What do leeches, limpets and worms have in common? Now, a sequenced genome

December 19, 2012

Leeches, despite the yuck factor, have captured the hearts of two University of California, Berkeley, scientists who are part of a team that this week is publishing the leech's complete genome sequence.

"This genome has revolutionized our studies," said David Weisblat, a UC Berkeley professor of molecular and cell biology who lobbied for inclusion of the leech in a genome sequencing initiative that has targeted a variety of animals in order to learn what they have in common with one another and with humans.

The initiative is being led by Daniel Rokhsar, UC Berkeley professor of molecular and cell biology and of physics and program lead for eukaryotic genomics at the Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, Calif. His multinational team published the genomes of the leech and two relatives, the limpet and the marine worm, or polychaete, in the Dec. 20 issue of the journal Nature. The publication comes after five years of efforts analyzing mountains of information provided by the initial sequencing effort.

"Through comparison of these diverse genomes with each other, we can learn what animals have in common with each other, which in turn tells us about the features that their common ancestors had," said Rokhsar. "That is a big driver for comparative genome sequencing - it is one of the few ways we have of looking back in deep time."

For these organisms, deep time means more than 500 million years ago, toward the end of the Precambrian era, when they split off from animals that eventually evolved to become vertebrates - animals with backbones - such as humans.

These three genomes are important because they represent a group of animals that makes up between one quarter and one-third of all marine creatures. Called lophotrochozoans, they range from clams, snails and octopuses to segmented worms and even earthworms, most of which develop from an egg to an intermediate larval stage called a trochophore before metamorphosing to their final form.

"These trochophores are small, free-swimming ciliated larva, first described over 100 years ago, and this mode of embryological development underlies a tremendous amount of animal diversity in the oceans," Rokhsar said.

"It's incredible to think that over half a billion years ago, there was an animal with a trochophore larva that was swimming around in the Precambrian seas - and that animal gave rise to so much modern diversity," he said.

Based on a preliminary analysis of the sequenced genomes, the three animals have a lot in common with not only humans, but with other animals that seem very distantly related, he said. For example, the gene content, gene structure and even chromosome organization of the owl limpet Lottia gigantea - a smaller relative of the abalone and the polychaete Capitella teleta, a marine segmented worm, are quite similar to other invertebrates, pointing to the unity of animal genetics and biology. This similarity extends to humans, despite the dramatic anatomical and physiological contrasts between humans and invertebrates.

There are some notable differences that turn up in the analysis as well. Vertebrates, including humans, have a unique and complex immune system, for example, whereas invertebrates have a primitive immune system.

Weisblat, one of leading scientists in the world studying leech development, said the new leech genome sequence has greatly extended his research into how leech embryos develop. For example, he hopes to explore how and when body segments arose, as exemplified by the segmented marine worms and the leech, but not the limpet.

"When people learn I work on leeches, some people think it's cool, others think it's yucky. But the leech we work with is really a beautiful animal," he said, noting that the sequenced leech, Helobdella robusta, and the close relative he works on are not blood suckers, but predators of snails.

Rokhsar noted that the three new genomes are the last of the animal genomes to be sequenced by the JGI, which has transitioned to focus on plants and microbes of interest to researchers in energy and the environment. Rokhsar and his team will continue to work on animal genomics at UC Berkeley.
-end-
Coauthors of the Nature paper include, in addition to Rokhsar and Weisblat, UC Berkeley post-doctoral fellow Eric Edsinger-Gonzalez and former UC Berkeley graduate student Oleg Simakov, now at the European Molecular Biology Laboratory in Heidelberg, Germany; University of Oxford researcher Ferdinand Marletaz; Nicholas Putnam, former UC Berkeley graduate student and current assistant professor of ecology and evolutionary biology at Rice University in Houston, Texas, Rice graduate student Jie Lv and scientific programmer Paul Havlak; and polychaete biologist Elaine Seaver of the University of Hawaii.

The research was supported by the Department of Energy, the Gordon and Betty Moore Foundation, Richard Melmon, the National Science Foundation, the National Institutes of Health, the Boehringer Ingelheim Fonds and the National Human Genome Research Institute.

University of California - Berkeley

Related Genome Articles from Brightsurf:

Genome evolution goes digital
Dr. Alan Herbert from InsideOutBio describes ground-breaking research in a paper published online by Royal Society Open Science.

Breakthrough in genome visualization
Kadir Dede and Dr. Enno Ohlebusch at Ulm University in Germany have devised a method for constructing pan-genome subgraphs at different granularities without having to wait hours and days on end for the software to process the entire genome.

Sturgeon genome sequenced
Sturgeons lived on earth already 300 million years ago and yet their external appearance seems to have undergone very little change.

A sea monster's genome
The giant squid is an elusive giant, but its secrets are about to be revealed.

Deciphering the walnut genome
New research could provide a major boost to the state's growing $1.6 billion walnut industry by making it easier to breed walnut trees better equipped to combat the soil-borne pathogens that now plague many of California's 4,800 growers.

Illuminating the genome
Development of a new molecular visualisation method, RNA-guided endonuclease -- in situ labelling (RGEN-ISL) for the CRISPR/Cas9-mediated labelling of genomic sequences in nuclei and chromosomes.

A genome under influence
References form the basis of our comprehension of the world: they enable us to measure the height of our children or the efficiency of a drug.

How a virus destabilizes the genome
New insights into how Kaposi's sarcoma-associated herpesvirus (KSHV) induces genome instability and promotes cell proliferation could lead to the development of novel antiviral therapies for KSHV-associated cancers, according to a study published Sept.

Better genome editing
Reich Group researchers develop a more efficient and precise method of in-cell genome editing.

Unlocking the genome
A team led by Prof. Stein Aerts (VIB-KU Leuven) uncovers how access to relevant DNA regions is orchestrated in epithelial cells.

Read More: Genome News and Genome Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.