Summary: A new study from Osaka University reveals that the DNA repair enzyme DNA polymerase β (Polβ) is essential for protecting the developing brain from damaging mutations. The researchers show that loss of Polβ causes a steep increase in small insertions and deletions (indels) at CpG dinucleotides—key regulatory sites in the genome—compromising genetic stability during critical stages of cortical development.
CpG-rich regions play a central role in regulating gene activity and undergo dynamic changes in DNA methylation during neuronal differentiation. The study demonstrates that Polβ helps repair DNA lesions that arise during active DNA demethylation. Without Polβ, indel formation near CpG sites rises dramatically, a change that could underlie certain neurodevelopmental disorders and has broader implications for cancer and aging research.
Key facts
- Polβ function: DNA polymerase β performs gap-filling during base excision repair and participates in repairing lesions formed during active DNA demethylation in developing neurons.
- Mutation increase: Loss of Polβ leads to roughly a ninefold increase in indel mutations at CpG dinucleotides and a notable rise in structural variants.
- Biological impact: These mutational changes disproportionately affect neuronal genes, producing frameshifts and amino acid changes and altering regulatory CpG sites—mechanisms that may contribute to neurodevelopmental disorders.
Source: Osaka University
Overview of the findings
The developing human brain follows tightly coordinated genetic programs, but these programs can be disrupted when DNA damage is not properly corrected. The research team used mouse-derived neural progenitor models and whole-genome sequencing to examine somatic mutations in immature cortical neurons. They found that indel mutations occur in both repetitive and nonrepetitive sequences under normal conditions, but the absence of Polβ substantially worsens the problem at CpG sites.
CpG dinucleotides are genomic hotspots for regulatory function and are subject to methylation and active demethylation during neuronal gene activation. Ten-Eleven Translocation (TET) enzymes help remove methyl groups as part of controlled gene regulation, and this demethylation process can transiently expose DNA to damage. Polβ appears to recognize and repair the resulting gaps and lesions, preventing misrepair that would otherwise generate indel mutations.
When Polβ is missing in neural progenitor cells, the study reports an approximate ninefold rise in indel frequency specifically at CpG dinucleotides, as well as a roughly fivefold increase in larger structural variants. Many of these mutations cluster in genes that are important for neuronal development and function, producing frameshifts and small insertions or deletions that can alter protein sequences and regulatory landscapes.
By showing that Polβ preferentially suppresses mutations generated by TET-mediated demethylation at CpG sites, the research provides a clearer molecular explanation for how somatic mutations can arise during cortical development and how defective repair may contribute to disease. The findings point to Polβ as a guardian of genomic stability in developing neurons and suggest that defects in this repair pathway could be a contributing factor in some neurodevelopmental disorders.
Dr. Noriyuki Sugo, lead author of the study, states: “This study is the first to demonstrate the crucial role of Polβ in preventing mutations in developing nerve cells.” The research team plans to continue investigating links between Polβ dysfunction and specific neurodevelopmental conditions, and to explore broader implications for neuroscience, cancer biology, and aging.
About this genetics and neurology research news
Author: Saori Obayashi
Source: Osaka University
Contact: Saori Obayashi – Osaka University
Image: Image credited to Neuroscience News
Original research: Open access. “DNA polymerase β suppresses somatic indels at CpG dinucleotides in developing cortical neurons” by Noriyuki Sugo et al., published in PNAS.
Abstract (concise)
DNA polymerase β suppresses somatic indels at CpG dinucleotides in developing cortical neurons
Somatic mutations in cortical neurons have been implicated in psychiatric and neurodevelopmental disorders. Endogenous DNA damage and imperfect repair during development are candidate sources of these mutations, but the detailed mutagenic mechanisms were not fully understood. Using mouse somatic cell nuclear transfer-derived embryonic stem cells differentiated into immature cortical neurons and whole-genome sequencing, the researchers found that insertions and deletions occur in both repeat and nonrepeat regions. Loss of Polβ, which fills gaps during base excision repair and assists TET-mediated active demethylation, causes an approximately ninefold increase in indels at CpG dinucleotides and substantially raises structural variant frequency. These mutations are enriched in neuronal genes and result in frameshifts, amino acid changes, and alterations to regulatory CpG sites. The study concludes that Polβ preferentially repairs lesions formed during active demethylation at CpG sites, thereby suppressing mutagenesis associated with neuronal gene activation during cortical development.