Genome Sequencing Complete On Three Lophotrochozoans
December 20, 2012

Freshwater Leech, Ocean-Dwelling Worm, Sea Snail Genomes Sequenced

redOrbit Staff & Wire Reports - Your Universe Online

With the sequencing of three new members of a group of creatures known as lophotrochozoans, researchers from a pair of US universities and the Department of Energy's Joint Genome Institute (JGI) have more than doubled the number of genomes from these often overlooked marine creatures.

Scientists from the JGI, Rice University, and the University of California-Berkeley announced on Thursday that they had sequenced and published the genomes of a freshwater leech known as Helobdella robusta, an ocean-dwelling worm known as Capitella teleta, and a type of sea snail known as Lottia gigantean.

Their work was set to appear in the journal Nature.

"Lophotrochozoans are a diverse group of animals that includes mollusks -- such as snails, clams and octopuses -- and annelids -- such as leeches and earthworms. Like humans and all other animals, lophotrochozoans can trace their evolutionary history to the earliest multicellular creatures. But the lophotrochozoan branch of the evolutionary tree diverged more than 500 million years ago from the branch that produced humans," the researchers explain.

"Most animals, including people, have body plans with bilateral symmetry, which means they have left and right sides that are mirror images of one other. When you look at all bilaterian species, you can divide them into three big groups that biologists call clade," added Nicholas Putnam, co-author of the study as well as an assistant professor of ecology and evolutionary biology at Rice. "Lophotrochozoans are one of these clades, and when we looked at all of the genomes that had been sequenced, we found that only two were lophotrochozoans. That left a big hole in the genetic record, and our goal with this study was to fill in some of the gaps in that blank space."

Previously, the only two lophotrochozoan genomes that had been sequenced were both from parasitic worms. However, with their work at the JGI facility in Walnut Creek, California, Putnam and his colleagues set out to change all that. They used new computational tools in order to analyze, compare, and contrast the features of the new lophotrochozoan genomes and hundreds previously sequenced genetic code, including those of humans and frequently studied biological species such as fruit flies.

Thanks to those tools, Putnam said that the researchers were able to discover specific evolutionary changes that came about in specific groups of genes. In fact, the Rice University professor said that his team was able to determine 17 different groups of genes similar in structure to chromosomes that all date back to the last common ancestor of all animals that have bilateral symmetry.

"For us, the interesting thing is finding genes that exist today in different species, tracing those to a single gene in a common ancestor and then using the patterns we find to test hypotheses about evolutionary processes," he said. "Sometimes the genes today might still have the same function, but other times they have evolved an entirely new function."

"These studies teach us important lessons about ourselves and other vertebrates," Putnam added. "Looking across the animal kingdom gives us more resolution and clarity about what in our genome is new and what has been preserved from our ancient ancestors."