LCDM medium supports the derivation of bovine extended pluripotent stem cells with embryonic and extraembryonic potency in bovine-mouse chimeras from iPSCs and bovine fetal fibroblasts

Livestock embryonic stem cells for reproductive biotechniques and genetic improvement

Embryonic stem cells (ESCs) have proven to be a great in vitro model that faithfully recapitulates the events that occur during in vivo embryogenesis, making them a unique tool to study the cellular and molecular mechanisms that define tissue specification during embryonic development. Livestock ESCs are particularly attractive and have broad prospects including drug selection and human disease modeling, improvement of reproductive biotechniques and agriculture-related applications such as production of genetically modified animals. While mice and human ESCs have been established many years ago, no significant advances were made in livestock species until recently. Nowadays, livestock ESCs are available from cattle, pigs, sheep, horses and rabbits with different states of pluripotency. In this review, we summarize the current advances on livestock ESCs establishment and maintenance along with their present and future applications.

Hallmarks of totipotent and pluripotent stem cell states

Though totipotency and pluripotency are transient during early embryogenesis, they establish the foundation for the development of all mammals. Studying these in vivo has been challenging due to limited access and ethical constraints, particularly in humans. Recent progress has led to diverse culture adaptations of epiblast cells in vitro in the form of totipotent and pluripotent stem cells, which not only deepen our understanding of embryonic development but also serve as invaluable resources for animal reproduction and regenerative medicine. This review delves into the hallmarks of totipotent and pluripotent stem cells, shedding light on their key molecular and functional features.

DPPA2/4 Promote the Pluripotency and Proliferation of Bovine Extended Pluripotent Stem Cells by Upregulating the PI3K/AKT/GSK3β/β-Catenin Signaling Pathway

Developmental pluripotency-associated 2 (DPPA2) and DPPA4 are crucial transcription factors involved in maintaining pluripotency in humans and mice. However, the role of DPPA2/4 in bovine extended pluripotent stem cells (bEPSCs) has not been investigated. In this study, a subset of bEPSC-related differentially expressed genes (DEGs), including DPPA2 and DPPA4, was identified based on multiomics data (ATAC-seq and RNA-seq). Subsequent investigations revealed that double overexpression of DPPA2/4 facilitates the reprogramming of bovine fetal fibroblasts (BFFs) into bEPSCs, whereas knockout of DPPA2/4 in BFFs leads to inefficient reprogramming. DPPA2/4 overexpression and knockdown experiments revealed that the pluripotency and proliferation capability of bEPSCs were maintained by promoting the transition from the G1 phase to the S phase of the cell cycle. By activating the PI3K/AKT/GSK3β/β-catenin pathway in bEPSCs, DPPA2/4 can increase the nuclear accumulation of β-catenin, which further upregulates lymphoid enhancer binding factor 1 (LEF1) transcription factor activity. Moreover, DPPA2/4 can also regulate the expression of LEF1 by directly binding to its promoter region. Overall, our results demonstrate that DPPA2/4 promote the reprogramming of BFFs into bEPSCs while also maintaining the pluripotency and proliferation capability of bEPSCs by regulating the PI3K/AKT/GSK3β/β-catenin pathway and subsequently activating LEF1. These findings expand our understanding of the gene regulatory network involved in bEPSC pluripotency.

Derivation of Arbas Cashmere Goat Induced Pluripotent Stem Cells in LCDM with Trophectoderm Lineage Differentiation and Interspecies Chimeric Abilities

The Arbas cashmere goat is a unique biological resource that plays a vital role in livestock husbandry in China. LCDM is a medium with special small molecules (consisting of human LIF, CHIR99021, (S)-(+)-dimethindene maleate, and minocycline hydrochloride) for generation pluripotent stem cells (PSCs) with bidirectional developmental potential in mice, humans, pigs, and bovines. However, there is no report on whether LCDM can support for generation of PSCs with the same ability in Arbas cashmere goats. In this study, we applied LCDM to generate goat induced PSCs (giPSCs) from goat fetal fibroblasts (GFFs) by reprogramming. The derived giPSCs exhibited stem cell morphology, expressing pluripotent markers, and could differentiate into three germ layers. Moreover, the giPSCs differentiated into the trophectoderm lineage by spontaneous and directed differentiation in vitro. The giPSCs contributed to embryonic and extraembryonic tissue in preimplantation blastocysts and postimplantation chimeric embryos. RNA-sequencing analysis showed that the giPSCs were very close to goat embryos at the blastocyst stage and giPSCs have similar properties to typical extended PSCs (EPSCs). The establishment of giPSCs with LCDM provides a new way to generate PSCs from domestic animals and lays the foundation for basic and applied research in biology and agriculture.

