Lack of effects of ooplasm transfer on early development of interspecies somatic cell nuclear transfer bison embryos

Review: Reproductive physiology of bison and application of assisted reproductive technologies to their conservation

Bison are an ecologically and culturally important species on the European and North American continents. Their near extirpation was met with conservation efforts that prevented their extinction but left few animals or highly fragmented populations. Contemporary conservation efforts are focused on building ecologically and genetically sustainable bison herds for long-term conservation of the species. Assisted reproductive technologies (ARTs) can play a key role in building these herds by facilitating the movement of genetics in the form of gametes and embryos, while protecting animal well-being and ensuring biosecurity of existing bison herds. In addition, ARTs such as gamete and embryo cryopreservation can be used to protect against future losses of genetic diversity through biobanking. In this review, a brief summary of basic bison reproductive physiology is presented followed by an overview of the current state of ART in Bison bison (American bison) and Bison bonasus (European bison or wisent). Research on ART ranging from artificial insemination to in vitro embryo transfer and cloning is discussed with particular regard to the application of ART for conservation purposes. While significant progress has been made in ART for bison, there are still many opportunities to improve these technologies and expand their impact for bison conservation.

Bovid Interspecies Somatic Cell Nuclear Transfer with Ooplasm Transfer

Interspecies somatic cell nuclear transfer (iSCNT) contributes to the preservation of endangered species, albeit nuclear-mitochondrial incompatibilities constrain its application. iSCNT, coupled with ooplasm transfer (iSCNT-OT), has the potential to overcome the challenges associated with species- and genus-specific differences in nuclear-mitochondrial communication. Our iSCNT-OT protocol combines the transfer of both bison (Bison bison bison) somatic cell and oocyte ooplasm by a two-step electrofusion into bovine (Bos taurus) enucleated oocytes. The procedures described herein could be used in further studies to determine the effects of crosstalk between nuclear and ooplasmic components in embryos carrying genomes from different species.

De novo transcription of thyroid hormone receptors is essential for early bovine embryo development in vitro

Thyroid hormone receptor (THR) α and THRβ mediate the genomic action of thyroid hormones (THs) that affect bovine embryo development. However, little is known about THRs in the preimplantation embryo. The aim of the present study was to investigate the importance of THRs in in vitro preimplantation bovine embryos. THR transcripts and protein levels were detected in developing preimplantation embryos up to the blastocyst stage. Embryonic transcription of THRs was inhibited by α-amanitin supplementation, and both maternal and embryonic transcription were knocked down by short interference (si) RNA microinjection. In the control group, mRNA and protein levels of THRs increased after fertilisation. In contrast, in both the transcription inhibition and knockdown groups there were significant (P<0.05) decreases in mRNA expression of THRs from the 2-cell stage onwards. However, protein levels of THRs were not altered at 2-cell stage, although they did exhibit a significant (P<0.05) decrease from the 4-cell stage. Moreover, inhibition of de novo transcripts of THRs using siRNA led to a significant (P<0.01) decrease in the developmental rate and cell number, as well as inducing a change in embryo morphology. In conclusion, THRs are transcribed soon after fertilisation, before major activation of the embryonic genome, and they are essential for bovine embryo development in vitro.

Potential role of intraspecific and interspecific cloning in the conservation of wild mammals

Intraspecific and interspecific cloning via somatic cell nuclear transfer (iSCNT) is a biotechnique with great possibilities for wild mammals because it allows the maintenance of biodiversity by recovering species, nuclear reprogramming for the production of pluripotency-induced cells, and studies related to embryonic development. Nevertheless, many areas in cloning, especially those associated with wild mammals, are still in question because of the difficulty in obtaining cytoplasmic donor cells (or cytoplasts). Conversely, donor cell nuclei (or karyoplasts) are widely obtained from the skin of living or post-mortem individuals and often maintained in somatic cell banks. Moreover, the creation of karyoplast–cytoplast complexes by fusion followed by activation and embryo development is one of the most difficult steps that requires further clarification to avoid genetic failures. Although difficult, cloning different species, such as wild carnivores and ungulates, can be successful via iSCNT with embryo development and the birth of offspring. Thus, novel research in the area that contributes to the conservation of biodiversity and knowledge of the physiology of species continues. The present review presents the failures and successes that occurred with the application of the technique in wild mammals, with the goal of helping future work on cloning via iSCNT.

