Transposable element activity captures human pluripotent cell states [ATAC-seq]

Human pluripotent stem cells (hPSCs) serve as powerful in vitro models to elucidate the molecular underpinnings of embryonic cell fate transitions. hPSCs can be maintained in two distinct states: a naïve state, corresponding to the pre-implantation epiblast, and a primed state, mirroring the post-implantation epiblast. Our research demonstrates that transposable elements act as sensitive indicators of these pluripotency states. We engineered hPSCs with fluorescent reporters that capture the temporal expression dynamics of two transposable elements, LTR5_Hs and MER51B. This dual reporter system facilitates real-time monitoring and isolation of stem cells as they transition from naïve to primed pluripotency and further towards differentiation. Unexpectedly, we identified a rare, metastable cell population within primed hPSCs, marked by transcripts associated with pre-implantation embryo development and triggered by DNA damage. Additionally, our system uncovered novel transcriptional regulators involved in pluripotency, naïve reprogramming, and differentiation. Our study provides key insights into the dynamic regulation of transposable elements during embryonic development and introduces a novel system for investigating and exploiting cellular plasticity.