Improved efficiency of bovine cloning by autologous somatic cell nuclear transfer

Use of mitochondrial sequencing to detect gene doping in horses via gene editing and somatic cell nuclear transfer

Gene editing and subsequent cloning techniques offer great potential not only in genetic disease correction in domestic animals, but also in livestock production by enhancement of desirable traits. The existence of the technology, however, leaves it open to potential misuse in performance-led sports such as horseracing and other equestrian events. Recent advances in equine gene editing, regarding the generation of gene-edited embryos using CRISPR/Cas9 technology and somatic cell nuclear transfer, has highlighted the need to develop tools to detect potential prohibited use of the technology. One possible method involves the characterisation of the mitochondrial genome (which is not routinely preserved during cloning) and comparing it to the sequence of the registered dam. We present here our approach to whole-mitochondrial sequencing using tiled long-range PCR and next-generation sequencing. To determine whether the background mutation rate in the mitochondrial genome could potentially confound results, we sequenced ten sets of dam and foal duos. We found variation between duos but none within duos, indicating that this method is feasible for future screening systems. Analysis of WGS data from over one hundred Thoroughbred horses revealed wide variation in the mitochondria sequence within the breed, further displaying the utility of this approach.

Mitochondrial DNA Depletion in Granulosa Cell Derived Nuclear Transfer Tissues

Somatic cell nuclear transfer (SCNT) is a key technology with broad applications that range from production of cloned farm animals to derivation of patient-matched stem cells or production of humanized animal organs for xenotransplantation. However, effects of aberrant epigenetic reprogramming on gene expression compromise cell and organ phenotype, resulting in low success rate of SCNT. Standard SCNT procedures include enucleation of recipient oocytes before the nuclear donor cell is introduced. Enucleation removes not only the spindle apparatus and chromosomes of the oocyte but also the perinuclear, mitochondria rich, ooplasm. Here, we use a Bos taurus SCNT model with in vitro fertilized (IVF) and in vivo conceived controls to demonstrate a ∼50% reduction in mitochondrial DNA (mtDNA) in the liver and skeletal muscle, but not the brain, of SCNT fetuses at day 80 of gestation. In the muscle, we also observed significantly reduced transcript abundances of mtDNA-encoded subunits of the respiratory chain. Importantly, mtDNA content and mtDNA transcript abundances correlate with hepatomegaly and muscle hypertrophy of SCNT fetuses. Expression of selected nuclear-encoded genes pivotal for mtDNA replication was similar to controls, arguing against an indirect epigenetic nuclear reprogramming effect on mtDNA amount. We conclude that mtDNA depletion is a major signature of perturbations after SCNT. We further propose that mitochondrial perturbation in interaction with incomplete nuclear reprogramming drives abnormal epigenetic features and correlated phenotypes, a concept supported by previously reported effects of mtDNA depletion on the epigenome and the pleiotropic phenotypic effects of mtDNA depletion in humans. This provides a novel perspective on the reprogramming process and opens new avenues to improve SCNT protocols for healthy embryo and tissue development.

Beneficial effects of diazepin-quinazolin-amine derivative (BIX-01294) on preimplantation development and molecular characteristics of cloned mouse embryos

