Embryogenesis entails dramatic shifts in mRNA translation and turnover that reprogram gene expression during cellular proliferation and differentiation. Codon identity modulates mRNA stability during early vertebrate embryogenesis, but how the composition of tRNA pools is matched to translational demand is unknown. By quantitative profiling of tRNA repertoires in zebrafish embryos during the maternal-to-zygotic transition, we show that zygotic tRNA repertoires are established after the onset of gastrulation, succeeding the major wave of zygotic mRNA transcription. Maternal and zygotic tRNA pools are distinct, but their reprogramming does not result in a better match to the codon content of the zygotic transcriptome. Instead, we find that an increase in global translation at gastrulation sensitizes decoding rates to tRNA supply, thus destabilizing maternal mRNAs enriched in slowly translated codons. Translational activation and zygotic tRNA expression temporally coincide with an increase of TORC1 activity at gastrulation, which phosphorylates and inactivates the RNA polymerase III repressor Maf1a/b. Our data indicate that a switch in global translation, rather than tRNA reprogramming, determines the onset of codon-dependent maternal mRNA decay during zebrafish embryogenesis.

中文翻译：

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斑马鱼早期胚胎发生过程中 tRNA 库的动力学和功能影响。


胚胎发生需要 mRNA 翻译和周转的巨大变化，这些变化会在细胞增殖和分化过程中重新编程基因表达。密码子身份在早期脊椎动物胚胎发生过程中调节 mRNA 稳定性，但 tRNA 库的组成如何与翻译需求相匹配尚不清楚。通过在母体到合子过渡期间对斑马鱼胚胎中的 tRNA 库进行定量分析，我们表明合子 tRNA 库是在原肠胚形成开始后建立的，继合子 mRNA 转录的主要浪潮之后。母体和合子 tRNA 库是不同的，但它们的重编程并不会导致与合子转录组的密码子内容更好地匹配。相反，我们发现原肠胚形成时全局翻译的增加使解码速率对 tRNA 供应敏感，从而破坏了富含慢翻译密码子的母体 mRNA 的稳定性。翻译激活和合子 tRNA 表达暂时与原肠胚形成时 TORC1 活性的增加相吻合，原肠胚形成时 TORC1 活性磷酸化并使 RNA 聚合酶 III 阻遏蛋白 Maf1a/b 失活。我们的数据表明，全局翻译的转换，而不是 tRNA 重编程，决定了斑马鱼胚胎发生过程中密码子依赖性母体 mRNA 衰变的开始。