演講公告
新聞標題： ( 2007-12-12 )
演講主題：The Systems Biology of Robust Cell Polarization
主講人：Dr. Ching-Shan Chou (Department of Mathematics, UC-Irvine)
演講日期：96年12月18日(星期二)<br>下午1:30 – 2:20
演講地點：(光復校區)科學一館223室
茶會時間：當天下午3:30於科學一館205室
摘要內容：
Cells localize (polarize) internal components to specic locations in response to external signals such as spatial gradients. For example, yeast cells form a mating projection toward the source of mating pheromone. There are specic challenges associated with cell polarization including amplication of shallow external gradients of ligand to produce steep internal gradients of protein components (e.g. localized distribution), response over a broad range of ligand concentrations, and tracking of moving signal sources.
In this work, we investigated the tradeoffs among these performance objectives using a generic model that captures the basic spatial dynamics of cell polarization. The tools were steady-state analysis along with simulations. We varied the positive feedback, cooperativity, and diffusion coefcients in the model to explore the nature of this tradeoff. Increasing the positive feedback gain resulted in better amplication, but also produced multiple steady-states and hysteresis that prevented the tracking of directional changes of the gradient. Feedforward/feedback coincidence detection in the positive feedback loop and multi-stage amplication both improved tracking with only a modest loss of amplication. Surprisingly, we found that introducing lateral surface diffusion increased the robustness of polarization and collapsed the multiple steady-states in the high-gain positive feedback case to a single steady-state at the cost of a reduction in polarization. Finally, in a model of yeast cell polarization, a surface diffusion coefcient between 0.01 and 0.001 m2 /s produced the best polarization performance, and this range is close to the measured value. This research is signicant because it provides an in-depth analysis of the performance tradeoffs that confront biological systems that sense and respond to chemical spatial gradients, proposes strategies for balancing this tradeoff, and highlights the critical role of lateral diffusion of proteins in the membrane on the robustness of polarization.
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