DYNAMICS OF THE CALCIUM SIGNAL THAT TRIGGERS MAMMALIAN EGG ACTIVATION

We have reviewed many aspects of Ca2+ changes at fertilization in mammals that have been discovered in the past decade or so. One of the main points that we have emphasized is that mammalian eggs are different from other eggs in that they undergo Ca2+oscillations, or repetitive Ca2+ spikes, during activation at fertilization. One of the central problems to be solved is the triggering mechanism for the oscillations at fertilization. Ca2+ oscillations have been described in a vast range of somatic cell types. In many cases the basic components of the signaling systems have been established. It is remarkable that the problem of signal transduction involving Ca2+ release in eggs at fertilization has not been solved in any species. There is still a split between the idea that the sperm either acts upon cell-surface receptors that somehow stimulate InsP, production, and the idea that the sperm introduces a soluble factor into the egg after fusion (Whitaker and Swann, 1993). Mammalian eggs can offer special advantages for resolving this debate because their Ca2+ signal at fertilization represents a fingerprint response that is not matched by parthenogenetic agents or injected Ca2+. © 1994 Academic Press, Inc.