ISOLATION AND CHARACTERIZATION OF A LEUKEMIA INHIBITORY FACTOR-INDEPENDENT EMBRYONIC STEM-CELL LINE

Leukemia inhibitory factor (LIF) is a mammalian cytokine that has a wi de range of physiological activities, including the inhibition of diff erentiation of embryonic stem (ES) cells. We have used insertional mut agenesis in an attempt to isolate molecules that participate in LIF si gnal transduction via the LIF receptor. Using a robust screen for undi fferentiated cells, we have isolated one ES cell line, Poly 27, that d oes not require exogenous LIF to remain undifferentiated in vitro. We present evidence that Poly 27 is not irreversibly committed to an undi fferentiated phenotype, but can differentiate iir vitro if cultured in the presence of chemical differentiating agents, while in syngeneic m ice Poly 27 cells form tumours which are composed largely of undiffere ntiated cells. We have characterized the mechanism of factor independe nce in Poly 27, and shown it to be a result of autocrine LIF productio n. This LIF production is potentially the result of a mutation in a ge ne critically involved in regulating LIF production in ES cells. (C) 1 997 Elsevier Science Ltd.