Or, what an interested lay person should know about epigenetics.
I've been promising
a post about epigenetics for ages, because it's one of the most exciting things that's happened in my field in the past decade or so, and it seems like most non-biologists aren't aware of it very much.
Why is it so exciting? Well, to start with there's the older insights which led to the modern field of epigenetics: in a multicellular organism, all cells have exactly the same genome, by definition, but the cells differentiate
to take on specialist structures and functions. So there must be something going on beyond (ἐπί, the Greek prefix epi) the sequence of bases forming genes and chromosomes. It turns out that something
is that the cell makes a series of chemical marks on the DNA and associated proteins, which turn genes on and off. Those marks are often surprisingly long-lasting, they're not just a short-term response to circumstances, something genes can also do. So you can't take a skin cell and transplant it to the liver, its epigenetic marks make it a permanent skin cell.
It's much more recently that we started to understand that patterns of epigenetic marks don't just follow a set developmental program – they can change in response to external circumstances. And the really mind-blowing thing is that some of these changes can be inherited
. This means that a female parent's life circumstances can cause measurable alterations in the genes of offspring and more distant descendants, and there's starting to be evidence for male-line transmission as well, at least in animals and probably in humans too.
The other thing that's cool about epigenetics is that we're getting to the point where we understand it well enough that we can directly manipulate the epigenetic marks. If you change epigenetics, you change the nature of the cell itself, just as much as by directly editing the gene sequence (which can be done but is massively technically difficult, and ethically questionable in humans.) Which is a possible approach for treating cancer, and that's the reason why I got into the epigenetics world, but there's an even more exciting application: we can make stem cells
. We can do the thing which was regarded as paradigmatically impossible throughout the twentieth century, we can effectively reverse the direction of development. So it's become possible to take an adult's cells and turn them into the rare kind which, like the cells of an early embryo, have the potential to become any type of tissue, manipulate them more or less at will in the lab, and return them to the same person's body to repair injuries and grow new tissue. In the very last couple of years, this is actually starting to be a treatment for real humans with real diseases. ( want to know more? )
OK, this post is ridiculously long, I will post it and do one on stem cells another day. Please do ask any questions, whether it's because I've assumed knowledge and explained things with too much jargon and technicalities, or because I've simplified and glossed over something and you want more detail or want to challenge me.