oncogenes

Counting down to the 200th anniversary of Darwin's birth, I'm going to keep with biology related posts for a while. I think they're more popular than quantum mechanics anyway!

When I was a graduate student in medical biophysics more than twenty years ago, there was a group of physicists like myself interested in medical imaging and then there were the cell biologists. We spoke rather different languages, but every week we would have a double seminar so that we would all be exposed to talks given by members of both groups. Having had no biology education whatsoever, I found the cell biology talks quite exciting, when they were at least slightly comprehensible to me.

One factoid that I grabbed onto was about oncogenes. A normal cell has bits of DNA that code for proteins that help regulate how much the cell manufactures other proteins, which then affects what type of cell it is. Everyone knows that cancer has to do with a breakdown of normal cellular regulation. So, not surprisingly, when these bits of DNA suffer some mutation, they can become cancer-causing oncogenes.

But the really interesting thing is that certain viruses are carrying these very same oncogenes and this explains how some viruses can induce cancer when they enter the body's cells. The origin of viruses is uncertain. Whether they were totally derived from cellular genetic material that escaped from cells or whether they coevolved as separate entities, they are always replicating inside host cells and so have a rather intimate relationship with cellular DNA. And so, at some stage, a virus can pick up an oncogene from a cell where a mutation has occurred, and can then spread it around. We normally think of viral or bacterial infections as a transmission of the viruses or bacteria themselves. But here, the virus basically picked up "cancer" some time in the past, and can do harm not only in the normal way - killing infected cells - but by destabilizing cells that take in the oncogene so that they become cancer-forming.

Now unless such a virus manages to infect a germ cell, this process is not going to directly affect our genetic lines. But for single-celled bacteria etc, it's another story. For these little creatures, the family tree can have strange horizontal paths that connect up totally different species. Bacteria grow by dividing asexually, but the viruses that infect them (called bacteriophages) can transfer DNA in a "sexual" sort of way with a virtuosity that we multi-cellular beings know nothing about. From the point of view of messing up a family tree, it would be like getting a whale to mate with a chaffinch. Then again, bacteria are pretty flexible about their group identity over time.