Nuclear cloning and epigenetic reprogramming of the genome

Interplay between the miRNome and the epigenetic machinery: Implications in health and disease

Epigenetics refers to functionally relevant genomic changes that do not involve changes in the basic nucleotide sequence. Majorly, these are of two types: DNA methylation and histone modifications. Small RNA molecules called miRNAs are often thought to mediate post-transcriptional epigenetic changes by mRNA degradation or translational attenuation. While DNA methylation and histone modifications have their own independent effects on various cellular events, several reports are suggestive of an obvious interplay between these phenomena and the miRNA regulatory program within the cell. Several miRNAs like miR-375, members of miR-29 family, miR-34, miR-200, and others are regulated by DNA methylation and histone modifications in various types of cancers and metabolic diseases. On the other hand, miRNAs like miR-449a, miR-148, miR-101, miR-214, and miR-128 target members of the epigenetic machinery and their dysregulation leads to diverse cellular aberrations. In spite of being independent cellular events, emergence of such reports that suggest a connection between DNA methylation, histone modification, and miRNA function in several diseases indicate that this connecting axis offers a valuable target with great therapeutic potential that might be exploited for disease management. We review the current status of crosstalk between the major epigenetic modifications and the miRNA machinery and discuss this in the context of health and disease.

Nuclear Treatment and Cell Cycle Synchronization for the Purpose of Mammalian and Primate Somatic Cell Nuclear Transfer (SCNT)

Mammalian somatic cell nuclear transfer (SCNT) is a technically and biologically challenging procedure inducing rapid reprogramming of the nucleus from the differentiated into the totipotent state in a few hours. This procedure was initially successfully accomplished in farm animals, then in rodents, and more recently in primates and in humans. Though ethical concerns regarding SCNT still exist, this procedure can be utilized to generate patient and disease-specific pluripotent embryonic stem cell lines, which carry a great promise in improving our understanding of major disease conditions and a hope for better therapies and regenerative medicine. In this section, we will survey the existing literature and describe how mouse SCNT is performed and the importance of donor cell treatment and cycle synchronization prior to SCNT.

Screening somatic cell nuclear transfer parameters for generation of transgenic cloned cattle with intragenomic integration of additional gene copies that encode bovine adipocyte-type fatty acid-binding protein (A-FABP)

Somatic cell nuclear transfer (SCNT) is frequently used to produce transgenic cloned livestock, but it is still associated with low success rates. To our knowledge, we are the first to report successful production of transgenic cattle that overexpress bovine adipocyte-type fatty acid binding proteins (A-FABPs) with the aid of SCNT. Intragenomic integration of additional A-FABP gene copies has been found to be positively correlated with the intramuscular fat content in different farm livestock species. First, we optimized the cloning parameters to produce bovine embryos integrated with A-FABP by SCNT, such as applied voltage field strength and pulse duration for electrofusion, morphology and size of donor cells, and number of donor cells passages. Then, bovine fibroblast cells from Qinchuan cattle were transfected with A-FABP and used as donor cells for SCNT. Hybrids of Simmental and Luxi local cattle were selected as the recipient females for A-FABP transgenic SCNT-derived embryos. The results showed that a field strength of 2.5 kV/cm with two 10-μs duration electrical pulses was ideal for electrofusion, and 4-6th generation circular smooth type donor cells with diameters of 15-25 μm were optimal for producing transgenic bovine embryos by SCNT, and resulted in higher fusion (80%), cleavage (73%), and blastocyst (27%) rates. In addition, we obtained two transgenic cloned calves that expressed additional bovine A-FABP gene copies, as detected by PCR-amplified cDNA sequencing. We proposed a set of optimal protocols to produce transgenic SCNT-derived cattle with intragenomic integration of ectopic A-FABP-inherited exon sequences.

Effect of Cell Cycle Interactions and Inhibition of Histone Deacetylases on Development of Porcine Embryos Produced by Nuclear Transfer

The aim of this study was to evaluate if the positive effects of inhibiting histone deacetylase enzymes on cell reprogramming and development of somatic cell nuclear transfer (SCNT) embryos is affected by the cell cycle stage of nuclear donor cells and host oocytes at the time of embryo reconstruction. SCNT embryos were produced with metaphase II (MII) or telophase II (TII) cytoplasts and nuclear donor cells that were either at the G1-0 or G2/M stages. Embryos reconstructed with the different cell cycle combinations were treated or not with the histone deacetylase inhibitor (HDACi) Scriptaid for 15 h and then cultured in vitro for 7 days. Embryos reconstructed with MII-G1-0 and TII-G2/M developed to the blastocyst stage with a higher frequency compared to the other groups, confirming the importance of cell cycle interactions on cell reprogramming and SCNT embryo development. Treatment with HDACi improved development of SCNT embryos produced with MII but not TII cytoplasts, independently of the cell cycle stage of nuclear donor cells. These findings provide evidence that the positive effect of HDACi treatment on development of SCNT embryos depends upon cell cycle interactions between the host cytoplast and the nuclear donor cells.

Aberrant Expression of TIMP-2 and PBEF Genes in the Placentae of Cloned Mice Due to Epigenetic Reprogramming Error

Cloned mice derived from somatic or ES cells show placental overgrowth (placentomegaly) at term. We had previously analyzed cloned and normal mouse placentae by using two-dimensional gel electrophoresis and mass spectrometry to identify differential protein expression patterns. Cloned placentae showed upregulation of tissue inhibitor of metalloproteinase-2 (TIMP-2), which is involved in extracellular matrix degradation and tissue remodeling, and downregulation of pre-B cell colony enhancing factor 1 (PBEF), which inhibits apoptosis and induces spontaneous labor. Here, we used Western blotting to further analyze the protein expression levels of TIMP-2 and PBEF in cloned placentae derived from cumulus cells, TSA-treated cumulus cells, intracytoplasmic sperm injection (ICSI), and natural mating (NM control). Cloned and TSA-treated cloned placentae had higher expression levels of TIMP-2 compared with NM control and ICSI-derived placentae, and there was a positive association between TIMP-2 expression and the placental weight of cloned mouse concepti. Conversely, PBEF protein expression was significantly lower in cloned and ICSI placentae compared to NM controls. To examine whether the observed differences were due to abnormal gene expression caused by faulty epigenetic reprogramming in clones, we investigated DNA methylation and histone modification in the promoter regions of the genes encoding TIMP-2 and PBEF. Sodium bisulfite sequencing did not reveal any difference in DNA methylation between cloned and NM control placentae. However, ChIP assays revealed that the level of H3-K9/K14 acetylation at the TIMP-2 locus was higher in cloned placentae than in NM controls, whereas acetylation of the PBEF promoter was lower in cloned and ICSI placenta versus NM controls. These results suggest that cloned placentae appear to suffer from failure of histone modification-based reprogramming in these (and potentially other) developmentally important genes, leading to aberrant expression of their protein products. These changes are likely to be involved in generating the abnormalities seen in cloned mouse placentae, including enlargement and/or a lack of proper placental function.

