Comparison of gene transcription in cloned bovine embryos produced by different nuclear transfer techniques

Induction of somatic cell haploidy by premature cell division

Canonical mitotic and meiotic cell divisions commence with replicated chromosomes consisting of two sister chromatids. Here, we developed and explored a model of premature cell division, where nonreplicated, G0/G1-stage somatic cell nuclei are transplanted to the metaphase cytoplasm of mouse oocytes. Subsequent cell division generates daughter cells with reduced ploidy. Unexpectedly, genome sequencing analysis revealed proper segregation of homologous chromosomes, resulting in complete haploid genomes. We observed a high occurrence of somatic genome haploidization in nuclei from inbred genetic backgrounds but not in hybrids, emphasizing the importance of sequence homology between homologs. These findings suggest that premature cell division relies on mechanisms similar to meiosis I, where genome haploidization is facilitated by homologous chromosome interactions, recognition, and pairing. Unlike meiosis, no evidence of recombination between somatic cell homologs was detected. Our study offers an alternative in vitro gametogenesis approach by directly reprogramming diploid somatic cells into haploid oocytes.

Choosing a culture medium for SCNT and iSCNT reconstructed embryos: from domestic to wildlife species

Over the past decades, in vitro culture media have been developed to successfully support IVF embryo growth in a variety of species. Advanced reproductive technologies, such as somatic cell nuclear transfer (SCNT), challenge us with a new type of embryo, with special nutritional requirements and altered physiology under in vitro conditions. Numerous studies have successfully reconstructed cloned embryos of domestic animals for biomedical research and livestock production. However, studies evaluating suitable culture conditions for SCNT embryos in wildlife species are scarce (for both intra- and interspecies SCNT). Most of the existing studies derive from previous IVF work done in conventional domestic species. Extrapolation to non-domestic species presents significant challenges since we lack information on reproductive processes and embryo development in most wildlife species. Given the challenges in adapting culture media and conditions from IVF to SCNT embryos, developmental competence of SCNT embryos remains low. This review summarizes research efforts to tailor culture media to SCNT embryos and explore the different outcomes in diverse species. It will also consider how these culture media protocols have been extrapolated to wildlife species, most particularly using SCNT as a cutting-edge technical resource to assist in the preservation of endangered species.

Synergistic effect of trichostatin A and scriptaid on the development of cloned rabbit embryos

The first successful rabbit SCNT was achieved more than one decade ago, yet rabbits remain one of the most difficult species to clone. The present study was designed to evaluate the effects of two histone deacetylase inhibitors (HDACis), namely trichostatin A (TSA) and scriptaid (SCP), on cloning efficiency in rabbits. The in vitro development, acetylation levels of histone H4 lysine 5 (H4K5), and octamer-binding transcription factor 4 (Oct-4) expression patterns of cloned embryos were systemically examined after various HDACi treatments. Supplementation of TSA (50 nM) or SCP (250 nM) in the culture medium for 6 hours improved blastocyst development rates of cloned embryos compared with the treatment without HDACi. The combined treatment with TSA (50 nM) and SCP (250 nM) further enhanced morula (58.6%) and blastocyst (49.4%) rates in vitro. More importantly, compared with single HDACi treatments, embryos with the combined treatment had a higher level of H4K5 and an increased total cell number (203.7 ± 14.4 vs. 158.9 ± 9.0 or 162.1 ± 8.2; P < 0.05) with a better Oct-4 expression pattern in hatching blastocysts, indicating substantially improved embryo quality. This was apparently the first report regarding Oct-4 expression in cloned rabbit embryos. We inferred that most cloned rabbit embryos had an aberrant inner cell mass (ICM) structure accompanied with abnormal spatial distribution of Oct-4 signals. This study demonstrated a synergistic effect of TSA and SCP treatments on cloned rabbit embryos, which might be useful to improve cloning efficiency in rabbits.

Fibroblast growth factor 2 promotes primitive endoderm development in bovine blastocyst outgrowths

Primitive endoderm (PE) is the second extraembryonic tissue to form during embryogenesis in mammals. The PE develops from pluripotent cells of the blastocyst inner cell mass. Experimental results described herein provide evidence that FGF2 stimulates PE development during bovine blastocyst development in vitro. Bovine blastocysts were cultured individually on a feeder layer-free, Matrigel-coated surface in the presence or absence of FGF2. A majority of blastocysts cultures formed outgrowths (76.8%) and the rate of outgrowth formation was not affected by FGF2 supplementation. However, supplementation with FGF2 increased the incidence of PE outgrowths on Days 13 and 15 after in vitro fertilization. Presumptive PE cultures contained cells with a phenotype distinct from trophectoderm (TE). Cell identity was validated by expression of GATA4 and GATA6 mRNA and transferrin protein, all markers of the PE lineage. Expression of GATA4 occurred coincident with blastocyst expansion and hatching. These cells did not express IFNT and CDX2 (TE lineage markers). Profiles of FGF receptor (FGFR) isoforms were distinct between PE and TE cultures. Specifically, FGFR1b and FGFR1c were the predominant FGFR transcripts in PE whereas FGFR2b transcripts were abundant in TE. Supplementation with FGF2 increased the mitotic index of PE but not TE. Moreover, FGF signaling appears important for initiation of PE formation in blastocysts, presumably by lineage committal from NANOG-positive epiblast cells, because chemical disruption of FGFR kinase activity with PD173074 reduces GATA4 expression and increases NANOG expression. Collectively, these results indicate that FGF2 and potentially other FGFs specify PE formation and mediate PE proliferation during early pregnancy in cattle.

Aberrant expression patterns of genes involved in segregation of inner cell mass and trophectoderm lineages in bovine embryos derived from somatic cell nuclear transfer

High rates of embryonic, fetal, or placental abnormalities have consistently been observed in bovine cloning. Segregation of inner cell mass (ICM) and trophectoderm (TE) lineages in early embryos is an important process for fetal and placental formation. In mouse embryos, differentiation of ICM and TE is regulated by various transcription factors, such as OCT-4, CDX2, and TEAD4, but molecular mechanisms that regulate differentiation in bovine embryos remain unknown. To clarify gene transcripts involved in segregation of ICM and TE lineages in bovine embryos, we examined the relative abundances of OCT-4, CDX2, TEAD4, GATA3, NANOG, and FGF4 transcripts in blastocyst embryos derived from in vitro fertilization (IVF). Furthermore, transcript levels of such genes in bovine embryos derived from somatic cell nuclear transfer (NT-SC) and in vivo (Vivo) were also compared. OCT-4, NANOG, and FGF4 transcript levels in IVF embryos were significantly higher in ICM than in TE. In contrast, the CDX2 transcript level was lower in ICM than in TE. In NT-SC embryos at the blastocyst stage, transcript levels of all genes except CDX2 were lower than that in Vivo embryos. In the elongated stage, expression levels of the six genes did not differ between NT-SC and Vivo embryos. We observed aberrant expression patterns of various genes involved in segregation of ICM and TE lineages in bovine NT-SC embryos. These results raise the possibility that abnormalities in the cloned fetus and placenta are related to the aberrant expression of genes involved in segregation and differentiation process in the early developmental stage.

Lineage-specific expression of heterochromatin protein 1gamma in post-compaction, in vitro-produced bovine embryos

Heterochromatin protein 1gamma (HP1gamma) is a highly conserved regulator of euchromatic and heterochromatic gene expression. Mammalian HP1gamma is essential for both successful preimplantation embryo development and maintenance of pluripotency in embryonic stem cells in vitro. Here, we describe HP1gamma protein localisation in matured (MII) bovine oocytes and IVF preimplantation embryos at defined developmental stages. HP1gamma is expressed in post-compaction embryos in a highly lineage-specific pattern. In embryonic stages preceding the maternal to embryonic transition (MET), HP1gamma protein was primarily cytoplasmic, whereas in 8-16-cell embryos (post MET), HP1gamma was primarily nuclear. Lineage-specific patterns of HP1gamma protein localisation become evident from compaction, being restricted to peripheral, extraembryonic cells at the morula and blastocyst stages (Days 7-9). Surprisingly, we detected HP1gamma mRNA in both embryonic and extraembryonic cells in blastocysts by fluorescence in situ hybridisation. In trophectoderm cells, HP1gamma protein was localised in specific patterns at the mitotic and interphase stages of the cell cycle. These results demonstrate lineage- and cell cycle-specific patterns of HP1gamma protein localisation in the post-compaction, preimplantation bovine embryo and raise interesting questions about the role of HP1gamma in early embryo development.

Changes in the expression of pluripotency-associated genes during preimplantation and peri-implantation stages in bovine cloned and in vitro produced embryos

In cattle, embryos elongate before implantation and after hatching. Changes in gene expression during this transition are not well studied. Especially important are variations in the expression of pluripotency-associated genes as a result of assisted reproductive biotechnologies, such as cloning and in vitro fertilization (IVF). We hypothesize that there will be a decline in the expression of key pluripotency-associated genes and an increase in the expression of IFN-tau in elongated embryos when compared with day-7 blastocysts. To test this we generated cloned and IVF bovine day-7 blastocyst and day-17 elongated embryos (day 0 = day of nucleus transfer or IVF). Gene expression in all embryos was assessed via RT-qPCR. OCT4 was overexpressed (p < 0.05) in the cloned blastocysts when compared with IVF. No differences in gene expression at this stage between cloned and IVF embryos were found for EOMES, NANOG and FGF4. At elongation EOMES, NANOG and FGF4 were upregulated in IVF embryos (p < 0.05). IFN-tau and OCT4 were expressed at similar levels. There were changes in the expression levels for all transcripts between blastogenesis and elongation. NANOG, IFN-tau and EOMES were overexpressed in all the elongated embryos (p < 0.05), FGF4 was underexpressed in both treatments. OCT4 dropped drastically in the cloned elongated embryos, but not in the IVF. Interestingly only adult donor cells (but not fetal) from which the cloned embryos originated also expressed high levels of OCT4. Our findings might help to understand the shift of gene expression during elongation and to identify key markers of embryonic development useful for embryo screening purposes.

Differential gene expression in bovine elongated (Day 17) embryos produced by somatic cell nucleus transfer and in vitro fertilization

Somatic cloning in cattle is associated with impaired embryo development, caused by inappropriate epigenetic reprogramming during embryogenesis; however, there is a paucity of data regarding gene expression at the critical elongation and peri-implantation stages. The objective of the present study was to identify genes differentially expressed in bovine cloned embryos at Day 17 of development (Day 0=day of nucleus transfer or IVF). Day 7 blastocysts (Hand Made Cloned or IVP) were transferred to recipient cattle and collected at Day 17. The efficiency of recovery of elongated embryos was similar, however cloned embryos elongated less than IVP embryos (91.8+/-45.8 vs. 174+/-50mm) and fewer had embryonic discs (63 vs. 83%). Qualitative and quantitative PCR detected expression of OCT4, NANOG, IFNtau, EOMES, FGF4, SOX2, and CDX2 in all IVP embryos. In most cloned embryos, NANOG and FGF4 were absent (verified by qPCR); NANOG, EOMES, and FGF4 were underexpressed, whereas IFNtau was overexpressed in cloned embryos. Based on qPCRs, other genes, i.e., SPARC, SNRB1, and CBPP22, were down-regulated in cloned embryos, whereas HSP70 and TDKP1 were overexpressed. In bovine microarrays, 47 genes (3.6%) were deregulated in cloned embryos, including several involved in trophoblast growth and differentiation. In conclusion, we inferred that these data were indicative of incomplete epigenetic reprogramming after cloning; this could lead to aberrant gene expression and subsequently early pregnancy loss. There was an apparent association between incomplete morphological elongation and aberrant reprogramming of a subset of genes critical for early embryonic development.

MicroRNA expression profiling of elongated cloned and in vitro-fertilized bovine embryos

The objective of this study was to identify microRNAs (miRNAs) expressed in bovine (Bos Taurus) cloned embryos at Day 17 of development (Day 0=day of nucleus transfer or in vitro fertilization) during elongation. Day 7 bovine expanded blastocysts produced by hand made cloning (HMC) or in vitro fertilization were bulk-transferred to synchronized recipient cattle (48 HMC embryos to 10 recipients and 28 in vitro-produced embryos to four recipients). Elongated embryos were retrieved at Day 17; miRNAs were isolated and subjected to microarray screening using custom composite slides spotted with human, mouse, and rat and in silico-predicted miRNAs. An initial profile of expressed miRNAs was determined in cloned embryos and somatic donor cells; this profile changed after somatic cell nucleus transfer, identifying differentially expressed miRNAs between cloned and in vitro-produced bovine embryos. Furthermore, microarray data were validated using a miRNA-specific quantitative reverse transcription-polymerase chain reaction (qRT-PCR) approach (miR-Q). There was an 83% correlation (P=0.01) between microarray and qPCR data. Based on qRT-PCR, correct reprogramming of some miRNAs from the donor cells was confirmed in cloned bovine embryos, whereas other somatic miRNAs were not appropriately reprogrammed. Some of the miRNAs that were equally reprogrammed clustered on the same chromosomal location in the bovine genome. In conclusion, reprogramming of miRNAs seemed to occur in cloned bovine embryos. This could have profound implications for elucidating nuclear reprogramming in somatic cloning, as well as for the role of miRNAs in preimplantation mammalian development.

Studies on gene expression in bovine embryos derived from somatic cell nuclear transfer

The low efficiency of animal production using somatic cell nuclear transfer (NT-SC) procedures is considered to be the result of an incomplete reprogramming of donor cell nucleus, which leads to abnormal expression of developmentally important genes. We analyzed the abundance of gene transcripts of Insulin-like growth factor (IGF)- related genes in single embryos derived from NT-SC, and determined changes in the transcription of IGF-related genes in blastocyst and elongated stage embryos produced by NT-SC. The present results of an analysis of mRNA transcripts at two different stages of development demonstrate that bovine NT-SC embryos show deviations in their expression patterns with respect to IGF-related genes. Changes in the expression of the IGF family may be responsible for the altered growth characteristics seen in fetuses and offspring originating from bovine embryos obtained using the NT-SC procedure.

Elongation and gene expression in bovine cloned embryos transferred to temporary recipients

Elongated embryos provide a unique source of information about trophoblastic differentiation, gene expression and maternal-embryonic interactions; however they are difficult and costly to obtain, especially elongated cloned embryos. One alternative is their production in heterologous temporary recipients such as sheep and goats. We aimed to produce elongated bovine cloned embryos using heterologous transfer to temporary recipients. Day-7 cloned cattle blastocysts were transferred to the uteri of ewes and goats and recovered as elongated structures at day 17. We evaluated elongation, length, presence of embryonic disc and expression of several important genes for embryonic development. We also produced homologous (cloned cattle embryos transferred into cattle uteri). Cloned bovine blastocysts were able to proceed with preimplantation development through elongation with high efficiency despite the species to which they were transferred. In qualitative and quantitative RT-PCR experiments we found differences in the pattern of gene expression among embryos recovered from different species. Sox2, Nanog and FGF-4 were markedly deregulated. No previous reports about the expression pattern of the studied genes had been published for elongated bovine cloned embryos produced in intermediate recipients, furthermore, the pattern of expression of Nanog, Oct4, Eomes, Cdx2, IFN-tau, Dicer, FGF-4 and Sox2 shown here are novel for elongated cloned bovine embryos created by hand-made cloning. Our data confirmed that sheep and goats can be used as temporary recipients. This model could serve as a basis for further research on gene expression and cellular changes during bovine peri-implantation development.

Overexpression of IGF2R and IGF1R mRNA in SCNT-produced goats survived to adulthood

The procedure of somatic cell nuclear transfer (SCNT) is likely to affect the expression level of growth-related genes especially imprinting genes. In this study, expressions of growth-related genes including three imprinting genes (H19, IGF2, and IGF2R) and four non-imprinting genes (IGF1, IGF1R, GHR, and GHSR) in adult nuclear transferred (NT) goats were investigated by real-time PCR. The expressions of these genes in adult clones were found largely normal, but IGF2R and IGF1R were more highly expressed in cloned goats than in non-NT goats (P < 0.01). Analysis on mono-allelic expression pattern of imprinting genes indicated that mono-allelic expression patterns of H19 and IGF2 in cloned goats were similar to that in non-NT goats. In addition, the sequence of goat IGF2 gene and the putative amino acid sequence were obtained. The 986 nucleotide cDNA of goat IGF2 gene contained an open-reading frame of 540 nucleotides coding for 179 amino acids. Both cDNA sequence and amino acid sequence of IGF2 in goat showed their higher homology with that in sheep than in cattle; the partial cDNA fragments of H19, IGF2R, GHSR, IGF1R, and GHR in goat were also cloned and sequenced, which shared higher sequence identities with those in sheep than in cattle.

Trichostatin A improves histone acetylation in bovine somatic cell nuclear transfer early embryos

Epigenetic aberrancies likely preclude correct and complete nuclear reprogramming following somatic cell nuclear transfer (SCNT), and may underlie the observed reduced viability of cloned embryos. In the present study, we tested the effects of the histone deacetylase inhibitor (HDACi), trichostatin A (TSA), on development and histone acetylation of cloned bovine preimplantation embryos. Our results indicated that treating activated reconstructed SCNT embryos with 50 nM TSA for 13 h produced eight-cell embryos with levels of acetylation of histone H4 at lysine 5 (AcH4K5) similar to fertilized counterparts and significantly greater than in control NT embryos (p < 0.005). Further, TSA treatment resulted in SCNT embryos with preimplantation developmental potential similar to fertilized counterparts, as no difference was observed in cleavage and blastocyst rates or in blastocyst total cell number (p > 0.05). Measurement of eight selected developmentally important genes in single blastocysts showed a similar expression profile among the three treatment groups, with the exception of Nanog, Cdx2, and DNMT3b, whose expression levels were higher in TSA-treated NT than in in vitro fertilized (IVF) embryos. Data presented herein demonstrate that TSA can improve at least one epigenetic mark in early cloned bovine embryos. However, evaluation of development to full-term is necessary to ascertain whether this effect reflects a true increase in developmental potential.

Putative imprinted gene expression in uniparental bovine embryo models

Altered patterns of gene expression and the imprinted status of genes have a profound effect on cell physiology and can markedly alter embryonic and fetal development. Failure to maintain correct imprinting patterns can lead to abnormal growth and behavioural problems, or to early pregnancy loss. Recently, it has been reported that the Igf2R and Grb10 genes are biallelically expressed in sheep blastocysts, but monoallelically expressed at Day 21 of development. The present study investigated the imprinting status of 17 genes in in vivo, parthenogenetic and androgenetic bovine blastocysts in order to determine the prevalence of this unique phenomenon. Specifically, the putatively imprinted genes Ata3, Impact, L3Mbtl, Magel2, Mkrn3, Peg3, Snrpn, Ube3a and Zac1 were investigated for the first time in bovine in vitro fertilised embryos. Ata3 was the only gene not detected. The results of the present study revealed that all genes, except Xist, failed to display monoallelic expression patterns in bovine embryos and support recent results reported for ovine embryos. Collectively, the data suggest that monoallelic expression may not be required for most imprinted genes during preimplantation development, especially in ruminants. The research also suggests that monoallelic expression of genes may develop in a gene- and time-dependent manner.

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

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

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

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

Aberrant gene expression in deceased transgenic cloned calves

Several transgenic cloned species have been obtained; however, the efficiency of transgenic cloning remains very low, even lower than cloning. Many experiments have demonstrated abnormal growth and development, and inappropriate gene expression in cloned animals. In this study, we examined the expression of 19 development-related genes in lungs of three normal controls and three aberrant transgenic cloned calves. Results showed in transgenic cloned calves, 84.2% genes had decreased expression levels, however, 5.3% genes had increased levels. This study suggests transgenic cloning and the aberrant expression would cause abnormal growth and development in transgenic cloned calves. To our knowledge, this is the first time that gene expression was examined in transgenic cloned cattle. These findings may have some implications in understanding the low efficiency of the transgenic cloning.

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

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

Comparative gene expression analysis of bovine nuclear-transferred embryos with different developmental potential by cDNA microarray and real-time PCR to determine genes that might reflect calf normality

Placental abnormalities are the main factor in the high incidence of somatic cell clone abnormalities. The expression of several trophoblast cell-specific molecules is enhanced during gestational days 7 to 14. To determine the possible genes whose expression patterns might reflect calf normality, we first compared the gene expression profiles on day 15 between in vitro-fertilized (IVF) embryos and two types of somatic cell nuclear-transferred embryos with either a high (FNT) or low (CNT) incidence of neonatal abnormalities using a cDNA microarray containing 16 of 21 placenta-specific genes developed from tissues collected across gestation. To identify significant genes from the screening of day 15 embryos, genes with a less than two-fold difference in expression between IVF and CNT embryos, and those with a greater than two-fold difference between IVF and FNT and between CNT and FNT were considered to contribute to clone abnormalities. These two comparisons revealed 18 down-regulated and 18 upregulated genes of the 1722 genes examined. We then examined the expression levels of 10 genes with known functions in eight-cell and blastocyst-stage embryos by real-time PCR. The mRNA expression pattern of interferon (IFN)-tau, a trophectoderm-related gene, differed between IVF, CNT, and FNT eight-cell embryos; few or none of the IVF or CNT eight-cell embryos expressed IFN-tau mRNA, but all eight-cell FNT embryos expressed IFN-tau. IFN-tau mRNA expression was significantly higher in IVF blastocysts, however, than in nuclear-transferred blastocysts. Average IFN-tau mRNA expression in FNT blastocysts was not different from that in CNT blastocysts, due to one CNT blastocyst with high expression. The precise relation between early expression of IFN-tau mRNA and inferior developmental potential in cloned embryos should be examined further.

Nuclear remodeling and nuclear reprogramming for making transgenic pigs by nuclear transfer

A better understanding of the cellular and molecular events that occur when a nucleus is transferred to the cytoplasm of an oocyte will permit the development of improved procedures for performing nuclear transfer and cloning. In some cases it appears that the gene(s) are reprogrammed, while in other cases there appears to be little effect on gene expression. Not only does the pattern of gene expression need to be reprogrammed, but other structures within the nucleus also need to be remodeled. While nuclear transfer works and transgenic and knockout animals can be created, it still is an inefficient process. However, even with the current low efficiencies this technique has proved very valuable for the production of animals that might be useful for tissue or organ transplantation to humans.

Pregnancy and fetal characteristics after transfer of vitrified in vivo and cloned bovine embryos

This study was conducted to examine pregnancy progression and fetal characteristics following transfer of vitrified bovine nuclear transfer versus in vivo-derived embryos. Nuclear transfer (NT) was conducted using cumulus cells collected from an elite Holstein-Friesian dairy cow. Expanding and hatching blastocysts on Day 7 were vitrified using liquid nitrogen surface vitrification. Day 7 in vivo embryos, produced using standard superovulation procedures applied to Holstein-Friesian heifers (n=6), were vitrified in the same way. Following warming, embryos were transferred to synchronized recipients (NT: n=65 recipients; Vivo: n=20 recipients). Pregnancies were monitored by ultrasound scanning on Days 25, 45 and 75 and a sample of animals were slaughtered at each time point to recover the fetus/placenta for further analyses. Significantly more animals remained pregnant after transfer of in vivo-derived embryos than NT embryos at all time points: Day 25 (95.0 versus 67.7%, P<0.05), Day 45 (92.8 versus 49.1%, P<0.01) and Day 75 (70.0 versus 20.8%, P<0.0). There was no significant difference (P=0.10) in the weight of the conceptus on Day 25 from NT transfers (1.14+/-0.23 g, n=8) versus in vivo transfers (0.75+/-0.19 g, n=8). On Day 45, there was no significant difference in the weight of either fetus (P=0.393) or membranes (P=0.167) between NT embryos (fetus: 2.76+/-0.40, n=12; membranes: 59.0+/-10.0, n=11) or in vivo-derived embryos (fetus: 2.60+/-0.15, n=6; membranes: 41.8+/-5.2, n=4). However, on Day 75 the weight of the fetus and several of the major organs were heavier from NT embryos. These data suggest that morphological abnormalities involving the fetus and the placenta of cloned pregnancies are manifested after Day 45.

Effect of exogenous DMNPE-caged ATP on in vitro-matured bovine oocytes prior to parthenogenetic activation, fertilisation and nuclear transfer

Adenosine triphosphate (ATP) plays an important role during fertilisation of the mammalian oocyte through its ability to alter the frequency and duration of calcium oscillations. It has also been shown that higher ATP levels correlate with increased developmental competence in bovine and human oocytes. During somatic cell nuclear transfer (NT), the incoming nucleus is remodelled extensively, undoubtedly using a variety of ATP-dependent enzymes. The aim of the present study was to determine whether additional exogenous ATP influences activation of parthenogenetic (PA), in vitro-fertilised (IVF) or cloned (NT) in vitro-matured bovine oocytes. Blastocyst development and cell numbers in PA embryos were found to increase in a dose-dependent manner following the photorelease of 0, 50, 100, 500 and 1000 microm DMNPE-caged ATP (adenosine 5'-triphosphate, P3-(1-(4,5-dimethoxy-2-nitrophenyl)ethyl) ester, disodium salt). No cleavage was found following release of 2 and 5 mm DMNPE-caged ATP or with DMNPE-caged ATP (not photoreleased). There were also no differences in blastocyst rates or cell numbers between the control group and groups treated with caged, but not photoreleased, ATP. The addition of exogenous ATP before IVF or to NT couplets did not result in a significant increase in blastocyst development or cell number. Embryo transfer is necessary to determine whether exogenous ATP can positively affect reprogramming, resulting in higher cloned pregnancy rates or live-term births.

Ribosomal RNA and nucleolar proteins from the oocyte are to some degree used for embryonic nucleolar formation in cattle and pig

The nucleolus is the site of ribosomal RNA (rRNA) and ribosome production. In the bovine primordial follicle oocyte, this organelle is inactive, but in the secondary follicle an active fibrillo-granular nucleolus develops and proteins involved in rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) localize to it. At the end of the oocyte growth phase, the nucleolus is inactivated again and transforms into a solid remnant. The nucleolar remnant is dissolved when meiosis is resumed. Upon fertilization, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities are engaged in the re-establishment of fibrillo-granular nucleoli at the major activation of the embryonic genome. This nucleolar formation can be classified into two different modes: one where nucleolus development occurs inside NPBs (internal; e.g. cattle) and the other where it occurs on the surface of NPBs (external; e.g. pig). Oocyte derived proteins engaged in late rRNA processing (nucleolin and nucleophosmin) may to some degree be re-used for nucleolar formation in the embryo, while the other nucleolar proteins require de novo embryonic transcription in order to be allocated to the developing nucleoli. Moreover, unprocessed rRNA inherited from the oocyte targets to the developing embryonic nucleoli. In conclusion, the nucleolus is important for the development of oocytes and embryos and may serve as a marker for the completion of oocyte growth and the normality of activation of the embryonic genome.

Gene profiling of cattle blastocysts derived from nuclear transfer, in vitro fertilization and in vivo development based on cDNA library

Gene expression analysis of cloned embryos would enable us to better understand the early biological events during preimplantation after NT (nuclear transfer). Routine RT-PCR and Northern-blot were limited because it could not analyze tens of thousands of genes at one time and were impeded by minimum material. Based on the developed RT-PCR methodology, we previously constructed cDNA libraries with equivalent to single embryo from the pooled AI-blastocysts (artificial insemination and in vivo developed blastocysts) of cattle. To identify gene expression profiles in NT- and IVF (in vitro fertilized)-blastocysts, and search for new candidate genes involved during this period, here we created cDNA sources from three types of blastocysts (AI-, IVF- and NT-blastocysts). The expressions of 60 genes previously identified from cDNA library were compared in three types of blastocyst. Results showed that the gene expression profile of NT-blastocysts was more similar to that of AI-blastocysts than that of created from IVF-blastocysts. Several important genes, such as Oct-4 and IFN-iota, only detected in the early embryonic development, were highly expressed in three types of blastocysts and showed no significant difference, it indicated that the donor nuclear undergone efficient reprogramming by the blastocyst stage and gained totipotential after nuclear transfer. The gene expression profiles in three types of blastocysts suggested that nuclear transfer and in vitro culture environments impaired the viability of embryos in different ways.

Bovine Oocytes with the Potential to Reprogram Somatic Cell Nuclei Have a Unique 23-kDa Protein, Phosphorylated Transcriptionally Controlled Tumor Protein (TCTP)

Despite the long-held assumption that reprogramming factors are present in mammalian oocytes at the second metaphase stage, the molecular nature of these factors is not known. Here, we demonstrated that oocytes with the potential to reprogram somatic cell nuclei have a unique 23-kDa protein, phosphorylated transcriptionally controlled tumor protein (TCTP). Injection of TCTP double-stranded RNA into germinal vesicle oocytes decreased the potential of nuclear-transferred (NT) oocytes, but not in vitro fertilized oocytes, to develop into blastocysts. Phosphorylated TCTP is considered to facilitate the first step of somatic cell reprogramming. After transfer of blastocysts that developed from NT oocytes fused with cumulus cells in which phosphorylated TCTP peptide was previously incorporated, the recipient pregnancy rate (47%) increased and the abortion rate (13%) decreased. Moreover, all seven cloned calves survived for at least 1 month after parturition, and had no morphologic abnormalities. The present study demonstrated that pretreatment of donor cells with phosphorylated TCTP peptide has a beneficial effect on the potential of bovine somatic cell nuclei to develop into normal cloned calves. Before widespread application of TCTP for bovine cloning, however, a large-scale embryo transfer study using different donor cell lines of various origins is necessary.

Transcriptional reprogramming of somatic cell nuclei during preimplantation development of cloned bovine embryos

While somatic cell nuclear transfer (SCNT) techniques have been successfully implemented in several species to produce cloned embryos and offspring, the efficiencies of the procedures are extremely low, possibly due to insufficient reprogramming of somatic nuclei. Employing GeneChip microarrays, we describe global gene expression analysis of bovine in vitro fertilized (IVF) and SCNT blastocysts as well as respective donor cell lines to characterize differences in their transcription profiles. Gene expression profiles of our donor cell lines were significantly different from each other; however, the SCNT and IVF blastocysts displayed surprisingly similar gene expression profiles, suggesting that a major reprogramming activity had been exerted on the somatic nuclei. Despite this remarkable phenomenon, a small set of genes appears to be aberrantly expressed and may affect critical developmental processes responsible for the failures observed in SCNT embryos. Our data provide the most comprehensive transcriptome database of bovine IVF and SCNT blastocysts to date.

Differential gene expression patterns in porcine nuclear transfer embryos reconstructed with fetal fibroblasts and mesenchymal stem cells

The present study compared the developmental ability and gene expression pattern at 4-cell, 8-cell, morula, and blastocyst stages of porcine nuclear transfer (NT) embryos from fetal fibroblasts (FFs) and mesenchymal stem cells (MSCs), in vitro fertilized (IVF), and in vivo derived embryos. MSC-NT embryos showed enhanced blastocyst formation, higher total cell number, and a low incidence of apoptosis compared to FF-NT embryos. Alterations in the expression pattern of genes implicated in transcription and pluripotency (Oct4, Stat3, Nanog), DNA methylation (Dnmt1, Dnmt3a), histone deacetylation (Hdac2), growth factor signaling, and imprinting (Igf2, Igf2r) and apoptosis (Bax, Bcl2) regulation were observed in NT embryos. The expression of transcripts in MSC-NT embryos more closely followed that of the in vivo derived embryos compared with FF-NT embryos. In conclusion, MSCs with a relatively undifferentiated genome might serve as suitable donors that could be more efficiently reprogrammed to re-activate expression of early embryonic genes in porcine NT.

Dynamic changes in the localization of five members of the methyl binding domain (MBD) gene family during murine and bovine preimplantation embryo development

There are five methyl binding domain (MBD) proteins characterized by a methyl CpG-binding domain. Four MBD proteins (MeCP2 and MBDs 1-3) are linked to transcriptional repression and one (MBD4), to DNA repair. During preimplantation development, the embryo undergoes global demethylation following fertilization and selective remethylation following the maternal to zygotic transition (MZT). This study characterized changes in MBD mRNA expression and protein localization during both murine and bovine preimplantation development. These species were selected because they undergo MZT at different developmental stages. Gene expression profiling during preimplantation development detected the presence of all MBDs examined, although stage and species-specific differences were observed. MBD2 was not expressed in murine or bovine oocytes and MeCP2 was not detected in murine blastocysts, subcellular protein localization was found to vary at time points critical in development. Most MBDs showed species-specificity in localization patterns and differences were found between individual MBDs. MBD1 localization is consistent with a novel role during MZT for both species. MBD3, known to play a crucial role in murine embryogenesis, was highly localized to the nucleus before and after, but not during the MZT in the bovine. MBD2, MBD4, and MeCP2 show varying patterns of localization which indicate possible roles in the early cleavage stages and in inner cell mass differentiation. Further experiments are currently underway to define discreet functional roles for specific MBDs during bovine preimplantation embryogenesis.

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.

Expression of insulin-like growth factors systems in cloned cattle dead within hours after birth

Cloning by somatic nuclear transfer is an inefficient process in which many of the cloned animals die shortly after birth and display organ abnormalities. In an effort to determine the possible roles IGFs played in neonatal death and organ abnormalities, we have examined expression patterns of eight genes in insulin-like growth factor (IGF) systems (IGF1, IGF2, IGF1R, IGF2R, IGFBP-1, IGFBP-2, IGFBP-3, and IGFBP-4) in six organs (heart, liver, spleen, lung, kidney, and brain) of both neonatal death cloned bovines (n = 9) and normal control calves (n = 3) produced by artificial insemination (AI) using real-time quantitative RT-PCR. The effect of the age of the fibroblast donor cell on the gene expression profiles was also investigated. Aberrant expressions of six genes (IGF2, IGF1R, IGF2R, IGFBP-2, IGFBP-3, and IGFBP-4) were found in some studied tissues, but the expression of two genes (IGF1 and IGFBP-1) had similar levels with the normal controls. For the studied genes, kidney was the organ that was most affected (five genes) by gene downregulation, whereas spleen was the organ that was not affected. The two upregulation genes were in brain, but both of downregulation and upregulation were found in the heart, liver, and lung. The expression of three genes (IGF2R, IGFBP-4, and IGF2) in some tissues showed significant differences between AF cell-derived and FF cell-derived clones. Our results suggest that aberrations in gene expression within IGF systems were found in most cloned bovine tissues of neonatal death. Because IGF systems play an important role in embryo development and organogenesis, the aberrant transcription patterns detected in these clones may contribute to the defects of organs reported in neonatal death of clones.

Simultaneous gene quantitation of multiple genes in individual bovine nuclear transfer blastocysts

During somatic cell nuclear transfer (NT), the transcriptional status of the donor cell has to be reprogrammed to reflect that of an embryo. We analysed the accuracy of this process by comparing transcript levels of four developmentally important genes (Oct4,Otx2,Ifitm3,GATA6), a gene involved in epigenetic regulation (Dnmt3a) and three housekeeping genes (β-actin, β-tubulinandGAPDH) in 21 NT blastocysts with that in genetically half-identicalin vitroproduced (IVP,n=19) andin vivo(n=15) bovine embryos. We have optimised an RNA-isolation and SYBR-green-based real-time RT-PCR procedure allowing the reproducible absolute quantification of multiple genes from a single blastocyst. Our data indicated that transcript levels did not differ significantly between stage and grade-matched zona-free NT and IVP embryos except for Ifitm3/Fragilis, which was expressed at twofold higher levels in NT blastocysts.Ifitm3expression is confined to the inner cell mass at day 7 blastocysts and to the epiblast in day 14 embryos. No ectopic expression in the trophectoderm was seen in NT embryos. Gene expression in NTand IVP embryos increased between two- and threefold for all eight genes from early to late blastocyst stages. This increase exceeded the increase in cell number over this time period indicating an increase in transcript number per cell. Embryo quality (morphological grading) was correlated to cell number for NT and IVP embryos with grade 3 blastocysts containing 30% fewer cells. However, only NT embryos displayed a significant reduction in gene expression (50%) with loss of quality. Variability in gene expression levels was not significantly different in NT, IVP orin vivoembryos but differed among genes, suggesting that the stringency of regulation is intrinsic to a gene and not affected by culture or nuclear transfer.Oct4levels exhibited the lowest variability. Analysing the total variability of all eight genes for individual embryos revealed thatin vivoembryos resembled each other much more than did NT and IVP blastocysts. Furthermore,in vivoembryos, consisting of 1.5-fold more cells, generally contained two- to fourfold more transcripts for the eight genes than did their cultured counterparts. Thus, culture conditions (in vivoversusin vitro) have greater effects on gene expression than does nuclear transfer when minimising genetic heterogeneity.

Exposure of mouse cumulus cell nuclei to porcine ooplasmic extract eliminates TATA box protein binding to chromatin, but has no effect on DNA methylation

PURPOSE

The low cloning efficiency with SCNT is due to incomplete or partial reprogramming of the donor somatic cell nuclei after microinjection into the enucleated oocyte. A possible solution may be to initiate nuclear reprogramming prior to SCNT.

METHODS

Pre-exposure of donor somatic cell nuclei to a novel porcine ooplasmic extract prior to microinjection could possibly extend the duration of exposure to ooplamic nuclear reprogramming factors. The effects of the porcine ooplamic extract on two major markers of nuclear preprogramming: (1) TATA box protein binding to chromation and (2) DNA methylation was investigated.

RESULTS

The results showed that pre-exposure of mouse cumulus cell nuclei to porcine ooplamic extract drastically reduced TATA box protein binding to chromatin, but had no effect on DNA methylation.

CONCLUSIONS

Pre-exposure to the porcine ooplasmic extract had some limited effects on nuclear reprogramming. Whether this can lead to enhanced cloning efficiency needs to be further investigated.

Human therapeutic cloning (NTSC)

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

Changes in the mRNA transcripts of insulin-like growth factor ligand, receptors and binding proteins in bovine blastocysts and elongated embryos derived from somatic cell nuclear transfer

The objective of this study was to determine changes in the transcription of insulin-like growth factor (IGF)-related genes in blastocyst (BC)- and elongated (EL)-stage embryos produced by nuclear transfer using somatic cells (NT-SC). Bovine BC (day 7)- and EL (day 15)-stage embryos were obtained from NT-SC or in vivo production (Vivo). The relative abundance of mRNA was examined by RT- real-time PCR. The transcript of IGF-II was only detected at the EL stage in both the NT-SC and Vivo embryos. The level of transcription of the IGF-I receptor (r) in the NT-SC embryos was decreased at the EL stage and was significantly (P<0.05) lower than at the BC stage. In contrast, the IGF-IIr levels did not differ significantly between the NT-SC and Vivo embryos, regardless of the developmental stage. IGF-binding protein (IGFBP)-2 levels were markedly decreased in the NT-SC and Vivo embryos at the EL stage (P<0.05). The IGFBP-3 level in Vivo was significantly (P<0.05) increased at the EL stage compared with at the BC stage. However, the IGFBP-3 levels in NT-SC embryos were unchanged and lower (P<0.05) than in the Vivo embryos at the EL stage. These results suggest that there are differences in the levels and changes in the transcription of IGF-related genes in bovine embryos produced by NT-SC compared with those produced by Vivo.

Developmental competence of human in vitro aged oocytes as host cells for nuclear transfer

BACKGROUND

Improving human nuclear transfer (NT) efficiencies is paramount for the development of patient-specific stem cell lines, although the opportunities remain limited owing to difficulties in obtaining fresh mature oocytes.

METHODS

Therefore, the developmental competence of aged, failed-to-fertilize human oocytes as an alternate cytoplasmic source for NT was assessed and compared with use of fresh, ovulation-induced oocytes. To further characterize the developmental potential of aged oocytes, parthenogenetic activation, immunocytochemical analysis of essential microtubule proteins involved in meiotic and mitotic division, and RT-PCR in single oocytes (n = 6) was performed to determine expression of oocyte-specific genes [oocyte-specific histone 1 (H1FOO), growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), zygote arrest 1 (ZAR1)] and microtubule markers [nuclear mitotic arrest (NuMA), minus-end directed motor protein HSET and the microtubule kinesin motor protein EG5].

RESULTS

For NT, enucleation and fusion rates of aged oocytes were significantly lower compared with fresh oocytes (P < 0.05). Cleavage rates and subsequent development were poor. In addition, parthenote cleavage was low. Immunocytochemical analysis revealed that many oocytes displayed aberrant expression of NuMA and EG5, had disrupted meiotic spindles and tetrapolar spindles. One of the six oocytes misexpressed GDF9, BMP15 and ZAR1. Two oocytes expressed EG5 messenger RNA (mRNA), and HSET and NuMA were not detectable. RT-PCR of mRNA for oocyte specific genes and microtubule markers in single aged oocytes.

CONCLUSIONS

Thus, aneuploidy and spindle defects may contribute to poor parthenogenetic development and developmental outcomes following NT.

Epigenetic characteristics of cloned and in vitro-fertilized swamp buffalo (Bubalus bubalis) embryos1

Swamp buffalos are becoming endangered due to reproductive inefficiencies. This is of concern because many countries depend heavily on their products. Somatic cell nuclear transfer (SCNT) is a potential strategy for preserving endangered species. To date, SCNT in swamp buffalo has succeeded in the creation of blastocyst embryos. However, development to term of SCNT swamp buffalos is extremely limited, and only 1 live birth has been reported. An abnormal epigenetic mechanism is suspected to be the cause of developmental failure, as is also seen in other species. The DNA methylation and histone acetylation are key players in epigenetic modification and display marked variability during embryonic preimplantation development. Knowledge of epigenetic modifications will aid in solving the developmental problems of SCNT embryos and improving reproductive technology in the swamp buffalo. The objective of this study was to determine the relationship between preimplantation embryonic development and 2 epigenetic patterns, global DNA methylation and histone acetylation, in SCNT and in vitro-fertilized (IVF) swamp buffalo embryos. In addition, we examined the correlations between those 2 mechanisms in the SCNT and IVF swamp buffalo embryos throughout the developmental stages using double immunostaining and quantification of the emission intensities using confocal microscopy. We discovered an aberrant methylation pattern in early preimplantation-stage swamp buffalo SCNT embryos. In addition, greater variability in the DNA methylation levels among nuclei within SCNT embryos was discovered. Hyperacetylation was also observed in SCNT embryos compared with IVF embryos at the 4- and 8-cell stages (P < 0.05). Dynamic changes and interplay between these 2 epigenetic mechanisms could be crucial for embryonic development during the early preimplantation period. The aberrancies uncovered here may contribute to the low efficiency of SCNT.

Nuclear transfer in cats and its application

Nuclear transfer (NT) technology is typically used for generating identical individuals, but it is also a powerful resource for understanding the cellular and molecular aspects of nuclear reprogramming. Most recently, the procedure has been used in humans for producing patient-specific embryonic stem cells. The successful application of NT in cats was demonstrated by the birth of domestic and non-domestic cloned kittens at a similar level of efficiency to that reported for other mammalian species. In cats, it has been demonstrated that either in vivo or in vitro matured oocytes can be used as donor cytoplasts. The length of in vitro oocyte maturation affects in vitro development of reconstructed embryos, and oocytes matured in vitro for shorter periods of time are the preferred source of donor cytoplasts. For NT, cat somatic cells can be synchronized into the G0/G1 phase of the cell cycle by using different methods of cell synchronization without affecting the frequency of in vitro development of cloned embryos. Also, embryo development to the blastocyst stage in vitro is not influenced by cell type, but the effect of cell type on the percentage of normal offspring produced requires evaluation. Inter-species NT has potential application for preserving endangered felids, as live offspring of male and female African wildcats (AWC, Felis silvestris lybica) have been born and pregnancies have been produced after transferring black-footed cat (Felis nigripes) cloned embryos into domestic cat (Felis silvestris catus) recipients. Also, successful in vitro embryo development to the blastocyst stage has been achieved after inter-generic NT of somatic cells of non-domestic felids into domestic cat oocytes, but no viable progeny have been obtained. Thus, while cat cytoplasm induces early nuclear remodeling of cell nuclei from a different genus, the high incidence of early embryo developmental arrest may be caused by abnormal nuclear reprogramming. Fetal resorption and abortions were frequently observed at various stages of pregnancy after transfer of AWC cloned embryos into domestic cat recipients. Abnormalities, such as abdominal organ exteriorization and respiratory failure and septicemia were the main causes of death in neonatal cloned kittens. Nonetheless, several live domestic and AWC cloned kittens have been born that are seemingly normal and healthy. It is important to continue evaluating these animals throughout their lives and to examine their capability for natural reproduction.

Anomalous mRNA levels of chromatin remodeling genes in swamp buffalo (Bubalus bubalis) cloned embryos

The swamp buffalo (Bubalus bubalis) is a multi-purpose animal in agriculture that is challenged by extinction due to low reproductive efficiency. Nuclear transfer (NT) has been used to preserve special breeds of buffalo, as well as to increase the number of animals. However, cloned buffalo embryos have impaired development, as in other species. To understand the chromatin remodeling activities in cloned embryos and to improve NT technology, we examined the expression profiles of five genes involved in DNA and histone modifications, DNMT1, DNMT3A, DNMT3B, HAT1 and HDAC1, in single swamp buffalo metaphase II oocytes, NT and in vitro fertilized (IVF) embryos from the two-cell to the blastocyst stage, by quantitative real time RT-PCR. We observed similar expression dynamics for all genes studied in the NT and IVF embryos: relatively constant levels of expression for all genes were found from the MII oocyte up to the eight-cell stage; the levels of mRNA for HAT1 and DNMT3B continued to be stably expressed up to the blastocyst stage; while dramatic increases were seen for DNMT3A and HDAC1. Alternatively, the levels of DNMT1 started to decrease at the eight-cell stage. Despite the similarity in the dynamics of gene expression, dramatic differences in the relative levels of these genes between NT and IVF embryos were observed. The expression levels of all DNA modifying genes were higher in the NT embryos than in the IVF embryos at the eight-cell and blastocyst stages. The genes HDAC1 and HAT1 were also expressed significantly higher at the blastocyst stage in the NT embryos. Our results suggested differences in chromatin remodeling between NT and IVF embryos and that lower levels of DNA passive demethylation and higher levels of DNA de novo methylation occurred in the NT embryos. These observations are novel in the species of buffalo, and may be associated with developmental failure of cloned buffalo embryos due to the transcriptional repression effect of most genes studied here.

Semen and reproductive profiles of genetically identical cloned bulls

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

Differences in gene expression patterns between somatic cell nuclear transfer embryos constructed with either rabbit granulosa cells or their derivatives

Successful production of offspring by somatic cell nuclear transfer (SCNT) is affected by the nature of the donor cells used. The purpose of this study was to determine whether characteristic changes induced in donor cells by culture conditions influenced gene expression patterns in the resultant SCNT embryos. Rabbit granulosa cells (rGC) were cultured under different conditions, either with or without hCG, and the two derivative cell types obtained (named respectively cGC+ and cGC-) were used as donor cells for SCNT. There were characteristic differences between fresh rGC and the two derivative cell types: p450scc expression and progesterone secretion were both higher in cGC+ than in cGC-; expression of bmp4 and fgfr2 was decreased in cGC+ and cGC- compared with rGC; and cGC+ and cGC- cell types gained collagenIV expression. Use of fresh rGC, or cGC+ and cGC- derivative cells, did not alter either the developmental potencies of SCNT oocytes or cell numbers at the blastocyst stage. The expression patterns of four genes (bmp4, fgfr2, gata4, oct3/4) in SCNT embryos and in fertilized embryos were analyzed by quantitative RT-PCR. We found that oct3/4 was expressed in all embryos. The expression patterns of the other three genes showed considerable variation between the different types of embryo: bmp4 was found in most fertilized embryos but only some of rGC and none of cGC+ and cGC- derived SCNT embryos; fgfr2 was present in fertilized embryos but was present in some rGC and cGC- NT embryos and in all cGC+ NT embryos; gata4 was not expressed in fertilized embryos but was present in a few rGC and cGC+ NT embryos and in most cGC- NT embryos. Our results suggest that the gene expression patterns in SCNT embryos derived from granulosa donor cells are affected by characteristic changes to the cells during in vitro culture.

Gene expression profiling of individual bovine nuclear transfer blastocysts

During somatic cell nuclear transfer the gene expression profile of the donor cell has to be changed or reprogrammed extensively to reflect that of a normal embryo. In this study we focused on the switching on of embryonic genes by screening with a microarray consisting of 5000 independent cDNA isolates derived from a bovine blastocyst library which we constructed for this purpose. Expression profiling was performed using linearly amplified RNA from individual day 7 nuclear transfer (NT) and genetically half-identicalin vitroproduced (IVP) blastocysts. We identified 92 genes expressed at lower levels in NT embryos whereas transcripts of 43 genes were more abundant in NT embryos (P≤ 0.05, ≥ 1.5-fold change). A range of functional categories was represented among the identified genes, with a preponderance of constitutively expressed genes required for the maintenance of basal cellular function. Using a stringent quantitative SYBR-green real time RT-PCR based approach we found, when comparing the means of the expression levels of a larger set of individual embryos, that differences were small (< 2-fold) and only significant for two of the seven analysed genes (KRT18,SLC16A1). Notably, examination of transcript levels of a single gene in individual embryos could not distinguish an NT from a control embryo. This unpredictability of individual gene expression on a global background of multiple gene expression changes argues for a predominantly stochastic nature of reprogramming errors.

Messenger RNA expression patterns in bovine embryos derived from in vitro procedures and their implications for development

The preimplantation bovine embryo is initially under the control of maternal genomic information that is accumulated during oogenesis. The genetic programme of development soon becomes dependent on new transcripts derived from activation of the embryonic genome. The early steps in development, including the timing of the first cleavage, activation of the embryonic genome, compaction and blastocyst formation, can be affected by the culture media and conditions, as well as the production procedure itself. These perturbations can possibly result in a marked decrease in the quality of the resulting blastocysts and may even affect the viability of offspring born after transfer. In vitro procedures such as in vitro production and somatic nuclear transfer of bovine embryos have been shown to be correlated with significant up- or downregulation, de novo induction or silencing of genes critical for undisturbed fetal and neonatal development. These alterations are likely to be caused by epigenetic modifications, such as DNA methylation and histone modifications. Analysis of perturbed epigenetic reprogramming and of the related phenomena, such as genomic imprinting and X-chromosome inactivation, in bovine embryos is promising for understanding the underlying mechanisms of developmental abnormalities, such as large offspring syndrome.

Placental abnormalities associated with post-natal mortality in sheep somatic cell clones

We report on cloning experiments designed to explore the causes of peri- and post-natal mortality of cloned lambs. A total of 93 blastocysts obtained by nuclear transfer of somatic cells (granulosa cells) were transferred into 41 recipient ewes, and pregnancies were monitored by ultrasound scanning. In vitro derived, fertilized embryos (IVF, n=123) were also transferred to assess oocyte competence, and naturally mated ewes (n=120) were analysed as well. Cloned embryos developed to the blastocyst stage and implanted at the same rate as IVF embryos. After day 30 of gestation, however, dramatic losses occurred, and only 12 out of 93 (13%) clones reached full-term development, compared to 51 out of 123 (41.6%) lambs born from the IVF control embryos. Three full-term lamb clones were delivered stillborn, as a result of placental degeneration. A further five clone recipients developed hydroallantois. Their lambs died within 24h following delivery by caesarian section, and displayed degenerative lesions in liver and kidney resulting from the severe hydroallantois. One set of twins was delivered by assisted parturition at day 150, but died 24h later due to respiratory distress syndrome. The remaining two clone recipients underwent caesarian section, and the corresponding two lambs displayed signs of respiratory dysfunction and died at approximately 1 month of age due to a bacterial complication. Blood samples collected from the cloned lambs after birth revealed a wide range of abnormalities indicative of kidney and liver dysfunction. Macroscopical and histopathological examination of the placentae revealed a marked reduction in vascularization, particularly at the apex of the villous processes, as well as a loss of differentiation of the trophoblastic epithelium. Our results strongly suggest that post-mortality in cloned lambs is mainly caused by placental abnormalities.

Analysis of Development-Related Gene Expression in Cloned Bovine Blastocysts with Different Developmental Potential

The high incidence of abnormalities in cloned calves is a most serious problem for bovine somatic cell nuclear transfer (NT) technology. Because there is little information on the differences in mRNA expression in cloned blastocysts with donor cells of different sex and origin, we compared development-related gene expression in two types of cloned bovine blastocysts with different potentials to develop into normal calves, a female adult cumulus cell line (high potential to develop into live calves) and a male fibroblast cell line (low potential to develop into live calves) to examine the correlation between the normality of cloned calves and blastocyst mRNA expression patterns. We analyzed 12 genes involved in apoptosis, growth factor signaling, metabolism, and DNA methylation in blastocysts originating from two types of donor cells and in vitro-fertilized blastocysts using quantitative real-time polymerase chain reaction. Expression of the pro-apoptotic Bax gene and anti-apoptotic Bcl-2 and Glut-1 genes in fibroblast-derived blastocysts was significantly higher than in cumulus cell-derived and in vitro-fertilized blastocysts. The high Bcl-2 and Glut-1 gene expression suggests that some embryonic cells with damaged DNA in fibroblast-derived blastocysts are not removed, and their descendants later manifest abnormal placenta or fetus formation. Transfer of pre-selected cloned blastocysts into recipients is required, however, to determine whether the expression pattern of these apoptosis-related genes reflects differences in the potential to develop into normal calves.