Bovine Pluripotent Stem Cells: Current Status and Prospects

Pluripotent stem cells (PSCs) can differentiate into three germ layers and diverse autologous cell lines. Since cattle are the most commonly used large domesticated animals, an important food source, and bioreactors, great efforts have been made to establish bovine PSCs (bPSCs). bPSCs have great potential in bovine breeding and reproduction, modeling in vitro differentiation, imitating cancer development, and modeling diseases. Currently, bPSCs mainly include bovine embryonic stem cells (bESCs), bovine induced pluripotent stem cells (biPSCs), and bovine expanded potential stem cells (bEPSCs). Establishing stable bPSCs in vitro is a critical scientific challenge, and researchers have made numerous efforts to this end. In this review, the category of PSC pluripotency; the establishment of bESCs, biPSCs, and bEPSCs and its challenges; and the application outlook of bPSCs are discussed, aiming to provide references for future research.

Acquisition and maintenance of pluripotency are influenced by fibroblast growth factor, leukemia inhibitory factor, and 2i in bovine-induced pluripotent stem cells

Several opportunities for embryo development, stem cell maintenance, cell fate, and differentiation have emerged using induced pluripotent stem cells (iPSCs). However, the difficulty in comparing bovine iPSCs (biPSCs) with embryonic stem cells (ESCs) was a challenge for many years. Here, we reprogrammed fetal fibroblasts by transient expression of the four transcription factors (Oct4, Sox2, Klf4, and c-Myc, collectively termed “OSKM” factors) and cultured in iPSC medium, supplemented with bFGF, bFGF2i, leukemia inhibitory factor (LIF), or LIF2i, and then compared these biPSC lines with bESC to evaluate the pluripotent state. biPSC lines were generated in all experimental groups. Particularly, reprogrammed cells treated with bFGF were more efficient in promoting the acquisition of pluripotency. However, LIF2i treatment did not promote continuous self-renewal. biPSCs (line 2) labeled with GFP were injected into early embryos (day 4.5) to assess the potential to contribute to chimeric blastocysts. The biPSC lines show a pluripotency state and are differentiated into three embryonic layers. Moreover, biPSCs and bESCs labeled with GFP were able to contribute to chimeric blastocysts. Additionally, biPSCs have shown promising potential for contributing to chimeric blastocysts and for future studies.

Genetically modified animals for use in biopharmacology: from research to production

Introduction: In this review, the analysis of technologies for obtaining biologically active proteins from various sources is carried out, and the comparative analysis of technologies for creating producers of biologically active proteins is presented. Special attention is paid to genetically modified animals as bioreactors for the pharmaceutical industry of a new type. The necessity of improving the technology of development transgenic rabbit producers and creating a platform solution for the production of biological products is substantiated.

The advantages of using TrB for the production of recombinant proteins: The main advantages of using TrB are the low cost of obtaining valuable complex therapeutic human proteins in readily accessible fluids, their greater safety relative to proteins isolated directly from human blood, and the greater safety of the activity of the native protein.

The advantages of the mammary gland as a system for the expression of recombinant proteins: The mammary gland is the organ of choice for the expression of valuable recombinant proteins because milk is easy to collect in large volumes.

Methods for obtaining transgenic animals: The modern understanding of the regulation of gene expression and the discovery of new tools for gene editing can increase the efficiency of creating bioreactors for animals and help to obtain high concentrations of the target protein.

The advantages of using rabbits as bioreactors producing recombinant proteins in milk: The rabbit is a relatively small animal with a short duration of gestation, puberty and optimal size, capable of producing up to 5 liters of milk per year per female, receiving up to 300 grams of the target protein.

