Nuclear Transfer of Sand Cat Cells into Enucleated Domestic Cat Oocytes is Affected by Cryopreservation of Donor Cells

Aspects of in vivo oocyte production, blastocyst development, and embryo transfer in the cat

A brief overview of the progress made during the past approximately 40 years on the development of methods for in vitro production of cat embryos and intra- and interspecies embryo transfer is described. The presentation is focused primarily on research done over the past 30 years at the Cincinnati Zoo (1980-1995) and at the Audubon Nature Institute, New Orleans (1996-present) beginning with original studies on determining optimal doses of porcine FSH for ovarian stimulation and uterine embryo recovery, cryopreservation, and transfer. A key early finding was the ability of cats to respond to multiple gonadotropin (porcine FSH) treatments by repeated stimulation of follicular development. With a ≥ 6-month interval between FSH treatments, over the past 15 years (1998-2013), we have done 1603 laparoscopic oocyte retrievals on 337 cats and recovered >38,000 mature oocytes (mean = 24.1 per laparoscopic oocyte retrieval). The limited information available on in vivo blastocyst development in the cat during the latter portion of the preimplantation period (approximately Days 8 to 12 after coitum or approximately Days 7 to 11 after ovulation) was assembled for the purpose of comparing and contrasting it with the growth, expansion, and zona functioning of in vitro-derived blastocysts. Also, results of transferring morulae and/or blastocysts into synchronous recipients are described to emphasize evidence that appears to allude to an essential role for an intact zona pellucida in successful implantation and subsequent development in the cat. Until 2003, our in vitro-derived embryos were transferred into the uterine horns of recipients to determine the feasibility of producing offspring from such primary methods as IVF, intracytoplasmic sperm injection, SCNT, and embryo cryopreservation. With the exception of SCNT embryos, pregnancy rates were satisfactory, but embryo survival rates were not. Subsequently, after finding that SCNT embryo survival rate could be improved using laparoscopic transfer of early cleavage stage embryos into the oviduct, we applied the technique to embryos derived using IVF with sex-sorted sperm, oocyte vitrification, and embryo cryopreservation. Overall, a pregnancy rate of 67% (14/21) has resulted. Most recently, with the oviductal embryo transfer technique, two litters of Black-Footed cat kittens have been born from intra- and interspecies transfer of cryopreserved embryos.

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.

Interspecies somatic cell nuclear transfer: advancements and problems

Embryologists working with livestock species were the pioneers in the field of reprogramming by somatic cell nuclear transfer (SCNT). Without the "Dolly experiment," the field of cellular reprogramming would have been slow and induced plutipotent cells (iPSCs) would not have been conceived. The major drive of the work in mammalian cloning was the interest of the breeding industry to propagate superior genotypes. Soon it was realized that the properties of oocytes could be used also to clone endangered mammalian species or to reprogram the genomes of unrelated species through what is known as interspecies (i) SCNT, using easily available oocytes of livestock species. iSCNT for cloning animals works only for species that can interbreed, and experiments with taxonomically distant species have not been successful in obtaining live births or deriving embryonic stem cell (ESC) lines to be used for regenerative medicine. There are controversial reports in the literature, but in most cases these experiments have underlined some of the cellular and molecular mechanisms that are incomplete during cell nucleus reprogramming, including the failure to organize nucleoli, silence somatic cell genes, activate the embryonic genome, and resume mitochondrial replication and function, thus indicating nucleus-cytoplasmic incompatibility.

Scriptaid and 5-aza-2'deoxycytidine enhanced expression of pluripotent genes and in vitro developmental competence in interspecies black-footed cat cloned embryos

Somatic cell nuclear transfer offers the possibility of preserving endangered species including the black-footed cat, which is threatened with extinction. The effectiveness and efficiency of somatic cell nuclear transfer (SCNT) depends on a variety of factors, but 'inappropriate epigenetic reprogramming of the transplanted nucleus is the primary cause of the developmental failure of cloned embryos. Abnormal epigenetic events such as DNA methylation and histone modifications during SCNT perturb the expression of imprinted and pluripotent-related genes that, consequently, may result in foetal and neonatal abnormalities. We have demonstrated that pregnancies can be established after transfer of black-footed cat cloned embryos into domestic cat recipients, but none of the implanted embryos developed to term and the foetal failure has been associated to aberrant reprogramming in cloned embryos. There is growing evidence that modifying the epigenetic pattern of the chromatin template of both donor cells and reconstructed embryos with a combination of inhibitors of histone deacetylases and DNA methyltransferases results in enhanced gene reactivation and improved in vitro and in vivo developmental competence. Epigenetic modifications of the chromatin template of black-footed cat donor cells and reconstructed embryos with epigenetic-modifying compounds enhanced in vitro development, and regulated the expression of pluripotent genes, but these epigenetic modifications did not improve in vivo developmental competence.

