| Aim To study the error occurred in the first meiosis of oocytes and explore the possible reason of age and folate metabolize related aneuploidy.Methods The unfertilized human oocytes were fixed 1-2days after oocyte retrieval and spectral karyotyping(SKY) was performed.Spindle and chromosome configuration as well as karyotype of chromosome 16 was examined in mouse oocytes aged 0～72h after oocyte retrieval by immunocytochemistry and fluorescence in situ hybridization(FISH).Spindle and chromosome configuration was examined in dayl unfertilized human oocytes after IVF and ICSI by immunocytochemistry.The expression of mitogen activated protein kinase (MAPK) was detected in mouse oocytes with different maternal age by immunocytochemistry and confocal microscopy.To explore the relationship between genetic polymorphisms in methylenetetrahydrofolate reductase(MTHFR),methionine synthase reductase(MTRR),the central enzymes in folate metabolism that affects DNA methylation and synthesis,and the risk of Down syndrome.Results Of 44 oocytes with SKY results,64%of oocytes were normal,36%of oocytes were aneuploidy,of which 22%were due to nondisjunction(NDJ) and 14% unbalanced predivision(UBP).Balanced predivision(BP) was found in 24(55%) oocytes. BP occurred only in 7%of newly ovulated mouse oocytes,in oocytes cultured 24h,48h and 72h in vitro,BP was 32%,51%and 62%,respectively,with the significant difference between them(P＜0.01 and P＜0.001).The abnormal spindle and chromosome configuration in newly ovulated mouse oocytes was 9%,while it increased to 63%,83%and 98%in oocytes after 24h,48h and 72h culture in vitro,respectively(P＜0.001).Statistically significant differences were observed on normal spindle and chromosome configurations of oocytes between 25-29 maternal age group(33%and 31%,respectively),and 30-34 age group(12%and 9%,respectively,P＜0.05,P＜0.025) as well as 35-40 age group(0%, P＜0.01).The expression of ERK1/2 was(78.21±13.34) in oocytes of 6-8 week mouse, much higher than that of 45-50 week mouse(61.45±15.67 P＜0.05).It was obvious difference between experiment and control grc,up in MTHFR gene C677T mutation allele (T),MTRR gene A66G mutation allele(G) frequency(p＜0.05,for both),MTHFR 677 TT and CC had obvious difference(p＜0.05).Conclusion NDJ,UBP and BP are three mechanisms of oocyte aneuploidy.BP can also occur during postovulatory ageing,which may be related to change of spindle and chromosome configuration.Incidence of abnormal spindle and chromosome configuration in oocytes is related to maternal age,which may be due to the decrease expression of MAPK in aged oocytes.High incidence of abnormal spindle and chromosomal configuration in oocytes with advanced maternal age could be an important reason of age related oocyte aneuploidy.MTHFR and MTRR gene mutation allele are related to Down syndrome,CT,TT,GG gene mutation type increased the risk of Down syndrome and CC type perhaps were the protective factor in decreasing the risk of Down syndrome. |
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