Remodeling of donor nuclei, DNA-synthesis, and ploidy of bovine cumulus cell nuclear transfer embryos: effect of activation protocol

Timing of the First Cleavage and In Vitro Developmental Potential of Bovine Somatic Cell Nuclear Transfer Embryos Activated by Different Protocols

The objective of this study was to examine the relationship between the timing of the first cleavage and in vitro development of somatic cell nuclear transfer (SCNT) embryos produced by different activation protocols. SCNT embryos were activated with calcium ionophore A23187 and further treated with 6-dimethylaminopurine (DMAP group), cycloheximide (CHX group), or anisomycin (ANI group). The proportion of SCNT embryos that cleaved within 18 hours after activation was significantly higher in the DMAP group (20%) than that in the CHX and ANI groups (3% and 2%, respectively). More than 70% of the cleaved embryos were observed within 24 hours in the DMAP and CHX groups, and within 26 hours in the ANI group. The blastocyst formation rate of SCNT embryos decreased gradually as the time from activation to the first cleavage increased in the DMAP group. The blastocyst formation rate of SCNT embryos cleaved at 22 hours (>20 to ≤22 hours) in the CHX group or within 26 hours in the ANI group was significantly higher than that of SCNT embryos cleaved more than 26 hours in each group. These results indicate that the activation protocol affects the timing of the first cleavage and subsequent in vitro development potential of bovine SCNT embryos and that late-cleaving embryos have a low developmental potential irrespective of the activation protocol.

Visualization of the spatial arrangement of nuclear organization using three-dimensional fluorescence in situ hybridization in early mouse embryos: A new "EASI-FISH chamber glass" for mammalian embryos

The fertilized oocyte begins cleavage, leading to zygotic gene activation (ZGA), which re-activates the resting genome to acquire totipotency. In this process, genomic function is regulated by the dynamic structural conversion in the nucleus. Indeed, a considerable number of genes that are essential for embryonic development are located near the pericentromeric regions, wherein the heterochromatin is formed. These genes are repressed transcriptionally in somatic cells. Three-dimensional fluorescence in situ hybridization (3D-FISH) enables the visualization of the intranuclear spatial arrangement, such as gene loci, chromosomal domains, and chromosome territories (CTs). However, the 3D-FISH approach in mammalian embryos has been limited to certain repeated sequences because of its unfavorable properties. In this study, we developed an easy-to-use chamber device (EASI-FISH chamber) for 3D-FISH in early embryos, and visualized, for the first time, the spatial arrangements of pericentromeric regions, the ZGA-activated gene (Zscan4) loci, and CTs (chromosome 7), simultaneously during the early cleavage stage of mouse embryos by 3D-FISH. As a result, it was revealed that morphological changes of the pericentromeric regions and CTs, and relocation of the Zscan4 loci in CTs, occurred in the 1- to 4-cell stage embryos, which was different from those in somatic cells. This convenient and reproducible 3D-FISH technique for mammalian embryos represents a valuable tool that will provide insights into the nuclear dynamics of development.

Developmental Outcome and Related Abnormalities in Goats: Comparison Between Somatic Cell Nuclear Transfer- and In Vivo-Derived Concepti During Pregnancy Through Term

Cloning by somatic cell nuclear transfer (SCNT) is characterized by low efficiency and the occurrence of developmental abnormalities, which are rather poorly studied phenomena in goats. This study aimed at comparing overall SCNT efficiency in goats by using in vitro-matured (IVM) or in vivo-matured oocytes and fibroblast donor cells (mock transfected, transgenic, or wild type), also characterizing symptoms of the Abnormal Offspring Syndrome (AOS) in development, comparing results with pregnancies produced by artificial insemination (AI) and in vivo-derived (IVD) embryos. The SCNT group had lower pregnancy rate (18.3%, 11/60), total number of concepti (20.0%, 12/60), term births (3.3%, 2/60), and live births (1.7%, 1/60) than both the IVD (77.8%, 7/9; 155.5%, 14/9; 122.2%, 11/9; 88.8%, 8/9) and the AI (71.4%, 10/14; 121.4%, 17/14; 100%, 14/14; 78.5%, 11/14) groups, respectively (p < 0.05). No SCNT pregnancies reached term using IVM oocytes, but in vivo-matured oocytes resulted in two term transgenic cloned kids. The proportion fetal membrane (FM) weight/birth weight reflected an increase in FM size and cotyledonary enlargement in clones, for disproportionally bigger newborns in relation to cotyledonary numbers. Overall, goat cloning showed losses and abnormality patterns similar to the AOS in cloned cattle and sheep, which have not been previously well recognized in goats.

