MP13:Brett:Saccharomyces cerevisiae Response to a Rapidly Rotating Pheromone Gradient in a Microfluidic Device

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Marie-Elena Brett1, Reagan DeFlorio2, David Stone2, David T. Eddington1
Department of Bioengineering, University of Illinois at Chicago, USA
2 Department of Biological Sciences, University of Illinois at Chicago, USA

Chemotropism, or directed cell growth in response to a chemical gradient, is integral to many biological processes. The mating response of the budding yeast, Saccharomyces cerevisiae, is a well studied model chemotropic system. Yeast cells of opposite mating type signal their positions by secreting soluble mating pheromones. The mutual exchange of pheromones induces the cells to grow towards one another, resulting in “mating projections” or “shmoos.” Yeast cells exhibit a remarkable ability to orient their growth toward the nearest potential mating partner, and to reorient (i.e., bend their mating projections) in response to a change in the direction of the pheromone gradient. Although a number of microfluidic devices have been used to generate linear pheromone gradients and to measure initial orientation 1-3, none of them have the capability to change the direction of the gradient, other than to invert it. We have developed a microfluidic device that can produce stable pheromone gradients and rapidly rotate them in 90° increments, mimicking the dynamic gradients yeast are exposed to in situ, and allowing for the study of reorientation as well as initial orientation. The mean angle of orientation exhibited by gradient-stimulated yeast cells in this device was 56.9°. In control experiments, cells subjected to pheromone coming from all four directions showed no evidence of orientation. Switching the direction of the pheromone source by 90˚induced 83.6% of the polarized cells to change their direction of growth. Of these, 85.2% bent their mating projections toward the second source, demonstrating the utility of this device in the study of reorientation with specifically controlled gradients.

1. Paliwal, S. et al. MAPK-mediated Bimodal Gene Expression and Adaptive Gradient Sensing in Yeast. Nature 446, 46-51 (2007).
2. Moore, T. I., Chou, C-S., Nie, Q., Jeon, N.L., and Yi, T-M. Robust Spatial Sensing of Mating Pheromone Gradients by Yeast Cells. Ed. Amy S. Gladfelter. PLoS ONE 3, E3865 (2008).
3.Hao, N., et al. Regulation of Cell Signaling Dynamics by the Protein Kinase-Scaffold Ste5. Mol. Cell 30, 649-56 (2008).
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