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Long-term experimental evolution reveals purifying selection on piRNA-mediated control of transposable element
Ulfar Bergthorsson1, Caroline J Sheeba2,3, Anke Konrad1,4
1Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, 77845, USA.
BMC Biology
|November 7, 2020
Summary
Natural selection maintains low transposable element (TE) expression in C. elegans. Small population sizes accelerate TE expression by disrupting piRNA silencing, revealing TE dynamics and epigenomic regulation.
Area of Science:
- Genomics
- Evolutionary Biology
- Molecular Biology
Background:
- Transposable elements (TEs) are widespread in eukaryotic genomes.
- Piwi-interacting RNAs (piRNAs) and repressive chromatin typically control TE activity.
- TE content and silencing dynamics across evolutionary timescales remain poorly understood.
Purpose of the Study:
- Investigate transposable element expression dynamics over 409 generations in experimentally evolved Caenorhabditis elegans populations.
- Examine the impact of population size on TE expression and silencing mechanisms.
- Identify epigenomic features associated with TE silencing.
Main Methods:
- Utilized experimentally evolved C. elegans populations at varying population sizes (1, 10, 100 individuals).
- Analyzed transposable element expression levels relative to ancestral populations.
- Assessed piRNA-mediated silencing and chromatin states in relation to TE activity.
- Investigated the influence of sequence context on TE silencing.
Main Results:
- Observed increased transposable element expression, particularly in smaller populations, indicating reduced silencing efficiency.
- TE transcriptional activation correlated with failed piRNA-mediated silencing in active genomic regions.
- Desilenced TEs within repressed chromatin domains retained small RNAs.
- Sequence context near TEs influenced their propensity to lose silencing.
Conclusions:
- Natural selection actively maintains low transposable element expression levels in C. elegans.
- Failure of piRNA-mediated silencing, influenced by population size and sequence context, drives TE activation.
- Epigenomic features play a critical role in regulating transposable element activity and silencing.
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