Comparison of two approaches to nuclear transfer in the bovine: hand-made cloning with modifications and the conventional nuclear transfer technique

Production of Water Buffalo SCNT Embryos by Handmade Cloning

Cloning by somatic cell nuclear transfer (SCNT) involves the transfer of a somatic nucleus into an enucleated oocyte followed by chemical activation and embryo culture. Further, handmade cloning (HMC) is a simple and efficient SCNT method for large-scale embryo production. HMC does not require micromanipulators for oocyte enucleation and reconstruction since these steps are carried out using a sharp blade controlled by hand under a stereomicroscope. In this chapter, we review the status of HMC in the water buffalo (Bubalus bubalis) and further describe a protocol for the production of buffalo-cloned embryos by HMC and assays to estimate their quality.

Early Cell Specification in Mammalian Fertilized and Somatic Cell Nuclear Transfer Embryos

Early cell specification in mammalian preimplantation embryos is an intricate cellular process that leads to coordinated spatial and temporal expression of specific genes. Proper segregation into the first two cell lineages, the inner cell mass (ICM) and the trophectoderm (TE), is imperative for developing the embryo proper and the placenta, respectively. Somatic cell nuclear transfer (SCNT) allows the formation of a blastocyst containing both ICM and TE from a differentiated cell nucleus, which means that this differentiated genome must be reprogrammed to a totipotent state. Although blastocysts can be generated efficiently through SCNT, the full-term development of SCNT embryos is impaired mostly due to placental defects. In this review, we examine the early cell fate decisions in fertilized embryos and compare them to observations in SCNT-derived embryos, in order to understand if these processes are affected by SCNT and could be responsible for the low success of reproductive cloning.

Efficient production of GGTA1 knockout porcine embryos using a modified handmade cloning (HMC) method

Handmade cloning is a zona-free nuclear transfer approach and an economical, efficient, and simple micromanipulation-free alternative to dolly based traditional cloning (TC). In this study, based on handmade cloning with minor modifications, an optimized bi-oocyte fusion (BOF) cloning method was established to produce GGTA1 KO porcine embryos using the CRISPR/Cas9 gene editing system. The GGTA1 gene is responsible for the generation of Gal epitopes on the surface of porcine cells, triggering hyperacute immune rejection in preclinical porcine-to-human xenotransplantation. The purpose of the present study is to establish an efficient protocol for activation of porcine oocyte cytoplast-fibroblast fused constructs developed to GGTA1 KO blastocysts by the zona-free bi-oocyte fusion cloning method. High percentages of cleavage (90 ± 2.6%) and blastocyst rates (39 ± 4.0%) were achieved upon treatment with demecolcine-assisted oocyte enucleation followed by 6 V alternating current for proper alignment and single-step fusion technique using a single direct current pulse of 1.0 kV/cm for 9 μs duration, compared to the double-step fusion method with combined chemical activation using thimerosal and dithiothreitol. Overall blastocyst rate was higher for oocyte enucleation by demecolcine (0.4 μg/ml) and 45 min incubation (42 ± 1.5%) compared to without demecolcine incubation followed by complete chemical thimerosal/dithiothreitol activation (33 ± 1.1%). The blastocyst rate (39 ± 1.0%) was found to be significantly higher 1 h post-electrofusion, compared to at 0 and 4 h (28 ± 1.5 and 6 ± 1.5%, respectively). Blastocyst development rates for GGTA1 knockout embryos (38 ± 1.76%) were comparable to those obtained with wild-type embryos (41.1 ± 0.67%). In conclusion, we achieved high overall efficiency in production of GGTA1 KO blastocysts by modified HMC protocol.

Survival, re-expansion, and pregnancy outcome following vitrification of dromedary camel cloned blastocysts: A possible role of vitrification in improving clone pregnancy rate by weeding out poor competent embryos

There is a clinical demand for efficient cryopreservation of cloned camel embryos with considerable logistic and economic advantage. Vitrification of in vivo derived embryos has been reported in camels, but there is no study on vitrification of cloned embryos. Moreover, whether characteristic differences between cloned and in vivo derived embryos imply different vitrification requirement is unresolved. Here, we compared survival, re-expansion and pregnancy rates of cloned embryos vitrified using two commercial vitrification kits (Cryotec and Kitazato), developed basically for human embryos, and a vitrification protocol developed for in vivo camel embryos (CVP). Cloned embryos responded dynamically to vitrification-warming steps in commercial kits, with a flat shrinkage in the final vitrification solution and a quick re-expansion to the original volume immediately after transferring to the isotonic warming solution. Contrarily, full shrinkage was not observed in CVP method, and majority of embryos were still collapsed post-warming. The immediate re-expansion was highly associated and predictive of higher survival and total cell number, and also better redox state of embryos vitrified by Cryotec and Kitazato kits compared to CVP method. Importantly, while 30% blastomere loss, verified by differential dye exclusion test, was tolerated in vitrified embryos, >50% blastomeres loss in non-expanded blastocysts implied the minimal essential cell survival rate for blastocoelic cavity re-expansion in vitrified cloned camel blastocysts, irrespective of vitrification method. A protocol-based exposure of embryos to cryoprotectants indicated that cryoprotectant toxicity, per se, may not be involved in lower cryosurvival of embryos in CVP vs. Cryotec and Kitazato. The initial pregnancy rates were numerically higher in Cryotec and Kitazato frozen transfers compared to fresh transfer (56.3, 60 and 33.3%, respectively), and importantly, a higher percentage of established pregnancies in vitrified groups passed the critical 3 months period of early embryonic loss compared to sibling fresh clone pregnancies (50, 40, and 10%, respectively). Results confirmed the suitability of Cryotec and Kitazato kits for vitrification of cloned camel embryos and that vitrification may improve pregnancy outcome by weeding out poor competent embryos.

