The ability to culture homogeneous populations of pluripotent embryonic stem (ES) cells in the presence of leukemia inhibitory factor (LIF) or IL-6 (interleukin) family cytokines provides an experimentally tractable system for the investigation of gene function in pluripotent cell biology. The availability of a range of in vitro differentiation protocols (
1 –
7 ), in combination with systems for the generation of gain- or loss-of-function mutations in ES cells, provides an unparalleled opportunity for investigation of the genetic control of cell differentiation and early mammalian development (
see Fig. 1 ). Gain-of-function mutations are generally generated by cDNA overexpression and in this chapter we review the status of heterologous gene expression systems that can be used for this purpose in ES cells.
Fig. 1. Diagram illustrating use of the ES cell system for analysis of the genetic control of pluripotent stem cell renewal or differentiation. Loss- or gain-of-function mutations are generated in stable ES cell lines (ESM ) by genetic manipulation. The cellular consequences of altered gene expression are assessed in ES cells, or in their differentiated progeny produced by a variety of techniques in vitro.