An international team of nearly 250 scientists reported Friday that they had determined the exact order of all 814 million letters of DNA code that carry the instructions for making and maintaining a sea urchin.

	Charles Hollahan Sea urchins -- Strongylocentrotus purpuratus -- have 23,300 genes, only slightly fewer than humans have. Click photo for larger image.

If you think that's relevant only to scuba divers and sea otters, you're wrong. Among life forms that lack backbones, these spiky critters -- which are kissing cousins of starfish and can live for more than 100 years -- are our closest relatives. They are more similar to us than fruit flies or worms, those classic laboratory workhorses that for decades have provided insights into human biology and genetics.

Sea urchins, it turns out, have 23,300 genes, only slightly fewer than humans have. Many are similar to genes that cause human diseases, including Huntington's disease and muscular dystrophy. That means urchins may provide a new venue for studying the molecular origins of those ailments.

Surprisingly, urchins have 979 genes that, by the looks of them, are involved in sensing light or odors -- not bad, considering they have neither eyes nor noses. Lots of those genes are most active in urchin "feet," suggesting those appendages are as important for vision and other senses as for movement.

"I've been looking at these organisms for 31 years, and now I know they were looking back at me," said Gary Wessel of Brown University, part of a group that was led by Richard Gibbs and George Weinstock of Baylor College of Medicine.

In reports in the Nov. 10 issue of the journal Science and the Dec. 1 issue of Developmental Biology, the team also anticipates learning from the urchin's spectacular array of immune system genes and the genes for making its dome-shaped skeleton -- which is made of different minerals than ours.

Sea urchin expert Charles Ettensohn, of Carnegie Mellon University, and his team were part of the multicenter, international consortium. They focused on the genes for skeleton formation, known as biomineralization.

Complete sequencing of the sea urchin genome will make many more experiments possible, he said.

"It's good times for those of us who work with the system," Dr. Ettensohn said. "It's almost like nirvana."

For more than 150 years, sea urchins have been used to study embryonic development. The embryos develop outside the adult in a couple of days, and are as "clear as glass," the scientist said. "You can see every single cell."

Now that the genome has been decoded, it is possible to knock out or disrupt the function of particular genes and gauge the impact on the embryo and adult, Dr. Ettensohn explained.