Project description:mRNA degradation is a critical aspect of gene expression which dictates mRNA steady-state levels in conjunction with transcription rate. Previous studies in other model organisms have demonstrated that enrichment of specific codons within the open reading frame (ORF) can influence mRNA stability, primarily by modulating translation elongation speed. Despite advancements in our understanding of mRNA stability regulation by microRNAs and 3'UTR-based factors in mammalian systems, the importance of other mRNA regions such as the ORF sequence on dictating cellular mRNA levels are incompletely understood. To characterize the effects of the coding sequence on mRNA decay in mammals, we analyzed mRNA stability in human and Chinese Hamster Ovary (Cricetulus griseus) cells by both global metabolic labeling and single-gene mRNA reporter transcription shutoffs. In agreement with previous studies, we observed that synonymous codon usage impacts mRNA stability in mammalian cells. Unexpectedly, we also found that amino acid content is a potent determinant of mRNA stability in humans and other mammalian species. Codon and amino acid effects on decay correlate with tRNA levels measured by tRNA-Seq or intracellular amino acid levels measured by HPLC, respectively. These results suggest that both tRNA and amino acid levels have complementary effects on regulation of mRNA stability in mammals, hinting at the possibility of dynamic control of mRNA levels via altered tRNA or amino acid levels.
Project description:The control of mRNA stability plays a central role in regulating gene expression. In metazoans, the earliest stages of development are driven by maternally supplied mRNAs. The degradation of these maternal mRNAs is critical for promoting the maternal-to-zygotic transition of developmental programs, although the underlying mechanisms are poorly understood in vertebrates. Here, we characterized maternal mRNA degradation pathways in zebrafish using a transcriptome analysis and systematic reporter assays. Our data demonstrate that ORFs enriched with uncommon codons promote deadenylation by the CCR4-NOT complex in a translation-dependent manner. This codon-mediated mRNA decay is conditional on the context of the 3â² UTR, with long 3â² UTRs conferring resistance to deadenylation. These results indicate that the combined effect of codon usage and 3â² UTR length determines the stability of maternal mRNAs in zebrafish embryos. Our study thus highlights the codon-mediated mRNA decay as a conserved regulatory mechanism in eukaryotes. zebrafish embryonic mRNA profile at 2 different stages (2 hpf and 6 hpf) in wildtype and 3 additional conditions (miR-430 inhibition, RNApol II inhibition and CNOT7 inhibition) at 6 hpf. All experiments are performed as triplicates
Project description:The control of mRNA stability plays a central role in regulating gene expression. In metazoans, the earliest stages of development are driven by maternally supplied mRNAs. The degradation of these maternal mRNAs is critical for promoting the maternal-to-zygotic transition of developmental programs, although the underlying mechanisms are poorly understood in vertebrates. Here, we characterized maternal mRNA degradation pathways in zebrafish using a transcriptome analysis and systematic reporter assays. Our data demonstrate that ORFs enriched with uncommon codons promote deadenylation by the CCR4-NOT complex in a translation-dependent manner. This codon-mediated mRNA decay is conditional on the context of the 3′ UTR, with long 3′ UTRs conferring resistance to deadenylation. These results indicate that the combined effect of codon usage and 3′ UTR length determines the stability of maternal mRNAs in zebrafish embryos. Our study thus highlights the codon-mediated mRNA decay as a conserved regulatory mechanism in eukaryotes.
Project description:Messenger RNA (mRNA) translation can lead to higher rates of mRNA decay, suggesting a role for the ribosome in mRNA destruction. Furthermore, features of an mRNA, such as codon identities, that are directly probed by the ribosome also correlate with mRNA decay rates. Specifically, many amino acids are encoded by synonymous codons, and some synonymous codons are decoded by more abundant tRNAs leading to more optimal translation and increased mRNA stability. In addition to different translation rates, the presence of individual codons can lead to higher or lower rates of amino acid misincorporation which could potentially lead to protein misfolding if an individual amino acid makes many critical contacts in a structure. Here, we directly test whether amino acid misincorporation affects mRNA stability, taking advantage of an aminoglycoside antibiotic (G418) which promotes higher error rates in the ribosome. We observe that G418 decreases firefly luciferase mRNA stability in an in vitro system, and we similarly observe that G418 reduces mRNA stability in mouse embryonic stem cells (mESCs). G418-sensitive mRNAs are enriched for suboptimal hydrophobic amino acid codons as well as other codons that are known to result in higher rates of amino acid misincorporation. Since protein folding is highly sensitive to the identity of hydrophobic amino acids, these results strongly suggest that defects in protein folding are linked to mRNA decay.
Project description:Limitation for amino acids is thought to regulate translation in mammalian cells primarily by signaling through the kinases mTORC1 and GCN2. We find that limitation for the amino acid arginine causes a selective loss of tRNA charging, which regulates translation through ribosome pausing at two of six arginine codons. Interestingly, limitation for leucine, an essential and abundant amino acid in protein, results in little or no ribosome pausing. Chemical and genetic perturbation of mTORC1 and GCN2 signaling revealed that their robust response to leucine limitation prevents ribosome pausing, while an insufficient response to arginine limitation led to loss of arginine tRNA charging and ribosome pausing. Codon-specific ribosome pausing decreased protein production and triggered premature ribosome termination without significantly reducing mRNA levels. Together, our results suggest that amino acids which are not optimally sensed by the mTORC1 and GCN2 pathways still regulate translation through an evolutionarily conserved mechanism based on synonymous codon usage.
Project description:The control of mRNA stability plays a central role in regulating gene expression patterns. While much is known about the roles of 5´ and 3´ untranslated regions in the mRNA stability control, the impact of protein-coding sequences on mRNA stability had been obscure. Recently, several groups reported that codon composition in the ORF affects mRNA deadenylation and degradation rates in a translation-dependent manner. Hence, codons define not only the amino acid sequences to be synthesized but also the stability of mRNAs. However, how 61 codons differently affect mRNA stability remains unclear. Besides, aberrant stalling of the ribosome induces ribosome quality control (RQC) and No-go decay. The relationship between the two co-translational mRNA decay pathways is not systematically analyzed. To precisely characterize the effects of 61 codons on mRNA stability, we developed a simplified reporter system that allows detection of the effect of every single codon on mRNA stability in zebrafish embryos. Using this system, we show that the effect of codons on mRNA stability is partially but significantly correlated with the translation elongation rate and tRNA abundance. Interestingly, the codon effect is still maintained in zebrafish embryos lacking Znf598, an essential mediator of RQC and NGD. Znf598-dependent NGD targets a particular type of ribosome stalling but has limited impact on endogenous mRNA stability. Our study thus defines two related co-translational mRNA decay pathways during animal development.
Project description:Messenger RNA (mRNA) stability substantially impacts steady-state gene expression levels in a cell. mRNA stability is strongly affected by codon composition in a translation-dependent manner across species, through a mechanism termed codon optimality. We have developed iCodon (www.iCodon.org), an algorithm for customizing mRNA expression through the introduction of synonymous codon substitutions into the coding sequence. iCodon is optimized for four vertebrate transcriptomes: mouse, human, frog, and fish. Users can predict the mRNA stability of any coding sequence based on its codon composition and subsequently generate more stable (optimized) or unstable (deoptimized) variants encoding for the same protein. Further, we show that codon optimality predictions correlate with both mRNA stability using a massive reporter library and expression levels using fluorescent reporters and analysis of endogenous gene expression in zebrafish embryos and/or human cells. Therefore, iCodon will benefit basic biological research, as well as a wide range of applications for biotechnology and biomedicine.