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Many scientists believe that the further a cell is from the embryonic stem cell stage, the harder it is to make a successful clone using that cell's genetic material. Now, researchers at MIT and the Whitehead Institute for Biomedical Research have cloned mice using olfactory neurons -- cells far removed from the embryonic state. What's more, the mice have a full range of smell, offering new information about central nervous system development.
For the study, published Feb. 15 in the online edition of the journal Nature, researchers successfully cloned mice from nuclei taken from olfactory cells, something that until now was thought impossible. But a team of researchers led by Rudolf Jaenisch and Andrew Chess, scientists at Whitehead and professors in the MIT Department of Biology, and by Richard Axel of Columbia University showed that even a cell as highly specialized as an olfactory neuron can produce successful clones.
"These findings shift the spotlight away from the type of cell used to produce a clone to the more fundamental question of how the egg cell reactivates the donated genetic material," Jaenisch said.
The experiment also counters current theories on how central nervous system cells develop. Many researchers have long assumed that nervous system cells distinguish themselves from each other the same way immune system cells do -- that is, by removing all pieces of genetic information that the cell doesn't need for its particular function.
The cells scramble this unnecessary genetic information in such a way that it can't be restored. Thus, when a mouse is cloned from an immune system cell, its immune system has lost much of its diversity. If the central nervous system acted in the same way, a mouse cloned from an olfactory cell should have a very limited sense of smell. However, the mice in this experiment maintained full olfactory range, the scientists noted.
"There must be some other unique mechanism for gene expression in mammals which is still not yet defined," said Kevin Eggan, the study's lead author and former postdoc in Jaenisch's lab who is now a junior fellow in the Harvard Society of Fellows at Harvard University.
For now, Jaenisch's lab is continuing to investigate ways to produce healthier animal clones by studying how genomes of donated nuclei are reactivated.
This work was funded by the NIH.