Comparison of electro-fusion and intracytoplasmic nuclear injection methods in pig cloning

The combination of rolipram and cilostamide improved the developmental competence of cloned porcine embryos

In vitro maturation of porcine oocytes is characterized by asynchronous cytoplasmic and nuclear maturation, leading to less competent oocytes supporting embryo development. The purpose of this study was to evaluate the combined effect of rolipram and cilostamide as cyclic Adenine monophosphate (cAMP) modulators to find the maximum cAMP levels that temporarily arrest meiosis. We determined the optimal time to maintain functional gap junction communication during pre-in vitro maturation to be four hours. Oocyte competence was evaluated by the level of glutathione, reactive oxygen species, meiotic progression, and gene expression. We evaluated embryonic developmental competence after parthenogenetic activation and somatic cell nuclear transfer. The combined treatment group showed significantly higher glutathione and lower reactive oxygen species levels and a higher maturation rate than the control and single treatment groups. Cleavage and blastocyst formation rates in parthenogenetic activation and somatic cell nuclear transfer embryos were higher in two-phase in vitro maturation than in the other groups. The relative levels of BMP15and GDF9 expression were increased in two-phase in vitro maturation. Somatic cell nuclear transfer blastocysts from two-phase in vitro maturation oocytes showed a lower level of expression of apoptotic genes than the control, indicating better pre-implantation developmental competence. The combination of rolipram and cilostamide resulted in optimal synchrony of cytoplasmic and nuclear maturation in porcine in vitro matured oocytes and there by enhanced the developmental competence of pre-implantation embryos.

Extranuclear Inheritance of Mitochondrial Genome and Epigenetic Reprogrammability of Chromosomal Telomeres in Somatic Cell Cloning of Mammals

The effectiveness of somatic cell nuclear transfer (SCNT) in mammals seems to be still characterized by the disappointingly low rates of cloned embryos, fetuses, and progeny generated. These rates are measured in relation to the numbers of nuclear-transferred oocytes and can vary depending on the technique applied to the reconstruction of enucleated oocytes. The SCNT efficiency is also largely affected by the capability of donor nuclei to be epigenetically reprogrammed in a cytoplasm of reconstructed oocytes. The epigenetic reprogrammability of donor nuclei in SCNT-derived embryos appears to be biased, to a great extent, by the extranuclear (cytoplasmic) inheritance of mitochondrial DNA (mtDNA) fractions originating from donor cells. A high frequency of mtDNA heteroplasmy occurrence can lead to disturbances in the intergenomic crosstalk between mitochondrial and nuclear compartments during the early embryogenesis of SCNT-derived embryos. These disturbances can give rise to incorrect and incomplete epigenetic reprogramming of donor nuclei in mammalian cloned embryos. The dwindling reprogrammability of donor nuclei in the blastomeres of SCNT-derived embryos can also be impacted by impaired epigenetic rearrangements within terminal ends of donor cell-descended chromosomes (i.e., telomeres). Therefore, dysfunctions in epigenetic reprogramming of donor nuclei can contribute to the enhanced attrition of telomeres. This accelerates the processes of epigenomic aging and replicative senescence in the cells forming various tissues and organs of cloned fetuses and progeny. For all the above-mentioned reasons, the current paper aims to overview the state of the art in not only molecular mechanisms underlying intergenomic communication between nuclear and mtDNA molecules in cloned embryos but also intrinsic determinants affecting unfaithful epigenetic reprogrammability of telomeres. The latter is related to their abrasion within somatic cell-inherited chromosomes.

Xenotransplantation: back to the future?

The field of xenotransplantation has fluctuated between great optimism and doubts over the last 50 years. The initial clinical attempts were extremely ambitious but faced technical and ethical issues that prompted the research community to go back to preclinical studies. Important players left the field due to perceived xenozoonotic risks and the lack of progress in pig-to-nonhuman-primate transplant models. Initial apparently unsurmountable issues appear now to be possible to overcome due to progress of genetic engineering, allowing the generation of multiple-xenoantigen knockout pigs that express human transgenes and the genomewide inactivation of porcine endogenous retroviruses. These important steps forward were made possible by new genome editing technologies, such as CRISPR/Cas9, allowing researchers to precisely remove or insert genes anywhere in the genome. An additional emerging perspective is the possibility of growing humanized organs in pigs using blastocyst complementation. This article summarizes the current advances in xenotransplantation research in nonhuman primates, and it describes the newly developed genome editing technology tools and interspecific organ generation.

Direct introduction of gene constructs into the pronucleus-like structure of cloned embryos: a new strategy for the generation of genetically modified pigs

Due to a rising demand of porcine models with complex genetic modifications for biomedical research, the approaches for their generation need to be adapted. In this study we describe the direct introduction of a gene construct into the pronucleus (PN)-like structure of cloned embryos as a novel strategy for the generation of genetically modified pigs, termed "nuclear injection". To evaluate the reliability of this new strategy, the developmental ability of embryos in vitro and in vivo as well as the integration and expression efficiency of a transgene carrying green fluorescence protein (GFP) were examined. Eighty percent of the cloned pig embryos (633/787) exhibited a PN-like structure, which met the prerequisite to technically perform the new method. GFP fluorescence was observed in about half of the total blastocysts (21/40, 52.5%), which was comparable to classical zygote PN injection (28/41, 68.3%). In total, 478 cloned embryos injected with the GFP construct were transferred into 4 recipients and from one recipient 4 fetuses (day 68) were collected. In one of the fetuses which showed normal development, the integration of the transgene was confirmed by PCR in different tissues and organs from all three primary germ layers and placenta. The integration pattern of the transgene was mosaic (48 out of 84 single-cell colonies established from a kidney were positive for GFP DNA by PCR). Direct GFP fluorescence was observed macro- and microscopically in the fetus. Our novel strategy could be useful particularly for the generation of pigs with complex genetic modifications.

Nuclear transfer and transgenesis in the pig

Somatic cell nuclear transfer (SCNT) using genetically modified donor cells facilitates the generation of tailored pig models for biomedical research and for xenotransplantation. Up to now, SCNT is the main way to generate gene-targeted pigs, since germ line-competent pluripotent stem cells are not available for this species. In this chapter, we introduce our routine workflow for the production of genetically engineered pigs, especially focused on the genetic modification of somatic donor cells, SCNT using in vitro matured oocytes, and laparoscopic embryo transfer.

Genetic polymorphisms, growth performance, hematological parameters, serum enzymes, and reproductive characteristics in phenotypically normal Landrace boars produced by somatic cell nuclear transfer

Understanding the performances of cloned pigs and their offspring is critical to evaluate the practical applications of somatic cell nuclear transfer. In this study, genetic polymorphism, growth performance, hematological parameters, and reproduction characteristics of cloned Landrace boars were compared with those of controls. In addition, the growth performance of clone offspring was also evaluated. A total of 479 reconstructed embryos were transferred to five recipient pigs and resulted in the delivery of 14 piglets (overall cloning of 2.9%) from two litters. Analyses of microsatellite markers and polymorphisms of the specific genes confirmed that the 14 clones were genetically identical to the nuclear donor and maintained the desirable genotypes. Growth performance of five healthy, phenotypically normal cloned boars from one litter and eight of their male offspring did not differ from age, breed, and management-matched controls. Although some significant differences were observed between cloned and control boars in hematological and serum enzymes, most of these parameters were within the normal range. Cloned boars had less (P < 0.05) normal sperm in the ejaculated boars than in control boars (71.4% vs. 77.9%, respectively), but sperm production (ejaculate volume, sperm concentration, and total sperm) did not differ between these groups. In addition, use of frozen-thawed semen from cloned boars for insemination produced results that seemed comparable to a control. In conclusion, the present study reported that somatic cell nuclear transfer is effective in reproducing preferred genetic traits and has potential applications to conserve elite bloodlines in a routine pig breeding program.

Generation of transgenic Wuzhishan miniature pigs expressing monomeric red fluorescent protein by somatic cell nuclear transfer

Red fluorescent protein and its variants enable researchers to study gene expression, localization, and protein-protein interactions in vitro in real-time. Fluorophores with higher wavelengths are usually preferred since they efficiently penetrate tissues and produce less toxic emissions. A recently developed fluorescent protein marker, monomeric red fluorescent protein (mRFP1), is particularly useful because of its rapid maturation and minimal interference with green fluorescent protein (GFP) and GFP-derived markers. We generated a pCX-mRFP1-pgk-neoR construct and evaluated the ability of mRFP1 to function as a fluorescent marker in transgenic Wuzhishan miniature pigs. Transgenic embryos were generated by somatic cell nuclear transfer (SCNT) of nuclei isolated from ear fibroblasts expressing mRFP1. Embryos generated by SCNT developed into blastocysts in vitro (11.65%; 31/266). Thereafter, a total of 685 transgenic embryos were transferred into the oviducts of three recipients, two of which became pregnant. Of these, one recipient had six aborted fetuses, whereas the other recipient gave birth to four offspring. All offspring expressed the pCX-mRFP1-pgk-neoR gene as shown by PCR and fluorescence in situ hybridization analysis. The transgenic pigs expressed mRFP1 in all organs and tissues at high levels. These results demonstrate that Wuzhishan miniature pigs can express mRFP1. To conclude, this transgenic animal represents an excellent model with widespread applications in medicine and agriculture.

A simplified one-step nuclear transfer procedure alters the gene expression patterns and developmental potential of cloned porcine embryos

Various somatic cell nuclear transfer (SCNT) techniques for mammalian species have been developed to adjust species-specific procedures to oocyte-associated differences among species. Species-specific SCNT protocols may result in different expression levels of developmentally important genes that may affect embryonic development and pregnancy. In the present study, porcine oocytes were treated with demecolcine that facilitated enucleation with protruding genetic material. Enucleation and donor cell injection were performed either simultaneously with a single pipette (simplified one-step SCNT; SONT) or separately with different pipettes (conventional two-step SCNT; CTNT) as the control procedure. After blastocysts from both groups were cultured in vitro, the expression levels of developmentally important genes (OCT4, NANOG, EOMES, CDX2, GLUT-1, PolyA, and HSP70) were analyzed by real-time quantitative polymerase chain reaction. Both the developmental rate according to blastocyst stage as well as the expression levels CDX2, EOMES, and HSP70 were elevated with SONT compared to CTNT. The genes with elevated expression are known to influence trophectoderm formation and heat stress-induced arrest. These results showed that our SONT technique improved the development of SCNT porcine embryos, and increased the expression of genes that are important for placental formation and stress-induced arrest.

Factors influencing the efficiency of generating genetically engineered pigs by nuclear transfer: multi-factorial analysis of a large data set

BACKGROUND

Somatic cell nuclear transfer (SCNT) using genetically engineered donor cells is currently the most widely used strategy to generate tailored pig models for biomedical research. Although this approach facilitates a similar spectrum of genetic modifications as in rodent models, the outcome in terms of live cloned piglets is quite variable. In this study, we aimed at a comprehensive analysis of environmental and experimental factors that are substantially influencing the efficiency of generating genetically engineered pigs. Based on a considerably large data set from 274 SCNT experiments (in total 18,649 reconstructed embryos transferred into 193 recipients), performed over a period of three years, we assessed the relative contribution of season, type of genetic modification, donor cell source, number of cloning rounds, and pre-selection of cloned embryos for early development to the cloning efficiency.

RESULTS

109 (56%) recipients became pregnant and 85 (78%) of them gave birth to offspring. Out of 318 cloned piglets, 243 (76%) were alive, but only 97 (40%) were clinically healthy and showed normal development. The proportion of stillborn piglets was 24% (75/318), and another 31% (100/318) of the cloned piglets died soon after birth. The overall cloning efficiency, defined as the number of offspring born per SCNT embryos transferred, including only recipients that delivered, was 3.95%. SCNT experiments performed during winter using fetal fibroblasts or kidney cells after additive gene transfer resulted in the highest number of live and healthy offspring, while two or more rounds of cloning and nuclear transfer experiments performed during summer decreased the number of healthy offspring.

CONCLUSION

Although the effects of individual factors may be different between various laboratories, our results and analysis strategy will help to identify and optimize the factors, which are most critical to cloning success in programs aiming at the generation of genetically engineered pig models.

