Science Questions

I'm home schooling my son and we've been studying cell division. In one of the textbooks it - that specialised cells, such as muscle cells, don't divide. Why? Richard via email

That's a very good question and it's the question that's been frustrating stem cell biologists and people who want to fix the human body. It's for exactly the same reason as when you have a stroke, part of your brain gets damaged forever and doesn't really recover very well. It's also the reason that when you have a heart attack, part of the muscle dies and doesn't recover. When an egg is fertilised it turns from being one cell and divides into many more cells. What these cells do is to specialise. As they divide and turn into tissues, they specialise and sub-specialise for the job that they're going to do. It's a bit like when you go into medical school: at the start you can become any kind of doctor. After you go through lots of training, you might end up as a surgeon but you don't really do much medicine anymore. The next thing you do is become, say, a specialist in vascular surgery and only work on that. Then you become so good that you only do surgery on people's aneurisms. That's the kind of specialisation that happens in our bodies as we develop. This means that the tissues in our bodies are specialised to do one kind of job and that means that they've turned off the genes that make them a general cell and they lock onto being one kind of cell. That's a process called differentiation, and it seems in some tissues to be an irreversible step. But now we're beginning to see that it might be possible to persuade cells to go back the other way with the right environment. The other way is to go back and get a stem cell that can turn into anything.

September 2006