Cloning. Pigs is pigs

Treatment of porcine donor cells and reconstructed embryos with the antioxidant melatonin enhances cloning efficiency

This study was conducted to investigate the effect of melatonin during the culture of donor cells and cloned embryos on the in vitro developmental competence and quality of cloned porcine embryos. At concentrations of 10(-6 )M or 10(-8) M, melatonin significantly enhanced the proliferation of porcine fetal fibroblasts (PFFs), and the blastocyst rate was significantly increased in the 10(-10) M melatonin-treated donor cell group. Cloned embryo development was also improved in embryo culture medium that was supplemented with 10(-9) M or 10(-12) M melatonin. When both donor cells and cloned embryos were treated with melatonin, the cleavage rate and total cell number of blastocysts were not significantly affected; however, the blastocyst rate was increased significantly (20.0% versus 11.7%). TUNEL assays showed that combined melatonin treatment reduced the rate of apoptotic nuclei (3.6% versus 6.1%). Gene expression analysis of the apoptosis-related genes BAX, BCL2L1, and p53 showed that the expression of BCL2L1 was significantly elevated 2.7-fold relative to the control group, while the expression of BAX and p53 was significantly decreased by 3.7-fold and 23.2-fold, respectively. In addition, we detected the expression of two melatonin receptors (MT1 and MT2) in PFFs but not in porcine cloned embryos. We conclude that exogenous melatonin enhances the development of porcine cloned embryos and improves embryo quality by inhibiting p53-mediated apoptotic pathway. The proliferation of PFFs may be mediated by receptor binding, but the beneficial effects of melatonin on embryonic development may be receptor-independent, possibly through melatonin's ability to directly scavenge free radicals.

Somatic cell nuclear transfer efficiency: how can it be improved through nuclear remodeling and reprogramming?

Fertile offspring from somatic cell nuclear transfer (SCNT) is the goal of most cloning laboratories. For this process to be successful, a number of events must occur correctly. First the donor nucleus must be in a state that is amenable to remodeling and subsequent genomic reprogramming. The nucleus must be introduced into an oocyte cytoplasm that is capable of facilitating the nuclear remodeling. The oocyte must then be adequately stimulated to initiate development. Finally the resulting embryo must be cultured in an environment that is compatible with the development of that particular embryo. Much has been learned about the incredible changes that occur to a nucleus after it is placed in the cytoplasm of an oocyte. While we think that we are gaining an understanding of the reorganization that occurs to proteins in the donor nucleus, the process of cloning is still very inefficient. Below we will introduce the procedures for SCNT, discuss nuclear remodeling and reprogramming, and review techniques that may improve reprogramming. Finally we will briefly touch on other aspects of SCNT that may improve the development of cloned embryos.

The mammalian centrosome and its functional significance

Primarily known for its role as major microtubule organizing center, the centrosome is increasingly being recognized for its functional significance in key cell cycle regulating events. We are now at the beginning of understanding the centrosome’s functional complexities and its major impact on directing complex interactions and signal transduction cascades important for cell cycle regulation. The centrosome orchestrates entry into mitosis, anaphase onset, cytokinesis, G1/S transition, and monitors DNA damage. Recently, the centrosome has also been recognized as major docking station where regulatory complexes accumulate including kinases and phosphatases as well as numerous other cell cycle regulators that utilize the centrosome as platform to coordinate multiple cell cycle-specific functions. Vesicles that are translocated along microtubules to and away from centrosomes may also carry enzymes or substrates that use centrosomes as main docking station. The centrosome’s role in various diseases has been recognized and a wealth of data has been accumulated linking dysfunctional centrosomes to cancer, Alstrom syndrome, various neurological disorders, and others. Centrosome abnormalities and dysfunctions have been associated with several types of infertility. The present review highlights the centrosome’s significant roles in cell cycle events in somatic and reproductive cells and discusses centrosome abnormalities and implications in disease.