Improved cloning efficiency and developmental potential in bovine somatic cell nuclear transfer with the oosight imaging system

In somatic cell nuclear transfer (SCNT) procedures, exquisite enucleation of the recipient oocyte is critical to cloning efficiency. The purpose of this study was to compare the effects of two enucleation systems, Hoechst staining and UV irradiation (hereafter, irradiation group) and Oosight imaging (hereafter, Oosight group), on the in vitro production of bovine SCNT embryos. In the Oosight group, the apoptotic index (2.8 ± 0.5 vs. 7.3 ± 1.2) was lower, and the fusion rate (75.6% vs. 62.9%), cleavage rate (78.0% vs. 63.7%), blastocyst rate (40.2% vs. 29.2%), and total cell number (128.3±4.8 vs. 112.2 ± 7.6) were higher than those in the irradiation group (all p<0.05). The overall efficiency after SCNT was twice as high in the Oosight group as that in the irradiation group (p<0.05). The relative mRNA expression levels of Oct4, Nanog, Interferon-tau, and Dnmt3A were higher and those of Caspase-3 and Hsp70 were lower in the Oosight group compared with the irradiation group (p<0.05). This is the first report to show the positive effect of the Oosight imaging system on molecular gene expression in the SCNT embryo. The Oosight imaging system may become the preferred choice for enucleation because it is less detrimental to the developmental potential of bovine SCNT embryos.

Prolonged interval between fusion and activation impairs embryonic development by inducing chromosome scattering and nuclear aneuploidy in pig somatic cell nuclear transfer

The aim of the present study was to examine the effect of various intervals between electrofusion and activation (FA interval) on the nuclear remodelling and development of somatic cell nuclear transfer (SCNT) embryos in pigs. Reconstructed oocytes were activated at 0 (simultaneous fusion and activation; SFA), 1, 2 and 3 h (delayed activation) after electrofusion; these groups were designated as DA1, DA2 and DA3, respectively. When oocyte nuclear status was examined at 0.5, 1, 2 and 3 h after electrofusion, the incidence of chromosome scattering was increased (P < 0.01) as the FA interval was extended (0.0%, 12.0%, 77.3% and 78.0%, respectively). Extending the FA interval led to an increase (P < 0.01) in the percentage of oocytes containing multiple (>or=3) pseudopronuclei (PPN) (0.0% of SFA; 5.3% of DA1; 21.7% of DA2; and 33.5% of DA3). The development of SCNT embryos to the blastocyst stage was decreased (P < 0.05) in DA2 (5.7%) and DA3 (5.0%) compared with SFA (18.1%) and DA1 (19.5%). Our results demonstrate that extending the FA interval impairs the development of SCNT pig embryos by inducing chromosome scattering and the formation of multiple PPN, which may result in increased nuclear aneuploidy.

Production of cloned pigs by nuclear transfer of preadipocytes following cell cycle synchronization by differentiation induction

Four methods of cell cycle synchronization of porcine preadipocytes for use as nuclear donors in somatic cell cloning were compared: serum starvation, differentiation induction, contact inhibition and roscovitine treatment. After three days of differentiation induction, the percentage of nuclear donor cells synchronized at the G0/G1 phase reached a peak value of 91.8%, which was significantly higher (P<0.05) than the percentage attained by serum starvation (84.9-89.8%), contact inhibition (78.3-83.7%) or roscovitine treatment (67.8-80.3%). Cell cycle synchronization by serum starvation, contact inhibition and roscovitine treatment all increased the percentage of apoptotic cells, while no increase was observed when the donor-cell cycle was synchronized by differentiation induction (Annexin V-positive: 15.7% to 19.3% vs. 7.7%, P<0.05; TUNEL-positive: 12.8% to 14.0% vs. 8.3%, P<0.05). Additionally, comparison of the in vitro development of nuclear transfer (NT) embryos formed from the nuclei of differentiation-induced or serum-starved preadipocytes revealed that, in both cases, a high proportion of embryos developed to the blastocyst stage (39.0 and 33.7%, respectively). In this study, NT embryos reconstructed with preadipocytes synchronized by differentiation induction were transferred to four recipient pigs, three of which gave birth to a total of 17 piglets (4.2%, 17/403). These results demonstrate that donor-cell cycle synchronization by differentiation induction enables effective production of cloned pigs. The findings also indicate that differentiation induction of multipotent cells is an excellent method of cell cycle synchronization that permits highly efficient synchronization of cells at the G0/G1 phase.