Importance of WNT-dependent signaling for derivation and maintenance of primed pluripotent bovine embryonic stem cells†

The WNT signaling system plays an important but paradoxical role in the regulation of pluripotency. In the cow, IWR-1, which inhibits canonical WNT activation and has WNT-independent actions, promotes the derivation of primed pluripotent embryonic stem cells from the blastocyst. Here, we describe a series of experiments to determine whether derivation of embryonic stem cells could be generated by replacing IWR-1 with other inhibitors of WNT signaling. Results confirm the importance of inhibition of canonical WNT signaling for the establishment of pluripotent embryonic stem cells in cattle and indicate that the actions of IWR-1 can be mimicked by the WNT secretion inhibitor IWP2 but not by the tankyrase inhibitor XAV939 or WNT inhibitory protein dickkopf 1. The role of Janus kinase-mediated signaling pathways for the maintenance of pluripotency of embryonic stem cells was also evaluated. Maintenance of pluripotency of embryonic stem cells lines was blocked by a broad inhibitor of Janus kinase, even though the cells did not express phosphorylated signal transducer and activator of transcription 3 (pSTAT3). Further studies with blastocysts indicated that IWR-1 blocks the activation of pSTAT3. A likely explanation is that IWR-1 blocks differentiation of embryonic stem cells into a pSTAT3+ lineage. In conclusion, results presented here indicate the importance of inhibition of WNT signaling for the derivation of pluripotent bovine embryonic stem cells, the role of Janus kinase signaling for maintenance of pluripotency, and the participation of IWR-1 in the inhibition of activation of STAT3.

Establishment of bovine expanded potential stem cells

Embryonic stem cells (ESCs) and induced pluripotent stem cells have the potential to differentiate to all cell types of an adult individual and are useful for studying development and for translational research. However, extrapolation of mouse and human ESC knowledge to deriving stable ESC lines of domestic ungulates and large livestock species has been challenging. In contrast to ESCs that are usually established from the blastocyst, mouse expanded potential stem cells (EPSCs) are derived from four-cell and eight-cell embryos. We have recently used the EPSC approach and established stem cells from porcine and human preimplantation embryos. EPSCs are molecularly similar across species and have broader developmental potential to generate embryonic and extraembryonic cell lineages. We further explore the EPSC technology for mammalian species refractory to the standard ESC approaches and report here the successful establishment of bovine EPSCs (bEPSCs) from preimplantation embryos of both wild-type and somatic cell nuclear transfer. bEPSCs express high levels of pluripotency genes, propagate robustly in feeder-free culture, and are genetically stable in long-term culture. bEPSCs have enriched transcriptomic features of early preimplantation embryos and differentiate in vitro to cells of the three somatic germ layers and, in chimeras, contribute to both the embryonic (fetal) and extraembryonic cell lineages. Importantly, precise gene editing is efficiently achieved in bEPSCs, and genetically modified bEPSCs can be used as donors in somatic cell nuclear transfer. bEPSCs therefore hold the potential to substantially advance biotechnology and agriculture.

Characterisation of bovine embryos following prolonged culture in embryonic stem cell medium containing leukaemia inhibitory factor

In order to help elucidate the process of epiblast and trophoblast cell differentiation in bovine embryos invitro, we attempted to develop a suitable culture medium to allow extended embryo culture. Day 7 bovine blastocysts developed in conventional medium were cultured further in embryonic stem cell medium with or without leukaemia inhibitory factor (LIF) until Day 23. At Day 14, the expression of octamer-binding transcription factor 3/4 (OCT3/4) and VIMENTIN was significantly higher in embryos cultured with than without LIF, but embryonic disc formation was not observed. Although expression of SRY (sex determining region Y)-box 17 (SOX17) mRNA was significantly lower in Day 14 embryos cultured with and without LIF than in invivo embryos, hypoblast cells formed just inside the trophoblast cells of the invitro-cultured embryos. On Day 23, expression of placental lactogen (PL) and prolactin-related protein 1 (PRP1) was not affected by LIF in invitro-cultured embryos, levels of both genes were significantly lower in the invitro than invivo embryos. Similar to invivo embryos, binucleate cell clusters seen in Day 23invitro-cultured embryos were composed of PL-negative and -positive cells. These results suggest that our culture system partially reproduced the differentiation process of trophoblast cells invivo.

