Egg activation at fertilization: where it all begins.
A centrally important factor in initiating egg activation at fertilization is a rise in free Ca(2+) in the egg cytosol. In echinoderm, ascidian, and vertebrate eggs, the Ca(2+) rise occurs as a result of inositol trisphosphate-mediated release of Ca(2+) from the endoplasmic reticulum. The release of Ca(2+) at fertilization in echinoderm and ascidian eggs requires SH2 domain-mediated activation of a Src family kinase (SFK) and phospholipase C (PLC)gamma. Though some evidence indicates that a SFK and PLC may also function at fertilization in vertebrate eggs, SH2 domain-mediated activation of PLC gamma appears not to be required. Much work has focused on identifying factors from sperm that initiate egg activation at fertilization, either as a result of sperm-egg contact or sperm-egg fusion. Current evidence from studies of ascidian and mammalian fertilization favors a fusion-mediated mechanism; this is supported by experiments indicating that injection of sperm extracts into eggs causes Ca(2+) release by the same pathway as fertilization.
Runft
Linda L
LL
Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA. runft@lifesci.ucsb.edu
Jaffe
Laurinda A
LA
Mehlmann
Lisa M
LM
D000818:Animals; D020013:Calcium Signaling; D004447:Echinodermata / Q000196:embryology / Q000378:metabolism; D005306:Fertilization; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013084:Sperm-Ovum Interactions; D010738:Type C Phospholipases / Q000378:metabolism; D014561:Urochordata / Q000196:embryology / Q000378:metabolism; D015053:Zygote / Q000166:cytology* / Q000378:metabolism*
D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases