Mice With Human Brain Cells Created

Brian Handwerk
for National Geographic News
December 14, 2005

Researchers in California have created living mice with functioning human stem cells in their brains.

The feat could boost stem cell therapy research on brain diseases like Parkinson's and Alzheimer's—and raises the specter of animal-human hybrids.

Geneticist Fred Gage injected embryonic human cells into two-week-old fetal mice as they developed in the womb. When the mice matured, some human stem cells survived and became functional components of the mice's brains and nervous systems.

Less than one-tenth of one percent of the test mice's brain cells are human.

"When we characterized these cells two months later, we found that [they] had the [form and structure] and characteristics of mouse cells," said Gage, co-director of the genetics laboratory at the Salk Institute for Biological Studies in San Diego.

"It is truly amazing that these human stem cells, although they are very immature, can still … respond to different cues in their environment and can fit right in with their mouse neighbors."

"This illustrates that injecting human stem cells into mouse brains doesn't restructure the brain," Gage added.

The study was published in yesterday's issue of the journal Proceedings of the National Academy of Sciences.

Medical Promise or Ethical Peril?

Some scientists hope that stem cells, which may develop into many different kinds of human cells, could someday be used to replace missing or damaged neurons in people with degenerative nerve diseases.

"This research is significant because it suggests that it will be possible to create mouse 'models' of human brain tissue, enabling scientists to try out both stem cell interventions and other potential cures on living human brain cells without having to use humans in the process," said Glenn McGee, director of the Alden March Bioethics Institute at Albany Medical College in New York State.

In short, it's a new way to test potential cures for human diseases, without harming human test subjects in the process.

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