Donor cell lines considerably affect the outcome of somatic nuclear transfer in the case of bovines

SIRT6 Knockdown in Buffalo Fetal Fibroblasts Exacerbates Premature Senescence Caused by DNA and Telomere Damage

As a gene with antiaging functions, sirtuin6 (SIRT6) belonging to the sirtuin family plays a vital role in DNA repair, telomerase function, and cellular senescence, as well as maintains epigenomic stability and promotes longevity. However, its role in cell senescence in large animals, such as buffaloes, remains unknown. Fibroblasts are commonly used for somatic reprogramming, and their physiological characteristics affect the efficiency of this process. We aimed to elucidate the role of SIRT6 in cellular senescence and proliferation and analyze its effect on the biological function of buffalo fibroblasts to help improve the efficiency of buffalo somatic cell reprogramming. The expression of SIRT6 and related DNA damage was measured in buffalo fibroblasts obtained at different developmental stages (in the fetus and at 3 and 10 years of age), and the effect of SIRT6 knockdown on the senescence of buffalo fetal fibroblast was investigated. An inverse relationship was observed between SIRT6 expression and senescence in buffalo fibroblasts obtained from animals of various ages. This was accompanied by decreased cell growth, viability, and increased DNA damage. Short hairpin RNA-mediated SIRT6 knockdown accelerated the senescence of buffalo fetal fibroblasts. It blocked the cell cycle during in vitro cell culture, which further enhanced DNA damage, particularly with respect to the telomeres. Collectively, our findings suggest that SIRT6 expression was closely associated with buffalo senescence in fibroblasts. These findings serve as a foundation to better understand the cellular functions of SIRT6 and also aid in selecting donor cells for buffalo somatic cell reprogramming.

Improving porcine SCNT efficiency by selecting donor cells size

Considerable advancements have recently been achieved in porcine somatic cell nuclear transfer (SCNT), but the efficiency remains low. Donor cell size might play an important role in SCNT, but its effects in pigs remain unclear. This study aimed to evaluate the efficiency of porcine SCNT by selecting donor cells of suitable size. Porcine fetal fibroblasts (PFFs) were divided into three groups, group S (small, d ≤ 13 μm), group M (medium, 13 μm<d ≤ 18 μm), and group L (large, d > 18 μm), and their biological characteristics were analyzed. Next, SCNT was performed using PFFs of different sizes to evaluate the developmental potential of reconstructed embryos. The data showed that PFFs in groups S, M and L accounted for 17.5%, 47.7% and 34.8% of cells, respectively. Morphologically, cells in group S exhibited clear and regular cell membranes and nuclei, whereas cells in groups M and L displayed varying degrees of cell membrane protuberance, karyo-pyknosis, autophagy and mitochondrial abnormalities. In addition, the growth status and proliferation capabilities of cells in group S were significantly better than those of group M and group L. The percentage of cells at G0/G1 in group S and M were significantly greater than group L. The senescence rate of group S was lower than group M and group L. The apoptosis rate of group S was significantly lower than that of group L but comparable to that of group M . The cleavage rate of group S was also significantly greater than that of group M but comparable to that of group L . The blastocyst rate of group S was significantly greater than that of group M and group L. The blastocyst cell numbers of group S were also significantly greater than those of group M and group L. These findings suggested that small PFFs with a diameter of less than 13 μm are more suitable donor cells for SCNT in pigs.Abbreviations: DMEM: Dulbecco's modified Eagle's medium; FBS: Fetal bovine serum; PBS: Phosphate buffer saline; PFFs: Porcine fetal fibroblast cells; SCNT: Somatic cell nuclear transfer.

Use of trichostatin A alters the expression of HDAC3 and KAT2 and improves in vitro development of bovine embryos cloned using less methylated mesenchymal stem cells