Influences of somatic donor cell sex on in vitro and in vivo embryo development following somatic cell nuclear transfer in pigs

Objective

The present study investigates pre- and post-implantation developmental competence of nuclear-transferred porcine embryos derived from male and female fetal fibroblasts.

Methods

Male and female fetal fibroblasts were transferred to in vitro-matured enucleated oocytes and in vitro and in vivo developmental competence of reconstructed embryos was investigated. And, a total of 6,789 female fibroblast nuclear-transferred embryos were surgically transferred into 41 surrogate gilts and 4,746 male fibroblast nuclear-transferred embryos were surgically transferred into 25 surrogate gilts.

Results

The competence to develop into blastocysts was not significantly different between the sexes. The mean cell number of female and male cloned blastocysts obtained by in vivo culture (143.8±10.5 to 159.2±14.8) was higher than that of in vitro culture of somatic cell nuclear transfer (SCNT) groups (31.4±8.3 to 33.4±11.1). After embryo transfer, 5 pregnant gilts from each treatment delivered 15 female and 22 male piglets. The average birth weight of the cloned piglets, gestation length, and the postnatal survival rates were not significantly different (p<0.05) between sexes.

Conclusion

The present study found that the sex difference of the nuclear donor does not affect the developmental rate of porcine SCNT embryos. Furthermore, postnatal survivability of the cloned piglets was not affected by the sex of the donor cell.

Epigenetic regulation of cognition: A circumscribed review of the field

The last decade has been marked by an increased interest in relating epigenetic mechanisms to complex human behaviors, although this interest has not been balanced, accentuating various types of affective and primarily ignoring cognitive functioning. Recent animal model data support the view that epigenetic processes play a role in learning and memory consolidation and help transmit acquired memories even across generations. In this review, we provide an overview of various types of epigenetic mechanisms in the brain (DNA methylation, histone modification, and noncoding RNA action) and discuss their impact proximally on gene transcription, protein synthesis, and synaptic plasticity and distally on learning, memory, and other cognitive functions. Of particular importance are observations that neuronal activation regulates the dynamics of the epigenome's functioning under precise timing, with subsequent alterations in the gene expression profile. In turn, epigenetic regulation impacts neuronal action, closing the circle and substantiating the signaling pathways that underlie, at least partially, learning, memory, and other cognitive processes.

An Improved System for Generation of Diploid Cloned Porcine Embryos Using Induced Pluripotent Stem Cells Synchronized to Metaphase

Pigs provide outstanding models of human genetic diseases due to their striking similarities with human anatomy, physiology and genetics. Although transgenic pigs have been produced using genetically modified somatic cells and nuclear transfer (SCNT), the cloning efficiency was extremely low. Here, we report an improved method to produce diploid cloned embryos from porcine induced pluripotent stem cells (piPSCs), which were synchronized to the G2/M stage using a double blocking method with aphidicolin and nocodazole. The efficiency of this synchronization method on our piPSC lines was first tested. Then, we modified our traditional SCNT protocol to find a workable protocol. In particular, the removal of a 6DMAP treatment post-activation enhanced the extrusion rate of pseudo-second-polar bodies (p2PB) (81.3% vs. 15.8%, based on peak time, 4hpa). Moreover, an immediate activation method yielded significantly more blastocysts than delayed activation (31.3% vs. 16.0%, based on fused embryos). The immunofluorescent results confirmed the effect of the 6DMAP treatment removal, showing remarkable p2PB extrusion during a series of nuclear transfer procedures. The reconstructed embryos from metaphase piPSCs with our modified protocol demonstrated normal morphology at 2-cell, 4-cell and blastocyst stages and a high rate of normal karyotype. This study demonstrated a new and efficient way to produce viable cloned embryos from piPSCs when synchronized to the G2/M phase of the cell cycle, which may lead to opportunities to produce cloned pigs from piPSCs more efficiently.

A transgenic-cloned pig model expressing non-fluorescent modified Plum

Genetically modified pigs that express fluorescent proteins such as green and red fluorescent proteins have become indispensable biomedical research tools in recent years. Cell or tissue transplantation studies using fluorescent markers should be conducted, wherein the xeno-antigenicity of the fluorescent proteins does not affect engraftment or graft survival. Thus, we aimed to create a transgenic (Tg)-cloned pig that was immunologically tolerant to fluorescent protein antigens. In the present study, we generated a Tg-cloned pig harboring a derivative of Plum modified by a single amino acid substitution in the chromophore. The cells and tissues of this Tg-cloned pig expressing the modified Plum (mPlum) did not fluoresce. However, western blot and immunohistochemistry analyses clearly showed that the mPlum had the same antigenicity as Plum. Thus, we have obtained primary proof of principle for creating a cloned pig that is immunologically tolerant to fluorescent protein antigens.

PCI-24781 can improve in vitro and in vivo developmental capacity of pig somatic cell nuclear transfer embryos

OBJECTIVE

To examine the effect of PCI-24781 (abexinostat) on the blastocyst formation rate in pig somatic cell nuclear transferred (SCNT) embryos and acetylation levels of the histone H3 lysine 9 and histone H4 lysine 12.

RESULTS

Treatment with 0.5 nM PCI-24781 for 6 h significantly improved the development of cloned embryos, in comparison to the control group (25.3 vs. 10.5 %, P < 0.05). Furthermore, PCI-24781 treatment led to elevated acetylation of H3K9 and H4K12. TUNEL assay and Hoechst 33342 staining revealed that the percentage of apoptotic cells in blastocysts was significantly lower in PCI-24781-treated SCNT embryos than in untreated embryos. Also, PCI-24781-treated embryos were transferred into three surrogate sows, one of whom became pregnant and two fetuses developed.

CONCLUSION

PCI-24781 improves nuclear reprogramming and the developmental potential of pig SCNT embryos.

