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A Squirt of Ciona DNA Yields Clues to Evolution

SAN FRANCISCO, Dec. 12 - Researchers had a party for a sea squirt, and after a week left with some new insights into evolution.


An "annotation jamboree" last spring brought researchers from the US, Japan, Italy, France, Scotland, Canada, and Australia to Walnut Creek, Calif., home of the US Department of Energy's Joint Genome Institute, to pore over the genome of Ciona intestinalis, or common sea squirt. They found a genome, sequenced at the end of 2001, with some 16,000 genes, about 80 percent which are also found in humans, according to JGI.


While C. intestinalis may have got its name from its sucking of water through its body and squirting it back into the ocean, its designation as "squirt" could also apply to its relatively small genome compared to vertebrates, which makes it an attractive organism for comparative genomics. Ciona has single copies of a large number of genes that vertebrates have in multiply copies, explained Daniel Rokhsar, head of JGI's computational genomics department.


"One of two things can happen to these redundant copies," Rokhsar said in a statement. "Either they mutate away and disappear, or they evolve to perform other functions. By looking at Ciona's genome, we can see what innovations occurred in the human lineage that enabled us to advance in complexity."


The results of the analysis, published today in Science, include the findings that the sea squirt contains genes involved in heart formation, light-sensing, and an immune system that are very similar to vertebrate genes.


"Bringing the community together was essential," Rokhsar said. "Only by a collaborative effort could we hope to get a coherent sense of the relationship of the Ciona to other organisms, which in turn illuminates the mechanisms of evolution." 

The analysis team, led by JGI, included researchers from the University of California, Berkley's department of molecular and cellular biology and Center for Integrative Genomics, Kyoto University's department of zoology, and Japan's National Institute of Genetics.


Click here for more information about the sea squirt genome.

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