N6-methyladenosine (m6A) is the most prevalent internal (non-cap) modification present in the messenger RNA (mRNA) of all higher eukaryotes1,2. Although essential to cell viability and development3–5, the exact role of m6A modification remains to be determined. The recent discovery of two m6A demethylases in mammalian cells highlighted the importance of m6A in basic biological functions and disease6–8. Here we show that m6A is selectively recognized by the human YTH domain family 2 (YTHDF2) protein to regulate mRNA degradation. We identified over 3,000 cellular RNA targets of YTHDF2, most of which are mRNAs, but which also include non-coding RNAs, with a conserved core motif of G(m6A)C. We further establish the role of YTHDF2 in RNA metabolism, showing that binding of YTHDF2 results in the localization of bound mRNA from the translatable pool to mRNA decay sites, such as processing bodies9. The C-terminal domain of YTHDF2 selectively binds to m6A-containing mRNA whereas the N-terminal domain is responsible for the localization of the YTHDF2-mRNA complex to cellular RNA decay sites. Our results indicate that the dynamic m6A modification is recognized by selective-binding proteins to affect the translation status and lifetime of mRNA.

N6-methyladenosine (m6A) is the most prevalent and reversible internal modification in mammalian messenger and non-coding RNAs. We report here that human METTL14 catalyzes m6A RNA methylation. Together with METTL3, the only previously known m6A methyltransferase, these two proteins form a stable heterodimer core complex of METTL3-14 that functions in cellular m6A deposition on mammalian nuclear RNAs. WTAP, a mammalian splicing factor, can interact with this complex and affect this methylation.

N6 -methyladenosine (m 6 A) is the most prevalent and internal modification that occurs in the messenger RNAs (mRNA) of most eukaryotes, although its functional relevance remained a mystery for decades. This modification is installed by the m 6 A methylation "writers" and can be reversed by demethylases that serve as "erasers." In this review, we mainly summarize recent progress in the study of the m 6 A mRNA methylation machineries across eukaryotes and discuss their newly uncovered biological functions. The broad roles of m 6 A in regulating cell fates and embryonic development highlight the existence of another layer of epigenetic regulation at the RNA level, where mRNA is subjected to chemical modifications that affect protein expression.

N6-methyladenosine (m6A) is enriched in 3′untranslated region (3′UTR) and near stop codon of mature polyadenylated mRNAs in mammalian systems and has regulatory roles in eukaryotic mRNA transcriptome switch. Significantly, the mechanism for this modification preference remains unknown, however. Herein we report a characterization of the full m6A methyltransferase complex in HeLa cells identifying METTL3/METTL14/WTAP/VIRMA/HAKAI/ZC3H13 as the key components, and we show that VIRMA mediates preferential mRNA methylation in 3′UTR and near stop codon. Biochemical studies reveal that VIRMA recruits the catalytic core components METTL3/METTL14/WTAP to guide region-selective methylations. Around 60% of VIRMA mRNA immunoprecipitation targets manifest strong m6A enrichment in 3′UTR. Depletions of VIRMA and METTL3 induce 3′UTR lengthening of several hundred mRNAs with over 50% targets in common. VIRMA associates with polyadenylation cleavage factors CPSF5 and CPSF6 in an RNA-dependent manner. Depletion of CPSF5 leads to significant shortening of 3′UTR of over 2800 mRNAs, 84% of which are modified with m6A and have increased m6A peak density in 3′UTR and near stop codon after CPSF5 knockdown. Together, our studies provide insights into m6A deposition specificity in 3′UTR and its correlation with alternative polyadenylation.

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DNA N6-methyldeoxyadenosine (6mA) is a well-known prokaryotic DNA modification that has been shown to exist and play epigenetic roles in eukaryotic DNA. Here we report that 6mA accumulates up to ∼0.1–0.2% of total deoxyadenosine during early embryogenesis of vertebrates, but diminishes to the background level with the progression of the embryo development. During this process a large fraction of 6mAs locate in repetitive regions of the genome.

