How a Sea Squirt Could Help You Grow New Limbs

PHOTO: Star Ascidian

The closest relative we humans have in the huge population of invertebrates that blanket the earth is a tiny, inconspicuous flower-like marine critter that is amazing in its abilities to regenerate its damaged tissue from its blood vessels alone.

Scientists believe this odd character, just one of many spineless animals known as "sea squirts," or "tunicates," may hold the genetic secrets that might eventually allow humans to regrow a lost arm, or accept a heart from someone else without danger of rejection.

But, alas, if this unpretentious little animal is going to be our medical salvation, we may have to accept its dark side. It can also foul our beaches and our boats, and smother crabs and oysters while killing off much native wildlife. And it feels right at home in a heavily polluted harbor.

Botryllus schlosseri, commonly known as the golden star, perhaps because it is frequently golden in color and looks kind of like a star, or a flower, or a blob, may be a bit player in the world of animals without a backbone, which make up 95 percent of the species in the animal world. But it could have a huge future in the world of medicine.

It is believed to have been the first invertebrate to have a vasculature heart system, similar to that in humans, with blood cells traveling through blood vessels. But astonishingly, it can regrow everything just with its blood vessels.

"The whole body can regenerate from the vasculature alone, the heart, digestive system, sophisticated tissues," Ayelet Voskoboynik of Stanford University's Stem Cell Institute said in releasing a study. "And it can do this relatively fast, probably using stem cells."

Voskoboynik and an international team of scientists have just sequenced the genome of Botryllus schlosseri, which we shall henceforth just call the "star." The hope is that once scientists understand how the genes operate in the star, they will be able to come up with new treatments for a wide range of human diseases.

The star has only 580 million base pairs of DNA, compared to 3 billion base pairs in humans, but there is a surprising amount of common ground. The researchers found that 77 percent of human genes were also present in the star.

"We found genes that are critical to the development and function of the vertebrate heart, and eye, and the ability to hear," they report in their study, published in the journal eLIFE. "Mutations in these genes are implicated in a variety of human diseases and disorders, including heart diseases, cataracts, and deafness."

There is reason to believe the star may hold the genetic secrets that have plagued cardiac patients who have received a new heart only to have it rejected by their own body.

The star forms colonies comprised of individuals that form clusters in various patterns, star-like, flowers, or opals. But amazingly, when one colony meets another, it can either merge with the other, gradually becoming one, or both can remain separate, suggesting the animal knows how to accept or reject another set of organs. It would be good to know exactly what that is.

Although usually orange to yellow in color, it can also be red, black, green, or an assortment of colors, and it can form many different shapes, depending on which solid substance the colony latches onto, frequently the bottom of a boat, or a piece of valuable marine gear in near-shore areas. And that's where the conflict comes in.

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