Livestock pluripotency is finally captured in vitro

Pluripotent stem cells (PSCs) have demonstrated great utility in improving our understanding of mammalian development and continue to revolutionise regenerative medicine. Thanks to the improved understanding of pluripotency in mice and humans, it has recently become feasible to generate stable livestock PSCs. Although it is unlikely that livestock PSCs will be used for similar applications as their murine and human counterparts, new exciting applications that could greatly advance animal agriculture are being developed, including the use of PSCs for complex genome editing, cellular agriculture, gamete generation and invitro breeding schemes.

In vitro breeding: application of embryonic stem cells to animal production†

Embryonic stem cells (ESCs) are derived from the inner cell mass of preimplantation blastocysts. For decades, attempts to efficiently derive ESCs in animal livestock species have been unsuccessful, but this goal has recently been achieved in cattle. Together with the recent reconstitution of the germ cell differentiation processes from ESCs in mice, these achievements open new avenues for the development of promising technologies oriented toward improving health, animal production, and the environment. In this article, we present a strategy that will notably accelerate genetic improvement in livestock populations by reducing the generational interval, namely in vitro breeding (IVB). IVB combines genomic selection, a widely used strategy for genetically improving livestock, with ESC derivation and in vitro differentiation of germ cells from pluripotent stem cells. We also review the most recent findings in the fields on which IVB is based. Evidence suggests this strategy will be soon within reach.

Establishment of porcine nuclear transfer-derived embryonic stem cells using induced pluripotent stem cells as donor nuclei

We investigated whether sequential reprogramming via porcine induced pluripotent stem cells (piPSCs) or exposure to oocyte cytoplasm following nuclear transfer could generate nuclear transfer-derived ESCs (piPSCs-ntESCs). Nuclear transfer embryos were reconstructed with piPSCs possessing a ZsGreen fluorescent marker for expression of exogenous Nanog and Lin28. Reconstructed oocytes developed to morphologically normal 8-cell/morulae (35/93, 37.6%) and blastocysts (12/93, 12.9%). Although most green fluorescent protein-positive blastocysts showed efficient outgrowth (8/10, 80%), none formed primary colonies and all cultures degenerated. Conversely, 15% of fluorescent positive 8-cell/morula stage embryos showed outgrowth (6/40), with three forming primary colonies (7.5%). All three were expanded and maintained as piPSC-ntESC lines. These cell lines expressed stem cell marker genes and proteins. Despite inactivation of one X chromosome, all piPSC-ntESC lines formed teratomas comprising derivatives from all three embryonic germ layers. Strong SSEA1, 3, and 4 expression was detected at the 8-cell/morula stage in embryos reconstructed from both piPSCs and porcine embryonic fibroblasts (PEFs). SSEA3 was notably absent from IVF controls at pre-implantation embryo stages. Finally, we attempted to establish ntESCs from 8-cell/morulae reconstructed with PEFs using the same culture conditions as those for piPSC-ntESC derivation. Although eight primary colonies arose from 107 embryos (7.5%), they all degenerated after the first passage culture. Early and sustained expression of key reprogramming regulatory factors may be critical for pluripotent stem cell derivation to derive piPSC-ntESCs from 8-cell/morula stages, while the expression of SSEAs may be involved in the initial stem cell colony formation phases.

