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Fossil Genes: Another Gift from Yeast
by Christine Mlot
Working in the lab of Sean Carroll (R), Chris Todd Hittinger (L) made a big discovery in odd patterns in yeast data.
FOR THE PAST FEW THOUSAND YEARS, yeast has lived a life of service, fermenting fruits and grains into wine and beer and breathing height into bread. More recently, yeast answered the call of science, serving as a model for countless experiments in genetics, genomics, and molecular biology. But long before it was so tamed, Saccharomyces cerevisiae and its single-celled cousins lived in the wilds of soil and foliage, grubbing out an existence from whatever sugar sources they could find.
At some point in that ancient history, millions of years ago, a number of those organisms lost their tastes for particular types of sugar. And as the yeasts acquired new tastes, they proceeded down different evolutionary paths. That divergence is recorded in the yeast genome today, as HHMI predoctoral fellow Chris Todd Hittinger at the University of Wisconsin–Madison has discovered. He reported the tale of this genetic and evolutionary change in the September 28, 2004, issue of the Proceedings of the National Academy of Sciences, in a paper coauthored with postdoctoral fellow Antonis Rokas and HHMI investigator Sean B. Carroll.
Using a menagerie of species, Carroll's lab studies the evolution of animal form and the closely related question of how animals develop from a single cell. Hittinger came to the lab in late 2001 with a double major in chemistry and biology from Southeast Missouri State University. "I was particularly interested in molecular evolution," he says.
For his graduate work Hittinger has been studying Hox genes, a class of genes that play a crucial regulatory role in the development of fruit flies and other animals by turning whole networks of genes on and off. Given the wealth of genomic data on yeast, he went on to examine a yeast gene that plays a similar regulatory role. The gene turns on the biochemical pathway that yeast uses to digest galactose, a common sugar that most organisms—from microbes to mammals—can consume. Galactose is an important component of mother's milk.
Photo: David Nevala
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Chris Todd Hittinger's yeast finding is the latest in a spate of recent papers that connect physical or physiological change in an organism to its genetic evolution. One 2004 paper, for example, related jaw development in primates to a mutation in a muscle gene. This growing body of "evolutionary genomics" has implications for understanding how agents of disease, such as those involved in AIDS, make themselves difficult for the host's body and medical caregivers to target. As the field develops, "We'll have a good feeling for how evolution proceeds at the molecular and genetic level," says Hittinger. "It will likely give researchers a better perspective on how organisms will respond to various treatment regimes."
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