Mixing species (Mouse with brain made of human neurons)

By Jonathan Krim, Washington Post Staff Writer

Mixing species--
and crossing a line?
Sun Oct 19, 8:00 PM ET BY NELL BOYCE
<snip>Goldstein wanted to trace how well human embryonic stem cells turn into specific tissues and organs--the very shape-shifting quality that could make these cells an endless source of transplant tissues to treat diseases like Parkinson's and diabetes. He did not let the eggs hatch, and he made sure the human cells could not mingle with all of the developing chicks' tissues to create true chimeras. But even some of his scientific colleagues expressed disapproval recently when he presented his work, saying he had crossed a contentious ethical line. "This is a very, very gray area right now," Goldstein says.

Man or mouse? Yet other researchers are pursuing far more intimate marriages of human and animal tissue. South Korean scientists say they've created early mouse embryos marbled with human embryo cells--the very outcome Goldstein set out to avoid with his chicks. And U.S. researchers have proposed slipping another kind of stem cell into a mouse fetus to make an animal with a brain formed entirely of human neurons. Crossing species barriers in the lab is nothing new--scientists have created mice with human immune-system cells and organ-donor pigs with human genes. To many people, though, implanting stem cells in an animal is a different matter because these cells are the clay from which human beings are made.
<snip>

Late last year at a stem-cell conference in New York, researchers pondered adding human embryonic cells to early mouse embryos to create chimeric animals. "It was pretty hotly debated, even among the scientists," recalls Fred Gage, a biologist at the Salk Institute for Biological Studies in La Jolla, Calif. To some, the scientific payoff seemed appealing. Putting human embryonic stem cells in these early embryos, called blastocysts, might prove better than any other lab test how well these cells produce all cell types.
Parent trap. Yet human stem cells added to a mouse blastocyst could even turn into sperm and eggs, producing an altered mouse with human gametes. Suppose it mated with another animal also carrying human germ cells, ethicists asked. "You're putting the possibility of creating future human beings into the animals," notes Cynthia Cohen, a bioethicist at Georgetown University.<snip>

Primates, he says, are a different story. "Nobody expects a mouse to stand up on its hind legs and say, `Hi, I'm Mickey,' " Greely says. "If you proposed doing this experiment on fetal chimps, I would be a lot more leery."

Pinky and the Brain

One is a genius
The other insane

They're labratory mice
They're genes have been spliced

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we didn't have enough Republicans already?