THE DYNAMIC INTERPLAY BETWEEN HOMEODOMAIN TRANSCRIPTION FACTORS AND CHROMATIN ENVIRONMENT REGULATES PRONEURAL FACTOR OUTCOMES

SUMMARY Generation of neurons of vast diversity involves early spatial and temporal patterning of the neuronal precursors by morphogenic gradients and combinatorial expression of transcription factors. While the proneuronal function of the basic-helix-loop-helix (bHLH) transcription factor Ngn2 is well established, its role in neuronal subtype specification remains unclear. Here, we found that coexpressing NGN2 with the forebrain homeobox factor EMX1 converts human pluripotent stem cells into a highly homogeneous glutamatergic forebrain neurons without partial cholinergic and monoaminergic gene programs observed in cells infected with NGN2 only. Our molecular characterization revealed that transcriptional output and genomic targeting of Ngn2 is altered by co-factors such as EMX1 explaining the more focused subtype specification. Ngn2 function is less modified by the chromatin environment and does not affect regionalization of pre-patterned neural progenitors. These results enable improved strategies for generating a plethora of defined neuronal subpopulations from pluripotent stem cells for therapeutic or disease-modeling purposes. Highlights NGN2 converts human ES cells into glutamatergic neurons some of which co-express a partial cholinergic program NGN2 directly binds to and activates ISL1 in ES cells which together with PHOX2A/B induce cholinergic genes Anterior-posterior regionalization affects NGN2 binding and transcriptional output but does not focus subtype specification Forebrain homeobox factors including EMX1 and FOXG1 redirect NGN2 chromatin binding and repress posterior and cholinergic genes, resulting in homogeneous forebrain excitatory neurons