Production of viable cloned miniature pig embryos using oocytes derived from domestic pig ovaries

For production of viable somatic cell nuclear transferred (SCNT) miniature pig embryos, in vitro condition for controlling the quality of recipient oocytes derived from domestic pig ovaries should be evaluated. In the present study, to get information on optimal in vitro maturation (IVM) condition of oocytes, we investigated the effect of IVM duration of recipient oocytes on subsequent development of SCNT miniature pig embryos, the maturation-promoting factor (MPF) activity in recipient oocytes before and after SCNT, and the occurrence of premature chromosome condensation (PCC) and spindle morphologies of donor nuclei following SCNT. The optimal window of the IVM period in terms of in vitro developmental ability of SCNT embryos was determined to be 36-40 h after the start of IVM. The use of recipient oocytes matured for 36 and 40 h resulted in a high level of MPF activity before and after SCNT, and increased the occurrence of PCC in transferred nuclei compared to the use of oocytes matured for 44 and 52 h. The proportion of abnormal spindle-like structures increased as the IVM period was prolonged. In addition, SCNT embryos constructed from recipient cytoplasts obtained after 40 h of maturation by using fetal fibroblasts of miniature pigs were transferred to surrogate miniature pigs, and developed to full term. These results suggest that recipient oocytes matured for 36 h and 40 h effectively induce PCC with a normal cytoskeletal structure because of a high level of MPF activity; furthermore, the 40-h IVM period improves in vitro development of SCNT embryos to the blastocyst stage, resulting in the production of viable cloned miniature pigs.

Transgenic-cloned pigs systemically expressing red fluorescent protein, Kusabira-Orange

Genetically engineered pigs with cell markers such as fluorescent proteins are highly useful in lines of research that include the tracking of transplanted cells or tissues. In this study, we produced transgenic-cloned pigs carrying a gene for the newly developed red fluorescent protein, humanized Kusabira-Orange (huKO), which was cloned from the coral stone Fungia concinna. The nuclear transfer embryos, reconstructed with fetal fibroblast cells that had been transduced with huKO cDNA using retroviral vector D Delta Nsap, developed efficiently in vitro into blastocysts (28.0%, 37/132). Nearly all (94.6%, 35/37) of the cloned blastocysts derived from the transduced cells exhibited clear huKO gene expression. A total of 429 nuclear transfer embryos were transferred to four recipients, all of which became pregnant and gave birth to 18 transgenic-cloned offspring in total. All of the pigs highly expressed huKO fluorescence in all of the 23 organs and tissues analyzed, including the brain, eyes, intestinal and reproductive organs, skeletal muscle, bone, skin, and hoof. Furthermore, such expression was also confirmed by histological analyses of various tissues such as pancreatic islets, renal corpuscles, neuronal and glial cells, the retina, chondrocytes, and hematopoietic cells. These data demonstrate that transgenic-cloned pigs exhibiting systemic red fluorescence expression can be efficiently produced by nuclear transfer of somatic cells retrovirally transduced with huKO gene.

A comparative study on the efficiency of two enucleation methods in pig somatic cell nuclear transfer: effects of the squeezing and the aspiration methods

In this study, two enucleation methods, the squeezing and the aspiration methods, were compared. The efficiency of these two methods to enucleate pig oocytes and the in vitro and in vivo viability of somatic cell nuclear transfer (SCNT) pig embryos, were evaluated. In the squeezing method, the zona pellucida was partially dissected and a small amount of cytoplasm containing metaphase II (MII) chromosomes and the first polar body (PB) were pushed out. In the aspiration method, the PB and MII chromosomes were aspirated using a beveled micropipette. After injection of fetal fibroblasts into the perivitelline space, reconstructed oocytes were fused and activated electrically, and then cultured in vitro for 6 days or transferred to surrogates. The squeezing method resulted in a higher proportion of degenerated oocytes than the aspiration method (14% vs. 5%). The squeezing method took longer to enucleate 100 oocytes (306 minutes) than the aspirating method (113 minutes). Fusion rate (72-78%) and cleavage rate (67%) were not influenced by the enucleation method but blastocyst formation was improved (P < 0.05) in oocytes enucleated by the aspiration method (5 vs. 9%). When SCNT embryos were transferred to recipients, pregnancy rates to term were similar (27%, 3/11 and 27%, 3/11) in both methods with the birth of 10 piglets/3 litters and 16 piglets/3 litters in the squeezing and the aspiration methods, respectively. Our results indicate that the aspiration method for oocyte enucleation is more efficient than the squeezing method in producing a large number of pig SCNT embryos with normal in vivo viability.

