DNA methylation enables transposable element-driven genome expansion.

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• Eukaryotic genome size varies significantly, largely due to transposable elements (TEs).
• TEs can influence host gene regulation and contribute substantially to cellular DNA mass.
• Cytosine methylation of CpG dinucleotides is a key mechanism for suppressing TE activity.

Purpose of the Study:

• To investigate the role of DNA methylation in the long-term accommodation and expansion of TEs within eukaryotic genomes.
• To explore the relationship between TE content, genome size, and CpG methylation patterns.
• To understand how TE methylation influences their potential for acquiring regulatory functions.

Main Methods:

• Analysis of whole-genome sequences from 53 diverse eukaryotic organisms.
• Correlation analysis between genome size, TE percentage, and CpG observed/expected (O/E) ratios.
• Examination of TE distribution relative to genomic features like promoters, transcription start sites, and enhancers.

Main Results:

• A positive correlation was observed between genome size and the percentage of TEs across the studied organisms.
• A negative correlation was found between genome size and the CpG O/E ratio in both TEs and host DNA.
• TEs were less frequent at promoters and transcription start sites but enriched at enhancers, often bearing mutations from deamination.

Conclusions:

• DNA methylation of TEs is essential for their stable integration and subsequent genome expansion.
• The deamination of methylated cytosines in TEs leads to CpG loss and C-to-T mutations, facilitating regulatory role acquisition.
• TE methylation provides a mechanism for genome expansion and generates novel regulatory elements, impacting host gene control.