Question

A research study involving humans has shown that maternal anxiety during pregnancy can decrease the methylation of the ICR located between the H19 gene and the Igf2 gene. How would this decrease affect the expression of the maternal and paternal alleles that the offspring carries? Would you expect the decrease to affect growth?

Answer 1

Compelling evidence suggests that maternal mental health in pregnancy can influence fetal development. The imprinted genes, insulin-like growth factor 2 (IGF2) and H19, are involved in fetal growth and each is regulated by DNA methylation. This study aimed to determine the association between maternal mental well-being during pregnancy and differentially methylated regions (DMRs) of IGF2 (DMR0) and the IGF2/H19 imprinting control region (ICR) in newborn offspring.

Birth weight and sex modified the association between prenatal anxiety and infant methylation. When stratified into lower and higher birth weight groups using the median birth weight, there was a stronger association between anxiety and ICR methylation in the lower birth weight group, with no association in the higher birth weight group. When stratified by infant sex, there was a stronger association in female infants and no association in males. All the linear regression models were adjusted for maternal age, smoking and folate intake. These findings show that maternal anxiety in pregnancy is associated with decreased IGF2/H19 ICR DNA methylation in progeny at birth, particularly in female, low birth weight neonates. ICR methylation may help link poor maternal mental health and adverse birth outcomes, but further investigation is needed.

The H19/Igf2 imprinting control region (ICR) functions as an insulator exclusively in the unmethylated maternal allele, where enhancer-blocking by CTCF protein prevents the interaction between the Igf2 promoter and the distant enhancers. DNA methylation inhibits CTCF binding in the paternal ICR allele.

Allele-specific gene expression by Sequenom SNuPE- Allele-specific H19 and Igf2 RNA gene expression analysis was based on SNPs between of inbred 129S1 and CAST/Ei (CS) mouse strains and was analyzed by reverse-transcription PCR SNuPE assays, except mass spectrometry quantified the extension primers (EP) based on molecular mass difference between alleles. Amplified samples were spotted onto a 384 SpectroCHIP Array. Automated spectra acquisition was performed in a MassArray Compact mass spectrometer (Sequenom) using the Spectroacquire program (Sequenom) and was analyzed by MassArray Typer v3.4. We applied skew correction using a true heterozygote DNA sample to correct for any allelic imbalance in the SNP allele products. The % expression of each allele in the total expression was calculated at each given SNP.

In the kidney and liver of perinatal fetuses, H19 levels were more than 2-fold than in normal siblings and H19 was biallelically expressed indicating that, unlike the fully methylated ICR, the hypomethylated (mChbGI)2 was not capable of inactivating the H19 promoter in the paternal allele during post-fertilization development. Contrary to the (ChbGI)2, the (mChbGI)2 did not overactivate the H19 in the paternal allele relative to the maternal allele. The paternal and maternal H19 alleles each contributed 50% of total H19 expression. This suggests that USF and VEZF1 proteins in the (ChbGI)2 were responsible for overactivating H19 in cis.