Criteria that optimize the potential of murine embryonic stem cells for in vitro and in vivo developmental studies.

Cultured mouse embryonic stem (ES) cells are used for both in vitro and in vivo studies. The uncommitted pluripotent cells provide a model system with which to study cellular differentiation and development; they can also be used as vectors to carry specific mutations into the mouse genome by homologous recombination. To ensure successful integration into the germ line, competent totipotent diploid ES cell lines are selected using a cell injection bioassay that is both time consuming and technically demanding. The prolonged in vitro culture of rapidly dividing ES cells can lead to accumulated changes and chromosomal abnormalities that will compromise the biological function and abrogate germ line transmission of chimeric mice carrying novel genetic mutations. Such in vitro conditions will vary between individual laboratories; for example, differences in the serums used for maintenance. Using a number of different criteria we attempt in this paper to define the parameters that we found to be key factors for optimization of the biological potential of established ES cell lines. The successful integration into the germ line is dependant on acquiring or deriving a competent totipotent mouse ES diploid cell line. In this paper parameters and criteria are defined which we found to be key factors for the optimization of the biological potential of established ES cell lines.