Reducing the cytoplasmic volume during hand-made cloning adversely affects the developmental competence and quality, and alters relative abundance of mRNA transcripts and epigenetic status of buffalo (Bubalus bubalis) embryos

Hand-made cloning (HMC) is a method of choice for somatic cell nuclear transfer (SCNT). There is 20% to 50% of cytoplasm lost during manual enucleation of oocytes with HMC. To compensate, two enucleated demicytoplasts, instead of one, are fused with each donor cell, which leads to cytoplasm pooling from two different demicytoplasts. In this study, effects of using one, instead of two demicytoplasts (controls) was examined, for production of embryos using HMC. Use of one demicytoplast decreased blastocyst development (12.7 ± 1.98% compared with 47.6 ± 3.49%, P < 0.001), total cell number (TCN, 167.6 ± 14.66 compared with 335.9 ± 58.96, P < 0.01), apoptotic index (2.11 ± 0.38 compared with 3.43±0.38, P < 0.05) but did not significantly alter inner cell mass:trophectoderm cell number ratio (0.17 ± 0.01 compared with 0.19 ± 0.02) and the global content of H3K9ac and H3K27me3 of blastocysts, compared to controls. There were gene expression alterations in pluripotency- (SOX2 and NANOG but not OCT4), epigenetic- (DNMT1 but not DNMT3a and HDAC1), apoptosis- (CASPASE3 but not BCL-2 and BAX), trophectoderm- (CDX2), development- (G6PD but not GLUT1) and cell cycle check point control-related related genes (P53) compared with controls. Transfer of cloned blastocysts from one demicytoplast (n = 8) to recipients resulted in a live calf birth that after 12 days died whereas, with transfer of control blastocysts (n = 14) there was birth of a healthy calf. In conclusion, use of one, instead of two demicytoplasts for HMC, compromises in vitro developmental competence, and alters expression of several important genes affecting embryo development.

High Pregnancy and Calving Rates with a Limited Number of Transferred Handmade Cloned Bovine Embryos

A major obstacle of widespread commercial application of bovine somatic cell nuclear transfer is the low overall efficiency, that is, healthy calf-late pregnancy per transferred embryo rate. In this study, we report a series of experiments with a limited number of embryos created with handmade cloning (HMC) and transferred without or after open pulled straw vitrification. Embryo reconstruction was performed by using in vitro matured oocytes and adult ear skin fibroblasts. In two experiments, a total of 53 D7 blastocysts were developed from 188 reconstructed embryos. Fresh transfer of seven blastocysts into six recipients has resulted in three early pregnancies, two of them developed over 90 days and eventually resulted in healthy calves (33% offspring/transfer rate). In another two experiments, a total of 11 D7 blastocysts were obtained from 36 reconstructed embryos. Out of these, eight have reexpanded 18 hours after vitrification and warming. Transfer of these blastocysts into eight recipients has resulted in four early pregnancies and two live births; 25% offspring/transfer rate. These results indicate that low overall efficiency may not be an intrinsic feature of cattle cloning, and selection of the right procedures may help to overcome the actual limitations.

Effects of fusion-activation interval and embryo aggregation on in vitro and in vivo development of bovine cloned embryos

Nuclear reprogramming in somatic cell cloning is one of the key factors for proper development, with variations in the protocol appearing to improve cloning efficiency. This study aimed to determine the effects of two fusion-activation intervals and the aggregation of bovine cloned embryos on subsequent in vitro and in vivo development. Zygotes produced by handmade cloning were exposed to two fusion-activation intervals (2 h or 4 h), and then cultured in microwells either individually (1 × 100%) or after aggregation of two structures (2 × 100%). Zona-intact oocytes and zona-free oocytes and hemi-oocytes were used as parthenote controls under the same fusion-activation intervals. Day-7 cloned blastocysts were transferred to synchronous recipients. Cleavage (Day 2), blastocyst (Day 7) and pregnancy (Day 30) rates were compared by the χ² test (P < .05). Extending fusion-activation interval from 2 to 4 h reduced cleavage (91.0 vs. 74.4%) but not blastocyst (34.8 vs. 42.0%) rates. On a microwell basis, cloned embryo aggregation (2 × 100%) increased cleavage (91.5% vs. 74.4%) and blastocyst (46.0% vs. 31.3%) rates compared to controls (1 × 100%), but did not improve the overall embryo production efficiency on Day 7 (23.0% vs. 31.3%), on a per reconstructed embryo basis, respectively. Treatments had no effects on in vitro developmental kinetics, embryo quality, and in vivo development. In summary, the fusion-activation interval and/or the aggregation of cloned bovine embryos did not affect cloning efficiency based on the in vitro development to the blastocyst stage and on pregnancy outcome.

An update: Reproductive handmade cloning of water buffalo (Bubalus bubalis)

The first birth of a cloned animal produced through the Handmade cloning (HMC) technique was reported more than 15 years ago in cattle. This method of somatic cell nuclear transfer (SCNT) has subsequently been evolving as a much simpler alternative to the classical micromanipulator-based SCNT. Several farm animal species such as cattle, buffalo, pigs, sheep, and goats have been successfully cloned using HMC. In buffalo, HMC technique is now well established, and several births of cloned calves have been reported by us. Several factors such as source of somatic cells, quality of recipient oocytes, cell cycle stage prior to SCNT, electrofusion and culture conditions, and epigenetic status of somatic cells, have been optimized leading to the production of good quality cloned embryos. The preservation through cloning of proven breeding bulls that have died by producing live offspring using somatic cells isolated from frozen semen as donor cells and birth of a cloned calf from urine-derived cells are impressive examples of the success of HMC in buffalo. In conclusion, HMC is a valued reproductive technique in buffalo that offers the opportunity to make multiple copies of highly valuable animals, particularly proven breeding bulls. In this review, there is a discussion of the advancement of the HMC technique in buffalo and factors responsible for the efficient production of cloned embryos.

