Human RNA Nm-MTase FTSJ1: new tRNA targets and role in the regulation of brain-specific genes.

FTSJ1 is a phyllogenetically conserved human 2-O-methyltransferase (Nm-MTase) which modifies position 32 as well as the wobble position 34 in the AntiCodon Loop (ACL) of specific tRNAs: tRNAPhe(GAA), tRNATrp(CCA) and tRNALeu(UAA). FTSJ1s loss of function has been linked to Non-Syndromic X-Linked Intellectual Disability (NSXLID), and more recently in cancers. However, the exact molecular mechanisms underlying FTSJ1-related pathogenesis are unknown and a potential extended variety of FTSJ1s tRNA targets hasnt been fully addressed yet. We performed unbiased and comprehensive RiboMethSeq analysis of the Nm profiles for human tRNA population extracted from cells derived from NSXLID patients blood bearing various characterized loss of function mutations in FTSJ1. In addition, we reported a novel FTSJ1 pathogenic variant from a NSXLID patient bearing a de novo mutation in the FTSJ1 gene. Some of the newly identified FTSJ1s tRNA targets are also conserved in Drosophila as shown by our previous study on the fly homologues Trm7_32 and Trm7_34, whose loss affects small RNA silencing pathways. In the current study, we reveal a conserved deregulation in both the miRNA and mRNA populations when FTSJ1 function is compromised. In addition, a cross-analysing between deregulated miRNA and mRNA obtained in FTSJ1 mutants highlighted upregulation of miR10a-5p which has the capacity to silence the SPARC gene mRNA, downregulated in FTSJ1 mutant cells. This suggests that FTSJ1 loss may influence gene expression deregulation by modulation of miRNA silencing. A gene-ontology (GO) enrichment analysis of the deregulated mRNAs primarily matched to brain morphogenesis terms, followed by metabolism and translation related genes. In parallel, the deregulated miRNAs are mostly known for their implication in brain functions and cancers. Based on these results, we suggest that miRNA silencing variations may play a role in the pathological mechanisms of FTSJ1-dependent NSXLID. Finally, our results highlight miR-181a-5p as a potential companion diagnostic test in clinical settings for FTSJ1-related intellectual disability.