Abstract:
The production of transgenic farm animals will be greatly enhanced with thedevelopment of cultured cell lines that remain totipotent following nucleartransfer. Here, data are presented that demonstrate the generation of bothmale and female cloned lambs from two established embryonic cell lines.Cytoplasts derived from in vivo oocytes resulted inslightly greater development to blastocyst (24%v. 17%) and survival to term (7%v. 2%) compared within vitro oocytes. There was no advantage in co-culturingcloned embryos with oviductal epithelial cells compared with syntheticoviductal fluid medium in terms of development to blastocyst (18%v. 31%) or survival to term (both 8%).Although the survival of cloned embryos immediately after transfer was highbased on ‘biochemical’ pregnancy, 64-80% of embryosfailed over the attachment phase with in vivocytoplasts. Although the co-transfer of trophoblastic vesicles improved embryosurvival to Day 35 (45% v. 25%), there wasno difference at term. A high proportion of fetuses were lost during the lasttrimester (43%), resulting in 11% of embryos transferreddeveloping to term using in vivo cytoplasts(12/112). Five lambs have survived and two rams are fertile. The currentnuclear transfer process is inefficient and further research is needed toimprove the development of healthy fetuses.