Defining codon-mediated mRNA decay and No-go decay in zebrafish embryos

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. Overall design: Ribosome profiling