Capabilities and challenges of examination of gene expression for quality assessment of domestic cat embryos

Early embryos are characterized by an accurately controlled gene expression pattern that might be deregulated during in vitro culture (IVC). The expression pattern of the developmental genes may serve as markers for embryo quality. Here, we examined the temporal pattern of relative mRNA abundance of genes important for early embryonic development in embryos produced by different fertilization methods [in vitro fertilization (IVF) vs intracytoplasmic sperm cell injection (ICSI)] and sperm sources (fresh vs frozen-thawed) applying reverse transcriptase (RT) PCR. The temporal pattern of gene expression was found to be gene specific and similar in all four examined groups in a semi-quantitative assay. In morulae, higher relative mRNA levels were found in embryos generated with fresh sperm, whereas in blastocysts, mRNA abundance tended to be higher in embryos produced with cryopreserved sperm cells. This indicates an influence of sperm cryopreservation on the temporal gene expression pattern in early cat embryos. We also examined relative mRNA abundances by real-time quantitative RT-PCR in blastocysts. In this context, blastocysts produced with fresh semen tended to have lower DNA methyltransferase 3A (DNMT3A) but higher gap junction protein alpha 1 (GJA1) and octamer-binding transcription factor 4 (OCT4) mRNA levels compared with those derived with frozen-thawed semen. We conclude that assessing embryo quality by measuring gene expression pattern in early embryos is challenging because of a high variability between individual embryos.

Sodium butyrate improves the cloned yak embryo viability and corrects gene expression patterns

Interspecies somatic cell nuclear transfer (iSCNT), a powerful tool in basic scientific research, has been used widely to increase and preserve the population of endangered species. Yak (Bos grunniens) is one of these species. Development to term of interspecies cloned yak embryos has not been achieved, possibly due to abnormal epigenetic reprogramming. Previous studies have demonstrated that treatment of intraspecies cloned embryos with (NaBu) significantly improves nuclear–cytoplasmic reprogramming and viability in vitro. Therefore, in this study, we evaluated the effect of optimal NaBu concentration and exposure time on preimplantation development of yak iSCNT embryos and on the expression patterns of developmentally important genes. The results showed that 8-cell rate, blastocyst formation rate and total cell number increased significantly compared with their untreated counterparts when yak iSCNT embryos were treated with 5 nM NaBu for 12 h after activation, but that the 2-cell stage embryo rate was not significantly different. The treatment of NaBu also increased significantly the expression levels of Oct-4 and decreased the expression levels of HDAC-2, Dnmt-1 and IGF-1; the expression patterns of these genes were more similar to that of their bovine–yak in vitro fertilization (BY-IVF) counterparts. The results described above indicated that NaBu treatment improved developmental competence in vitro and ‘corrected’ the gene expression patterns of yak iSCNT embryos.

Somatic cell nuclear transfer and transgenesis in large animals: current and future insights

Somatic cell nuclear transfer (SCNT) was first developed in livestock for the purpose of accelerating the widespread use of superior genotypes. Although many problems still exist now after fifteen years of research owing to the limited understanding of genome reprogramming, SCNT has provided a powerful tool to make copies of selected individuals in different species, to study genome pluripotency and differentiation, opening new avenues of research in regenerative medicine and representing the main route for making transgenic livestock. Besides well-established methods to deliver transgenes, recent development in enzymatic engineering to edit the genome provides more precise and reproducible tools to target-specific genomic loci especially for producing knockout animals. The interest in generating transgenic livestock lies in the agricultural and biomedical areas and it is, in most cases, at the stage of research and development, with few exceptions that are making the way into practical applications.