Somatic cell nuclear transfer is frequently associated with abnormal epigenetic modifications that may lead to the developmental failure of cloned embryos. BIX-01294 (a diazepine–quinazoline–amine derivative) is a specific inhibitor of the histone methyltransferase G9a. The aim of the present study was to investigate the effects of BIX-01294 on development, dimethylation of histone H3 at lysine 9 (H3K9), DNA methylation and the expression of imprinted genes in cloned mouse preimplantation embryos. There were no significant differences in blastocyst rates of cloned embryos treated with or without 0.1 μM BIX-01294. Relative to clone embryos treated without 0.1 μM BIX-01294, exposure of embryos to BIX-01294 decreased histone H3K9 dimethylation and DNA methylation in cloned embryos to levels that were similar to those of in vivo-fertilised embryos at the 2-cell and blastocyst stages. Cloned embryos had lower expression of octamer-binding transcription factor 4 (Oct4) and small nuclear ribonucleoprotein N (Snrpn), but higher expression of imprinted maternally expressed transcript (non-protein coding) (H19) and growth factor receptor-bound protein 10 (Grb10) compared with in vivo-fertilised counterparts. The addition of 0.1 μM BIX-01294 to the activation and culture medium resulted in lower H19 expression and higher cyclin dependent kinase inhibitor 1C (Cdkn1c) and delta-like 1 homolog (Dlk1) expression, but had no effect on the expression of Oct4, Snrpn and Grb10. The loss of methylation at the Grb10 cytosine–phosphorous–guanine (CpG) islands in cloned embryos was partially corrected by BIX-01294. These results indicate that BIX-01294 treatment of cloned embryos has beneficial effects in terms of correcting abnormal epigenetic modifications, but not on preimplantation development.

Effect of BIX-01294 on H3K9me2 levels and the imprinted gene Snrpn in mouse embryonic fibroblast cells

BIX-01294 (a diazepin-quinazolin-amine derivative) has important biological effects and its epigenetic regulation at imprinting control regions is highly complex. BIX-01294 may reduce global H3K9me2 levels and affect epigenetic modifications of small nuclear ribonucleoprotein N (Snrpn) in MEFs.

Histone H3 lysine 9 dimethylation (H3K9me2) hypermethylation is thought to be a major influential factor in cellular reprogramming, such as somatic cell nuclear transfer (SCNT) and induction of pluripotent stem cells (iPSCs). The diazepin-quinazolin-amine derivative (BIX-01294) specifically inhibits the activity of histone methyltransferase EHMT2 (euchromatic histone-lysine N-methyltransferase 2) and reduces H3K9me2 levels in cells. The imprinted gene small nuclear ribonucleoprotein N (Snrpn) is of particular interest because of its important biological functions. The objective of the present study was to investigate the effect of BIX-01294 on H3K9me2 levels and changes in Snrpn DNA methylation and histone H3K9me2 in mouse embryonic fibroblasts (MEFs). Results showed that 1.3 μM BIX-01294 markedly reduced global levels of H3K9me2 with almost no cellular toxicity. There was a significant decrease in H3K9me2 in promoter regions of the Snrpn gene after BIX-01294 treatment. A significant increase in methylation of the Snrpn differentially methylated region 1 (DMR1) and slightly decreased transcript levels of Snrpn were found in BIX-01294-treated MEFs. These results suggest that BIX-01294 may reduce global levels of H3K9me2 and affect epigenetic modifications of Snrpn in MEFs.

Factors affecting the development of somatic cell nuclear transfer embryos in Cattle

Nuclear transfer is a complex multistep procedure that includes oocyte maturation, cell cycle synchronization of donor cells, enucleation, cell fusion, oocyte activation and embryo culture. Therefore, many factors are believed to contribute to the success of embryo development following nuclear transfer. Numerous attempts to improve cloning efficiency have been conducted since the birth of the first sheep by somatic cell nuclear transfer. However, the efficiency of somatic cell cloning has remained low, and applications have been limited. In this review, we discuss some of the factors that affect the developmental ability of somatic cell nuclear transfer embryos in cattle.

