Abstract
Exocytosis of secretory granules (SG) is a fundamental biological process that is critical for many physiological functions. Exocytosis requires recruitment of SG and their fusion with the plasma membrane. The actin cortex plays two contradictory roles in SG recruitment: it captures them through Myosin Va motors, bringing them to the periphery of the cell; yet at the same time, it acts as a passive mechanical barrier preventing their approach to the plasma membrane. How do cells consolidate these two opposing roles of the actin cortex? We show, using live-cell multi-color TIRF microscopy, that activation of the FceRI pathway in RBL-2H3 cells results in coordinated oscillation of Ca2+, PIP2, N-WASP, F-actin and Myosin Va. These oscillations alternate between high actin levels that promote SG capture, and low actin levels that reduce the mechanical barrier. This temporal partitioning resolves the conflicting roles of the actin cortex as both a carrier and a barrier of SG.
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