How electromagnetic fields can influence adult stem cells: positive and negative impacts

The electromagnetic field (EMF) has a great impact on our body. It has been successfully used in physiotherapy for the treatment of bone disorders and osteoarthritis, as well as for cartilage regeneration or pain reduction. Recently, EMFs have also been applied in in vitro experiments on cell/stem cell cultures. Stem cells reside in almost all tissues within the human body, where they exhibit various potential. These cells are of great importance because they control homeostasis, regeneration, and healing. Nevertheless, stem cells when become cancer stem cells, may influence the pathological condition. In this article we review the current knowledge on the effects of EMFs on human adult stem cell biology, such as proliferation, the cell cycle, or differentiation. We present the characteristics of the EMFs used in miscellaneous assays. Most research has so far been performed during osteogenic and chondrogenic differentiation of mesenchymal stem cells. It has been demonstrated that the effects of EMF stimulation depend on the intensity and frequency of the EMF and the time of exposure to it. However, other factors may affect these processes, such as growth factors, reactive oxygen species, and so forth. Exploration of this research area may enhance the development of EMF-based technologies used in medical applications and thereby improve stem cell-based therapy and tissue engineering.

Genetic and environmental influences interact with age and sex in shaping the human methylome

The methylome is subject to genetic and environmental effects. Their impact may depend on sex and age, resulting in sex- and age-related physiological variation and disease susceptibility. Here we estimate the total heritability of DNA methylation levels in whole blood and estimate the variance explained by common single nucleotide polymorphisms at 411,169 sites in 2,603 individuals from twin families, to establish a catalogue of between-individual variation in DNA methylation. Heritability estimates vary across the genome (mean=19%) and interaction analyses reveal thousands of sites with sex-specific heritability as well as sites where the environmental variance increases with age. Integration with previously published data illustrates the impact of genome and environment across the lifespan at methylation sites associated with metabolic traits, smoking and ageing. These findings demonstrate that our catalogue holds valuable information on locations in the genome where methylation variation between people may reflect disease-relevant environmental exposures or genetic variation.

Differential impact of genetic and environmental influences on DNA methylation may result in sex- and age-related physiological variation and disease susceptibility. By analysing DNA methylome of 2,603 individuals from twin families, here, the authors establish a catalogue of between-individual variation in DNA methylation.

Epigenomic analysis detects aberrant super-enhancer DNA methylation in human cancer

BACKGROUND

One of the hallmarks of cancer is the disruption of gene expression patterns. Many molecular lesions contribute to this phenotype, and the importance of aberrant DNA methylation profiles is increasingly recognized. Much of the research effort in this area has examined proximal promoter regions and epigenetic alterations at other loci are not well characterized.

RESULTS

Using whole genome bisulfite sequencing to examine uncharted regions of the epigenome, we identify a type of far-reaching DNA methylation alteration in cancer cells of the distal regulatory sequences described as super-enhancers. Human tumors undergo a shift in super-enhancer DNA methylation profiles that is associated with the transcriptional silencing or the overactivation of the corresponding target genes. Intriguingly, we observe locally active fractions of super-enhancers detectable through hypomethylated regions that suggest spatial variability within the large enhancer clusters. Functionally, the DNA methylomes obtained suggest that transcription factors contribute to this local activity of super-enhancers and that trans-acting factors modulate DNA methylation profiles with impact on transforming processes during carcinogenesis.

CONCLUSIONS

We develop an extensive catalogue of human DNA methylomes at base resolution to better understand the regulatory functions of DNA methylation beyond those of proximal promoter gene regions. CpG methylation status in normal cells points to locally active regulatory sites at super-enhancers, which are targeted by specific aberrant DNA methylation events in cancer, with putative effects on the expression of downstream genes.

Designer nanoparticle: nanobiotechnology tool for cell biology

This article discusses the use of nanotechnology for subcellular compartment isolation and its application towards subcellular omics. This technology review significantly contributes to our understanding on use of nanotechnology for subcellular systems biology. Here we elaborate nanobiotechnology approach of using superparamagnetic nanoparticles (SPMNPs) optimized with different surface coatings for subcellular organelle isolation. Using pulse-chase approach, we review that SPMNPs interacted differently with the cell depending on its surface functionalization. The article focuses on the use of functionalized-SPMNPs as a nanobiotechnology tool to isolate high quality (both purity and yield) plasma membranes and endosomes or lysosomes. Such nanobiotechnology tool can be applied in generating subcellular compartment inventories. As a future perspective, this strategy could be applied in areas such as immunology, cancer and stem cell research.

Genome-Wide Dynamic Profiling of Histone Methylation during Nuclear Transfer-Mediated Porcine Somatic Cell Reprogramming

The low full-term developmental efficiency of porcine somatic cell nuclear transfer (SCNT) embryos is mainly attributed to imperfect epigenetic reprogramming in the early embryos. However, dynamic expression patterns of histone methylation involved in epigenetic reprogramming progression during porcine SCNT embryo early development remain to be unknown. In this study, we characterized and compared the expression patterns of multiple histone methylation markers including transcriptionally repressive (H3K9me2, H3K9me3, H3K27me2, H3K27me3, H4K20me2 and H4K20me3) and active modifications (H3K4me2, H3K4me3, H3K36me2, H3K36me3, H3K79me2 and H3K79me3) in SCNT early embryos from different developmental stages with that from in vitro fertilization (IVF) counterparts. We found that the expression level of H3K9me2, H3K9me3 and H4K20me3 of SCNT embryos from 1-cell to 4-cell stages was significantly higher than that in the IVF embryos. We also detected a symmetric distribution pattern of H3K9me2 between inner cell mass (ICM) and trophectoderm (TE) in SCNT blastocysts. The expression level of H3K9me2 in both lineages from SCNT expanded blastocyst onwards was significantly higher than that in IVF counterparts. The expression level of H4K20me2 was significantly lower in SCNT embryos from morula to blastocyst stage compared with IVF embryos. However, no aberrant dynamic reprogramming of H3K27me2/3 occurred during early developmental stages of SCNT embryos. The expression of H3K4me3 was higher in SCNT embryos at 4-cell stage than that of IVF embryos. H3K4me2 expression in SCNT embryos from 8-cell stage to blastocyst stage was lower than that in the IVF embryos. Dynamic patterns of other active histone methylation markers were similar between SCNT and IVF embryos. Taken together, histone methylation exhibited developmentally stage-specific abnormal expression patterns in porcine SCNT early embryos.

