Mice get human brain cells
13/12/2005 14:54 - (SA)
San Francisco - Add another creation to the strange scientific menagerie where animal species are being mixed together in ever more exotic combinations.
Scientists announced on Monday that they had created mice with small amounts of human brain cells in an effort to make realistic models of neurological disorders such as Parkinson's disease.
Led by Fred Gage of the Salk Institute in San Diego, the researchers created the mice by injecting about 100 000 human embryonic stem cells per mouse into the brains of 14-day-old rodent embryos.
Those mice were each born with about 0.1% of human cells in each of their heads, a trace amount that doesn't remotely come close to "humanising" the rodents.
"This illustrates that injecting human stem cells into mouse brains doesn't restructure the brain," Gage said.
Still, the work adds to the growing ethical concerns of mixing human and animal cells when it comes to stem cell and cloning research. After all, mice are 97.5% genetically identical to humans.
"The worry is if you humanise them too much you cross certain boundaries," said David Magnus, director of the Stanford Medical Centre for Biomedical Ethics. "But I don't think this research comes even close to that."
Researchers are nevertheless beginning to bump up against what bio ethicists call the "yuck factor".
Three top cloning researchers, for instance, have applied for a patent that contemplates fusing a complete set of human DNA into animal eggs in order to manufacturer human embryonic stem cells.
Researchers argue that co-mingling human and animal tissue is vital to ensuring that experimental drugs and new tissue replacement therapies are safe for people.
Doctors have transplanted pig valves into human hearts for years, and scientists have injected human cells into lab animals for even longer.
But the brain poses an additional level of concern because some envision nightmare scenarios in which a human mind might be trapped in an animal head.
"Human diseases, such as Parkinson's disease, might be amenable to stem cell therapy, and it is conceivable, although unlikely, that an animal's cognitive abilities could also be affected by such therapy," a report issued in April by the influential National Academies of Science that sought to draw some ethical research boundaries.
So the report recommended that such work be allowed, but with strict ethical guidelines established.
At the same time, the report did endorse research that co-mingles human and animal tissue as vital to ensuring that experimental drugs and new tissue replacement therapies are safe for people.
No known human has ever received an injection of embryonic stem cells because so little is known about how those cells will mature once inside the body.
Snyder is injecting human embryonic stem cells into monkeys and is convinced that there's little danger.