From: Allison Winter, ENN
Published December 20, 2012 01:38 PM

Leeches...and Limpets...and Worms...Oh My!

Genome sequencing not only helps scientists decode genes, but also helps us understand how genes work together to direct the growth, development, and maintenance of an entire organism. Understanding the genes of other organisms allow scientists to compare these creatures not only to one another but to the human genome which may give vital insight into our own genetic secrets.


Furthering this genome progress is a team of scientists who have completed the genome sequence of an organism with the "yuck factor": the leech. Daniel Rokhsar, UC Berkeley professor and program lead for eukaryotic genomics at the Department of Energy's Joint Genome Institute (JGI), is leading the leech genome initiative. His multinational team published the genomes of the leech and two relatives, the limpet and the marine worm, or polychaete.

"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.

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.

The paper can be found in the journal Nature.

Read more at the UC Berkeley News Center.

Leech image via Shutterstock.

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