Regulation of Cell Fate Decisions in Early Mammalian Embryos

Early embryogenesis is characterized by the segregation of cell lineages that fulfill critical roles in the establishment of pregnancy and development of the fetus. The formation of the blastocyst marks the emergence of extraembryonic precursors, needed for implantation, and of pluripotent cells, which differentiate toward the major lineages of the adult organism. The coordinated emergence of these cell types shows that these processes are broadly conserved in mammals. However, developmental heterochrony and changes in gene regulatory networks highlight unique evolutionary adaptations that may explain the diversity in placentation and in the mechanisms controlling pluripotency in mammals. The incorporation of new technologies, including single-cell omics, imaging, and gene editing, is instrumental for comparative embryology. Broadening the knowledge of mammalian embryology will provide new insights into the mechanisms driving evolution and development. This knowledge can be readily translated into biomedical and biotechnological applications in humans and livestock, respectively.

Correction of a Disease Mutation using CRISPR/Cas9-assisted Genome Editing in Japanese Black Cattle

Isoleucyl-tRNA synthetase (IARS) syndrome is a recessive disease of Japanese Black cattle caused by a single nucleotide substitution. To repair the mutated IARS gene, we designed clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to create a double-strand break near the mutation site. CRISPR/Cas9 and donor DNA that contained a synonymous codon for the correct amino acid and an Aequorea coerulescens Green Fluorescent Protein (AcGFP) cassette with a piggyBac transposase recognition site at both ends were introduced into bovine fetal fibroblast (BFF) cells isolated from a homozygous mutant calf. Recombinant cells were enriched on the basis of expression of AcGFP, and two cell lines that contained the repaired allele were subcloned. We generated somatic cell nuclear transfer (SCNT) embryos from the repaired cells and transferred 22 blastocysts to recipient cows. In total, five viable fetuses were retrieved at Days 34 and 36. PiggyBac transposase mRNA was introduced into BFF cells isolated from cloned foetuses and AcGFP-negative cells were used for second round of cloning. We transferred nine SCNT embryos to recipient cows and retrieved two fetuses at Day 34. Fetal genomic DNA analysis showed correct repair of the IARS mutation without any additional DNA footprint.

States and Origins of Mammalian Embryonic Pluripotency In Vivo and in a Dish

Mouse embryonic stem cells (ESC), derived from preimplantation embryos in 1981, defined mammalian pluripotency for many decades. However, after the derivation of human ESC in 1998, comparative studies showed that different types of pluripotency exist in early embryos and that these can be captured in vitro under various culture conditions. Over the past decade much has been learned about the key signaling pathways, growth factor requirements, and transcription factor profiles of pluripotent cells in embryos, allowing improvement of derivation and culture conditions for novel pluripotent stem cell types. More recently, studies using single-cell transcriptomics of embryos from different species provided an unprecedented level of resolution of cellular interactions and cell fate decisions that are informing new ways to understand the emergence of pluripotency in different organisms. These new approaches enhance knowledge of species differences during early embryogenesis and will be instrumental for improving methodologies for generating intra- and interspecies chimeric animals using pluripotent stem cells. Here, we discuss the recent developments in our understanding of early embryogenesis in different mammalian species.

Establishment of bovine embryonic stem cells after knockdown of CDX2

Bovine embryonic stem cells (bESCs) have not been successfully established yet. One reason could be that CDX2, as the trophectoderm regulator, expresses in bovine inner cell mass (ICM), which probably becomes a technical barrier for maintaining the pluripotency of bESCs in vitro. We hypothesized that CDX2 knockdown (CDX2-KD) could remove such negative effort, which will be helpful for capturing complete and permanent capacity of pluripotency. Expression and localization of pluripotent genes were not affected in CDX2-KD blastocysts. The CDX2-KD bESCs grew into monolayers on feeder layer. Pluripotent genes expressed at an improved levels and lasted longer time in CDX2-KD bESCs, along with down-regulation of DNA methylation on promoters of both OCT4 and SOX2. The cystic structure typical for trophoblast cells did not show during culturing CDX2-KD bESCs. CDX2-KD bESC-derived Embryoid bodies showed with compact morphology and with the improved levels of differentiations in three germ layers. CDX2-KD bESCs still carried the capacity of forming teratomas with three germ layers after long-term culture. In summary, CDX2 in bovine ICM was inducer of trophoblast lineage with negative effect on maintenance of pluripotency of bESCs. Precise regulation CDX2 expression to switch on/off will be studied next for application on establishment of bESCs.