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.

Generation of parthenogenetic goat blastocysts: effects of different activation methods and culture media

The present study was carried out to investigate the effects of different activation methods and culture media on the in vitro development of parthenogenetic goat blastocysts. Calcium (Ca2+) ionophore, ethanol or a combination of the two, used as activating reagents, and embryo development medium (EDM), modified Charles Rosenkrans (mCR2a) medium and research vitro cleave (RVCL) medium were used to evaluate the developmental competence of goat blastocysts. Quantitative expression of apoptosis, stress and developmental competence-related genes were analysed in different stages of embryos. In RVCL medium, the cleavage rate of Ca2+ ionophore-treated oocytes (79.61 ± 0.86) was significantly (P < 0.05) higher than in ethanol (74.90 ± 1.51) or in the combination of both Ca2+ ionophore and ethanol. In mCR2a or EDM, hatched blastocyst production rate of Ca2+ ionophore-treated oocytes (8.33 ± 1.44) was significantly higher than in ethanol (6.46 ± 0.11) or in the combined treatment (6.70 ± 0.24). In ethanol, the cleavage, blastocyst and hatched blastocyst production rates in RVCL medium (74.90 ± 1.51, 18.30 ± 1.52 and 8.24 ± 0.15, respectively) were significantly higher than in EDM (67.81 ± 3.21, 14.59 ± 0.27 and 5.59 ± 0.42) or mCR2a medium (65.09 ± 1.57, 15.36 ± 0.52 and 6.46 ± 0.11). The expression of BAX, Oct-4 and GlUT1 transcripts increased gradually from 2-cell stage to blastocyst-stage embryos, whereas the transcript levels of Bcl-2 and MnSOD were significantly lower in blastocysts. In addition, different activation methods and culture media had little effect on the pattern of variation and relative abundance of the above genes in different stages of parthenogenetic activated goat embryos. In conclusion, Ca2+ ionophore as the activating agent, and RVCL as the culture medium are better than other tested options for development of parthenogenetic activated goat blastocysts.

The combined treatment of calcium ionophore with strontium improves the quality of ovine SCNT embryo development

Poor embryo quality is a major problem that contributes to the failure of pregnancy in somatic cell nuclear transfer (SCNT). The aims of this study were to improve the quality of ovine SCNT embryos by modifying the conventional activation protocol with the addition of SrCl2. In order to achieve this objective we conducted a series of experiments with in vitro-matured oocytes to optimize conditions for oocyte activation with strontium, and subsequently applied the protocol to SCNT embryos. The results showed that in vitro-matured oocytes could be activated effectively by 10 mM SrCl2 + 5 mg/ml cytochalasin B (CB) for 5 h in the absence of Ca2+ and that the blastocyst rate on day 7 (33.2%) was similar to that in the control group (31.0%) (5 M calcium ionophore [IP] A23187 for 5 min and cultured in CB/cycloheximide [CHX] for 5 h; P > 0.05). In SCNT experiments, the total cell number/blastocyst (104.12 ± 6.86) in the IP + SrCl2/CB-treatment group was, however, significantly higher than that in the control group (81.07 ± 3.39; P < 0.05). Apoptotic index (12.29 ± 1.22%) was significantly lower than the control (17.60 ± 1.39%; P < 0.05) when a combination of IP and SrCl2/CB was applied to SCNT embryos. In addition, karyotyping of the SCNT embryos showed that the percentage of diploid blastocysts in the IP + SrCl2/CB-treatment group was slightly higher than that in the control (P > 0.05). We conclude that the modified activation protocol with IP + SrCl2/CB can improve significantly the quality of ovine SCNT embryos in terms of total cell number, apoptosis and ploidy.

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.

