Model of reprogramming stages. Initially the cell population undergoes relatively uniform small fold changes in miRNA expression or experiences heterogeneous expression within the population. The downregulation of Dlk1-Dio3 miRNAs at this stage may set up an initial EMT to prepare the sample for subsequent MET. The initial stochasticity is followed by a hierarchical phase where only a few miRNAs are differentially expressed, but at high fold changes. ESC, embryonic stem cell.