The Ability of EK Cells to Form Chimeras after Selection of Clones in G418 and Some Observations on the Integration of Retroviral Vector Proviral DNA into EK Cells

The use of tumor-derived embryonal carcinoma (EC) cells and embryo-derived stem cells (EK cells) as models for studying aspects of early mouse embryogenesis is well established (Evans et al. 1983). The advent both of methods for establishing primary cultures of pluripotential cells directly from the embryo (Evans and Kaufman 1981; Martin 1981) and of the ability to maintain these cells in a fully totipotential and karyotypically unaltered form during in vitro culture (Robertson et al. 1983; Evans et al. 1985) reopens the issue of the practicality of attempting to assay in vivo, mutants produced in vitro.