Formation of viable chimaeras by aggregation between teratocarcinomas and preimplantation mouse embryos.

The formation of viable teratocarcinoma-adult chimaeras, by aggregation rather than by microinjection, is described. Aggregation chimaeras were produced using two pluripotential EC cell lines, PSA-1/NG-2 and PSA-4/TG12. The frequency and distribution of chimaerism were assessed, for the EC cells, in conceptuses recovered from in utero and in adults. In utero 37% of the morphologically normal conceptuses formed from PSA-1/NG-2 aggregations and 73% of the morphologically normal conceptuses produced from PSA-4/TG12 aggregations were found to be chimaeric. However, the frequency of chimaeric adults formed from both cell lines was lower. The reason for the discrepancy appeared to be that in the chimaeric conceptuses, the predominant tissues colonized by the EC cells were the extraembryonic membranes.