Abstract

Although cloning by somatic cell nuclear transfer (SCNT) has been achieved in various mammalian species, its efficiency has been very low (Han et al. 2003 Theriogenology 59, 33–44). Successful cloning requires conversion from differentiated donor nuclei to embryonic nuclei after transfer of the somatic nuclei into enucleated oocytes. Reprogramming of the transferred somatic nuclei must be completed by the time when normal activation of the embryonic genome occurs (Solter 2000 Nat. Rev. Genet. 1, 199–207). Recently, both full-term development and pre-implantation development of mouse SCNT embryos were significantly enhanced by treatment with trichostatin A (TSA), an inhibitor of histone deacetylase (Kishigami et al. 2006 Biochem. Biophys. Res. Commun. 340, 183–189; Rybouchkin et al. 2006 Biol. Reprod. 74, 1083–1089). The objective of this study was to investigate the effects of TSA on the development of bovine SCNT embryos. Bovine fibroblasts were cultured under serum starvation (0.4% FCS) for 7 days and then used as donor cells. The cells were electro-fused with bovine enucleated matured oocytes, and activated with a calcium ionophore and cycloheximide. They were subsequently cultured in mSOF medium until 168 h post-activation (hpa). The NT embryos were exposed to 0 (control), 5, 50, and 500 nM TSA from the start of activation to 48 hpa. Experiments were repeated 3 times, and the data were analyzed with Fisher's PLSD test following ANOVA. The cleavage rates were the same among the groups (60 to 80%; P >0.05). However, the blastocyst rate of NT embryos treated with 50 nM TSA was higher than that of control embryos (40% vs. 19%, respectively; P < 0.05). On the other hand, the blastocyst rate was lower with 500 nM TSA than with 5 or 50 nM TSA (7% vs. 33% or 40%; P < 0.05). These data suggest that proper TSA treatment after somatic cloning improves the rate of development of bovine cloned embryos to the blastocyst stage. Further research is needed to examine whether NT embryos derived from different cell lines or types have similar susceptibility to TSA.