Transcriptome-wide analysis of epitranscriptome and translational efficiency associated with heterosis in maize.

Heterosis has been extensively utilized to increase productivity in crops, yet the underlying molecular mechanisms remain largely elusive. Here, we generated transcriptome-wide profiles of mRNA abundance, m6A methylation, and translational efficiency from the maize F1 hybrid B73×Mo17 and its two parental lines to ascertain the contribution of each regulatory layer to heterosis at the seedling stage. We documented that although the global abundance and distribution of m6A remained unchanged, a greater number of genes had gained an m6A modification in the hybrid. Superior variations were observed at the m6A modification and translational efficiency levels when compared with mRNA abundance between the hybrid and parents. In the hybrid, the vast majority of genes with m6A modification exhibited a non-additive expression pattern, the percentage of which was much higher than that at levels of mRNA abundance and translational efficiency. Non-additive genes involved in different biological processes were hierarchically coordinated by discrete combinations of three regulatory layers. These findings suggest that transcriptional and post-transcriptional regulation of gene expression make distinct contributions to heterosis in hybrid maize. Overall, this integrated multi-omics analysis provides a valuable portfolio for interpreting transcriptional and post-transcriptional regulation of gene expression in hybrid maize, and paves the way for exploring molecular mechanisms underlying hybrid vigor.

Natural Variation in RNA m6A Methylation and Its Relationship with Translational Status.

N 6 -methyladenosine (m6A) is the most abundant modification of eukaryotic mRNA. Although m6A has been demonstrated to affect almost all aspects of RNA metabolism, its global contribution to the post-transcriptional balancing of translational efficiency remains elusive in plants. In this study, we performed a parallel analysis of the transcriptome-wide mRNA m6A distribution and polysome profiling in two maize (Zea mays) inbred lines to assess the global correlation of m6A modification with translational status. m6A sites are widely distributed in thousands of protein-coding genes, confined to a consensus motif and primarily enriched in the 3' untranslated regions, and highly coordinated with alternative polyadenylation usage, suggesting a role of m6A modification in regulating alternative polyadenylation site choice. More importantly, we identified that the m6A modification shows multifaceted correlations with the translational status depending on its strength and genic location. Moreover, we observed a substantial intraspecies variation in m6A modification, and this natural variation was shown to be partly driven by gene-specific expression and alternative splicing. Together, these findings provide an invaluable resource for ascertaining transcripts that are subject to m6A modification in maize and pave the way to a better understanding of natural m6A variation in mediating gene expression regulation.

RNA epigenetic modification: N6-methyladenosine.

N(6)-methyladenosine (m(6)A) is one of the most prevalent internal modifications in eukaryotic messenger RNA. The dynamic and reversible modification is installed by methyltransferase complex charactered three subunits: METTL3 (Methyltransferase-like protein 3), METTL14 (Methyltransferase-like protein 14) and WTAP (Wilms tumor 1-associating protein), and erased by two independent demethylases, FTO (Fat mass and obesity associated protein) and ALKBH5 (AlkB homolog 5), in an α-ketoglutarate (α-KG)- and Fe(II)-dependent manner. m(6)A plays funtions in controlling RNA metabolism through the recognition by m(6)A reader proteins, the YTH domain family proteins and HNRNPA2B1 (Heterogeneous nuclear ribonucleoproteins A2B1) . In this review, we summarized distributive features and vital roles of m(6)A and its associated proteins in RNA metabolisms and biological significance, which will help us better understand this new exciting emerging epitranscriptome research field.

Decreased N(6)-methyladenosine in peripheral blood RNA from diabetic patients is associated with FTO expression rather than ALKBH5.

CONTEXT: N(6)-methyladenosine (m(6)A) modification plays a fundamental role in the epigenetic regulation of the mammalian transcriptome. m(6)A can be demethylated by fat mass- and obesity-associated (FTO) protein and α-ketoglutarate-dependent dioxygenase alkB homolog 5 (ALKBH5) protein. However, the importance of m(6)A alteration in type 2 diabetes mellitus (T2DM) has not been explored. OBJECTIVE: The objective of the study was to investigate whether m(6)A content was reduced in T2DM patients and whether m(6)A content was correlated with the mRNA expression levels of the FTO and ALKBH5 genes. METHODS: In this case-control study, peripheral blood samples were obtained from 88 T2DM patients and 92 healthy controls. For the diabetic animal model experiment, blood samples were obtained from seven diabetic and eight nondiabetic rats. A sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry method was developed for the determination of the m(6)A content in RNA, quantitative real-time PCR was used to examine the mRNA expression levels of the FTO and ALKBH5 genes, and high-resolution melting and DNA sequencing were used to detect FTO single-nucleotide polymorphisms. RESULTS: Our results showed that the m(6)A contents in the RNA from T2DM patients and diabetic rats were significantly lower compared with the control groups (P = 2.6 × 10(-24) for T2DM patients; P = .001 for diabetic rats, respectively), and T2DM can be characterized by the content of m(6)A. The mRNA expression level of FTO was significantly higher in T2DM patients than that of the controls (P = .0007) and was associated with the risk of T2DM (odds ratio 2.797, 95% confidence interval 1.452-5.389, P = .002). Moreover, the m(6)A contents were correlated with FTO mRNA expression. CONCLUSIONS: 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.

