- Mutant Fish Safely Store Toxins in Fat
- Moon Race Brings 29 Teams to the Starting Line
- Helpful Mutations Didn’t Sweep Through Early Humans
- The Mystery of the Missing Moon Trees
Posted: 18 Feb 2011 02:00 PM PST
Some fish in New York's Hudson River have become resistant to several of the waterway's more toxic pollutants. Instead of getting sick from dioxins and related compounds including some polychlorinated biphenyls, Atlantic tomcod harmlessly store these poisons in fat, a new study finds.
But what's good for this bottom-dwelling species could be bad for those feeding on it, says Isaac Wirgin of the New York University School of Medicine's Institute of Environmental Medicine in Tuxedo. Each bite of tomcod that a predator takes, he explains, will move a potent dose of toxic chemicals up the food chain — eventually into species that could end up on home dinner tables.
From 1947 to 1976, two General Electric manufacturing plants along the Hudson River produced PCBs for a range of uses, including as insulating fluids in electrical transformers. Over the years, PCB and dioxin levels in the livers of the Hudson's tomcod rose to become "among the highest known in nature," Wirgin and his colleagues note online Feb. 17 in Science. Because these fish don't detoxify PCBs, Wirgin explains, it was a surprise that they could accumulate such hefty contamination without becoming poisoned. His team now reports that the tomcod's protection traces to a single mutation in one gene. The gene is responsible for producing a protein needed to unleash the pollutants' toxicity.
All vertebrates contain molecules in their cells that will bind to dioxins and related compounds. Indeed, these proteins — aryl hydrocarbon receptors, or AHRs — are often referred to as dioxin receptors. Once these poisons diffuse into an exposed cell, each molecule can mate with a receptor and together they eventually pick up a third molecule. This trio can then dock with select segments of DNA in the cell's nucleus to inappropriately turn on genes that can poison the host animal.
The tomcod actually has two types of AHRs, with AHR-2 offering the most effective binding to dioxin-like pollutants. But one naturally occurring AHR-2 variant, the result of a gene mutation, proves a very poor mate, Wirgin's team has found. It takes five times more of the pollutants to get substantial binding than is needed with the conventional AHR-2.
In local rivers relatively free of dioxins and PCBs, 95 percent of tomcod possess AHR-2 only in the conventional form. But in the PCB-rich Hudson, Wirgin's group finds, the only kind of AHR-2 protein in 99 percent of tomcod is the poorly binding variant.
The mutant receptor appears to have evolved long ago and to be widely dispersed. But in the Hudson, fish with the gene to make the mutant receptor have thrived, while those without it have died out, Wirgin notes.
Adaptation to resist poisons occurs throughout biology, observes molecular toxicologist John Stegeman of the Woods Hole Oceanographic Institution in Massachusetts. This process explains why some pesticides no longer kill their targets and why some microbes become immune to antibiotics.
Stegeman has been chronicling resistance to toxic PCBs and polycyclic aromatic hydrocarbons in another coastal species, a killifish. "But the mechanism in the killifish has not been uncovered, despite a long effort to determine it," he says.
Knowing the genetic underpinnings for chemical resistance can help predict the likelihood of that resistance developing, he explains, and can point to "how one might exploit resistance — even understand why chemicals are toxic." Genetic mechanisms for chemical resistance in wild species are known for some invertebrates, such as bugs. Stegeman says, to his knowledge, this tomcod finding is the first in a vertebrate.
Image: Tomcod can grow to 10 inches long. Those in the Hudson produce a mutant protein that allows them to thrive in waters heavily contaminated with toxic PCBs. (Science/AAAS)
Posted: 18 Feb 2011 12:30 PM PST
When a couple dozen companies sign contracts containing the words "moon" and "landing," it's a good indication that private lunar exploration is heating up.
The X Prize Foundation on Thursday announced that 29 teams had signed contracts making them the official Google Lunar X Prize competitors, contending for more than $30 million in prizes. The competitors, headquartered in 17 different countries, have been crafting promising business plans and rolling out prototypes. One team, Astrobotic Technology, has even arranged its rocket ride to the moon already.
"We could be intimidated by that development, but it's good for everyone who's serious about going to the moon," said Michael Joyce, president of team Next Giant Leap. "It shows this industry has moved beyond being an idea, that it is really going to happen."
To claim the first-place prize of $20 million before 2015 (it drops to $5 million after that), a team must land a robot on the moon, move it at least 500 meters and beam back high-definition imagery. Additional $2 million bonuses are available for robots that can survive one bitterly cold two-week lunar night or travel 5 kilometers, among other challenges.
Google and the X Prize Foundation jointly announced the competition in September 2007, but the duo has worked with dozens of teams for years to finalize fair rules that foster progress instead of stunts.
