Regulation of Adipocyte Differentiation by METTL4, a 6 mA Methylase

As one of the most abundant DNA methylation form in prokaryotes, N(6)-methyladenine nucleotide (6 mA) was however only recently identified in eukaryotic genomes. To explore the implications of N(6)-adenine methylation in adipogenesis, genomic N(6)-adenine methylation was examined across adipocyte differentiation stages of 3T3-L1 cells. When the N(6)-adenine methylation profiles were analyzed and compared with the levels of gene expression, a positive correlation between the density of promoter 6 mA and gene expression level was uncovered. By means of in vitro methylation and gene knockdown assay, METTL4, a homologue of Drosophila methylase CG14906 and C. elegans methylase DAMT-1, was demonstrated to be a mammalian N(6)-adenine methylase that functions in adipogenesis. Knockdown of Mettl4 led to altered adipocyte differentiation, shown by defective gene regulation and impaired lipid production. We also found that the effects of N(6)-adenine methylation on lipid production involved the regulation of INSR signaling pathway, which promotes glucose up-taking and lipid production in the terminal differentiation stage.