Use of avian cytokines in mammalian embryonic stem cell culture.

Mouse blastocyst-derived embryonic stem (ES) cells are multipotent cells that can be used in vitro as models of differentiation and in vivo can contribute to all embryonic tissues including the germ line. The culture of ES cells requires a source of leukemia inhibitory factor (LIF), often provided by culture with a mouse fibroblast (STO) feeder layer, buffalo rat liver cell-conditioned media (BRL-CM), or the addition of recombinant LIF. To date, all of the ES cell culture systems use mammalian sources of LIF. We found that mouse ES cells can be maintained for over 10 passages in an undifferentiated state with media conditioned by a chicken liver cell line (LMH-CM) or on a feeder layer made with primary chicken embryonic fibroblasts (CEF). These ES cells can undergo both spontaneous and induced differentiation, which is associated with the disappearance or reduction of the expression of alkaline phosphatase and SSEA-1, similar to that observed for ES cells cultured with BRL-CM or STO feeder layers. The ES cells cultured in LMH-CM did not express cytokeratin Endo-A antigen recognized by TROMA-1, but their differentiated progeny did express this antigen. In contrast to LMH-CM, Endo-A was expressed in ES cells cultured on CEF feeder layers and in differentiated progeny. These results indicate that avian cells can produce a LIF-like cytokine that is active in inhibiting the differentiation of mouse ES cells. This could provide a biological end point for the isolation and characterization of avian LIF.