Abstract:
To preserve the female genetics of an endangered breed of cattle, adapted tosub-Antarctic con-ditions, adult somatic cell nuclear transfer was used toclone the last surviving Enderby Island cow from mural granulosa cells.Embryos reconstructed with metaphase II cytoplasts and quiescent cells wereeither activated and fused simultaneously (AFS) at 24 or 30 hours postmaturation (hpm) or alternatively, fused 4-6 h before activation at26-30 hpm (FBA). A significantly higher proportion of fused embryosdeveloped in vitro to grade 1-3 blastocysts on Day7 with FBA (39.82.8%) compared to AFS with activation either at 24 hpm(10.63.9%, P<0.01) or at 30 hpm (18.64.1%, P<0.01).Following the transfer of 74 embryos from the FBA treatment over twoexperiments, survival rates on Days 30, 55, 85, 150 and 190 of pregnancy were38%, 30%, 23%, 16% and 15%, respectively.Of 22 embryos transferred in the first experiment, two calves were born alivewith one calf surviving. DNA analyses confirmed that the calves weregenetically identical to the Enderby Island cow. Additional pregnancies arecurrently ongoing. These data show that embryo development is increased byprolonged exposure of quiescent somatic cell nuclei to oocyte cytoplasm beforeartificial activation, possibly facilitating nuclear reprogramming. Thesuccessful demonstration of somatic cell nuclear transfer in animalconservation extends the applications of the technology beyond the mainagri-cultural and biomedical interests.