For the last decade, everyone has been excited about the medical possibilities of stem cells.
Need a new liver? What if we could grow one for you in essentially the same way that you grew your first liver when you were in your mother’s womb?
That’s the promise of stem cells, that scientists could take an undifferentiated cell, just like the cells that made you up before you were even you, insert your own DNA into it, and direct it to differentiate into a new liver or kidney or heart. Even better, because the new liver has your own DNA, your body’s immune system will welcome it as one of its own. In a traditional transplant, your immune system must be suppressed, or it will recognize the new liver as an outsider and “reject” it (that’s a euphemism for killing the new organ).
One problem. Those embryonic cells, known as embryonic stem cells, come from only one place: embryos. This fact has made a lot of people uneasy or worse, especially because human embryonic stem cells are derived from aborted embryos. So you can imagine everyone’s excitement a few years ago, when scientists were able to take adult cells and turn them into stem cells. These are called induced pluripotent stem cells—“induced” because they didn’t start out as stem cells, and “pluripotent,” because they have the potential to become many (think “plural”) different types of cells.
This achievement eliminated the ethical problems of using aborted embryos. Even better, it could still produce cells that were genetically identical to the person receiving them, thereby avoiding that pesky immune system problem.
So scientists assumed. But sometimes identical genes just aren’t enough, as it turns out. Thus transpires another opportunity for us all to learn that genes aren’t everything!
“Epigenetic effects” are biological changes in cells that are outside or beyond (that’s “epi”) of the genes. Throughout my life, my genetic sequence remains the same in every cell of my body. Clearly, however, in different cells and at different ages, those genes are “expressed” differently, meaning that different proteins are produced from the same genes under different conditions. My poor old cells know that I am heading into my mid-30s, despite the fact that their DNA is identical to the DNA of the fresh young cells that I rocked in my 20s.
Sadly, some adult cells induced into becoming stem cells may not be able to forget their real age either. A group in San Diego just published a paper in Nature showing that some types of induced pluripotent stem cells overproduce certain proteins, which allow the immune systems of the animals (mice, in this case) receiving the implanted cells to recognize them as intruders and kill them.
There are other ways of inducing pluripotency, so it’s really not the end of this kind of research. But hopefully it’s the end of assuming that it’s enough to be genetically identical. It’s also one more reason to reconsider the use of embryonic stem cells. Even on the cellular level, youth is one thing you just can’t fake.
For further reading on this research, see the link to the Nature paper above and check out the New York Times coverage.
For further reading on how scientists became fixated on DNA as a “master molecule,” check out the work of some fantastic females from my field and enjoy Evelyn Fox Keller‘s The Century of the Gene and Lily Kay‘s Who Wrote the Book of Life? A History of the Genetic Code.