Meclofenamic acid selectively inhibits FTO demethylation of m6A over ALKBH5.

Two human demethylases, the fat mass and obesity-associated (FTO) enzyme and ALKBH5, oxidatively demethylate abundant N(6)-methyladenosine (m(6)A) residues in mRNA. Achieving a method for selective inhibition of FTO over ALKBH5 remains a challenge, however. Here, we have identified meclofenamic acid (MA) as a highly selective inhibitor of FTO. MA is a non-steroidal, anti-inflammatory drug that mechanistic studies indicate competes with FTO binding for the m(6)A-containing nucleic acid. The structure of FTO/MA has revealed much about the inhibitory function of FTO. Our newfound understanding, revealed herein, of the part of the nucleotide recognition lid (NRL) in FTO, for example, has helped elucidate the principles behind the selectivity of FTO over ALKBH5. Treatment of HeLa cells with the ethyl ester form of MA (MA2) has led to elevated levels of m(6)A modification in mRNA. Our collective results highlight the development of functional probes of the FTO enzyme that will (i) enable future biological studies and (ii) pave the way for the rational design of potent and specific inhibitors of FTO for use in medicine.

FTO-dependent demethylation of N6-methyladenosine regulates mRNA splicing and is required for adipogenesis.

The role of Fat Mass and Obesity-associated protein (FTO) and its substrate N6-methyladenosine (m6A) in mRNA processing and adipogenesis remains largely unknown. We show that FTO expression and m6A levels are inversely correlated during adipogenesis. FTO depletion blocks differentiation and only catalytically active FTO restores adipogenesis. Transcriptome analyses in combination with m6A-seq revealed that gene expression and mRNA splicing of grouped genes are regulated by FTO. M6A is enriched in exonic regions flanking 5'- and 3'-splice sites, spatially overlapping with mRNA splicing regulatory serine/arginine-rich (SR) protein exonic splicing enhancer binding regions. Enhanced levels of m6A in response to FTO depletion promotes the RNA binding ability of SRSF2 protein, leading to increased inclusion of target exons. FTO controls exonic splicing of adipogenic regulatory factor RUNX1T1 by regulating m6A levels around splice sites and thereby modulates differentiation. These findings provide compelling evidence that FTO-dependent m6A demethylation functions as a novel regulatory mechanism of RNA processing and plays a critical role in the regulation of adipogenesis.

Stereoselective kinetic study of hexaconazole enantiomers in the rabbit.

Hexaconazole [(RS)-2-(2,4-dichlorophenyl)-1-(1H-1,2,4-triazol-1-yl)hexan-2-ol] is a potent triazole fungicide. The (-) isomer accounts for most of the fungicidal activity. The stereo- and/or enantioselective kinetics of hexaconazole were investigated in rabbits by intravenous injection. The concentrations of (-)- and (+)-hexaconazole in plasma, liver, and kidney tissue were determined by HPLC with a cellulose tris(3,5-dimethylphenylcarbamate)-based chiral stationary phase and by gas chromatography-mass spectrometry. After intravenous administration of racemic hexaconazole (rac-hexaconazole) at 30 mg/kg, plasma, liver, and kidney levels of the (+)-enantiomer decreased more rapidly than those of the (-)-enantiomer. The (-)-/(+)-enantiomer ratio of the area under the concentration-time curve (AUC(0-infinity)) was 1.35. The total plasma clearance value (CL) of (+)-enantiomer was more than 1.3-fold higher than that of the (-)-hexaconazole. The enantiomeric ratio (ER) increased with time in plasma, liver, and kidney. Other pharmacokinetic parameters of the enantiomers were also different. These results indicate substantial stereoselectivity in the kinetics of hexaconazole enantiomers in rabbits.