Age-associated changes in mouse oocytes during postovulatory in vitro culture: possible role for meiotic kinases and survival factor BCL2.
To elucidate molecular mechanisms underlying oocyte senescence, we investigated whether oocytes from female mice of advanced reproductive age exhibit a precocious postovulatory aging that, in turn, may be responsible for the precocious activation of an apoptotic program. During a 9-h in vitro culture, the frequency of oocytes showing MII aberrations, spontaneous activation, and cellular fragmentation increased in old oocytes (P < 0.05), whereas it did not change in the young group. In old oocytes, the activities of MPF (a complex of the cyclin-dependent kinase cdc2 and cyclin B1) and MAPK (mitogen-activated protein kinase) decreased precociously, showing a first drop as early as 3 h after the beginning of in vitro culture (P < 0.05). Immunoblotting and immunocytochemical analysis revealed that, in oocytes of the old group, reduction of BCL2 expression at protein level occurred earlier than in the young group (P < 0.05) and was not associated to the loss of BCL2 transcripts detected by RT-PCR. These changes are followed by an abrupt increase of the rate of TUNEL-positive oocytes after 24 h of culture to a value of 67% +/- 6%. Exposure of young oocytes to 20 microM roscovitine or 20 microM U0126, specific inhibitors of MPF and MAPK, resulted in the decreased percentage of oocytes showing positive immunostaining for BCL2 and in an increased rate of DNA fragmentation. Present results suggest that the developmental competence of oocytes ovulated by aging mice may be negatively influenced by a downregulation of MPF and MAPK activities that in turn induces the activation of a proapoptotic signaling pathway.
Tatone
Carla
C
Department of Biomedical Sciences and Technologies, University of L'Aquila, 67100 L'Aquila, Italy. ctatone@univaq.it
Carbone
Maria Cristina
MC
Gallo
Rita
R
Delle Monache
Simona
S
Di Cola
Mario
M
Alesse
Edoardo
E
Amicarelli
Fernanda
F
D000367:Age Factors; D000818:Animals; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002478:Cells, Cultured; D016922:Cellular Senescence; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008183:Luteal Phase / Q000502:physiology*; D008540:Meiosis; D000090204:Mesothelin; D051379:Mice; D008815:Mice, Inbred Strains; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046912:Multiprotein Complexes; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*
C534700:Ccnb1 protein, mouse; D019926:Cyclin B; D056744:Cyclin B1; D004791:Enzyme Inhibitors; C000715528:Msln protein, mouse; D046912:Multiprotein Complexes; D019253:Proto-Oncogene Proteins c-bcl-2; D016203:CDC2 Protein Kinase; D020928:Mitogen-Activated Protein Kinases; D000090204:Mesothelin