Science Special Section Explores Purple Sea Urchin Genome

Spawning S. purpuratus. [Image courtesy of Charles Hollahan]

The latest edition of Science examines the purple sea urchin genome

Researchers have sequenced and analyzed the genome of one of biology's most beloved model organisms, the purple sea urchin, Strongylocentrotus purpuratus, according to a special section in the 10 November 2006 issue of the journal Science.

The purple sea urchin represents the first sequenced genome from the phylum echinodermata, which are the closest known relatives of the phylum chordata, the group that includes humans and other vertebrates. Both the echinoderms and the chordates belong to the major animal group Deuterostomia.

In one of the lead reports, George Weinstock of the Human Genome Sequencing Center at the Baylor College of Medicine in Houston, Tex., and colleagues reported the sequence, which encodes about 23,300 genes, includes many genes previously thought to be exclusive to vertebrates such as humans. In addition, the researchers identified several genes thought to be found solely outside the Deuterostomia group.

Weinstock's research confirms that these echinoderms—some of which may live for over a century—are more closely related to humans and other vertebrates than fruit flies or nematodes, two other model organisms whose genomes have been sequenced.

Another researcher, David Bottjer of the University of California, Los Angeles, found that purple sea urchin genes involved in the formation of the hard, rigid tissue called stereom likely did the same job in the earliest echinoderms 520 million years ago.

The fossil record shows that hard, "biomineralized" tissue first appeared just before the Cambrian period, around 540 million years ago, coinciding with the rapid increase in diversity of complex life known as the Cambrian explosion.

Research by Jonathan Rast of the University of Toronto revealed that the urchin genome suggests an immune system with a vast repertoire of innate immune receptors that is part of a ready-made artillery for fighting pathogens. In fact, the sea urchin has an order of magnitude more of these receptors than vertebrates.

Other highlights of the special section include research on gene expression in the S. purpuratus embryo and insights on the animal's role in maintaining the ecological balance between luxuriant kelp forests and species-poor sea-urchin "barrens."

Kathy Wren

9 November 2006