Additional mitochondrial DNA influences the interactions between the nuclear and mitochondrial genomes in a bovine embryo model of nuclear transfer

We generated cattle embryos using mitochondrial supplementation and somatic cell nuclear transfer (SCNT), named miNT, to determine how additional mitochondrial DNA (mtDNA) modulates the nuclear genome. To eliminate any confounding effects from somatic cell mtDNA in intraspecies SCNT, donor cell mtDNA was depleted prior to embryo production. Additional oocyte mtDNA did not affect embryo development rates but increased mtDNA copy number in blastocyst stage embryos. Moreover, miNT-derived blastocysts had different gene expression profiles when compared with SCNT-derived blastocysts. Additional mtDNA increased expression levels of genes involved in oxidative phosphorylation, cell cycle and DNA repair. Supplementing the embryo culture media with a histone deacetylase inhibitor, Trichostatin A (TSA), had no beneficial effects on the development of miNT-derived embryos, unlike SCNT-derived embryos. When compared with SCNT-derived blastocysts cultured in the presence of TSA, additional mtDNA alone had beneficial effects as the activity of glycolysis may increase and embryonic cell death may decrease. However, these beneficial effects were not found with additional mtDNA and TSA together, suggesting that additional mtDNA alone enhances reprogramming. In conclusion, additional mtDNA increased mtDNA copy number and expression levels of genes involved in energy production and embryo development in blastocyst stage embryos emphasising the importance of nuclear-mitochondrial interactions.

Factors Affecting Mouse Somatic Cell Nuclear Reprogramming by Rabbit Ooplasms

Successful development of interspecies somatic cell nuclear transfer (iSCNT) embryos depends on compatibilities between ooplasmic and nuclear components. However, the mechanisms by which the compatibilities are regulated are still unknown. In this study, using mouse Oct4-green fluorescent protein (GFP) cells as donors and rabbit oocytes as recipients, we show that Oct4 and other pluripotency related genes were reactivated in some of mouse-rabbit iSCNT embryos, which could also activate Oct4 promoter-driven GFP reporter gene expression. Series nuclear transfer improved the efficiency of Oct4 reactivation. DNA demethylation of Oct4 promoter was detected in GFP positive iSCNT blastocysts, whereas GFP negative iSCNT embryos showed a low efficiency. Our results demonstrate that Oct4-GFP can well label the embryos with epigenetic remodeling and reactivation of pluripotent gene expression. Abundant rabbit mitochondria specific DNAs were identified in reconstructed mouse-rabbit embryos throughout preimplantation stages. Our data demonstrate that epigenetic remodeling and the complete mitochondrial match are not necessary for successful iSCNT embryo development before implantation.

Ooplasmic transfer in human oocytes: efficacy and concerns in assisted reproduction

BACKGROUND

Ooplasmic transfer (OT) technique or cytoplasmic transfer is an emerging technique with relative success, having a significant status in assisted reproduction. This technique had effectively paved the way to about 30 healthy births worldwide. Though OT has long been invented, proper evaluation of the efficacy and risks associated with this critical technique has not been explored properly until today. This review thereby put emphasis upon the applications, efficacy and adverse effects of OT techniques in human.

MAIN BODY

Available reports published between January 1982 and August 2017 has been reviewed and the impact of OT on assisted reproduction was evaluated. The results consisted of an update on the efficacy and concerns of OT, the debate on mitochondrial heteroplasmy, apoptosis, and risk of genetic and epigenetic alteration.

SHORT CONCLUSION

The application of OT technique in humans demands more clarity and further development of this technique may successfully prove its utility as an effective treatment for oocyte incompetence.