Project description:To investigate the effects of the coding sequence on mRNA decay, we globally analyzed the stability of endogenous mRNAs as well as those derived from the human ORFeome collection, which contains full-length coding sequences in the context of invariant UTRs.
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:A translating ribosome is typically thought to follow the reading frame defined by the selected start codon. Using super-resolution ribosome profiling, here we report pervasive out-of-frame translation from the start codon. Unlike programmable frameshifting during elongation, start codon-associated ribosome frameshifting (SCARF) stems from the slippage of the initiating ribosome. Using a massively paralleled reporter assay, we uncovered sequence elements acting as SCARF enhancers or repressors, implying that start codon recognition is coupled with reading frame fidelity. This finding explains thousands of mass spectrometry spectra unannotated from human proteome. Mechanistically, we find that the eukaryotic initiation factor 5B (eIF5B) maintains the reading frame fidelity during the transition from initiation to elongation. Intriguingly, amino acid starvation induces SCARF by proteasomal degradation of eIF5B. The stress-induced SCARF products provide a degradative source to mitigate amino acid scarcity during starvation. Our findings illustrate the beneficial effect of divergent translation in nutrient stress adaptation.
Project description:Usage of synonymous codons represents a characteristic pattern of preference in each organism. It has been inferred that such bias of codon usage has evolved as a result of adaptation for efficient synthesis of proteins. Here we examined synonymous codon usage in genes of the fission yeast Schizosaccharomyces pombe, and compared codon usage bias with expression levels of the gene. In this organism, synonymous codon usage bias was correlated with expression levels of the gene; the bias was most obvious in two-codon amino acids. A similar pattern of the codon usage bias was also observed in Saccharomyces cerevisiae, Arabidopsis thaliana, and Caenorhabditis elegans, but was not obvious in Oryza sativa, Drosophila melanogaster, Takifugu rubripes and Homo sapiens. As codons of the highly expressed genes have greater influence on translational efficiency than codons of genes expressed at lower levels, it is likely that codon usage in the S. pombe genome has been optimized by translational selection through evolution. Relative amounts of mRNA for each ORF were measured by DNA microarray using genomic DNA as a reference, and the copy number of mRNA was calculated using an estimate of the total mRNA number in the cell as 100,000 copies.
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:Usage of synonymous codons represents a characteristic pattern of preference in each organism. It has been inferred that such bias of codon usage has evolved as a result of adaptation for efficient synthesis of proteins. Here we examined synonymous codon usage in genes of the fission yeast Schizosaccharomyces pombe, and compared codon usage bias with expression levels of the gene. In this organism, synonymous codon usage bias was correlated with expression levels of the gene; the bias was most obvious in two-codon amino acids. A similar pattern of the codon usage bias was also observed in Saccharomyces cerevisiae, Arabidopsis thaliana, and Caenorhabditis elegans, but was not obvious in Oryza sativa, Drosophila melanogaster, Takifugu rubripes and Homo sapiens. As codons of the highly expressed genes have greater influence on translational efficiency than codons of genes expressed at lower levels, it is likely that codon usage in the S. pombe genome has been optimized by translational selection through evolution.