Segregation of donor cell mitochondrial DNA in gaur-bovine interspecies somatic cell nuclear transfer embryos, fetuses and an offspring

The fate of foreign mitochondrial DNA (mtDNA) following somatic cell nuclear transfer (SCNT) is still controversial. In this study, we examined the transmission of the heteroplasmic mtDNA of gaur donor cells and recipient bovine oocytes to an offspring and aborted and mummified fetuses at various levels during the development of gaur-bovine interspecies SCNT (iSCNT) embryos. High levels of the donor cell mtDNA were found in various tissue samples but they did not have any beneficial effect to the survival of iSCNT offspring. However, the factors on mtDNA inheritance are unique for each iSCNT experiment and depend on the recipient oocyte and donor cell used, which might play an important role in the efficiency of iSCNT.

Influence of culture medium composition on relative mRNA abundances in domestic cat embryos

Different culture conditions have been used to produce domestic cat embryos. As part of the in vitro procedures, the medium composition significantly affects the quality of the embryo development also. Quality assessments based on cleavage kinetics and blastomere symmetry are useful, but embryos also can differ in their relative gene expression patterns despite similar morphological characteristics. The aim of this study was to compare cat embryos produced with two different in vitro culture systems routinely used in two different laboratories [Smithsonian Conservation Biology Institute, Washington D.C., USA (SCBI) and Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany (IZW)]. Specifically, relative mRNA expression patterns of critical genes for pre-implantation embryo development were assessed in both conditions. Embryos were produced in parallel in both culture systems by IVF using frozen-thawed ejaculated semen in the United States and fresh epididymal sperm in Germany. Success of embryo development in vitro was recorded as well as relative mRNA abundances [DNA methyltransferases 1 and 3A (DNMT1, DNMT3A), gap junction protein alpha 1 (GJA1), octamer-binding transcription factor 4 [OCT4], insulin-like growth factors 1 and 2 receptors (IGF1R, IGF2R), beta-actin (ACTB)] in pools of days 4-5 morulae by semi-quantitative RT-PCR assay. Percentages of cleaved embryos were similar (p > 0.05) between both culture systems, regardless of the location. OCT4 mRNA abundance was higher (p < 0.05) in embryos derived in the SCBI culture system compared with those from the IZW system when epididymal sperm was used for IVF. No clear correlation between the expression pattern and the culture system could be found for all other genes. It is suggested that OCT4 expression might be affected by the media composition in some conditions and can be the indicator of a better embryo quality.

Development of interspecies cloned embryos reconstructed with rabbit (Oryctolagus cuniculus) oocytes and cynomolgus monkey (Macaca fascicularis) fibroblast cell nuclei

Interspecies somatic cell nuclear transfer (ISCNT) has been proposed as a technique to produce cloned offspring of endangered species as well as to investigate nucleus-cytoplasm interactions in mammalian embryo. However, it is still not known which embryo culture medium is optimal for ISCNT embryos for the nuclear donor or the oocyte recipient. We assessed the effects of the culture medium on the developmental competence of the ISCNT embryos by introducing cynomolgus monkey (Macaca fascicularis) fibroblast nuclei into enucleated rabbit (Oryctolagus cuniculus) oocytes (monkey-rabbit embryo). The monkey-rabbit ISCNT embryos that were cultured in mCMRL-1066 developed to the blastocyst stage, although all monkey-rabbit ISCNT embryos cultured in M199 were arrested by the 4-cell stage. When monkey-rabbit ISCNT and rabbit-rabbit somatic cell nuclear transfer (SCNT) embryos were cultured in mCMRL-1066, the blastocyst cell numbers of the monkey-rabbit ISCNT embryos corresponded to the cell numbers of the control rabbit-rabbit SCNT embryos, which were produced from a rabbit fibroblast nucleus and an enucleated rabbit oocyte. In addition, the presence of mitochondria, which were introduced with monkey fibroblasts into rabbit recipient cytoplasm, was confirmed up to the blastocyst stage by polymerase chain reaction (PCR). This study demonstrated that: (1) rabbit oocytes can reprogramme cynomolgus monkey somatic cell nuclei, and support preimplantation development; (2) monkey-rabbit ISCNT embryos developed well in monkey culture medium at early embryonic developmental stages; (3) the cell number of monkey-rabbit ISCNT embryos is similar to that of rabbit-rabbit SCNT embryos; and (4) the mitochondrial fate of monkey-rabbit ISCNT embryos is heteroplasmic from the time just after injection to the blastocyst stage that has roots in both rabbit oocytes and monkey fibroblasts.

