Exploring the Role of DNMT1 in RNA m⁵C Methylation (eCLIPseq II)

DNA methyltransferase 1 (DNMT1) is an enzyme known for DNA methylation maintenance. However, point mutations in its RFTS domain lead to late-onset neurodegeneration such as the autosomal dominant cerebellar ataxia-deafness and narcolepsy (ADCA-DN) disorder. Here we demonstrated that wild-type DNMT1 also has the capability to bind to mRNA transcripts and facilitate 5-methylcytosine (m5C) RNA methylation by recruiting NOP2/Sun RNA methyltransferase 2 (NSUN2). RNA m5C methylation, in turn, promotes RNA stability for those genes modulating mitochondrial function. When DNMT1 RFTS domain is mutated in the case of ADCA-DN disorder, it triggers aberrant DNMT1-RNA interaction and significantly elevated m5C RNA methylation and RNA stability for a portion of metabolic genes. Consequently, increased levels of metabolic RNA transcripts contribute to cumulative oxidative stress, mitochondrial dysfunction, and neurological symptoms. Collectively, our results highlight a novel role for DNMT1 in regulating both DNA and RNA methylation as well as mitochondrial function, shedding light on the pathogenic mechanism of DNMT1 mutation-induced neurodegeneration.