Our research focuses on understanding the mechanism and role of small regulatory RNAs in embryonic stem (ES) cells. ES cells have the remarkable capacity to self-renew and to differentiate into all cell types and are of potential therapeutic value for numerous degenerative diseases. However, the molecular foundations of stem cell maintenance and cellular pluripotency remain poorly defined. It is emerging that cells possess a wide repertoire of tiny regulatory RNAs that are critical for a variety of biological pathways and can repress genes via numerous mechanisms. For posttranscriptional gene silencing, microRNAs (miRNAs), and small inhibitoryRNAs (siRNAs), function as guide molecules inducing mRNA degradation or translational repression.