Genome-wide DNA methylation map of human neutrophils reveals widespread inter-individual epigenetic variation

The extent of variation in DNA methylation patterns in healthy individuals is not yet well documented. Identification of inter-individual epigenetic variation is important for understanding phenotypic variation and disease susceptibility. Using neutrophils from a cohort of healthy individuals, we generated base-resolution DNA methylation maps to document inter-individual epigenetic variation. We identified 12851 autosomal inter-individual variably methylated fragments (iVMFs). Gene promoters were the least variable, whereas gene body and upstream regions showed higher variation in DNA methylation. The iVMFs were relatively enriched in repetitive elements compared to non-iVMFs, and were associated with genome regulation and chromatin function elements. Further, variably methylated genes were disproportionately associated with regulation of transcription, responsive function and signal transduction pathways. Transcriptome analysis indicates that iVMF methylation at differentially expressed exons has a positive correlation and local effect on the inclusion of that exon in the mRNA transcript.

Faithful expression of imprinted genes in donor cells of SCNT cloned pigs

To understand if the genomic imprinting status of the donor cells is altered during the process of SCNT (somatic cell nuclear transfer), cloned pigs were produced by SCNT using PEF (porcine embryonic fibroblast) and P-PEF (parthenogenetic-PEF) cells as donors. Then, the gene expression and methylation patterns of H19, IGF2, NNAT and MEST were compared between PEF vs. C-PEF (cloned-PEF), P-PEF vs. CP-PEF (cloned-P-PEF), respectively. Taken together, the results revealed that there was no significant difference in the expression of imprinted genes and conserved genomic imprints between the donor and cloned cells.

Effects of Scriptaid on the Histone Acetylation, DNA Methylation and Development of Buffalo Somatic Cell Nuclear Transfer Embryos

The present study was undertaken to examine the effect of Scriptaid treatment on histone acetylation, DNA methylation, expression of genes related to histone acetylation, and development of buffalo somatic cell nuclear transfer (SCNT) embryos. Treatment of buffalo SCNT embryos with 500 nM Scriptaid for 24 h resulted in a significant increase in the blastocyst formation rate (28.2% vs. 13.6%, p<0.05). Meanwhile, treatment of buffalo SCNT embryos with Scriptaid also resulted in higher acetylation levels of H3K18 and lower methylation levels of global DNA at the blastocyst stage, which was similar to fertilized counterparts. The expression levels of CBP, p300, HAT1, Dnmt1, and Dnmt3a in SCNT embryos treated with Scriptaid were significantly lower than the control group at the eight-cell stage (p<0.05), but the expression of HAT1 and Dnmt1a was higher than the control group at the blastocyst stage (p<0.05). When 96 blastocysts developed from Scriptaid-treated SCNT embryos were transferred into 48 recipients, 11 recipients (22.9%) became pregnant, whereas only one recipient (11.1%) became pregnant following transfer of 18 blastocysts developed from untreated SCNT embryos into nine recipients. These results indicate that treatment of buffalo SCNT embryos with Scriptaid can improve their developmental competence, and this action is mediated by resulting in a similar histone acetylation level and global DNA methylation level compared to in vitro-fertilized embryos through regulating the expression pattern of genes related to histone acetylation and DNA methylation.

DNA methylation dynamics at imprinted genes during bovine pre-implantation embryo development

Background

In mammals, maternal differentially methylated regions (DMRs) acquire DNA methylation during the postnatal growth stage of oogenesis, with paternal DMRs acquiring DNA methylation in the perinatal prospermatagonia. Following fusion of the male and female gametes, it is widely accepted that murine DNA methylation marks at the DMRs of imprinted genes are stable through embryogenesis and early development, until they are reprogrammed in primordial germ cells. However, the DNA methylation dynamics at DMRs of bovine imprinted genes during early stages of development remains largely unknown. The objective of this investigation was to analyse the methylation dynamics at imprinted gene DMRs during bovine embryo development, from blastocyst stage until implantation.

Results

To this end, pyrosequencing technology was used to quantify DNA methylation at DMR-associated CpG dinucleotides of six imprinted bovine genes (SNRPN, MEST, IGF2R, PLAGL1, PEG10 and H19) using bisulfite-modified genomic DNA isolated from individual blastocysts (Day 7); ovoid embryos (Day 14); filamentous embryos (Day 17) and implanting conceptuses (Day 25). For all genes, the degree of DNA methylation was most variable in Day 7 blastocysts compared to later developmental stages (P < 0.05). Furthermore, mining of RNA-seq transcriptomic data and western blot analysis revealed a specific window of expression of DNA methylation machinery genes (including DNMT3A, DNMT3B, TRIM28/KAP1 and DNMT1) and proteins (DNMT3A, DNMT3A2 and DNMT3B) by bovine embryos coincident with imprint stabilization.

Conclusion

The findings of this study suggest that the DNA methylation status of bovine DMRs might be variable during the early stages of embryonic development, possibly requiring an active period of imprint stabilization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0060-2) contains supplementary material, which is available to authorized users.

Identification of differentially expressed microRNAs in placentas of cloned and normally produced calves by Solexa sequencing

Aberrant gene expression caused by aberrant nuclear reprogramming results in developmental abnormalities in cloned animals and ultimately their death. MicroRNAs (miRNAs), a family of ∼ 22 nucleotide, non-coding, single-stranded RNA molecules, are considered as key regulators of gene expression. Numerous miRNAs and their expression patterns have been identified in various species. However, the significance of miRNAs in developmental abnormalities in cloned animals is unclear. Small RNA libraries were generated from the placentas of cloned (somatic cell nuclear transfer, SCNT) and normally produced (control) calves. A total of 18,815,541 clean reads were obtained from the SCNT library and 19,329,352 from the control library. In total, 430 conserved bovine miRNAs were identified in bovine placenta. Furthermore, the family, expression predominance, and base substitution of the conserved miRNAs were also analyzed. We found 135 conserved miRNAs that were differentially expressed significantly between the two samples, which suggest that these miRNAs may affect developmental abnormalities in cloned cattle and ultimately their death. The miRNA target prediction, gene ontology, and pathway analysis for these target genes were also carried out. The present study expands the collection of bovine miRNAs and could initiate further studies on the functions of miRNAs in developmental abnormalities and death in cloned animals.

