Abstract: Embryonic stem cells (ES) have the unique capacity to proliferate extensively while maintaining pluripotency. ES cell lines can also be generated from human blastocyst embryos, and are considered promising donor sources for cell transplantation therapies for diseases such as juvenile diabetes, Parkinson’s disease, and heart failure. However, as for organ transplants, tissue rejection remains a significant concern for ES cell transplantation. Another concern is the use of human embryos. One possible means to avoid these issues is by reprogramming the nuclei of differentiated cells to ES celllike, pluripotent cells. Several extrinsic signals such as LIF, BMP and Wnt can support the selfrenewal and pluripotency of embryonic stem (ES) cells through regulating the “pluripotent genes”. A unique homeobox transcription factor, Nanog, is one of the key downstream effectors of these signals. Elevated level of Nanog can maintain the mouse ES cell self-renewal independent of LIF and enable human ES cell growth without feeder cells. In addition to the external signal pathways, intrinsic transcription factors such as FoxD3, P53 and Oct4 are also involved in regulating the expression of Nanog. Functionally, Nanog works together with other key pluripotent factors such as Oct4 and Sox2 to control a set of target genes that have important functions in ES cell pluripotency. These key factors form a regulatory network to support or limit each other’s expression level, which maintains the properties of ES cells.

Key words: Nanog; embryonic stem cells; LIF; self-renewal; pluripotency