Development of intergeneric and intrageneric somatic cell nuclear transfer (SCNT) cat embryos and the determination of telomere length in cloned offspring

Somatic cell nuclear transfer (SCNT) holds potential as a useful tool for agricultural and biomedical applications. In vitro development of marbled cat intergeneric SCNT reconstructed into domestic cat cytoplast revealed that cloned, marbled cat embryo development was blocked at the morula stage. No pregnancies resulted from the transfer of one- to eight-cell stage embryos into domestic cat surrogate mothers. This suggested that abnormalities occurred in the cloned marbled cat embryos, which may be associated with incomplete reprogramming during early embryo development. Two pregnancies were established in surrogate mothers that received cloned domestic cat embryos, but SCNT offspring developed abnormally. Some specific phenotypes that were observed included incomplete abdominal wall disclosure, improper fetal development. In addition, some of the fetuses were mummified or stillbirths. The two live births died within 5 days. Telomere lengths of cloned kittens as determined by qualtitative polymerase chain reaction (qPCR) were inconclusive: some were found to be shorter, longer, or the same as donor control cells. Our findings support the hypothesis that telomere lengths do not govern the health of these cloned animals. A lack of complete reprogramming may lead to developmental failure and the abnormalities observed in cloned offspring.

Gene expression profiling of pluripotency and differentiation-related markers in cat oocytes and preimplantation embryos

During mammalian preimplantation development, two successive differentiation events lead to the establishment of three committed lineages with separate fates: the trophectoderm, the primitive endoderm and the pluripotent epiblast. In the mouse embryo, the molecular mechanisms underlying these two cell fate decisions have been studied extensively, leading to the identification of lineage-specific transcription factors. Species-specific differences in expression patterns of key regulatory genes have been reported, raising questions regarding their role in different species. The aim of the present study was to characterise the gene expression patterns of pluripotency (OCT4, SOX2, NANOG) and differentiation (CDX2, GATA6)-related markers during feline early development using reverse transcription–quantitative polymerase chain reaction. In addition, we assessed the impact of in vitro development on gene expression by comparing transcript levels of the genes investigated between in vitro and in vivo blastocysts. To normalise quantitative data within different preimplantation embryo stages, we first validated a set of stable reference genes. Transcript levels of all genes investigated were present and changed over the course of preimplantation development; a highly significant embryo-stage effect on gene expression was observed. Transcript levels of OCT4 were significantly reduced in in vitro blastocysts compared with their in vivo counterparts. None of the other genes investigated showed altered expression under in vitro conditions. The different gene expression patterns of OCT4, SOX2, CDX2 and GATA6 in cat embryos resembled those described in mouse embryos, indicative of a preserved role for these genes during early segregation. However, because of the absence of any upregulation of NANOG transcription levels after embryonic genome activation, it is unlikely that NANOG is a key regular of lineage segregation. Such results support the hypothesis that the behaviour of early lineage markers can be species specific. The present study also revealed a pool of maternal NANOG mRNA transcripts, the role of which remains to be elucidated. Comparing transcription levels of these genes between in vivo and in vitro blastocysts revealed low levels of OCT4 mRNA in the latter, which may contribute to the reduced developmental competence of embryos under suboptimal conditions.

Effect of cryopreservation and in vitro culture of bovine fibroblasts on histone acetylation levels and in vitro development of hand-made cloned embryos

In this study, the relative acetylation levels of histone 3 in lysine 9 (H3K9ac) in cultured and cryopreserved bovine fibroblasts was measured and we determined the influence of the epigenetic status of three cultured (C1, C2 and C3) donor cell lines on the in vitro development of reconstructed bovine embryos. Results showed that cryopreservation did not alter the overall acetylation levels of H3K9 in bovine fibroblasts analysed immediately after thawing (frozen/thawed) compared with fibroblasts cultured for a period of time after thawing. However, reduced cleavage rates were noted in embryos reconstructed with fibroblasts used immediately after thawing. Cell passage affects the levels of H3K9ac in bovine fibroblasts, decreasing after P1 and donor cells with lower H3K9ac produced a greater frequency of embryo development to the blastocyst stage. Cryopreservation did not influence the total cell and ICM numbers, or the ICM/TPD ratios of reconstructed embryos. However, the genetic source of donor cells did influence the total number of cells and the trophectoderm cell numbers, and the cell passage influenced the total ICM cell numbers.

