Statement of Benefit to California:
Year 1Human ES cells are routinely grown on feeders with medium containing serum or serum replacements supplemented with bFGF. Although progress has been made in improving culture conditions, the pathways involved in the maintenance of human ES cell self-renewal remain largely unknown. The main purpose of this project was to decipher the requirements for sustaining human ES cell self-renewal and to understand the molecular basis of these requirements. So far we have made the following findings: 1. Sustained activation of STAT3 supports mouse ES cell self-renewal in the absence of feeders ,whereas activation of STAT3 induces differentiation of human ES cells and epiblast-derived stem cells (EpiSCs); 2. Self-renewal of mouse/rat ES cells, but not human ES cells or EpiSCs, is sustained by inhibition of glycogen synthase kinase-3 (GSK3) and mitogen activated protein kinase (MAPK); 3. Activation of integrin pathway enhances self-renewal of human ES cells, but not mouse cells; 4. bFGF supports human ES cell self-renewal through an Erk1/2-dependent pathway. Our findings suggest that the requirements for sustaining self-renewal of human and rodent ES cells are fundamentally different and that human ES cells are most likely analogous to rodent EpiSCs. We are currently generating and characterizing human cells that resemble mouse/rat ES cells. Understanding the basic mechanisms involved in human ES cell maintenance will eventually lead us to develop better methods for the growth of human ES cells, which is clearly important if these cells are to be used clinically.