An epigenetic barrier in neural progenitor cells and early neurons sets the timing of human neuronal maturation

A challenge for understanding the development of brain circuits is to identify the factors that instruct neurons to accomplish each developmental steps at the appropriate stage. Neuronal maturation follows an intrinsic species-specific developmental pace that is extremely protracted in humans and that is retained during human pluripotent stem cells (hPSCs) differentiations. Using a novel platform that synchronized the generation of cortical neurons from hPSC, we established morphological, functional, and molecular roadmaps of maturation. We found that the temporal unfolding of maturation programs proceeds gradually and is limited by the retention of complex epigenetic signatures. Loss-of-function of multiple such epigenetic factors at the neuron stage triggered precocious molecular and functional maturation. Remarkably, transient pharmacological manipulation of a subset of epigenetic factors, including EZH2, EHMT1/2 and DOT1L, at the progenitor cell stage can prime precursors to reach enhanced molecular and functional signatures of maturity as neurons. Our results indicate that the rate at which neurons mature is set well before neurogenesis through the establishment of an “epigenetic barrier” in progenitor cells that gets slowly erased in neurons, allowing the gradual onset of maturation programs. Overall design: Neural induction of WA09 (H9) hPSC was completed using the dual SMAD inhibition protocol and WNT inhibition on Matrigel coated dishes. hPSC-derived neurons were maintained on poly-L-ornithine and Laminin/ Fibronectin coated plates in Neurobasal medium supplemented with B27, L-glutamine and DAPT, dissociated at d27 using Accutase and Papain and processed for scRNAseq.