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futurity_sci_tech 00998.txt

#Yeast reveals secret of hitchhiker mutations It takes a group effort of genetic mutations to give organisms the best shot at evolutionary survival a new study suggests. Evolution occurs when an individual experiences a spontaneous beneficial mutation in its genome that improves its ability to adapt to its environment. The common view was that a single mutation could boost the survival of an individual which would then reproduce and pass on the mutation to its offspring. Instead researchers studying 1000 generations of adaptation in 40 yeast populations have found that rather than just one mutation causing enhanced survival about five to seven mutations are required. These extra mutations are termed hitchhikers because they don t appear to contribute to the enhanced fitness of the organism Our study indicates that evolution is more of a group effort says Gregory Lang an associate research scholar in the laboratory of David Botstein at Princeton university s Lewis-Sigler Institute for Integrative Genomics. Lang is first author on the paper which appears in the journal Nature. Drivers and hitchhikers The finding goes against the traditional view of evolution being determined by individual mutations that provide a large fitness advantage by themselves says Michael Desai a former Princeton fellow who is currently at Harvard university. We found that small groups which we call cohorts of mutations were associated with increased survival. No single mutation is driving adaptation. The whole group which includes hitchhikers drives adaptation together. The relatively small subset of gene mutations that were found to enhance survival Botstein says suggests that there are only a limited number of ways in which organisms can substantially increase their fitness. Understanding the basic process in yeast translates to other organisms he says. The knowledge of how mutations drive evolution can inform our understanding of how tumors resist chemotherapeutics and how bacteria evolve resistance to antibiotics. Although the researchers refer to the groups of mutations as containing drivers and hitchhikers Desai says that additional research is being done to explore which mutations are necessary for adaptation and which ones are along for the ride. He noted that the mutations are located not near each other nor do they appear to have similar functions. The study helps expand our understanding of how evolution arises from a combination of genetic mutations which are thought of as occurring spontaneously and environmental pressures says Botstein. We ve shown that this first component the genetics involves not just one gene mutation but several that need to coexist before evolution can happen. By following genomic changes across cell populations over time this study allows a rare glimpse of evolution in progress says Stefan Maas of the National institute of health s National Institute of General Medical sciences which partially funded the research. This systems biology approach yields insights that could help us understand how mutations spread through other evolving systems such as cancer cells or disease-causing microbes. Previous evidence suggests that yeast may experience beneficial mutations that inactivate genes they no longer need. For example Lang and Botstein in collaboration with Andrew Murray at Harvard university reported in 2009 that if grown in conditions where the yeast can only reproduce asexually mutations that inactivate genes for proteins involved in sexual reproduction boost survival because the organisms do not waste metabolic energy producing unneeded proteins. The team which includes researchers from Washington University School of medicine plans to explore whether the mutations identified in the new study confer specific survival advantages. The National Science Foundation Graduate Research Fellowship the National Institute of General Medical sciences Centers of Excellence the National institutes of health the James S. Mcdonnell Foundation the Alfred P. Sloan Foundation and the Harvard Milton Fund helped support the study. Source: Princeton Universityyou are free to share this article under the Creative Commons Attribution-Noderivs 3. 0 Unported license e

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