title: Spindle function in Xenopus oocytes involves possible nanodomain calcium signaling.
abstract: Intracellular calcium transients are a universal phenomenon at fertilization and are required for egg activation, but the exact role of Ca2+in second-polar-body emission remains unknown. On the other hand, similar calcium transients have not been demonstrated during oocyte maturation, and yet, manipulating intracellular calcium levels interferes with first-polar-body emission in mice and frogs. To determine the precise role of calcium signaling in polar body formation, we used live-cell imaging coupled with temporally precise intracellular calcium buffering. We found that BAPTA-based calcium chelators cause immediate depolymerization of spindle microtubules in meiosis I and meiosis II. Surprisingly, EGTA at similar or higher intracellular concentrations had no effect on spindle function or polar body emission. Using two calcium probes containing permutated GFP and the calcium sensor calmodulin (Lck-GCaMP3 and GCaMP3), we demonstrated enrichment of the probes at the spindle but failed to detect calcium increase during oocyte maturation at the spindle or elsewhere. Finally, endogenous calmodulin was found to colocalize with spindle microtubules throughout all stages of meiosis. Our results-most important, the different sensitivities of the spindle to BAPTA and EGTA-suggest that meiotic spindle function in frog oocytes requires highly localized, or nanodomain, calcium signaling.
authors: Ottawa Hospital Research Institute, Ottawa Hospital-General Campus, Ottawa, ON K1H 8L6, Canada.
authors: Ruizhen
authors: R
authors: Li
authors: Ottawa Hospital Research Institute, Ottawa Hospital-General Campus, Ottawa, ON K1H 8L6, Canada.|Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
authors: Julie
authors: J
authors: Leblanc
authors: Ottawa Hospital Research Institute, Ottawa Hospital-General Campus, Ottawa, ON K1H 8L6, Canada.
authors: Kevin
authors: K
authors: He
authors: Ottawa Hospital Research Institute, Ottawa Hospital-General Campus, Ottawa, ON K1H 8L6, Canada jliu@ohri.ca.|Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada.|Department of Obstetrics and Gynaecology, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
authors: X Johné
authors: XJ
authors: Liu
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism; D060833:Cellular Microenvironment / Q000502:physiology; D005260:Female; D005306:Fertilization / Q000502:physiology; D008540:Meiosis / Q000502:physiology; D008870:Microtubules / Q000502:physiology; D009865:Oocytes / Q000378:metabolism / Q000502:physiology; D009866:Oogenesis / Q000502:physiology; D059705:Polar Bodies; D008941:Spindle Apparatus / Q000378:metabolism* / Q000502:physiology*; D014981:Xenopus / Q000378:metabolism
chemical_list: D002147:Calmodulin; D002118:Calcium