Effects of different feeder layers on culture of bovine embryonic stem cell-like cells in vitro

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.

Development of Reproducible and Scalable Culture Conditions for In Vitro Maintenance of Pig Embryonic Stem Cells Using the Sandoz Inbred Swiss Mouse Thioguanine-Resistant Ouabain-Resistant Cell Line as a Feeder Layer

Feeder cells play a crucial role in maintaining the pluripotency of embryonic stem cells (ESCs) by secreting various extrinsic regulators, such as extracellular matrix (ECM) proteins and growth factors. Although primary mouse embryonic fibroblasts (MEFs) are the most widely used feeder cell type for the culture of ESCs, they have inevitable disadvantages such as batch-to-batch variation and labor-intensive isolation processes. Here, we revealed that the Sandoz inbred Swiss Mouse (SIM) thioguanine-resistant ouabain-resistant (STO) cell line, an immortalized cell line established from mouse SIM embryonic fibroblasts, can be used as a feeder layer for in vitro culture of authentic pig ESCs instead of primary MEFs. First, the expression of genes encoding ECM proteins and growth factors was analyzed to compare their secretory functions as feeder cells. Quantitative real-time polymerase chain reaction (qPCR) showed that the gene expression of these pluripotency-associated factors was downregulated in STO cells compared to primary MEFs of similar density. Therefore, subsequent optimization of the culture conditions was attempted using higher STO cell densities. Notably, pig ESCs cultured on STO cell density of 3 × (187,500 cells/cm2) exhibited the most similar pluripotent state to pig ESCs cultured on primary MEF density of 1 × (62,500 cells/cm2), as determined by alkaline phosphatase staining, qPCR, and immunocytochemistry. In addition, pig ESCs cultured on STO cell density of 3 × formed complex teratoma containing multiple types of tissues derived from all three germ layers. Our culture conditions using optimal STO cell density can be applied to fields requiring reproducible and scalable production of pig ESCs, such as preclinical research and cellular agriculture.

Naïve-like conversion of bovine induced pluripotent stem cells from Sertoli cells

Feeder cells are essential to derive pluripotent stem cells (PSCs). Mouse embryonic fibroblasts (MEF) are widely used as feeder to generate and culture embryonic stem cells (ESCs) and induced PSCs (iPSCs) in many species. However it may not be suitable for livestock ESCs/iPSCs due to interspecies difference. Previously we derived bovine iPSCs from bovine Sertoli cells using MEF feeder. Here we compared the effects of MEF feeder and bovine embryonic fibroblasts (BEF) feeder on the maintenance of bovine iPSC pluripotency and morphology as well their contributions to the naïve-like conversion, based on a naïve medium (NM). The results showed successful conversion of the primed bovine iPSCs to naïve-like state within 3-4 days both on MEF feeder and BEF feeder in NM (termed as MNM and BNM respectively). These naïve-like iPSCs showed normal karyotype. There were more iPSC colonies under BNM condition than MNM condition. Epigenetically, histone modification H3K4 was upregulated, while H3K27 was downregulated in the naïve-like iPSCs. We further analyzed the naïve markers and differentiation potential both in vitro and in vivo of these cells, which were all reserved throughout the maintenance. Together, bovine naïve-like iPSCs can be generated both on MEF and BEF feeder in NM condition. The BNM condition is able to sustain the pluripotency and differentiation potential of the naïve-like bovine iPSCs, and improve the conversion efficiency.

Mitotically inactivated mosquito cells support robust Wolbachia infection and replication

Wolbachia is an obligate intracellular bacterium that infects many species of insects, and has been of particular interest in recent efforts to reduce disease transmission by mosquitoes. Two aspects of Wolbachia biology underlie its applications for insect control: first, the bacterium behaves as a natural gene drive agent and, second, when introduced into mosquitoes that do not harbor Wolbachia in nature, infection reduces survival of pathogens. These properties support efforts to explore the basic biology of Wolbachia in insect cell lines, which can produce sufficient infectious material for microbiological studies and microinjection into novel hosts. When introduced into naïve C7-10 Aedes albopictus mosquito cells, the yield of Wolbachia strain wStri improves, roughly in proportion to the size of the inoculum, as exponential growth of the host cell ceases. Wolbachia yields also increase when persistently infected C/wStri1 cells or naive, newly infected cells are treated with 20-hydroxyecdysone (20E), which inhibits growth in the G1 phase of the cell cycle. These observations suggest that Wolbachia infection and replication are independent of exponential growth and mitosis of host cells. To explore yields of infectious bacteria in cells arrested prior to infection, I tested host cells pre-treated with mitomycin C, an agent that crosslinks DNA and prevents cell division that is used to produce "feeder layers" with mammalian cells. Yields of wStri per plate increased by about 50-fold relative to exponentially growing cells, and the multiplicity of infection necessary for a robust infection was reduced to a single bacterium per cell. These results suggest that Wolbachia infection and replication are supported by mitotically arrested cells and provide new insights into biological processes that influence maintenance of a widespread obligate intracellular bacterium.

