The Sea Urchin Egg and Cortical Vesicles as Model Systems to Dissect the Fast, Ca2+-Triggered Steps of Regulated Exocytosis

Exocytosis is a fundamental process utilized by all eukaryotic organisms; this elegantly efficient process mediates such diverse functions as fertilization, synaptic transmission, and wound healing. Membrane fusion, the defining step of this process, has been well conserved through evolution. However, the mechanisms defining the priming, docking, and merger of two apposed native bilayer membranes have not been fully elucidated. Sea urchin cortical vesicles are locked at a stage just prior to Ca²⁺ -triggered membrane fusion and are thus an ideal system for fully defining the mechanisms underlying this process. Here we describe detailed methods to isolate these native secretory vesicles, monitor the fusion process, assess the minimal essential biochemical components, and identify their ultrastructural interactions that define the triggered exocytotic pathway.