Studies on Timing of the Oocyte Maturation Progression in Maturation of the Mouse Oocyte in Vitro

For the aim of clarifying oocyte maturation process in mammalian oocyte, we have studied the patterns of the germinal vesicles breakdown according to the stage of nuclear changes after various periods of culture.As the culture time was prolonged, the germinal vesicles breakdown were significantly increased and after nine hours of culture, 14% of the oocytes were in metaphase II. After 12 and 16 hours of culture, the germinal vesicles break down occurred 35% and 54% respectively.The oocytes of metaphase II were significantly accumulated after 9 hours of culture.Each steps of the meiotic division appeared to be asynchrony in maturation of oocytes in vitro.We have found that in vitro mouse oocyte can be occurred spontaneous maturation without the gonadotropin stimulation.