CHROMOSOME ENGINEERING: Extra help 23/9/05. By Lisa Melton Geneticists have managed to transplant most of human chromosome 21 into mice to produce an animal model of Down's syndrome.

Down's syndrome arises when people carry an extra copy of chromosome 21 in their cells. How this causes Down's symptoms, though, has remained frustratingly unclear – partly because no animal model exists. This obstacle may now have been overcome, thanks to the work of scientists from London and Newcastle.

The researchers extracted human chromosomes and injected them individually into mouse embryonic stem cells. Cells that had an extra copy of chromosome 21 (one or two cells out of tens of millions) were injected into early-stage mouse embryos, and the chimeric embryos were then implanted into foster mothers. Offspring with human chromosome 21 in their cells were then bred further.

The engineered mice showed a number of symptoms seen in people with Down's syndrome, such as memory, brain function and heart defects.

Until now, it has been possible to transfer only single genes or chromosomal fragments into mice. Transferring nearly an entire chromosome is a technical tour de force, and the resulting model will help scientists better understand the role of individual genes in the disorder.

Further reading

O'Doherty A et al. An aneuploid mouse strain carrying human chromosome 21 with Down syndrome phenotypes. Science 2005;309(5743):2033–7. Abstract

This research was part-funded by the Wellcome Trust.

Image credit: O'Doherty el al. Human chromosome 21 (green) among mouse chromosomes (blue).