Chemogenetic tuning reveals optimal MAPK signaling for cell-fate programming

Cell states evolve through the combined activity of signaling pathways and gene regulatory networks. While transcription factors can direct cell fate, these factors rely on a cell state that is receptive to transitions in cell identity. How signaling levels contribute to the emergence of receptive cell states remains poorly defined in primary cells. Using a well-defined model of direct conversion, we examined how levels of the MAPK-activating oncogene HRAS G12V influence direct conversion of primary fibroblasts to induced motor neurons. We demonstrate that an optimal ‘Goldilocks’ level of MAPK signaling efficiently drives cell-fate programming. Rates of direct conversion respond biphasically to increasing HRAS G12V levels. While intermediate HRAS G12V levels increase the rate of conversion, high levels of HRAS G12V induce senescence. Through chemogenetic tuning, we set optimal MAPK activity for high rates of conversion in the absence of HRAS mutants. As MAPK pathways influence cell-fate transitions in development and disease, our results highlight the need to tune therapeutic interventions within a non-monotonic landscape that is shaped by genetics and levels of gene expression. Highlights MAPK signaling drives proliferation and conversion of fibroblasts to motor neurons Cell-fate programming responds biphasically to HRAS G12V expression High HRAS G12V expression induces senescence, which reduces conversion Chemogenetic tuning of MAPK activity increases conversion rates A small-molecule MAPK inducer drives high rates of conversion in the absence of HRAS G12V