DYNAMICS OF MORPHOFUNCTIONAL CHANGES IN AGING
BOVINE OVA DURING THE PROLONGED CULTURE IN VITRO
I.Yu. Lebedeva,* G.N. Singina, A.V. Lopukhov, N.A. Zinovieva
All-Russian Research Institute of Animal Husbandry, Podolsk—Dubrovitsy;
*e-mail: irledv@mail.ru
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.
Key words: oocytes, cumulus cells, aging of ova, first polar body, state of metaphase chromosomes,
spontaneous parthenogenetic activation
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