Efficient induction and sustenance of pluripotent stem cells from bovine somatic cells

Although derivation of naïve bovine embryonic stem cells is unachieved, the possibility for generation of bovine induced pluripotent stem cells (biPSCs) has been generally reported. However, attempts to sustain biPSCs by promoting self-renewal have not been successful. Methods established for maintaining murine and human induced pluripotent stem cells (iPSCs) do not support self-renewal of iPSCs for any bovid species. In this study, we examined methods to enhance complete reprogramming and concurrently investigated signaling relevant to pluripotency of the bovine blastocyst inner cell mass (ICM). First, we identified that forced expression of SV40 large T antigen together with the reprogramming genes (OCT4, SOX2, KLF4 and MYC) substantially enhanced the reprogramming efficacy of bovine fibroblasts to biPSCs. Second, we uncovered that TGFβ signaling is actively perturbed in the ICM. Inhibition of ALK4/5/7 to block TGFβ/activin/nodal signaling together with GSK3β and MEK1/2 supported robust in vitro self-renewal of naïve biPSCs with unvarying colony morphology, steady expansion, expected pluripotency gene expression and committed differentiation plasticity. Core similarities between biPSCs and stem cells of the 16-cell-stage bovine embryo indicated a stable ground state of pluripotency; this allowed us to reliably gain predictive understanding of signaling in bovine pluripotency using systems biology approaches. Beyond defining a high-fidelity platform for advancing biPSC-based biotechnologies that have not been previously practicable, these findings also represent a significant step towards understanding corollaries and divergent aspects of bovine pluripotency.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: Pluripotency reprogramming by overcoming the stable epigenome of bovine cells, and uncovering precise early embryo self-renewal mechanisms enables sustenance and expansion of authentic induced pluripotent stem cells in vitro.

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.

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.

Revolutionize livestock breeding in the future: an animal embryo-stem cell breeding system in a dish

Meat and milk production needs to increase ~ 70–80% relative to its current levels for satisfying the human needs in 2050. However, it is impossible to achieve such genetic gain by conventional animal breeding systems. Based on recent advances with regard to in vitro induction of germ cell from pluripotent stem cells, herein we propose a novel embryo-stem cell breeding system. Distinct from the conventional breeding system in farm animals that involves selecting and mating individuals, the novel breeding system completes breeding cycles from parental to offspring embryos directly by selecting and mating embryos in a dish. In comparison to the conventional dairy breeding scheme, this system can rapidly achieve 30–40 times more genetic gain by significantly shortening generation interval and enhancing selection intensity. However, several major obstacles must be overcome before we can fully use this system in livestock breeding, which include derivation and mantaince of pluripotent stem cells in domestic animals, as well as in vitro induction of primordial germ cells, and subsequent haploid gametes. Thus, we also discuss the potential efforts needed in solving the obstacles for application this novel system, and elaborate on their groundbreaking potential in livestock breeding. This novel system would provide a revolutionary animal breeding system by offering an unprecedented opportunity for meeting the fast-growing meat and milk demand of humans.

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.

Expression and secretory profile of buffalo fetal fibroblasts and Wharton's jelly feeder layers

The present study examined the comparative expression and secretory profile of vital signaling molecules in buffalo fetal fibroblasts (BFF) and Wharton's jelly (BWJ) feeder layers at different passages. Both feeder layers were expanded up to 8th passage. Signaling molecules viz. bone morphogenetic protein 4 (BMP4), fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF) and transforming growth factor beta 1 (TGFB1) and pluripotency-associated transcriptional factors (POU5F1, SOX2, NANOG, KLF4, MYC and FOXD3) were immunolocalized in the both feeder types. A clear variation in the expression pattern of key signaling molecules with passaging was registered in both feeders compared to primary culture (0 passage). The conditioned media (CM) was collected from different passages (2, 4, 6, 8) of both the feeder layers and was quantified using enzyme-linked immunosorbent assay (ELISA). Concomitant to expression profile, protein quantification also revealed differences in the concentration of signaling molecules at different time points. Conjointly, expression and secretory profile revealed that 2nd passage of BFF and 6th passage of BWJ exhibit optimal levels of key signaling molecules thus may be selected as best passages for embryonic stem cells (ESCs) propagation. Further, the effect of mitomycin-C (MMC) treatment on the expression profile of signaling molecules in the selected passages of BFF and BWJ revealed that MMC modulates the expression profile of these molecules. In conclusion, the results indicate that feeder layers vary in expression and secretory pattern of vital signaling molecules with passaging. Based on these findings, the appropriate feeder passages may be selected for the quality propagation of buffalo ESCs.

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.