Nanoparticles Pass Muster as Vectors for Gene Therapy

Image: COURTESY OF THE PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES

Gene therapy, in which a viral vector is used to modify defective genes or replace missing ones, has shown significant potential as a way of treating disease in animal models. But its use in humans has been hampered by safety concerns, including some fatalities in clinical trials. Researchers have thus been looking into the possibility of using nonviral vectors, which should carry fewer inherent risks, to deliver therapeutic genes. In a paper published online this week by the Proceedings of the National Academy of Sciences, scientists report that silicon nanoparticles can perform this task successfully in mice.
Paras N. Prasad of the State University of New York (SUNY) at Buffalo and his colleagues manufactured nanoparticles using organically modified silicon. The surface of these particles can be tailored to target specific cells. The team used the tiny units to transport a fluorescent marker gene to dopamine neurons in the brains of mice. After injecting the nanoparticles, the researchers observed brain cells fluorescing using a new imaging technique that works on live animals. According to the report, the study is the first in which a nonviral vector has shown efficacy comparable to that of a viral delivery system in an animal model. What is more, a month later none of the animals had experienced adverse effects from the procedure.

The researchers also investigated the possibility of manipulating the behavior of specific brain cells, instead of solely tagging their presence. In so doing, they discovered that the nanoparticles can be used to reactivate adult stem cells by altering a nuclear growth factor receptor. The team will next test the approach on larger animals. "In the future," says study co-author Earl J. Bergey, also at SUNY Buffalo, "this technology may make it possible to repair neurological damage caused by disease, trauma or stroke." --Sarah Graham

Why Cats Don't Cotton to Sweets Explained

The lure of sweets is the downfall of many a dieter. Cats, however, are indifferent to sugar, a trait that is rare in the mammal kingdom. Now scientists have figured out why. Felines apparently carry a defect in a gene that encodes part of the mammalian sweet taste receptor.
A lack of interest in sweets has been observed not only in house cats, but also in wild ones such as lions, tigers and jaguars. "One possible explanation for this behavior is that felines are unable to detect sweet-tasting compounds like sugars and high intensity sweeteners because their sweet taste receptor is defective," remarks Xia Li of the Monell Chemical Senses Center in Philadelphia. Li led a team of researchers to investigate the genetics of taste in cats. They determined that the animals lack 247 base pairs in a gene called Tas1r2, which encodes T1R2, one of two protein subunits that make up the sweet receptor in most mammals. "This type of gene is known as a pseudogene and is somewhat like a molecular fossil," Li says. "It presumably once coded a functional protein, but no longer does so."

The other half of the sweet receptor, known as T1R3, is normal in cats. "What we still don't know is, which came first: carnivorous behavior or the loss of the T1R2 protein," notes senior author Joseph G. Brand of Monell. "With regard to the gene, is this a case of 'use it or lose it'"? The scientists describe the work in the July issue of the journal PLoS Genetics. --Sarah Graham

New Planet Discovered in the Solar System?

John Roach
for National Geographic News

August 1, 2005
A chunk of rock and ice that may be a planet has been discovered in the farthest reaches of the solar system, astronomers announced Friday. The object, currently called 2003 UB313, orbits the sun and is larger than Pluto, traditionally considered the ninth planet in the solar system.

The news came hot on the heels of the announcement of the discovery of a separate planet-like object at the edge of the solar system (see "New Pluto-Size Object Discovered in Solar System")—and amid fears that a rogue astronomer may been attempting to announce the UB313 discovery as his or her own.


The discovery of UB313 is likely to reignite the debate over the definition of "planet"—and over how many objects in the solar system are deserving of the name.

The sequence of events surrounding the UB313 announcement may also change how such objects are announced in the future, according to Brian Marsden, director of the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts.

UB313 is being called a scattered disk object or an extreme member of the Kuiper belt. The belt is a ring of icy debris that floats on the fringes of the solar system beyond Neptune.

The object is currently about 97 times farther from the sun than Earth is, or about three times farther from the sun than Pluto. Its orbit is more eccentric than Pluto's, taking it from 38 to 97 times the sun-Earth distance over a 560-year period.

UB313 is the farthest known object in the solar system—even further than Sedna, a planetoid discovered nearly two years ago (see "New Planetoid Found in Solar System—Most Distant Yet"). The newfound object is also among the five brightest Kuiper belt objects, as seen from Earth.

The sheer size of the object means that it can only be classified as a planet, according to Mike Brown, an astronomer at the California Institute of Technology in Pasadena, who announced the object's discovery.

Brown made the discovery with Chad Trujillo of the Gemini Observatory on the Mauna Kea volcano in Hawaii, and David Rabinowitz of Yale University in New Haven, Connecticut.

