38: Loss of imprinting in first trimester human placentas

Article Outline

• Objective
• Study Design
• Results
• Conclusion
• Copyright

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Objective 

To investigate patterns of imprinting in first trimester human placentas.

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Study Design 

Using samples of 17 1st trimester placentas and 14 term placentas from uncomplicated pregnancies, we assessed loss of imprinting (LOI) at the RNA level in a panel of 13 genes known to be imprinted in the placenta. By applying a quantitative allele-specific PCR that relies on a common single nucleotide polymorphism (SNP) in the transcript appearing in the heterozygous form, we compared 1st trimester placentas to term placentas. We genotyped them for SNPs in the genes known to be imprinted in the placenta. We assessed LOI in 13 imprinted genes using a quantitative allele-specific PCR analysis of RT-PCR products for those genes containing SNPs. This method is not limited to a particular epigenetic mechanism. It has sensitivity of <1%. Of the genes that contained usable SNPs in the transcripts, we measured LOI in 167 gene heterozygosities of 31 placentas.

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Results 

There is loss of imprinting (ie bi-allelic expression) in all 13 genes in 1st trimester placentas as compared to term.

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• Loss of Imprinting in First Trimester Placentas

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Conclusion 

Our results show that LOI is more common in 1st trimester placentas than in term human placentas. This is the first biological observation suggesting that genetic imprinting is not completely established and occurs beyond the 1st trimester of pregnancy. Genes like CD44, MEG3, PLAGL1, DLK1, H19 and SNRPN show appreciable rates of LOI in the1st trimester placentas, but become totally imprinted by the 3d trimester of human gestation. Our findings also suggest that many mechanisms, rather then methylation alone, might be responsible for imprinting in the placenta.