Cytoplasmic volume of recipient oocytes affects the nucleus reprogramming and the developmental competence of HMC buffalo (Bubalus bubalis) embryos

The present study was undertaken to examine the effects of cytoplasmic volume on nucleus reprogramming and developmental competence of buffalo handmade cloning (HMC) embryos. We found that both HMC embryos derived from ~150% cytoplasm or ~225% cytoplasm resulted in a higher blastocyst rate and total cell number of blastocyst in comparison with those from ~75% cytoplasm (25.4 ± 2.0, 27.9 ± 1.6% vs. 17.9 ± 3.1%; 150 ± 10, 169 ± 12 vs. 85 ± 6, P<0.05). Meanwhile, the proportions of nuclear envelope breakdown (NEBD) and premature chromosome condensation (PCC) were also increased in the embryos derived from ~150 or ~225% enucleated cytoplasm compared to those from ~75% cytoplasm. Moreover, HMC embryos derived from ~225% cytoplasm showed a decrease of global DNA methylation from the 2-cell to the 4-cell stage in comparison with those of ~75% cytoplasm (P<0.05). Furthermore, the expression of embryonic genome activation (EGA) relative genes (eIF1A and U2AF) in HMC embryos derived from ~225% cytoplasm at the 8-cell stages was also found to be enhanced compared with that of the ~75% cytoplasm. Two of seven recipients were confirmed to be pregnant following transfer of blastocysts derived from ~225% cytoplasm, and one healthy cloned calf was delivered at the end of the gestation period, whereas no recipients were pregnant after the transfer of blastocysts derived from ~75% cytoplasm. These results indicate that the cytoplasmic volume of recipient oocytes affects donor nucleus reprogramming, and then further accounted for the developmental ability of the reconstructed embryos.

Morphometric developmental pattern of bovine handmade cloned concepti in late pregnancy

Cloning procedures often interfere with conceptus growth and life ex utero, in a set of symptoms known as abnormal offspring syndrome (AOS). The aim of the present study was to compare the developmental pattern of in vivo-derived (IVD), IVF-derived and handmade cloning-derived (NT-HMC) Day 225 bovine concepti using established procedures. Pregnancy diagnosis was performed on Day 30 following blastocyst transfer on Day 7. Conceptus morphometry was assessed by ultrasonography on Day 51, and on Day 225 pregnant cows were killed for morphological examination of concepti. Pregnancy outcome was similar between groups, with greater pregnancy losses in the first trimester (70.6%) and smaller fetuses on Day 51 in the NT-HMC group than in the IVD (14.3%) and IVF (20.0%) groups. However, NT-HMC-derived concepti were twofold larger on Day 225 of gestation than controls. A higher frequency (63.5%) of placentomes larger than the largest in the IVD group was observed in the NT-HMC group, which may be relevant to placental function. Conceptus traits in the IVF group were similar to the IVD controls, with only slight changes in placentome types. Morphological changes in cloned concepti likely affected placental function and metabolism, disrupting the placental constraining mechanism on fetal growth in mid- to late pregnancy.

Handmade cloning: recent advances, potential and pitfalls

Handmade cloning (HMC) is the most awaited, simple and micromanipulator-free version of somatic cell nuclear transfer (SCNT). The requirement of expensive micromanipulators and skilled expertise is eliminated in this technique, proving it as a major revolution in the field of embryology. During the past years, many modifications have been incorporated in this technique to boost its efficiency. This alternative approach to micromanipulator based traditional cloning (TC) works wonder in generating comparable or even higher birth rates in addition to declining costs drastically and enabling cryopreservation. This technique is not only applicable to intraspecies nuclear transfer but also to interspecies nuclear transfer (iSCNT) thus permitting conservation of endangered species. It also offers unique possibilities for automation of SCNT which aims at production of transgenic animals that can cure certain human diseases by producing therapeutics hence, providing a healthier future for the wellbeing of humans. The present review aims at highlighting certain aspects of HMC including recent advancements in procedure and factors involved in elevating its efficiency besides covering the potentials and pitfalls of this technique.

The aggregation of four reconstructed zygotes is the limit to improve the developmental competence of cloned equine embryos

Embryo aggregation has been demonstrated to improve cloning efficiency in mammals. However, since no more than three embryos have been used for aggregation, the effect of using a larger number of cloned zygotes is unknown. Therefore, the goal of the present study was to determine whether increased numbers of cloned aggregated zygotes results in improved in vitro and in vivo embryo development in the equine. Zona-free reconstructed embryos (ZFRE's) were cultured in the well of the well system in four different experimental groups: I. 1x, only one ZFRE per microwell; II. 3x, three per microwell; III. 4x, four per microwell; and IV. 5x, five ZFRE's per microwell. Embryo size was measured on day 7, after which blastocysts from each experimental group were either a) maintained in culture from day 8 until day 16 to follow their growth rates, b) fixed to measure DNA fragmentation using the TUNEL assay, or c) transferred to synchronized mares. A higher blastocyst rate was observed on day 7 in the 4x group than in the 5x group. Non-aggregated embryos were smaller on day 8 compared to those aggregated, but from then on the in vitro growth was not different among experimental groups. Apoptotic cells averaged 10% of total cells of day 8 blastocysts, independently of embryo aggregation. Only pregnancies resulting from the aggregation of up to four embryos per microwell went beyond the fifth month of gestation, and two of these pregnancies, derived from experimental groups 3x and 4x, resulted in live cloned foals. In summary, we showed that the in vitro and in vivo development of cloned zona-free embryos improved until the aggregation of four zygotes and declined when five reconstructed zygotes were aggregated.

