Self-regulation of the DNA N⁶-adenine methyltransferase AMT1 in the unicellular eukaryoteTetrahymena thermophila

Abstract

DNA N6-adenine methylation (6mA) is involved in gene transcription as a potential epigenetic mark in eukaryotes. Despite the reported methyltransferase (MTase) for 6mA methylation in several eukaryotes, the regulatory mechanisms that govern the activity of 6mA MTase remain elusive. Here, we exploited the 6mA MTase AMT1 to elucidate its self-regulation in the unicellular eukaryote Tetrahymena thermophila. Firstly, detailed endogenous localization of AMT1 was delineated both in vegetative and sexual stages, revealing a correlation between the 6mA reestablishment in the new MAC and the occurrence of zygotically expressed AMT1. Catalytically inactive AMT1 reduced 6mA level on the AMT1 gene and its expression level, suggesting that AMT1 modulated its own transcription via 6mA. Furthermore, AMT1-dependent 6mA regulated the transcription of its target genes thus affecting the cell fitness, as demonstrated by manipulating the dosage of AMT1 using AMT1-RNAi strains. Our findings unveil a positive feedback loop of transcriptional activation on the AMT1 gene and highlight the crucial role of AMT1-dependent 6mA for gene transcription.