Drs. Ridgway and Freeman have recently discovered that the eggs and embryos of several species of hydrozoans contain endogenous calcium indicators similar to aequorin. Because the calcium indicators are natural, exist in high concentration, and emit light specifically in the presence of calcium, these preparations offer unique opportunities for studying the role of calcium in early development. They propose to investigate the mechanism that controls the appearance of calcium channels in the membrane at first cleavage in these organisms. These channels could play a role in establishing the anterior-posterior axis of the developing embryo. They will determine where and why these channels appear by using image intensification and image enhancement techniques in conjunction with microinjection of heterochronic cytoplasm. They have discovered that potassium depolarization of cleavage stage embryos leads to a bright flash which is due in part to calcium release from an internal store. They will investigate the mechanism that couples the calcium entry through the calcium channels to the calcium release internally. They will study the propagation of four sorts of calcium waves: 1. those due to IP3 diffusion in unfertilized eggs, 2. those that may occur at fertilization, 3. those due to depolarization of cleavage stage embryos, and 4. those accompanying metamorphosis. %%% The importance of calcium as a regulator of a number of cellular processes has been established. The question remains as to how is the level of calcium itself controlled. Drs. Ridgway and Freeman have developed a powerful model system in which to address this question. It exploits a naturally occurring luminescent protein found in hydrozoan embryos which emits light in the presence of calcium.