The aim of this work was to investigate the methylation and hydroxymethylation status of mesenchymal stem cells (MSC) from amniotic fluid (MSC-AF), adipose tissue (MSC-AT) and fibroblasts (FIB-control) and to verify the effect of trichostatin A (TSA) on gene expression and development of cloned bovine embryos produced using these cells. Characterization of MSC from two animals (BOV1 and BOV2) was performed by flow cytometry, immunophenotyping and analysis of cellular differentiation genes expression. The cells were used in the nuclear transfer in the absence or presence of 50 nM TSA for 20 hr in embryo culture. Expression of HDAC1, HDAC3 and KAT2A genes was measured in embryos by qRT-PCR. Methylation results showed difference between animals, with MSC from BOV2 demonstrating lower methylation rate than BOV1. Meanwhile, MSC-AF were less hydroxymethylated for both animals. MSC-AF from BOV2 produced 44.92 ± 8.88% of blastocysts when embryos were exposed to TSA and similar to embryo rate of MSC-AT also treated with TSA (37.96 ± 15.80%). However, when methylation was lower in FIB compared to MSC, as found in BOV1, the use of TSA was not sufficient to increase embryo production. MSC-AF embryos expressed less HDAC3 when treated with TSA, and expression of KAT2A was higher in embryos produced with all MSC and treated with TSA than embryos produced with FIB. The use of MSC less methylated and more hydroxymethylated in combination with embryo incubation with TSA can induce lower expression of HDAC3 and higher expression of KAT2A in the embryos and consequently improve bovine embryo production.

The expression of β-galactosidase during long-term cultured goat skin fibroblasts and the effect of donor cell passage on in vitro development of nuclear transfer embryos

The present study aimed to detect the expression of β-galactosidase during long-term cultured goat skin fibroblasts and investigate the effects of donor goat age, sex, and cell passage on senescence and the effects of donor cell passage on in vitro development of nuclear transfer embryos. The results showed that, in the same cell passage, more β-galactosidase-positive cells were detected in cells from older donors than younger donors. Irrespective of the donor age, the number of positive cells was higher in later passages from passages 20 to 50. In the same passage from 20 to 50, the β-galactosidase-positive rate was higher in cells from 5-yr female goat than 5-yr male goat. Using fibroblasts from male goats at various passages as donor cells, reconstructed embryos had similar fusion and cleavage rates, but the blastocyst rate was higher for cells at passages 10 and 20 than passage 30. In conclusion, donor goat age and cell passage had significant effects on the β-galactosidase-positive rate; also, cells from 5-yr female goat had a higher β-galactosidase-positive rate than those from 5-yr male goat, and the donor cell passage affected the developmental potential of nuclear transfer embryos.

Recent progress in bovine somatic cell nuclear transfer

Bovine somatic cell nuclear transfer (SCNT) embryos can develop to the blastocyst stage at a rate similar to that of embryos produced by in vitro fertilization. However, the full-term developmental rate of SCNT embryos is very low, owing to the high embryonic and fetal losses after embryo transfer. In addition, increased birth weight and postnatal mortality are observed at high rates in cloned calves. The low efficiency of SCNT is probably attributed to incomplete reprogramming of the donor nucleus and most of the developmental problems of clones are thought to be caused by epigenetic defects. Applications of SCNT will depend on improvement in the efficiency of production of healthy cloned calves. In this review, we discuss problems and recent progress in bovine SCNT.

Establishment and characterization of fetal fibroblast cell lines for generating human lysozyme transgenic goats by somatic cell nuclear transfer

This study was performed to qualify goat fetal fibroblast (GFF) cell lines for genetic modification and somatic cell nuclear transfer (SCNT) to produce human lysozyme (hLYZ) transgenic goats. Nine GFF cell lines were established from different fetuses, and the proliferative lifespan and chromosomal stability were analyzed. The results suggested that cell lines with a longer lifespan had stable chromosomes compared with those of cells lines with a shorter lifespan. According to the proliferative lifespan, we divided GFF cell lines into two groups: cell lines with a long lifespan (GFF1/2/7/8/9; group L) and cell lines with a short lifespan (GFF3/4/5/6; group S). Next, a hLYZ expression vector was introduced into these cell lines by electroporation. The efficiencies of colony formation, expansion in culture, and the quality of transgenic clonal cell lines were significant higher in group L than those in group S. The mean fusion rate and blastocyst rate in group L were higher than those in group S (80.3 ± 1.7 vs. 65.1 ± 4.2 % and 19.5 ± 0.6 vs. 15.1 ± 1.1 %, respectively, P < 0.05). After transferring cloned embryos into the oviducts of recipient goats, three live kids were born. PCR and Southern blot analyses confirmed integration of the transgene in cloned goats. In conclusion, the lifespan of GFF cell lines has a major effect on the efficiency to produce transgenic cloned goats. Therefore, the proliferative lifespan of primary cells may be used as a criterion to characterize the quality of cell lines for genetic modification and SCNT.

