At fertilisation of mammalian and ascidian eggs the sperm induces a series of Ca²⁺ oscillations. These Ca²⁺ oscillations are triggered by a sperm-borne Ca²⁺-releasing factor whose identity is still unresolved. In both mammals and ascidians Ca²⁺ oscillations in eggs are associated with the period leading up to exit from meiosis and entry into the first embryonic cell cycle. Thus, in mammals Ca²⁺ oscillations continue for several hours but are complete by within 30 min in the ascidian. In mammals and ascidians Ca²⁺ oscillations stop at around the time when pronuclei form in the 1-cell embryo. There is evidence to show that cell cycle factors are important in regulating the fertilisation Ca²⁺ signal. If the formation of pronuclei is blocked either in mammals (by spindle disruption) or in ascidians (by clamping maturation promoting factor levels high) then Ca²⁺ oscillations continue indefinitely. Here, we explore the nature of the sperm Ca²⁺-releasing factor and examine the relationship between cell cycle resumption and the control of Ca²⁺ oscillations at fertilisation.
Biology of the Cell Vol. 92, Issue 3-4, p. 187-196