Development and quality of porcine embryos in different culture system and embryo-producing methods

In this study, the developmental ability and cellular composition of porcine IVF, parthenote and somatic cell nuclear transfer (SCNT) embryos were evaluated following different in vitro culture systems. Group 1, embryos were cultured in NCSU-23 with 5.55 mM D-glucose (NCSU+) until day 6 on 20% O(2) or 5% O(2) (Group 2). Group 3, embryos were cultured in D-glucose-free NCSU-23 (NCSU-) with 0.17 mM Na pyruvate/2.73 mM Na lactate for 58 h and subsequently cultured in NCSU+ until day 6 (NCSU -/+) on 20% O2 or 5% O(2) (Group 4). IVF blastocysts did not differ significantly with O(2) concentrations, but differed significantly with major energy source (glucose and pyruvate/lactate). In Group 3 and 4 IVF blastocysts, the total cell number and apoptosis rates were not significantly different with different O(2) concentrations. Blastocyst rate, total cell number and apoptosis rate in Groups 3 and 4 parthenote embryos also were not significantly different. Parthenote and SCNT, under the same culture treatment, exhibited significant differences in blastocyst and apoptosis rates (47.5 +/- 16.1 vs. 24.0 +/- 4.0 and 4.9 +/- 9.0 vs. 22.8 +/- 23.3). Apoptosis-generating rate increased in the order parthenote, IVF and then SCNT. In conclusion, in vitro development of porcine embryos was not affected by O(2) concentrations but was affected by major energy source. Even so, the concentration of each major energy source and the timing of its inclusion in culture could accomplish relatively high embryonic development, the apoptosis rate stressed that more work still needs to be done in developing a better defined culture system that could support SCNT embryos equivalent to in vivo preimplantation porcine embryos.

Effects of different states of sheep fetal fibroblasts as donor cells on the early development in vitro of reconstructed sheep embryos

To investigate the effects of different states of donor cells on the development of reconstructed sheep embryos, we designed five treatments of donor cells, including cell passage, cell size, serum starvation, colchicine treatment and gene transfection. Results are as follows: (I) Compared with 16-18 passage cells, the morula/blastocyst rate of 5-7 passage cells as donor nuclei was significantly higher (17.3% vs. 4.9%, P<0.05), suggesting the advantage of short-time cultured cells in supporting the development of reconstructed embryos. (II) The mourla/blastocyst rate of reconstructed embryos derived from medium cells (15-25 microm) as donor nuclei was higher than that from large cells (25-33 microm) and small cells (8-15 microm)(20.0% vs. 8.0%, 9.7%), indicating that reconstructed embryos from medium cells had a greater potentiality to develop into morula/blastocysts than those from small or large ones. (III) The morula/blastocyst rate of reconstructed embryos from donor cells of SS (serum starvation) was lower than that from donor cells of NSS (non-serum starvation), but no significant difference was detected between SS and NSS(11.8% vs. 18.6%, P>0.05). (IV) Fetal fibroblasts treated with 0.05 micromol/L colchicine exhibited a higher morula/blastocyst rate of reconstructed embryos than those treated with 0.10 micromol/L colchicine and untreated ones (27.5% vs. 12.1%, 17.1%), however, no significant difference among the three treatments was detected (P>0.05). (V) The morula/blastocyst rate of reconstructed embryos from fetal fibroblasts transfected with GFP gene only was 3.1%, significantly lower than that from non-transgenic cells (3.1% vs. 20.4%, P<0.05). In conclusion, our results demonstrated that fetal fibroblasts of fewer passages, medium size could ensure a higher morula/blastocyst rate of reconstructed embryos. Serum starvation of donor cells might be unnecessary to the development of reconstructed embryos. Donor cells treated with 0.05 micromol/L colchicine could facilitate the development of reconstructed embryos. Additionally, as cells transfected with GFP gene were used as donor nuclei, adverse effect on the development of reconstructed embryos was observed. Therefore, the developmental efficiency of reconstructed embryos could be improved if proper treatments to donor cells were used.