Production of a mitochondrial-DNA identical cloned foal using oocytes recovered from immature follicles of selected mares

Cloned animals possess mitochondria derived from the host ooplast, which typically differ genetically from those of the donor. This is of special concern to horse breeders, as maternal lines are prized and athletic performance is a key factor in genetic value. To evaluate the feasibility of producing mitochondrial-identical cloned foals, we collected oocytes from immature follicles of two mares, BL and SM, maternally related to the donor stallion. In vitro matured, enucleated oocytes were treated with roscovitine-synchronized donor cells and blastocysts were transferred transcervically to recipient mares. In Mare BL, 10 aspiration sessions yielded 45 oocytes, of which 12 matured and seven were successfully recombined. One blastocyst was produced, which did not yield a pregnancy. In Mare SM, three aspiration sessions yielded 53 oocytes, of which 27 successfully recombined. These were assigned to either Scriptaid or Scriptaid plus Vitamin C treatments for the first 12 to 16 hours of embryo culture. Two blastocysts were produced from each treatment. One pregnancy was established after transfer from the Scriptaid treatment. This resulted in a viable foal whose genomic DNA and mitochondrial DNA matched to those of the donor animal. These results indicate that production of mitochondrial-identical cloned foals can be achieved using oocyte recovery from a very small number of selected mares. Despite mitochondrial homogeneity, the results varied with mare; Mare BL yielded both significantly fewer oocytes per aspiration session (P < 0.001) and significantly fewer reconstructed oocytes per oocyte recovered ( P < 0.001) than did Mare SM.

Transcriptome profile of bovine elongated conceptus obtained from SCNT and IVP pregnancies

In the present study we analyzed the gene expression changes induced by somatic cell nuclear transfer (SCNT) and in vitro production (IVP) in bovine elongated embryos using Affymetrix bovine genome array. For this, Day-16 bovine embryos from SCNT, IVP, and artificial insemination (AI) were recovered from recipients and used for transcriptome analysis. Despite comparable in vivo development rates, considerable reduction in elongation size was observed in SCNT compared to non-cloned embryos (93.3 mm for SCNT vs. 186.6 mm and 196.3 mm for IVP and AI embryos, respectively). Gene expression analysis revealed that the transcript levels of 477 genes, which are involved in various pathways including arginine and proline or glycerolipid and fatty acid metabolism, were significantly altered in SCNT compared to AI embryos. Similarly, 365 genes were differentially expressed in IVP embryos compared to AI. Thus, several pathways including TNRF-1 signaling and tight junction pathways were affected. To predict whether the altered transcripts were associated with culture condition or errors in transcriptional reprogramming, unique or common differentially expressed genes were analyzed in SCNT and IVP embryos compared to AI or fibroblast donor cells. Accordingly, 71 transcripts were found to be not transcriptionally reprogrammed, as their expression resembled the donor cells more than AI embryos; the remaining transcripts were either partially or incompletely reprogrammed. In conclusion, the present study identified deviations in elongation size, gene expression, and the corresponding molecular pathways in Day-16 SCNT and IVP conceptuses compared to their AI counterparts, which may subsequently be associated with the outcome of fetal development.

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.

Using cell banks as a tool in conservation programmes of native domestic breeds: the production of the first cloned Anatolian Grey cattle

The aim of this study was to clone native Anatolian Grey cattle by using different donor cell types, such as fibroblast, cartilage and granulosa cells cryopreserved in a gene bank and oocytes aspirated from ovaries of Holstein cows as the recipient cytoplasm source. One male calf from fibroblast, three female calves from granulosa cells and one female calf from cartilage cells were born healthy and at normal birthweights. No calves were lost after birth. The results demonstrated that the cloned calves had the same microsatellite alleles at 11 loci as their nuclear donors. However, the mtDNAs of the five Anatolian Grey cloned calves had different haplotypes from their donor cells and mtDNA heteroplasmy could not be detected in any of the clones. The birth of healthy clones suggests that the haplotype difference between the cell and oocyte donor did not affect the pre- or post-implantation development of the bovine nuclear transfer derived embryos in our study. The results showed that well established nuclear transfer protocols could be useful in conserving endangered species. In conclusion, somatic cell banking can be suggested as a tool in conservation programmes of animal genetic resources.

