THEY look like mouse brain cells, they behave like mouse brain cells, yet they came originally from a human embryo. When human embryonic stem cells (ESCs) were injected into the brains of two-week-old mouse fetuses, they developed and functioned like normal mouse cells. They were not rejected by the mouse鈥檚 immune system, and even grew to the same size as mouse cells.
The finding that human ESCs can fit in so well in their new home is encouraging news for researchers hoping to use them to treat neurological diseases. It also lessens ethical concerns about inadvertently creating animals with part-human brains when therapies are tested.
鈥淭his work lessens ethical concerns about inadvertently creating animals with part-human brains鈥�
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鈥淲e were struck by the fact that the immature human cells appear to be able to respond to cues from the mouse to become more mouse-like,鈥� says Fred Gage of the Salk Institute for Biological Studies in La Jolla, California, head of the team which reports its results in Proceedings of the National Academy of Sciences (vol 102, p 18638). 鈥淭hey seem to be hitch-hiking along with the other cells, responding to cues in a similar way.鈥�
Although only some hundreds of the 100,000 human cells injected into each mouse survived, making up less than 0.1 per cent of the mouse鈥檚 brain, they dispersed throughout the organ and seemed to function normally. What鈥檚 more, they ended up the same smaller size as mouse cells, about 11 micrometres across, instead of the 17 micrometres typical of human brain cells.
鈥淚t鈥檚 interesting that human neural cells respond completely to the mouse brain environment,鈥� says Irving Weissman, a stem cell biologist at Stanford University in California, who has proposed creating mice in which all the neurons are of human origin (快猫短视频, 25 June, p 39).
Gage鈥檚 findings could win over those who are worried about the ethics of using animals to test therapies based on human ESCs, if that led to the creation of creatures with partly human mental characteristics. 鈥淚t provides evidence that a 鈥榟um-mouse鈥� would not emerge,鈥� says Cynthia Cohen of the Kennedy Institute of Ethics at Georgetown University in Washington DC.
