title: Calcium influx-mediated signaling is required for complete mouse egg activation.
abstract: Mammalian fertilization is accompanied by oscillations in egg cytoplasmic calcium (Ca(2+)) concentrations that are critical for completion of egg activation. These oscillations are initiated by Ca(2+) release from inositol 1,4,5-trisphosphate (IP(3))-sensitive intracellular stores. We tested the hypothesis that Ca(2+) influx across the plasma membrane was a requisite component of egg activation signaling, and not simply a Ca(2+) source for store repletion. Using intracytoplasmic sperm injection (ICSI) and standard in vitro fertilization (IVF), we found that Ca(2+) influx was not required to initiate resumption of meiosis II. However, even if multiple oscillations in intracellular Ca(2+) occurred, in the absence of Ca(2+) influx, the fertilized eggs failed to emit the second polar body, resulting in formation of three pronuclei. Additional experiments using the Ca(2+) chelator, BAPTA/AM, demonstrated that Ca(2+) influx is sufficient to support polar body emission and pronucleus formation after only a single sperm-induced Ca(2+) transient, whereas BAPTA/AM-treated ICSI or fertilized eggs cultured in Ca(2+)-free medium remained arrested in metaphase II. Inhibition of store-operated Ca(2+) entry had no effect on ICSI-induced egg activation, so Ca(2+) influx through alternative channels must participate in egg activation signaling. Ca(2+) influx appears to be upstream of CaMKIIγ activity because eggs can be parthenogenetically activated with a constitutively active form of CaMKIIγ in the absence of extracellular Ca(2+). These results suggest that Ca(2+) influx at fertilization not only maintains Ca(2+) oscillations by replenishing Ca(2+) stores, but also activates critical signaling pathways upstream of CaMKIIγ that are required for second polar body emission.
authors.affiliation: Reproductive Medicine Group, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
authors.forename: Yi-Liang
authors.initials: YL
authors.lastname: Miao
authors.forename: Paula
authors.initials: P
authors.lastname: Stein
authors.forename: Wendy N
authors.initials: WN
authors.lastname: Jefferson
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Padilla-Banks
authors.forename: Carmen J
authors.initials: CJ
authors.lastname: Williams
mesh_terms: D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005307:Fertilization in Vitro; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D010063:Ovum / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D020554:Sperm Injections, Intracytoplasmic
chemical_list: D002021:Buffers; D002843:Chromatin; D004533:Egtazic Acid; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium