title: Cell cycle progression of parthenogenetically activated mouse oocytes to interphase is dependent on the level of internal calcium.
abstract: Nuclear maturation of the mouse oocyte becomes arrested in metaphase of the second meiotic division (MII). Fertilization or parthenogenetic activation induces meiotic completion, chromosomal decondensation and formation of a pronucleus. This completion of meiosis is probably triggered by a transient increase in cytosolic calcium ions. When activated just after ovulation by a low concentration of the calcium ionophore A23187, the majority of the mouse oocytes go through a metaphase to anaphase transition and extrude their second polar body but they do not proceed into interphase; instead their chromatids remain condensed and a microtubular metaphase spindle reforms (metaphase III). However, a high percentage of these oocytes will undergo a true parthenogenetic activation assessed by the formation of a pronucleus, when exposed to a higher concentration of the calcium ionophore. The capacity of the mouse oocyte to pass into metaphase III is lost with increasing time post-ovulation. Direct measurement of intracellular calcium with Fura-2 reveals higher levels of cytosolic calcium in aged oocytes and/or using higher concentrations of calcium ionophore for activation. It is concluded that the internal free calcium level determines the transition to interphase.
authors: Department of Anatomy, University of Cambridge, England.
authors: C
authors: C
authors: Vincent
authors: T R
authors: TR
authors: Cheek
authors: M H
authors: MH
authors: Johnson
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000008:administration & dosage; D002118:Calcium / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D005089:Exocytosis; D005260:Female; D066298:In Vitro Techniques; D007399:Interphase / Q000502:physiology; D008540:Meiosis / Q000502:physiology; D008677:Metaphase / Q000502:physiology; D051379:Mice; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D010312:Parthenogenesis / Q000502:physiology
chemical_list: D000001:Calcimycin; D002118:Calcium