated on the DNA by up to 1 million nucleotides.

"We've been asking the right questions, but using the wrong interpretation tools to answer them," said Bejerano. "We don't expect that this tool will help three labs. We expect that it will help 3,000 labs. GREAT can look at thousands of binding sites and tell you things that your transcription factor is doing that have never been reported before."

Other members of the Bejerano lab at Stanford involved in the work include postdoctoral scholar Michael Hiller, PhD; graduate student Shoa Clarke; and research associate Bruce Schaar, PhD.

The research was funded by the Packard Foundation, Searle Scholar Network, an Edward Mallinckrodt Jr. Foundation junior faculty grant and the National Institutes of Health.

Journal Reference:

1. Cory Y McLean, Dave Bristor, Michael Hiller, Shoa L Clarke, Bruce T Schaar, Craig B Lowe, Aaron M Wenger, Gill Bejerano. GREAT improves functional interpretation of cis-regulatory regions. Nature Biotechnology, 2010; DOI: 10.1038/nbt.1630

Courtesy: ScienceDaily

Male or Female? In Flies, Some Cells Can't Tell

An experienced fruit fly researcher can tell at a glance whether the fly she is observing is male or female; a distinct pigmentation pattern on a fly's body (a type of bristle found only on the legs of males) and differences in the genitalia are dead giveaways. But most of the fly's body parts look identical in males and females, and until now, scientists had no idea whether "maleness" or "femaleness" extended to all of the insect's cells and tissues.

In a study publishing in the online, open access journal PLoS Biology, researchers at the Janelia Farm Research Campus of the Howard Hughes Medical Institute find that most cells in flies' bodies are identical, regardless of whether they are in a male or a female.

This is because the influence of sex-determining genes is restricted to specific tissues, says Bruce Baker, a group leader who conducted the research with colleagues Carmen Robinett, Alex Vaughan, and Jon Michael Knapp. Baker has been studying the genetics of fruit fly sex for 30 years. By the early 1980s, it was known that a cascade of genes determines how tissues and organs develop in a sex-specific manner.

In this bureaucratic chain of command, each gene tells the next one how and when to act. The doublesex gene, the master gene that determines sexual characteristics, is the last gene in the cascade. In flies, females express one form of doublesex, and males another. This gene is viewed as a master switch that tells female cells to create female sexual characteristics and male cells to make male ones. Until now, fly geneticists clung to the notion that the male version of doublesex was switched on in every cell of male flies, while the female version was present in every cell in female flies.

Prompted by other labs reporting that doublesex is turned on only in small areas in the fly embryo and only in specific parts of the brain, Robinett and her colleagues employed a genetic engineering technique to detect doublesex expression in the cells of developing flies. The technique attaches a reporter gene to doublesex that makes cells expressing the gene glow green. Tracking doublesex then becomes as easy as watching for green spots in fly embryos, larvae, and adults.

With this approach, Baker's group found that during fly development, doublesex switches on and off at different times and in different tissues. As expected, they saw doublesex protein in the genitalia and in other body parts that display differences between males and females. But in body parts where there are not overt differences between males and females, they found that doublesex was expressed only in certain cells and not expressed in many other types of cells.

"It's a simple observational study with profound implications," Baker says. This study demonstrates that only a subset of cells is likely to know whether they are male or female. Robinett and her colleagues found that male and female fruit flies are really a mixture of cells that are sex-specific and cells that are sexless. Many of the fly's cells never turn on the doublesex gene. So while, some cells "know" their sex and take on sex-appropriate characteristics during development, those that do not express doublesex remain identical in males and females.

Because doublesex or analogous genes are present in myriad organisms, including humans, this theme may apply to more than fruit flies. "It may be broadly true that males and females are made up of a mosaic of cells that know their sex and cells that don't," Baker says. This could prompt other researchers to check for similar doublesex patterns in other model organisms such as roundworms, zebrafish, and mice. If similar findings emerge, it could shake up the entire notion of sex differences in the animal kingdom. And if the finding applies to humans -- a big "if" at this point -- the implications could be even more significant.

"If it applies to people, it's certainly going to change our sociological view of what we think of as maleness and femaleness."