Influence of Insulin-Like Growth Factor-I on Cytoplasmic Maturation of Horse Oocytes In Vitro and Organization of the First Cell Cycle Following Nuclear Transfer and Parthenogenesis1

In vitro maturation of horse oocytes cultured with or without IGF-I supplementation and their first cell cycle organization were studied in reconstructed horse oocytes made by somatic cell nuclear transfer versus intact oocytes stimulated parthenogenetically. The rates of metaphase II oocytes (47% and 45%) and of reconstructed oocytes that developed to the two-cell (27% and 25%) and blastocyst stages (11% and 3%) were not different between the media, with or without IGF-I, respectively. However, significantly more parthenogenetic embryos exhibited two-cell development with IGF-I (P < 0.05). The results also demonstrated that the first cell cycle organization in the reconstructed oocytes involved two different ways of nuclear remodeling. The donor nucleus in the Type I embryo showed normal nuclear remodeling that resulted in normal embryonic development. In the Type II embryos, however, the donor nucleus formed a polyploid nucleus or the embryo fragmented. Addition of IGF-I to the maturation medium significantly increased the rate of normal Type I embryonic development from the reconstructed oocytes (45% vs. 28%, P < 0.05). Maturation-promoting factor (MPF; including cdc2 and cyclin B) and mitogen-activated protein kinase (MAPK; including ERK1 and ERK2) were present at the beginning of culture, just after the oocytes had been harvested from the ovaries. The quantities of cyclin B remained stable no matter how long a period of in vitro culture the oocytes underwent, whereas cdc2 showed a tendency to accumulate in the oocytes toward the end of the 30-h culture period. Addition of IGF-I to the medium may induce a bigger accumulation of MAPK in the cytoplasm of the horse oocyte, especially in the ERK2 component, which might, in turn, increase the chance of the reconstructed oocyte undergoing nuclear remodeling to form a Type I embryo following nuclear transfer.

Apoptosis and in vitro development of preimplantation porcine embryos derived in vitro or by nuclear transfer

Apoptosis occurs during preimplantation development in both in vivo- and in vitro-produced embryos, and it may contribute to embryonic loss. The present study investigated the development of porcine nuclear transfer (NT) embryos reconstructed by using fetal fibroblasts as compared to embryos produced by in vitro fertilization (IVF). The onset and the frequency of apoptosis in NT and IVF embryos were examined via morphological and nuclear changes and TUNEL assay. The NT blastocysts had a similar number of nuclei as compared to IVF blastocysts and appeared to be morphologically similar. Relative to IVF embryos, the NT embryos had a lower cleavage rate (42.7% vs. 71.0%) and a lower developmental rate (11.1% vs. 28.6%) to the blastocyst stage. The earliest positive TUNEL signals were detected in the NT embryos on Day 5 of culture. The percentage of cells undergoing apoptosis in the NT embryos was higher than that of the IVF embryos and increased with time in vitro. Some of the abnormal morphological changes observed during early development related to apoptosis. Cytoplasmic fragmentation, developmental arrest, and nuclear condensation were typical characteristics of embryos undergoing apoptosis. Some mechanisms of the apoptotic pathway were triggered by changes in the NT embryos. The developmental rates of NT embryos might be improved by identifying specific apoptotic pathways and then intervening in these pathways to improve development.

Maturation/M-phase promoting factor regulates aging of porcine oocytes matured in vitro

Control of oocyte aging during manipulation of matured oocytes should have advantages for recently developed reproductive technologies, such as cloning after nuclear transfer. We have shown that the enhanced activation ability and fragmentation of porcine in vitro matured and aged oocytes bore a close relationship to the gradual decrease in maturation/M-phase promoting factor (MPF) activity and that porcine aged oocytes contained plenty of MPF, but it was in an inactive form, pre-MPF, as a result of phosphorylation of its catalytic subunit p34(cdc2) and, therefore, had low MPF activity. We incubated porcine oocytes with vanadate and caffeine, which affected the phosphorylation status and MPF activity, and evaluated their activation abilities and fragmentation frequencies. Incubation of nonaged oocytes with vanadate increased p34(cdc2) phosphorylation and reduced MPF activity to levels similar to those of aged oocytes and increased their parthenogenetic activation and fragmentation rates compared with those of the control oocytes. Conversely, treating aged oocytes with caffeine reduced p34(cdc2) phosphorylation and increased MPF activity. These oocytes showed significantly lower parthenogenetic activation and fragmentation rates than aged mature oocytes. These results suggest that MPF activity is a key mechanism of oocyte aging and controlling MPF activity by altering p34(cdc2) phosphorylation with these chemicals may enable oocyte aging to be manipulated in vitro. We expect those ideas will be applied practically to pig cloning.