Production of viable cloned miniature pigs by aggregation of handmade cloned embryos at the 4-cell stage

The aim of the present study was to improve the quality of handmade cloned porcine embryos by multiple embryo aggregations. Embryos derived from aggregation of three cloned embryos (3×) had a better blastocyst rate than cloned control (1×) embryos (73.6% vs 35.1%, respectively; P<0.05), but did not differ from those produced by aggregation of two cloned embryos (2×; 63.0%). Total cell numbers differed among treatments (P<0.05), with the greatest cell numbers (126) in the 3× group and the lowest (55) in the control group. The ratio of inner cell mass:total cell number was comparable in the 2× and 3× groups (25.1% vs 26.1%, respectively) and was significantly better than that in the control group (15.3%). The proportion of apoptotic cells in 2× and 3× groups was lower than that in the control group (2.7% and 2.2% vs 4.7%, respectively; P<0.05). Expression of Oct4 and Cdx2 was higher, whereas that of Bax was lower (P<0.05), in the 3× compared with non-aggregate group. Seven piglets were born to two surrogate mothers after embryo transfer of 3× aggregated blastocysts. In conclusion, aggregated embryos had greater total cell numbers and better pluripotency gene expression, with reduced expression of the pro-apoptosis gene Bax. Collectively, these improvement may be associated with the development of cloned embryos to term.

Application of a novel population of multipotent stem cells derived from skin fibroblasts as donor cells in bovine SCNT

Undifferentiated stem cells are better donor cells for somatic cell nuclear transfer (SCNT), resulting in more offspring than more differentiated cells. While various stem cell populations have been confirmed to exist in the skin, progress has been restricted due to the lack of a suitable marker for their prospective isolation. To address this fundamental issue, a marker is required that could unambiguously prove the differentiation state of the donor cells. We therefore utilized magnetic activated cell sorting (MACS) to separate a homogeneous population of small SSEA-4⁺ cells from a heterogeneous population of bovine embryonic skin fibroblasts (BEF). SSEA-4⁺ cells were 8-10 μm in diameter and positive for alkaline phosphatase (AP). The percentage of SSEA-4⁺ cells within the cultured BEF population was low (2-3%). Immunocytochemistry and PCR analyses revealed that SSEA-4⁺ cells expressed pluripotency-related markers, and could differentiate into cells comprising all three germ layers in vitro. They remained undifferentiated over 20 passages in suspension culture. In addition, cloned embryos derived from SSEA-4 cells showed significant differences in cleavage rate and blastocyst development when compared with those from BEF and SSEA-4⁻ cells. Moreover, blastocysts derived from SSEA-4⁺ cells showed a higher total cell number and lower apoptotic index as compared to BEF and SSEA-4^– derived cells. It is well known that nuclei from pluripotent stem cells yield a higher cloning efficiency than those from adult somatic cells, however, pluripotent stem cells are relatively difficult to obtain from bovine. The SSEA-4⁺ cells described in the current study provide an attractive candidate for SCNT and a promising platform for the generation of transgenic cattle.

Use of hybrid chitosan membranes and human mesenchymal stem cells from the Wharton jelly of umbilical cord for promoting nerve regeneration in an axonotmesis rat model

Many studies have been dedicated to the development of scaffolds for improving post-traumatic nerve regeneration. The goal of this study was to assess the effect on nerve regeneration, associating a hybrid chitosan membrane with non-differentiated human mesenchymal stem cells isolated from Wharton's jelly of umbilical cord, in peripheral nerve reconstruction after crush injury. Chromosome analysis on human mesenchymal stem cell line from Wharton's jelly was carried out and no structural alterations were found in metaphase. Chitosan membranes were previously tested in vitro, to assess their ability in supporting human mesenchymal stem cell survival, expansion, and differentiation. For the in vivo testing, Sasco Sprague adult rats were divided in 4 groups of 6 or 7 animals each: Group 1, sciatic axonotmesis injury without any other intervention (Group 1-Crush); Group 2, the axonotmesis lesion of 3 mm was infiltrated with a suspension of 1 250–1 500 human mesenchymal stem cells (total volume of 50 μL) (Group 2-CrushCell); Group 3, axonotmesis lesion of 3 mm was enwrapped with a chitosan type III membrane covered with a monolayer of non-differentiated human mesenchymal stem cells (Group 3-CrushChitIIICell) and Group 4, axonotmesis lesion of 3 mm was enwrapped with a chitosan type III membrane (Group 4-CrushChitIII). Motor and sensory functional recovery was evaluated throughout a healing period of 12 weeks using sciatic functional index, static sciatic index, extensor postural thrust, and withdrawal reflex latency. Stereological analysis was carried out on regenerated nerve fibers. Results showed that infiltration of human mesenchymal stem cells, or the combination of chitosan membrane enwrapment and human mesenchymal stem cell enrichment after nerve crush injury provide a slight advantage to post-traumatic nerve regeneration. Results obtained with chitosan type III membrane alone confirmed that they significantly improve post-traumatic axonal regrowth and may represent a very promising clinical tool in peripheral nerve reconstructive surgery. Yet, umbilical cord human mesenchymal stem cells, that can be expanded in culture and induced to form several different types of cells, may prove, in future experiments, to be a new source of cells for cell therapy, including targets such as peripheral nerve and muscle.

Effect of crotamine, a cell-penetrating peptide, on blastocyst production and gene expression of in vitro fertilized bovine embryos

The present study investigated the effects of crotamine, a cell-penetrating peptide from rattlesnake venom, at different exposure times and concentrations, on both developmental competence and gene expression (ATP1A1, AQP3, GLUT1 and GLUT3) of in vitro fertilized (IVF) bovine embryos. In Experiment 1, presumptive zygotes were exposed to 0.1 μM crotamine for 6, 12 or 24 h and control groups (vehicle and IVF) were included. In Experiment 2, presumptive zygotes were exposed to 0 (vehicle), 0.1, 1 and 10 μM crotamine for 24 h. Additionally, to visualize crotamine uptake, embryos were exposed to rhodamine B-labelled crotamine and subjected to confocal microscopy. In Experiment 1, no difference (P > 0.05) was observed among different exposure times and control groups for cleavage and blastocyst rates and total cells number per blastocyst. Within each exposure time, mRNA levels were similar (P > 0.05) in embryos cultured with or without crotamine. In Experiment 2, concentrations as high as 10 μM crotamine did not affect (P > 0.05) the blastocyst rate. Crotamine at 0.1 and 10 μM did not alter mRNA levels when compared with the control (P > 0.05). Remarkably, only 1 μM crotamine decreased both ATP1A1 and AQP3 expression levels relative to the control group (P < 0.05). Also, it was possible to visualize the intracellular localization of crotamine. These results indicate that crotamine can translocate intact IVF bovine embryos and its application in the culture medium is possible at concentrations from 0.1–10 μM for 6–24 h.

