It’s the Whole, not the Part…

Uber science-writer Carl Zimmer muses on some utterly fascinating research on rewiring E.coli’s gene networks…

The More We Know About Genes, the Less We Understand

In the latest issue of Nature, scientists reported an experiment in which they wreaked havoc with E. coli’s network. They randomly added new links between the transcription factors at the top of the microbe’s hierarchy. Now a transcription factor could turn on another one that it never had before. The scientists randomly rewired the network in 598 different ways and then stepped back to see what happened to the bacteria.

You might expect that they all died. After all, if you were to pop open the back of an iPod and start linking its components together in random ways, you’d expect it to crash. But that’s not what happened.

About 95 percent of the rewired bacteria did just fine with their new networks. They went on with their lives, feeding, growing and dividing. Some even performed better than microbes with the original wiring, under some conditions.

…which is an incredible result. Carl muses there’s “something about gene networks” – gene networks being the program that controls an organism’s DNA activities – which lets them handle massive perturbations like a total rewiring. The puzzle is profound, but it indicates a great truth in biology – the whole, the organism, is greater than the sum of its parts, the genes, proteins and so forth that make it. They work together in a harmony that may have a higher-level abstract structure that allows great stability.

Here’s the Nature paper in abstract… Evolvability and hierarchy in rewired bacterial gene networks Ref: Nature 452, 840-845 (17 April 2008) | doi:10.1038/nature06847

…and it’s truly an amazing result. But just what does it mean? I think it means that genetic mutation – via gene changes or changes to regulator sequences – is just one step in the process leading from genome to living thing. The whole of an organism acts as an “editor” that decides if a DNA change makes sense – that’s the first level of “natural selection” and it seems a lot more able than the old “random mechanism” view that treated cells as intricate clockwork. Instead the cellular system is much more responsive and dynamic in a way we have trouble grasping because so much collective molecular behaviour is involved.