The role of methylation, DNA polymorphisms and microRNAs on HLA-G expression in human embryonic stem cells.

The human leukocyte antigen (HLA)-G gene seems to play a pivotal role in maternal tolerance to the fetus. Little is known about HLA-G expression and its molecular control during in vivo human embryogenesis. Human embryonic stem cells (hESC) provide an interesting in vitro model to study early human development. Different studies reported discrepant findings on whether HLA-G mRNA and protein are present or absent in hESC. Several lines of evidence indicate that promoter CpG methylation and 3' untranslated region (3'UTR) polymorphisms may influence HLA-G expression. We investigated how HLA-G expression is linked to the patterns of promoter methylation and explored the role of the 3'UTR polymorphic sites and their binding microRNAs on the post-transcriptional regulation of HLA-G in eight hESC lines. We showed that, while the gross expression levels of HLA-G are controlled by promoter methylation, the genetic constitution of the HLA-G 3'UTR, more specifically the 14bp insertion in combination with the +3187A/A and +3142G/G SNP, plays a major role in HLA-G mRNA regulation in hESC. Our findings provide a solid first step towards future work using hESC as tools for the study of early human developmental processes in normal and pregnancy-related disorders such as preeclampsia.