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Sea Squirt Savants Celebrate

Kristen Philipkoski Email 04.16.02
WALNUT CREEK, California -- A tiny sea creature known as the sea squirt is so compelling that 50 scientists flew from the far corners of the earth last week just to look at the little critter's DNA.

Scientists from Japan, Australia, Italy, France, Scotland and the United States gathered here for the Sea Squirt Genome Jamboree. They had been studying different aspects of the squirt's DNA for the past year, and the jamboree, hosted by the Joint Genome Institute, was their chance to finally see the whole genome in one piece.

It was a gorgeous, unseasonably warm 84-degree day in San Francisco suburb of Walnut Creek on Friday, but the jamboree attendees couldn't have cared less about the weather. Packed into one room, they stared at the sea squirt genome data on their laptops. Someone announced lunch. No one looked up. A reporter snapped their photographs -- still, no one moved.

"They've worked on aspects of this animal in some cases for most of their lives," said Dan Rokhsar, associate director for computational genomics at JGI and organizer of the jamboree. "This is their first glimpse of what the genome looks like."

The researchers were giddy to be in the same place at the same time.

"There's a cross-fertilization happening," said Bernie Degnan of the University of Queensland in Australia. "We're getting people to talk to each other and see how they use the (sea squirt) genome.

"This jamboree is very successful because it's gotten together (researchers from) various fields and approaches," said Nori Satoh, a professor of zoology at the Japanese Genome Center in Kyoto.

The sea squirt is basically made of two attached tubes -- one sucks in water, the other squirts the water out after filtering nutrients. They attach themselves to the sea floor or rocks, and usually remain in one place their entire lives, which lasts around three years.

"They're like barnacles, but they're squishy," said Paul Richardson, manager of functional genomics at the Joint Genome Institute.

Scientists are so fascinated by the sea squirt because even though it evolved about 550 million years ago, long before humans appeared about 100,000 years ago, they're similar in some important ways. It has many of the same genes as humans, and they happen to be genes that can cause disease when they malfunction.

Of all the animals without backbones, sea squirts are the closest relatives to humans. Although they don't have a backbone, they do have a "notochord" -- a precursor to the spine. They're also the only pre-vertebrate animals to have their nervous system on the back part of their bodies, like humans, rather than on their belly-side.

The sea squirt also has what scientists believe is the first creature with an immune system. They hope to understand how the human immune system is organized by studying the sea squirt's.

Sea squirts, like humans, will reject foreign tissues introduced to their bodies.

"We're looking for the rudiments of the immune system," said Tony de Tomaso, a post-doctoral student in comparative immunology at Stanford University.

Their embryos are also strikingly similar to a human's, so scientists are studying the early stages of their development. They're also the most primitive animals with a thyroid gland.

It's remarkable that such an unassuming little creature -- one that Aristotle thought was a plant -- could have so much in common with humans, researchers say. And decoding its genome could reveal the processes underlying some human diseases.

Genes that have survived in humans since the sea squirt's evolution have surely been preserved for good reasons. By comparing the genomes of different creatures to the human's, researchers can pinpoint which genes have survived hundreds of millions of years of evolution. Those that have survived throughout evolution are likely to have important functions.

Researchers all over the world are mapping the genome sequences of the chimp, mouse, rat, fruit fly, nematode worm and at least two types of pufferfish to perform such "comparative genomics." In other words, they compare these animal genomes to the human genome to see the similarities and differences -- and hopefully discover the secrets of evolution and disease.

Sea squirt jamboree attendees plan to publish a paper on their work by the end of this year.

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