U. study may shed light on tissue regeneration

A discovery by scientists at the Howard Hughes Medical Institute, University of Utah, just might lead to one of the most astounding advances in medicine: regeneration of limbs or organs.

The find, by the team of Alejandro Sanchez Alvarado, Kyle A. Gurley and Jochen C. Rink, was published earlier this month by Science Express, an online site maintained by the American Association for the Advancement of Science. Articles in Science Express have been selected for later printing in the journal Science.

Sanchez Alvarado is a professor in the Department of Neurobiology and Anatomy, while Gurley and Rink are postdoctoral fellows in Sanchez Alvarado's lab. This work took place over about the past year, Alvarado said.

The article, "Beta-Catenin Defines Head Versus Tail Identity During Planarian Regeneration and Homeostasis," involves research with freshwater planarians, or flatworms. These swimming, carnivorous little worms are able to regenerate missing parts. If a head is sliced from one, it grows a new head, eyes, brain and all; if a predator bites off the tail, it will regrow a tail.

Flatworms aren't rare. According to an ecology report written by Bridgette Jenne and placed on the Internet by Westminster College in Salt Lake City, "These small, free-living flatworms are found under rocks in the fresh water of Emigration Creek where it crosses the campus of Westminster College. ... We have identified the Emigration Creek species as Dugesia tigrina, a common North American flatworm."

Somehow, after a head is amputated, the flatworm section that remains will know it's missing a head, "so it'll grow a head," Alvarado said. "Why doesn't it make a tail?"

He, Gurley and Rink used a process called RNA interference to eliminate "specific messenger RNA molecules before they can get a chance to make the protein they encode," he said. One gene they aimed at is called Beta Catenin, which is important both to biology and disease. If it does not work correctly in humans, it causes cells to proliferate wildly, sometimes resulting in colon cancer.

But the same gene is needed to replace cells that die regularly, such as skin and blood cells, he said.

Although flatworm and human ancestors may have diverged onto separate evolutionary trees 400 million years ago, they share this genetic system. "Whether it's in a worm or a human," Sanchez Alvarado said, "the molecular functions are preserved."

B-Catenin works with another gene called Adenomatous polyposis coli (APC), which helps to control tumors in humans, especially in the colon, he said.

"Both of them appear to be essential for letting the amputated tissue know what to regenerate" in flatworms, he said.