SELF-RENEWAL OF EMBRYONIC STEM-CELLS IN THE ABSENCE OF FEEDER CELLS AND EXOGENOUS LEUKEMIA INHIBITORY FACTOR

To evaluate the role of leukaemia inhibitory factor (LIF) for maintain ing pluripotent embryonic stem (ES) cells in culture, we established s everal exogenous LIF-independent ES cell Lines by continuous passaging in culture, The newly established ES cells, Kli and CBli, sustained t heir growth and remained undifferentiated in LIF-deficient medium, Ana lysis of chimaeric animals, produced with the beta-galactosidase trans genic Kli ES cells, revealed that LIF-independent ES cells can contrib ute to all embryonic germ layers, There was no detectable LIF protein in ES cell conditioned medium, and no upregulation of LIF mRNA was fou nd, The addition of neutralising anti-LIF antibodies was not sufficien t to abrogate the self renewal of the Kli ES cells, These studies sugg est that the signalling pathway involving diffusible LIF can be bypass ed for maintaining the pluripotency in culture, and indicate a conside rable heterogeneity in growth factor dependence and differentiation of different ES cells.