Reprogramming progressive cells display low CAG promoter activity

There is wide variability in the propensity of somatic cells to reprogram into pluripotency in response to the Yamanaka factors. How to segregate these variabilities to enrich for cells of specific traits that reprogram efficiently remains challenging. Here we report that the variability in reprogramming propensity is associated with the activity of the MKL1/SRF transcription factor and concurs with small cell size as well as rapid cell cycle. Reprogramming progressive cells can be prospectively identified by their low activity of a widely used synthetic promoter, CAG. CAGlow cells arise and expand during cell cycle acceleration in the early reprogramming culture of both mouse and human fibroblasts. Our work illustrates a molecular scenario underlying the distinct reprogramming propensities and demonstrates a convenient practical approach for their enrichment. © AlphaMed Press 2020 SIGNIFICANCE STATEMENT: We report a novel and much simpler method to identify and enrich for reprogramming progressive cells. We benchmarked the identity of the CAG low cells by assessing their cell cycle, cell size and transcriptome. Due to its simplicity, this method should be widely useful for enriching reprogramming progressive cells.