Meiotic Maturation of the Mouse Oocyte Requires an Equilibrium between Cyclin B Synthesis and Degradation

AbstractAmong the proteins whose synthesis and/or degradation is necessary for a proper progression through meiotic maturation, cyclin B appears to be one of the most important. Here, we attempted to modulate the level of cyclin B1 and B2 synthesis during meiotic maturation of the mouse oocyte. We used cyclin B1 or B2 mRNAs with poly(A) tails of different sizes and cyclin B1 or B2 antisense RNAs. Oocytes microinjected with cyclin B1 mRNA showed two phenotypes: most were blocked in MI, while the others extruded the first polar body in advance when compared to controls. Moreover, these effects were correlated with the length of the poly(A) tail. Thus it seems that the rate of cyclin B1 translation controls the timing of the first meiotic M phase and the transition to anaphase I. Moreover, overexpression of cyclin B1 or B2 was able to bypass the dbcAMP-induced germinal vesicle block, but only the cyclin B1 mRNA-microinjected oocytes did not extrude their first polar body. Oocytes injected with the cyclin B1 antisense progressed through the first meiotic M phase but extruded the first polar body in advance and were unable to enter metaphase II. This suggested that inhibition of cyclin B1 synthesis only took place at the end of the first meiotic M phase, most likely because the cyclin B1 mRNA was protected. The injection of cyclin B2 antisense RNA had no effect. The life observation of the synthesis and degradation of a cyclin B1–GFP chimera during meiotic maturation of the mouse oocyte demonstrated that degradation can only occur during a given period of time once it has started. Taken together, our data demonstrate that the rates of cyclin B synthesis and degradation determine the timing of the major events taking place during meiotic maturation of the mouse oocyte

Meiotic Maturation of the Mouse Oocyte Requires an Equilibrium between Cyclin B Synthesis and Degradation

International audienceAmong the proteins whose synthesis and/or degradation is necessary for a proper progression through meiotic maturation, cyclin B appears to be one of the most important. Here, we attempted to modulate the level of cyclin B1 and B2 synthesis during meiotic maturation of the mouse oocyte. We used cyclin B1 or B2 mRNAs with poly(A) tails of different sizes and cyclin B1 or B2 antisense RNAs. Oocytes microinjected with cyclin B1 mRNA showed two phenotypes: most were blocked in MI, while the others extruded the first polar body in advance when compared to controls. Moreover, these effects were correlated with the length of the poly(A) tail. Thus it seems that the rate of cyclin B1 translation controls the timing of the first meiotic M phase and the transition to anaphase I. Moreover, overexpression of cyclin B1 or B2 was able to bypass the dbcAMP-induced germinal vesicle block, but only the cyclin B1 mRNA-microinjected oocytes did not extrude their first polar body. Oocytes injected with the cyclin B1 antisense progressed through the first meiotic M phase but extruded the first polar body in advance and were unable to enter metaphase II. This suggested that inhibition of cyclin B1 synthesis only took place at the end of the first meiotic M phase, most likely because the cyclin B1 mRNA was protected. The injection of cyclin B2 antisense RNA had no effect. The life observation of the synthesis and degradation of a cyclin B1-GFP chimera during meiotic maturation of the mouse oocyte demonstrated that degradation can only occur during a given period of time once it has started. Taken together, our data demonstrate that the rates of cyclin B synthesis and degradation determine the timing of the major events taking place during meiotic maturation of the mouse oocyte

