The regulatory role of N(6)-methyladenosine (m(6)A) and its nuclear binding protein YTHDC1 in pre-mRNA splicing remains an enigma. Here we show that YTHDC1 promotes exon inclusion in targeted mRNAs through recruiting pre-mRNA splicing factor SRSF3 (SRp20) while blocking SRSF10 (SRp38) mRNA binding. Transcriptome assay with PAR-CLIP-seq analysis revealed that YTHDC1-regulated exon-inclusion patterns were similar to those of SRSF3 but opposite of SRSF10. In vitro pull-down assay illustrated a competitive binding of SRSF3 and SRSF10 to YTHDC1. Moreover, YTHDC1 facilitates SRSF3 but represses SRSF10 in their nuclear speckle localization, RNA-binding affinity, and associated splicing events, dysregulation of which, as the result of YTHDC1 depletion, can be restored by reconstitution with wild-type, but not m(6)A-binding-defective, YTHDC1. Our findings provide the direct evidence that m(6)A reader YTHDC1 regulates mRNA splicing through recruiting and modulating pre-mRNA splicing factors for their access to the binding regions of targeted mRNAs.

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N-methyladenosine (mA) messenger RNA methylation is a gene regulatory mechanism affecting cell differentiation and proliferation in development and cancer. To study the roles of mA mRNA methylation in cell proliferation and tumorigenicity, we investigated human endometrial cancer in which a hotspot R298P mutation is present in a key component of the methyltransferase complex (METTL14). We found that about 70% of endometrial tumours exhibit reductions in mA methylation that are probably due to either this METTL14 mutation or reduced expression of METTL3, another component of the methyltransferase complex. These changes lead to increased proliferation and tumorigenicity of endometrial cancer cells, likely through activation of the AKT pathway. Reductions in mA methylation lead to decreased expression of the negative AKT regulator PHLPP2 and increased expression of the positive AKT regulator mTORC2. Together, these results reveal reduced mA mRNA methylation as an oncogenic mechanism in endometrial cancer and identify mA methylation as a regulator of AKT signalling.

N-methyladenosine (mA) has been identified as the most abundant modification on eukaryote messenger RNA (mRNA). Although the rapid development of high-throughput sequencing technologies has enabled insight into the biological functions of mA modification, the function of mA during vertebrate embryogenesis remains poorly understood. Here we show that mA determines cell fate during the endothelial-to-haematopoietic transition (EHT) to specify the earliest haematopoietic stem/progenitor cells (HSPCs) during zebrafish embryogenesis. mA-specific methylated RNA immunoprecipitation combined with high-throughput sequencing (MeRIP-seq) and mA individual-nucleotide-resolution cross-linking and immunoprecipitation with sequencing (miCLIP-seq) analyses reveal conserved features on zebrafish mA methylome and preferential distribution of mA peaks near the stop codon with a consensus RRACH motif. In mettl3-deficient embryos, levels of mA are significantly decreased and emergence of HSPCs is blocked. Mechanistically, we identify that the delayed YTHDF2-mediated mRNA decay of the arterial endothelial genes notch1a and rhoca contributes to this deleterious effect. The continuous activation of Notch signalling in arterial endothelial cells of mettl3-deficient embryos blocks EHT, thereby repressing the generation of the earliest HSPCs. Furthermore, knockdown of Mettl3 in mice confers a similar phenotype. Collectively, our findings demonstrate the critical function of mA modification in the fate determination of HSPCs during vertebrate embryogenesis.

The impact of mitochondrial protein acetylation status on neuronal function and vulnerability to neurological disorders is unknown. Here we show that the mitochondrial protein deacetylase SIRT3 mediates adaptive responses of neurons to bioenergetic, oxidative and excitatory stress. Cortical neurons lacking SIRT3 exhibit heightened sensitivity to glutamate-induced calcium overload and excitotoxicity, and oxidative and mitochondrial stress; AAV-mediated Sirt3 gene delivery restores neuronal stress resistance. In models relevant to Huntington’s disease and epilepsy, Sirt3−/− mice exhibit increased vulnerability of striatal and hippocampal neurons, respectively. SIRT3 deficiency results in hyperacetylation of several mitochondrial proteins including superoxide dismutase 2 and cyclophilin D. Running wheel exercise increases the expression of Sirt3 in hippocampal neurons, which is mediated by excitatory glutamatergic neurotransmission and is essential for mitochondrial protein acetylation homeostasis and the neuroprotective effects of running. Our findings suggest that SIRT3 plays pivotal roles in adaptive responses of neurons to physiological challenges and resistance to degeneration.

Background: Dynamic N 6-methyladenosine (m 6 A) RNA modification generated and erased by N 6methyltransferases and demethylases regulates gene expression, alternative splicing and cell fate. Ocular melanoma, comprising uveal melanoma (UM) and conjunctival melanoma (CM), is the most common primary eye tumor in adults and the 2nd most common melanoma. However, the functional role of m 6 A modification in ocular melanoma remains unclear. Methods: m 6 A assays and survival analysis were used to explore decreased global m 6 A levels, indicating a late stage of ocular melanoma and a poor prognosis. Multiomic analysis of miCLIP-seq, RNA-seq and Labelfree MS data revealed that m 6 A RNA modification posttranscriptionally promoted HINT2 expression. RNA immunoprecipitation (RIP)-qPCR and dual luciferase assays revealed that HINT2 mRNA specifically interacted with YTHDF1. Furthermore, polysome profiling analysis indicated a greater amount of HINT2 mRNA in the translation pool in ocular melanoma cells with higher m 6 A methylation. Results: Here, we show that RNA methylation significantly inhibits the progression of UM and CM. Ocular melanoma samples showed decreased m 6 A levels, indicating a poor prognosis. Changes in global m 6 A modification were highly associated with tumor progression in vitro and in vivo. Mechanistically, YTHDF1 promoted the translation of methylated HINT2 mRNA, a tumor suppressor in ocular melanoma. Conclusions: Our work uncovers a critical function for m 6 A methylation in ocular melanoma and provides additional insight into the understanding of m 6 A modification.

Our data revealed that, in T2D patients, high-glucose-enhanced FTO mRNA expression resulted in a decrease in m6A. The lower m6A content might be responsible for the upregulation of methyltransferases. Additionally, FTO induced mRNA expression of FOXO1, G6PC, and DGAT2 and was closely associated with glucose metabolism.

These data suggest that the increased mRNA expression of FTO could be responsible for the reduction of m(6)A in T2DM, which may further increase the risk of complications of T2DM. Low m(6)A should be investigated further as a novel potential biomarker of T2DM.