There is also research in progress to regress a more-differentiated cell back into a state similar to less-differentiated cells.
Essentially, rather than stopping the cells from making "what I want to be when I grow up" decisions, you're taking a grown-up cell and forcing it to forget all the decisions that its predecessors ever made. It's a bit more difficult.
In general, those decisions are recorded on the nuclear DNA by "tagging" it with methyl groups, like customizing a dictionary by using paper clips to bond together the pages that are least frequently accessed. You can look up the words you frequently need much faster, but you lose the ability to look up anything else in the clipped-together pages.
If you take one of those dictionaries, and remove all the paper clips, it's back to being a completely generalist reference, almost just like a new dictionary, that had never been customized in the first place. The most notable difference is that the old dictionary might have accumulated some damage over the years.
Furthermore, there is a differentiation hierarchy. Some cells only make a few decisions. So even if you can't suck fresh stem cells out of embyros or umbilical cords, there is the possibility that you could liposuction some adipose tissue, separate out the least-differentiated cells, and inject them into other tissues. Those cells could possibly repair bone, cartilage, and ligaments. Or you could crack open baby teeth, or suck out bone marrow, and produce different types of cells. With nerve cells, though, you're out of luck, because there's really no reservoir of cells that can be harvested.
So you take some of those liposuctioned fat cells, chemically treat them to remove all the clips from their respective dictionaries, and try to make them switch to nerve cells by attaching new clips to different pages. Those cells will be cells with your own DNA, but it might just be old, damaged DNA that can't make certain proteins correctly any more.
Essentially, rather than stopping the cells from making "what I want to be when I grow up" decisions, you're taking a grown-up cell and forcing it to forget all the decisions that its predecessors ever made. It's a bit more difficult.
In general, those decisions are recorded on the nuclear DNA by "tagging" it with methyl groups, like customizing a dictionary by using paper clips to bond together the pages that are least frequently accessed. You can look up the words you frequently need much faster, but you lose the ability to look up anything else in the clipped-together pages.
If you take one of those dictionaries, and remove all the paper clips, it's back to being a completely generalist reference, almost just like a new dictionary, that had never been customized in the first place. The most notable difference is that the old dictionary might have accumulated some damage over the years.
Furthermore, there is a differentiation hierarchy. Some cells only make a few decisions. So even if you can't suck fresh stem cells out of embyros or umbilical cords, there is the possibility that you could liposuction some adipose tissue, separate out the least-differentiated cells, and inject them into other tissues. Those cells could possibly repair bone, cartilage, and ligaments. Or you could crack open baby teeth, or suck out bone marrow, and produce different types of cells. With nerve cells, though, you're out of luck, because there's really no reservoir of cells that can be harvested.
So you take some of those liposuctioned fat cells, chemically treat them to remove all the clips from their respective dictionaries, and try to make them switch to nerve cells by attaching new clips to different pages. Those cells will be cells with your own DNA, but it might just be old, damaged DNA that can't make certain proteins correctly any more.