Chimeras: Mice with Human Brain Cells
An AP story today reports on a research project at the Salk Institute in San Diego led by Fred Gage. 100,000 human embryonic stem cells were injected into the brains of 14-day-old mouse embryos. The mice were born with one-tenth of one percent of human cells in their head. The findings are key to modeling human neurological diseases in test animals. A paper will be published in the upcoming Proceedings of the National Academy of Sciences.
A second story is how the news was covered. The New York Times carried a relatively careful headline: "Trace of Human Stems Cells Put Into Unborn Human Mice Brains." The Toronto Star focused on the small percentage involved: "Scientists create mice with brains that are 0.1% human" But the Sydney Morning Herald jumped right ahead to: Mice with human brains[!]
Creating chimeras — combining parts from different animals — has been part of medicine for years. Senator Jesse Helms famously had a pig valve installed in his heart. But combining genes and stem cells creates chimeras that grow into their new states blending human and animal characteristics, prompting what ethicists call the "yuck factor." (See the September article Transgenic Pigs’ Milk to Treat Cancer.) Sen. Sam Brownback, R-Kan., has introduced legislation banning chimerical research.