Egg Activation


The interaction between sperm and egg at fertilization stimulates the egg to begin development, a process known as egg activation. The fertilizing sperm not only contributes its complement of chromatin at fertilization, but also provides the signal that releases the egg from meiotic arrest and permits embryonic development.

Keywords: fertilization; egg; activation of development; calcium; inositol trisphosphate

Figure 1.

The calcium wave at fertilization of the frog egg is prevented by inhibition of IP3‐induced calcium release. (a) Confocal images of the normal calcium wave in a fertilized Xenopuslaevis egg that was previously injected with the calcium indicator Ca green dextran. (b) Images of a fertilized egg that was previously injected with Ca green dextran and a function‐blocking antibody to the IP3 receptor. Although the calcium wave is inhibited, small spots of localized calcium release are detected in some eggs, as shown in (b). These hot spots may be localized calcium rises at the site of sperm–egg fusion which are not completely blocked and are observed with other agents that inhibit the calcium wave (Glahn et al., 1999). Images in (a) and (b) are shown at 40‐s intervals. From Runft et al., with permission.

Figure 2.

Sperm‐induced calcium oscillations in the mammalian egg. Changes in intracellular calcium were monitored with the fluorescent calcium indicator Fura‐dextran. The fluorescence emission signal is displayed as the ratio of fluorescence for the 350‐nm/385‐nm excitation wavelengths. An increase in the fluorescence ratio represents an increase in intracellular free calcium.



Carroll DJ, Albay DT, Terasaki M, Jaffe LA and Foltz KR (1999) Identification of PLCγ‐dependent and ‐independent events during fertilization of sea urchin eggs. Developmental Biology 206: 232–247.

Giusti AF, Carroll DJ, Abassi YA and Foltz KR (1999) Evidence that a starfish egg Src family tyrosine kinase associates with PLC‐γ1 SH2 domains at fertilization. Developmental Biology 208: 189–199.

Kimura Y, Yanagimachi R, Kuretake S et al. (1998) Analysis of mouse oocyte activation suggests the involvement of sperm perinuclear material. Biology of Reproduction 58: 1407–1415.

Mehlmann LM, Carpenter G, Rhee SG and Jaffe LA (1998) SH2 domain‐mediated activation of phospholipase Cγ is not required to initiate Ca2+ release at fertilization of mouse eggs. Developmental Biology 203: 221–232.

Parrington J, Jones KT, Lai FA and Swann K (1999) The soluble sperm factor that causes Ca2+ release from sea‐urchin (Lytechinus pictus) egg homogenates also triggers Ca2+ oscillations after injection into mouse eggs. Biochemical Journal 341: 1–4.

Runft LL, Watras J and Jaffe LA (1999) Calcium release at fertilization of Xenopus eggs requires type I IP3 receptors, but not SH2 domain‐mediated activation of PLCγ or Gq‐mediated activation of PLCβ. Developmental Biology 214: 399–411.

Sakurai A, Oda S, Kuwabara Y and Miyazaki S (1999) Fertilization, embryonic development, and offspring from mouse eggs injected with round spermatids combined with Ca2+ oscillation‐inducing sperm factor. Molecular Human Reproduction 5: 132–138.

Sato Y, Miyazaki S, Shikano T et al. (1998) Adenophostin, a potent agonist of the inositol 1,4,5‐trisphosphate receptor, is useful for fertilization of mouse oocytes injected with round spermatids leading to normal offspring. Biology of Reproduction 58: 867–873.

Sato K, Iwao Y, Fujimura T et al. (1999) Evidence for the involvement of a Src‐related tyrosine kinase in Xenopus egg activation. Developmental Biology 209: 308–320.

Terasaki M and Sardet C (1991) Demonstration of calcium uptake and release by sea urchin egg cortical endoplasmic reticulum. Journal of Cell Biology 115: 1031–1037.

Further Reading

Glahn D, Mark SD, Behr RK and Nuccitelli R (1999) Tyrosine kinase inhibitors block sperm‐induced egg activation in Xenopus laevis. Developmental Biology 205: 171–180.

Jones KT (1998) Ca2+ oscillations in the activation of the egg and development of the embryo in mammals. International Journal of Developmental Biology 42: 1–10.

Kline D, Mehlmann LM, Fox C and Terasaki M (1999) The cortical endoplasmic reticulum (ER) of the mouse egg: localization of ER clusters in relation to the generation of repetitive calcium waves. Developmental Biology 215: 431–442.

Lee SJ and Shen SS (1998) The calcium transient in sea urchin eggs during fertilization requires the production of inositol 1,4,5‐trisphosphate. Developmental Biology 193: 195–208.

Miyazaki S, Shirakawa H, Nakada K and Honda Y (1993) Essential role of the inositol 1,4,5‐trisphosphate receptor/Ca2+ release channel in Ca2+ waves and Ca2+ oscillations at fertilization of mammalian eggs. Developmental Biology 158: 62–78.

Palermo GD, Avrech OM, Colombero LT et al. (1997) Human sperm cytosolic factor triggers Ca2+ oscillations and overcomes activation failure of mammalian oocytes. Molecular Human Reproduction 3: 367–374.

Rongish BJ, Wu W and Kinsey WH (1999) Fertilization‐induced activation of phospholipase C in the sea urchin egg. Developmental Biology 215: 147–154.

Stricker SA (1999) Comparative biology of calcium signaling during fertilization and egg activation in animals. Developmental Biology 211: 157–176.

Swann K and Parrington J (1999) Mechanism of Ca2+ release at fertilization in mammals. Journal of Experimental Zoology 285: 267–275.

Williams CJ, Mehlmann LM, Jaffe LA, Kopf GS and Schultz RM (1998) Evidence that Gq family G proteins do not function in mouse egg activation at fertilization. Developmental Biology 198: 116–127.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Kline, Douglas(Apr 2001) Egg Activation. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0003300]