Quantitative Imaging and Simulation Study for Analyzing Exocytosis in PC12 Cell

点击翻译按钮获取中文摘要

Exocytosis is an important biological phenomenon, especially for neural and endocrine cells. Although several experimental techniques from various fields of sciences including biophysics, cell biology, biochemistry and also molecular biology have been developed for analyzing this phenomenon, we have not reached the quantitative understandings for exocytosis. We, therefore, developed a systems biological approach for exocytosis with the combinatorial method of biological imaging and stochastic simulation. For the quantitative simulation, simultaneous imaging for intracellular Ca increase as a trigger of exocytosis, and also for quantitative counting of events of exocytosis is required. An imaging method by a dual view technique enables us to visualize the intracellular Ca response by a fluorescent dye, Fura-red and exocytosis by GFP-fused neuropeptide Y. Stimulation by ATP induced a quick and transient response of Ca and following exocytosis with a several seconds delay. This indicates that we can trace the exocytosis from the first trigger response of intracellular Ca and the final event of neurotransmitter release in single cells. Next, we develop a new simulation technique based on the stochastic Gillespie method. Pre-fusion process of exocytosis was divided to 5 stages, and the transition probabilities were estimated to fit the experimental data We succeed to reveal the exocytosis induced by a transient intracellular Ca increase. This stochastic model includes the enzymatic activity for modulating exocytosis. Finally, we also succeed to simulate the sequential exocytosis reported in chromaffin cells with double cascade of the single stochastic model. We conclude that simultaneous imaging and quantitative stochastic simulation provide us a new analytical technique for systems biology of exocytosis.