Transgenic swine for biomedicine and agriculture

Initial technologies for creating transgenic swine only permitted random integration of the construct. However, by combining the technology for homologous recombination in fetal somatic cells with that of nuclear transfer (NT), it is now possible to create specific modifications to the swine genome. The first such example is that of knocking out a gene that is responsible for hyperacute rejection (HAR) when organs from swine are transferred to primates. Because swine are widely used as models of human diseases, there are opportunities for genetic modification to alter these models or to create additional models of human disease. Unfortunately, some of the offspring resulting from NT have abnormal phenotypes. However, it appears that these abnormal phenotypes are a result of epigenetic modifications and, thus, are not transmitted to the offspring of the clones. Although the technique of producing animals with specific genetic modifications by NT has been achieved, improvements to the NT technique as well as improvements in the culture conditions for somatic cells and the techniques for genetic modification are still needed.

Nuclear reprogramming of cloned embryos produced in vitro

Despite the fact that cloned animals derived from somatic cells have been successfully generated in a variety of mammalian species, there are still many unsolved problems with current cloning technology. Somatic cell nuclear transfer has shown several developmental aberrancies, including a high rate of abortion during early gestation and increased perinatal death. One cause of these developmental failures of cloned embryos may reside in the epigenetic reprogramming of somatic donor genome. In mammals, DNA methylation is an essential process in the regulation of transcription during embryonic development and is generally associated with gene silencing. A genome-wide demethylation may be a prerequisite for the formation of pluripotent stem cells that are important for later development. We analyzed methylation patterns in cloned bovine embryos to monitor the epigenetic reprogramming process of donor genomic DNA. Aberrant methylation profiles of cloned bovine embryos were observed in various genomic regions, except in single-copy gene sequences. The overall genomic methylation status of cloned embryos was quite different from that of normal embryos produced in vitro or in vivo. These results suggest that the developmental failures of cloned embryos may be due to incomplete epigenetic reprogramming of donor genomic DNA. We expect that advances in understanding the molecular events for reprogramming of donor genome will contribute to clarify the developmental defects of cloned embryos.

Transgenic pig expressing the enhanced green fluorescent protein produced by nuclear transfer using colchicine-treated fibroblasts as donor cells

Fetal-derived fibroblast cells were transduced with replication defective vectors containing the enhanced green fluorescent protein (EGFP). The transgenic cells were treated with colchicine, which theoretically would synchronize the cells into G2/M stage, and then used as donor nuclei for nuclear transfer. The donor cells were transferred into the perivitalline space of enucleated in vitro matured porcine oocytes, and fused and activated with electrical pulses. A total of 8.3% and 28.6% of reconstructed oocytes showed nuclear envelope breakdown and premature chromosome condensation 0.5 and 2 hr after activation, respectively. Percentage of pronuclear formation was 62.5, 12 hr after activation. Most (91.4%) of the 1-cell embryos with pronuclei did not extrude a polar body. Most (77.2%) embryos on day 5 were diploid. Within 2 hr after fusion, strong fluorescence was detectable in most reconstructed oocytes (92.3%). The fluorescence in all NT embryos became weak 15 hr after fusion and disappeared when culture to 48 hr. But from day 3, cleaved embryos at the 2- to 4-cell stage started to express EGFP again. On day 7, 85.8% of cleaved embryos expressed EGFP. A total of 9.4% of reconstructed embryos developed to blastocyst stage and 71.5% of the blastoctysts expressed EGFP. After 200 reconstructed 1-cell stage embryos were transferred into four surrogate gilts, three recipients were found to be pregnant. One of them maintained to term and delivered a healthy transgenic piglet expressing EGFP. Our data suggest that the combination of transduction of somatic cells by a replication defective vector with the nuclear transfer of colchicine-treated donors is an alternative to produce transgenic pigs. Furthermore, the tissues expressing EGFP from descendents of this pig may be very useful in future studies using pigs that require genetically marked cells.

