Department of Systems Biology, Harvard Medical School, Boston, United States.
Department of Neurobiology, Harvard Medical School, Boston, United States.
Elife. 2017 Oct 9;6:e26945. doi: 10.7554/eLife.26945.
In embryonic development, cells differentiate through stereotypical sequences of intermediate states to generate particular mature fates. By contrast, driving differentiation by ectopically expressing terminal transcription factors (direct programming) can generate similar fates by alternative routes. How differentiation in direct programming relates to embryonic differentiation is unclear. We applied single-cell RNA sequencing to compare two motor neuron differentiation protocols: a standard protocol approximating the embryonic lineage, and a direct programming method. Both initially undergo similar early neural commitment. Later, the direct programming path diverges into a novel transitional state rather than following the expected embryonic spinal intermediates. The novel state in direct programming has specific and uncharacteristic gene expression. It forms a loop in gene expression space that converges separately onto the same final motor neuron state as the standard path. Despite their different developmental histories, motor neurons from both protocols structurally, functionally, and transcriptionally resemble motor neurons isolated from embryos.
在胚胎发育过程中，细胞通过典型的中间状态序列分化，以产生特定的成熟命运。相比之下，通过异位表达终末转录因子（直接编程）驱动分化可以通过替代途径产生相似的命运。直接编程中的分化与胚胎分化的关系尚不清楚。我们应用单细胞 RNA 测序比较了两种运动神经元分化方案：一种是近似胚胎谱系的标准方案，另一种是直接编程方法。两者最初都经历了类似的早期神经承诺。后来，直接编程途径分支出一个新的过渡状态，而不是遵循预期的胚胎脊髓中间状态。直接编程中的新状态具有特定的、非典型的基因表达。它在基因表达空间中形成一个循环，分别汇聚到与标准途径相同的最终运动神经元状态。尽管它们的发育历史不同，但两种方案的运动神经元在结构、功能和转录上都与从胚胎中分离的运动神经元相似。