Expression profile of developmentally important genes between hand-made cloned buffalo embryos produced from reprogramming of donor cell with oocytes extract and selection of recipient cytoplast through brilliant cresyl blue staining and in vitro fertilized embryos

PURPOSE

To compare the expression profile of developmentally important genes between hand-made cloned buffalo embryos produced from reprogramming of donor cell with oocyte extracts and selection of recipient cytoplast through brilliant cresyl blue staining and in vitro fertilized (IVF) embryos.

METHODS

Hand-made cloned embryos were produced using oocyte extracts treated donor cells and brilliant cresyl blue (BCB) stained recipient cytoplasts. IVF embryos were produced by culturing 15-20 COCs in BO capacitated sperms from frozen thawed buffalo semen and the mRNA expression patterns of genes implicated in metabolism (GLUT1), pluripotency (OCT4), DNA methylation (DNMT1), pro- apoptosis (BAX) and anti-apoptosis (BCL2) were evaluated at 8- to16- cell stage embryos.

RESULTS

A significantly (P < 0.05) higher number of 8- to16- cell and blastocyst stages (73.9 %, 32.8 %, respectively) were reported in hand-made cloning (HMC) as compared to in vitro fertilization (49.2 %, 24.2 %, respectively). The amount of RNA recovered from 8- to 16- cell embryos of HMC and in vitro fertilization did not appear to be influenced by the method of embryo generation (3.76 ± 0.61 and 3.82 ± 0.62 ng/μl for HMC and in vitro fertilization embryos, respectively). There were no differences in the expression of the mRNA transcripts of genes (GLUT1, OCT4, DNMT1, BAX and BCL2) were analysed by real-time PCR between hand-made cloned and IVF embryos.

CONCLUSIONS

Pre-treatment of donor cells with oocyte extracts and selection of developmentally competent oocytes through BCB staining for recipient cytoplast preparations may enhance expression of developmentally important genes GLUT1, OCT4, DNMT1, BAX, and BCL2 in hand-made cloned embryos at levels similar to IVF counterparts. These results also support the notion that if developmental differences observed in HMC and in vitro fertilization produced foetuses and neonates are the results of aberrant gene expression during the pre-implantation stage, those differences in expression are subtle or appear after the maternal to zygotic transition stage of development.

Developmental potential and kinetics of pig embryos with different cytoplasmic volume

The effects of cytoplasmic volumes on development and developmental kinetics of in vitro produced porcine embryos were investigated. During hand-made cloning (HMC), selected cytoplasts were separated into two groups according to their size in relation to the initial oocyte: ~75% or ~50%. Following two fusion steps and activation (day 0), reconstructed embryos were cultured in vitro for 6 days. Cleavage rates on day 2 as well as blastocyst rates and cell numbers on day 6 were recorded. Results showed that embryo development was no different for ~50% versus ~75% cytoplasm at first fusion. This result was used in the following experiments, where the effect of varying cytoplasm volume in second fusion to obtain a final cytoplasm volume of ~75% to ~200% was tested. The results showed that the lowest quality was obtained when the final cytoplasm volume was ~75% and the highest quality at ~200% of the original oocyte. Similar results were observed in parthenogenetic (PA) embryos activated with different cytoplasmic volumes. A common pattern for the developmental kinetics of HMC and PA embryos was observed: the smaller group tended to have a longer time for the first two cell cycles, but subsequently a shorter time to form morula and blastocyst. In conclusion, the developmental kinetics of in vitro produced embryos was affected by the cytoplasm volume of the initial oocyte, and this further accounted for the developmental ability of the reconstructed 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.

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.

Hand-made cloned goat (Capra hircus) embryos—a comparison of different donor cells and culture systems

Nuclear transfer is a very effective method for propagation of valuable, extinct, and endangered animals. Hand-made cloning (HMC) is an efficient alternative to the conventional micromanipulator-based technique in some domestic species. The present study was carried out for the selection of suitable somatic cells as a nuclear donor and development of an optimum culture system for in vitro culture of zona-free goat cloned embryos. Cleavage and blastocyst rates were observed 72.06 ± 2.94% and 0% for fresh cumulus cells, 81.95 ± 3.40% and 12.74 ± 2.12% for cultured cumulus cells, and 92.94 ± 0.91% and 23.78 ± 3.33% for fetal fibroblast cells, respectively. There was a significant (p < 0.05) increase in blastocyst production in goats when cultured on a flat surface (FS) (23.78 ± 3.33 %) than well of wells (WOW) (15.84 ± 2.12 %) and microdrops (MD) (0.7 ± 0.7%). Furthermore, cleavage and blastocyst production rates were significantly (p < 0.05) more in the WOW (15.84 ± 2.12%) than the MD (0.7 ± 0.7%) system. The quality of HMC blastocysts was studied by differential staining. Genetic similarity was confirmed by polymerase chain reaction (PCR)-based amplification of the second exon of the MHC class II DRB gene, which gave similar bands in electrophoresis (286 bp) both in cloned embryos and donor cells. In conclusion, the present study describes that the fetal fibroblast cell is a suitable candidate as nuclear donor, and the flat surface culture system is suitable for zona-free blastocyst development by the hand-made cloning technique in the goat.