Analysis of cell growth and gene expression of porcine adipose tissue-derived mesenchymal stem cells as nuclear donor cell

In several laboratory animals and humans, adipose tissue-derived mesenchymal stem cells (ASC) are of considerable interest because they are easy to harvest and can generate a huge proliferation of cells from a small quantity of fat. In this study, we investigated: (i) the expression patterns of reprogramming-related genes in porcine ASC; and (ii) whether ASC can be a suitable donor cell type for generating cloned pigs. For these experiments, ASC, adult skin fibroblasts (AF) and fetal fibroblasts (FF) were derived from a 4-year-old female miniature pig. The ASC expressed cell-surface markers characteristic of stem cells, and underwent in vitro differentiation when exposed to specific differentiation-inducing conditions. Expression of DNA methyltransferase (DNMT)1 in ASC was similar to that in AF, but the highest expression of the DNMT3B gene was observed in ASC. The expression of OCT4 was significantly higher in FF and ASC than in AF (P < 0.05), and SOX2 showed significantly higher expression in ASC than in the other two cell types (P < 0.05). After somatic cell nuclear transfer (SCNT), the development rate of cloned embryos derived from ASC was comparable to the development of those derived using FF. Total cell numbers of blastocysts derived using ASC and FF were significantly higher than in embryos made with AF. The results demonstrated that ASC used for SCNT have a potential comparable to those of AF and FF in terms of embryo in vitro development and blastocyst formation.

Dysregulation of genome-wide gene expression and DNA methylation in abnormal cloned piglets

Background

Epigenetic modifications (especially altered DNA methylation) resulting in altered gene expression may be one reason for development failure or abnormalities in cloned animals, but the underlying mechanism of the abnormal phenotype in cloned piglets remains unknown. Some cloned piglets in our study showed abnormal phenotypes such as large tongue (longer and thicker), weak muscles, and exomphalos. Here we conducted DNA methylation (DNAm) immunoprecipitation and high throughput sequencing (MeDIP-seq) and RNA sequencing (RNA-seq) of muscle tissues of cloned piglets to investigate the relationship of abnormal DNAm with gene dysregulation and the unusual phenotypes in cloned piglets.

Results

Analysis of the methylomes revealed that abnormal cloned piglets suffered more hypomethylation than hypermethylation compared to the normal cloned piglets, although the DNAm level in the CpG Island was higher in the abnormal cloned piglets. Some repetitive elements, such as SINE/tRNA-Glu Satellite/centr also showed differences. We detected 1,711 differentially expressed genes (DEGs) between the two groups, of which 243 genes also changed methylation level in the abnormal cloned piglets. The altered DNA methylation mainly affected the low and silently expressed genes. There were differences in both pathways and genes, such as the MAPK signalling pathway, the hypertrophic cardiomyopathy pathway, and the imprinted gene PLAGL1; all of which may play important roles in development of the abnormal phenotype.

Conclusions

The abnormal cloned piglets showed substantial changes both in the DNAm and the gene expression. Our data may provide new insights into understanding the molecular mechanisms of the reprogramming of genetic information in cloned animals.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-811) contains supplementary material, which is available to authorized users.

DNA demethylation, Tet proteins and 5-hydroxymethylcytosine in epigenetic reprogramming: an emerging complex story

Epigenetic reprogramming involves processes that lead to the erasure of epigenetic information, reverting the chromatin template to a less differentiated state. Extensive epigenetic reprogramming occurs both naturally during mammalian development in the early embryo and the developing germ line, and artificially in various in vitro reprogramming systems. Global DNA demethylation appears to be a shared attribute of reprogramming events, and understanding DNA methylation dynamics is thus of considerable interest. Recently, the Tet enzymes, which catalyse the iterative oxidation of 5-methylcytosine to 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine, have emerged as potential drivers of epigenetic reprogramming. Although some of the recent studies point towards the direct role of Tet proteins in the removal of DNA methylation, the accumulating evidence suggests that the processes underlying DNA methylation dynamics might be more complex. Here, we review the current evidence, highlighting the agreements and the discrepancies between the suggested models and the experimental evidence.

Effects of histone deacetylase inhibitor oxamflatin on in vitro porcine somatic cell nuclear transfer embryos

Low cloning efficiency is considered to be caused by the incomplete or aberrant epigenetic reprogramming of differentiated donor cells in somatic cell nuclear transfer (SCNT) embryos. Oxamflatin, a novel class of histone deacetylase inhibitor (HDACi), has been found to improve the in vitro and full-term developmental potential of SCNT embryos. In the present study, we studied the effects of oxamflatin treatment on in vitro porcine SCNT embryos. Our results indicated that the rate of in vitro blastocyst formation of SCNT embryos treated with 1 μM oxamflatin for 15 h postactivation was significantly higher than all other treatments. Treatment of oxamflatin decreased the relative histone deacetylase (HDAC) activity in cloned embryos and resulted in hyperacetylation levels of histone H3 at lysine 9 (AcH3K9) and histone H4 at lysine 5 (AcH4K5) at pronuclear, two-cell, and four-cell stages partly through downregulating HDAC1. The suppression of HDAC6 through oxamflatin increased the nonhistone acetylation level of α-tubulin during the mitotic cell cycle of early SCNT embryos. In addition, we demonstrated that oxamflatin downregulated DNA methyltransferase 1 (DNMT1) expression and global DNA methylation level (5-methylcytosine) in two-cell-stage porcine SCNT embryos. The pluripotency-related gene POU5F1 was found to be upregulated in the oxamflatin-treated group with a decreased DNA methylation tendency in its promoter regions. Treatment of oxamflatin did not change the locus-specific DNA methylation levels of Sus scrofa heterochromatic satellite DNA sequences at the blastocyst stage. Meanwhile, our findings suggest that treatment with HDACi may contribute to maintaining the stable status of cytoskeleton-associated elements, such as acetylated α-tubulin, which may be the crucial determinants of donor nuclear reprogramming in early SCNT embryos. In summary, oxamflatin treatment improves the developmental potential of porcine SCNT embryos in vitro.