Production efficiency and telomere length of the cloned pigs following serial somatic cell nuclear transfer

The aim of the present study was to examine the production efficiency of cloned pigs by serial somatic cell nuclear transfer (SCNT) and to ascertain any changes in the telomere lengths of multiple generations of pigs. Using fetal fibroblasts as the starting nuclear donor cells, porcine salivary gland progenitor cells were collected from the resultant first-generation cloned pigs to successively produce second- and third-generation clones, with no significant differences in production efficiency, which ranged from 1.4% (2/140) to 3.3% (13/391) among the 3 generations. The average telomere lengths (terminal restriction fragment values) for the first, second and third generation clones were 16.3, 18.1 and 20.5 kb, respectively, and were comparable to those in age-matched controls. These findings suggest that third-generation cloned pigs can be produced by serial somatic cell cloning without compromising production efficiency and that the telomere lengths of cloned pigs from the first to third generations are normal.

Production of transgenic and non-transgenic clones in miniature pigs by somatic cell nuclear transfer

Miniature pigs have been recognized as valuable experimental animals in various fields such as medical and pharmaceutical research. However, the amount of information on somatic cell cloning in miniature pigs, as well as genetically modified miniature pigs, is much less than that available for common domestic pigs. The objective of the present study was to establish an efficient technique of cloning miniature pigs by somatic cell nuclear transfer. A high pregnancy rate was achieved following transfer of parthenogenetic (3/3) and cloned (5/6) embryos using female miniature pigs in the early pregnancy period as recipients after estrus synchronization with prostaglandin F2 alpha analog and gonadotrophins. The production efficiency of the cloned miniature pigs using male and female fetal fibroblasts as nucleus donors was 0.9% (2/215 and 3/331, respectively). Cloned miniature pigs were also produced efficiently (7.8%, 5/64) by transferring reconstructed embryos into the uteri of common domestic pigs. When donor cells transfected with the green fluorescent protein (GFP) gene were used in nuclear transfer, the production efficiency of the reconstructed embryos and rate of blastocyst development were comparable to those obtained by non-transfected cells. When transfected cell-derived reconstructed embryos were transferred to three common domestic pig recipients, all became pregnant, and a total of ten transgenic cloned miniature pigs were obtained (piglet production efficiency: 2.7%, 10/365). Hence, we were able to establish a practical system for producing cloned and transgenic-cloned miniature pigs with a syngeneic background.

Production of transgenic-clone pigs by the combination of ICSI-mediated gene transfer with somatic cell nuclear transfer

The objective of this study was to examine whether the ICSI-mediated gene transfer method using in vitro matured oocytes and frozen sperm head could actually produce transgenic pigs. We also aimed at examining whether transgenic pigs can be cloned from somatic cells of a transgenic pig generated by the ICSI-mediated method. A bicistronic gene constituted of the human albumin (hALB) and enhanced green fluorescent protein (EGFP) genes was introduced into pig oocytes by the ICSI-mediated method. Transfer of 702 embryos produced by the ICSI-mediated method into five gilts resulted in 4 pregnancies. When three of the recipients, which had received total 312 of the embryos were autopsied, 32 including 1 transgenic fetuses were obtained. One of the recipients gave birth to three live piglets including one transgenic pig, showing a strong green fluorescence in the eyeballs, oral mucous membrane and subcutaneous tissues. Fluorescent microscopy revealed uniform GFP expression in all cell lines established from kidney, lung and muscle of the founder transgenic pig obtained. Nuclear transfer of these cells resulted in stable in vitro development of cloned embryos into the blastocyst stage, ranging from 12.9 to 19.8%. When 767 of the nuclear transfer embryos were transferred to 5 recipients, all became pregnant and gave birth to a total of six live transgenic-clones. The transgene copy number and integrity in the founder pig were maintained in the primary culture cells established from the founder as well as in the clones produced from these cells. Our study demonstrates that the ICSI-mediated gene transfer is an efficient and practical method to produce transgenic pigs, using frozen sperm heads and in vitro matured oocytes. It was also shown that combination of ICSI-mediated transgenesis and nuclear transfer is a feasible technology of great potential in transgenic pig production.