Production of bovine hand-made cloned embryos by zygote-oocyte cytoplasmic hemi-complementation

The aim of this study was to evaluate the effect of the cytoplast type and activation process on development of cloned embryos. Bovine oocytes (MII) or zygotes at the one-cell stage (IVF) were manually bisected and segregated in MII or IVF hemi-cytoplasts or hemi-karyoplasts. Adult skin cells from a bovine female were used as nucleus donors (SC). Experimental groups were composed of IVF embryos; parthenogenetic embryos; hand-made cloned (HMC) embryos; and reconstructed HMC embryos using IVF hemi-cytoplast + MII hemi-cytoplast + SC (G-I); IVF hemi-cytoplast + IVF hemi-cytoplast + SC (G-II); MII hemi-cytoplast + IVF hemi-karyoplast (G-III); and IVF hemi-cytoplast + IVF hemi-karyoplast (G-IV). Embryos from G-I to G-IV were allocated to subgroups as sperm-activated (SA) or were further chemically activated (SA + CA). Embryos from all groups and subgroups were in vitro cultured in the WOW system. Blastocyst development in subgroup G-I SA (28.2%) was similar to IVF (27.0%) and HMC (31.4%) controls, perhaps due to a to a more suitable activation process and/or better complementation of cytoplasmic reprogramming factors, with the other groups and subgroups having lower levels of development. No blastocyst development was observed when using IVF hemi-karyoplasts (G-III and G-IV), possibly due to the manipulation process during a sensitive biological period. In summary, the presence of cytoplasmic factors from MII hemi-oocytes and the sperm activation process from hemi-zygotes appear to be necessary for adequate in vitro development, as only the zygote-oocyte hemi-complementation was as efficient as controls for the generation of bovine cloned blastocysts.

Developmental potential of bovine hand-made clone embryos reconstructed by aggregation or fusion with distinct cytoplasmic volumes

Animal cloning has been associated with developmental abnormalities, with the level of heteroplasmy caused by the procedure being one of its potential limiting factors. The aim of this study was to determine the effect of the fusion of hemicytoplasts or aggregation of hemiembryos, varying the final cytoplasmic volume, on development and cell density of embryos produced by hand-made cloning (HMC), parthenogenesis or by in vitro fertilization (IVF). One or two enucleated hemicytoplasts were paired and fused with one skin somatic cell. Activated clone and zona-free parthenote embryos and hemiembryos were in vitro cultured in the well-of-the-well (WOW) system, being allocated to one of six experimental groups, on a per WOW basis: single clone or parthenote hemiembryos (1 x 50%); aggregation of two (2 x 50%), three (3 x 50%), or four (4 x 50%) clone or parthenote hemiembryos; single clone or parthenote embryos (1 x 100%); or aggregation of two clone or parthenote embryos (2 x 100%). Control zona-intact parthenote or IVF embryos were in vitro cultured in four-well dishes. Results indicated that the increase in the number of aggregated structures within each WOW was followed by a linear increase in cleavage, blastocyst rate, and cell density. The increase in cytoplasmic volume, either by fusion or by aggregation, had a positive effect on embryo development, supporting the establishment of pregnancies and the birth of a viable clone calf after transfer to recipients. However, embryo aggregation did not improve development on a hemicytoplast basis, except for the aggregation of two clone embryos.

Nuclear replacement of in vitro-matured porcine oocytes by a serial centrifugation and fusion method

The objective of the present study was to establish a method for nuclear replacement in metaphase-II (M-II) stage porcine oocytes. Karyoplasts containing M-II chromosomes (K) and cytoplasts without chromosomes (C) were produced from in vitro-matured oocytes by a serial centrifugation method. The oocytes were then reconstructed by fusion of one karyoplast with 1, 2, 3 or 4 cytoplasts (K + 1C, K + 2C, K + 3C and K + 4C, respectively). Reconstructed oocytes, karyoplasts without fusion of any cytoplast (K) and zona-free M-II oocytes (control) were used for experiments. The rates of female pronucleus formation after parthenogenetic activation in all groups of reconstructed oocytes (58.2-77.4%) were not different from those of the K and control groups (58.2% and 66.0%, respectively). In vitro fertilization was carried out to assay the fertilization ability and subsequent embryonic development of the reconstructed oocytes. The cytoplast : karyoplast ratio did not affect the fertilization status (penetration and male pronuclear formation rates) of the oocytes. A significantly high monospermy rate was found in K oocytes (p < 0.05, 61.6%) compared with the other groups (18.2-32.8%). Blastocyst formation rates increased significantly as the number of the cytoplasts fused with karyoplasts increased (p < 0.05, 0.0-15.3%). The blastocyst rate in the K + 4C group (15.3%) was comparable with that of the control (17.8%). Total cell numbers in both the K + 3C and K + 4C groups (16.0 and 15.3 cells, respectively) were comparable with that of the control (26.2 cells). Our results demonstrate that a serial centrifugation and fusion (Centri-Fusion) is an effective method for producing M-II chromosome transferred oocytes with normal fertilization ability and in vitro development. It is suggested that the number of cytoplasts fused with a karyoplast plays a critical role in embryonic development.

