Clonal analysis of the change in growth phenotype during embryonal carcinoma cell differentiation.

Retinoic acid has been shown to induce the differentiation of mouse embryonal carcinoma cells. Previous workers have reported that bulk cultures of the differentiated derivatives have a slower growth rate and a reduced capacity to form tumours. We have analysed this change in growth rate for a sub-tetraploid EC cell line, PC13 clone 5 MA2, at a clonal level and have shown that the production of cells with a slower growth rate is not a result of cell selection. We have also demonstrated that the action of retinoic acid on growth rate is delayed for approximately 48 h and that the new growth phenotype, once attained, is stable. Finally we have confirmed at a clonal level that the differentiated derivatives of EC cells exposed to retinoic acid have a reduced capacity to form tumours. Clones of EC cells exposed to retinoic acid for longer than 96 h are unable to form tumours in a 30-day period, whilst 87% of their untreated counterparts are able to do so.