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Genome-wide DNA hydroxymethylation changes are associated with neurodevelopmental genes in the developing human brain

ABSTRACT: 5-hydroxymethylcytosine (5-hmC) is a newly discovered modified form of cytosine that has been suspected to be an important epigenetic modification in neurodevelopment. While DNA methylation dynamics have already been implicated during neurodevelopment, little is known about hydroxymethylation in this process. Here we report DNA hydroxymethylation dynamics during cerebellum development in the human brain. Overall, we find a positive correlation between 5-hmC levels and cerebellum development. Genome-wide profiling reveals that 5-hmC is highly enriched on specific gene regions, including exons and especially the untranslated regions (UTRs), but it is depleted on introns and intergenic regions. Furthermore, we have identified fetus-specific and adult-specific differentially hydroxymethylated regions (DhMRs), most of which overlap with genes and CpG island shores. Surprisingly, during development DhMRs are highly enriched in genes encoding mRNAs that can be regulated by fragile X mental retardation protein (FMRP), some of which are disrupted in autism, as well as in many known autism genes. Our results suggest that 5-hmC-mediated epigenetic regulation may broadly impact the development of the human brain, and its dysregulation could contribute to the molecular pathogenesis of neurodevelopmental disorders.

ORGANISM(S): Homo sapiens

PROVIDER: GSE40539 | GEO | 2012/09/30

SECONDARY ACCESSION(S): PRJNA174249

REPOSITORIES: GEO

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Project description:DNA methylation (5-mC) and hydroxymethylation (5-hmC) are regarded as important epigenetic hallmarks in the carcinogenesis of colorectal cancer by transcriptional regulation. 5hmC is an intermediate during active demethylation and maintains the equilibrium of DNA methylation. Previous studies on DNA methylation don’t differentiate 5-hmC from 5-mC. Here, in order to elucidate the epigenetic mechanisms of carcinogenesis of colorectal cancer, we integrate genome wide levels of 5-mC, 5-hmC and Transcriptional expression. 12 samples, including six colorectal tumor tissues and corresponding normal colonic tissues were recruited after surgery. Genome-wide DNA methylation was determined by methylated DNA immune- precipitation sequencing (MeDIP-seq), and hydroxymethylation by hydroxyl- methylated DNA immune-precipitation sequencing (hMedip-seq). Transcriptional expression was determined by RNA-seq. Group-wise different methylation region (DMR), different hydroxyl methylation region (DhMR) and different expressed gene (DEG) were identified. Epigenetic biomarkers were screened by integrating DMR, DhMR and DEG. We found that a genome-scale distinct hydroxymethylation pattern could be used as epigenetic biomarker for clearly differentiating colorectal cancer from normal tissues. 59249 differentially methylated regions (DMR), 187172 differentially hydroxymethylated region (DhMR) and 948 differentially expressed genes (DEGs) were identified. After cross-matched genes containing DMRs or DhMRs with DEGs, seven genes were screened. Furthermore, hypermethylation of HADHB was persistently found to be correlated with its down-regulation of transcription in CRC, potentially suggesting its role as TSG. The differences of methylation, hydroxymethylation and transcriptional expression in HADHB between cancerous and normal tissues were validated among additional colorectal cancer patients. To further validate this assumption, we also performed functional analysis and found that the expression of HADHB obviously reduced cancer cells migration and invasiveness. This study provided valuable basic data for screening epigenetic biomarkers and elucidated the epigenetic mechanisms of carcinogenesis of colorectal cancer.

Project description:DNA hydroxymethylation (5hmC) represents a new layer of epigenetic regulation in addition to DNA methylation (5mC). The genome-wide patterns of 5hmC distribution in many tissues and cells have recently been revealed by hydroxymethylated DNA immunoprecipitation (hMeDIP) followed by high throughput sequencing or tiling arrays. However, the DNA hydroxymethylome data generated by the conventional hMeDIP-seq method can not be used for direct quantitative comparison across different samples. In this study, we report a new quantitative hMeDIP-seq method, which uses barcode technology to label different DNA samples and performs hMeDIP-seq for multiple samples in one reaction system. Using this new method, we profiled and compared the DNA hydroxymethylomes of mouse ES cells (ESCs) and mouse ESCs-derived neural progenitor cells (NPCs). 5hmC levels around TSS in either ESCs or NPCs had negative correlation with gene expression levels，while 5hmC levels at gene body regions had different correlation with gene expression, depending on cell types. We identified differential hydroxymethylated regions (DHMRs) by comparing the 5hmC density of all 5hmC peaks between ESCs and NPCs. Many selected DHMRs (e.g., Ankrd23, Hist1h2aa, Fbxw7, and Epha2) were validated by hMeDIP-qPCR. Furthermore, we analyzed the relationship between the alteration of DNA hydroxymethylation and the gene expression change during neural differentiation, and our data suggest that both up- and down-regulated genes exhibited dramatic decrease in 5hmC during neural differentiation while the alteration of 5hmC had weak positive correlation with the changes in gene expression. Taken together, our data demonstrate that quantitative hMeDIP-seq is a powerful approach for genome-wide comparison of DNA hydroxymethylation across multiple samples. Importantly, the DHMRs between ESCs and NPCs uncovered in this study may provide clues for further investigation of the function of 5hmC in gene regulation and neural differentiation. Comparision of the genome-wide distribution of 5hmC in mouse embryonic stem cells and mouse ES-derived neural progenitor cells.

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Genome-wide DNA hydroxymethylation changes are associated with neurodevelopmental genes in the developing human brain

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