Association between mitochondrial DNA haplotype compatibility and increased efficiency of bovine intersubspecies cloning

Reconstructed embryos derived from intersubspecies somatic cell nuclear transfer (SCNT) have poorer developmental potential than those from intrasubspecies SCNT. Based on our previous study that Holstein dairy bovine (HD) mitochondrial DNA (mtDNA) haplotype compatibility between donor karyoplast and recipient cytoplast is crucial for SCNT embryo development, we performed intersubspecies SCNT using HD as donor karyoplast and Luxi yellow heifer (LY) as recipient cytoplast according to mtDNA haplotypes determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. The results demonstrated that intersubspecies mtDNA homotype SCNT embryos had higher pre- and post-implantation developmental competence than intrasubspecies mtDNA heterotype embryos as well as improved blastocyst reprogramming status, including normal H3K9 dimethylation pattern and promoter hypomethylation of pluripotent genes such as Oct4 and Sox2, suggesting that intersubspecies SCNT using LY oocytes maintains HD cloning efficiency and may reprogram HD nuclei to develop into a normal cloned animal ultimately. Our results indicated that karyoplast-cytoplast interactions and mtDNA haplotype compatibility may affect bovine intersubspecies SCNT efficiency. This study on bovine intersubspecies SCNT is valuable for understanding the mechanisms of mtDNA haplotype compatibility between karyoplast and cytoplast impacting the bovine SCNT efficiency, and provides an alternative and economic resource for HD cloning.

Multiplex polymerase chain reaction used for bovine embryo sex determination

Widely used bovine sexing primers were compared in terms of suitability in determining the sex of bovine embryos. Under optimized multiplex PCR conditions, the ConBV/ConEY couple primers did not show accurate results when combined together in multiplex PCR, but worked well when the couple primers were used separately. The S4BF/S4BR primers showed accurate results; however, some unexpected bands were detected. When the BY/BSP couple primers were used to determine one-cell, two-cell, four-cell and eight-cell stage embryos of known sexed SCNT-derived embryos, the results showed 100% accuracy. The BY/BSP couple primers were also able to identify the sex of one-cell and two-cell IVF-derived embryos.

Effect of microinjection of a single IVF-derived blastomere on the development of cloned embryos at the eight-cell stage in bovine

This study was conducted to determine the effect of microinjection of a single blastomere from in vitro fertilization (IVF)-derived eight-cell embryo into eight-cell cloned embryos harboring the gene encoding recombinant human lactoferrin (rhLF), GFP, and NEO markers in bovine. The reconstructed chimeric embryos were assessed for their development to blastocyst, or to term after transfer, and tissues of offspring were evaluated by polymerase chain reaction (PCR) for the presence of nuclear transfer (NT)-derived transgenic cells, and the cloned embryos without microinjection were used as controls. The chimeric embryos showed slightly higher blastocyst rate than that for controls. The single IVF-derived blastomere appeared to preferential contribute to inner cell mass (ICM) in the chimeric blastocysts. After transfer, the rates of development of chimeric embryos to day 60, to term, and to weaning were significantly higher than those of controls. Sixty-three chimeric blastocysts were transferred and 11 calves were born: 7 calves of them were dead, and the remaining 4 calves are apparently normal and healthy. Most of the tissues collected from dead fetus were transgenic, whereas NT-derived transgenic cells were not detected in some tissues of the living calves. Our results indicated that a single blastomere from IVF-derived eight-cell embryo improves the in vivo developmental potential of transgenic cloned eight-cell embryos in bovine; however, the single IVF-derived blastomere appears to be better able to populate the ICM and many tissues of offspring than NT-derived blastomeres.

