Characteristics of induced pluripotent stem (iPS) cells are consistent with those of embryonic stem (ES) cells. However, exogenous genes integrated by using retrovirus delivery systems cannot be completely removed from the cells. In a recent report, activation-induced cytosine deaminase (AID) and thymine DNA glycosylase (TDG) can induce pluripotency state in mouse differentiated cells through the process of DNA demethylation. Thus, we hypothesized that the two reprogramming factors may convert efficiently bovine differentiated cells into pluripotency state. So, genes of AID and TDG were integrated into pCMV6-AC-IRES-GFP-Puro expression vector, which was transfected into bovine differentiated cells. As results, the colonies derived from AID+TDG-induced bovine cells were formed on day 7 after culture. The number of AP positively colonies in AID+TDG-induced bovine cells was significantly higher than in AID-induced bovine cells (p<0.05). Additionally, expression of pluripotent genes (OCT-3/4, NANOG, SOX2) was slightly increased in AID+TDG-induced bovine cells, as compared to AID-induced bovine cells. Protein expressions of OCT-3/4, NANOG and SOX2 in AID+TDG-induced bovine cells were slightly increased rather than AID-induced bovine cells. Finally, DNA demethylation in the promoter regions of pluripotent markers in AID+TDG-induced bovine cells was increased than that of AID-induced bovine cells. In conclusion, pluripotent stem cells could be efficiently produced from bovine differentiated cells by using non-integrating delivery system with the reprogramming factors (AID and TDG).

The cloning efficiency is extremely low despite successful somatic cell nuclear transfer (SCNT) method producing cloned animals in several mammals. In general, faulty epigenetic modifications underlying the incomplete reprogramming of donor cell nuclei after SCNT mainly results in low cloning efficiency. The nuclear reprogramming process involves epigenetic modifications, such as DNA demethylation and histone acetylation, which may be an important factor in enhancing the cloning efficiency. Recently, the histone deacetylase inhibitors (HDACi), such as trichosatin A (TSA) and m-carboxycinnamic acid bishydroxamide (CBHA), to increase histone acetylation have been used to improve the developmental competence of SCNT embryos. Therefore, we compared the effects of TSA with CBHA on the in vitro developmental competence and pluripotency-related gene expression (Oct4, Nanog and Sox2) in porcine cloned blastocysts and histone acetylation pattern (H3K9ac). The porcine cloned embryos were treated with a 50nM concentration of TSA and 100μM concentration of CBHA during the in vitro early culture (10h) after cell fusion and then were assessed to cleavage rate, development to the blastocyst stage and pluripotency-related gene expression in NT blastocyst also, level of histone acetylation in zygote, 2cell, 4cell stage. As results, Although NT, TSA and CBHA treated NT embryos were not different between all groups for cleavage rates, the developmental competence to the blastocyst stage was significantly increased in CBHA treated embryos (22.7%) compared to that of normal NT and TSA treated NT embryos (8.1% and 15.4%)(p<0.05). In addition, all of pluripotent transcription factors (Oct4, Nanog and Sox2) were expressed in the CBHA treated NT embryos, however, Sox2 and Oct4 were expressed in TSA treated NT embryos and expression pattern of CBHA treated NT embryos is particularly similar to that of IVF embryos. Also, CBHA treated NT embryos were increased in level of histone acetylation (H3K9ac) at the zygote, 2-cell, 4-cell stage compared to those of NT and TSA treated NT embryos. In conclusion, the treatment of CBHA as a histone deacetylase inhibitor significantly increased the developmental competence of porcine NT embryos and pluripotency-related gene expressions(Oct4, Nanog and Sox2) in NT blastocysts and level of histone acetylation (H3K9ac).

Differentiated nuclei can experimentally be returned to an undifferentiated embryonic status after nuclear transfer (NT) to unfertilized metaphase II (MII) oocytes. Nuclear reprogramming is triggered immediately after somatic cell nucleus transfer (SCNT) into recipient cytoplasm and this period is regarded as a key stage for optimizing reprogramming. In a recent study (Dai et al., 2010), use of m-carboxycinnamic acid bishydroxamide (CBHA) as a histone deacetylase inhibitor during the in vitro early culture of murine cloned embryos modifies the acetylation status of somatic nuclei and increases the developmental competence of SCNT embryos. Thus, we examined the effects of CBHA treatment on the in vitro preimplantation development of porcine SCNT embryos and on the acetylated status of histone H3K9 on cloned embryos at the zygote stage. We performed the three groups SCNT: SCNT (NT), CBHA treatment at the porcine fetus fibroblast cells (PFFs) used as donor cells prior to SCNT (CBHA-C) and CBHA treatment at the porcine SCNT embryos during the in vitro early culture after oocyte activation (CBHA-Z). The PFFs were treated with a 15 μM of CBHA (8 h) for the early culture and the porcine cloned embryos were treated with a 100 μM concentration of CBHA during the in vitro early culture (10 h). Cleavage rates and development to the blastocyst stage were assessed. No significant difference was observed the cleavage rate among the groups (82.6%, 76.4% and 82.2%, respectively). However, the development competence to the blastocyst stage was significantly increased in CBHA-Z embryos (22.7%) as compared to SCNT and CBHA-C embryos (8.6% and 4.1%)(p<0.05). Total cell numbers and viable cell numbers at the blastocyst stage of porcine SCNT embryos were increased in CBHA-Z embryos as compared to those in CBHA-C embryos (p<0.05). Signal level of histone acetylation (H3K9ac) at the zygote stage of SCNT was increased in CBHA-Z embryos as compared to SCNT and CBHA-C embryos. The results of the present study suggested that treatment with CBHA during the in vitro early culture (10 h) had significantly increased the developmental competence and histone acetylation level at the zygote stage.

The technique of SCNT is now well established but still remains inefficient. The in vitro development of SCNT embryos is dependent upon numerous factors including the recipient cytoplast and karyoplast. Above all, the metaphase of the second meiotic division (MII)　oocytes have typically become the recipient of choice. Generally high level of MPF present in MII oocytes induces the transferred nucleus to enter mitotic division precociously and causes NEBD and PCC, which may be the critical role for nuclear reprogramming. In the present study we investigated the in vitro development and pregnancy of White-Hanwoo SCNT embryos treated with caffeine (a protein kinase phosphatase inhibitor). As results, the treatment of 10 mM caffeine for 6 h significantly increased MPF activity in bovine oocytes but does not affect the developmental competence to the blastocyst stage in bovine SCNT embryos. However, a significant increase in the mean cell number of blastocysts and the frequency of pregnant on 150 days of White-Hanwoo SCNT embryos produced using caffeine treated cytoplasts was observed. These results indicated that the recipient cytoplast treated with caffeine for a short period prior to reconstruction of SCNT embryos is able to increase the frequency of pregnancy in cow.