Analysis of H19 methylation in control and abnormal human embryos, sperm and oocytes
Résumé
ART is suspected to generate increased imprinting errors in the lineage. Following an ICSI (Intra Cytoplamic Sperm Injection) procedure, a certain number of embryos fail to develop normally and imprinting disorders may be associated to the developmental failure. To evaluate this hypothesis, we analysed the methylation profile of H19DMR, a paternally imprinting control region, in high graded blastocysts, in embryos showing developmental anomalies, in the matching sperm and in oocytes of the concerned couples when they were available. Significant hypomethylation of the paternal allele was observed in half the embryos, independently of the stage at which they were arrested (morula, compacted morula, pre blastocyst or BC graded blastocysts). Conversely, some embryos showed significant methylation on the maternal allele, whereas few others showed both, hypomethylation of the paternal allele and abnormal methylation of the maternal allele. The matching sperm at the origin of the embryos exhibited normal methylated H19 patterns. Thus, hypomethylation of the paternal allele in the embryos does not appear inherited from the sperm but likely reflects instability of the imprint during the demethylating process which occurred in the early embryo. Analysis of a few oocytes suggests that the defect in erasure of the paternal imprint in the maternal germ line may be responsible for the residual methylation of the maternal allele in some embryos. None of these imprinting alterations could be related to a particular stage of developmental arrest; compared to high grade blastocysts, embryos with developmental failure are more likely to have abnormal imprinting at H19 (p<0.05).
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