Recent advances in stem cell-based blastocyst models

Early embryo development is a highly dynamic process that plays a crucial role in determining the health and characteristics of an organism. For many years, embryonic and extraembryonic stem cell lines representing various developmental stages have served as valuable models for studying early embryogenesis. As our understanding of stem cell culture and embryo development has advanced, researchers have been able to create more sophisticated 3D structures mimicking early embryos, such as blastocyst-like structures (blastoids). These innovative models represent a significant leap forward in the field. In this mini-review, we will discuss the latest progress in stem cell-based embryo models, explore potential future directions, and examine how these models contribute to a deeper understanding of early mammalian development.

Establishment of bovine trophoblast stem cells

Here, we report that a chemical cocktail (LCDM: leukemia inhibitory factor [LIF], CHIR99021, dimethinedene maleate [DiM], minocycline hydrochloride), previously developed for extended pluripotent stem cells (EPSCs) in mice and humans, enables de novo derivation and long-term culture of bovine trophoblast stem cells (TSCs). Bovine TSCs retain developmental potency to differentiate into mature trophoblast cells and exhibit transcriptomic and epigenetic (chromatin accessibility and DNA methylome) features characteristic of trophectoderm cells from early bovine embryos. The bovine TSCs established in this study will provide a model to study bovine placentation and early pregnancy failure.

Bovine blastocyst-like structures derived from stem cell cultures

Understanding the mechanisms of blastocyst formation and implantation is critical for improving farm animal reproduction but is hampered by a limited supply of embryos. Here, we developed an efficient method to generate bovine blastocyst-like structures (termed blastoids) via assembling bovine trophoblast stem cells and expanded potential stem cells. Bovine blastoids resemble blastocysts in morphology, cell composition, single-cell transcriptomes, in vitro growth, and the ability to elicit maternal recognition of pregnancy following transfer to recipient cows. Bovine blastoids represent an accessible in vitro model for studying embryogenesis and improving reproductive efficiency in livestock species.

Review: Progress in producing chimeric ungulate livestock for agricultural applications

The progress made in recent years in the derivation and culture of pluripotent stem cells from farm animals opens up the possibility of creating livestock chimeras. Chimeras producing gametes exclusively derived from elite donor stem cells could pass superior genetics on to the next generation and thereby reduce the genetic lag that typically exists between the elite breeding sector and the commercial production sector, especially for industries like beef and sheep where genetics is commonly disseminated through natural service mating. Chimeras carrying germ cells generated from genome-edited or genetically engineered pluripotent stem cells could further disseminate useful genomic alterations such as climate adaptation, animal welfare improvements, the repair of deleterious genetic conditions, and/or the elimination of undesired traits such as disease susceptibility to the next generation. Despite the successful production of chimeras with germ cells generated from pluripotent donor stem cells injected into preimplantation-stage blastocysts in model species, there are no documented cases of this occurring in livestock. Here, we review the literature on the derivation of pluripotent stem cells from ungulates, and progress in the production of chimeric ungulate livestock for agricultural applications, drawing on insights from studies done in model species, and discuss future possibilities of this fast-moving and developing field. Aside from the technical aspects, the consistency of the regulatory approach taken by different jurisdictions towards chimeric ungulate livestock with germ cells generated from pluripotent stem cells and their progeny will be an important determinant of breeding industry uptake and adoption in animal agriculture.

Review: Embryonic stem cells as tools for in vitro gamete production in livestock

The goal of in vitro gametogenesis is to reproduce the events of sperm and oocyte development in the laboratory. Significant advances have been made in the mouse in the last decade, but evolutionary divergence from the murine developmental program has prevented the replication of these advances in large mammals. In recent years, intensive work has been done in humans, non-human primates and livestock to elucidate species-specific differences that regulate germ cell development, due to the number of potential applications. One of the most promising applications is the use of in vitro gametes to optimize the spread of elite genetics in cattle. In this context, embryonic stem cells have been posed as excellent candidates for germ cell platforms. Here, we present the most relevant advances in in vitro gametogenesis of interest to livestock science, including new types of pluripotent stem cells with potential for germline derivation, characterization of the signaling environment in the gonadal niche, and experimental systems used to reproduce different stages of germ cell development in the laboratory.

Stem Cells as Nuclear Donors for Mammalian Cloning

Mammals are routinely cloned by introducing somatic nuclei into enucleated oocytes. Cloning contributes to propagating desired animals, to germplasm conservation efforts, among other applications. A challenge to more broader use of this technology is the relatively low cloning efficiency, which inversely correlates with donor cell differentiation status. Emerging evidence suggests that adult multipotent stem cells improve cloning efficiency, while the greater potential of embryonic stem cells for cloning remains restricted to the mouse. The derivation of pluripotent or totipotent stem cells from livestock and wild species and their association with modulators of epigenetic marks in donor cells should increase cloning efficiency.