The prevalence of embryonic remnants following the recovery of post-hatching bovine embryos produced in vitro or by somatic cell nuclear transfer

The reliable collection of peri-implantation embryos in the bovine has important ramifications to post-transfer consequences, particularly in the elucidation of mechanisms associated with post-hatching embryo development and to perturbations in developmental growth following transfer. This study analyzed both in vitro produced (IVP) and somatic cell nuclear transfer (SCNT) embryo-like structures (ELS) recovered at Day (D) 14 and D21. The recovered ELS were subsequently processed for histological examination. At D14 and D21, many of the embryos recovered in the IVP group conformed to the appropriate stage of development. However, a significant number of anomalies were present in the SCNT groups when examined in more detail. Histological examination revealed that irrespective of whether these embryos had undergone trophoblast expansion to an ovoid, tubular or filamentous morphology, many had a degenerated hypoblast layer and a large proportion did not possess an epiblast and therefore could not differentiate into any of the three germ layers as would be expected at the neural groove or somite stage. The prevalence of this developmental pattern was random and did not correlate with treatment (IVP or SCNT) or with types of structures recovered. The rapid embryo elongation period also coincides with the time of greatest embryonic loss and these observations could have important implications for assessing the recovery of embryos post-transfer where incorrect morphological assessment could lead to false implantation and pregnancy determination rates. The implementation of additional methodology is required to adequately characterize the quality of IVP and SCNT-derived embryos collected post-transfer.

Developmental disparity between in vitro-produced and somatic cell nuclear transfer bovine days 14 and 21 embryos: implications for embryonic loss

In ruminants, the greatest period of embryonic loss coincides with the period of elongation when the embryonic disc is formed and gastrulation occurs prior to implantation. The impact of early embryonic mortality is not only a major obstacle to the cattle breeding industry but also impedes the application of new reproductive technologies such as somatic cell nuclear transfer (SCNT). In the present study, days 14 and 21 bovine embryos, generated by either in vitro-production (IVP) or SCNT, performed by either subzonal injection (SUZI) or handmade cloning (HMC), were compared by stereomicroscopy, immunohistochemistry, and transmission electron microscopy to establish in vivo developmental milestones. Following morphological examination, samples were characterized for the presence of epiblast (POU5F1), mesoderm (VIM), and neuroectoderm (TUBB3). On D14, only 25, 15, and 7% of IVP, SUZI, and HMC embryos were recovered from the embryos transferred respectively, and similar low recovery rates were noted on D21, suggesting that most of the embryonic loss had already occurred by D14. A number of D14 IVP, SUZI, and HMC embryos lacked an epiblast, but presented trophectoderm and hypoblast. When the epiblast was present, POU5F1 staining was limited to this compartment in all types of embryos. At the ultrastructural level, SCNT embryos displayed abundant secondary lysosomes and vacuoles, had fewer mitochondria, polyribosomes, tight junctions, desmosomes, and tonofilaments than their IVP counterparts. The staining of VIM and TUBB3 was less distinct in SCNT embryos when compared with IVP embryos, indicating slower or compromised development. In conclusion, SCNT and to some degree, IVP embryos displayed a high rate of embryonic mortality before D14 and surviving embryos displayed reduced quality with respect to ultrastructural features and differentiation markers.

Regulation of blastocyst stage gene expression and outgrowth interferon tau activity of somatic cell clone aggregates

The inefficiency of mammalian somatic cell cloning is associated with abnormal gene expression presumably caused by errors in reprogramming of the transplanted genome. In the mouse, aggregation of four-cell stage clones leads to an improvement of both gene expression and development. To determine whether clone-clone aggregation at postgenomic activation stages influences gene expression in bovine clones, we profiled, in single and aggregated embryos at the blastocyst stage, expression of developmentally relevant genes namely Oct4, Dnmt1, Dnmt3, Glut1, Glut3, and a housekeeping gene, Poly(A) polymerase (PolyA) by real-time RT-PCR. Compared to embryos generated by in vitro fertilization (IVF), individual clones more frequently exhibited transcript levels that were more than twofold higher or lower than the average value of IVF embryos. This was observed less often in clone aggregates for Oct4, Dnmt1, Dnmt3, and PolyA, but not for Glut1 and Glut3. The analysis of interferon tau bioactivity as a marker of trophectoderm function in blastocyst outgrowths showed that both single clones and clone aggregates have less extraembryonic potential in vitro compared to IVF embryos, with no apparent consequence of aggregation. These findings indicate that aggregation of bovine clones with each other at later cleavage stages can change gene expression patterns at preimplantation stages, but does not rescue trophectoderm function in vitro.

Mitochondrial DNA inheritance after SCNT

Mitochondrial biogenesis and function is under dual genetic control and requires extensive interaction between biparentally inherited nuclear genes and maternally inherited mitochondrial genes. Standard SCNT procedures deprive an oocytes' mitochondrial DNA (mtDNA) of the corresponding maternal nuclear DNA and require it to interact with an entirely foreign nucleus that is again interacting with foreign somatic mitochondria. As a result, most SCNT embryos, -fetuses, and -offspring carry somatic cell mtDNA in addition to recipient oocyte mtDNA, a condition termed heteroplasmy. It is thus evident that somatic cell mtDNA can escape the selective mechanism that targets and eliminates intraspecific sperm mitochondria in the fertilized oocyte to maintain homoplasmy. However, the factors responsible for the large intra- and interindividual differences in heteroplasmy level remain elusive. Furthermore, heteroplasmy is probably confounded with mtDNA recombination. Considering the essential roles of mitochondria in cellular metabolism, cell signalling, and programmed cell death, future experiments will need to assess the true extent and impact of unorthodox mtDNA transmission on various aspects of SCNT success.

