The eggs and embryos of several species of hydrozoans contain endogenous calcium indicators similar to aequorin. These preparations offer unique opportunities for studying the role of calcium in early development. Two calcium transients, one at fertilization, and another at cleavage, are crucial for normal development. This project will employ photon counting techniques and image intensified video microscopy methods to determine if the fertilization calcium transient is due to a calcium wave, and microinjection experiments to determine what second messengers participate in its initiation and propagation. Cytokinesis in hydrozoans is slow and requires external calcium. Photon counting, fluorescent dye injection, and drugs will be used to investigate how the calcium transient during cytokinesis is regulated. Voltage dependent calcium channels first become functional about one hour after fertilization. These channels play a major role in rapid calcium influx but very little is known about the developmental events that lead to the onset of channel function. This project will define the factors that are responsible for initiating calcium channel function in hydrozoans. When calcium rises in the cytosol of cleavage stage embryos, calcium is simultaneously transported from the endoplasmic reticulum to the external medium. This project will identify the mechanism that mediates this calcium efflux.
