Genome sequence of lancelet shows how genes quadrupled during vertebrate...(50 million years ago when a creature sim...),Health

Date:6/18/2008

50 million years ago, when a creature similar to the lancelet evolved and diverged into three types of chordates: cephalocordates like the lancelet; urochordates like the sea squirt; and vertebrates like us. Cephalocordates and urochordates are invertebrates that have a flexible notochord rather than a bony spine protecting their spinal cord.

The Florida lancelet, Branchiostoma floridae, looks a lot like a fish, but has a stiff cartilaginous notochord that it vibrates to swim and burrow in the sand, where it nestles during the day with its head sticking out to filter phytoplankton from the water. The lancelets typically emerge from the sand at night and swim with lateral movements.

"If you think about what the original ancestor of all bilaterally symmetric animals looked like, you can make a pretty good argument that it was a sort of worm-like creature - a finger length-long, floppy kind of worm like amphioxus," Rokhsar said.

With the aim of understanding the evolution of chordates, the JGI sequenced the amphioxus genome using lancelets that Holland collected from the 15-foot-deep waters of Tampa Bay, Fla. A thorough analysis led by Putnam, Rokhsar, Holland and colleagues Peter Holland of Oxford University in the U.K. and Noriyuki Satoh of Kyoto University shows that the creature's 19 chromosomes map onto the human genome in 17 segments, each of which is represented four times in the human genome.

"The human genome is a mosaic of these 17 ancestral pieces constructed by two rounds of duplication, followed by gene loss and chromosome rearrangments and fusions. That took some computational gymnastics to sort out, but the evidence is still there," said Rokhsar.

Putnam's analysis of the genome shows that many of the duplicated genes were subsequently lost, "mainly the housekeeping genes that code for structural proteins, enzymes, metabolic pathways - things you don't really need more than one copy of," Linda Holland said.

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Contact: Robert Sanders rsanders@berkeley.edu 510-643-6998 University of California - Berkeley Source:Eurekalert

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