The Speculist

Cellular Competence

A pair of stem cell stories out today demonstrates the broad impact that stem cell technology will have on medicine:

Research that will be presented at the American Academy of Neurology 56th Annual Meeting in San Francisco, Calif., April 24 – May 1, 2004, shows that cells taken from adult human bone marrow can be converted into brain stem cells that meet the criteria for transplantation into the brain.

Also today, scientists from King's College, London announced success in getting mice to grow new permanent teeth from stem cell packets injected into the gums.

The procedure is fairly simple. Doctors take stem cells from the patient. These are unique in their ability to form any of the tissues that make up the body. By carefully nurturing the stem cells in a laboratory, scientists can nudge the cells down a path that will make them grow into a tooth. After a couple of weeks, the ball of cells, known as a bud, is ready to be implanted. Tests reveal what type of tooth - for example, a molar or an incisor - the bud will form.

The scientists involved see no reason why this technology can't be adapted for humans.

Both of these stories beg the question "how does the stem cell know how to incorporate itself into the body?" In both of these cases the stem cells are coaxed by scientists into becoming brain cells or tooth cells, but such cells would be useless on their own. Brain cells have to interact with other brain cells. Tooth cells need to work with other tooth cells and the surrounding tissue in order to form a healthy tooth. How is this accomplished?

William Atkinson touched on the answer in the last chapter of his book, "Nanocosm."

My only problem with "Nanocosm" was Atkinson's relentless criticism of Eric Drexler (I posted on it here and here). It took me awhile to understand the disagreement. Atkinson accepted the possibility of self-assembling nanofactories, so what was his problem with Drexler?

Finally Atkinson explained his real disagreement with Drexler - the issue of control. If Atkinson's characterization of Drexler's position is correct, Drexler believes that we will be able to micromanage the work of the molecular assemblers.

Atkinson argued that such top down control is not practical (you can't micromanage the work of millions of molecular assemblers) or even possible. Certainly, nature doesn't attempt to micromanage the work of cells. Our brains are not in control of cellular activity within our body. The cells have to be autonomous workers – cellular automata that know their place within the overall scheme of things. Atkinson suggests that in this respect our molecular assemblers must emulate life.

Consider the nautilus. This beautiful structure was self-assembled at the molecular level. How? The mathematical description of this structure is incredibly complex. Do the cells understand the complex mathematics involved? No. Then how was it done?

The nautilus develops from the innermost chamber out. According to Atkinson the cells that build these chambers follow a simple program not unlike the following:

If prior chamber = nonexistent, then build chamber size A

If prior chamber = existent, then build chamber size 110% of prior chamber size

These two lines of code give every nautilus cell much of the information needed to perform a very complex task. This is a simple, elegant solution to a difficult problem. All multicellular organisms require their cells to have some competence in the overall design of the organism, their place within it, and the activity of their neighbors.

Posted by Stephen Gordon at May 3, 2004 04:08 PM | TrackBack