35 DEVELOPMENT OF INTERSPECIES CLONED MOUSE EMBRYOS RECONSTRUCTED WITH PORCINE ENUCLEATED OOCYTES

Abstract

Interspecies somatic cell nuclear transfer (iSCNT) offers significant opportunities for the derivation of embryonic stem cells (ESCs) that can model diseases. In this study, we investigated the development of murine-porcine iSCNT embryos and compared these to outcomes associated with porcine-porcine SCNT embryos. Enucleation was performed on in vitro-matured porcine oocytes using the Oosight spindle viewer system (CRI, UK). Either murine embryonic fibroblasts or porcine cumulus cells were injected into porcine ooplasm using a piezo-electric micromanipulator. After being exposed to the porcine ooplasm for 1 h, the reconstructed oocytes were activated by a combination of A23187 and 6-DMAP for 3.5 h. For the murine-porcine embryos (n = 9375), we used a serial culture method, namely porcine zygote medium (PZM) for 48 h followed by incubation with KSOM for another 5 days. We found that the majority of murine-porcine embryos (73.58%) arrested at the 4- to 8-cell stage, whilst a very small minority progressed through to blastocyst (0.064%). Porcine-porcine SCNT reconstructed oocytes (n = 142) cultured in PZM achieved a 15% blastocyst development rate. In the murine-porcine embryos, 10/44 embryos had chromosomal DNA loss associated with apoptosis, as determined by immunocytochemistry using the H2A.X antibody. We also found that at later stages, morula to blastocyst, the mouse-to-pig reconstructed embryos did not exhibit murine-specific Oct-4 expression patterns. Furthermore, murine mitochondrial DNA tended to be eliminated rather than preserved by the murine nuclei, which could render any subsequently derived ESCs dysfunctional due to 2 diverse genomes contributing genes to the electron transfer chain.