Decoding the Sea Urchin Genome

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Scientists have just spent considerable effort reading the complete gene set of the sea urchin. It turns out, the sea urchin has a lot to tell us about how we develop from a single cell into a complete human being.

STEVE INSKEEP, host:

Some scientists have taken a special interest in a humble creature with a humble name that makes you think of some Charles Dickens story. It's called a see urchin. And though it doesn't seem like much, two scientists at the California Institute of Technology are passionate about reading its genes. And they say there is a reason you should care about its genome.

NPR's Richard Harris explains.

RICHARD HARRIS: If you've ever waited in tide pools along the Pacific Coast, you've no doubt seen the spiky, purple see urchin lurking about. They basically eat kelp and get eaten by sea otters. End of story? Not quite. For well over a hundred years, biologists have also had a soft spot for sea urchins.

Mr. ERIC DAVIDSON (California Institute of Technology): Scientists go where the opportunities lie, like prospectors.

HARRIS: Eric Davidson at Caltech says urchins have been a goldmine for biologists. He fell for them decades ago, and not just because they were an excuse to go diving off the California Coast. It turns out they are extremely handy for studying how a single cell develops into a complete organism. Davidson says the embryos grow easily in seawater, which is not hard to come by, and they are produced by the millions; plus these days it's easy to add DNA to them for genetic experiments.

Mr. DAVIDSON: The embryos develop rapidly, and so you inject the DNA on Monday, and you start getting your answers on Tuesday and Wednesday.

HARRIS: But they're just sea urchins, right? Well, yes and no. That is, it turns out that we share a lot of basic biology with sea urchins.

Mr. DAVIDSON: Because the way animal development works is fundamentally similar across the whole world of animal life.

HARRIS: So these days more than 200 biologists in 70 labs are at work on sea urchin biology. A few years ago, they convinced the powers that be that it would be worthwhile to decode the purple sea urchin's entire genetic sequence - it's genome. Eric Davidson's colleague at Caltech, Andrew Cameron, even donated the sea urchin tissue that provided the DNA for this project.

Did that individual have a name, perchance?

Mr. ANDREW CAMERON (California Institute of Technology): It's pretty boring. It was A3.

HARRIS: Cameron says A3 is no longer living at Caltech. He can't remember whether it died or if it was returned to the ocean, as many specimens are. But A3's genetic code is now here for all to see. And Eric Davidson says it contains some pretty big surprises.

Mr. DAVIDSON: If you look at a sea urchin, you don't see anything that looks like an antennae or an eyeball or a nose, but it turns out that the genome revealed hundreds of genes which look like smell receptors and light sensitive - and then (unintelligible) light sensitive proteins.

HARRIS: Andrew Cameron has a pretty good idea where to look now for undiscovered sea urchin sensory organs.

Mr. CAMERON: Sea urchins attach themselves to rocks by means of multiple rows of two feet, and it's looking like at least some of the genes are being expressed in the two foot.

HARRIS: The other big surprise in the gene sequence is that these starfish relatives seem to have an amazingly advanced immune system to ward off infection. Eric Davidson says that makes sense.

Mr. DAVIDSON: These are very long-lived animals. They probably have lifespans equivalent to ours, and so if you going to live a long time, you better have a good immune system. And they have a wonderful immune system, but it works entirely differently from anything that's been seen before.

HARRIS: Davidson and Cameron, of course, don't need to be convinced themselves that sea urchins are a lot more sophisticated than they seem at first glance. The genome helps Cameron make that case.

Mr. CAMERON: Now I have an easy way of explaining to people that here's an animal that does not look very much like us, but is much more like us than we ever thought.

HARRIS: And all the details are published in the latest issue of Science magazine.

Richard Harris, NPR News.

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