Molecular Control Of Aging And Fate Of The First Polar Bodies Of Mouse Oocytes

In most mammals, matured oocytes are arrested at metaphase-II, and will not resume meiosis until they are activated by penetrating spermatozoa or other stimulations. If not fertilized or activated timely, the MII oocytes will undergo aging. Aged and non-aged oocytes are identical in morphology but the molecular changes occurring in the cytoplasm are different. During aging of oocytes, first polar bodied (FPB) move, degenerate and disappear at last. These changes would affect the success of some embryo technologies (such as animal cloning and intracytoplasmic sperm injection). It is therefore necessary to investigate the molecular changes during oocyte aging and the fate of FPB. In this study, timing of formation, deviation and degeneration of FPB, changes in parthenogenetic activation and the activity of MPF during in vivo and in vitro aging of both in vivo and in vitro matured mouse oocytes were studied, and the control of oocyte aging was attempted with Caffeine and Sodium Vanadate. The results are summarized as follows:1. Oocytes started FPB extrusion at 8 h post hCG during in vivo maturation, and the number of FPB reached maximum 10 h post hCG, and some FPB degenerated at ovulation. All FPB degenerated at 20 h post hCG and most FPB disappear at 32 h post hCG. 2. During in vitro maturation, Oocytes started FPB extrusion at 8 h of culture, and the number of FPB reached maximum at 14h of culture. Some FPB began to degenerate at 10 of culture, and all FPB degenerated 34 h of culture but few disappeared by this time.3. During in vivo and in vitro aging of both in vivo and in vitro matured mouse oocytes, the distance between FPB and the spindle increased with time and PVS enlargement. 4. Even if put in the relative still conditions in vitro, FPB deviated, but they migrated more slowly in the in vitro matured oocytes than in the in vivo matured. Ovulation and denudation performed after FPB extrusion markedly enhanced its deviation.5. During in vivo and in vitro aging of the in vivo matured oocytes, the activation rate of the oocytes increased and the activity of MPF decreased.