[New advances in animal transgenic technology]

Animal transgenic technology is one of the fastest growing biotechnology in the 21st century. It is used to integrate foreign genes into the animal genome by genetic engineering technology so that foreign genes can be expressed and inherited to the offspring. The transgenic efficiency and precise control of gene expression are the key limiting factors on preparation of transgenic animals. A variety of transgenic techniques are available, each of which has its own advantages and disadvantages and still needs further study because of unresolved technical and safety issues. With the in-depth research, the transgenic technology will have broad application prospects in the fields of exploration of gene function, animal genetic improvement, bioreactor, animal disease models, organ transplantation and so on. This article reviews the recently developed animal gene transfer techniques, including germline stem cell mediated method to improve the efficiency, gene targeting to improve the accuracy, RNA interference (RNAi)-mediated gene silencing technology, and the induced pluripotent stem cells (iPS) transgenic technology. The new transgenic techniques can provide a better platform for the study of trans-genic animals and promote the development of medical sciences, livestock production, and other fields.

Donor-host mitochondrial compatibility improves efficiency of bovine somatic cell nuclear transfer

Background

The interaction between the karyoplast and cytoplast plays an important role in the efficiency of somatic cell nuclear transfer (SCNT), but the underlying mechanism remains unclear. It is generally accepted that in nuclear transfer embryos, the reprogramming of gene expression is induced by epigenetic mechanisms and does not involve modifications of DNA sequences. In cattle, oocytes with various mitochondrial DNA (mtDNA) haplotypes usually have different ATP content and can further affect the efficiency of in vitro production of embryos. As mtDNA comes from the recipient oocyte during SCNT and is regulated by genes in the donor nucleus, it is a perfect model to investigate the interaction between donor nuclei and host oocytes in SCNT.

Results

We investigated whether the in vitro development of reconstructed bovine embryos produced by SCNT would be influenced by mtDNA haplotype compatibility between the oocytes and donor cells. Embryos from homotype A-A or B-B showed significantly higher developmental ability at blastocyst stages than the heterotype A-B or B-A combinations. Post-implantation development ability, pregnancy rate up to day 90 of gestation, as well as percent of term births were higher in the homotype SCNT groups than in the heterotype groups. In addition, homotype and heterotype SCNT embryos showed different methylation patterns of histone 3-lysine 9 (H3K9) genome-wide and at pluripotency-related genes (Oct-4, Sox-2, Nanog).

Conclusion

Both histone and DNA methylation show that homotype SCNT blastocysts have a more successful epigenetic asymmetry pattern than heterotype SCNT blastocysts, which indicates more complete nuclear reprogramming. This may result from variability in their epigenetic patterns and responses to nuclear reprogramming. This suggests that the compatibility of mtDNA haplotypes between donor cells and host oocytes can significantly affect the developmental competence of reconstructed embryos in SCNT, and may include an epigenetic mechanism.

Improved efficiency of bovine somatic cell nuclear transfer by optimizing operational procedures

To improve bovine somatic cell nuclear transfer (SCNT) efficiency, we studied various aspects to optimize the experimental procedures. Firstly, donor cells were treated with pronase, which resulted in a higher fusion rate than that of cells without the pronase treatment (78.3 vs. 53.9%). Secondly, when fused embryos were activated either by chemical (ionomycin + cyclohemixide (CHX)) or electrical + CHX stimulation, the cleavage and blastocyst formation rates were comparable amongst these treatment groups (P>0.05); however, mortality following electrical + CHX activation was significantly higher than that observed with the chemical activation, regardless of the pronase treatment (P<0.05). Finally, we compared the culture conditions of the reconstructed embryos using ACM medium plus mouse embryonic fibroblasts (MEF) vs. B2 medium plus granulose cells (GC), and the results clearly demonstrated that the former culture conditions led to a higher blastocyst rate, 90-day pregnancy rate, and newborn rate, than that observed for culture in B2 medium plus GC (46.7 vs. 34.7%, 36.1 vs. 9.6% and 25.9 vs. 5.8% for the blastocyst, pregnancy and newborn rates, respectively). In summary, the efficiency of bovine SCNT can be greatly improved using optimized operational procedures, including treating the donor cells with pronase, activation of fused embryos by ionomycin + CHX and the culture of the reconstructed embryos in ACM + MEF media.