CYCLINES B ET CONTROLE DE LA MATURATION MEIOTIQUE DE L'OVOCYTE DE SOURIS

CE TRAVAIL PORTE SUR LE ROLE DU METABOLISME DE LA CYCLINE B1 (UNE DES SOUS-UNITES DU MPF (M-PHASE PROMOTING FACTOR) DANS LA PROGRESSION DE LA MATURATION MEIOTIQUE DE L'OVOCYTE DE SOURIS. LES VARIATIONS DU TAUX DE CYCLINE B SONT PRIMORDIALES POUR LE CONTROLE DE L'ACTIVITE DU MPF. LA SUREXPRESSION DE LA CYCLINE B1 PERMET L'ENTREE EN PHASE M EN PRESENCE D'INHIBITEUR DE LA REPRISE DE MEIOSE. LE TAUX DE SYNTHESE DE LA CYCLINE B1 CONTROLE LA CINETIQUE D'ACTIVATION DU MPF, LA DUREE DE LA PREMIERE PHASE M DE MEIOSE ET LA TRANSITION METAPHASEI/ANAPHASEI. DE PLUS, UNE FENETRE TEMPORELLE DE DEGRADATION EXISTE EN FIN DE MI. SUFFISAMMENT DE CYCLINE B1 DOIT ETRE DEGRADEE PENDANT CETTE PERIODE POUR PERMETTRE LA SORTIE DE MI. UN EQUILIBRE PRECIS ENTRE LA SYNTHESE ET LA DEGRADATION DE CETTE PROTEINE EST DONC NECESSAIRE AU BON DEROULEMENT DE LA MATURATION MEIOTIQUE. NOUS AVONS MONTRE QU'UNE REGULATION POST-TRANSCRIPTIONNELLE DU NIVEAU DE SYNTHESE DE LA CYCLINE B1 EXISTE ET QU'UN OU DES FACTEUR(S) NUCLEAIRE(S) PRESENTS DANS L'OVOCYTE SERAIENT IMPLIQUES. L'INHIBITION DE LA SYNTHESE DE LA CYCLINE B1 PAR DES ARN ANTI-SENS DIRIGES CONTRE L'ARNM DE CYCLINE B1, N'EST POSSIBLE QU'EN FIN DE MI. CETTE INHIBITION TARDIVE SERAIT LIEE A UN MASQUAGE DE L'ARNM DE CYCLINE B1 PAR DES FACTEURS NON IDENTIFIES. DE PLUS, NOUS AVONS OBSERVE QUE LA TAILLE DE LA QUEUE POLY(A) DE L'ARNM CODANT POUR LA CYCLINE B1 POURRAIT ETRE RESPONSABLE DES VARIATIONS DU TAUX DE SYNTHESE DE LA CYCLINE B1. LA POLYADENYLATION JOUERAIT DONC UN ROLE IMPORTANT DANS LE CONTROLE DE LA SYNTHESE DE LA CYCLINE B1 CHEZ LA SOURIS. L'INHIBITION DE LA SYNTHESE DE LA CYCLINE B2 NE SEMBLE PAS PERTURBER LE BON DEROULEMENT DE LA MATURATION MEIOTIQUE. PAR CONTRE, SA SUREXPRESSION PERMET COMME POUR B1, LA REPRISE SPONTANEE DE LA MEIOSE EN PRESENCE D'INHIBITEUR DE LA REPRISE DE LA MEIOSE. MAIS LA CYCLINE B2 NE MODIFIE NI LA DUREE DE LA PREMIERE PHASE M DE MEIOSE NI SA SORTIE. SON ROLE EVENTUEL DANS LA MATURATION MEIOTIQUE RESTE A ELUCIDER.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Cyclin synthesis controls the progression of meiotic maturation in mouse oocytes.

International audienceTo study the mechanisms involved in the progression of meiotic maturation in the mouse, we used oocytes from two strains of mice, CBA/Kw and KE, which differ greatly in the rate at which they undergo meiotic maturation. CBA/Kw oocytes extrude the first polar body about 7 hours after breakdown of the germinal vesicle (GVBD), whilst the oocytes from KE mice take approximately 3-4 hours longer. In both strains, the kinetics of spindle formation are comparable. While the kinetics of MAP kinase activity are very similar in both strains (although slightly faster in CBA/Kw), the rise of cdc2 kinase activity is very rapid in CBA/Kw oocytes and slow and diphasic in KE oocytes. When protein synthesis is inhibited, the activity of the cdc2 kinase starts to rise but arrests shortly after GVBD with a slightly higher level in CBA/Kw oocytes, which may correspond to the presence of a larger pool of cyclin B1 in prophase CBA/Kw oocytes. After GVBD, the rate of cyclin B1 synthesis is higher in CBA/Kw than in KE oocytes, whilst the overall level of protein synthesis and the amount of messenger RNA coding for cyclin B1 are identical in oocytes from both strains. The injection of cyclin B1 messenger RNA in KE oocytes increased the H1 kinase activity and sped up first polar body extrusion. Finally, analysis of the rate of maturation in hybrids obtained after fusion of nuclear and cytoplasmic fragments of oocytes from both strains suggests that both the germinal vesicle and the cytoplasm contain factor(s) influencing the length of the first meiotic M phase. These results demonstrate that the rate of cyclin B1 synthesis controls the length of the first meiotic M phase and that a nuclear factor able to speed up cyclin B synthesis is present in CBA/Kw oocytes