Nuclear donor cell lines considerably influence cloning efficiency and the incidence of large offspring syndrome in bovine somatic cell nuclear transfer

Total five ear skin fibroblast lines (named F1, F2, F3, F4 and F5) from different newborn Holstein cows have been used as nuclear donor cells for producing cloned cows by somatic cell nuclear transfer (SCNT). The effects of these cell lines on both in vitro and in vivo developmental rates of cloned embryos, post-natal survivability and incidence of large offspring syndrome (LOS) were examined in this study. We found that the different cell lines possessed the same capacity to support pre-implantation development of cloned embryos, the cleavage and blastocyst formation rates ranged from 80.2 ± 0.9 to 84.5 ± 2.5% and 28.5 ± 0.9 to 33.3 ± 1.4%, respectively. However, their capacities to support the in vivo development of SCNT embryos showed significant differences (p < 0.05). The pregnancy rates at 90 and 240 day were significantly lower in groups F2 (4.9% and 3.3%) and F3 (5.4% and 5.4%) compared to groups F1 (23.3% and 16.3%), F4 (25.7% and 18.6%) and F5 (25.9% and 19.8%) (p < 0.05). The cloning efficiency was significantly higher in group F5 than those in group F1, F2, F3 and F4 (9.3% vs 4.1%, 1.2%, 2.0% and 5.0%, respectively, p < 0.05). Moreover, large offspring syndrome (LOS) incidence in group F5 was significantly lower than those in other groups (p < 0.05). All cloned offspring from cell line F1, F2, F3 and F4 showed LOS and gestation length delay, while all cloned offspring from F5 showed normal birthweight and gestation length. We concluded that the nuclear donor cell lines have significant impact on the in vivo development of cloned embryos and the incidence of LOS in cloned calves.

Equine cloning: in vitro and in vivo development of aggregated embryos

The production of cloned equine embryos remains highly inefficient. Embryo aggregation has not yet been tested in the equine, and it might represent an interesting strategy to improve embryo development. This study evaluated the effect of cloned embryo aggregation on in vitro and in vivo equine embryo development. Zona-free reconstructed embryos were individually cultured in microwells (nonaggregated group) or as 2- or 3-embryo aggregates (aggregated groups). For in vitro development, they were cultured until blastocyst stage and then either fixed for Oct-4 immunocytochemical staining or maintained in in vitro culture where blastocyst expansion was measured daily until Day 17 or the day on which they collapsed. For in vivo assays, Day 7-8 blastocysts were transferred to synchronized mares and resultant vesicles, and cloned embryos were measured by ultrasonography. Embryo aggregation improved blastocyst rates on a per well basis, and aggregation did not imply additional oocytes to obtain blastocysts. Embryo aggregation improved embryo quality, nevertheless it did not affect Day 8 and Day 16 blastocyst Oct-4 expression patterns. Equine cloned blastocysts expanded and increased their cell numbers when they were maintained in in vitro culture, describing a particular pattern of embryo growth that was unexpectedly independent of embryo aggregation, as all embryos reached similar size after Day 7. Early pregnancy rates were higher using blastocysts derived from aggregated embryos, and advanced pregnancies as live healthy foals also resulted from aggregated embryos. These results indicate that the strategy of aggregating embryos can improve their development, supporting the establishment of equine cloned pregnancies.

An inter-subspecies cloned buffalo (Bubalus bubalis) obtained by transferring of cryopreserved embryos via somatic cell nuclear transfer

The aim of this study was to explore the feasibility of cryopreservation of inter-subspecies cloned embryos in buffalo. In our experiment, river buffalo ear fibroblast nucleus was fused into swamp buffalo oocyte cytoplasm. The blastocyst formation rate for nuclear transfer of freshly thawed cells was not different from those of growing cells, confluent or serum-starved cells. A total of 122 cloned blastocysts derived from cryopreserved fibroblasts were cryopreserved and thawed, 37 were survived, the cryosurvival rate was 30.3%. The survived blastocysts were transferred into 15 recipient buffalos. Five of the recipients established pregnancy, but four of them aborted on day 53, 59, 145 and 179 of gestation respectively. One cross-bred buffalo (Murrah × Swamp buffalo (2n = 49) received three embryos delivered a 40.5 kg female calf by natural delivery on day 320 of gestation. Up to now (13-month old), the cloned calf has been growing well with no abnormity observed. These results demonstrated that cryopreservation of inter-subspecies cloned embryos is feasible to produce buffalo offspring.