Journal Reference:

1. Robinett CC, Vaughan AG, Knapp J-M, Baker BS. Sex and the Single Cell. II. There Is a Time and Place for Sex. PLoS Biology, 2010; 8 (5): e1000365 DOI: 10.1371/journal.pbio.1000365

Courtesy: Science Daily

Global Warming: Future Temperatures Could Exceed Livable Limits, Researchers Find

Reasonable worst-case scenarios for global warming could lead to deadly temperatures for humans in coming centuries, according to research findings from Purdue University and the University of New South Wales, Australia. Researchers for the first time have calculated the highest tolerable "wet-bulb" temperature and found that this temperature could be exceeded for the first time in human history in future climate scenarios if greenhouse gas emissions continue at their current rate.

Wet-bulb temperature is equivalent to what is felt when wet skin is exposed to moving air. It includes temperature and atmospheric humidity and is measured by covering a standard thermometer bulb with a wetted cloth and fully ventilating it.

The researchers calculated that humans and most mammals, which have internal body temperatures near 98.6 degrees Fahrenheit, will experience a potentially lethal level of heat stress at wet-bulb temperature above 95 degrees sustained for six hours or more, said Matthew Huber, the Purdue professor of earth and atmospheric sciences who co-authored the paper that will be published in the Proceedings of the National Academy of Sciences.

"Although areas of the world regularly see temperatures above 100 degrees, really high wet-bulb temperatures are rare," Huber said. "This is because the hottest areas normally have low humidity, like the 'dry heat' referred to in Arizona. When it is dry, we are able to cool our bodies through perspiration and can remain fairly comfortable. The highest wet-bulb temperatures ever recorded were in places like Saudi Arabia near the coast where winds occasionally bring extremely hot, humid ocean air over hot land leading to unbearably stifling conditions, which fortunately are short-lived today."

The study did not provide new evaluations of the likelihood of future climate scenarios, but explored the impacts of warming. The challenges presented by the future climate scenarios are daunting in their scale and severity, he said.

"Whole countries would intermittently be subject to severe heat stress requiring large-scale adaptation efforts," Huber said. "One can imagine that such efforts, for example the wider adoption of air conditioning, would cause the power requirements to soar, and the affordability of such approaches is in question for much of the Third World that would bear the brunt of these impacts. In addition, the livestock on which we rely would still be exposed, and it would make any form of outside work hazardous."

While the Intergovernmental Panel on Climate Change central estimates of business-as-usual warming by 2100 are seven degrees Fahrenheit, eventual warming of 25 degrees is feasible, he said.

"We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world's population in an uninhabitable environment," Huber said. "When it comes to evaluating the risk of carbon emissions, such worst-case scenarios need to be taken into account. It's the difference between a game of roulette and playing Russian roulette with a pistol. Sometimes the stakes are too high, even if there is only a small chance of losing."

Steven Sherwood, the professor at the Climate Change Research Centre at the University of New South Wales, Australia, who is the paper's lead author, said prolonged wet-bulb temperatures above 95 degrees would be intolerable after a matter of hours.

"The wet-bulb limit is basically the point at which one would overheat even if they were naked in the shade, soaking wet and standing in front of a large fan," Sherwood said. "Although we are very unlikely to reach such temperatures this century, they could happen in the next."

Humans at rest generate about 100 watts of energy from metabolic activity. Wet-bulb temperature estimates provide upper limits on the ability of people to cool themselves by sweating and otherwise dissipating this heat, he said. In order for the heat dissipation process to work, the surrounding air must be cooler than the skin, which must be cooler than the core body temperature. The cooler skin is then able to absorb excess heat from the core and release it into the environment. If the wet-bulb temperature is warmer than the temperature of the skin, metabolic heat cannot be released and potentially dangerous overheating can ensue depending on the magnitude and duration of the heat stress.

The National Science Foundation-funded research investigated the long-term implications of sustained greenhouse gas emissions on climate extremes. The team used climate models to compare the peak wet-bulb temperatures to the global temperatures for various climate simulations and found that the peak wet-bulb temperature rises approximately 1 degree Centigrade for every degree Centigrade increase in tropical mean temperature.

Huber did the climate modeling on supercomputers operated by Information Technology at Purdue (ITaP), Purdue's central information technology organization. Sherwood performed the wet-bulb calculations.

"These temperatures haven't been seen during the existence of hominids, but they did occur about 50 million years ago, and it is a legitimate possibility that the Earth could see such temperatures again," Huber said. "If we consider these worst-case scenarios early enough, perhaps we can do something to address the risk through mitigation or new technological advancements that will allow us to adapt."

Journal Reference:

1. Steven C. Sherwood, Matthew Huber. An adaptability limit to climate change due to heat stress. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.0913352107

Courtesy: Science Daily