Mosaic gene expression in nuclear transfer-derived embryos and the production of cloned transgenic pigs from ear-derived fibroblasts

Genetically modified domestic animals have many potential applications ranging from basic research to production agriculture. One of the goals in transgenic animal production schemes is to reliably predict the expression pattern of the foreign gene. Establishing a method to screen genetically modified embryos for transgene expression before transfer to surrogates may improve the likelihood of producing offspring with the desired expression pattern. In order to determine how transgene expression may be regulated in the early embryo, we generated porcine embryos from two distinct genetically modified cell lines by using the nuclear transfer (NT) technique. Both cell lines expressed the enhanced green fluorescent protein (eGFP); the first was a fibroblast cell line derived from the skin of a newborn pig that expressed eGFP, whereas the second was a fetal derived fibroblast cell line into which the eGFP gene was introduced by a retroviral vector. The reconstructed embryos were activated by electrical pulses and cultured in NCSU23. Although the in vitro developmental ability of each group of NT embryos was not different, the eGFP expression pattern was different. All embryos produced from the transduced fetal cell line fluoresced, but only 26% of the embryos generated from the newborn cell line fluoresced, and among those that did express eGFP, more than half had a mosaic expression pattern. This was unexpected because the fetal cell line was not clonally selected, and each cell had potentially different sites of integration. Embryos generated from the newborn cell line were surgically transferred to five surrogate gilts. One gilt delivered four female piglets, all of which expressed eGFP, and all had microsatellites identical to the donor. Here we demonstrate that transgene expression in all the blastomeres of an NT embryo is not uniform. In addition, transgene expression in a genetically manipulated embryo may not be an accurate indicator of expression in the resulting offspring.

Successful piglet production after transfer of blastocysts produced by a modified in vitro system

Porcine in vitro production (IVP) systems, including in vitro maturation (IVM) and in vitro fertilization (IVF) of oocytes and their subsequent in vitro culture (IVC), have been modified by many researchers, but are still at a low level because of a low developmental rate of embryos to the blastocyst stage and their poor qualities. Our objectives were to establish reliable IVP procedures for porcine blastocysts and to examine the ability of the blastocysts to develop to term after transfer to recipients. Porcine cumulus-oocyte complexes were matured in vitro under 5% O(2) or 20% O(2), fertilized in vitro under 5% O(2), and subsequently cultured under 5% O(2) in 1) IVC medium supplemented with glucose (IVC-Glu) from Day 0 (the day of IVF) to Day 6; 2) IVC-Glu from Days 0 to 2, then IVC medium supplemented with pyruvate and lactate (IVC-PyrLac) from Days 2 to 6; 3) IVC-PyrLac from Days 0 to 2, then IVC-Glu from Days 2 to 6; and 4) IVC-PyrLac from Days 0 to 6. There were no significant differences in blastocyst formation rates on Day 6 between the 5% O(2) and 20% O(2) conditions (19.9% and 14.0%, respectively). However, the quality of blastocysts, as evaluated by the total cell number, was better after IVM under 5% O(2) than under 20% O(2) (mean cell number, 43.5 and 37.8, respectively). When IVP embryos were cultured in IVC-PyrLac from Days 0 to 2 and subsequently in IVC-Glu from Days 2 to 6, the rate of blastocyst formation (25.3%) and cell number (48.7) were higher than the rates (5.8% to 18.1%) and numbers (35.4 to 37.1) with the IVC-Glu then IVC-Glu, the IVC-Glu then IVC-PyrLac, and the IVC-PyrLac then IVC-PyrLac regimens, respectively. We then prepared conditioned medium (CM) from culture of porcine oviductal epithelial cells for 2 days in IVC-PyrLac and evaluated its effect on development to the blastocyst stage. Cultivation in CM for the first 2 days, followed by IVC-Glu for a further 4 days, had a significantly greater effect in increasing the number of cells in the blastocyst (58.3) than did in IVC-PyrLac (48.4). Finally, we evaluated the ability of blastocysts, generated by IVM under 5% O(2) and IVC in CM, to develop to term. When Day 5 expanding blastocysts (mean cell number, 49.7) were transferred to an estrus-synchronized recipient (50 blastocysts per recipient), the recipient remained pregnant and farrowed eight normal piglets. Furthermore, when Day 6 expanded blastocysts (mean cell number, 80.2) were transferred to two estrus-synchronized recipients, both gilts remained pregnant and farrowed a total of 11 piglets. These results suggest that an excellent piglet production system can be established by using this modified IVP system, which produces high-quality porcine blastocysts. This system has advantages for the generation of cloned and transgenic pigs.

