H-2 analyses of blastocyst-derived cell lines from mice bearing T and tw18 mutations.

T/T and tw18/tw18 blastocysts appear to survive in culture for periods of 3 weeks at frequencies equal to that of normal embryos. We have, therefore, undertaken to generate cell lines with a homozygous mutant genotype. We attempted to identify these cells by H-2 haplotype analysis. The results indicate that barring recombination, which would be expected to occur at a frequency of about 15%, 1 of 10 blastocyst-derived cell lines from a (+/tw18 x +/tw18) cross had a tw18/tw18 genotype and 1 of 4 lines from a (T/+ x T/+) cross had a T/T genotype. Unexpectedly, all of the remaining lines were heterozygous; no +/+ lines were observed. The putative homozygous mutant lines might be useful in attempts to characterize tw18-specific antigens.