Protein kinase C-dependent and independent events in mouse egg activation.
The involvement of calcium- or protein kinase C (PKC)-dependent pathways in cortical granule exocytosis (CGE) and pronucleus formation was examined in mouse eggs using the specific PKC stimulator OAG (1-oleyl-2-acetyl-sn-glycerol) at different external calcium concentrations ([Ca2+]e) ranging from 1.7 mM to 0.1 microM. A 10 min exposure of eggs to 150 microM OAG in the presence of 1.7 mM [Ca2+]e caused a large calcium influx, cortical granule release and 82% activation. The increased permeability of the egg membrane to Ca2+ ions after OAG treatment lasted 20 min. At [Ca2+]e lower than 1.7 mM, both OAG-induced calcium influx and CGE decreased, reaching a non-detectable level at 0.1 microM and 100 microM [Ca2+]e, respectively. Resumption of meiosis was not affected by [Ca2+]e above 200 microM but it was reduced at any lower [Ca2+]e, with a minimum activation frequency of 46% at 0.1 microM [Ca2+]e. Loading of eggs with > or = 3 microM of the calcium chelator BAPTA AM (1,2-bis(o-aminophenoxy)ethane-N',N',N',N'-tetraacetic acid-acetoxymethyl ester) prior to OAG treatment caused a reduction in meiosis resumption with 50% of eggs forming pronuclei. Potent inhibitors of PKC, such as acridine orange and sphingosine, did not interfere with OAG-induced CGE. Conversely, these compounds prevented OAG-induced pronucleus formation in a dose-dependent manner with an IC50 (inhibiting concentration, 50%) of 5 microM and 30 microM for acridine orange and sphingosine, respectively. Microinjection of inositol 1,4,5-trisphosphate into eggs at 0.1 microM elicited Ca2+ release from intracellular stores and the cortical reaction, but failed to stimulate pronucleus formation. These results indicate that, in mouse eggs, CGE is a PKC-independent event, and that the transition from M-phase to interphase may require PKC activity for stimulation.
Colonna
R
R
Dipartimento di Scienze e Tecnologie Biomediche e di Biometria, Universita' dell'Aquila, Italy.
Tatone
C
C
D000165:Acridine Orange / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects; D003594:Cytoplasmic Granules / Q000187:drug effects; D004075:Diglycerides / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D051379:Mice; D010063:Ovum / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D013110:Sphingosine / Q000494:pharmacology
D004075:Diglycerides; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; C038237:1-oleoyl-2-acetylglycerol; D011493:Protein Kinase C; D000165:Acridine Orange; D013110:Sphingosine; D002118:Calcium