PARACRINE INDUCTION OF STEM-CELL RENEWAL BY LIF-DEFICIENT CELLS - A NEW ES CELL REGULATORY PATHWAY

The propagation of pluripotential mouse embryonic stem (ES) cells is s ustained by leukemia inhibitory factor (LIF) or related cytokines that act through a common receptor complex comprising the LIF receptor sub mit (LIF-R) and the signal transducer gp130. However, the findings tha t embryos lacking LIF-R or gp130 can develop beyond gastrulation argue for the existence of an alternative pathway(s) governing the maintena nce of pluripotency in vivo. In order to define those factors that con tribute to self-renewal in ES cell cultures, we have generated ES cell s in which both copies of the lif gene are deleted These cells showed a significantly reduced capacity for regeneration of stem cell colonie s when induced to differentiate, confirming that LIF is the major endo genous regulatory cytokine in ES cell cultures. However, self-renewal was not abolished and undifferentiated ES cell colonies were still obt ained in the complete absence of LIP. A differentiated, LIF-deficient, parietal endoderm-like cell line was derived and shown to support ES cell propagation via production of a soluble, macromolecular, trypsin- sensitive activity. This activity, which we name ES cell renewal facto r (ESRF), is distinct from members of the IL-6/LIF family because (i) it is effective on ES cells lacking LTE-R; (ii) it is not blocked by a nti-gp130 neutralizing antibodies; and (iii) it acts without activatio n of STAT3. ES cells propagated clonally using ESRF alone can contribu te fully to chimaeras and engender germline transmission. These findin gs establish that ES cell pluripotency can be sustained via a LIF-R/gp 130-independent, STAT-S independent, signaling pathway. Operation of t his pathway in vivo could play an important role in the regulation of pluripotency in the epiblast and account for the viability of lifr -/- and gp230 -/- embryos. (C) 1998 Academic Press.