Myogenic Progenitor Cell Lineage Specification by CRISPR/Cas9-based Transcriptional Activators

Engineered CRISPR/Cas9-based transcriptional activators can potently and specifically activate endogenous fate-determining genes to direct differentiation of pluripotent stem cells. Here, we demonstrate that endogenous activation of the PAX7 transcription factor results in stable epigenetic remodeling and directly reprograms human pluripotent stem cells into skeletal myoblast progenitor cells. Compared to the exogenous overexpression of PAX7 cDNA, we find that endogenous activation results in the generation of more proliferative myogenic progenitors that can maintain PAX7 expression over multiple passages in serum-free conditions while preserving the capacity for terminal myogenic differentiation. Transplantation of human myogenic progenitors derived from endogenous activation of PAX7 into immunodeficient mice resulted in a greater number of human dystrophin+ myofibers compared to exogenous PAX7 overexpression. RNA-seq analysis also revealed transcriptome-wide differences between myogenic progenitors generated via CRISPR-based endogenous activation of PAX7 and exogenous PAX7 cDNA overexpression. These studies demonstrate the utility of CRISPR/Cas9-based transcriptional activators for progenitor cell specification and their potential for regenerative medicine. Transcriptional profiling of differentiated human iPSCs that had been treated with either PAX7-targeting gRNA only, VP64dCas9VP64 with gRNA, cDNA encoding PAX7-A isoform, or cDNA encoding PAX7-B isoform at day 14 of differentiation.