[Dynamics of morphofunctional changes in aging bovine ova during the prolonged culture in vitro]

In the absence of activating stimuli, aging processes are initiated in matured mammalian oocytes, which negatively affect the quality of ova and their capacity for further development. On the model of the prolonged culture of bovine oocytes, the dynamics of a number of morphofunctional changes associated with the postovulatory aging was investigated in the present work. In cumulus-enclosed oocytes, migration of the first polar body relative to metaphase II chromosomes started between 18 and 22 h of maturation. The angle of the body deviation from the metaphase plate rose as the culture time increased to 30 h. By 32 h of culture, a gain in the rate of ova with the abnormal chromosome morphology was observed that continued up to 56 h. Furthermore, after 56 h, signs of spontaneous parthenogenetic activation were revealed in 16 percent of matured oocytes. During the prolonged culture of oocytes deprived of cumulus cells after 20 h of maturation, an increase in the frequency of chromosomal abnormalities was found only by 44 h. At the same time the cumulus elimination did not affect the maintenance of the meiosis II blockade in aging ova. Meanwhile, destructive chromosomal changes in oocytes were attended by a gradual rise in the level of apoptotic degeneration and reduction in the proliferative activity of surrounding cumulus cells. The results obtained point to the various temporal dynamics of distinct morphofunctional changes and to the participation of cumulus cells in modulation of the speed of metaphase chromosome destructive modifications in aging bovine ova.