The development of safe, efficient and controllable gene-delivery vectors has become a bottleneck to human gene therapy. Synthetic polymeric vectors, although safer than viral carriers, generally do not possess the required efficacy, apparently due to a lack of functionality to overcome at least one of many intracellular gene-delivery obstacles. Currently, the exact mechanisms of how these polymeric vectors navigate each intracellular obstacle ("slit"), as well as their particular physical/chemical properties that contribute to efficient intracellular trafficking remain largely unknown, making it rather difficult to further improve the efficacy of non-viral polymeric vectors in vitro and in vivo. In this review, we first give a brief overview of synthetic polymeric vectors that have been designed and developed for gene delivery and highlight some promising candidates for clinical applications. Our main focus is on discussing the intracellular trafficking mechanisms of the DNA-polymer complexes ("polyplexes"), with less effort on the DNA-polymer complexation in the extracellular space as well as the in vivo systemic administration of genes in animal models and human clinical trials. In particular, we identified and discussed four critical, YananYUE received her B.S. degree in Polymer Materials and Engineering from Zhejiang University in 2007 and her Ph.D. in Chemistry at the Chinese University of Hong Kong, under the supervision of Professor Chi WU. Her research interests mainly focus on the development of nonviral vectors for molecular medicines, especially the effect of free polycationic chains on the intracellular trafficking of DNApolymer complexes in gene transfection. She is now working in the Department of Chemistry, the University of Chicago, under the supervision of Professor Chuan HE. Chi WU graduated from the Department of Chemical Physics at the University of Science and Technology of China (USTC) in 1982. After obtaining his Ph.D. in 1987 followed by two-year postdoctoral experience under the supervision of Professor Benjamin Chu in the State University of New York at Stony Brook, he moved to BASF (Ludwigshafen, Germany) in 1989; first as an Alexander von Humboldt Fellow for one year with Dr. Dieter Horn and then as the supervisor of laser light-scattering laboratory. In 1992, he resigned from BASF and joined the Department of Chemistry at the Chinese University of Hong Kong (CUHK) as a Lecturer. He underwent a double promotion directly to Reader in 1996; and became a Chair Professor of Chemistry and Honorary Professor of Physics in 1999. Recently, he has been appointed as a Wei Lun Chair Professor of Chemistry since 2010.

Hyperbranched poly(2,5-silole)s [hb-P1(m), m = 1, 6] are synthesized for the first time in this work. 1,1-Dialkyl-2,5-bis(4-ethynylphenyl)-3,4-diphenylsiloles [1(m)] were polymerized by TaBr5, affording hb-P1(m) with high molecular weights (M w up to 2.5 × 105) in high yields (up to 98%). The structures of hb-P1(m) were characterized by spectroscopic methods and the degree of branching of hb-P1(6) was determined to be 0.55. The hyperbranched polymers are soluble and stable, with no changes in solubility observed after they have been stored under ambient conditions for more than two years. Absorption and emission spectra of hb-P1(m) are red-shifted from those of 1(m), indicating that the polymers are more conjugated than the monomers. Both 1(m) and hb-P1(m) are nonemissive or weekly fluorescent when dissolved in their good solvents but become highly emissive when aggregated in their poor solvents or fabricated into thin solid films, showing unusual phenomena of aggregation-induced (AIE) and -enhanced emissions (AEE). Restriction of intramolecular rotations in the aggregate state is rationalized to be the main cause for the AIE and AEE effects. Photoluminescence (PL) of 1(m) and hb-P1(m) is tunable by varying their concentrations and morphologies. The polymers are readily cured when heated to high temperatures or upon photoirradiation, furnishing cross-linked networks with novel excitation wavelength-dependent emissions in the red spectral region. Photolithography of hb-P1(m) generates fluorescent photopatterns, with the exposed and unexposed areas emitting lights with different colors. The polymers function as sensitive fluorescent chemosensors for the detection of explosives, with a superamplification effect observed in the emission quenching of the polymer nanoaggregates by picric acid.