Production of Live Piglets Following Cryopreservation of Embryos Derived from In Vitro-Matured Oocytes1

We have successfully produced healthy piglets following cryopreservation of embryos derived from oocytes matured and fertilized in vitro. The appropriate timing of cryopreservation pretreatment (removal of cytoplasmic lipid droplets [delipation] and vitrification) was initially determined using parthenogenetic embryos derived from in vitro-matured (IVM) oocytes. Viable embryos were obtained at the highest rate when embryos were delipated at the four- to eight-cell stages (Day 2 of embryo culture) and were vitrified approximately 15 h later (Day 3) by means of the minimum volume cooling method. After cryopreservation of embryos derived from oocytes matured and fertilized in vitro under the most appropriate conditions, 401 embryos were transferred to five recipient gilts, and the recipients all became pregnant. At autopsy of one of the recipients, which had received 47 embryos, eight fetuses (17.0%) were found. Three recipients each gave birth to two to four piglets (1.4%-6.0%). These results demonstrate that normal offspring can be produced from vitrified porcine embryos derived from IVM oocytes by a strategic combination of delipation and vitrification at the early cleavage stages. This approach has great potential in the reproduction of micromanipulated porcine embryos, such as cloned and sperm-injected embryos, produced from IVM oocytes.

Association Between Embryonic Loss and Damage to the Zona Pellucida by Invasive Micromanipulation During Oviductal Transfer of Early-Stage Embryos in Pigs

The aim of this study was to examine the impact of zona pellucida damage, which might arise during somatic cell nuclear transfer (SCNT), on the development and survival of transferred embryos. The zonae pellucidae of in vitro matured oocytes were either punctured with 8- to 10-microm square-ended nuclear injection pipettes and piezo pulses or slit with 35- to 40-microm enucleation pipettes. Intact oocytes were used as controls. These oocytes were electroactivated to induce parthenogenesis and transferred to the oviducts of estrus-synchronized recipient gilts. After 5 to 7 days, the recipient uteri were flushed to collect embryos, and embryonic development (morula-blastocyst stage embryos/collected embryos) and survival (viable embryos/collected embryos) were determined. In total, 221 zona-punctured, 129 zona-slitted and 57 intact embryos were transplanted into four, two and two gilts, respectively. The efficiency of embryo recovery was similar in all groups (64.3 to 79.1%). However, the zona-penetrated and incised embryos exhibited unstable development and survival compared with the controls; development and survival of the control embryos were 94.7 and 87.7%, whereas those of the zona-punctured embryos were 69.0 and 47.9% (P<0.01) and those of the zona-slit embryos were 64.7 and 50.0% (P<0.01). Cells with large foci that appeared to be macrophage giant cells were observed at the surface or inside the degenerated zona-damaged embryos. These results indicate that the recipient's immune response to damage to the zona pellucida may impair embryonic development after transplantation to the oviduct. This may be one of the factors causing the reduced efficiency of live progeny production by SCNT.

Production of Cloned Pigs by Nuclear Transfer of Preadipocytes Established from Adult Mature Adipocytes

The aim of the present study was to determine whether porcine preadipocytes can be efficient donor cells for somatic cell nuclear transfer (SCNT) in pigs. Primary culture of porcine preadipocytes was established by de-differentiating mature fat cells taken from an adult pig. The cell cycle of the preadipocytes could be synchronized by serum starvation for 1 day, with a higher efficiency than control fetal fibroblasts. Incidence of premature chromosome condensation following nuclear transfer (NT) of preadipocytes was as high as that observed after NT with fetal fibroblasts. In vitro developmental rate of the NT embryos reconstructed with preadipocyte was equivalent to that of the fetal fibroblast derived embryos. Transfer of 732 NT embryos with preadipocytes to five recipients gave rise to five cloned piglets. These data demonstrate that preadipocyites collected from an adult pig are promising nuclear donor cells for pig cloning.

