Changes in the behaviour of teratocarcinoma cells cultivated in vitro

Abstract

MOUSE teratocarcinoma cells have been recognised as important material for studying in vitro the processes of determination and differentiation that take place during normal embryogenesis^1,2. But in order for the system to be exploited maximally, it must be possible to manipulate at will the differentiation of mass cultures of pluripotent cells into endoderm, ectoderm and mesoderm derivatives. Martin and Evans showed that they could trigger the appearance of endoderm cells in undifferentiated cultures of the SIKR teratocarcinoma line by suspending aggregates of the cells in bacteriological Petri dishes to which they could not adhere^3,4. Within about 2 d the aggregates developed into simple embryoid bodies, resembling egg cylinders of normal embryos with an outer layer of endoderm cells surrounding a core of undifferentiated cells. In some SIKR clones, but not others, the inner cells later differentiate into neuroectoderm and mesoderm and the embryoid bodies develop fluid cysts resembling the visceral yolk sac vesicles of normal early embryos cultured in vitro. Not all lines of pluripotent teratocarcinoma cells, however, can be induced to form embryoid bodies in such a convenient way (ref. 5 and my observations). This could be because certain teratocarcinomas are for some reason intrinsically unable to form embryoid bodies, or because the cells can lose this ability during cultivation in vitro. In the course of isolating a new clonal line of teratocarcinoma cells I noticed that their ability to differentiate was strongly influenced by the way in which they were maintained in vitro. As long as the cells were grown on layers of feeder fibroblasts they retained the ability to form embryoid bodies but this was progressively lost as the cells were adapted to grow on gelatin-coated dishes.