Reducing PIP2 hydrolysis, Ins(1,4,5)P3 receptor availability, or calcium gradients inhibits progesterone-stimulated Xenopus oocyte maturation.
In this report, we investigated the possibility that a product of phosphatidylinositol 4,5-bisphosphate (PIP2) breakdown, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), and its downstream effector, Ca2+, is involved in oocyte maturation. Microinjection of monoclonal antibody specifically directed to PIP2 into oocytes prior to progesterone addition inhibited meiotic maturation. In addition, preventing or suppressing the progesterone-induced increase in [Ca2+]i and maintaining cytosolic free Ca2+ of oocyte at 0.1 or 0.3 microM by Br2-BAPTA buffered Ca2+ solutions, completely blocked maturation. However, raising cytosolic Ca2+ concentration of oocyte to 1.0 or 3.0 microM, the inhibitory Br2-BAPTA effects on oocyte maturation was greatly diminished. Finally, microinjection of heparin, a potent antagonist of Ins(1,4,5)P3 receptor, inhibited progesterone-induced oocyte maturation in a manner that is linearly proportional to its cytoplasmic concentration. These results strongly support the hypothesis that PIP2 turnover as well as Ins(1,4,5)P3-induced Ca2+ release play crucial roles in regulating normal meiotic cell division in Xenopus oocyte.
Han
J K
JK
Department of Life Sciences, Pohang University of Science and Technology, South Korea.
Lee
S K
SK
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007158:Immunologic Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008540:Meiosis / Q000187:drug effects*; D009865:Oocytes / Q000166:cytology*; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology*; D011493:Protein Kinase C / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015290:Second Messenger Systems; D014982:Xenopus laevis
D015220:Calcium Channels; D002614:Chelating Agents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D018160:Receptors, Cytoplasmic and Nuclear; C053459:5,5'-dibromo-1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D011374:Progesterone; D004533:Egtazic Acid; D011493:Protein Kinase C; D002118:Calcium