Rescue of Embryonic Cells Homozygous for a Lethal Haplotype of the T/t Complex: t super(w12)

A series of recessive mutations which arrest embryonic development are located within the T/t region of chromosome 17 in the mouse. We removed the embryonic cells from normal developmental constraints and attempted to grow them ectopically in vivo and in vitro. Teratomas and teratocarcinomas were produced by transplantation of inner cell masses from blastocysts of t super(w12)/+ and t super(w12)/t super(w12) genotypes. The ability of embryonic cells to grow as tumors was not affected by their genotype. 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 super(w12) homozygous tumors, while both tissues were present in 3 of 4 t super(w12) heterozygous tumors. This observation is compatible with the abnormalities characteristic of t super(w12)/t super(w12) embryos, which show very localized effects in nervous tissue and more general effects on bone and cartilage formation. The lethality associated with the t super(w12) haplotype is due to lethality of specific cells, and not all cell types.