A-type lamin dynamics in bovine somatic cell nuclear transfer embryos

The persistence of A-type nuclear lamin in somatic cell nuclear transfer (SCNT) embryos has been proposed as a marker for incomplete nuclear reprogramming. Using monoclonal antibodies to A/C- (A/C-346 and A/C-131C3) and B-type lamin, we compared distribution during early development of bovine IVF, parthenogenetic and SCNT embryos. A/C-346 staining was observed in the pronuclei of IVF embryos and in nuclei at the two-cell stage, but was not detected in subsequent cleavage stages up to and including hatched blastocysts. In contrast, A/C-131C3 and anti-lamin B2 stained all preimplantation stage embryos. Parthenogenetic and SCNT embryos had similar staining patterns to IVF embryos for all three antibodies, demonstrating correct nuclear architecture reprogramming. Inhibiting protein synthesis with cycloheximide (CHX) in parthenogenetic and SCNT embryos did not affect lamin A/C localisation, suggesting that lamin A/C is maternal in origin. However, activation with CHX delayed lamin A/C incorporation compared with 6-dimethylaminopurine activation. In SCNT embryos, staining for both A/C- and B-type lamin was delayed compared with parthenotes, although lamin B2 incorporation preceded lamin A/C in both. In conclusion, the lamin A/C distribution in SCNT bovine embryos paralleled that of IVF and parthenogenetic controls and therefore is not a marker of incomplete reprogramming.

Treatment of ovine oocytes with caffeine increases the accessibility of DNase I to the donor chromatin and reduces apoptosis in somatic cell nuclear transfer embryos

Caffeine treatment of ovine oocytes increases the activity of maturation-promoting factor (MPF) and mitogen-activated protein kinases (MAPKs) and, in somatic cell nuclear transfer (SCNT) embryos, increases the frequency of nuclear envelope breakdown (NEBD) and premature chromosome condensation (PCC). At the blastocyst stage, caffeine-treated SCNT embryos have increased cell numbers. One explanation for this is that NEBD and PCC release chromatin-bound somatic factors, allowing greater access of oocyte factors involved in DNA synthesis and nuclear reprogramming to donor chromatin. This could advance DNA replication and cleavage in the first cell cycle, resulting in increased cell numbers. Alternatively, increased MAPK activity may affect localisation of heat shock proteins (HSPs) and reduce apoptosis. To investigate these possibilities, we investigated chromatin accessibility, the timing of DNA synthesis and first cleavage, the localisation of HSP27 during early development and the frequency of apoptotic nuclei at the blastocyst stage. Compared with control SCNT (non-caffeine treatment), caffeine treatment (10 mM caffeine for 6 h prior to activation) increased the accessibility of DNase I to donor chromatin (P < 0.05 at 1.5 h post activation (h.p.a.)), advanced DNA synthesis (43.5% v. 67.6%, respectively; P < 0.01 at 6 h.p.a.) and first cleavage (27.3% v. 40.5% at 20 h.p.a., respectively) and increased nuclear localisation of HSP27. Although development to the blastocyst stage was not affected, caffeine increased total cell numbers (98.5 v. 76.6; P < 0.05) and reduced the frequency of apoptotic nuclei (11.27% v. 20.3%; P < 0.05) compared with control SCNT group.

Efficient production of nuclear transferred rat embryos by modified methods of reconstruction

In this study we investigated spontaneous oocyte activation and developmental ability of rat embryos of the SD-OFA substrain. We also tried to improve the somatic cell nuclear transfer (SCNT) technique in the rat by optimizing methods for the production of reconstructed embryos. About 20% of oocytes extruded the second polar body after culture for 3 hr in vitro and 84% of oocytes were at the MII stage. MG132 blocked spontaneous activation but decreased efficiency of parthenogenetic activation. Pronuclear formation was more efficient in strontium-activated oocytes (66.1-80.9%) compared to roscovitine activation (24.1-54.5%). Survival rate after enucleation was significantly higher (89.4%) after slitting the zona pellucida and then pressing the oocyte with a holding pipette in medium without cytochalasin B (CB) compared to the conventional protocol using aspiration of the chromosomes after CB treatment (67.7%). Exposure of rat ova to UV light for 30 sec did not decrease their in vitro developmental capacity. Intracytoplasmic cumulus cell injection dramatically decreased survival rate of oocytes (42%). In contrast, 75.9% of oocytes could be successfully electrofused. Development to the 2-cell stage was reduced after SCNT (24.6% compared 94.6% in controls) and none from 244 reconstructed embryos developed in vitro beyond this stage. After overnight in vitro culture, 74.4% of the SCNT embryos survived and 56.1% formed pronuclei. The pregnancy rate of 33 recipients after the transfer of 695 of these cloned embryos was, however, very low (18.2%) and only six implantation sites could be detected (0.9%) without any live fetuses and offspring.

