Tuesday, March 17, 2009

Thrust to greatness

"Some are born great, some achieve greatness, and some have greatness thrust upon 'em," says Malvolio in Shakespeare's Twelfth Night, quoting Maria's letter.

Caenorhabditis elegans, the little worm I mentioned here yesterday, had greatness thrust upon it. This lowly creature has been chosen from a million species of its nematode cousins to become one of the best understood animals on Earth. Why? Why have these tiny worms, as thin as spider silk, a millimeter long, been rocketed to fame?

Their life cycle is quick, a three-day generation time, which is handy for genetic studies. They reproduce happily in the lab. They can be frozen for storage, and revived as needed. Best of all, they are transparent; their insides are as easy to see as their outsides.

And they are simple. Wriggle, eat, defecate: life reduced to basics. They are mostly self-fertilizing, so they don't even have to bother looking for a mate. For these minimal activities, C. elegans requires a mere 959 body cells. The "parts list" of this tiny worm is about as long as that of your washing machine -- and as exactly known. But your washing machine doesn't start with one part (a gasket, say) and grow into a thousand (gaskets, drums, valves, dials, etc.). Your washing machine doesn't squirm, eat and defecate. Your washing machine doesn't make other washing machines. Your washing machine doesn't colonize every habitat on Earth.

Every cell in the nematode is sublimely more complex than anything you'd find in a hardware store.

We have much, much more to learn about the machinery of life. For example, how do those DNA strands, which are snarls to start with, unwind and reproduce over and over without getting hopelessly tangled? How are errors in the DNA code corrected, at lightning-fast speed? How does a "one-dimensional" genetic code (a sequence of nucleotides) reliably build three-dimensional shapes? How does a DNA molecule always find just the right chemical compounds it needs to reproduce itself -- or make a protein? How do genes tell some cells to become gut and other cells to become muscles?

How, how, how? C. elegans is one of the best-understood animals on Earth, but it is still a millimeter-long bundle of mystery.

A lowly worm, thrust to greatness by human curiosity.