Regulatory factors of embryonic stem cells.

The analysis of factors which regulate cell proliferation and differentiation in early mammalian development has been facilitated by the existence of cell lines derived from pluripotential stem cells of the early embryo; embryonal carcinoma (EC) cells and embryonic stem (ES) cells. EC cells have proved to be a useful source of embryonic growth factors. A potent mitogen, ECDGF has been isolated from EC cell conditioned medium. ECDGF appears to be a novel member of the heparin binding growth factor family. A remarkable feature of heparin binding growth factors is their ability to induce mesodermal differences in Xenopus laevis animal pole explants. ES cell differentiation in vitro is controlled by exogenous factors, in particular a novel differentiation inhibitory factor DIA. Controlled bipotential differentiation of ES cells can be achieved by exposing ES cells to different combinations of regulatory signals.