"We want to encourage a financially sustainable era of lunar exploration. The Apollo program and Soviet programs were fantastically inspiring, but they stopped just as they really started to scratch the surface," said planetary scientist William Pomerantz, a senior director at the X Prize Foundation. "Flags and footprints aren't sustainable. We want the teams to trigger business much larger in value than our prize."
'Flags and footprints aren't sustainable. We want the teams to trigger business much larger in value than our prize.'
Most of that value may rest in raw, untapped resources. Recent moon-surveying missions have revealed methane, ammonia and water — useful ingredients for moon bases and rockets — are hiding on the surface. A rare isotope of helium may also be abundant, and it could fuel pollution-free (although still-theoretical) fusion reactors.
Lunar science could also get a boost from more frequent visits, as multibillion-dollar moon missions launched every decade or so by the government are too infrequent and too risky to encourage much growth in the field.
"Doctoral students who want to do lunar science shouldn't have to gamble their Ph.D.s on one launch," Pomerantz said. "If lunar shots can go every six months or so, we'll see a much higher volume of scientific results as well as scientists."
To find out who is leading the race to seed such developments, technology security consultant Michael Doornbos has spent years interviewing the competitors and tracking their progress. The result of his work is a scorecard that ranks teams based on criteria such as funding, industry connections and progress.
"No one had any way to tell where we were at in the competition, making it almost impossible to be a fan or, especially, a super fan like me. So I decided to make a visual representation," Doornbos said. "I'm not a space industry expert, but I do talk to them to keep it updated. And a lot of people tell me they see great value in it because I'm an outsider."
David Gump, president of Astrobotic, said the scorecard is helpful, but that it may be impossible to know who is actually out in front.
"Many teams are playing their hands very close to the vest," Gump told Wired.com. "They're not saying much."
Whoever is leading the competition, there's a slim chance it may not matter. Organizers of the prize aren't happy about the prospect — they may lose rights to video and images from the first privatized lunar landing — but they may get their wish of a burgeoning moon-based industry without awarding a dollar.
Over the years, teams have made business plans with revenues projected to exceed the prize's one-team maximum of $24 million after just one successful launch. And as the start-up lunar businesses work multimillion-dollar deals with third parties, concerns about GLXP's contractual language have cropped up.
One clause that ruffled teams' feathers states that GLXP will get intellectual property rights related to multimedia. Pomerantz explained it's there to allow his organization to document and share the story of the competition with the world for free.
"We're an educational non-profit organization. We're here to inspire the next generation, and it's why we're supported by our donors and sponsors," Pomerantz said. "On the same token, we're not here to interfere with anyone's ability to do business. We want to be the initial push that gets the teams over that first bump."
Still, some teams are working big deals with cable TV providers to license content to their networks.
"They have 3-D channels on their systems, and they need something to fill them," Gump said. "A documentary about a 3-D-seeing lunar robot would work quite well."
Given the prestige — and cash — to be bestowed upon the winner, Pomerantz said it's an unlikely hypothetical that anyone will withdraw, especially because such wrinkles have been ironed out, he said. If a team wants to withdraw from the competition, however, it can rip up the GLXP contract as late as 6 months before a moonshot.
Still, propulsion engineer Tim Pickens, who leads the Rocket City Space Pioneers team, says the prize isn't the greatest of his concerns.
"If you need the prize to make your team's business work, you're hosed," said Pickens, who helped build SpaceShipOne and win the Ansari X PRIZE in 2004 — a win that spawned Virgin Galactic and a nearly $1 billion private industry in suborbital flights.
"The prize money is an awesome consolation and a great way to recoup development costs, but it isn't going to cover your mission costs," Pickens said. "There are much, much less risky ways to make money. For the value of the prize versus the risk, you might as well be doing something else."
Images: 1) Illustration of the Rocket City Space Pioneers' lunar lander and rover combination. 2) Locations of the GLXP's 29 teams. Dark green shows where teams are headquartered, and light green shows countries where team members are from. (Courtesy of Google Lunar X Prize.)
Posted: 18 Feb 2011 07:30 AM PST
Humans probably didn't get swept up in evolution.
Scientists have favored a model of evolution in which beneficial gene mutations quickly and dramatically sweep through a population due to the evolutionary advantages they confer. Such mutations would become nearly universal in a population. But this selective sweep model may not be accurate for humans, a new study indicates. Human evolution likely followed a more subtle and complicated path, say population geneticists Molly Przeworski of the University of Chicago and Guy Sella of Hebrew University of Jerusalem and colleagues.
Computational analysis of 179 genomes belonging to people from Europe, Asia and Africa reveal that selective sweeps have been rare in human evolution, the researchers report in the Feb. 18 Science.
"I'm convinced," says Andrew Clark, a population geneticist at Cornell University. Clark was among the first to find evidence that selective sweeps can shape evolution. The idea of a favored gene sweeping in to save the evolutionary day is so attractive that other forms of natural selection have been largely ignored, he says. The new study could change that. "I think this will be taken to heart and people will take a step back and start asking what other signatures of selection may be present."