Methanol fixed feeder layers altered the pluripotency and metabolism of bovine pluripotent stem cells

The pluripotency maintenance of pluripotent stem cells (PSCs) requires the suitable microenvironment, which commonly provided by feeder layers. However, the preparation of feeder layers is time consuming and labor exhaustive, and the feeder cells treated with mitomycin C or γ-ray irradiation bring heterologous contamination. In this study, mouse embryonic fibroblasts (MEFs) were treated by methanol to generate chemical fixed feeder cells, and bovine embryonic stem cells F7 (bESC-F7) cultured on this feeder layer. Then the pluripotency and metabolism of bESC-F7 cultured on methanol-fixed MEFs (MT-MEFs) named MT-F7 was compared with mitomycin C treated MEFs (MC-MEFs). The results showed that bESC-F7 formed alkaline phosphatase positive colonies on MT-MEFs, the relative expression of pluripotent markers of these cells was different from the bESCs cultured on the MC-MEFs (MC-F7). The long-term cultured MT-F7 formed embryoid bodies, showed the ability to differentiate into three germ layers similar to MC-F7. The analyses of RNA-seq data showed that MT-MEFs lead bESCs to novel steady expression patterns of genes regulating pluripotency and metabolism. Furthermore, the bovine expanded pluripotent stem cells (bEPSCs) cultured on MT-MEFs formed classical colonies, maintained pluripotency, and elevated metabolism. In conclusion, MT-MEFs were efficient feeder layer that maintain the distinctive pluripotency and metabolism of PSCs.

Pluripotent Core in Bovine Embryos: A Review

Early development in mammals is characterized by the ability of each cell to produce a complete organism plus the extraembryonic, or placental, cells, defined as pluripotency. During subsequent development, pluripotency is lost, and cells begin to differentiate to a particular cell fate. This review summarizes the current knowledge of pluripotency features of bovine embryos cultured in vitro, focusing on the core of pluripotency genes (OCT4, NANOG, SOX2, and CDX2), and main chemical strategies for controlling pluripotent networks during early development. Finally, we discuss the applicability of manipulating pluripotency during the morula to blastocyst transition in cattle species.

Establishment of Bovine-Induced Pluripotent Stem Cells

Pluripotent stem cells (PSCs) have been successfully developed in many species. However, the establishment of bovine-induced pluripotent stem cells (biPSCs) has been challenging. Here we report the generation of biPSCs from bovine mesenchymal stem cells (bMSCs) by overexpression of lysine-specific demethylase 4A (KDM4A) and the other reprogramming factors OCT4, SOX2, KLF4, cMYC, LIN28, and NANOG (K_dOSKMLN). These biPSCs exhibited silenced transgene expression at passage 10, and had prolonged self-renewal capacity for over 70 passages. The biPSCs have flat, primed-like PSC colony morphology in combined media of knockout serum replacement (KSR) and mTeSR, but switched to dome-shaped, naïve-like PSC colony morphology in mTeSR medium and 2i/LIF with single cell colonization capacity. These cells have comparable proliferation rate to the reported primed- or naïve-state human PSCs, with three-germ layer differentiation capacity and normal karyotype. Transcriptome analysis revealed a high similarity of biPSCs to reported bovine embryonic stem cells (ESCs) and embryos. The naïve-like biPSCs can be incorporated into mouse embryos, with the extended capacity of integration into extra-embryonic tissues. Finally, at least 24.5% cloning efficiency could be obtained in nuclear transfer (NT) experiment using late passage biPSCs as nuclear donors. Our report represents a significant advance in the establishment of bovine PSCs.

Simplification of culture conditions and feeder-free expansion of bovine embryonic stem cells

Bovine embryonic stem cells (bESCs) extend the lifespan of the transient pluripotent bovine inner cell mass in vitro. After years of research, derivation of stable bESCs was only recently reported. Although successful, bESC culture relies on complex culture conditions that require a custom-made base medium and mouse embryonic fibroblasts (MEF) feeders, limiting the widespread use of bESCs. We report here simplified bESC culture conditions based on replacing custom base medium with a commercially available alternative and eliminating the need for MEF feeders by using a chemically-defined substrate. bESC lines were cultured and derived using a base medium consisting of N2B27 supplements and 1% BSA (NBFR-bESCs). Newly derived bESC lines were easy to establish, simple to propagate and stable after long-term culture. These cells expressed pluripotency markers and actively proliferated for more than 35 passages while maintaining normal karyotype and the ability to differentiate into derivatives of all three germ lineages in embryoid bodies and teratomas. In addition, NBFR-bESCs grew for multiple passages in a feeder-free culture system based on vitronectin and Activin A medium supplementation while maintaining pluripotency. Simplified conditions will facilitate the use of bESCs for gene editing applications and pluripotency and lineage commitment studies.

Strategy to Establish Embryo-Derived Pluripotent Stem Cells in Cattle

Stem cell research is essential not only for the research and treatment of human diseases, but also for the genetic preservation and improvement of animals. Since embryonic stem cells (ESCs) were established in mice, substantial efforts have been made to establish true ESCs in many species. Although various culture conditions were used to establish ESCs in cattle, the capturing of true bovine ESCs (bESCs) has not been achieved. In this review, the difficulty of establishing bESCs with various culture conditions is described, and the characteristics of proprietary induced pluripotent stem cells and extended pluripotent stem cells are introduced. We conclude with a suggestion of a strategy for establishing true bESCs.