The initiation and propagation of the fertilization wave in sea urchin eggs

Calcium waves sweep across most eggs of the deuterostome lineage at fertili zation. The precise timing of the initiation and propagation of a fertiliza tion calcium wave has been best studied in sea urchin embryos, since the ra pid depolarization caused by sperm egg fusion can be detected as a calcium influx using confocal imaging of calcium indicator dyes. The time between s perm egg fusion and the first sign of the calcium increase that constitutes the calcium wave is comparable to the time it takes for the wave to sweep across the egg, once initiated. The latency and rise time of the calcium re sponse is sensitive to inhibitors of the InsP(3) signalling pathway, as rep orted previously. Using calcium green dextran and confocal microscopy, we c onfirm that the propagation time of the calcium wave is lengthened and that initiation of the calcium wave involves activation of calcium release at h ot spots that may represent clusters of calcium release channels, as has be en seen in other cell types. (C) 2000 Editions scientifiques et medicales E lsevier SAS.