Hydroxymethylation is uniquely distributed within term placenta, and is associated with gene expression.

Area of Science:

• Epigenetics
• Genomics
• Gene Expression Regulation

Background:

• Cytosine modifications, including 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), play crucial roles in regulating gene expression.
• 5hmC is a derivative of 5mC with potentially distinct regulatory functions.
• Understanding the distribution and role of these modifications in the placenta is vital for developmental biology and disease research.

Purpose of the Study:

• To investigate the distribution and gene expression associations of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in the human placenta.
• To characterize the genomic landscape of 5hmC, particularly its relationship with enhancers and gene activity.

Main Methods:

• Parallel processing of genomic DNA using bisulfite and oxidative bisulfite conversion.
• RNA sequencing to assess gene expression.
• Integration of epigenetic modification data with enhancer marks (H3K27ac, H3K4me1) and gene transcription levels.

Main Results:

• Identified approximately 21,000 loci with consistently elevated 5hmC levels in the term placenta.
• Observed absence of 5hmC in CpG islands and enrichment in poised enhancers, with depletion in active enhancers.
• Found 5hmC and 5mC elevated in transcriptionally silent genes, while 5hmC showed a positive association with transcription only in actively transcribed genes.

Conclusions:

• Dynamic cytosine regulation, including 5hmC, is uniquely distributed within the term placenta and is associated with gene expression.
• These findings provide a comprehensive epigenomic landscape of the human placenta, valuable for future research.
• 5hmC's distinct distribution and association with specific regulatory elements and gene activity suggest a unique role in placental function.