Calcium release at fertilization of Xenopus eggs requires type I IP(3) receptors, but not SH2 domain-mediated activation of PLCgamma or G(q)-mediated activation of PLCbeta.
Elevation of intracellular Ca2+ at fertilization is essential for the initiation of development in the Xenopus egg, but the pathway between sperm-egg interaction and Ca2+ release from the egg's endoplasmic reticulum is not well understood. Here we show that injection of an inhibitory antibody against the type I IP(3) receptor reduces Ca2+ release at fertilization, indicating that the Ca2+ release requires IP(3). We then examine how IP(3) production is initiated. Xenopus eggs were injected with specific inhibitors of the activation of two phospholipase C isoforms, PLCgamma and PLCbeta. The Src-homology 2 (SH2) domains of PLCgamma were used to inhibit SH2-mediated activation of PLCgamma, and an antibody against G(q) family G-proteins was used to inhibit G(q)-mediated activation of PLCbeta. Though the PLCgamma SH2 domains inhibited platelet-derived growth factor (PDGF)-induced Ca2+ release in eggs with exogenously expressed PDGF receptors, they did not inhibit the Ca2+ rise at fertilization. Similarly, the G(q) family antibody blocked serotonin-induced Ca2+ release in eggs with exogenously expressed serotonin 2C receptors, but not the Ca2+ rise at fertilization. A mixture of PLCgamma SH2 domains and the G(q) antibody also did not inhibit the Ca2+ rise at fertilization. These results indicate that Ca2+ release at fertilization of Xenopus eggs requires type I IP(3)-gated Ca2+ channels, but not SH2 domain-mediated activation of PLCgamma or G(q)-mediated activation of PLCbeta.
Runft
L L
LL
Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
Watras
J
J
Jaffe
L A
LA
D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D005306:Fertilization; D019204:GTP-Binding Proteins / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes / Q000502:physiology*; D008297:Male; D008856:Microscopy, Fluorescence; D054799:Phospholipase C beta; D051966:Phospholipase C gamma; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013094:Spermatozoa / Q000378:metabolism; D013997:Time Factors; D010738:Type C Phospholipases / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology*; D018909:src Homology Domains / Q000502:physiology*
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007527:Isoenzymes; D010982:Platelet-Derived Growth Factor; D018160:Receptors, Cytoplasmic and Nuclear; D012701:Serotonin; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D051966:Phospholipase C gamma; D019204:GTP-Binding Proteins; D002118:Calcium