After the fusion of the sperm plasma membrane and the egg plasma membrane after fertilization, animal eggs go through a process called egg activation to prepare the egg for development.

There are three functions of egg activation:

1. Block to polyspermy
2. Activation of egg metabolism
3. Resumption of the cell cycle

Sperm trigger of egg activation

The sperm proteins that interact with receptors on plasma membrane of the egg is still unknown. The results of this interaction activates a signal transduction pathway that uses second messengers. The inositol signaling system has been tagged as the one involved with egg activation. IP₃ and DAG are produced from the cleavage of PIP₂ by phospholipase C (PLC). It is unknown how PLC is activated. It is possible that a G protein receptor is activated by the sperm binding which activates a tyrosine kinase which then activates PLC. A recent paper shows that mammaliam sperm brings to the egg a PLC isoform which can start the signaling cascade^[1] In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. ... In biology, second messengers are low-weight diffusible molecules that are used in signal transduction to relay signals within a cell. ... PLC may stand for: Palestinian Legislative Council, law-making body of the Palestinian Authority Parti Libéral du Canada, the term in French for the Liberal Party of Canada Partido Liberal Constitucionalista (or Constitutional Liberal Party), a major political party in Nicaragua Phospholipase C Platoon Leaders Class Polish-Lithuanian Commonwealth...

Fast and Slow Block to Polyspermy

Polyspermy is the condition when multiple sperm fuse with a single egg. This results in duplications of genetic material. In sea urchins, the block to polyspermy comes from two mechanisms: the fast block and the slow block. The fast block is an electrical block to polyspermy. The resting potential of an egg is -70mV. After contact with sperm, an influx of sodium ions from the sea water increase the potential up to +20mV. The slow block is through a biochemical mechanism triggered by a wave of calcium increase. The rise of calcium is both necessary and sufficient to trigger the slow block. In the cortical reaction, cortical granules directly beneath the plasma membrane are released into the space between the plasma membrane and the vitelline membrane (the perivitelline space). An increase in calcium triggers this release. The contents of the granules contain proteases, mucopolysaccharides, hyalin, and peroxidases. The proteases cleave the bridges connecting the plasma membrane and the vitelline membrane and cleave the bindin to release the sperm. The mucopolysaccharides attract water to raise the vitelline membrane. The hyalin forms a layer adjacent to the plasma membrane and the peroxidases cross-link the protein in the vitelline membrane to harden it and make it impenetrable to sperm. Through these molecules the vitelline membrane is transformed into the fertilization membrane or fertilization envelope. In mice, the zona reaction is the equivalent to the cortical reaction in sea urchins. The terminal sugars from ZP3 are cleaved to release the sperm and prevent new binding. In biology, Polyspermy describes an egg that has been fertilized by more than one sperm. ... After a spermatozoan makes contact with the oocyte membrane, a chain reaction is provoked, which prevents further spermatozoa from fertilizing the oocyte. ... Peptidases (proteases [pronounced pro-tea-aces] and proteolytic enzymes are also commonly used) are enzymes which break peptide bonds of proteins. ... Glycosaminoglycans (GAGs) are long unbranched polysaccharides, made up of repeating disaccharides that may be sulphated (e. ... Glutathione Peroxidase 1 A peroxidase (eg. ...

Late Responses

The combined increase of calcium signal and pH leads to a dramatic increase in protein synthesis. The protein synthesis uses mRNAs that are already present in the oocyte. These proteins direct the next events of embryogenesis such as the fusion of the egg and sperm pronuclei to form the diploid embryonic nucleus. The fusion is driven my microtubule-dependent movement of the female pronucleus to the male pronucleus. Pronuclei - plural for pronucleus. ...

References

1. ^ Saunders C, Larman M, Parrington J, Cox L, Royse J, Blayney L, Swann K, Lai F (2002). "PLC zeta: a sperm-specific trigger of Ca(2+) oscillations in eggs and embryo development.". Development 129 (15): 3533-44. PMID 12117804.