Activation of bovine somatic cell nuclear transfer embryos by PLCZ cRNA injection

The production of cloned animals by the transfer of a differentiated somatic cell into an enucleated oocyte circumvents fertilization. During fertilization, the sperm delivers a sperm-specific phospholipase C (PLCZ) that is responsible for triggering Ca(2)(+) oscillations and oocyte activation. During bovine somatic cell nuclear transfer (SCNT), oocyte activation is artificially achieved by combined chemical treatments that induce a monotonic rise in intracellular Ca(2)(+) and inhibit either phosphorylation or protein synthesis. In this study, we tested the hypothesis that activation of bovine nuclear transfer embryos by PLCZ improves nuclear reprogramming. Injection of PLCZ cRNA into bovine SCNT units induced Ca(2)(+) oscillations similar to those observed after fertilization and supported high rates of blastocyst development similar to that seen in embryos produced by IVF. Furthermore, gene expression analysis at the eight-cell and blastocyst stages revealed a similar expression pattern for a number of genes in both groups of embryos. Lastly, levels of trimethylated lysine 27 at histone H3 in blastocysts were higher in bovine nuclear transfer embryos activated using cycloheximide and 6-dimethylaminopurine (DMAP) than in those activated using PLCZ or derived from IVF. These results demonstrate that exogenous PLCZ can be used to activate bovine SCNT-derived embryos and support the hypothesis that a fertilization-like activation response can enhance some aspects of nuclear reprogramming.

Oocyte activation and preimplantation development of bovine embryos obtained by specific inhibition of cyclin-dependent kinases

The efficiency of bohemine and roscovitine in combination with ionomycin on parthenogenetic activation and initial embryonic development of bovine oocytes was studied. Two experiments were performed: in the first, different concentrations (0, 50, 75 or 100µM) and different exposure periods (2, 4 or 6 hours) to bohemine or roscovitine were tested for activation rates of in vitro matured (IVM) bovine oocytes, which were pre-exposed to ionomycin. The best treatments, 75µM bohemine and 50µM roscovitine, both for 6h, were used in the second experiment, in which IVM bovine oocytes were exposed to ionomycin, followed or not by bohemine or roscovitine treatment, and evaluated for nuclear status, activation rate and blastocyst development were assessed. The combined treatments (ionomycin + cyclin-dependent kinases inhibitors - CDKIs) showed better results for activation rates (77.3%) and initial embryonic development (35.2%) than the single ionomycin treatment (69.4% for activation and 21.9% for development); and also lead to a more uniform activation (nearly 90% single pronucleus development). The results showed that CDKIs improve the effects of ionomycin on parthenogenetic activation and blastocyst development in bovine oocytes and could help to achieve more efficient activation protocols, increasing the developmental competence of embryos obtained by reproductive biotechniques.

Activation of oocytes after nuclear transfer

After nuclear transfer, the recipient oocyte must be stimulated to initiate development. This stimulation is achieved by inducing changes in the oocyte cytoplasm that normally are triggered by the sperm during fertilization. In most cases, such changes include a transient increase in the intracellular-free calcium concentration induced by an electrical pulse or alternatively, by chemical agents. Many times, particularly in aged oocytes, this calcium signal is sufficient to stimulate the oocyte developmental program. Other activation protocols were designed to target pathways downstream of the initial calcium signal to affect the activity of regulatory proteins that play central roles in maintaining developmental arrest. This is achieved by the application of protein kinase or protein synthesis inhibitors; combined with a calcium stimulus such inhibitors are widely used for oocyte activation after nuclear transfer and are able to support embryonic development to term.

Handmade Somatic Cell Cloning in Cattle

Apart from the biological and ethical problems, technical difficulties also hamper the improvement and widespread application of somatic cell nuclear transfer (NT). Recently introduced zona-free procedures may offer a solution for the latter problem. The most radical approach of these techniques is the so-called handmade cloning (HMC). It does not require micromanipulators because the manipulations required for both enucleation and nucleus transfer are performed by hand. The HMC technique includes manual bisection of zona-free oocytes, selection of cytoplasts by staining, and the simultaneous fusion of the somatic cell with two cytoplasts to produce a cloned embryo. HMC is a rapid and efficient technique that suits large-scale NT programs. It requires less expertise and time than traditional NT methods and the cost of equipment is significantly less. Production efficiency is high and embryo quality, in terms of pregnancy rates and live births, is not compromised. Although HMC has been developed particularly for bovine NT, the technique is applicable to other species. The method may become a useful tool for both experimental and commercial somatic cell cloning because it allows for standardization of procedures and provides the possibility of automation.

