Abstract
BackgroundDNA methylation is a significant epigenetic modification that is evolutionarily conserved in various species and often serves as a repressive mark for transcription. DNA methylation levels and patterns are regulated by a balance of opposing enzyme functions, DNA methyltransferases, DNMT1/3A/3B and methylcytosine dioxygenases, TET1/2/3. In mice, the TET enzyme converts DNA cytosine methylation (5mC) to 5-hydroxymethylcytosine (5hmC) at the beginning of fertilisation and gastrulation and initiates a global loss of 5mC, while the 5mC level is increased on the onset of cell differentiation during early embryonic development.ObjectiveGlobal loss and gain of DNA methylation may be differently regulated in diverged species.MethodsChicken B-cell lymphoma DT40 cells were used as an avian model to compare differences in the overall regulation of DNA modification with mammals.ResultsWe found that DNA methylation is maintained at high levels in DT40 cells through compact chromatin formation, which inhibits TET-mediated demethylation. Human and mouse chromosomes introduced into DT40 cells by cell fusion lost the majority of 5mC, except for human subtelomeric repeats.ConclusionOur attempt to elucidate the differences in the epigenetic regulatory mechanisms between birds and mammals explored the evidence that they share a common chromatin-based regulation of TET–DNA access, while chicken DNMT1 is involved in different target sequence recognition systems, suggesting that factors inducing DNMT–DNA association have already diverged.
Highlights
The chicken is the most commonly domesticated bird, classified as Gallus gallus domesticus
We have shown that TET enzymes preferentially convert 5mC to 5hmC in euchromatic regions in mouse embryonic stem cells (ESCs) using immunofluorescence staining (IF) analysis (Kubiura et al 2012)
Our results demonstrate that DNMT1, DNMT3B, and TET1-3 are abundantly expressed in DT40 cells, more so than in HH27 CEFs (Fig. 2c)
Summary
The chicken is the most commonly domesticated bird, classified as Gallus gallus domesticus. The TET enzyme converts DNA cytosine methylation (5mC) to 5-hydroxymethylcytosine (5hmC) at the beginning of fertilisation and gastrulation and initiates a global loss of 5mC, while the 5mC level is increased on the onset of cell differentiation during early embryonic development. Objective Global loss and gain of DNA methylation may be differently regulated in diverged species. Methods Chicken B-cell lymphoma DT40 cells were used as an avian model to compare differences in the overall regulation of DNA modification with mammals. Conclusion Our attempt to elucidate the differences in the epigenetic regulatory mechanisms between birds and mammals explored the evidence that they share a common chromatin-based regulation of TET–DNA access, while chicken DNMT1 is involved in different target sequence recognition systems, suggesting that factors inducing DNMT–DNA association have already diverged
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