May 14, 2010
Biologist finds key to the evolution of signal pathways in yeast cells
Signal pathways regulate biological processes, including those related to human physiology, and understanding them is fundamental to learning how cancers arise. Recently University of Iowa biologist David Soll and his colleagues opened a unique window into this area of research by examining a newly evolved pathway in the cells of the pathogenic yeast Candida albicans.
In an article published in the May 4 issue of the journal PLoS Biology, a flagship publication of the Public Library of Science, Soll and his colleagues describe the evolution of an entire pathway that evolved 40 million years ago in the ancestor of Candida albicans, the most pervasive human fungal pathogen and the cause of a variety of oral, genital and other human illnesses.
Significantly, the way in which this pathway evolved may be similar to the way in which comparable pathways evolved in human cells.
"This study provides the first glimpse into how the pathways that regulate responses to signals have evolved," Soll said. "They first evolve by borrowing every single component from ancestral pathways.
"Signal transduction pathways are important because they make you what you are as a human being. They determine how you respond to outside signals at every level of biological complexity. And we have found a glimpse of how these regulatory pathways have come to be," he said.
"We found that in Candida albicans, a signal transduction pathway evolved by taking parts of old pathways and using the same signals, but adding new target functions. Similarly, in human development, cancers and various other human diseases, signal transduction pathways may also have evolved by first borrowing everything. Then as the pathways become old and evolve, changes occur that blind us to how they first evolved," he said.
In describing his team's work with yeast cells, Soll said that researchers have known for some time that in order to mate, Candida must switch from a white form to an opaque form and that an elaborate genetic program regulates the switch. The capacity for Candida to switch was a very recent evolutionary event. The new pathway Soll and colleagues studied evolved when switching evolved. The new pathway, which functions in the white cell, borrowed the upper portion of the pathway that regulates mating of opaque cells. Because the new pathway in the sexually incompetent white cell facilitates sex in the opaque cell, it can share the same signals (sex pheromones) and receptor. But it uses them to induce white cell biofilm formation, which in turn facilitates sex between opaque cells. This may represent the first paradigm for how a new cell type can develop a signal transduction pathway for a new function, he said.
Soll's co-authors, all of the Department of Biology in the UI College of Liberal Arts and Sciences, are Nidhi Sahni, Song Yi, Karla J. Daniels, Guanghua Huang and Thyagarajan Srikantha. Soll, who serves as the Emil Witschi/Roy J. and Lucille A. Carver Professor, is internationally known for his work on Candida albicans, cell motility and several other research areas.
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