Cloning: Eight Years After Dolly

It is now 8 years since the birth of Dolly, the first animal produced by nuclear transfer using a donor cell population established from an adult animal. During this time, the technique of nuclear transfer has been successfully applied to a range of mammalian species for the production of offspring using a plethora of donor cell types derived from both foetal and adult tissues. In addition, when coupled with genetic manipulation of the donor cells, transgenic offspring have been produced with a range of genetic modifications including gene knockouts and gene knockings. Despite the apparent successes of the technology, the efficiency of development to live offspring has remained low and developmental abnormalities still occur. The objectives of this paper are to review some of the successes and failures of the nuclear transfer procedure since the production of Dolly. In particular, we will review the major steps in the procedure and discuss studies from our laboratory and others which have modified the procedure in ways which may impact on development.

Cell confluency is as efficient as serum starvation for inducing arrest in the G0/G1 phase of the cell cycle in granulosa and fibroblast cells of cattle

The cell cycle stage of donor cells is an important factor influencing developmental ability of nuclear transfer embryos. In the present experiment, cumulus and fibroblast cells of cattle were subjected to flow cytometric cell cycle analysis before being used in somatic cloning experiments. The following experimental groups were analyzed for each cell type: (1) actively dividing cells, (2) cells confluent for 4 days, (3) cells starved for 1, 2, 3 or 5 days. Using the propidium iodide flow cytometric assay, there were no significant differences (P > or = 0.05) in the percentage of cells in G0/G1 regardless of origin and type of cell, after confluency or serum starvation. Differences with the growing cells were found (P < or = 0.01). To determine what subset of cells in G0/G1 were in the G0 subphase of the cell cycle, an immunofluorescence analysis was conducted using monoclonal anti-PCNA antibodies in a FACS assay. There were not statistically significant differences in the percentage of cells that enter G0, between confluent and any starved group for either type of cells. Bovine fibroblast cells, confluent or serum starved for 3 days, were used in nuclear transfer experiments. A slight trend for a more desirable fusion rate in starved cells was detected, and embryo cleavage was greater in starved cells, however, in vitro development to blastocysts was similar between groups. Data indicate that prolonged culture of cells in the absence of serum does not imply a shift in the percentage of cells that enter G0/G1 or G0 alone, and that confluency is sufficient to induce quiescence. This finding can be beneficial in nuclear transfer programs, because there are negative effects such as apoptosis, associated with serum starvation.

Duration of In Vitro Maturation of Recipient Oocytes Affects Blastocyst Development of Cloned Porcine Embryos

This study investigated the effects of different incubation periods for oocyte maturation and contact inhibition of donor cells as well as different osmolarities for storage of recipient oocytes on fusion rates, cleavage rates, and blastocyst yields of porcine somatic nuclear transfer (SCNT) derived embryos. In addition, the in vivo developmental potential of cloned embryos derived from the most promising SCNT protocol was tested by transfer to recipient gilts. Storage of in vitro-matured oocytes for 7.5 h in calcium-free TL-HEPES medium at 295 or 320 mOsmol prior to activation yielded significantly (p < 0.05) higher parthenogenetic blastocyst rates compared to storage in TL-HEPES with an osmolarity of 270 mOsmol (24.4 +/- 3.0% and 26.2 +/- 4.3% vs. 18.3 +/- 6.4%, respectively, mean +/- SD) and improved the visibility of the polar body. Electrical fusion of fibroblasts to enucleated oocytes matured for 38, 40, or 42 h resulted in similar fusion and cleavage rates (74.8-84.4%). However, nuclear transfer with oocytes matured for 40 h in vitro yielded significantly higher (p < 0.05) development to the blastocyst stage after 7 days of culture (14.7 +/- 1.7%) than with oocytes matured for 38 h (9.5 +/- 2.1%) or 42 h (5.1 +/- 2.1%). Contact inhibition for 24, 48, or 72 h significantly (p < 0.05) increased the proportion of cells at G0/G1 compared with cycling fibroblasts. However, duration of contact inhibition of the donor cells for either 24, 48, or 72 h had no effect on blastocyst rates of SCNT embryos. Four gilts received an average of 150 SCNT embryos (range 138-161) reconstructed with oocytes matured for 40 h; two of these became pregnant; one of them went to term and farrowed four piglets on day 115 of pregnancy. Microsatellite analysis confirmed that the clones were genetically identical with the donor cells. These results show that changes of the in vitro maturation protocol may affect in vitro development of reconstructed porcine embryos, while duration of the contact inhibition period plays a minor role for the success of porcine SCNT. The effects on in vivo development are yet to be determined.