Evaluation of the quality of porcine somatic cell nuclear transfer embryo by gene transcription profiles

This study aimed to evaluate the quality of porcine somatic cell nuclear transfer (SCNT) embryos by examining its gene transcription patterns. Embryos were produced by SCNT, intracytoplasmic sperm injection (ICSI) or under different conditions, and transcripts of genes for fibroblast growth factor receptor (FGFr) 2IIIc, FGFr72IIIb, X inactive-specific transcript (Xist), interleukin 6 (IL6), IL6 receptor (IL6r) alpha and c-kit ligand, were detected by real-time RT-PCR. The percentages of embryos in which these transcripts were detected were similar in SCNT and ICSI embryos. On the other hand, the transcriptional levels of the FGFr72IIIb and IL6ralpha genes were 0.5 times less and 2 times more, respectively, in SCNT blastocysts than those of ICSI blastocysts (p<0.05). When nuclear transfer was performed before or after activation of oocytes, embryos in the latter case showed significantly lower frequencies of having FGFr72IIIb (74% vs. 90%) and Xist (3% vs. 33%) transcripts compared to the former case embryos (p<0.05). When two lines of nuclear donor cells with different developmental potencies were used, the transcriptional profiles in the reconstructed embryos did not show any significant differences. Our study suggests that expression profiles of FGFr72IIIb, IL6ralpha, and Xist can be used as markers for the diagnosis of the developmental potency of porcine nuclear transfer embryos.

Cloning of the transgenic pigs expressing human decay accelerating factor and N-acetylglucosaminyltransferase III

The present paper describes production of cloned pigs from fibroblast cells of transgenic pigs expressing human decay accelerating factor (DAF, CD55) and N-acetylglucosaminyltransferase III (GnT-III) that remodels sugar-chain biosynthesis. Two nuclear transfer protocols were used: a two-step activation (TA) method and a delayed activation (DA) method. Enucleated in vitro-matured oocytes and donor cells were electrically fused in a calcium-containing medium by TA method or in a calcium-free medium by DA method, followed by electrical activation 1-1.5 h later, respectively. In vitro blastocyst formation rates of nuclear transferred embryos reconstructed by TA and DA method were 8% and 14%, respectively. As a result of embryo transfer of the reconstructed embryos made by each method into recipient pigs, both gave rise to cloned piglets. These cloned pigs expressed transgene as much as their nuclear donor cells. In conclusions, (1) pig cloning can be carried out by TA or DA nuclear transfer methods, (2) expression of transgenes can be maintained to cloned pigs from the nuclear donor cells derived from transgenic animals.

Optimization of Ca2+ Concentrations in Fusion and Activation Media for Production of Cloned Embryos from Miniature Pig Somatic Cells

The effects of Ca(2+) concentration in activation medium and cytochalasin B treatment after activation on the parthenogenetic development of pig oocytes were examined. In addition, cloned embryos derived from miniature pig somatic cells were activated under optimal conditions and the effects of Ca(2+) in fusion medium on the development of embryos after activation was examined. When oocytes were activated in 0.1 mM Ca(2+) and then treated with cytochalasin B, the blastocyst formation rate (28.6%) was significantly higher than those activated in 0-0.05 or 1.0 mM (11.0-18.3%). Treatment with cytochalasin B decreased the second polar body extrusion rate of activated oocytes. The presence or absence of Ca(2+) in fusion medium did not affect the fusion rate of miniature pig somatic cells with recipient oocytes. A few cloned embryos developed to the blastocyst stage (2.7-9.0%) without an additional activation treatment. On the other hand, significantly more embryos developed to the blastocyst stage after activation treatment when they were fused in the absence (28.9%) of Ca(2+) rather than the presence (16.5%) of it. These results show that the highest blastocyst formation rate for miniature pig cloned embryos is obtained when donor cells and recipient oocytes are fused in the absence of Ca(2+) and then activated in 0.1 mM Ca(2+) and treated with cytochalasin B.