Abstract
Monozygotic mouse twins were produced by micromanipulation of 2-cell stage embryos and factors affecting the embryonic development were examined. In experiment 1, 2-cell embryos obtained from superovulated CD-1 strain or F1 (C57BL/6 × CBA) females mated with CD-1 strain males were separated into a single blastomere. Pairs of twin blastomeres were cultured with or without supplementation of growth factors, a mixture of IGF-1, TGF-β and EGF for 3 days and twin blastocysts developed were transferred to recipient females. Of 174 pairs of F1 embryos, 88 to 100% developed to twin blastocysts. In contrast, development of CD-1 embryos (835 pairs) was significantly lower (25 to 36%). Of 63 F1 twin blastocysts transferred, 7 to 29% developed to twin fetuses, whereas only 0 to 8% of 62 pairs of CD-1 embryos developed to twins. In experiment 2, one nucleus of a 2-cell stage F1 embryo was electrically fused with an enucleated recipient 2-cell embryo. The 2-cell embryo from which a nucleus was removed was cultured together with the reconstituted embryo as a monozygotic twin pairs. Of 24 and 28 twin pairs cultured with or without growth factors, 92 and 86% developed to twin blastocysts, respectively. After transfer of 13 twin blastocysts to recipients, 3 and 2 twin fetuses were obtained. These findings indicated that monozygotic twin mice can be produced more efficiently from F1 embryos than from CD-1 embryos. Methods of removal of zona pellucida and addition of growth factors to the culture medium had no effect on the efficiency of production of monozygotic twins.
