Stability of DNA Methylation in Nematostella and Its Implications
In the marine organism Nematostella, researchers have found that DNA methylation levels—specifically the presence of 5-methylcytosine (5mC)—remain surprisingly stable during its development. This contrasts with other animals, where significant methylation loss typically occurs as they age.
Researchers studied various developmental stages of Nematostella and found that global methylation levels averaged about 12% throughout its life cycle. This stability might reflect the unique properties of cnidarian stem cells, which show a continuous ability to renew themselves.
Interestingly, genes in Nematostella with high levels of a particular type of methylation (known as gene body methylation or gbM) maintained consistent transcription levels. This finding suggests that gbM marks stable genes rather than functioning as regulators that change frequently.
The impact of depleting DNA methylation was investigated through both chemical and genetic methods. Initial chemical treatments using cytidine analogues were toxic, leading to developmental issues. However, using a more refined drug, GSK-3484862, resulted in a sixfold decrease in global methylation levels without affecting the embryos’ development.
Gene expression analysis revealed that many genes experienced changes when gbM was reduced. While some genes became downregulated, others were upregulated, suggesting that the removal of methylation can lead to unexpected transcriptional outcomes.
Chromatin Accessibility and Transposon Activity
One significant outcome of reduced methylation was increased chromatin accessibility. The study showed that a substantial number of these accessible regions overlapped with transposable elements (TEs), which are segments of DNA that can move around within the genome. Some previously quiet TEs became active, indicating that the removal of methylation could “wake up” these genetic elements.
Further analyses revealed that many newly accessible regions contained binding sites for transcription factors, which help control gene expression. This suggests that demethylation opens the door to potential gene activation.
Methylation Recovery During Regeneration
An intriguing part of the study involved understanding whether methylation could recover over time after being reduced. Researchers bisected Nematostella polyps and monitored their ability to regenerate. They found that although the overall methylation remained lower during regeneration, some recovery did occur, particularly in the germline cells used for reproduction.
Examining the offspring of treated and untreated animals, the researchers observed that the global methylation levels were a blend of parental methylation states. This finding indicates a kind of epigenetic inheritance, where the methylation status of the parents can influence that of their offspring.
Implications for Evolution and Adaptation
These findings raise important questions about how organisms adapt to their environments. The ability of Nematostella to maintain stable methylation levels, even when subjected to genetic perturbations, highlights a form of resilience that could be beneficial for survival.
In addition, the research points to a mechanism by which epigenetic changes, influenced by environmental factors, can affect future generations. This suggests that non-genetic alterations could play a role in evolutionary processes, allowing populations to adapt without changes to their underlying DNA sequences.
As our understanding of methylation dynamics grows, it opens new avenues for research into genetic regulation and epigenetics, challenging the notion of strict genetic inheritance in favor of a more nuanced view that includes epigenetic factors.
Source link
Epigenetics,Epigenomics,Evolutionary developmental biology,Life Sciences,general,Ecology,Evolutionary Biology,Zoology,Paleontology,Biological and Physical Anthropology
