Posttranscriptional Control of the Stem Cell and Neurogenic Programs by the Nonsense-Mediated RNA Decay Pathway

• The NMD/RNA decay factor UPF1 promotes the undifferentiated cell state
• UPF1 is in a conserved circuit with miRNAs and TGF-β signaling components
• Neural differentiation is triggered by UPF1 downregulation
• Negative feedback loops stabilize the stem-like and differentiated cell states

SummaryThe mechanisms dictating whether a cell proliferates or differentiates have undergone intense scrutiny, but they remain poorly understood. Here, we report that UPF1, a central component in the nonsense-mediated RNA decay (NMD) pathway, plays a key role in this decision by promoting the proliferative, undifferentiated cell state. UPF1 acts, in part, by destabilizing the NMD substrate encoding the TGF-β inhibitor SMAD7 and stimulating TGF-β signaling. UPF1 also promotes the decay of mRNAs encoding many other proteins that oppose the proliferative, undifferentiated cell state. Neural differentiation is triggered when NMD is downregulated by neurally expressed microRNAs (miRNAs). This UPF1-miRNA circuitry is highly conserved and harbors negative feedback loops that act as a molecular switch. Our results suggest that the NMD pathway collaborates with the TGF-β signaling pathway to lock in the stem-like state, a cellular state that is stably reversed when neural differentiation signals that induce NMD-repressive miRNAs are received.

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