Rescue of embryonic cells homozygous for a lethal haplotype of the T/t complex: tw12

Abstract

A series of recessive mutations which arrest embryonic development are located within the T/t region of chromosome 17 in the mouse. To assess whether these mutations cause death in specific differentiating cells or in all cells of the embryo, we removed the embryonic cells from normal developmental constraints and attempted to grow them ectopically in vivo and in vitro. We have succeeded in producing teratomas and teratocarcinomas by transplantation of inner cell masses from blastocysts of t w12 + and t w12 t w12 genotypes. The ability of embryonic cells to grow as tumors was not affected by their genotype; 7 of the 17 tumors were homozygous for t w12 , 7 were heterozygous, and 3 could not be analyzed. Virtually all the tumors of both genotypes contained derivatives of all three germ layers. Neuroepithelial and mature nervous tissue was present in all homozygous tumors and all except one heterozygous tumor. However, no cartilage or bone was found in 5 of 5 t w12 homozygous tumors, while both tissues were present in 3 of 4 t w12 heterozygous tumors. This observation is compatible with the abnormalities characteristic of t w12 t w12 embryos, which show very localized effects in nervous tissue and more general effects on bone and cartilage formation. Cells derived from homozygous tumors were capable of at least limited growth in culture and a cell line has been derived from one of them. The p63/6.9a marker protein was used to determine the presence of the t w12 haplotype in the tumor and cultured cells. We conclude that the lethality associated with the t w12 haplotype is due to lethality of specific cells, and not all cell types.