This project is to continue studies on how calcium initiates cell division in the fertilized sand dollar egg. Evidence indicates that the calcium signal that is responsible for the breakdown of the nuclear envelope arises from localized release from membrane enclosed compartments in a region near the nucleus. Furthermore, this localized release seems to be triggered by a specific signaling molecule, leukotriene B4. The project addresses one of the central questions of calcium signaling: how can calcium, a second messenger involved in a seemingly vast array of different control pathways, initiate a very specific set of events and not others? The general assumption has been that the cell accomplishes this by limiting calcium signals to pulses of short duration at discrete sites within the cell. This project provides an experimental system to test this assumption. The project focuses on two general aspects of the calcium signaling in sand dollar eggs. Light microscopy and computer analysis will be used to determine the spatial and temporal features of the wave-like calcium signals in real time in the living egg under various experimental conditions. A luminescent calcium reporter called aequorin will be used in a way that is sensitive enough to detect quantal events of calcium release. The second area of interest is to verify that leukotriene B4 triggers this calcium release and that the enzymes that synthesize this upstream signaling molecule are located on the intracellular membranes that release calcium as defined by the microscopy studies. The project is potentially highly significant since this specific system for the localized control of calcium release may very well be found in many other types of cells.
