Monday, November 30, 2009

Stem Cells' Next Use: Fighting Extinction

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It's a lonely world for the two northern white rhinos at Escondido's Wild Animal Park. They are among less than a dozen of their kind left on Earth.

Conservationists work constantly through habitat protection and other means to save these and other endangered species. And now they are adding a new technology to their list of possible solutions to extinction -- stem cells.

Ryder's group wants to reprogram adult cells from drill monkeys and northern white rhinos into stem cells. Using a type of virus called a retrovirus, scientists introduce genes into the DNA of an adult cell that cause it to behave like an embryonic stem cell, a versatile cell that can divide to form any other cell type in the body.

The Zoo researchers are working in collaboration with world-renowned stem cell researcher Jeanne Loring and her lab at the Scripps Research Institute.

Exactly how or when science might use cell reprogramming technology in animals isn't yet clear. If this new application for stem cells succeeds, however, it could potentially be used to replace or regrow damaged tissues in animals, just as in humans.

Scientists could also clone an animal by injecting the stem cells into very early-stage embryos, and implanting them into a surrogate mother from a closely related species.

Reprogrammed stem cells are today's hottest topic in the world of stem cell research. Some researchers say the ability to convert adult cells into stem cells could lead to breakthroughs far sooner than they'd originally believed.

But the process also has its risks. Retroviruses sometimes can cause a cell to become cancerous. Researchers are working now on ways to deal with this problem.

And the San Diego Zoo has an additional resource that could help detect defects in the reprogrammed cells. The institute is home since the 1970s to the Frozen Zoo, one of the largest animal biobanks in the world. The Frozen Zoo stores DNA and tissue samples from more than 8,400 individual animals -- a Noah's Ark on ice that plays an ever-expanding role in conservation.

When it comes to reprogramming stem cells, the Frozen Zoo gives scientists another way to screen for problems. By comparing the chromosomes in the reprogrammed cells to normal chromosomes from the same species, scientists can check for certain kinds of abnormalities -- and hopefully reduce the possibility of defects.

Cloning, Then and Now
The San Diego Zoo has participated in a couple of attempts to clone endangered species in the past; a banteng at the Wild Animal Park was successfully cloned in 2003. The older and more common methods of cloning, however, are extremely inefficient. Producing Dolly the sheep, for example, took hundreds of attempts.

Stem cells could provide an easier and more efficient method of cloning. Cloning can't save endangered animals from serious threats like habitat loss or poaching, but it could assist in breeding efforts by duplicating valuable animals in a zoo’s collection or cloning from cells of dead animals stored in biobanks like the Frozen Zoo.

Recent breakthroughs have made cloning using stem cells a more viable proposition. Earlier this year, Chinese scientists cloned mice by reprogramming skin cells from the mice into stem cells. Scientists could potentially clone dead animals of an endangered species with the same technique, using the tissue samples ..........

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