The team had originally planned to report the discovery of UB313 in October after more detailed observations. But they decided on an early announcement after it became clear that savvy Web users could—if they were so inclined—track down UB313 observation data online and use it to claim the discovery as their own, Marsden said.

Planet Debate

Brown and his colleagues are uncertain of the exact size of the object, but its brightness and distance from the sun tell them that it is at least slightly larger than Pluto. At one-fifth the mass of our moon, Pluto is the smallest of the nine planets.

"We are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system," Brown said in a media statement.

Marsden, of the Minor Planet Center, said there "isn't much doubt" that 2003 UB313 is bigger than Pluto. However, he rejects the idea that the newly discovered object deserves planet status.


"If anything, it suggests we really seriously should go back to eight [planets in the solar system]—the traditional 19th-century ones," Marsden said.

Pluto was discovered in 1930. At the time, astronomers believed Pluto's mass was equal to Earth's. Since then refinements in measurement techniques have revealed the planet's relatively diminutive size.

Marsden said he proposed in 1999 to include Pluto in the catalog of what is now almost a hundred thousand sequentially numbered small bodies. The move would have effectively stripped Pluto of its status as a planet, at least in some astronomical circles.

The proposal was dropped, however, after objections from a minority of astronomers who wanted to preserve Pluto's historical significance.

Now that an object bigger than Pluto has been discovered, Marsden said, this is an ideal time to rectify matters.

If 2003 UB313 is to be called a planet, then a couple of dozen other Kuiper belt objects should be too, as well as the asteroid Ceres and perhaps a dozen other objects in the asteroid belt, Marsden added.

Discovery and Announcement

Brown, Trujillo, and Rabinowitz first observed 2003 UB313 on October 21, 2003, using the Samuel Oschin Telescope at Caltech's Palomar Observatory in San Diego County, California.

At the time, the object was so far away that its motion went undetected. It wasn't until January of this year that the object's orbital path was uncovered.

Since then the team has been studying UB313 with other telescopes. They planned to announce the discovery in October with more detailed information on its size and composition.

The team was also planning to announce the discovery of another large Kuiper belt object, 2005 FY9, in October.

The announcement of both objects was suddenly moved up to July 29 after an unexpected announcement from another group of astronomers, Marsden said. On July 28 a team led by Jose-Luis Ortiz at the Instituto de Astrofísica de Andalucía in Granada, Spain, had announced to the Minor Planet Center the discovery of 2003 EL61, another planet-like object at the edge of the solar system.

Brown's team also had independently observed EL61 and had posted on a Web site an abstract of a paper on the object on July 19. They plan to present their EL61 paper at an astronomy conference this September in Cambridge, England.

The U.S. astronomers, though, had not reported their EL61 discovery to the Minor Planet Center, which is the official governing body for the recognition of such discoveries.

The Minor Planet Center's Marsden said the timing of the Spanish team's discovery "struck me as a little odd," given that Brown's paper on EL61 had been posted online just ten days earlier. In e-mail discussions with Brown about the issue, the Caltech astronomer told Marsden about the two other objects and asked for advice.

"While he didn't care if the other object might [be] scooped, he did care about the big one [2003 UB313]," Marsden said.

Before Marsden replied to Brown, he learned from a colleague that someone had already calculated the orbits of 2003 UB313 and 2005 FY9. This other party had based his or her calculations on Brown's observation data from a Chilean telescope, which is readily available on the Web.

Marsden shared the information with Brown and urged him to make the announcement July 29.

"We had to assume that the [stranger's use of Brown's data] was malicious and that the person was going to use the information to attempt to claim he had discovered the objects himself. Thus we had to announce late on a Friday afternoon with no preparation," Brown wrote in an e-mail interview.

Marsden does not suspect that Ortiz's team is responsible for the suspected foul play. He also noted that Internet insecurity has made it tougher for scientists to check and double-check their findings before going public.

"It's a little startling to realize that the records of telescope pointings are available on the Internet. There's so much stuff out there that it's hard to keep something you found secret while you really study it and then prepare a proper publication about it," Marsden said.

Photo in the News: Panda Baby Boom Arrives on Pink Paws

July 12, 2005—Forget sharks: The summer of the panda is upon us, and it's padding in on 20 pink paws. Last week alone five giant panda cubs were born in captivity: one at Washington, D.C.'s National Zoo and two pairs of twins (one of which is pictured above) at China's Wolong panda reserve.
A newborn giant panda is about as big as a stick of butter and lacks the familiar black-and-white markings for its first month or so of life. Successful births in captivity are extremely rare—and extremely prized by conservationists, given the species's dwindling numbers. About 1,600 giant pandas remain in the wild, plus about 160 living in zoos and breeding centers, according to the National Zoo.

