BNC1 is a master regulator of human epicardial cell heterogeneity and function

Single cell RNAseq of a model of epicardium derived from human pluripotent stem cell (hPSC-epi) reveals that distinct epicardial sub-populations are defined by high levels of expression for the transcription factors BNC1 and TCF21. Cells positive for the transcription factor WT1 are included in the BNC1 population, which confirms the heterogeneity observed in the mouse with TCF21 and WT1. Analysis of genes differentially expressed between the two populations suggests differences in their biological activities. We identified THY1 as a membrane marker of the TCF21 population and we show that THY1+ cells can differentiate into cardiac fibroblast and smooth muscle cells while THY1- cells mostly produce the latter. Knocking-down BNC1 during the establishment of the populations led to an homogeneous epicardium containing mostly the TCF21high populations and differentiating mainly into cardiac fibroblasts. Using network inference methods and transcriptomic data from the different epicardial lineages derived from the hPSC-epi, we identified a core transcriptional network organized around WT1, TCF21 and BNC1 and orchestrated by BNC1. Enginnered lateral mesoderm and epicardium cells were sorted in 96 wells plates, their RNA extracted, libraries prepared using a SmartSeq approach and single-end sequencing at 100bp performed on an Illumina HiSeq 2500.