Treatment with a histone deacetylase inhibitor after nuclear transfer improves the preimplantation development of cloned bovine embryos

We examined the effects of treatment with histone deacetylase inhibitors (HDACi), trichostatin A (TSA) and scriptaid (SCR), on the blastocyst formation rate in bovine somatic cell nuclear transferred (SCNT) embryos derived from fibroblast cells. Three fibroblast cell lines (L1, L2 and L3) were used as somatic cell donors to produce SCNT embryos (L1, L2 and L3 embryos, respectively). In Experiment 1, we compared the in vitro developmental competence of L1 embryos treated with various concentrations of TSA for different time periods following chemical activation. Embryos treated with 5 nM TSA for 20 h showed a significantly increased blastocyst formation rate compared with untreated controls. In Experiment 2, we examined the effect of TSA (5 nM) treatment of L1, L2 and L3 embryos as well as the effect of treatment of L1, L2 and L3 embryos with various concentrations of SCR on in vitro developmental competence. It was found that 5 nM TSA treatment significantly increased the blastocyst formation rate in L1 and L3 embryos but did not have an influence on the development of L2 embryos. On the other hand, 5 nM SCR treatment significantly increased the blastocyst formation rates of L1 and L2 embryos compared with controls. However, there was no significant increase in the blastocyst formation rate of L3 embryos when they were treated with SCR. In Experiment 3, acetylation of H4K12 was examined in donor cells and pronuclear-stage L1, L2 and L3 embryos treated with 5 nM TSA or 5 nM SCR by immunostaining. The level of H4K12 acetylation was different among donor cells. The staining intensities in the TSA-treated L1 and L3 embryos and SCR-treated L2 embryos were significantly higher than those of untreated embryos. These results suggest that HDACi treatment of bovine SCNT embryos improves the blastocyst formation rate; however, the optimal treatment conditions may differ among donor cell lines.

Effect of cryopreservation and in vitro culture of bovine fibroblasts on histone acetylation levels and in vitro development of hand-made cloned embryos

In this study, the relative acetylation levels of histone 3 in lysine 9 (H3K9ac) in cultured and cryopreserved bovine fibroblasts was measured and we determined the influence of the epigenetic status of three cultured (C1, C2 and C3) donor cell lines on the in vitro development of reconstructed bovine embryos. Results showed that cryopreservation did not alter the overall acetylation levels of H3K9 in bovine fibroblasts analysed immediately after thawing (frozen/thawed) compared with fibroblasts cultured for a period of time after thawing. However, reduced cleavage rates were noted in embryos reconstructed with fibroblasts used immediately after thawing. Cell passage affects the levels of H3K9ac in bovine fibroblasts, decreasing after P1 and donor cells with lower H3K9ac produced a greater frequency of embryo development to the blastocyst stage. Cryopreservation did not influence the total cell and ICM numbers, or the ICM/TPD ratios of reconstructed embryos. However, the genetic source of donor cells did influence the total number of cells and the trophectoderm cell numbers, and the cell passage influenced the total ICM cell numbers.

Study on the inter-subspecies nuclear transfer of river buffalo somatic cell nuclei into swamp buffalo oocyte cytoplasm

The objective of this study was to explore the feasibility of inter-subspecies somatic cell nuclear transfer (SCNT) of river buffalo (50 chromosomes) somatic cell nuclei into swamp buffalo (48 chromosomes) oocyte cytoplasm. The enucleated swamp buffalo oocytes were fused with four different types of river buffalo cells: freshly thawed ear fibroblasts, serum-starved ear fibroblasts, cumulus cells and ear fibroblasts from a cloned buffalo calf. As a result, the developmental competence of embryos reconstructed with freshly thawed ear fibroblasts was the poorest (P<0.01), while those of the other three types were not different from each other. Furthermore, the efficiency of swamp-swamp buffalo, swamp-river buffalo and bovine-buffalo SCNT were also compared. The results showed that the blastocyst rate of swamp-river reconstructed embryos was not different from swamp-swamp embryos, while significantly higher than that of bovine-buffalo embryos (P<0.01). A total of thirty cloned blastocysts derived from freshly thawed ear fibroblasts were transferred into thirteen recipient buffaloes, four recipients established pregnancy, while three of them aborted on Days 65, 75 and 90 of gestation, respectively. One cross-bred buffalo (Murrah x swamp, 49 chromosomes) receiving three embryos delivered a 39 kg female calf on Day 335 of gestation. These results indicate that the inter-subspecies SCNT is feasible to produce swamp-river buffalo embryos, and these can develop to full term and result in live buffalo calves.