Adding a circle-of-life pallor to the otherwise rosy news, China this week announced that the world's oldest known giant panda, a female named Mei Mei, had died at a zoo in the city of Guilin at age 36—or about 108 in human years.

—Ted Chamberlain

Giant Catfish May Be World's Largest Freshwater Fish

Photograph by Suthep Kritsanavarin

Fishers in northern Thailand netted this huge catfish in the Mekong River on May 1. Nearly nine feet long (2.7 meters) and as big as a grizzly bear, the behemoth tipped the scales at 646 pounds (293 kilograms). Experts say the fish, which belongs to the species known as the Mekong giant catfish, may be the largest freshwater fish ever recorded.

Thai fishers struggled for more than an hour to haul in the record-breaking Mekong giant catfish. Officials from Thailand's Inland Fishery Deparment then used a performance-enhancing drug to stimulate the pituitary gland of the female fish in order to prepare it for a breeding program (above). Despite efforts to keep the bear-size catfish alive, it died and was later eaten by villagers.

The species is listed as critically endangered by the World Conservation Union (IUCN) and faces a high risk of extinction in the wild. The rare specimen, captured in the Mekong River in Chiang Khong district, is the largest since Thailand began keeping records in 1981.

Thai fisheries officials had hoped to release this adult female Mekong giant catfish after they stripped it of eggs (above) for a captive-breeding program. But the whopping fish, which was as big a grizzly bear, didn't survive.

Listed a critically endangered by the World Conservation Union (IUCN), the Mekong giant catfish is one of the world's largest freshwater fishes. Other contenders include the Chinese paddlefish and the dog-eating catfish—another Mekong River giant.

Editor's Note: It was initially reported incorrectly that the giant catfish caught in Thailand was male.

After a record-breaking Mekong giant catfish died, residents of Hat Khrai, a Thai village on the Mekong River, butchered the fish for its meat.

"Mekong people believe it's a sacred fish, because it persists on plant matter and 'meditates'"—in the deep, stony pools of the Mekong River—"somewhat like a Buddhist monk, said Zeb Hogan, a fisheries biologist who studies the largest freshwater fish in the world. A WWF conservation fellow and National Geographic Society Emerging Explorer, Hogan has received funding from the National Geographic Society Conservation Trust.

Mekong giant catfish attract high prices in Thailand, because eating the fish is supposed to bring good luck. Likewise, the Chinese believe that catfish meat boosts intelligence and prolongs life.

Mars Life May Be Contaminated by Spacecraft, Experts Warn

Hillary Mayell
for National Geographic News

July 26, 2005
Is there life on Mars? If there is, NASA might be contaminating it with microbes from Earth.

The concern prompted the Washington, D.C.-based National Research Council (NRC) to issue an advisory yesterday urging the U.S. space agency to adopt more stringent spacecraft-sterilization techniques.


Microbes (microscopic organisms that humans live with every day) can survive in much more extreme environments than previously believed—places of superheated temperatures, radiation, freezing cold, high salt concentrations, or extreme dryness.

"The science we've been operating on, gathered during the Viking 1 and 2 missions in the 1970s, is completely outdated," said University of California planetary scientist David Paige. Paige is also a member of the private, nonprofit NRC.

NASA's Viking landers were the first spacecraft to land on Mars and conduct scientific research. Viking 1 and Viking 2 landed on July 20 and September 3, 1976, respectively.

"The planetary protection policies that we have are rooted in the era of Viking. … ," Paige said. "Since then we've found that microbes are a lot more rugged than we originally thought," he added. "In addition, Mars might be more hospitable to life than we originally thought." For example, scientists have found evidence that there could be liquid water—which is necessary for life on Earth—at many places on the Mars. (See a photo of a "frozen sea" on Mars.)

Scaled-Back Sterilization

The early spacecraft that landed on Mars were thoroughly sterilized. But as money for the space program got tight, the expensive cleansing process was cut back.

Now that more is known about both Mars and microbes, the NRC is advising NASA to develop and implement new methods and rules to detect and eliminate microorganisms on robotic spacecraft. The techniques currently used to clean spacecraft only detect heat-resistant and spore-forming bacteria. The scientists are concerned that NASA's screening-and-cleaning process does not detect all the microbes that might be present on the spacecraft.

The advisory, which is based on a NASA-funded report by the NRC, recommends that all future landers be 100 percent sterilized. The NRC also suggests that NASA undertake a research program to find and test improved techniques within the next three years.