Two-cell embryos were collected from (C57BL/6 x CBA)F1 mice, microinjected with foreign DNA and transferred into temporary recipients. Intact and half 8-cell embryos recovered from oviducts 24 h later were frozen in microdrops of vitrification medium and stored in liquid nitrogen for 2 to 30 days. Development of frozen/thawed embryos was assessed by in vitro culture or transfer into day-1 recipients. From 1200 2-cell embryos 77% intact and 20% half embryos were obtained one hour after DNA injections. After transfer of 600 intact and 300 half embryos into temporary recipients, 77% intact and 73% half 8-cell embryos were recorded, respectively. Survival and in vitro development of frozen/thawed DNA-injected embryos were high, as 97% intact and 91% half 8-cell embryos developed to morulae or blastocysts. After transfer of 300 intact and 150 half 8-cell embryos into day-1 recipients, 99 (33%) and 19 (13%) young were born. None of the mice born from DNA-injected and cryopreserved embryos integrated injected genes.

Institute of Molecular Genetics Czechoslovak Academy of Sciences Praha