A phiC31 integrase-mediated integration hotspot in favor of transgene expression exists in the bovine genome

phiC31 integrase, a site-specific recombinase, can effectively mediate foreign genes bearing an attB sequence integrated into pseudo attP sites. We have previously identified two pseudo attP sites, BpsF1 and BpsM1 from the bovine genome. In this study, two new pseudo attP sites, BF4 and BF10, were discovered using half-nested inverse PCR from cow fibroblasts. The genomic locations of these two pseudo attP sites were identified by direct sequencing and a BLAST search, and it was confirmed that they reside at positions 4q31 and 10q35 by fluorescence in situ hybridization analysis. Subsequently, the distinct integration frequencies of the four pseudo attP sites were examined. The BF4 site was identified as a hotspot where site-specific integration occurred in most of the cell clones examined, accounting for 74% (42/57) of the integration; much more than the integration frequency for BF10 (7%; 4/57), BpsF1 (7%; 4/57) and BpsM1 (0/57). Interestingly, similar to other hotspots identified in the human and mouse genomes, in which transgenes integrated at hotspots result in high expression, the GFP gene integrated at hotspot BF4 was expressed at high levels in cow fibroblasts, as confirmed by fluorescence microscopy and FACS analysis. Furthermore, ELISA showed that the expression level of the GFP gene integrated at the BF4 site averaged approximately 328 microg x mg(-1), which is more than twofold higher than that integrated at the BF10 site. This study suggests that somatic cells carrying a desired gene integrated at the BF4 site can be used as nuclear donors to generate valuable transgenic animals by nuclear transfer.

Epigenetic modifications of embryonic stem cells: current trends and relevance in developing regenerative medicine

Epigenetics is a growing field not only in the area of cancer research but recently in stem cells including human embryonic stem cell (hESC) research. The hallmark of profiling epigenetic changes in stem cells lies in maintaining pluripotency or multipotency and in attaining lineage specifications that are relevant for regenerative medicine. Epigenetic modifications including DNA methylation, histone acetylation and methylation, play important roles in regulating gene expressions. Other epigenetic modifications include X chromosome silencing, genomic stability and imprinting and mammalian development. This review attempts to elucidate the mechanism(s) behind epigenetic modifications and review techniques scientists use for identifying each modification. We also discuss some of the trends of epigenetic modifications in the fields of directed differentiation of embryonic stem cells and de-differentiation of somatic cells.

Autologous somatic cell nuclear transfer in pigs using recipient oocytes and donor cells from the same animal

The objective of the present study was to examine the feasibility of the production of autologous porcine somatic cell nuclear transfer (SCNT) blastocysts using oocytes and donor cells from slaughtered ovaries. Therefore, we attempted to optimize autologous SCNT by examining the effects of electrical fusion conditions and donor cell type on cell fusion and the development of SCNT embryos. Four types of donor cells were used: 1) denuded cumulus cells (DCCs) collected from in vitro-matured (IVM) oocytes; 2) cumulus cells collected from oocytes after 22 h of IVM and cultured for 18 h (CCCs); 3) follicular cells obtained from follicular contents and cultured for 40 h (CFCs); and 4) adult skin fibroblasts. The DCCs showed a significantly (p < 0.01) lower rate of fusion than the CCCs when two pulses of 170 V/mm DC were applied for 50 µsec (19 ± 2% vs. 77 ± 3%). The rate of DCC fusion with oocytes was increased by the application of two DC pulses of 190 V/mm for 30 µsec, although this was still lower than the rate of fusion in the CCCs (33 ± 1% vs. 80 ± 2%). The rates of cleavage (57 ± 5%) and blastocyst formation (1 ± 1%) in the DCC-derived embryos did not differ from those (55 ± 6% and 3 ± 1%, respectively) in the CCC-derived SCNT embryos. Autologous SCNT embryos derived from CFCs (5 ± 2%) showed higher levels of blastocyst formation (p < 0.01) than CCC-derived autologous SCNT embryos (1 ± 0%). In conclusion, the results of the present study show that culturing cumulus and follicular cells before SCNT enhances cell fusion with oocytes and that CFCs are superior to CCCs in the production of higher numbers of autologous SCNT blastocysts.

