Mouse embryonic stem cells can differentiate via multiple paths to the same state [array]

In embryonic development, cells must differentiate through stereotypical sequences of intermediate states to generate mature states of a particular fate. By contrast, direct programming can generate similar fates through alternative routes, by directly expressing terminal transcription factors. Yet the cell state transitions defining these new routes are unclear. We applied single-cell RNA sequencing to compare two mouse motor neuron differentiation protocols: a standard protocol approximating the embryonic lineage, and a direct programming method. Both undergo similar early neural commitment. Then, rather than transitioning through spinal intermediates like the standard protocol, the direct programming path diverges into a novel transitional state. This state has specific and abnormal gene expression. It opens a 'loop' or 'worm hole' in gene expression that converges separately onto the final motor neuron state of the standard path. Despite their different developmental histories, motor neurons from both protocols structurally, functionally, and transcriptionally resemble motor neurons from embryos. Comparison of specific transitional progenitor states from each of two motor neuron differentiation protocols. This was a validation of the single-cell RNA sequencing analysis in this manuscript.