RNA N⁶-methyladenosine (m⁶A), the most abundant internal modification of mRNAs, plays key roles in human development and health. Post-translational methylation of proteins is often critical for the dynamic regulation of enzymatic activity. However, the role of methylation of the core methyltransferase METTL3/METTL14 in m⁶A regulation remains elusive. We find by mass spectrometry that METTL14 arginine 255 (R255) is methylated (R255me). Global mRNA m⁶A levels are greatly decreased in METTL14 R255K mutant mouse embryonic stem cells (mESCs). We further find that R255me greatly enhances the interaction of METTL3/METTL14 with WTAP and promotes the binding of the complex to substrate RNA. We show that protein arginine N-methyltransferases 1 (PRMT1) interacts with and methylates METTL14 at R255, and consistent with this, loss of PRMT1 reduces mRNA m⁶A modification globally. Lastly, we find that loss of R255me preferentially affects endoderm differentiation in mESCs. Collectively, our findings show that arginine methylation of METTL14 stabilizes the binding of the m⁶A methyltransferase complex to its substrate RNA, thereby promoting global m⁶A modification and mESC endoderm differentiation. This work highlights the crosstalk between protein methylation and RNA methylation in gene expression.

N6-methyladenosine (m⁶A) has been identified in various biological processes and plays important regulatory functions in diverse cells. However, there is still no visualization database for exploring global m⁶A patterns across cell lines. Here we collected all available MeRIP-Seq and m⁶A-CLIP-Seq datasets from public databases and identified 340,950 and 179,201 m⁶A peaks dependent on 23 human and eight mouse cell lines respectively. Those m⁶A peaks were further classified into mRNA and lncRNA groups. To better understand the potential function of m⁶A, we then mapped m⁶A peaks in different subcellular components and gene regions. Among those human m⁶A modification, 190,050 and 150,900 peaks were identified in cancer and non-cancer cells, respectively. Finally, all results were integrated and imported into a visualized cell-dependent m⁶A database CVm6A. We believe the specificity of CVm6A could significantly contribute to the research for the function and regulation of cell-dependent m⁶A modification in disease and development.

The fluctuating CDK‐CYCLIN complex plays a general role in cell‐cycle control. Many types of stem cells use unique features of the cell cycle to facilitate asymmetric division. However, the manner in which these features are established remains poorly understood. The cell cycle of Drosophila female germline stem cells (GSCs) is characterized by short G ₁ and very long G ₂ phases, making it an excellent model for the study of cell cycle control in stem cell fate determination. Using a Drosophila female GSC model, we found Gcn5, the first discovered histone acetyltransferase, to maintain germline stem cells in Drosophila ovaries. Results showed that Gcn5 is dispensable for the transcriptional silencing of bam , but interacts with Cyclin A to facilitate proper turnover in GSCs. Results also showed that Gcn5 promotes Cyclin A ubiquitination, which is dependent on its acetylating activity. Finally, results showed that knockdown of Cyclin A rescued the GSC‐loss phenotype caused by lack of Gcn5. Collectively, these findings support the conclusion that Gcn5 acts through acetylation to facilitate Cyclin A ubiquitination and proper turnover, thereby determining the fate of GSCs. —Liu, T., Wang, Q., Li, W., Mao, F., Yue, S., Liu, S., Liu, X., Xiao, S., Xia, L. Gcn5 determines the fate of Drosophila germline stem cells through degradation of Cyclin A. FASEB J. 31, 2185–2194 (2017). www.fasebj.org

An intricate network ofcis- andtrans-elements acts on RNAN⁶-methyladenosine (m⁶A), which in turn may affect gene expression and, ultimately, human health. A complete understanding of this network requires new approaches to accurately measure the subtle m⁶A differences arising from genetic variants, many of which have been associated with common diseases. To address this gap, we developed a method to accurately and sensitively detect transcriptome-wide allele-specific m⁶A (ASm⁶A) from MeRIP-seq data and applied it to uncover 12,056 high-confidence ASm⁶A modifications from 25 human tissues. We also identified 1184 putative functional variants for ASm⁶A regulation, a subset of which we experimentally validated. Importantly, we found that many of these ASm⁶A-associated genetic variants were enriched for common disease–associated and complex trait–associated risk loci, and verified that two disease risk variants can change m⁶A modification status. Together, this work provides a tool to detangle the dynamic network of RNA modifications at the allelic level and highlights the interplay of m⁶A and genetics in human health and disease.