Methylation is maintained specifically at imprinting control regions but not other DMRs associated with imprinted genes in mice bearing a mutation in the Dnmt1 intrinsically disordered domain

Differential methylation of imprinting control regions in mammals is essential for distinguishing the parental alleles from each other and regulating their expression accordingly. To ensure parent of origin-specific expression of imprinted genes and thereby normal developmental progression, the differentially methylated states that are inherited at fertilization must be stably maintained by DNA methyltransferase 1 throughout subsequent somatic cell division. Further epigenetic modifications, such as the acquisition of secondary regions of differential methylation, are dependent on the methylation status of imprinting control regions and are important for achieving the monoallelic expression of imprinted genes, but little is known about how imprinting control regions direct the acquisition and maintenance of methylation at these secondary sites. Recent analysis has identified mutations that reduce DNA methyltransferase 1 fidelity at some genomic sequences but not at others, suggesting that it may function differently at different loci. We examined the impact of the mutant DNA methyltransferase 1 P allele on methylation at imprinting control regions as well as at secondary differentially methylated regions and non-imprinted sequences. We found that while the P allele results in a major reduction in DNA methylation levels across the mouse genome, methylation is specifically maintained at imprinting control regions but not at their corresponding secondary DMRs. This result suggests that DNA methyltransferase 1 may work differently at imprinting control regions or that there is an alternate mechanism for maintaining methylation at these critical regulatory regions and that maintenance of methylation at secondary DMRs is not solely dependent on the methylation status of the ICR.

[Regulation and mechanism of miR-148a on cardiomyocyte differentiation induced by 5-aza in mesenchymal stem cells]

OBJECTIVE

To investigate the expression of miR-148a in the process of myocardial differentiation of human mesenchymal stem cells (hMSCs) induced by 5-azacytidine (5-aza) and study the effects of miR-148a on myocardial differentiation of hMSCs.

METHODS

The immunofluorescence analysis was used to detect the expressions of the associated mark genes of cardiac specific protein (α-MHC) in the process of myocardial differentiation of hMSCs induced by 5-aza. qRT-PCR and Western blot were used to analysis the expressions of miR-148a and DNA methyltransferase 1 (DNMT1) after myocardial differentiation of hMSCs, respectively. The expression of α-MHC after transfection with synthetic miR-148 mimics and miR-148a inhibitor was examined by Western blot. We used bioinformatics analysis to predict the potential target of miR-148a, and the dual luciferase report gene system was used to verify the predication. After co-transfected with DNMT1 shRNA and miR-148a inhibitors, hMSCs were used to explore the regulatory role and mechnism of miR-148a in the process of myocardial differentiation of hMSCs.

RESULTS

α-MHC was increased significantly after induced by 5-azacytidine. miR-148a was increased significantly in cardiomyocyte differentiation of hMSCs, while the gene and protein expression levels of DNMT1 were decreased significantly in this progress (P<0.01). The expression of α-MHC was up-regulated significantly in hMSCs when miR-148a was induced into cardiomyocyte differentiation and overexpressed. Instead, downregulation of miR-148a suppressed α-MHC expression (P<0.01). Knockdown of DNMT1 blocked the role of miR-148a in differentiation of hMSCs.

CONCLUSIONS

miR-148a was upregulated in cardiomyocyte differentiation of hMSCs, and miR-148a promoted myocardial differentiation of hMSCs via targeting DNMT1.