Thyroid Hormone Modulation of DNA Methylation in the Developing Brain.

[摘要] Postembryonic brain development is dependent on thyroid hormone (T3). The actions of T3 are mediated by T3 receptors (TRs) that bind T3 response elements (T3REs) in the genome and regulate gene transcription through recruitment of histone-modifying enzymes. Methylation of DNA is another critical epigenetic modification that controls gene transcription. Using mouse and frog (T3 controls tadpole metamorphosis), I investigated T3-dependent modulation of DNA methylation, regulation of genes that control this epigenetic modification, and roles of DNA methylation in regulation of gene expression programs in the brain.I discovered that TRs directly activate the transcription of the de novo DNA methyltransferase 3a (Dnmt3a) gene that encodes a key enzyme that establishes genome-wide patterns of DNA methylation in the developing brains of mouse and frog. I identified two functional T3REs that support T3-dependent transactivation of the Dnmt3a genes. I found strong sequence conservation of the mouse T3REs among eutherian mammals.I found that the tadpole brain genome became demethylated during metamorphosis, which correlated with activation of genes that are involved in active DNA demethylation (tet2, tet3, apobec2, gadd45β, gadd45γ and tdg). Treating premetamorphic tadpoles with exogenous T3 induced tet3, gadd45γ and tdg mRNAs. I found that T3REs for known T3-regulated genes (klf9 and dnmt3a) became demethylated during metamorphosis and in response to T3. In vitro methylation of DNA fragments containing these T3REs subcloned into reporter plasmids abrogated T3-dependent transactivity, suggesting that DNA demethylation of T3REs activates T3-regulated genes.To identify gene expression programs that are regulated by DNA methylation, I conducted methylated DNA capture sequencing and RNA-sequencing in tadpole brain. I identified ~142,000 genomic regions enriched for methylated DNA and 855 regions that showed changes during metamorphosis. More than 5,000 genes showed changes in expression, and I identified thirteen patterns of expression dynamics and enriched biological pathways among these genes. I found an inverse correlation between changes in expression of genes found within 50 kb neighborhood of regions that became differentially methylated.. My findings support that T3 modulates DNA methylation in the developing brain, and that these changes may be important for the coordination of gene expression programs during postembryonic neurological development.

[发布机构] University of Michigan

[效力级别] DNA METHYLATION

[关键词] THYROID HORMONE;DNA METHYLATION;BRAIN DEVELOPMENT;Molecular;Cellular and Developmental Biology;Science;Neuroscience