Siberian Sturgeon Oocyte Extract Induces Epigenetic Modifications of Porcine Somatic Cells and Improves Developmental Competence of SCNT Embryos

Somatic cell nuclear transfer (SCNT) has generally demonstrated that a differentiated cell can convert into a undifferentiated or pluripotent state. In the SCNT experiment, nuclear reprogramming is induced by exposure of introduced donor nuclei to the recipient cytoplasm of matured oocytes. However, because the efficiency of SCNT still remains low, a combination of SCNT technique with the ex-ovo method may improve the normal development of SCNT embryos. Here we hypothesized that treatment of somatic cells with extracts prepared from the germinal vesicle (GV) stage Siberian sturgeon oocytes prior to their use as nuclear donor for SCNT would improve in vitro development. A reversible permeability protocol with 4 μg/mL of digitonin for 2 min at 4°C in order to deliver Siberian sturgeon oocyte extract (SOE) to porcine fetal fibroblasts (PFFs) was carried out. As results, the intensity of H3K9ac staining in PFFs following treatment of SOE for 7 h at 18°C was significantly increased but the intensity of H3K9me3 staining in PFFs was significantly decreased as compared with the control (p<0.05). Additionally, the level of histone acetylation in SCNT embryos at the zygote stage was significantly increased when reconstructed using SOE-treated cells (p<0.05), similar to that of IVF embryos at the zygote stage. The number of apoptotic cells was significantly decreased and pluripotency markers (Nanog, Oct4 and Sox2) were highly expressed in the blastocyst stage of SCNT embryos reconstructed using SOE-treated cells as nuclear donor (p<0.05). And there was observed a better development to the blastocyst stage in the SOE-treated group (p<0.05). Our results suggested that pre-treatment of cells with SOE could improve epigenetic reprogramming and the quality of porcine SCNT embryos.

Disruption of imprinted gene expression and DNA methylation status in porcine parthenogenetic fetuses and placentas

Parthenogenetically activated oocytes cannot develop to term in mammals due to the lack of paternal gene expression and failed X chromosome inactivation (XCI). To further characterize porcine parthenogenesis, the expression of 18 imprinted genes was compared between parthenogenetic (PA) and normally fertilized embryos (Con) using quantitative real-time PCR (qRT-PCR). The results revealed that maternally expressed genes were over-expressed, whereas paternally expressed genes were significantly reduced in PA fetuses and placentas. The results of bisulfite sequencing PCR (BSP) demonstrated that PRE-1 and Satellite were hypermethylated in both Con and PA fetuses and placentas, while XIST DMRs were hypomethylated only in PA samples. Taken together, these results suggest that the aberrant methylation profile of XIST DMRs and abnormal imprinted gene expression may be responsible for developmental failure and impaired growth in porcine parthenogenesis.

Genomic imprinting analysis of Igf2/H19 in porcine cloned fetuses using parthenogenetic somatic cells as nuclear donors

To gain insight into parthenogenesis in pigs, we report for the first time that using parthenogenetic somatic cells as nuclear donors (PSCNT), the porcine parthenogenetic fetus can develop to gestational day 39. Weight and morphological analysis revealed that PSCNT fetuses were smaller and developmentally retarded when compared to normally fertilized controls. Quantitative gene expression analysis indicated that in PSCNT fetuses, H19 was over-expressed, whereas Igf2 was significantly reduced (p < 0.05) compared with their controls. In addition, bisulfite-sequencing PCR results demonstrated that H19 differentially DNA methylated regions (DMRs) were hypomethylated in PSCNT fetuses, while Igf2 DMRs were hypermethylated in both PSCNT and control fetuses. Our results suggest that extended development of the porcine parthenogenetic fetus can be accomplished using PSCNT and that abnormal DNA methylation of H19 DMRs might contribute to the critical barrier of parthenogenesis in pigs.

Epigenetic reprogramming, gene expression and in vitro development of porcine SCNT embryos are significantly improved by a histone deacetylase inhibitor--m-carboxycinnamic acid bishydroxamide (CBHA)

Insufficient epigenetic reprogramming of donor nuclei is believed to be one of the most important causes of low development efficiency of mammalian somatic cell nuclear transfer (SCNT). Previous studies have shown that both the in vitro and in vivo development of mouse SCNT embryos could be increased significantly by treatment with various histone deacetylase inhibitors (HDACi), including Trichostatin A, Scriptaid, and m-carboxycinnamic acid bishydroxamide (CBHA), in which only the effect of CBHA has not yet been tested in other species. In this paper we examine the effect of CBHA treatment on the development of porcine SCNT embryos. We have discovered the optimum dosage and time for CBHA treatment: incubating SCNT embryos with 2 μmol/L CBHA for 24 h after activation could increase the blastocyst rate from 12.7% to 26.5%. Immunofluorescence results showed that the level of acetylation at histone 3 lysine 9 (AcH3K9), acetylation at histone 3 lysine 18 (AcH3K18), and acetylation at histone 4 lysine 16 (AcH4K16) was raised after CBHA treatment. Meanwhile, CBHA treatment improved the expression of development relating genes such as pou5f1, cdx2, and the imprinted genes like igf2. Despite these promising in vitro results and histone reprogramming, the full term development was not significantly increased after treatment. In conclusion, CBHA improves the in vitro development of pig SCNT embryos, increases the global histone acetylation and corrects the expression of some developmentally important genes at early stages. As in mouse SCNT, we have shown that nuclear epigenetic reprogramming in pig early SCNT embryos can be modified by CBHA treatment.

Single cell analysis reveals the stochastic phase of reprogramming to pluripotency is an ordered probabilistic process

Despite years of research, the reprogramming of human somatic cells to pluripotency remains a slow, inefficient process, and a detailed mechanistic understanding of reprogramming remains elusive. Current models suggest reprogramming to pluripotency occurs in two-phases: a prolonged stochastic phase followed by a rapid deterministic phase. In this paradigm, the early stochastic phase is marked by the random and gradual expression of pluripotency genes and is thought to be a major rate-limiting step in the successful generation of induced Pluripotent Stem Cells (iPSCs). Recent evidence suggests that the epigenetic landscape of the somatic cell is gradually reset during a period known as the stochastic phase, but it is known neither how this occurs nor what rate-limiting steps control progress through the stochastic phase. A precise understanding of gene expression dynamics in the stochastic phase is required in order to answer these questions. Moreover, a precise model of this complex process will enable the measurement and mechanistic dissection of treatments that enhance the rate or efficiency of reprogramming to pluripotency. Here we use single-cell transcript profiling, FACS and mathematical modeling to show that the stochastic phase is an ordered probabilistic process with independent gene-specific dynamics. We also show that partially reprogrammed cells infected with OSKM follow two trajectories: a productive trajectory toward increasingly ESC-like expression profiles or an alternative trajectory leading away from both the fibroblast and ESC state. These two pathways are distinguished by the coordinated expression of a small group of chromatin modifiers in the productive trajectory, supporting the notion that chromatin remodeling is essential for successful reprogramming. These are the first results to show that the stochastic phase of reprogramming in human fibroblasts is an ordered, probabilistic process with gene-specific dynamics and to provide a precise mathematical framework describing the dynamics of pluripotency gene expression during reprogramming by OSKM.

