Adult somatic cell nuclear transfer is used to preserve the last surviving cow of the Enderby Island cattle breed

Abstract

To preserve the female genetics of an endangered breed of cattle, adapted to sub-Antarctic con-ditions, adult somatic cell nuclear transfer was used to clone the last surviving Enderby Island cow from mural granulosa cells. Embryos reconstructed with metaphase II cytoplasts and quiescent cells were either activated and fused simultaneously (AFS) at 24 or 30 hours post maturation (hpm) or alternatively, fused 4–6 h before activation at 26–30 hpm (FBA). A significantly higher proportion of fused embryos developed in vitro to grade 1–3 blastocysts on Day 7 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 two experiments, survival rates on Days 30, 55, 85, 150 and 190 of pregnancy were 38%, 30%, 23%, 16% and 15%, respectively. Of 22 embryos transferred in the first experiment, two calves were born alive with one calf surviving. DNA analyses confirmed that the calves were genetically identical to the Enderby Island cow. Additional pregnancies are currently ongoing. These data show that embryo development is increased by prolonged exposure of quiescent somatic cell nuclei to oocyte cytoplasm before artificial activation, possibly facilitating nuclear reprogramming. The successful demonstration of somatic cell nuclear transfer in animal conservation extends the applications of the technology beyond the main agri-cultural and biomedical interests.