Development, embryonic genome activity and mitochondrial characteristics of bovine-pig inter-family nuclear transfer embryos

The best results of inter-species somatic cell nuclear transfer (iSCNT) in mammals were obtained using closely related species that can hybridise naturally. However, in the last years, many reports describing blastocyst development following iSCNT between species with distant taxonomical relations (inter-classes, inter-order and inter-family) have been published. This indicates that embryonic genome activation (EGA) in xeno-cytoplasm is possible, albeit very rarely. Using a bovine-pig (inter-family) iSCNT model, we studied the basic characteristics of EGA: expression and activity of RNA polymerase II (RNA Pol II), formation of nucleoli (as an indicator of RNA polymerase I (RNA Pol I) activity), expression of the key pluripotency gene NANOG and alteration of mitochondrial mass. In control embryos (obtained by IVF or iSCNT), EGA was characterised by RNA Pol II accumulation and massive production of poly-adenylated transcripts (detected with oligo dT probes) in blastomere nuclei, and formation of nucleoli as a result of RNA Pol I activity. Conversely, iSCNT embryos were characterised by the absence of accumulation and low activity of RNA Pol II and inability to form active mature nucleoli. Moreover, in iSCNT embryos, NANOG was not expressed, and mitochondria mass was significantly lower than in intra-species embryos. Finally, the complete developmental block at the 16-25-cell stage for pig-bovine iSCNT embryos and at the four-cell stage for bovine-pig iSCNT embryos strongly suggests that EGA is not taking place in iSCNT embryos. Thus, our experiments clearly demonstrate poor nucleus-cytoplasm compatibility between these animal species.

How to improve the success rate of mouse cloning technology

It has now been 13 years since the first cloned mammal Dolly the sheep was generated from somatic cells using nuclear transfer (SCNT). Since then, this technique has been considered an important tool not only for animal reproduction but also for regenerative medicine. However, the success rate is still very low and the mechanisms involved in genomic reprogramming are not yet clear. Moreover, the NT technique requires donated fresh oocyte, which raises ethical problems for production of human cloned embryo. For this reason, the use of induced pluripotent stem cells for genomic reprogramming and for regenerative medicine is currently a hot topic in this field. However, we believe that the NT approach remains the only valid way for the study of reproduction and basic biology. For example, only the NT approach can reveal dynamic and global modifications in the epigenome without using genetic modification, and it can generate offspring from a single cell or even a frozen dead body. Thanks to much hard work by many groups, cloning success rates are increasing slightly year by year, and NT cloning is now becoming a more applicable method. This review describes how to improve the efficiency of cloning, the establishment of clone-derived embryonic stem cells and further applications.

Abnormalities in the transcription of reprogramming genes related to global epigenetic events of cloned endangered felid embryos

The present study examined transcription levels of the Oct4, DNMT1, DNMT3a, DNMT3b, HAT1 and HDAC1 genes in cloned felid embryos developing from single one-cell to blastocyst stages. IVF, cloned domestic and leopard cat embryos had low Oct4 and HAT1 levels during the early stages, but transcript expression increased at the eight-cell and blastocyst stages. In contrast, expression in the cloned marble cat embryos was low at all stages. Transcription patterns of HDAC1 were altered in cloned embryos compared with IVF embryos. Transcription levels of DNMT1 decreased markedly throughout development of both IVF and cloned embryos. In IVF embryos, DNMT3a transcripts rarely appeared in the four- to eight-cell stages, but levels increased in the morula to blastocyst stages. In contrast, in cloned embryos, DNMT3a transcript levels were high at the one- to two-cell stages, decreased during subsequent cell division and then increased again at the blastocyst stage. The IVF and cloned embryos showed similar DNMT3b transcription patterns, starting with low levels at the two-cell to morula stages and reaching a maximum at the blastocyst stage. These results suggest that the low level of Oct4 transcripts may be responsible, in part, for the failure of blastocyst production in the cloned marbled cat. However, higher transcription of the DNA methylation genes and lower transcription of the histone acetylation genes were observed in cloned compared with IVF embryos, suggesting that the felids’ donor nucleus could not completely reprogramme the nuclear genome and so the re-establishment of embryonic totipotency was not achieved.