Cellular extract facilitates nuclear reprogramming by altering DNA methylation and pluripotency gene expression

The functional reprogramming of a differentiated cell to a pluripotent state presents potential beneficial applications in disease mechanisms and regenerative medicine. Epigenetic modifications enable differentiated cells to perpetuate molecular memory to retain their identity. Therefore, the aim of this study was to investigate the reprogramming modification of yak fibroblast cells that were permeabilized and incubated in the extracts of mesenchymal stem cells derived from mice adipose tissue [adipose-derived stem cells (ADSCs)]. According to the results, the treatment of ADSC extracts promoted colony formation. Moreover, pluripotent gene expression was associated with the loss of repressive histone modifications and increased global demethylation. The genes Col1a1 and Col1a2, which are typically found in differentiated cells only, demonstrated decreased expression and increased methylation in the 5'-flanking regulatory regions. Moreover, yak fibroblast cells that were exposed to ADSC extracts resulted in significantly different eight-cell and blastocyst formation rates of cloned embryos compared with their untreated counterparts. This investigation provides the first evidence that nuclear reprogramming of yak fibroblast cells is modified after the ADSC extract treatment. This research also presents a methodology for studying the dedifferentiation of somatic cells that can potentially lead to an efficient way of reprogramming somatic cells toward a pluripotent state without genetic alteration.

Induced pluripotent stem cells from human hair follicle mesenchymal stem cells

Reprogramming of somatic cells into inducible pluripotent stem cells (iPSCs) provides an alternative to using embryonic stem cells (ESCs). Mesenchymal stem cells derived from human hair follicles (hHF-MSCs) are easily accessible, reproducible by direct plucking of human hairs. Whether these hHF-MSCs can be reprogrammed has not been previously reported. Here we report the generation of iPSCs from hHF-MSCs obtained by plucking several hairs. hHF-MSCs were isolated from hair follicle tissues and their mesenchymal nature confirmed by detecting cell surface antigens and multilineage differentiation potential towards adipocytes and osteoblasts. They were then reprogrammed into iPSCs by lentiviral transduction with Oct4, Sox2, c-Myc and Klf4. hHF-MSC-derived iPSCs appeared indistinguishable from human embryonic stem cells (hESCs) in colony morphology, expression of alkaline phosphotase, and expression of specific hESCs surface markers, SSEA-3, SSEA-4, Tra-1-60, Tra-1-81, Nanog, Oct4, E-Cadherin and endogenous pluripotent genes. When injected into immunocompromised mice, hHF-MSC-derived iPSCs formed teratomas containing representatives of all three germ layers. This is the first study to report reprogramming of hHF-MSCs into iPSCs.

Reshaping the transcriptional frontier: epigenetics and somatic cell nuclear transfer

Somatic-cell nuclear transfer (SCNT) experiments have paved the way to the field of cellular reprogramming. The demonstrated ability to clone over 20 different species to date has proven that the technology is robust but very inefficient, and is prone to developmental anomalies. Yet, the offspring from cloned animals exhibit none of the abnormalities of their parents, suggesting the low efficiency and high developmental mortality are epigenetic in origin. The epigenetic barriers to reprogramming somatic cells into a totipotent embryo capable of developing into a viable offspring are significant and varied. Despite their intimate relationship, chromatin structure and transcription are often not uniformly reprogramed after nuclear transfer, and many cloned embryos develop gene expression profiles that are hybrids between the donor cell and an embryonic blastomere. Recent advances in cellular reprogramming suggest that alteration of donor-cell chromatin structure towards that found in an normal embryo is actually the rate-limiting step in successful development of SCNT embryos. Here we review the literature relevant to the transformation of a somatic-cell nucleus into an embryo capable of full-term development. Interestingly, while resetting somatic transcription and associated epigenetic marks are absolutely required for development of SCNT embryos, life does not demand perfection.

Comparative proteomic analysis of hearts of adult SCNT Bama miniature pigs (Sus scrofa)

This study aims to determine the effects of SCNT on cardiac development of SCNT pigs through proteomic methods. Heart proteins from three adult SCNTs and two normal reproductive Bama miniature pigs were extracted, separated, and identified via comparative proteomic methods, including two-dimensional gel electrophoresis, mass spectrometry, and Western blot. Eleven differentially expressed spots were identified as differentially expressed proteins, of which five spots were upregulated proteins such as cardiac myosin heavy chain, cathepsin D, and heat shock protein beta-1 (HSP27). By contrast, six spots were downregulated proteins such as alpha skeletal muscle and actin. The results also demonstrated that nuclear transfer might result in abnormal expression of some important proteins in hearts from SCNT pigs, and affect the cardiac development in SCNT pigs' survival.

Somatic cells, stem cells, and induced pluripotent stem cells: how do they now contribute to conservation?

More than a decade has now passed since the birth of the first endangered species produced from an adult somatic cell reprogrammed by somatic cell nuclear transfer. At that time, advances made in domestic and laboratory animal species provided the necessary foundation for attempting cutting-edge technologies on threatened and endangered species. In addition to nuclear transfer, spermatogonial stem cell transplantation and induction of pluripotent stem cells have also been explored. Although many basic scientific questions have been answered and more than 30 wild species have been investigated, very few successes have been reported. The majority of studies document numerous obstacles that still need to be overcome to produce viable gametes or embryos for healthy offspring production. This chapter provides an overview of somatic cell and stem cell technologies in different taxa (mammals, fishes, birds, reptiles and amphibians) and evaluates the potential and impact of these approaches for animal species conservation.

A protocol for adult somatic cell nuclear transfer in medaka fish (Oryzias latipes) with a high rate of viable clone formation

Previously, we successfully generated fully grown, cloned medaka (the Japanese rice fish, Oryzias latipes) using donor nuclei from primary culture cells of adult caudal fin tissue and nonenucleated recipient eggs that were heat shock-treated to induce diploidization of the nuclei. However, the mechanism of clone formation using this method is unknown, and the rate of adult clone formation is not high enough for studies in basic and applied sciences. To gain insight into the mechanism and increase the success rate of this method of clone formation, we tested two distinct nuclear transfer protocols. In one protocol, the timing of transfer of donor nuclei was changed, and in the other, the size of the donor cells was changed; each protocol was based on our original methodology. Ultimately, we obtained an unexpectedly high rate of adult clone formation using the protocol that differed with respect to the timing of donor nuclei transfer. Specifically, 17% of the transplants that developed to the blastula stage ultimately developed into adult clones. The success rate with this method was 13 times higher than that obtained using the original method. Analyses focusing on the reasons for this high success rate of clone formation will help to elucidate the mechanism of clone formation that occurs with this method.