DNA methyltransferases and tRNA methyltransferase DNMT2 in developing pig brain - expression and promoter methylation

DNA methylation constitutes an epigenetic mechanism used by cells to control gene expression and chromatin organization. DNA methylation is a biochemical process, catalyzed by DNA methyltransferases, where a methyl group is added to a nucleotide base. In mammals, DNA methylation is essential for normal development. Here we report on the developmental expression of DNA methyltransferases and DNMT2, a tRNA methyltransferase, in various brain tissues in porcine embryos. Expressions of DNMT1, DNMT2, DMNT3A and DNMT3B transcripts were determined by qRT-PCR in five different brain tissues at four or five time points in embryo development. Low transcript levels from all these genes were detected as early as 60 days of gestation in all tissues examined. From 60 to 115 days of gestation, a reduction in DNMT1 and DMNT3A and DNMT3B mRNA was seen in brain stem, hippocampus, basal ganglia, cortex and cerebellum. No significant changes were seen for DNMT2 mRNA. In heart, a bimodal expression was observed for all four DNMTs analyzed. Analysis of DNA methylation status of two selected regions in the DNMT3A promoter revealed a very low degree of methylation (<3%). It was concluded that DNA methylation of the examined region of the DNMT3A gene is not determining expression of its transcript.