Transfer RNAs are essential for translating genetic information into proteins. The human genome contains hundreds of predicted tRNA genes, many in multiple copies. How their expression is regulated to control tRNA repertoires is unknown. Here we combined quantitative tRNA profiling and chromatin immunoprecipitation with sequencing to measure tRNA expression following the differentiation of human induced pluripotent stem cells into neuronal and cardiac cells. We find that tRNA transcript levels vary substantially, whereas tRNA anticodon pools, which govern decoding rates, are more stable among cell types. Mechanistically, RNA polymerase III transcribes a wide range of tRNA genes in human induced pluripotent stem cells but on differentiation becomes constrained to a subset we define as housekeeping tRNAs. This shift is mediated by decreased mTORC1 signalling, which activates the RNA polymerase III repressor MAF1. Our data explain how tRNA anticodon pools are buffered to maintain decoding speed across cell types and reveal that mTORC1 drives selective tRNA expression during differentiation.

转移 RNA 对于将遗传信息转化为蛋白质至关重要。人类基因组包含数百个预测的 tRNA 基因，其中许多有多个拷贝。如何调节它们的表达来控制 tRNA 库尚不清楚。在这里，我们将定量 tRNA 分析和染色质免疫沉淀与测序相结合，测量人诱导多能干细胞分化为神经元和心肌细胞后的 tRNA 表达。我们发现 tRNA 转录水平差异很大，而控制解码率的 tRNA 反密码子库在不同细胞类型中更加稳定。从机制上讲，RNA 聚合酶 III 在人类诱导多能干细胞中转录多种 tRNA 基因，但在分化时仅限于我们定义为管家 tRNA 的子集。这种转变是由 mTORC1 信号传导减少介导的，mTORC1 信号传导会激活 RNA 聚合酶 III 阻遏物 MAF1。我们的数据解释了 tRNA 反密码子库如何缓冲以维持跨细胞类型的解码速度，并揭示 mTORC1 在分化过程中驱动选择性 tRNA 表达。