The production of mouse fetal-placental chimeras using trisomy 16 and euploid blastocysts.

By means of a combination of immunosurgery and a modified method of microsurgery, blastocysts were reconstructed to produce viable chimeric fetal-placental units. Reciprocal reconstituted blastocysts were produced using euploid and trisomy 16 blastocysts. Reconstructed blastocysts yielded significantly smaller fetuses at day 17 of pregnancy than simultaneously transferred control blastocysts (mean body weight 0.49 g vs 0.64 g, P less than 0.01). However, apart from reduced size, no abnormalities were observed for any euploid fetus-euploid placenta construct. The three reconstructed blastocysts that yielded a trisomic fetus-trisomic placenta were viable when examined on day 17 and displayed the abnormalities typical of mouse trisomy 16. No reconstructed blastocyst that yielded a trisomic fetus-euploid placenta or a euploid fetus-trisomic placenta was viable beyond day 13 of development. One case in which a trisomic fetus had a placenta that was chimeric (euploid/trisomic) examined on day 17 displayed the abnormalities typical of a trisomic fetus but the placenta appeared histologically normal. The findings suggest that there is a coordination of the development of the fetus and the placenta that is essential for the development of the fetus.