Activation of a cortical neurogenesis transcriptional program during NEUROD1-induced astrocyte-to-neuron conversion

NEUROD1-induced astrocyte-to-neuron (AtN) conversion has garnered significant attention as a potential therapeutic intervention to neurological disorders. To gain insight into the molecular regulations underlying this neuronal reprogramming process, we applied single-cell multiomics analyses on in vitro ND1-induced AtN conversion to systematically investigate how ND1 changed the fate of astrocytes at transcriptomic and epigenetic levels. Our findings reveal that the initial immature astrocytes go through an intermediate state where both astrocytic and neuronal genes are activated at early stage of AtN conversion. ND1 directly reshapes the chromatin accessibility landscape of astrocytes to that of neurons, promoting expression of endogenous Neurod1 and other neurogenic genes such as Hes6, Insm1 etc. Interestingly, cell proliferation status is highly correlated with conversion rate, and inhibition of cell division significantly reduces the conversion ratio. Moreover, in comparison with another AtN reprogramming transcription factor, ASCL1, external ND1 can activate endogenous Neurod1 and directly promote neuronal gene transcription; whereas external ASCL1 hardly activates endogenous Ascl1, leading to slower and inefficient conversion. Together, our studies demonstrate that in vitro AtN conversion mimics neurogenic transcriptional program in embryonic neurogenesis.