Egg activation at fertilization: where it all begins
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Updated: Oct 1, 2026

In Vivo Visualization of Calcium Transients during Fertilization and Early Development in C. elegans
Published on: July 12, 2024
Linda L Runft1, Laurinda A Jaffe, Lisa M Mehlmann
1Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA. runft@lifesci.ucsb.edu
Abstract:
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.
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