Decoded sea urchin genome shows surprising relationship to man

An international team of scientists on Thursday announced the decoding and analysis of the genome sequence of the sea urchin, which include the novel immune system, unexpected sensory proteins and broad similarity to human genes.

"The sea urchin is surprisingly similar to humans," said George Weinstock, co-director of the project of studying sea urchin's genome sequence, at Baylor College of Medicine.

"Sea urchins don't look any more like humans than fruit flies, but about 70 percent of sea urchin's genes have a human counterpart whereas only about 40 percent of fruit fly genes do," Weinstock said.

In a special report detailed in the Nov. 10 issue of the Journal Science, research teams introduced the genome of a male California purple sea urchin, which revealed not only human-urchin similarities but also features such as the urchin's immune system, which far surpasses that of humans.

Sea urchins belong to the phylum Echinodermata, which includes starfish and sea cucumbers, whereas humans belong to the phylum Chordata, or all animals with backbones. Both the echinoderms and chordates belong to a larger group called the deuterostomes.

This relationship means sea urchins can serve as a model for the understanding of how the group of animals including humans split off and evolved different traits.

For the genome project, scientists identified 23,300 genes made from 814 million letters of DNA code taken from the California purple urchin (Strongylocentrotus purpuratus), and they found that 7,077 of them were also found in humans.

Analysis of the sea urchin genome revealed a surprisingly unique and complex immune system, which could explain their lengthy life spans of up to 100 years.

Whereas humans have an acquired immune system, in which our body must learn how to attach and destroy invaders once they enter the body, sea urchins are hard wired to detect foreign bacteria and viruses and begin an attack.

This rich toolbox of sea urchin genes could lead to new drugs for combating infectious diseases. In fact, sea urchins carry genes associated with many human diseases, including muscular dystrophy and Huntington's disease.

The sequence also helped scientists uncover complexities belied by the urchin's simple exterior. Sea urchins lack eyes and ears, but they sport genes associated with taste and smell, hearing and balance, the study said.

"Nobody would have predicted that sea urchins have such a robust gene set for visual perception," said Gary Wessel, a member of the Sea Urchin Genome Sequencing Consortium, at Brown University.

Some of the visual sensory proteins are clustered on an appendage known as the tube foot and is thought to aid processing of sensory of information.

"It is remarkable that the same sensory proteins are used in organs with such different structures in sea urchins and man," Weinstock said.

Source: Xinhua