title: Block of CDK1-dependent polyadenosine elongation of Cyclin B mRNA in metaphase-i-arrested starfish oocytes is released by intracellular pH elevation upon spawning.
abstract: Meiotic progression requires the translation of maternal mRNAs in a strict temporal order. In isolated animal oocytes, translation of maternal mRNAs containing a cytoplasmic polyadenylation element (CPE), such as cyclin B, is activated by in vitro stimulation of meiotic resumption which induces phosphorylation of CPEB (CPE-binding protein) and elongation of their polyadenosine (poly(A)) tails; whether or not this model can be applied in vivo to oocytes arrested at metaphase of meiosis I in ovaries is unknown. In this study, we found that active CDK1 (cyclin-dependent kinase 1) phosphorylated CPEB in ovarian oocytes arrested at metphase I in the starfish body cavity, but phosphorylation of CPEB was not sufficient for elongation of cyclin B poly(A) tails. Immediately after spawning, however, mRNA was polyadenylated, suggesting that an increase in intracellular pH (pHi ) upon spawning triggers the elongation of poly(A) tails. Using a cell-free system made from maturing oocytes at metaphase I, we demonstrated that polyadenylation was indeed suppressed at pH below 7.0. These results suggest that a pH-sensitive process, functioning after CPEB phosphorylation, is blocked under physiologically low pHi (<7.0) in metaphase-I-arrested oocytes. The increase in pHi (>7.0) that occurs after spawning triggers polyadenylation of cyclin B mRNA and progression into meiosis II.
authors.affiliation: Department of Biological Sciences, Ochanomizu University, Tokyo, Japan.
authors.forename: Hiroe
authors.initials: H
authors.lastname: Ochi
authors.affiliation: Department of Biological Sciences, Ochanomizu University, Tokyo, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Aoto
authors.affiliation: Laboratory of Cell and Developmental Biology, Graduate School of Bioscience, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Tachibana
authors.affiliation: Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Hara
authors.affiliation: Department of Biological Sciences, Ochanomizu University, Tokyo, Japan.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Chiba
mesh_terms: D000241:Adenosine / Q000378:metabolism; D000818:Animals; D016203:CDC2 Protein Kinase / Q000502:physiology*; D019926:Cyclin B / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D042541:Intracellular Space / Q000378:metabolism; D008018:Life Cycle Stages; D008540:Meiosis / Q000502:physiology; D008677:Metaphase / Q000502:physiology*; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D009866:Oogenesis / Q000502:physiology; D026723:Polyadenylation / Q000235:genetics; D011108:Polymers / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013215:Starfish / Q000502:physiology
chemical_list: D019926:Cyclin B; D011108:Polymers; D012333:RNA, Messenger; C069424:polyadenosine; D016203:CDC2 Protein Kinase; D000241:Adenosine