Responses of the Medaka Fish Egg (Oryzias latipes) to the Photolysis of Microinjected Nitrophenyl-EGTA, a Photolabile Calcium Chelator.

Photolabile calcium chelators (calcium cages) can be used to elevate cytosolic [Ca2+] at specific sites and times (1, 2, 3). They have been especially valuable in flash photolysis studies of muscle contraction (2) and secretion (4, 5). In the present report, I describe several responses of medaka eggs to thephotolysis of microinjected nitrophenyl-EGTA (NP-EGTA),a new calcium cage (6). When unfertilized eggs injected with NP-EGTA were irradiated with ultraviolet irradiation in a small region of the egg, the eggs were activated and ooplasm within the irradiated region contracted and accumulated there. Eggs into which NP-EGTA was injected could also be fertilized. Subsequent irradiation of such eggs, in addition to causing the contraction and accumulation of ooplasm, also caused a global contraction of dividing blastomeres and the contraction and blebbing of embryonic cells for up to 4 days after fertilization. Injection of NP-EGTA had no apparent effect on the maturation offertilized eggs, which developed normally and hatched.