Abstract: In mouse, matured oocytes are arrested at metaphase-Ⅱ (MⅡ) after ovulation. If the MⅡ oocytes are not fertilized on time, they will increasingly become aged in the oviduct. The aging of oocytes can lead to abnormal development of embryos. So it is important to study the mechanism of oocyte aging. Herein, we studied the change of oocyte chromosome after ovulation into the oviduct in vivo. Results indicated that 65% of old oocytes (34 h post hCG) showed aberrant MII, with chromosome misalignment and dispersal, in contrast to the young oocytes (14 h post hCG). In addition, chromosome changes may be associated with the increase of acetylation of histone 3 and histone 4, at lysine 14 and lysine 16 (H3K14 and H4K16), respectively. On the other hand, the decrease of methylation of histone 3 at lysine 9 (H3K9) presumably facilitated aberrant chromosome formation.

Key words: oocyte, aging, chromosome, histone, acetylation, methylation