An Intermediate Pluripotent State Controlled by microRNAs is Required for the Naïve to Primed Stem Cell Transition

The embryonic stem cell (ESC) transition from naive to primed pluripotency is marked by major changes in cellular properties and developmental potential. ISY1 is implicated in miRNA biogenesis yet its widespread role and relevance to ESC biology remain unknown. Here we find that highly dynamic ISY1 expression during the naïve to primed ESC transition defines a unique phase of ‘poised’ pluripotency characterized by distinct miRNA and mRNA transcriptomes and widespread poised cell contribution to mouse chimeras. Loss- and gain-of-function experiments reveal that ISY1 promotes exit from the naïve state, is necessary and sufficient to induce and maintain poised pluripotency, and that persistent ISY1 overexpression inhibits the transition from the naïve to the primed state. We identify a large subset of ISY1-dependent miRNAs that can rescue the inability of miRNA-deficient ESCs to establish the poised state and transition to the primed state. Thus, dynamic ISY1 regulates poised pluripotency through miRNAs to control ESC fate. mouse ESCs with ISY1 overexpression and depletion were used for EB and EpiLC differentiation. PolyA(+) RNA-seq and small RNA-seq were then performed from the samples at different time points to measure the mRNA and miRNA transcriptome changes during differentiation.