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By Maggie Fox, Health and Science Editor 2 hours, 41 minutes ago

WASHINGTON (Reuters) - Sea urchins may be blind, but they have the same genes that help people see, as well as genes for a sense of smell and one of the most complicated immune systems in the animal world, researchers reported on Thursday.
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They also have genes associated with diseases such as Huntington's and muscular dystrophy, offering new routes to understanding illnesses, the researchers write in Friday's issue of the journal Science.

The sea urchin -- a pincushion-shaped animal found at the bottom of the sea and perhaps best known for its long, sharp spines -- shares more than 7,000 genes with humans, the international team of researchers found.

It was long known to be more closely related to humans and other vertebrates than other creatures favored by biologists for research, such as fruit flies and C. elegans roundworms.

Comparing human genes to their counterparts in other species can help scientists figure out why they evolved, and find ways to help when things go wrong.

The series of studies published in Science confirm this relationship and also make some surprising findings, such as genes for sight found at the bottom of their feet.

"I've been looking at these organisms for 31 years and now I know they were looking back at me," said Gary Wessel, a biology professor at Brown University in Rhode Island who worked on one study.

"We've already learned an enormous amount from the sea urchin, from something as basic as how identical twins form to in vitro fertilization procedures," Wessel added in a statement.

"With a complete map of the urchin's DNA, we can now learn more quickly and easily how each process works during development," he said.

KELP-EATERS

The team of researchers, led by George Weinstock of Baylor College of Medicine, studied Strongylocentrotus purpuratus, commonly known as the California purple sea urchin. It eats kelp growing on the bottom of the Pacific.

They found that the urchin has about 979 genes for proteins that sense light and odors -- similar to what is found in vertebrates that actually do see and smell things. How the sea urchin uses them is not yet clear.

Also remarkable is the animal's immune system, said immunologist Jonathan Rast of the University of Toronto.

The immune system is one thing that differentiates one species from another -- humans have big differences from chimpanzees, for example -- and Rast hopes the sea urchin's immune system will help in understanding how the human immune system evolved.

Like people, sea urchins have many immune genes that are active in the gut, which may help in coping with symbiotic bacteria that help digest food.

"It is one thing to be able to recognize all bacteria and get rid of all of them. It is another thing to maintain that in a complex way that you don't kill all of them," Rast said in a telephone interview.

Vertebrates have adaptive immune systems as well as innate immune systems that attack invaders without necessarily recognizing them, but invertebrates do not.

Urchins appear to have the genetic predecessors to the adaptive immune system -- the antibodies and T-cells that can change and respond to new germs, the study showed.

"They are probably acting in a different way but it was a real surprise to find them," Rast said. "If we can understand how they are acting in a sea urchin, it will help us understand how the system emerged in vertebrates."