title: Ca(2+)(cyt) negatively regulates the initiation of oocyte maturation.
abstract: Ca(2+) is a ubiquitous intracellular messenger that is important for cell cycle progression. Genetic and biochemical evidence support a role for Ca(2+) in mitosis. In contrast, there has been a long-standing debate as to whether Ca(2+) signals are required for oocyte meiosis. Here, we show that cytoplasmic Ca(2+) (Ca(2+)(cyt)) plays a dual role during Xenopus oocyte maturation. Ca(2+) signals are dispensable for meiosis entry (germinal vesicle breakdown and chromosome condensation), but are required for the completion of meiosis I. Interestingly, in the absence of Ca(2+)(cyt) signals oocytes enter meiosis more rapidly due to faster activation of the MAPK-maturation promoting factor (MPF) kinase cascade. This Ca(2+)-dependent negative regulation of the cell cycle machinery (MAPK-MPF cascade) is due to Ca(2+)(cyt) acting downstream of protein kinase A but upstream of Mos (a MAPK kinase kinase). Therefore, high Ca(2+)(cyt) delays meiosis entry by negatively regulating the initiation of the MAPK-MPF cascade. These results show that Ca(2+) modulates both the cell cycle machinery and nuclear maturation during meiosis.
authors.affiliation: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, 4301 West Markham St., Slot 505, Little Rock, AR 72205, USA.
authors.forename: Lu
authors.initials: L
authors.lastname: Sun
authors.forename: Khaled
authors.initials: K
authors.lastname: Machaca
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D025461:Feedback, Physiological / Q000187:drug effects / Q000502:physiology; D005260:Female; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008540:Meiosis / Q000235:genetics*; D017232:Oncogene Proteins v-mos / Q000378:metabolism; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008941:Spindle Apparatus / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D018118:Chloride Channels; D017232:Oncogene Proteins v-mos; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium