Nuclear-cytoplasmic interactions affect in utero developmental capacity, phenotype, and cellular metabolism of bovine nuclear transfer fetuses

Generation of Monogenetic Cattle by Different Techniques of Embryonic Cell and Somatic Cell Cloning – Their Application to Biotechnological, Agricultural, Nutritional, Biomedical and Transgenic Research – A Review

The development of effective approaches for not only the in vitro maturation (IVM) of heifer/cow oocytes and their extracorporeal fertilization (IVF) but also the non-surgical collection and transfer of bovine embryos has given rise to optimizing comprehensive in vitro embryo production (IVP) technology and improving other assisted reproductive technologies (ART s), such as cattle cloning by embryo bisection, embryonic cell nuclear transfer (ECNT) and somatic cell nuclear transfer (SCNT). The primary goal of the present paper is to demonstrate the progress and achievements in the strategies utilized for embryonic cell cloning and somatic cell cloning in cattle. Moreover, the current article is focused on recognizing and identifying the suitability and reliability of bovine cloning techniques for nutritional biotechnology, agri-food and biopharmaceutical industry, biomedical and transgenic research and for the genetic rescue of endangered or extinct breeds and species of domesticated or wild-living artiodactyl mammals (even-toed ungulates) originating from the family Bovidae.

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.

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

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

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.

Can Reprogramming of Overall Epigenetic Memory and Specific Parental Genomic Imprinting Memory within Donor Cell-Inherited Nuclear Genome be a Major Hindrance for the Somatic Cell Cloning of Mammals? – A Review

Successful cloning of animals by somatic cell nuclear transfer (SCNT) requires epigenetic transcriptional reprogramming of the differentiated state of the donor cell nucleus to a totipotent embryonic ground state. It means that the donor nuclei must cease its own program of gene expression and restore a particular program of the embryonic genome expression regulation that is necessary for normal development. Transcriptional activity of somatic cell-derived nuclear genome during embryo pre- and postimplantation development as well as foetogenesis is correlated with the frequencies for spatial remodeling of chromatin architecture and reprogramming of cellular epigenetic memory. This former and this latter process include such covalent modifications as demethylation/re-methylation of DNA cytosine residues and acetylation/deacetylation as well as demethylation/re-methylation of lysine residues of nucleosomal core-derived histones H3 and H4. The main cause of low SCNT efficiency in mammals turns out to be an incomplete reprogramming of transcriptional activity for donor cell-descended genes. It has been ascertained that somatic cell nuclei should undergo the wide DNA cytosine residue demethylation changes throughout the early development of cloned embryos to reset their own overall epigenetic and parental genomic imprinting memories that have been established by re-methylation of the nuclear donor cell-inherited genome during specific pathways of somatic and germ cell lineage differentiation. A more extensive understanding of the molecular mechanisms and recognition of determinants for epigenetic transcriptional reprogrammability of somatic cell nuclear genome will be helpful to solve the problems resulting from unsatisfactory SCNT effectiveness and open new possibilities for common application of this technology in transgenic research focused on human biomedicine.

Disruption of Mitochondrion-To-Nucleus Interaction in Deceased Cloned Piglets

Most animals produced by somatic cell nuclear transfer (SCNT) are heteroplasmic for mitochondrial DNA (mtDNA). Oxidative phosphorylation (OXPHOS) in clones therefore requires the coordinated expression of genes encoded by the nuclear DNA and the two sources of mitochondria. Such interaction is rarely studied because most clones are generated using slaughterhouse oocytes of unrecorded origin. Here we traced the maternal lineages of seven diseased and five one-month-old live cloned piglets by sequencing their mtDNA. Additionally by using a 13K oligonucleotide microarray, we compared the expression profiles of nuclear and mtDNA-encoded genes that are involved in mitochondrial functions and regulation between the cloned groups and their age-matched controls (n=5 per group). We found that the oocytes used to generate the cloned piglets were of either the Large White or Duroc background, and oocyte genetic background was not related to the clones’ survival. Expression profiles of mtDNA-encoded genes in clones and controls showed intermixed clustering patterns without treatment or maternal lineage-dependency. In contrast, clones and controls clustered separately for their global and nuclear DNA-encoded mitochondrial genes in the lungs for both the deceased and live groups. Functional annotation of differentially expressed genes encoded by both nuclear and mtDNA revealed abnormal gene expression in the mitochondrial OXPHOS pathway in deceased clones. Among the nine differentially expressed genes of the OXPHOS pathway, seven were down-regulated in deceased clones compared to controls, suggesting deficiencies in mitochondrial functions. Together, these data demonstrate that the coordination of expression of mitochondrial genes encoded by nuclear and mtDNA is disrupted in the lung of diseased clones.

Maternal and paternal genomes differentially affect myofibre characteristics and muscle weights of bovine fetuses at midgestation

Postnatal myofibre characteristics and muscle mass are largely determined during fetal development and may be significantly affected by epigenetic parent-of-origin effects. However, data on such effects in prenatal muscle development that could help understand unexplained variation in postnatal muscle traits are lacking. In a bovine model we studied effects of distinct maternal and paternal genomes, fetal sex, and non-genetic maternal effects on fetal myofibre characteristics and muscle mass. Data from 73 fetuses (Day153, 54% term) of four genetic groups with purebred and reciprocal cross Angus and Brahman genetics were analyzed using general linear models. Parental genomes explained the greatest proportion of variation in myofibre size of Musculus semitendinosus (80–96%) and in absolute and relative weights of M. supraspinatus, M. longissimus dorsi, M. quadriceps femoris and M. semimembranosus (82–89% and 56–93%, respectively). Paternal genome in interaction with maternal genome (P<0.05) explained most genetic variation in cross sectional area (CSA) of fast myotubes (68%), while maternal genome alone explained most genetic variation in CSA of fast myofibres (93%, P<0.01). Furthermore, maternal genome independently (M. semimembranosus, 88%, P<0.0001) or in combination (M. supraspinatus, 82%; M. longissimus dorsi, 93%; M. quadriceps femoris, 86%) with nested maternal weight effect (5–6%, P<0.05), was the predominant source of variation for absolute muscle weights. Effects of paternal genome on muscle mass decreased from thoracic to pelvic limb and accounted for all (M. supraspinatus, 97%, P<0.0001) or most (M. longissimus dorsi, 69%, P<0.0001; M. quadriceps femoris, 54%, P<0.001) genetic variation in relative weights. An interaction between maternal and paternal genomes (P<0.01) and effects of maternal weight (P<0.05) on expression of H19, a master regulator of an imprinted gene network, and negative correlations between H19 expression and fetal muscle mass (P<0.001), suggested imprinted genes and miRNA interference as mechanisms for differential effects of maternal and paternal genomes on fetal muscle.

Mitochondrial DNA transmission and confounding mitochondrial influences in cloned cattle and pigs

Although somatic cell nuclear transfer (SCNT) is a powerful tool for production of cloned animals, SCNT embryos generally have low developmental competency and many abnormalities. The interaction between the donor nucleus and the enucleated ooplasm plays an important role in early embryonic development, but the underlying mechanisms that negatively impact developmental competency remain unclear. Mitochondria have a broad range of critical functions in cellular energy supply, cell signaling, and programmed cell death; thus, affect embryonic and fetal development. This review focuses on mitochondrial considerations influencing SCNT techniques in farm animals. Donor somatic cell mitochondrial DNA (mtDNA) can be transmitted through what has been considered a "bottleneck" in mitochondrial genetics via the SCNT maternal lineage. This indicates that donor somatic cell mitochondria have a role in the reconstructed cytoplasm. However, foreign somatic cell mitochondria may affect the early development of SCNT embryos. Nuclear-mitochondrial interactions in interspecies/intergeneric SCNT (iSCNT) result in severe problems. A major biological selective pressure exists against survival of exogenous mtDNA in iSCNT. Yet, mtDNA differences in SCNT animals did not reflect transfer of proteomic components following proteomic analysis. Further study of nuclear-cytoplasmic interactions is needed to illuminate key developmental characteristics of SCNT animals associated with mitochondrial biology.

Improvement of the nuclear transfer efficiency by using the same genetic background of recipient oocytes as the somatic donor cells in goats

We have compared the effect of the genetic background of recipient oocytes on the in vitro and in vivo development of nuclear transfer reconstructed embryos in goats. Adult fibroblast cells from Boer goats were used as donor cells, and recipient oocytes were obtained from Boer goats and Boer cross-breeds (Boer♂×Huanghuai♀). Nuclear transfer reconstructed embryos were cultured in vitro, or transferred into recipient goats. The mitochondrial origin of 2 cloned Boer goats was investigated by analysing the D-loop region based on polymorphisms via DNA sequencing. There was no significant difference in the fusion rate and cleavage rate of reconstructed embryos (P>0.05), when using Boer and cross-breeding goat oocytes as recipient cytoplast respectively. However, in vitro morula development of reconstructed embryos from Boer oocytes was significantly higher than that of cross-breeding embryos (34.1% versus 19.1%, P<0.05). There was no significant difference in the rate of pregnancy and foetus loss between the 2 breeds. However, the live-birth rate was significantly higher with Boer goat oocyte recipients than the cross-breeds (3.1% versus 0.8%, P<0.05). Mitochondrial analysis showed that the 2 cloned goats were similar to their respective oocyte donor goats, and significantly different from the nucleus donor. In conclusion, genetic background of recipient oocytes affected in vitro and in vivo development of reconstructed embryos, with the homologous background of cytoplast and nuclear donor benefiting development of reconstructed embryos. The mitochondrial origin of the 2 cloned Boer goats came from recipient oocytes, not donors.

Body growth, hematological profile, and clinical biochemistry of heifer calves sired by a bull or its clone

The aim of this paper was to compare body growth, hematological profile development, and clinical biochemistry in the female progeny of a sire with the female progeny of its clone. Sixteen Friesian female calves, 9 daughters from a tested bull (BULL) and 7 from its somatic cell nuclear transfer clone (CLONE) were monitored from birth to 60 wk of life. Body weight (BW), wither height (WH), hip height (HH), body length (BL), and hearth girth (HG) were measured at birth and 4, 8, 12, 16, 20, 24, 36, and 50 wk. Blood samples were taken from jugular vein at 12 to 48 h from birth and 1, 2, 3, 4, 8, 12, 16, 20, 24, and 36 wks of age, to be analyzed for hematological, serum protein, and metabolic profiles. At the same time, rectal temperature (RT) was recorded. Age at puberty was assessed on surviving heifers by measuring weekly plasma progesterone levels. Data were evaluated using a mixed model, taking into account the repeated measures in time on the calf. For each variable, different covariance structures were tested, choosing the best according to the Akaike's Information Criteria. Significant was set at P < 0.05, and a trend was considered for P < 0.10. At 24 wk of age, WH was lower in CLONE daughters than BULL daughters. Around 20 wk of age, there was a trend for lower BW in CLONE daughters than BULL daughters, confirmed from differences in HG. There was no difference in RT due to sire effect. Blood glucose concentration decreased in both groups during the first 4 wk of life; at birth, only a trend for higher blood glucose in CLONE daughters was recorded, whereas an opposite trend was observed for plasma creatinine. Total leukocyte count did not differ between progenies. Circulating lymphocytes tended to be lower in CLONE than BULL daughters. The neutrophil: lymphocyte ratio tended to be higher in CLONE than BULL calves. No difference was demonstrated for erythrocyte features, whereas mean platelet volume tended to be lower in CLONE than BULL progeny. From these results, there were no differences between progenies from BULL and its clone that suggest welfare problems in the first 6 mo of life.

Comparative proteomic analysis of liver mitochondrial proteins derived from cloned adult pigs reconstructed with Meishan pig fibroblast cells and European pig enucleated oocytes

Somatic cell nuclear transfer (SCNT) has been exploited in efforts to clone and propagate valuable animal lineages. However, in many instances, recipient oocytes are obtained from sources independent of donor cell populations. As such, influences of potential nuclear-cytoplasmic incompatibility, post SCNT, are largely unknown. In the present study, alterations in mitochondrial protein levels were investigated in adult SCNT pigs produced by microinjection of Meishan pig fetus fibroblast cells into enucleated matured oocytes (maternal Landrace genetic background). Mitochondrial fractions were prepared from liver samples by mechanical homogenization and differential centrifugation. Liver mitochondria were then subjected to two-dimensional difference gel electrophoresis (2-D DIGE). Protein expression changes were confirmed with a volume ratio greater than 2 fold (P<0.05). 2-D DIGE analysis further revealed differential expression of three proteins between the Meishan (n=3) and Landrace (n=3) breeds. Differential expression patterns of 16 proteins were detected in SCNT pig liver tissue (n=3) when compared with Meishan control samples. However, none of the 16 proteins correlated with the three differentially expressed Meishan and Landrace liver mitochondrial proteins. In summary, alteration of mitochondrial protein expression levels was observed in adult SCNT pigs that did not reflect the breed difference of the recipient oocytes. Comparative proteomic analysis represents an important tool for further studies on SCNT animals.

Comparison of liver mitochondrial proteins derived from newborn cloned calves and from cloned adult cattle by two-dimensional differential gel electrophoresis

Aberrant reprogramming of donor somatic cell nuclei may result in many severe problems in animal cloning. The inability to establish functional interactions between donor nucleus and recipient mitochondria is also likely responsible for such a developmental deficiency. However, detailed knowledge of protein expression during somatic cell nuclear transfer (SCNT) in cattle is lacking. In the present study, variations in mitochondrial protein levels between SCNT-derived and control cattle, and from calves derived by artificial insemination were investigated. Mitochondrial fractions were prepared from frozen liver samples and subjected to two-dimensional (2-D) fluorescence differential gel electrophoresis (DIGE) using CyDye™ dyes. Protein expression changes were confirmed with a volume ratio greater than 2.0 (P < 0.05). 2D-DIGE analysis revealed differential expression of three proteins for SCNT cattle (n = 4) and seven proteins for SCNT calves (n = 6) compared to controls (P < 0.05). Different protein patterning was observed among SCNT animals even if animals were generated from the same donor cell source. No differences were detected in two of the SCNT cattle. Moreover, there was no novel protein identified in any of the SCNT cattle or calves. In conclusion, variation in mitochondrial protein expression concentrations was observed in non-viable, neonatal SCNT calves and among SCNT individuals. This result implicates mitochondrial-related gene expression in early developmental loss of SCNT embryos. Comparative proteomic analysis represents an important tool for further studies on SCNT animals.

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.

Analysis of heterogeneous mitochondria distribution in somatic cell nuclear transfer porcine embryos

We previously reported that translocation of mitochondria from the oocyte cortex to the perinuclear area indicates positive developmental potential that was reduced in porcine somatic cell nuclear transfer (SCNT) embryos compared to in vitro220.). The present study is focused on distribution of donor cell mitochondria in intraspecies (pig oocytes; pig fetal fibroblast cells) and interspecies (pig oocytes; mouse fibroblast cells) reconstructed embryos by using either pig fibroblasts with mitochondria-stained MitoTracker CMXRos or YFP-mitochondria 3T3 cells (pPhi-Yellow-mito) as donor cells. Transmission electron microscopy was employed for ultrastructural analysis of pig oocyte and donor cell mitochondria. Our results revealed donor cell mitochondrial clusters around the donor nucleus that gradually dispersed into the ooplasm at 3 h after SCNT. Donor-derived mitochondria distributed into daughter blastomeres equally (82.8%) or unequally (17.2%) at first cleavage. Mitochondrial morphology was clearly different between donor cells and oocytes in which various complex shapes and configurations were seen. These data indicate that (1) unequal donor cell mitochondria distribution is observed in 17.2% of embryos, which may negatively influence development; and (2) complex mitochondrial morphologies are observed in IVF and SCNT embryos, which may influence mitochondrial translocation and affect development.

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

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

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.

Effect of oocyte mitochondrial DNA haplotype on bovine somatic cell nuclear transfer efficiency

The development capability of reconstructed bovine embryos via ovum pick-up (OPU)-somatic cell nuclear transfer (SCNT) technique has been influenced by the maternal lineage of oocyte cytoplasm, but the underlying mechanism remains unclear. Since mitochondria are the richest maternal-inherited organelle, in this study, we intended to clarify the effect of mtDNA haplotypes on cloning efficiency. By PCR-RFLP method, we identified mtDNA haplotypes A and B, differing in six restriction sites. Reconstructed embryos with haplotype A cytoplast achieved better fusion and blastocyst formation rate (64.6% and 39.4%), as compared with haplotype B (53.6% and 26.3%; P < 0.05). To further evaluate the role of mitochondria, the quantity of mtDNA, ATP content, and mRNA level of mtDNA-encoded COXI, COXIII in both oocytes were measured. Our data indicated that mtDNA copy number in haplotype A oocyte was significantly higher than that in haplotype B oocyte, both at the GV (10(5.03 +/- 0.69) vs. 10(4.81 +/- 0.86) copies/oocyte) and MII stages (10(5.31 +/- 0.71) vs. 10(5.13 +/- 0.63) copies/oocyte; logarithmically transformed values; P < 0.05). ATP content in type A oocyte was also greater at the GV (1.67 +/- 0.09 vs. 1.27 +/- 0.1 pmol) and MII stages (5.18 +/- 0.07 vs. 2.68 +/- 0.03 pmol; P < 0.05). Similarly, the mRNA expression level of mtDNA-encoded COXI and COXIII in haplotype A oocyte was significantly higher comparing to haplotype B oocyte (3.3 +/- 2.0 x 10(3) vs. 0.68 +/- 0.45 x 10(3); 24.9 +/- 10.5 x 10(3) vs. 9.4 +/- 3.3 x 10(3), respectively; P < 0.05). The data suggest that mitochondrial structure, quantity, and function may significantly affect the developmental competence of reconstructed embryos.

The Influence of Nuclear Content on Developmental Competence of Gaur × Cattle Hybrid In Vitro Fertilized and Somatic Cell Nuclear Transfer Embryos1

In nondomestic and endangered species, the use of domestic animal oocytes as recipients for exotic donor nuclei causes the normal pattern of cytoplasmic inheritance to be disrupted, resulting in the production of nuclear-cytoplasmic hybrids. Evidence suggests that conflict between nuclear and cytoplasmic control elements leads to a disruption of normal cellular processes, including metabolic function and cell division. This study investigated the effects of nuclear-cytoplasmic interactions on the developmental potential of interspecies embryos produced by in vitro fertilization and somatic cell nuclear transfer: cattle x cattle, gaur x cattle, hybrid x cattle. Cattle control and hybrid embryos were examined for development to the blastocyst stage and blastocyst quality, as determined by cell number and allocation, apoptosis incidence, and expression patterns of mitochondria-related genes. These analyses demonstrated that a 100% gaur nucleus within a domestic cattle cytoplasmic environment was not properly capable of directing embryo development in the later preimplantation stages. Poor blastocyst development accompanied by developmental delay, decreased cell numbers, and aberrant apoptotic and related gene expression profiles, all signs of disrupted cellular processes associated with mitochondrial function, were observed. Developmental potential was improved when at least a portion of the nuclear genome corresponded to the inherited cytoplasm, indicating that recognition of cytoplasmic components by the nucleus is crucial for proper cellular function and embryo development. A better understanding of the influence of the cytoplasmic environment on embryonic processes is necessary before interspecies somatic cell nuclear transfer can be considered a viable alternative for endangered species conservation.

Difficulties and possible solutions in the genetic management of mtDNA disease in the preimplantation embryo

Families who have had a child die of a severe, maternally inherited mitochondrial DNA (mtDNA) disease are usually desperate to avoid having further affected children. Here we discuss the problems of applying classical genetic management to mtDNA diseases (Poulton and Turnbull, 2000) and the biology underlying these problems. We explain why these disorders have lagged so far behind the genetics revolution. We then outline the directions in which management is likely to develop, including the use of preimplantation genetic diagnosis (PGD).

Cloning in companion animal, non-domestic and endangered species: can the technology become a practical reality?

Somatic cell nuclear transfer (SCNT) can provide a unique alternative for the preservation of valuable individuals, breeds and species. However, with the exception of a handful of domestic animal species, successful production of healthy cloned offspring has been challenging. Progress in species that have little commercial or research interest, including many companion animal, non-domestic and endangered species (CANDES), has lagged behind. In this review, we discuss the current and future status of SCNT in CANDES and the problems that must be overcome to improve pre- and post-implantation embryo survival in order for this technology to be considered a viable tool for assisted reproduction in these species.

Improved efficiency of bovine cloning by autologous somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) has been used for the cloning of various mammals. However, the rates of successful, healthy birth are generally poor. To improve cloning efficiency, we report the utilization of an ‘autologous SCNT’ cloning technique in which the somatic nucleus of a female bovine donor is transferred to its own enucleated oocyte recovered by ovum pick up, in contrast to the routine ‘allogeneic SCNT’ procedure using oocytes from unrelated females. Our results showed that embryos derived from autologous SCNThave significantly higher developmental competence than those derived from allogeneic SCNT, especiallyat the eight-cell (60 vs 44%), morula (45 vs 36%), and blastocyst (38 vs 23%) stages. The pregnancy and birth rates were also higher for the autologous (39 and 23%), compared to the allogeneic (22 and 6%) SCNT groups. Genome-wide histone3-lysine9 methylation profiles reveal that autologous SCNTembryos have less epigenetic defects than the allogeneic SCNTembryos. This study indicates that autologous SCNT can improve the efficiency of bovine cloning with less reprogramming deficiency.

Large Offspring or Large Placenta Syndrome? Morphometric Analysis of Late Gestation Bovine Placentomes from Somatic Nuclear Transfer Pregnancies Complicated by Hydrallantois

Somatic nuclear transfer (NT) in cattle is often complicated by fetal oversize (i.e., large offspring syndrome), hydrallantois, and placentomegaly in late gestation. The aims of this work were to obtain data on the placentome structure in NT-recipient cows with hydrallantois (NTH) and to relate these with fetal and placental weights to better understand the abnormalities observed in NTH pregnancies during the third trimester. Pregnant cows were slaughtered between Gestation Days 180 and 280. The fetuses were weighed, and the placentomes were numbered and weighed. Placentomes were examined by histologic and stereological techniques. Macroscopic data showed that placental overgrowth preceded fetal overgrowth, and the ratio of the fetal to the total placentome weight in the NTH group was lower than that in controls after Gestation Day 220. This suggests that placental overgrowth is due to placental default rather than due to fetal overgrowth, as shown also by stereological analysis showing primary deregulation of the growth of cotyledonary tissues. Observed alterations, such as thinning of the maternal epithelium within placentomes and increased trophoblastic surface, could be secondary adaptations. Thus, placental growth deregulations would be due to modifications of the expression of placental factors. Various examples of placental deficiency were observed, suggesting that some fetal abnormalities observed in NTH calves, such as enlarged heart, enlarged umbilical cord, and abdominal ascites, are consequences of placental dysfunction. Therefore, the condition described by the term "large offspring syndrome" might better be described by "large placenta syndrome," because this syndrome affects an average of 50% of late-gestation NT pregnancies. No conclusion can be drawn from this work on apparently normal pregnancies.

Mosaicism for mitochondrial DNA polymorphic variants in placenta has implications for the feasibility of prenatal diagnosis in mtDNA diseases

Women who have had a child with mitochondrial DNA (mtDNA) disease need to know the risk of recurrence, but this risk is difficult to estimate because mutant and wild-type (normal) mtDNA coexist in the same person (heteroplasmy). The possibility that a single sample may not reflect the whole organism both impedes prenatal diagnosis of most mtDNA diseases, and suggests radical alternative strategies such as nuclear transfer. We used naturally occurring mtDNA variants to investigate mtDNA segregation in placenta. Using large samples of control placenta, we demonstrated that the level of polymorphic heteroplasmic mtDNA variants is very similar in mother, cord blood and placenta. However, where placental samples were very small (< 10 mg) there was clear evidence of variation in the distribution of mtDNA polymorphic variants. We present the first evidence for variation in mutant load, that is, mosaicism for mtDNA polymorphic variants in placenta. This suggests that mtDNA mutants may segregate in placenta and that a single chorionic villous sample (CVS) may be unrepresentative of the whole placenta. Duplicates may be necessary where CVS are small. However, the close correlation of mutant load in maternal, fetal blood and placental mtDNA suggests that the average load in placenta does reflect the load of mutant mtDNA in the baby. Provided that segregation of neutral and pathogenic mtDNA mutants is similar in utero, our results are generally encouraging for developing prenatal diagnosis for mtDNA diseases. Identifying mtDNA segregation in human placenta suggests studies of relevance to placental evolution and to developmental biology.

Mitochondria and the success of somatic cell nuclear transfer cloning: from nuclear-mitochondrial interactions to mitochondrial complementation and mitochondrial DNA recombination

The overall success of somatic cell nuclear transfer (SCNT) cloning is rather unsatisfactory, both in terms of efficacy and from an animal health and welfare point of view. Most research activities have concentrated on epigenetic reprogramming problems as one major cause of SCNT failure. The present review addresses the limited success of mammalian SCNT from yet another viewpoint, the mitochondrial perspective. Mitochondria have a broad range of critical functions in cellular energy supply, cell signalling and programmed cell death and, thus, affect embryonic and fetal development, suggesting that inadequate or perturbed mitochondrial functions may adversely affect SCNT success. A survey of perinatal clinical data from human subjects with deficient mitochondrial respiratory chain activity has revealed a plethora of phenotypes that have striking similarities with abnormalities commonly encountered in SCNT fetuses and offspring. We discuss the limited experimental data on nuclear-mitochondrial interaction effects in SCNT and explore the potential effects in the context of new findings about the biology of mitochondria. These include mitochondrial fusion/fission, mitochondrial complementation and mitochondrial DNA recombination, processes that are likely to be affected by and impact on SCNT cloning. Furthermore, we indicate pathways that could link epigenetic reprogramming and mitochondria effects in SCNT and address questions and perspectives for future research.

The significance of mitochondria for embryo development in cloned farm animals

The role of mitochondria in remodeling of the donor cell nucleus in cloned animals has gained increased attention, as mitochondria interact in direct or indirect ways with the donor cell nuclear DNA. Mitochondria comprise 1% of the genetic material that is contributed to the developing embryo by the recipient oocyte and provide the energy that is required for embryo development. In this review we compare mitochondria distribution in various species and the importance of mitochondria distribution for embryo development. We also compare the inheritance pattern of mitochondria in cloned embryos that remains unresolved, as the donor cell nucleus is typically transferred with surrounding cytoplasm including mitochondria which become destroyed in some but not all species. We review the role of mitochondria in cloned farm animals with emphasis on nucleo-cytoplasmic interactions and consequences for embryo development.