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Published online: 13 June 2007; | doi:10.1038/news070611-8 / http://www.nature.com/news/2007/070611/full/070611-8.html

How a chill pains us

Researchers identify protein that signals cold-induced pain.

Heidi Ledford

Ouch: it's hard for anyone to stand on bare ice. Peter W. Reeh & Clemens Forster

Whether the pain comes from holding an ice cube for too long or staying out on a frigid winter day, the source is clear: it's the cold that hurts. Now researchers have found a protein responsible for provoking pain in response to extreme cold in mice.

The protein, called Na_v1.8, was already known to play a role in detecting tissue damage, and was previously associated with inflammation and pain in response to damaged nerves. Now it looks like the same protein gets involved when the temperature plummets.

Physiologist Katharina Zimmermann at the University of Erlangen-Nuremberg, Germany, and her colleagues found that mice lacking the protein became impervious to pain from cold. Normal mice placed on a plate chilled to 0°C will hop about and lift their feet, but mice engineered to lack Na_v1.8 do not, they found. The results are published this week in Nature.¹

The protein works by helping sodium ions to pass through the cell membrane of neurons, a process that is crucial to transmitting signals - including pain signals - along nerve fibres. It works unusually well in the cold; unlike other similar proteins, its activity doesn't decline as the temperature drops. "That goes against what cells are supposed to do in the cold," says Ardem Patapoutian, a cell biologist at Scripps Research Institute in La Jolla, California, who was not affiliated with the study.

Feeling the chill

The work adds to our increasing appreciation of how we sense temperature. A protein that responds to moderately cold temperatures (and the cool feel of menthol) was recently identified. When the temperature dips enough to get painful, though, Na_v1.8 becomes a key player.

It's likely that Na_v1.8 is involved in signalling other sensory experiences, such as heat or pressure, says neurobiologist David McKemy of the University of Southern California in Los Angeles. But it's still unclear whether the protein directly responds to cold or is instead transmitting a signal from another receptor, Patapoutian adds.

Zimmermann notes that Na_v1.8 is a member of a family of proteins that has been shared in similar form by a wide range of animals over time. The protein could be important, she speculates, for telling cold-blooded animals when it's time to seek out warmer locales.

References : Zimmerman K., et al. Nature, 447 . 855 - 858 (2007).

Published online: 13 June 2007; | doi:10.1038/news070611-9 / http://www.nature.com/news/2007/070611/full/070611-9.html

Giant bird-like dinosaur found

Chinese researchers unearth a surprising find.

David Cyranoski

Researchers in China have unearthed the bones of a gigantic bird-like dinosaur, dwarfing anything else in its category.

Good guess: Gigantoraptor is thought to have had a beak and feathers. Zhao Chuang and Xing Lida/IVPP

Alive, the beast is thought to have been 8 metres long, 3.5 metres high at the hip and 1,400 kilograms in weight - 35 times as heavy as its next largest family members and 300 times the size of smaller ones such as Caudiperyx. It has been classified as a new species and genus: Gigantoraptor erlianensis. The find is detailed this week in Nature.

The evolution of bird-like features had long been thought to be accompanied by a decrease in size, meaning the smaller the species, the more bird-like it is likely to be and vice versa. The new discovery shows that isn't necessarily true.

Gigantoraptor had long arms, bird-like legs, a toothless jaw, and probably a beak. There are no clear signs as to whether it was feathered. However, judging from its close affinity to other dinosaurs known to have been feathered, Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing speculates that it was.

The largest animal known to have had feathers is the extinct Stirton's thunder bird, which weighed in at 500 kilograms.

No one expected this type of bird-like dinosaur to get so big. Li Rongshan/IVPP

Comparison of the animal with other known dinosaurs - looking at more than a hundred characteristics, including limb proportions - puts Gigantoraptor firmly in the Oviraptoridae family. "We have really good diagnostic features for oviraptorosaurs," says Xu. The jaw, he notes, is particularly characteristic of this type of dinosaur.

"This is a dinosaur group we've known about for a hundred years. They are usually the size of a turkey or maybe an emu," says David Unwin, a dinosaur expert at the University of Leicester, UK. "No one would have predicted this. If they had, they'd be laughed at."

The bones date from the Late Cretaceous epoch, about 85 million years ago.

Accidental find

The animal was found by accident in April 2005, when Xu was re-enacting the find of a sauropod for a Japanese documentary film crew. While the cameras were rolling, Xu randomly picked out a bone from a dig site in the Gobi Desert, where a unique sauropod had previously been found. As he started clearing away the dirt, Xu soon realized that the bone was not from a sauropod. Its large size suggested a tyrannosaur, but he couldn't be sure. "I told them to stop filming," recalls Xu. "I said, 'This is not for your programme.'"

Xu's team later found an unusually complete collection of bones from the specimen, including a nearly complete forelimb, hind limb and lower jaw, a partial pelvis and some vertebrae.

The Gigantoraptor's diet is a mystery. It has the small head and long neck of a herbivore, but the sharp claws of a carnivore.

Several aspects of the skeleton are still confusing to the researchers. There's a large hole, of unknown purpose, in the vertebrae, Xu says.

Xu and his team also sliced through a bone to see how old the dinosaur was when it died: they think it was 11 years old, and despite its size was still a young adult at the time. The team says this means the animal grew much more rapidly than North American dinosaurs. They speculate that older creatures would have been even bigger.

Reference : Xu X., et al. Nature, 447 . 844 - 847 (2007).