In the study, the researchers based their analysis on the idea that when a gene containing a beneficial mutation becomes more common over successive generations it drags along big swaths of neighboring DNA. A sweep would happen so quickly that individual changes in the nearby DNA wouldn't have time to accumulate, so everyone in a population would end up with essentially the same genetic signature in the DNA regions surrounding the beneficial mutation.
The researchers searched for such troughs of genetic diversity around genes carrying mutations that would change an amino acid building block in the protein built from the gene — a sign of functional importance. The team reasoned that if the genetic changes were really beneficial, they ought to have deeper troughs than mutations that don't alter amino acids.
"But in fact, we found very little difference," says Sella. That could indicate that "very few of these mutations came into the population in the mode of a selective sweep." The researchers didn't find evidence of selective sweeps in regions of the genome that change how genes are turned on and off either.
It may have been difficult for selective sweeps to take hold in humans because of demographics, Clark says. People are scattered throughout the globe, so a beneficial mutation would have a long way to spread. Such a mutation would have to have dramatic effects on evolutionary fitness to go global.
Good evidence does exist for some mutations that did undergo selective sweeps in humans, such as those for skin pigmentation, hair and teeth morphology and the genetic change that allows adults in some populations to digest the milk sugar lactose. But those examples are the exception rather than the rule in human evolution.
"We have beautiful examples of selective sweeps. But there are not many of them, and our results suggest [there are] not many more to come," Przeworski says. "Our results do not suggest that adaptation was rare. Many protein changes in humans may well have been adaptive. What our results indicate is that the dominant mode of adaptation was not the classic sweep," she says.
"In looking for the genetic mechanisms of adaptation in the human lineage we'll have to turn to more elaborate models," Przeworski says.
Selective sweeps may have been more important in the evolution of some other species, though. Sella and colleagues recently reported evidence that selective sweeps happen often in some fruit flies.
Image: DNA profile of a human. (micahb37/Flickr)
Posted: 18 Feb 2011 06:00 AM PST
15 years after NASA astronomer David Williams started searching for them, hundreds of trees grown from space-faring seeds are still missing.
The "moon trees," whose seeds circled the moon 34 times in Apollo 14 astronaut Stuart Roosa's pocket, were welcomed back to Earth with great fanfare in 1971. One was planted in Washington Square in Philadelphia as part of the 1975 bicentennial celebrations. Another took root at the White House. Several found homes at state capitals and space-related sites around the country. Then-president Gerald Ford called the trees "living symbol[s] of our spectacular human and scientific achievements."
And then, mysteriously, everyone seemed to forget about them.
"The careful records weren't kept, or if they were kept they weren't maintained," Williams said. Williams, whose job includes archiving data from the Apollo missions, hadn't even heard of the moon trees until a third grade teacher e-mailed him in 1996 to ask about a tree at the Camp Koch Girl Scout Camp in Cannelton, Indiana.
"No one around here had ever heard of it," Williams said. "This is such a neat story, and no one seems to know about it."
Williams has made it his mission to find them. For the past 15 years, he has kept a record on the web of every known tree's location. When he started in 1996, he only knew where 22 trees were found. Now, that number has climbed to 80.
"It's been sort of a trickle," he said. "Most of the easy ones, the low-lying fruit had already been gathered."
Although most of the trees are long-lived species expected to last centuries, some have started to die off. According to Williams' most recent tree count, 21 of the 80 known trees are dead, including the Loblolly pine outside the White House, five sycamores and two pines outside the U.S. Space and Rocket Center in Huntsville, Alabama, and one New Orleans pine that was damaged in Hurricane Katrina.
"It's kind of sad, to see them going," Williams said.
The trees' poor health has nothing to do with their journey to space, Williams says.
"No one knew for sure whether being exposed to weightlessness or radiation would do something to the seeds," he said. "They grew control trees right next to each other to see if they grew differently. But they didn't find anything."
The healthy trees have given rise to a crop of half-moon trees, trees grown from the seeds of a moon tree.
"There's a lot of second generation moon trees being planted now," Williams said. "That's getting to the point where I can't keep up with it."
You can even buy half-moon seeds online and plant one in your own yard. Williams' yard hosts a second generation moon tree, a gift from the National Arboretum.
Although Williams will keep looking, there's no way to know when he's found them all, he says. But at least the trees won't be forgotten again.
"At least now there's a permanent home for it," he said. "It can't be lost now. At least all the information that comes in, we have that."
Update: If you think you've found a moon tree, you can contact Williams at firstname.lastname@example.org. Check the Moon Trees website to see if your tree has been reported before.
Image: 1) The plaque labeling the moon tree at NASA's Goddard Spaceflight Center, where Williams works. 2) NASA Goddard's moon sycamore. (Courtesy Jay Friedlander.)
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