Nuclear cloning, stem cells, and epigenetic reprogramming,
and the promise of this technology for customized tissue repair.
Rudolf Jaenisch, Whitehead Institute, MIT and Cambridge.
This is Dolly, the first cloned animal published no more than eight years ago.
The cloning of mammals raised a number of complex questions.
For example scientific questions,
why and how does this procedure work?
And more complex, should we use this technology for human applications?
This of course raises scientific, practical,
and importantly ethical, political, and other questions.
So the problem of nuclear cloning is genomic reprogramming.
In the case of Dolly, the donor cell was from the mammary gland.
These cells express the genes appropriate for mammary gland function,
not the genes which are important for embryonic development.
So the transplanted nucleus must activate these embryonic genes,
and that's where the problem is.
Only few clones manage to activate these genes,
and those which do manage to activate these genes are often not normal.
The key issue of nuclear cloning is the epigenetic reprogramming of the genome.
The problem is how to reset the adult pattern of gene expression of
the donor cell to an embryonic one which is appropriate for embryonic development.
First, you have to realize that reprogramming is
an important aspect of normal development. Let me illustrate
this. Epigenetic reprogramming in