Printed in Great Britain © Company of Biologists Limited 1979 Effect of the T-mutation on histogenesis of the mouse embryo under the testis capsule

Mouse embryos homozygous for the T-mutation show abnormalities, severer at the posterior embryonic regions, by day 9 of gestation and die before day 11 in utero. To analyse developmental potentiality of the T/T embryos, fragments of their anterior and posterior portions were grafted into the testes of adult T / + mice, and examined histo-logically for the tissues formed after 1 month. The grafted tissues of the T/T embryos grew beyond the destined lethal stage and gave rise to benign teratomas composed of mature tissues. Although there were some different features of the tissues formed in the teratomas derived from different portions and stages of the embryos, their types were essentially identical between wild-type and the mutant tera-tomas. Statistical analysis showed that frequency of the cartilage and/or bone formation was significantly lower in the posterior mutant teratomas. It cannot be concluded, however, that this difference is essentially caused by T-mutation. The main conclusion of present experiments is that grafted portions of T/T embryos have the potentiality to develop into-teratomas containing derivatives of all three germ layers