Generation of cloned goats (Capra hircus) from transfected foetal fibroblast cells, the effect of donor cell cycle

The neomycin-resistant gene (neo(r)) is probably the most commonly used selectable marker gene in gene targeting and gene transfection research. In this study, the neo(r) gene construct was introduced into in vitro cultured goat foetal fibroblast cells (IV-5), and the cells were selected with 900 microg/ml G418. The G418-resistant colonies were analysed by neo-specific PCR, karyotyping and anti-intermediate filament proteins antibody (anti-vimentin) staining. Cell cycle analysis of the neo(r) positive foetal fibroblast cell colony (IV-5.1) cultured in a variety of cell cycle-arresting medium indicated that 74.2% of cells cultured in serum-deprived medium for 3 days and 71.7% of cells grown to confluence were at G0/G1 stage of cell cycle, respectively, in comparison to 61.6% of cells in normal culture (cycling) medium. Nocodazole treatment for 17 hr in vitro culture could increase the number of cells at G2/M stage of cell cycle from 20.3% (in cycling medium) to 39.7%. In total, one early pregnancy was observed by B ultra-sound scanning in a surrogate transferred with cloned embryos from IV-5.1 cells at M stage (cells were cultured in nocodazole medium). Seven cloned goats, including two that miscarried at a late stage, were derived from the IV-5.1 cell clone cultured in starved medium (G0). Indeed, one surrogate receiving three blastocysts reconstituted from the starved donor cells, gave birth to three live cloned goats, all of which are healthy and doing well. PCR, Southern blot and G418 resistance in vitro of fibroblast cells from cloned goats confirmed that all cloned goats are positive for neo(r) transgene. This study demonstrates that a foreign gene, such as the neo-resistant gene, can be introduced into goat foetal fibroblast cells, and that the resulting transgenic cells are capable of being cloned to produce 100% transgenic animals.

Progress in producing knockout models for xenotransplantation by nuclear transfer

The pig is thought to be the most suitable non-human organ source for xenotransplantation. However, one of the major constraints to using pig organs for xenotransplantation is human natural antibody-mediated hyperacute rejection (HAR). Elimination of alpha(1, 3) galactosyltransferase (GGTA1) from the pig is expected to be a solution to the problem of hyperacute and delayed vascular rejection. Based on the extensive efforts made in characterization of GGTA1 in structure and function, improvement in the technique of DNA transfection of somatic cells and optimization of the pig nuclear transfer (NT) procedures, a specific modification has been made to one copy of the GGTA1 gene thus rendering it non-functional. When homozygosity of the genetic modification is achieved, this will allow concentrated efforts to address the role of galalpha(1, 3) gal specific natural antibody in HAR, acute vascular rejection and to examine the efficacy of xenotransplantation in a non-human primate model without HAR confounding the experiments. Since swine are widely used as models of human disease, the ability to make specific genetic modifications to swine as described here is predicted to have a large impact not only on production agriculture but also on biomedicine.

Typical demethylation events in cloned pig embryos. Clues on species-specific differences in epigenetic reprogramming of a cloned donor genome

We investigated whether a genomic demethylation process occurs in pig preimplantation embryos produced by either normal fertilization or somatic cell nuclear transfer. The methylation status of the centromeric satellite and the PRE-1 short interspersed element (SINE) sequences was characterized using bisulfite-sequencing technology. Typical demethylation processes were identified in these repetitive sequences of the cloned donor genome during cleavage, the patterns of which were similar to the ones detected in fertilized counterparts. These findings are different from previous observations with cloned bovine embryos where various repeated regions of the donor genome exhibited aberrant methylation patterns. Our results indicate that species-specific differences exist in modifying the epigenetic status of cloned donor genomes.