Loss of cytosine-5 methylation in tRNA triggers stress responses in a disease model for Intellectual Disability
Mutations in the cytosine-5 RNA methyltransferase NSun2 can cause Intellectual Disability (ID) and symptoms commonly found in patients with Dubowitz syndrome.   By analysing gene expression data with the global cytosine-5 RNA methylome in NSun2-deficient mice, we find that loss of cytosine-5 RNA methylation increases the fragmentation of transfer RNAs (tRNA) leading to an accumulation of 5’ halves. Cleavage of tRNAs by Angiogenin is a common cellular stress response to silence translational programmes, and we show that Angiogenin binds tRNAs lacking site-specific NSun2-methylation with higher affinity.  Furthermore, cells lacking functional NSun2 up-regulate stress markers, and deletion of NSun2 compromises cellular survival in response stress stimuli including UV-light and oxidative stress. The decreased tolerance of NSun2 null cells towards oxidative stress can be rescued through inhibition of Angiogenin.  In conclusion, cytosine-5 RNA methylation is an essential post-transcriptional mechanism during cellular stress responses and NSun2-mediated tRNA methylation protects from Angiogenin-dependent stress-induced RNA cleavage. Overall design: RNA Methylation profiling by high throughput sequencing small non-coding RNA profiling by high throughput sequencing Pol III Chromatin-IP profiling by high throughput sequencing