Ca(2+) oscillations promote APC/C-dependent cyclin B1 degradation during metaphase arrest and completion of meiosis in fertilizing mouse eggs.
Cyclin B1, the regulatory component of M phase-promoting factor (MPF), is degraded during the metaphase-anaphase transition in an anaphase-promoting complex/cyclosome (APC/C)-dependent process. MPF activity is stable in eggs, and a sperm-triggered Ca(2+) signal is needed to promote cyclin degradation. In frogs, a single Ca(2+) spike promotes cell cycle resumption, but, in mammals, the Ca(2+) signal is more complex, consisting of a series of spikes that stop several hours after sperm fusion. Using dual imaging in mouse eggs, we have examined how the Ca(2+) signal generates cyclin B1 destruction using destructible and nondestructible GFP-tagged constructs. APC/C activity was present in unfertilized eggs, giving cyclin B1 a half-life of 1.15 +/- 0.28 hr. However, APC/C-dependent cyclin degradation was elevated 6-fold when sperm raised cytosolic Ca(2+) levels above 600 nM. This activation was transitory since cyclin B1 levels recovered between Ca(2+) spikes. For continued cyclin degradation at basal Ca(2+) levels, multiple spikes were needed. APC/C-mediated degradation was observed until eggs had completed meiosis with the formation of pronuclei, and, at this time, Ca(2+) spikes stopped. Therefore, the physiological need for a repetitive Ca(2+) signal in mammals is to ensure long-term cyclin destruction during a protracted exit from meiosis.
Nixon
Victoria L
VL
Department of Physiological Sciences, The Medical School, Framlington Place, University of Newcastle, Newcastle NE2 4HH, United Kingdom.
Levasseur
Mark
M
McDougall
Alex
A
Jones
Keith T
KT
D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002453:Cell Cycle; D019926:Cyclin B / Q000235:genetics / Q000378:metabolism*; D056744:Cyclin B1; D004789:Enzyme Activation; D005260:Female; D005306:Fertilization / Q000502:physiology*; D049452:Green Fluorescent Proteins; D008025:Ligases / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D008540:Meiosis / Q000502:physiology*; D000090204:Mesothelin; D008677:Metaphase / Q000502:physiology; D051379:Mice; D010063:Ovum / Q000201:enzymology / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology; D043743:Ubiquitin-Protein Ligase Complexes
C534700:Ccnb1 protein, mouse; D019926:Cyclin B; D056744:Cyclin B1; D008164:Luminescent Proteins; C000715528:Msln protein, mouse; D049452:Green Fluorescent Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D008025:Ligases; D000090204:Mesothelin; D002118:Calcium