Transgenic bovine as bioreactors: Challenges and perspectives

The use of recombinant proteins has increased in diverse commercial sectors. Various systems for protein production have been used for the optimization of production and functional protein expression. The mammary gland is considered to be a very interesting system for the production of recombinant proteins due to its high level of expression and its ability to perform post-translational modifications. Cows produce large quantities of milk over a long period of lactation, and therefore this species is an important candidate for recombinant protein expression in milk. However, transgenic cows are more difficult to generate due to the inefficiency of transgenic methodologies, the long periods for transgene detection, recombinant protein expression and the fact that only a single calf is obtained at the end of each pregnancy. An increase in efficiency for transgenic methodologies for cattle is a big challenge to overcome. Promising methodologies have been proposed that can help to overcome this obstacle, enabling the use of transgenic cattle as bioreactors for protein production in milk for industry.

Pluripotent Stem Cells from Domesticated Mammals

This review deals with the latest advances in the study of embryonic stem cells (ESC) and induced pluripotent stem cells (iPSC) from domesticated species, with a focus on pigs, cattle, sheep, goats, horses, cats, and dogs. Whereas the derivation of fully pluripotent ESC from these species has proved slow, reprogramming of somatic cells to iPSC has been more straightforward. However, most of these iPSC depend on the continued expression of the introduced transgenes, a major drawback to their utility. The persistent failure in generating ESC and the dependency of iPSC on ectopic genes probably stem from an inability to maintain the stability of the endogenous gene networks necessary to maintain pluripotency. Based on work in humans and rodents, achievement of full pluripotency will likely require fine adjustments in the growth factors and signaling inhibitors provided to the cells. Finally, we discuss the future utility of these cells for biomedical and agricultural purposes.

Generation of Naïve Bovine Induced Pluripotent Stem Cells Using PiggyBac Transposition of Doxycycline-Inducible Transcription Factors

Generation of pluripotent stem cells (PSCs) in large domestic animals has achieved only limited success; most of the PSCs obtained to date have been classified as primed PSCs, which possess very little capacity to produce chimeric offspring. By contrast, mouse PSCs have been classified as naïve PSCs that can contribute to most of the tissues of chimeras, including germ cells. Here, we describe the generation of two different types of bovine induced pluripotent stem cells (biPSCs) from amnion cells, achieved through introduction of piggyBac vectors containing doxycycline-inducible transcription factors (Oct3/4, Sox2, Klf4, and c-Myc). One type of biPSCs, cultured in medium supplemented with knockout serum replacement (KSR), FGF2, and bovine leukemia inhibitory factor (bLIF), had a flattened morphology like human PSCs; these were classified as primed-type. The other type biPSCs, cultured in KSR, bLIF, Mek/Erk inhibitor, GSK3 inhibitor and forskolin, had a compact morphology like mouse PSCs; these were classified as naïve-type. Cells could easily be switched between these two types of biPSCs by changing the culture conditions. Both types of biPSCs had strong alkaline phosphatase activity, expressed pluripotent markers (OCT3/4, NANOG, REX1, ESRRβ, STELLA, and SOCS3), and formed embryoid bodies that gave rise to differentiated cells from all three embryonic germ layers. However, only naïve-type biPSCs showed the hallmarks of naïve mouse PSCs, such as LIF-dependent proliferation, lack of FGF5 expression, and active XIST expression with two active X chromosomes. Furthermore, naïve-type biPSCs could contribute to the inner cell mass (ICM) of host blastocysts and most tissues within chimeric embryos. This is the first report of generation of biPSCs with several characteristics similar to those of naïve mouse PSCs and a demonstrated potential to contribute to chimeras.