The dynamic translatome of retinal ganglion cell axons during assembly and maintenance of the mouse visual system

Local mRNA translation mediates the adaptive responses of axons to extrinsic signals but direct evidence that it occurs in mammalian CNS axons in vivo is scant. We developed an axon-TRAP-RiboTag approach in mouse that allows deep-sequencing analysis of ribosome-bound mRNAs in the retinal ganglion cell axons of the developing and adult retinotectal projection in vivo. The embryonic-to-postnatal axonal translatome comprises an evolving subset of enriched genes with axon-specific roles suggesting distinct steps in axon wiring, such as elongation, pruning and synaptogenesis. Adult axons, remarkably, have a complex translatome with strong links to axon survival, neurotransmission and neurodegenerative disease. Translationally co-regulated mRNA subsets share common upstream regulators, and novel sequence elements generated by alternative splicing that promote axonal mRNA translation. Our results indicate that intricate regulation of compartment-specific mRNA translation in mammalian CNS axons supports the formation and maintenance of neural circuits in vivo. The profiling of ribosome-bound mRNAs in mouse retinal ganglion cell axons at 4 different developmental stages局部mRNA翻译（local mRNA translation）介导轴突对外源信号的适应性应答，但目前在体哺乳动物中枢神经系统（central nervous system, CNS）轴突中直接证实该过程存在的证据仍较为匮乏。我们在小鼠中构建了轴突-TRAP-RiboTag技术，可实现在体对发育中及成熟视网膜顶盖投射通路的视网膜神经节细胞轴突内结合于核糖体的mRNA进行深度测序分析。胚胎期至产后的轴突翻译组（translatome）包含一组动态变化的富集基因子集，这些基因具有轴突特异性功能，对应轴突搭建过程中的不同阶段，如轴突延伸、突触修剪与突触形成。值得注意的是，成熟轴突拥有复杂的翻译组，其与轴突存活、神经递质传递及神经退行性疾病紧密相关。受翻译共调控的mRNA子集共享共同的上游调控因子，且存在由可变剪接（alternative splicing）产生的新型序列元件，可促进轴突内mRNA翻译。我们的研究结果表明，哺乳动物中枢神经系统轴突中区域特异性mRNA翻译的精密调控，可在体支持神经环路的形成与维持。本数据集针对4个不同发育阶段的小鼠视网膜神经节细胞轴突内结合于核糖体的mRNA开展了表达谱分析。