METT-1: a karyotypically normal in vitro line of developmentally totipotent mouse teratocarcinoma cells.

A karyotypically normal, chromosomally female (X/X) in vitro line of mouse teratocarcinoma stem cells was established from a malignant mouse teratocarcinoma of the 129/Sv Sl C P inbred strain. The tumor of origin was experimentally induced by ectopic transplantation of a 6-day embryo. The normal number of chromosomes was observed in 92% of metaphases of the cultured cells. This high frequency of euploidy, as well as karyotypic normalcy, were maintained during numerous passages in culture without a feeder-cell layer and after freezing and thawing of the cells. The line has been designated METT-1 (Mouse Euploid Totipotent Teratocarcinoma), signifying that it is the first such in vitro line that has proved (in tests by T. Stewart and B. Mintz, manuscript in preparation) to be developmentally totipotent, i.e., capable of both somatic and germinal differentiation when injected into blastocysts, even after freezing and thawing and prolonged culture. This unique ensemble of properties renders the cell line suitable for selection of specific mutant genes and for gene-transfer experiments in culture, for the purpose of producing from the mutant cells new strains of mice with predetermined genetic changes.