Nuclear reprogramming: what has been done and potential avenues for improvements

A major challenge for reproductive biologists is the development of novel strategies to improve cloning efficiency. Even in species for which cloning is relatively successful, like cattle, the efficiency is still unacceptably low. In this review article we critically analyse all approaches that have been suggested by different laboratories in the field so far. As will be discussed below, so far none of these gives rise to a dramatic increase in cloning efficiency. Possibly, a multi-step approach including a pre-treatment of donor cells to modify their chromatin, along with improved culture system for cloned embryos would be the most promising.

Aberrant gene expression patterns in placentomes are associated with phenotypically normal and abnormal cattle cloned by somatic cell nuclear transfer

Transcription profiling of placentomes derived from somatic cell nuclear transfer (SCNT, n = 20), in vitro fertilization (IVF, n = 9), and artificial insemination (AI, n = 9) at or near term development was performed to better understand why SCNT and IVF often result in placental defects, hydrops, and large offspring syndrome (LOS). Multivariate analysis of variance was used to distinguish the effects of SCNT, IVF, and AI on gene expression, taking into account the effects of parturition (term or preterm), sex of fetus, breed of dam, breed of fetus, and pathological finding in the offspring (hydrops, normal, or other abnormalities). Differential expression of 20 physiologically important genes was confirmed with quantitative PCR. The largest effect on placentome gene expression was attributable to whether placentas were collected at term or preterm (i.e., whether the collection was because of disease or to obtain stage-matched controls) followed by placentome source (AI, IVF, or SCNT). Gene expression in SCNT placentomes was dramatically different from AI ( n = 336 genes; 276 >2-fold) and from IVF ( n = 733 genes; 162 >2-fold) placentomes. Functional analysis of differentially expressed genes (DEG) showed that IVF has significant effects on genes associated with cellular metabolism. In contrast, DEG associated with SCNT are involved in multiple pathways, including cell cycle, cell death, and gene expression. Many DEG were shared between the gene lists for IVF and SCNT comparisons, suggesting that common pathways are affected by the embryo culture methods used for IVF and SCNT. However, the many unique gene functions and pathways affected by SCNT suggest that cloned fetuses may be starved and accumulating toxic wastes due to placental insufficiency caused by reprogramming errors. Many of these genes are candidates for hydrops and LOS.

Effect of individual heifer oocyte donors on cloned embryo development in vitro

The aim of this study was to determine the effect of individual oocyte donors on cloned embryo development in vitro. Five Holstein heifers of varied genetic origins were subject to ovum pick up (OPU) once weekly. In total, 913 oocytes were recovered from 1304 follicles. A mean of 7.7+/-0.4 oocytes was recovered per session per animal. Individual mean oocyte production varied significantly in quantity but not in quality (morphological categories) among heifers. Oocytes from individual heifers were used as recipient cytoplasm for somatic cell nuclear transfer (SCNT). Cumulus cells, collected from a single Holstein cow genetically unrelated to the oocyte donor, were used as donor cells. Although the percentage of reconstructed embryos that started to cleave was nearly constant, the percentage of cleaved embryos that developed into blastocysts showed clear individual heifer variation (61%, 51%, 31%, 28% and 24%, respectively), with a mean of 38% showing blastocyst formation. In vitro fertilization (IVF) was also conducted with oocyte from the same heifers used in SCNT. A variation of blastocyst production among individual heifers was also shown in the IVF experiment, but the rank of oocyte donor based on the blastocyst rate was changed. In conclusion, individual oocyte donor may have an effect on cloned embryo development in vitro, which differed from the effect on IVF embryos.