Aberrant DNA methylation of imprinted loci in superovulated oocytes.
BACKGROUND
There is an increased incidence of rare imprinting disorders associated with assisted reproduction technologies (ARTs). The sex-specific epigenetic modifications that are imposed during gametogenesis act as a primary imprint to distinguish maternal and paternal alleles. The most likely candidate for the gametic mark is DNA methylation. However, the timing of DNA methylation acquisition in adult oocytogenesis and the effects of superovulation are unknown.


METHODS
We examined the maternal methylation of PEG1(MEST), LIT1(KCNQ1OT1) and ZAC(PLAGL1) and the paternal methylation of H19 in adult growing oocytes of humans and mice and compared them with the methylation status of mouse neonatal growing oocytes by using bisulphite sequencing. Furthermore, we examined the effects of superovulation in the human and mouse.


RESULTS
Maternal methylation of these genes has already been initiated to some extent in adult human and mouse non-growing oocytes but not in mouse neonates. In addition, the methylation dynamics during adult human and mouse oocyte development changed more gradually than those during neonatal oocyte development. Furthermore, we found the demethylation of PEG1 in growing oocytes from some ART-treated infertile women and a gain in the methylation of H19. We also detected methylation changes in superovulated mice.


CONCLUSIONS
Our studies in the human and mouse suggest that superovulation can lead to the production of oocytes without their correct primary imprint and highlight the need for more research into ARTs.
Sato
A
A
St Luke Clinic, Tsumori, Oita, Japan.
Otsu
E
E
Negishi
H
H
Utsunomiya
T
T
Arima
T
T
D000328:Adult; D000818:Animals; D000831:Animals, Newborn; D018797:Cell Cycle Proteins / Q000235:genetics; D019175:DNA Methylation; D005260:Female; D018392:Genomic Imprinting / Q000502:physiology*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D009865:Oocytes / Q000737:chemistry / Q000378:metabolism*; D010062:Ovulation Induction / Q000009:adverse effects; D016133:Polymerase Chain Reaction; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D011506:Proteins / Q000235:genetics; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects*; D013480:Superovulation / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics
D018797:Cell Cycle Proteins; C094335:H19 long non-coding RNA; C485621:KCNQ1OT1 long non-coding RNA, human; D008565:Membrane Proteins; C106464:PLAGL1 protein, human; D024642:Potassium Channels, Voltage-Gated; D011506:Proteins; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C103637:mesoderm specific transcript protein