Hand-made cloning approach: potentials and limitations

Two major drawbacks hamper the advancement of somatic cell nuclear transfer in domestic animals. The first is a biological problem that has been studied extensively by many scientists and from many viewpoints, including the cell, molecular and developmental biology, morphology, biochemistry and tissue culture. The second is a technical problem that may be responsible for 50% or more of quantitative and/or qualitative failures of routine cloning experiments and is partially the result of the demanding and complicated procedure. However, even the relatively rare documented efforts focusing on technique are usually restricted to details and accept the principles of the micromanipulator-based approach, with its inherent limitations. Over the past decade, a small alternative group of procedures, called hand-made cloning (HMC), has emerged that has the common feature of removal of the zona pellucida prior to enucleation and fusion, resulting in a limited (or no) requirement for micromanipulators. The benefits of HMC are low equipment costs, a simple and rapid procedure and an in vitro efficiency comparable with or higher than that of traditional nuclear transfer. Embryos created by the zona-free techniques can be cryopreserved and, although data are still sparse, are capable of establishing pregnancies and resulting in the birth of calves. Hand-made cloning may also open the way to partial or full automation of somatic cell nuclear transfer. Consequently, the zona- and micromanipulator-free approach may become a useful alternative to traditional cloning, either in special situations or generally for the standardisation and widespread application of somatic cell nuclear transfer.

Effect of protein supplementation in potassium simplex optimization medium on preimplantation development of bovine non-transgenic and transgenic cloned embryos

The present study evaluated the effect of protein supplementation in potassium simplex optimization medium (KSOM) on bovine preimplantation embryo development. The in vitro fertilized (IVF) (Experiment 1), non-transgenic (Experiment 2) and transgenic cloned embryos (Experiment 3) were cultured for 192 h in KSOM supplemented with 0.8% BSA (KSOM-BSA), 10% FBS (KSOM-FBS) or 0.01% PVA (KSOM-PVA). Transfected cumulus cells with an expression plasmid for human alpha1-antitrypsin gene and a green fluorescent protein (GFP) marker were used to produce transgenic cloned embryos. Modified synthetic oviductal fluid (mSOF) supplemented with 0.8% BSA (mSOF-BSA) was used as a control medium. In Experiment 1, cleavage rate was significantly (P < 0.05) lower (69.1%) in IVF embryos cultured in KSOM-FBS than in KSOM-BSA (80.3%). The rate of hatching/hatched blastocyst formation was significantly (P < 0.05) lower in embryos cultured in KSOM-PVA than in KSOM-FBS (2.2% versus 10.8%). Blastocysts cultured in KSOM-FBS contained significantly (P < 0.06) higher numbers of inner cell mass cells (50.4 +/- 20.2) than those cultured in mSOF-BSA (36.9 +/- 19.2). In Experiment 2, the rate of blastocyst formation was significantly (P < 0.05) lower (20.5%) in embryos cultured in KSOM-PVA than in other culture media (33.3-38.5%). The rate of hatching/hatched blastocysts was significantly (P < 0.05) lower in KSOM-PVA (13.9%) and KSOM-FBS (17.1%) than in KSOM-BSA (30.8%) and mSOF-BSA (33.9%). The numbers of total and trophectoderm cells (104.6 +/- 32.2 and 71.7 +/- 25.5, respectively) were significantly (P < 0.05) lower in blastocysts cultured in KSOM-PVA than in KSOM-BSA (125.7 +/- 39.7 and 91.7 +/- 36.2, respectively). In Experiment 3, no significant differences in embryo development, GFP expression and blastocyst cell numbers were observed among the culture groups. In conclusion, the present study demonstrated that KSOM and mSOF supplemented with BSA were equally effective in supporting development of bovine non-transgenic and transgenic cloned embryos. Moreover, different developmental competence in response to protein supplementation of KSOM was observed between bovine non-transgenic and transgenic cloned embryos.

An interclass nuclear transfer between fowl and mammal: In vitro development of chicken-to-cattle interclass embryos and the detection of chicken genetic complements

An attempt was made to develop an interclass somatic cell nuclear transfer method as an alternative means of establishing chicken embryonic stem cells. Chicken-to-cattle interclass embryos that activated calcium ionophore, cycloheximide, and cytochalasin D were developed into blastocysts, and the developing interclass embryos had chicken genetic complements.

