Control of metaphase I formation in Xenopus oocyte: effects of an indestructible cyclin B and of protein synthesis.
A cytological analysis was performed in order to determine how the formation of the metaphase I- and metaphase II-spindles is dependent upon p34cdc2 kinase activity and protein synthesis during the meiotic maturation of Xenopus oocytes. The p34cdc2 kinase activity increases abruptly during the prophase-prometaphase I transition, then drops to a minimum level at the metaphase I/anaphase I transition and further increases again until reaching a maximum stable level at metaphase II. The injection of an indestructible cyclin B into oocytes arrests the maturation process at the onset of anaphase I and prevents the re-increase of p34cdc2 activity which accompanies normal entry into metaphase II. Inhibition of protein synthesis between the germinal vesicle breakdown and the onset of metaphase I spindle induces exit from M-phase and leads to an 'interphase-like' state characterized by the organization of nuclear-like structures. In contrast, inhibition of protein synthesis at metaphase II stage does not affect the metaphase II spindle nor p34cdc2 activity, indicating that metaphase I- and metaphase II-spindles are not regulated by the same effectors. When protein synthesis is inhibited before induction of M-phase by MPF transfer, it prevents the formation of the metaphase I spindle, despite a transient elevated level of p34cdc2 activity. To dissociate the role of protein synthesis and of p34cdc2 kinase activity, the indestructible cyclin B was microinjected in the absence of protein synthesis. This allows the in vivo maintenance of a stable p34cdc2 activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Huchon
D
D
Laboratoire de Physiologie de la Reproduction, INRA/CNRS-URA 1449, Université P et M Curie, Paris, France.
Rime
H
H
Jessus
C
C
Ozon
R
R
D000705:Anaphase / Q000502:physiology; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D016922:Cellular Senescence / Q000502:physiology; D016213:Cyclins / Q000494:pharmacology*; D004527:Egg Proteins / Q000096:biosynthesis*; D005260:Female; D007399:Interphase / Q000502:physiology; D016200:Maturation-Promoting Factor / Q000378:metabolism; D008540:Meiosis / Q000502:physiology; D008677:Metaphase / Q000187:drug effects*; D009865:Oocytes / Q000166:cytology / Q000187:drug effects*; D008941:Spindle Apparatus / Q000502:physiology; D014982:Xenopus laevis
D016213:Cyclins; D004527:Egg Proteins; D016203:CDC2 Protein Kinase; D016200:Maturation-Promoting Factor