Wednesday, December 27, 2006
Environmental regulation of gene expression
Gilbert argued that the environment regulates and instructs gene expression through:
- The neuroendocrine system (example: Butterflies are differently colored based on ecdysone, which is produced based on temperature and daylight signals)
- As an embryonic inducer (example: Bacteria help gut formation)
- As a transcriptional modulator (example: proper methylation is dependent on diet)
Gilbert's main thesis is that the environment provides information to the developing organism. I actually agree with his thesis, but I don't think that what he has presented is a forceful argument for the proposition.
If I give you a set of instructions, and the instructions have a requirements list, if the requirements were not available then the end result would be different, probably a little worse off. For example, if you were baking bread and lacked flour, that would lead to improper bread formation (though I know a few cooks who could probably pull it off). That doesn't mean that the flour is in any meaningful way instructing the bread-making. The instructions are still fully-contained within the recipe and/or the cook's mind. If the requirements are not present, the result is deficient, not different.
If, however, the recipe says "buy X from the store and follow the preparation instructions on the package (varies by brand)", then in fact the ingredients are instructing the development of the recipe. Having different brands gives you different results, but none of them are deficient. Gilbert's paper suffered greatly because he used deficiency as a substitute for difference.
If the environment is truly instructing the organism (and I think it is), here's some things we may expect to find:
- If an organism is transplanted from one environment to another, it will develop symbioses with different bacteria after a generation or two.
- Different (healthy) diets of mothers will cause different methylation patterns. These methylation patterns will activate/repress genes as appropriate for the type and quantity of food being consumed. The methylation patterns will prepare the new baby for the nutrition available.
- Different temperatures/conditions will cause a change in an organism that will benefit the organism in the environment they will face, for the season they will be born into..
Gilbert's previous paper actually made a much better case, and I'm surprised he mentioned it only briefly. It focused on predator/prey relationships that were managed by kairomones (where the prey would develop differently based on predators in the area!) among other things.
Anyway, I have great hope for this line of research, but this particular paper doesn't get us there.