Efficient Production of Cloned Bovine Embryos Using cdc2 kinase Inhibitor

This study was carried out to compare the effects of the combination of ionomycin with a H1-histone kinase inhibitor (dimethylaminopurine, DMAP) or cdc2 kinase inhibitor (sodium pyrophosphate, SPP) on the development of reconstituted bovine eggs. For this study, the enucleated bovine oocytes were injected with a presumptive primordial germ cell pre-treated with 1% sodium citrate, and randomly allocated into three activation groups: Group 1 (ionomycin 5 microm, 5 min), Group 2 (ionomycin + DMAP 1.9 mm, 3 h), and Group 3 (ionomycin + SPP 2 mm, 3 h). The reconstituted eggs were compared on the rates of cleavage and development with the blastocyst stage and the ploidy of embryos at 96 h post-activation. Cleavage rates and blastocyst development in Groups 1, 2 and 3 were 7 and 0%, 63 and 17%, and 53 and 14%, respectively. The chromosomal composition differed significantly (p < 0.05) among treatments. Although the embryos in Group 1 had significantly lower developments, 60% of embryos evaluated had diploid chromosomal sets. In contrast, approximately 60% of embryos in Group 2 had abnormal ploidy (21% polyploid and 38% mixoploid). In Group 3, the appearance of abnormal chromosome sets was reduced with the proportion of diploid embryos being increased to 86% (19 of 22), significantly higher (p < 0.05) than in Group 2. It can be concluded that the use of SPP with ionomycin reduces greatly the incidence of chromosomal abnormalities, and may be applicable for the activation of nuclear transplant bovine embryos.

The effect of activation of Mammalian oocytes on remodeling of donor nuclei after nuclear transfer

Activation of bovine oocytes by experimental procedures that closely mimic normal fertilization is essential both for intracytoplasmic sperm injection and for nuclear transfer (NT). Therefore, with the goal of producing haploid activated oocytes, we evaluated whether butyrolactone I and bohemine, either alone or in combination with ionomycin, are able to activate young matured mammalian oocytes. Furthermore, the effect on the patterns of DNA synthesis after pronuclear formation as well as changes in histone H1 kinase and MAP kinase activities during the process of activation were studied. Our results with bohemine show that the specific inhibition of cyclin-dependent kinases (CDKs) in metaphase II bovine oocytes induces parthenogenetic activation in a dose dependent manner (25, 50, and 100 microM, respectively), either alone (3%, 30%, and 50%) or in combination with ionomycin (30%, 70%, and 87.5%). The effect of two activation protocols on nuclear remodeling, DNA synthesis during the first cell cycle, chromosome segregation after first mitosis, and development to blastocyst of embryos produced by somatic nuclear transfer were studied. Pronuclear formation was significantly higher when activation lasted 5 h compared to 3 h for both ethanol-cycloheximide and ionomycin-bohemine treatment. Initiation of DNA synthesis was delayed in ethanol-cycloheximide group, however, after 12-h labeling 100% of embryos synthesized DNA in both groups. Analysis of two-cell embryos with DNA probes for chromosome 6, 7, and 15 by fluorescence in situ hybridization showed that at least 50% of NT embryos were of normal ploidy, independent of the activation protocol.

Handmade somatic cell cloning in cattle: analysis of factors contributing to high efficiency in vitro

Widespread application of somatic cell cloning has been hampered by biological and technical problems, which include complicated and time-consuming procedures requiring skilled labor. Recently, zona-free techniques have been published with limited or no requirement for micromanipulators. The purpose of the present work was to optimize certain steps of the micromanipulator-free (i.e., handmade) procedure, to analyze the morphology of the developing blastocysts, and to explain factors involved in the high efficiencies observed. Optimization of the procedure included selection of the appropriate medium for enucleation, orientation of pairs at fusion, timing of fusion, and culture conditions. As a result of these improved steps, in vitro efficiency as measured by blastocysts per reconstructed embryo and blastocysts per working hour was among the highest described so far. The cattle serum used in our experiments was superior to other protein sources for in vitro embryo development. One possible explanation of this effect is the considerable mitogenic activity of the cattle serum compared with that of commercially available fetal calf serum. Morphological analysis of blastocysts by inverted microscopy, inner cell mass-trophoblast differential staining, and transmission electron microscopy revealed high average quality. A high initial pregnancy rate was achieved after the transfer of single blastocysts derived by aggregation of two nuclear transfer embryos into recipients. The improved handmade somatic cell nuclear transfer method may become a useful technology as a simple, inexpensive, and efficient alternative to traditional somatic cell nuclear transfer.