Piglets born from handmade cloning, an innovative cloning method without micromanipulation

Porcine handmade cloning (HMC), a simplified alternative of micromanipulation based traditional cloning (TC) has been developed in multiple phases during the past years, but the final evidence of its biological value, births of piglets was missing. Here we report the first births of healthy piglets after transfer of blastocysts produced by HMC. As a cumulative effect of technical optimization, 64.3+/-2.3 (mean+/-S.E.M.) reconstructed embryos from 151.3+/-4.8 oocytes could be obtained after 3-4h manual work, including 1h pause between fusion and activation. About half (50.1+/-2.8%, n=16) of HMC reconstructed embryos developed to blastocysts with an average cell number of 77+/-3 (n=26) after 7 days in vitro culture (IVC). According to our knowledge, this is the highest in vitro developmental rate after porcine somatic cell nuclear transfer (SCNT). A total of 416 blastocysts from HMC, mixed with 150 blastocysts from TC using a cell line from a different breed were transferred surgically to nine synchronized recipients. Out of the four pregnancies (44.4%) two were lost, while two pregnancies went to term and litters of 3 and 10 piglets were delivered by Caesarean section, with live birth/transferred embryo efficiency of 17.2% (10/58) for HMC. Although more in vivo experiments are still needed to further stabilize the system, our data proves that porcine HMC may result in birth of healthy offspring. Future comparative examinations are required to prove the value of the new technique for large-scale application.

Somatic cell nuclear transfer: Past, present and future perspectives

It is now over a decade since the birth, in 1996, of Dolly the first animal to be produced by nuclear transfer using an adult derived somatic cell as nuclear donor. Since this time similar techniques have been successfully applied to a range of species producing live offspring and allowing the development of transgenic technologies for agricultural, biotechnological and medical uses. However, though applicable to a range of species, overall, the efficiencies of development of healthy offspring remain low. The low frequency of successful development has been attributed to incomplete or inappropriate reprogramming of the transferred nuclear genome. Many studies have demonstrated that such reprogramming occurs by epigenetic mechanisms not involving alterations in DNA sequence, however, at present the molecular mechanisms underlying reprogramming are poorly defined. Since the birth of Dolly many studies have attempted to improve the frequency of development, this review will discuss the process of animal production by nuclear transfer and in particular changes in the methodology which have increased development and survival, simplified or increased robustness of the technique. Although much of the discussion is applicable across species, for simplicity we will concentrate primarily on published data for cattle, sheep, pigs and mice.

Development to the Blastocyst Stage of Porcine Somatic Cell Nuclear Transfer Embryos Reconstructed by the Fusion of Cumulus Cells and Cytoplasts Prepared by Gradient Centrifugation

The present study was designated to examine the possibility of producing somatic cell nuclear transfer (SCNT) embryos in pigs using oocyte cytoplasm fragments (OCFs), prepared by centrifugations, as recipient cytoplasts. In Experiment 1, in vitro matured oocytes were centrifuged at 13,000 x g for 3, 6, and 9 min to stratify the cytoplasm, and then the oocytes were freed from zona pellucida and recentrifuged at 5,000 x g for 4 sec in Percoll gradient solution to produce OCFs as the source of recipient cytoplasts. It was found that a long duration of the first centrifugation tends to produce large-sized OCFs after the second centrifugation. In Experiment 2, two or three cytoplasts without chromosomes were aggregated, and then they were fused with a cumulus cell to produce SCNT embryos. The results showed that 66.4 +/- 9.4% of the reconstructed embryos underwent premature chromosome condensation at 1 h after activation, and 85.2 +/- 7.1% and 61.6 +/- 7.0% of them had pseudopronuclei at 10 and 24 h after activation, respectively. In Experiment 3, when SCNT embryos reconstructed by the fusion of three cytoplasts and one cumulus cell, a significantly higher (p < 0.05) rate of reconstructed embryos developed to the blastocyst stage (10.6 +/- 1.8%) than that of reconstructed with two cytoplasts and one cumulus cell (5.2 +/- 1.5%). These results indicate that cytoplasts obtained by two centrifugations can support the remodeling of a transferred somatic nucleus, resulting in the development of the reconstructed porcine embryos to the blastocyst stage.

Cloning cattle: the methods in the madness

Somatic cell nuclear transfer (SCNT) is much more widely and efficiently practiced in cattle than in any other species, making this arguably the most important mammal cloned to date. While the initial objective behind cattle cloning was commercially driven--in particular to multiply genetically superior animals with desired phenotypic traits and to produce genetically modified animals-researchers have now started to use bovine SCNT as a tool to address diverse questions in developmental and cell biology. In this paper, we review current cattle cloning methodologies and their potential technical or biological pitfalls at any step of the procedure. In doing so, we focus on one methodological parameter, namely donor cell selection. We emphasize the impact of epigenetic and genetic differences between embryonic, germ, and somatic donor cell types on cloning efficiency. Lastly, we discuss adult phenotypes and fitness of cloned cattle and their offspring and illustrate some of the more imminent commercial cattle cloning applications.

