Quality improvement of transgenic cloned bovine embryos using an aggregation method: Effects on cell number, cell ratio, embryo perimeter, mitochondrial distribution, and gene expression profile

Abstract The production of cloned embryos using conventional methods has extremely low success rates owing to low embryo quality. To improve the quality of cloned bovine embryos expressing enhanced green fluorescent protein (EGFP), we applied an aggregation culture method. The EGFP gene was transfected into bovine fetal fibroblasts using a retroviral vector system. Somatic cell nuclear transfer was performed using these cells, and the resulting embryos were cultured in aggregates or individually. Gene expression was analyzed by a microarray, and differentially expressed genes were validated by quantitative real-time polymerase chain reaction. The total number of cells per blastocyst and the ratio of inner cell mass cells to trophectoderm cells were higher in aggregated transgenic cloned blastocysts (agBL; 368.7 ± 109.6 and 1:4.8, respectively) than in in vitro –fertilized blastocysts (ivfBL; 189.8 ± 65.8 and 1:2.6, respectively) and nonaggregated transgenic cloned blastocysts (sBL; 113.1 ± 36.3 and 1:1.5, respectively; P   0.05). Expression of the heat shock 70-kDa protein 1A gene, which is associated with apoptosis, was 12-fold higher in the sBL group than in the ivfBL and agBL groups (P   0.05). Taken together, these data suggest that the aggregation method improves the quality of cloned embryos expressing EGFP and might be helpful in animal cloning.