Human stem cells maintain a state of self-renewal and pluripotency through a variety of genetic regulatory mechanisms. While significant amounts of work has been focused on understanding the ways in which epigenetic and transcriptional control of gene expression keeps stem cells from spontaneously differentiating to specific lineages, very little has focused on the post-transcriptional control (PTC) of cellular homeostasis. In our proposal, we set out to solve the major problem of which genes are direct targets of microRNAs and an RNA binding protein LIN28, together they define two modes of PTC of expression in pluripotency and reprogramming. In the first year of funding, we have made significant progress in elucidating the regulatory network of RNAs regulated by LIN28. A fraction of our results has been accepted for publication, but the remainder of the project is still underway. We have adapted new advanced genome-wide approaches to studying LIN28’s function in the first year of funding, and we expect to reveal unexpected findings in the next year. We have also initiated Aims 2 and Aims 3 of our proposal, which is to define the miRNA targets in human pluripotent stem cells, and to compare these targets with LIN28 targets. In the next two years of funding, we expect to successfully accomplish our proposed aims to reveal the importance of PTC in controlling pluripotency and reprogramming of human stem cells.