Calcium signalling during mammalian fertilization.
The fertilized mammalian egg is a nice model system for analysing spatiotemporal Ca2+ signalling in the intact cell. Hamster eggs show repetitive Ca2+ transients, associated in the initial response with Ca2+ waves which begin from the site of sperm attachment and are propagated across the deep cytoplasm to the opposite pole. In unfertilized eggs, a regenerative Ca2+ wave is induced by injection of either inositol 1,4,5-trisphosphate (InsP3) or Ca2+, and Ca2+ oscillations are produced by continuous injection of InsP3. These Ca2+ waves and oscillations in both fertilized and unfertilized eggs are inhibited in a dose-dependent manner by a monoclonal antibody to the type 1 InsP3 receptor. Ryanodine receptors (both skeletal and cardiac types) are not detected by physiological or immunoblot analyses. Positive and negative feedback between cytosolic Ca2+ and Ca2+ release from InsP3-sensitive pools accounts for the spatiotemporal Ca2+ signalling. In addition to intracellular Ca2+ release, Ca2+ entry from outside the egg is necessary to refill the Ca2+ pools and maintain Ca2+ oscillations. Evidence suggests that inositol 1,3,4,5-tetrakisphosphate activates the Ca2+ influx. The signal transduction process leading to the production of InsP3 and the mechanism of egg activation following the Ca2+ response still remain to be elucidated.
Miyazaki
S
S
Department of Physiology, Tokyo Women's Medical College, Japan.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D006224:Cricetinae; D005306:Fertilization / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008322:Mammals; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D002118:Calcium