Nuclear Transfer: Preservation of a Nuclear Genome at the Expense of Its Associated mtDNA Genome(s)

Nuclear transfer technology has uses across theoretical and applied applications, but advances are restricted by continued poor success rates and health problems associated with live offspring. Development of reconstructed embryos is dependent upon numerous interlinking factors relating both to the donor cell and the recipient oocyte. For example, abnormalities in gene expression following somatic cell nuclear transfer (SCNT) have been linked with an inability of the oocyte cytoplasm to sufficiently epigenetically reprogram the nucleus. Furthermore, influences on the propagation of mitochondria and mitochondrial DNA (mtDNA) could be of great importance in determining the early developmental potential of NT embryos and contributing to their genetic identity. mtDNA encodes some of the subunits of the electron transfer chain, responsible for cellular ATP production. The remaining subunits and those factors required for mtDNA replication, transcription and translation are encoded by the nucleus, necessitating precise intergenomic communication. Additionally, regulation of mtDNA copy number, via the processes of mtDNA transcription and replication, is essential for normal preimplantation embryo development and differentiation. Unimaternal transmission following natural fertilization usually results in the presence of a single identical population of mtDNA, homoplasmy. Heteroplasmy can result if mixed populations of mtDNA genomes co-exist. Many abnormalities observed in NT embryos, fetuses, and offspring may be caused by deficiencies in OXPHOS, perhaps resulting in part from heteroplasmic mtDNA populations. Additionally, incompatibilities between the somatic nucleus and the cytoplast may be exacerbated by increased genetic divergence between the two genomes. It is important to ensure that the nucleus is capable of sufficiently regulating mtDNA, requiring a level of compatibility between the two genomes, which may be a function of evolutionary distance. We suggest that abnormal expression of factors such as TFAM and POLG in NT embryos will prematurely drive mtDNA replication, hence impacting on early development.

Human therapeutic cloning (NTSC)

Human therapeutic cloning or nuclear transfer stem cells (NTSC) to produce patient-specific stem cells, holds considerable promise in the field of regenerative medicine. The recent withdrawal of the only scientific publications claiming the successful generation of NTSC lines afford an opportunity to review the available research in mammalian reproductive somatic cell nuclear transfer (SCNT) with the goal of progressing human NTSC. The process of SCNT is prone to epigenetic abnormalities that contribute to very low success rates. Although there are high mortality rates in some species of cloned animals, most surviving clones have been shown to have normal phenotypic and physiological characteristics and to produce healthy offspring. This technology has been applied to an increasing number of mammals for utility in research, agriculture, conservation, and biomedicine. In contrast, attempts at SCNT to produce human embryonic stem cells (hESCs) have been disappointing. Only one group has published reliable evidence of success in deriving a cloned human blastocyst, using an undifferentiated hESC donor cell, and it failed to develop into a hESC line. When optimal conditions are present, it appears that in vitro development of cloned and parthenogenetic embryos, both of which may be utilized to produce hESCs, may be similar to in vitro fertilized embryos. The derivation of ESC lines from cloned embryos is substantially more efficient than the production of viable offspring. This review summarizes developments in mammalian reproductive cloning, cell-to-cell fusion alternatives, and strategies for oocyte procurement that may provide important clues facilitating progress in human therapeutic cloning leading to the successful application of cell-based therapies utilizing autologous hESC lines.

Interspecies somatic cell nuclear transfer and preliminary data for horse-cow/mouse iSCNT

Nuclear transfer (NT) experiments in mammals have demonstrated that adult cells are genetically equivalent to early embryonic cells and the reversal of the differentiated state of a cell to another that has characteristics of the undifferentiated embryonic state can be defined as nuclear reprogramming. The feasibility of interspecies somatic cell NT (iSCNT) has been demonstrated by blastocyst formation and the production of offspring in a number of studies. Embryo and oocyte availability is a major limiting factor in conducting NT to obtain, blastocysts for both reproductive NT studies in genetically endangered animals and in embryonic stem cell derivation for species such as the horse and human. One approach to generate new embryonic stem cells in human as disease models, or in species where embryos and oocytes are not widely available, is to use oocytes from another species. Utilization of oocytes for recipient cytoplasts from other species that are accessible and abundant, such as the cow and rabbit, would greatly benefit ongoing research on reprogramming and stem cell sciences. The use of iSCNT is an exciting possibility for species with limited availability of oocytes as well as for endangered or exotic species where assisted reproduction is needed. However, the mechanisms involved in nuclear reprogramming by the oocyte are still unknown and the extent of the "universality" of ooplasmic reprogramming of development remains under investigation.

Semen and reproductive profiles of genetically identical cloned bulls

In this comparative study, reproductive parameters and semen characteristics of cloned bulls (n = 3) derived from somatic cell nuclear transfer (SCNT) were compared to their original cell donor Holstein-Friesian (n = 2) bulls from the same enterprise to assess the differences in reproductive potential between a donor bull and its clones. The parameters evaluated included motility of fresh, frozen-thawed and Percoll-treated frozen-thawed spermatozoa, as well as in vitro fertilization (IVF) ability, embryo quality, birth and survival of calves following IVF and embryo transfer with frozen-thawed semen. With fresh semen, spermatozoa from one cloned bull had lower motility than its donor. Cloned bulls had higher velocity parameters in fresh semen, but those effects were not obvious in frozen-thawed or frozen-thawed semen selected with a Percoll gradient. Semen collected from cloned bulls had significantly higher IVF rates compared to donors; however, embryo development per cleaved embryo or quality of blastocysts did not differ between donors and cloned bulls. Pregnancy and live offspring rates from one donor and its cloned bull did not differ between fresh (40%, 16/40 versus 46%, 17/37) and vitrified/thawed (13%, 2/16 versus 25%, 4/16) embryo transfer following IVF. A total of 26 calves were obtained from genotypically identical donor and cloned bulls with no signs of phenotypical abnormalities. These preliminary results suggested that the physiology of surviving postpubertal cloned bulls and quality of collected semen had equivalent reproductive potential to their original cell donor, with no evidence of any deleterious effects in their progeny.