CTCF maintains differential methylation at the Igf2/H19 locus

Area of Science:

• Genetics
• Epigenetics
• Molecular Biology

Background:

• Genomic imprinting involves parental-specific DNA methylation controlling allele expression.
• CTCF protein binds to imprinting control regions (ICRs) of Igf2 and H19 genes.
• CTCF's role in establishing and maintaining allelic methylation in vivo is not fully understood.

Purpose of the Study:

• To investigate the in vivo function of CTCF in regulating DNA methylation and gene expression at the Igf2/H19 imprinting control region (ICR).
• To determine if CTCF binding is necessary for establishing the unmethylated maternal ICR during oogenesis.
• To elucidate CTCF's role in enhancer-blocking activity and gene transcription at the Igf2/H19 locus.

Main Methods:

• Utilized mice with point mutations in all four CTCF binding sites within the ICR.
• Analyzed DNA methylation patterns of mutant ICRs in oocytes, blastocysts, and neonatal mice.
• Assessed gene expression of Igf2 and H19 on maternal chromosomes with mutant ICRs.

Main Results:

• Maternally transmitted mutant ICRs showed heterogeneous methylation in neonatal mice, but were unmethylated in oocytes and blastocysts.
• CTCF binding is not required for establishing the unmethylated maternal ICR.
• Mutant ICRs lost enhancer-blocking activity, leading to Igf2 activation and reduced H19 expression on maternal chromosomes.

Conclusions:

• CTCF plays essential roles in maintaining allelic methylation and regulating gene expression at the Igf2/H19 locus in vivo.
• CTCF is required for the enhancer-blocking activity of the maternal ICR.
• CTCF positively influences maternal H19 transcription.