Editors' ChoiceEVOLUTION

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Science Signaling  22 Apr 2008:
Vol. 1, Issue 16, pp. ec137
DOI: 10.1126/stke.116ec137

The most common source of genetic variation that can lead to evolution is certainly single-nucleotide mutations. But less frequent events like gene duplication are likely also important, as they allow more dramatic changes that result in rewiring of genetic regulatory networks. Isalan et al. explored in bacteria the repercussions of duplication events that would allow splicing of a regulatory promoter sequence of one gene with the open reading frame of another gene. They engineered almost 600 such events in genes encoding transcription factors and monitored effects on survival, growth, and evolvability of the bacterial strains. The remarkable robustness of gene regulatory networks was confirmed by the fact that over 95% of these changes did not prevent viability of the bacteria. Only 16% of the strains showed any change in growth, and some grew even better than wild-type bacteria. The authors also subjected the strains to selective pressures in the lab over many generations and found that even their relatively small (in evolutionary terms) sampling of 600 new networks yielded a dozen or so with apparent evolutionary advantages in fitness. Although some of the rewiring events caused new positive or negative transcriptional feedback loops, these did not cause changes in the amounts of green fluorescent protein–tagged proteins produced from the experimental genes. This suggests that the regulatory networks themselves can compensate for such a change and emphasize that posttranscriptional mechanisms should not be underestimated in comparison with transcriptional control mechanisms. Bennett and Hasty add valuable commentary, noting that you would not want to try such rewiring of processing units in your home computer (analogies between biological control mechanism and systems design in modern technology go only so far) and that advocates of "intelligent design" who claim that the complexity of biological systems would cause them to fail in the presence of randomly generated changes will have to take into account these new data to the contrary.

M. Isalan, C. Lemerle, K. Michalodimitrakis, C. Horn, P. Beltrao, E. Raineri, M. Garriga-Canut, L. Serrano, Evolvability and hierarchy in rewired bacterial gene networks. Nature 452, 840-845 (2008). [PubMed]

M. R. Bennett, J. Hasty, Genome rewired. Nature 452, 824-825 (2008). [PubMed]

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