26 EFFECT OF TREATMENT OF BOVINE DONOR CELLS WITH MOUSE EMBRYONIC STEM CELL EXTRACT ON THE DEVELOPMENT OF EMBRYOS AFTER NUCLEAR TRANSFER

Abstract

The efficiency of somatic cell cloning is very low, probably because of incomplete reprogramming of the somatic cell nucleus. In recent studies, it is suggested that transient exposure of donor somatic cells to mouse embryonic stem cell (ESC) extract enhances pluripotency of the cells in vitro (Bru et al. 2008 Exp. Cell Res. 314, 1634–1642; Xu et al. 2009 Anat. Rec. 292, 1229–1234). In the present study, we examined the effect of treatment of donor cells with mouse ESC extract on the in vitro development of bovine NT embryos. First, in order to examine effect of treatment of donor cells with streptolysin O (SLO), which reversibly permeabilizes the plasma membrane, we compared the in vitro development of NT embryos using donor cells treated with 5 μg mL^–1 SLO (SLO group) and untreated donor cells (control group). As donor cells for NT, bovine fibroblast cells of passages 3 to 5 were used. Fibroblasts were treated with 5 μg mL^–1 SLO for 45 min, and then incubated for resealing in DMEM including 2 mM CaCl₂ for 60 min. NT was performed as previously described (Akagi et al. 2003 Mol. Reprod. Dev. 66, 264–272). After in vitro culture for 8 days, blastocyst formation and cell number of blastocysts were examined. There were no significant differences between SLO and control groups in the fusion rate (80% and 72%, respectively), cleavage rate (60% and 65%, respectively), developmental rate to the blastocyst stage of NT embryos (31% and 28%, respectively), and blastocyst cell number (127 ± 6 and 112 ± 14, respectively). These results suggest that SLO treatment of donor cells has no negative effect on the in vitro development of NT embryos. Next, we examined the in vitro developmental ability of NT embryos using donor cells treated with mouse ESC extract (ES extract group). After SLO treatment for 45 min, permeabilized fibroblast cells were treated with mouse ESC extract for 45 min, and then incubated in DMEM including 2 mM CaCl₂ for 60 min, and used for producing NT embryos. There were no differences between ES extract and control groups in the fusion rate (68% and 69%, respectively), cleavage rate (86.7% and 80.6%, respectively), and developmental rate to the blastocyst stage of NT embryos (39.8% and 43.5%, respectively). The cell number of NT embryos at the blastocyst stage in ES extract group (201 ± 30) was significantly (t-test; P < 0.05) higher than that in control group (140 ± 14). In conclusion, treatment of bovine donor cell with mouse ESC extract did not affect the in vitro developmental ability of NT embryos, but improved the quality of blastocysts.