Transcription driven somatic DNA methylation within the imprinted Gnas cluster

Area of Science:

• Epigenetics
• Genomic Imprinting
• DNA Methylation

Background:

• Genomic imprinting involves differential DNA methylation in female and male gametes, crucial for gene expression regulation.
• In oocytes, transcription across differentially methylated regions (DMRs) is often required for de novo methylation.
• At the Gnas cluster, oocyte-specific Nesp transcription drives methylation of intragenic DMRs, regulating Gnas and Gnasxl expression.

Purpose of the Study:

• To investigate the effects of ectopic Nesp transcription on the paternal Gnas cluster in mouse models.
• To determine if transcription-driven DNA methylation occurs outside the germline.

Main Methods:

• Utilized mutant mouse models with altered Nesp transcription patterns.
• Analyzed DNA methylation status of DMRs within the Gnas cluster.
• Assessed Gnas and Gnasxl transcript expression levels.

Main Results:

• Ectopic Nesp transcription on the paternal allele induced de novo methylation of the Exon1A DMR in somatic cells post-fertilization.
• This methylation event led to Gnas de-repression, mirroring maternal allele regulation.
• Gnasxl expression was repressed, and the affected paternal Gnas cluster became 'maternalized' in its expression profile.

Conclusions:

• Demonstrates the first instance of transcription-driven de novo DNA methylation of an intragenic CpG island in mouse somatic tissues.
• Suggests that transcription-driven methylation is not exclusively confined to the germline.
• Ectopic Nesp expression in males can reprogram paternal Gnas cluster imprinting, leading to altered phenotypes.