The Relationship Between Acetylation Of Histone In Human Oocytes And Advanced Maternal Age

Objective:With the development of the society, the number of older women seeking for fertility treatment increases gradually. The compromised quality of oocytes from older women is the one of factors associated with the age-related poor fertile ability. Oocytes of decline quality are known to have reduced developmental competence and to be extremely prone to aneuploidy. Although the studies of mitosis and meiosis suggest that defective remodeling of chromatin plays a causative role in aneuploidy, the exact mechanisms and the specific genes/proteins involved are still unknown. During the process of oocytes growth, the dynamic changes of acetylation/ deacetylation of histone H3, H4 participate in the regulation of the chromatin structure and gene expression. However, whether these processes are related to the proper segregation of chromosomes in meiotic, there is no definite conclusion from current studies. This research adopts cell immunofluorescence technique, analyzing the histone acetylation status changes of H3K9 and H4K12 during each stage of human oocytes development, in order to find out if the defective epigenetic regulation is related to maternal age and leads to segregation errors.Methods:This study collected abandoned oocytes of different meiotic maturation stages [germinal vesicle (GV)(209), metaphase (M)I(124) and MII(111)] from 160 patients of The First People Hospital of Yunnan Province, Department of Reproduction, who are on standard IVF/ICSI treatment. This research adopted cell immunofluorescence technique, epifluorescence microscopy, laser confocal technique in order to analyze acetylation status changes of histone H3K9 and H4K12 during each oocyte development period, and the relationship between acetylation status of MII period oocyte histone, microtubule structure and the arrangement of chromosomes.Results:Human GV oocytes had an intense staining of the chromatin for both histone 3 1ysine9 and histone 4 lysine 12 acetylations. About 50%of the MI oocytes’ acetylation level has been lowered. Approximately 48.4%of MII stage oocytes histone H4K12 acetylation showed weak or no staining. The staining of the histone H3K9 acetylation is barely detected in MII oocytes. The histone acetylation level of MII oocyte in the older age group is higher than those in the younger age group (62.8% vs 37.9%, P=0.047). The age of women significantly correlated with the histone acetylation level of MII oocyte (r=0.975, P=0.013). In the group of MII oocytes which is in the status of abnormal chromosome arrangement,88%of the oocytes showed high level of histone H4K12 acetylation and only 33%showed completely deacetylation status (P<0.001). Human MII oocytes exposed at room temperature (25 ℃) results in high acetylation level of histone H4K12. Residual H4K12 acetylation was more frequently found in oocytes obtained from multipronuclear human zygotes group (58.3%vs.30.0%, P= 0.011).Conclusion:We conclude that defective deacetylation during human female meiosis increases with maternal age and is correlated with misaligned chromosomes. As chromosome misalignment predisposes to segregation errors, our data imply that defective regulation of histone deacetylation could be an important factor in age-related aneuploidy. Moreover, roomd temperature exposal will lead to the high level of defect H4K12 deacetylation in MII oocytes. According to the data from IVF treatment, we suggest that defective regulation of histone deacetylation could be an important factor in multipronuclear human zygotes.