Imprecise DNMT1 activity coupled with neighbor-guided correction enables robust yet flexible epigenetic inheritance

Proteins in DNA methylation and their role in neural stem cell proliferation and differentiation

BACKGROUND

Epigenetic modifications, namely non-coding RNAs, DNA methylation, and histone modifications such as methylation, phosphorylation, acetylation, ubiquitylation, and sumoylation play a significant role in brain development. DNA methyltransferases, methyl-CpG binding proteins, and ten-eleven translocation proteins facilitate the maintenance, interpretation, and removal of DNA methylation, respectively. Different forms of methylation, including 5-methylcytosine, 5-hydroxymethylcytosine, and other oxidized forms, have been detected by recently developed sequencing technologies. Emerging evidence suggests that the diversity of DNA methylation patterns in the brain plays a key role in fine-tuning and coordinating gene expression in the development, plasticity, and disorders of the mammalian central nervous system. Neural stem cells (NSCs), originating from the neuroepithelium, generate neurons and glial cells in the central nervous system and contribute to brain plasticity in the adult mammalian brain.

MAIN BODY

Here, we summarized recent research in proteins responsible for the establishment, maintenance, interpretation, and removal of DNA methylation and those involved in the regulation of the proliferation and differentiation of NSCs. In addition, we discussed the interactions of chemicals with epigenetic pathways to regulate NSCs as well as the connections between proteins involved in DNA methylation and human diseases.

CONCLUSION

Understanding the interplay between DNA methylation and NSCs in a broad biological context can facilitate the related studies and reduce potential misunderstanding.

FoxA-dependent demethylation of DNA initiates epigenetic memory of cellular identity

Tissue-specific DNA methylation patterns are created by transcription factors that recruit methylation and demethylation enzymes to cis-regulatory elements. To date, it is not known whether transcription factors are needed to continuously maintain methylation profiles in development and mature tissues or whether they only establish these marks during organ development. We queried the role of the pioneer factor FoxA in generating hypomethylated DNA at liver enhancers. We discovered a set of FoxA-binding sites that undergo regional, FoxA-dependent demethylation during organ development. Conditional ablation of FoxA genes in the adult liver demonstrated that continued FoxA presence was not required to maintain the hypomethylated state, even when massive cell proliferation was induced. This study provides strong evidence for the stable, epigenetic nature of tissue-specific DNA methylation patterns directed by lineage-determining transcription factors during organ development.

Mitotic inheritance of DNA methylation: more than just copy and paste

Decades of investigation on DNA methylation have led to deeper insights into its metabolic mechanisms and biological functions. This understanding was fueled by the recent development of genome editing tools and our improved capacity for analyzing the global DNA methylome in mammalian cells. This review focuses on the maintenance of DNA methylation patterns during mitotic cell division. We discuss the latest discoveries of the mechanisms for the inheritance of DNA methylation as a stable epigenetic memory. We also highlight recent evidence showing the rapid turnover of DNA methylation as a dynamic gene regulatory mechanism. A body of work has shown that altered DNA methylomes are common features in aging and disease. We discuss the potential links between methylation maintenance mechanisms and disease-associated methylation changes.

Epigenetic crosstalk between hypoxia and tumor driven by HIF regulation

Hypoxia is the major influence factor in physiological and pathological courses which are mainly mediated by hypoxia-inducible factors (HIFs) in response to low oxygen tensions within solid tumors. Under normoxia, HIF signaling pathway is inhibited due to HIF-α subunits degradation. However, in hypoxic conditions, HIF-α is activated and stabilized, and HIF target genes are successively activated, resulting in a series of tumour-specific activities. The activation of HIFs, including HIF-1α, HIF-2α and HIF-3α, subsequently induce downstream target genes which leads to series of responses, the resulting abnormal processes or metabolites in turn affect HIFs stability. Given its functions in tumors progression, HIFs have been regarded as therapeutic targets for improved treatment efficacy. Epigenetics refers to alterations in gene expression that are stable between cell divisions, and sometimes between generations, but do not involve changes in the underlying DNA sequence of the organism. And with the development of research, epigenetic regulation has been found to play an important role in the development of tumors, which providing accumulating basic or clinical evidences for tumor treatments. Here, given how little has been reported about the overall association between hypoxic tumors and epigenetics, we made a more systematic review from epigenetic perspective in hope of helping others better understand hypoxia or HIF pathway, and providing more established and potential therapeutic strategies in tumors to facilitate epigenetic studies of tumors.

Unbelievable but True: Epigenetics and Chromatin in Fungi

Evolutionary innovations in chromatin biology have been recently discovered through the study of fungi. In Saccharomyces cerevisiae, a prion form of a deacetylase complex assembles over subtelomeric domains that produces a heritable gene expression state that enables resistance to stress. In Candida albicans, stress triggers adaptive chromosome destabilization via erasure a centromeric histone H3, CENP-A; a process that cooperates with a newly evolved H2A variant lacking a mitotic phosphorylation site. Finally, in Cryptococcus neoformans, the loss of a cytosine DNA methyltransferase at least 50 million years ago has enabled the Darwinian evolution of methylation patterns over geological timescales. These studies reveal a remarkable genetic and epigenetic evolutionary plasticity of the chromatin fiber, despite the highly conserved structure of the nucleosome.