Embryonic stem (ES) cells, the totipotent outgrowths of blastocysts, can be cultured and manipulated in vitro and then returned to the embryonic environment where they develop normally and can contribute to all cell lineages. Maintenance of the stem-cell phenotype in vitro requires the presence of a feeder layer of fibroblasts or of a soluble factor, differentiation inhibitory activity (DIA) produced by a number of sources; in the absence of DIA the ES cells differentiate into a wide variety of cell types. We recently noted several similarities between partially purified DIA and a haemopoietic regulator, myeloid leukaemia inhibitory factor (LIF), a molecule which induces differentiation in M1 myeloid leukaemic cells and which we have recently purified, cloned and characterized. We demonstrate here that purified, recombinant LIF can substitute for DIA in the maintenance of totipotent ES cell lines that retain the potential to form chimaeric mice.

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The practical application of advanced breeding technologies and genetic manipulation of domestic animals is dependent on the efficient and routine isolation of embryonic stem (ES) cell lines from these species. ES cell lines of proven totipotency have thus far been isolated only from the mouse. Murine ES cells can be identified by a number of criteria including morphology and characteristics in culture, the presence of specific markers, differentiative capacity and contribution to chimaeras. Reported cell lines derived from ruminant preimplantation embryos do not stably exhibit these characteristics. As demonstrated for the mouse, primordial germ cells may provide an alternative source for pluripotential cell lines. The isolation, culture and preliminary characterization of bovine primordial germ cell-derived (PGCd) cells are described in this paper. The PGCd cells are capable of differentiation in vitro and display murine ES cell markers including alkaline phosphatase. With farm animals, long generation intervals and small numbers of offspring make it important to develop techniques for evaluating chimaeric embryos in vitro before embarking on expensive in vivo programmes. A method for labelling putative pluripotential cells with a fluorochrome marker to follow the fate of such cells was developed. Labelled PGCd cells were injected into blastocysts and the chimaeric embryos were monitored in vitro. Preliminary results demonstrate that the labelled PGCd cells incorporate preferentially within the inner cell mass of the host blastocyst.(ABSTRACT TRUNCATED AT 250 WORDS)

We have previously characterized, purified and cloned a novel murine and human regulator [leukaemia inhibitory factor, LIF] which induces the differentiation of certain murine and human myeloid leukaemic cells. Recently we have shown that there are specific LIF receptors on murine embryonic stem [ES] and embryonal carcinoma [EC] cells and that purified recombinant LIF can substitute for feeder cells and crude sources of differentiation inhibiting activity [DIA] [such as BRL-cell-conditioned medium] in the maintenance of ES cells in a pluripotential state in vitro. Furthermore, ES cells maintained in culture in recombinant LIF for a prolonged period can give rise to germline chimaeric mice. Thus, based on a number of biochemical and biological similarities, it is likely that LIF and DIA are the same molecule. The identification of LIF as a molecule, necessary and sufficient for the maintenance of ES cells in culture, should have a profound impact on the use of these cells for genetic manipulations.

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