Tuesday, February 11, 2003
B17 Upson Hall
Evolutionary Causes and Consequences of Robustness in Complex Gene Networks
The molecular chaperone Hsp90 has been termed an 'evolutionary capacitor' because it has been shown, in Drosophila and Arabidopsis, to: 1) suppress phenotypic variation under normal conditions and release this variation when functionally compromised, 2) lose function under environmental stress, and 3) exert pleiotropic effects on key developmental processes. There is considerable debate whether these properties necessarily make Hsp90 a significant and unique facilitator of adaptation1. Using numerical simulations of complex gene networks, as well as genome-scale expression data from yeast single-gene deletion strains, we show that the first property is not unique to Hsp90, in that most, perhaps all, genes reveal phenotypic variation when functionally compromised. We also show, in the first demonstration of the plausibility of evolutionary capacitance, that the availability of loss-of-function mutations speeds adaptation to a new optimum phenotype. However, this effect does not require the mutations to be conditional, so Hsp90's second property is unnecessary. Because many genes may act as capacitors, the third property is less important. Thus, rather than being unique, Hsp90 may serve as a model of a more subtle, general phenomenon.