Thyroid Hormone Induces DNA Demethylation in Xenopus Tadpole Brain

Area of Science:

• Developmental Biology
• Epigenetics
• Neuroscience

Background:

• Thyroid hormone (T3) is essential for vertebrate development, regulating gene transcription via nuclear T3 receptors (TRs).
• DNA methylation patterns are dynamically regulated and influence gene expression during development.
• Previous findings indicated DNA demethylation in the Xenopus tadpole brain during metamorphosis, a T3-dependent stage.

Purpose of the Study:

• To investigate whether thyroid hormone (T3) induces DNA demethylation in the developing Xenopus tadpole brain in vivo.
• To identify the molecular mechanisms by which T3 might regulate DNA demethylation.

Main Methods:

• Treatment of premetamorphic tadpoles with T3 and analysis of DNA demethylation intermediates (5-hmC, 5-carboxylcytosine) and TET3.
• Locus-specific DNA demethylation analysis using 5-hmC immunoprecipitation and methylation-sensitive restriction enzyme digestion.
• Chromatin immunoprecipitation (ChIP) assays for TET3 and TR binding sites, and gene expression analysis of demethylation enzymes.

Main Results:

• T3 treatment increased levels of DNA demethylation intermediates and TET3 in specific brain regions.
• T3 induced locus-specific DNA demethylation near T3 response elements in the DNA methyltransferase 3a and Krüppel-like factor 9 genes.
• T3 promoted TET3 recruitment to these loci and upregulated the expression of genes encoding DNA demethylation enzymes.

Conclusions:

• Thyroid hormone (T3) actively promotes DNA demethylation in the developing tadpole brain.
• T3-induced DNA demethylation is mediated, in part, by TET3 recruitment to specific genomic regions.
• T3 also enhances DNA demethylation through the induction of genes encoding demethylation enzymes.