Effect of Activation Methods for Bovine Oocytes after Intracytoplasmic Injection

A principal nuclear transfer procedure is to inject a donor cell into the perivitelline space in an enucleated oocyte and then electric fusion is performed (cell fusion method). The effects of activation methods in reconstructed oocytes for the serum-starved somatic cell cloning procedure were investigated in this study by means of intracytoplasmic injection (i.c.i.). Bovine oocytes were enucleated at 18-22 h for in vitro maturation, and subsequently the nucleus of cumulus cell collected from Japanese Black Bulls (JBCC) after 5-7 days of starved culture was injected into the recipient cytoplast with a piezo-micromanipulator. At 1 h after i.c.i., reconstructed oocytes were stimulated with ethanol (ET) or calcium ionophore (CaI) as the first activation treatment, followed by cycloheximide (CHX) or 6-dimethylaminopurin (DMAP) treatment as the second activation. In the experiment on the first activation method, the proportion of reconstructed oocytes developing to the blastocyst stage was significantly (p<0.01) higher in the ET activation method than that with CaI (10.5% and 4.7%, respectively). And the experiment on the second activation method after ET treatment showed similar proportions of blastocyst development in both CHX and DMAP treatments (5.9% and 2.8%, respectively). The present results indicated that combined activation treatment with ET and CHX was efficient for reconstructed bovine oocytes by i.c.i.

In vitro development of bovine nuclear transfer embryos from transgenic clonal lines of adult and fetal fibroblast cells of the same genotype

This study examined bovine cloning strategies that may be used for gene targeting in animals of known phenotypic traits. Fibroblast cells derived from an adult and a fetus of the same genotype were transfected with a plasmid (pEGFP-N1) containing the enhanced green fluorescence protein and neomycin-resistant genes. After transfecting 2 x 10(5) cells, 49 adult and 35 fetal cell colonies were obtained. Green fluorescence expression was observed in 35 out of 49 (71.4%) adult clones and in 30 out of 35 (85.7%) fetal clones. Developmental rates to the blastocyst stage following nuclear transfer (NT) did not differ among nontransfected cell lines (adult, 20.0%; NT fetal, 18.3%), whereas developmental rates were significantly lower for adult and fetal cell lines expressing enhanced green fluorescent protein (EGFP; 11.3% and 6.4%, respectively, P < 0.05). However, there was no decrease in NT developmental rates (19.8%) when donor nuclei from EGFP-transfected cell lines not expressing EGFP but retaining neomycin-resistant gene expression were used as donor nuclei. NT embryos from adult and fetal cell lines had similar morphology, cell number, and ploidy. The results indicated that adult and NT fetal cells (identical genotype) can complete clonal propagation, including transfection and selection, and can be used to produce transgenic NT embryos; however, a possible deleterious effect of EGFP on embryo development should be considered in future gene targeting studies.

Bovine somatic cell nuclear transfer using recipient oocytes recovered by ovum pick-up: effect of maternal lineage of oocyte donors

The efficiency of bovine nuclear transfer using recipient oocytes recovered by ultrasound-guided follicle aspiration (ovum pick-up [OPU]) was investigated. Oocyte donors were selected from 2 distinct maternal lineages (A and B) differing in 11 nucleotide positions of the mitochondrial DNA control region. A total of 1342 cumulus-oocyte complexes (COCs) were recovered. The numbers of total COCs and class I/II COCs recovered from donors of lineage A were higher (P < 0.001) than those obtained from lineage B. Follicle aspiration once per week yielded a higher (P < 0.001) total number of COCs per session than aspiration twice per week, whereas the reproduction status of donors (heifer vs. cow) had no effect on OPU results. Of the 1342 oocytes recovered, 733 (55%) were successfully matured in vitro and used for nuclear transfer. Fusion was achieved in 550 (75%) karyoplast-cytoplast complexes (KCCs), resulting in 277 (50%) cleaved embryos on Day 3. On Day 7 of culture, 84 transferable embryos (15% based on fused KCCs) were obtained. After 38 transfers (10 single, 22 double, and 6 triple transfers), 9 recipients (8 double and 1 triple transfer) were diagnosed as pregnant on Day 28, corresponding to a pregnancy rate of 24%. The proportion of transferable embryos on Day 7 was significantly (P < 0.05) influenced by maternal lineage of oocyte donors and by the frequency of follicle aspiration. Our study demonstrates the feasibility of generating nuclear transfer embryos with defined cytoplasmic background. These will be valuable tools to experimentally dissect the effects of nuclear and cytoplasmic components on embryonic, fetal, and postnatal development.