Pluripotency network in porcine embryos and derived cell lines

Use of Epigenetic Cues and Mechanical Stimuli to Generate Blastocyst-Like Structures from Mammalian Skin Dermal Fibroblasts

Mammalian embryogenesis is characterized by complex interactions between embryonic and extra-embryonic tissues that coordinate morphogenesis, coupling bio-mechanical and bio-chemical cues, to regulate gene expression and influence cell fate. Deciphering such mechanisms is essential to understand early embryogenesis, as well as to harness differentiation disorders. Currently, several early developmental events remain unclear, mainly due to ethical and technical limitations related to the use of natural embryos.Here, we describe a three-step approach to generate 3D spherical structures, arbitrarily defined "epiBlastoids," whose phenotype is remarkably similar to natural embryos. In the first step, adult dermal fibroblasts are converted into trophoblast-like cells, combining the use of 5-azacytidine, to erase the original cell phenotype, with an ad hoc induction protocol, to drive erased cells into the trophoblast lineage. In the second step, once again epigenetic erasing is applied, in combination with mechanosensing-related cues, to generate inner cell mass (ICM)-like spheroids. More specifically, erased cells are encapsulated in micro-bioreactors to promote 3D cell rearrangement and boost pluripotency. In the third step, chemically induced trophoblast-like cells and ICM-like spheroids are co-cultured in the same micro-bioreactors. The newly generated embryoids are then transferred to microwells, to encourage further differentiation and favor epiBlastoid formation. The procedure here described is a novel strategy for in vitro generation of 3D spherical structures, phenotypically similar to natural embryos. The use of easily accessible dermal fibroblasts and the lack of retroviral gene transfection make this protocol a promising strategy to study early embryogenesis as well as embryo disorders.

Inhibition of TGF-β pathway improved the pluripotency of porcine pluripotent stem cells

Porcine pluripotent stem cells had been derived from different culture systems. PeNK6 is a porcine pluripotent stem cell line that we established from an E5.5 embryo in a defined culture system. Signaling pathways related with pluripotency had been assessed in this cell line, and TGF-β signaling pathway-related genes were found upregulated significantly. In this study, we elucidated the role of the TGF-β signaling pathway in PeNK6 through adding small molecule inhibitors, SB431542 (KOSB) or A83-01 (KOA), into the original culture medium (KO) and analyzing the expression and activity of key factors involved in the TGF-β signaling pathway. In KOSB/KOA medium, the morphology of PeNK6 became compact and the nuclear-to-cytoplasm ratio was increased. The expression of the core transcription factor SOX2 was significantly upregulated compared with cell lines in the control KO medium, and the differentiation potential became balanced among three germ layers rather than bias to neuroectoderm/endoderm as the original PeNK6 did. The results indicated that inhibition of TGF-β has positive effects on the porcine pluripotency. Based on these results, we established a pluripotent cell line (PeWKSB) from E5.5 blastocyst by employing TGF-β inhibitors, and the cell line showed improved pluripotency.

Synergistic Effect of miR-200 and Young Extracellular Matrix-based Bio-scaffolds to Reduce Signs of Aging in Senescent Fibroblasts

Aging is defined as a complex, multifaceted degenerative process that causes a gradual decline of physiological functions and a rising mortality risk with time. Stopping senescence or even rejuvenating the body represent one of the long-standing human dreams. Somatic cell nuclear transfer as well as cell reprogramming have suggested the possibility to slow or even reverse signs of aging. We exploited miR-200 family ability to induce a transient high plasticity state in human skin fibroblasts isolated from old individuals and we investigated whether this ameliorates cellular and physiological hallmarks of senescence. In addition, based on the assumption that extracellular matrix (ECM) provides biomechanical stimuli directly influencing cell behavior, we examine whether ECM-based bio-scaffolds, obtained from decellularized ovaries of young swine, stably maintain the rejuvenated phenotype acquired by cells after miR-200 exposure. The results show the existence of multiple factors that cooperate to control a unique program, driving the cell clock. In particular, miR-200 family directly regulates the molecular mechanisms erasing cell senescence. However, this effect is transient, reversible, and quickly lost. On the other hand, the use of an adequate young microenvironment stabilizes the miR-200-mediated rejuvenating effects, suggesting that synergistic interactions occur among molecular effectors and ECM-derived biomechanical stimuli. The model here described is a useful tool to better characterize these complex regulations and to finely dissect the multiple and concurring biochemical and biomechanical cues driving the cell biological clock.

Oviduct Epithelial Cell-Derived Extracellular Vesicles Improve Porcine Trophoblast Outgrowth

Porcine species have a great impact on studies on biomaterial production, organ transplantation and the development of biomedical models. The low efficiency of in vitro-produced embryos to derive embryonic stem cells has made achieving this goal a challenge. The fallopian tube plays an important role in the development of embryos. Extracellular vesicles (EVs) secreted by oviductal epithelial cells play an important role in the epigenetic regulation of embryo development. We used artificially isolated oviductal epithelial cells and EVs. In this study, oviductal epithelial cell (OEC) EVs were isolated and characterized through transmission electron microscopy, nanoparticles tracking analysis, western blotting and proteomics. We found that embryo development and blastocyst formation rate was significantly increased (14.3% ± 0.6% vs. 6.0% ± 0.6%) after OEC EVs treatment. According to our data, the inner cell mass (ICM)/trophectoderm (TE) ratio of the embryonic cell number increased significantly after OEC EVs treatment (43.7% ± 2.3% vs. 28.4% ± 2.1%). Meanwhile, the attachment ability of embryos treated with OEV EVs was significantly improved (43.5% ± 2.1% vs. 29.2% ± 2.5%, respectively). Using quantitative polymerase chain reaction (qPCR), we found that the expression of reprogramming genes (POU5F1, SOX2, NANOG, KLF4 and c-Myc) and implantation-related genes (VIM, KRT8, TEAD4 and CDX2) significantly increased in OEC EV-treated embryos. We report that OEC EV treatment can improve the development and implantation abilities of embryos.

Blastomere aggregation using phytohemagglutinin-L improves the establishment efficiency of porcine parthenogenesis-derived embryonic stem-like cell lines

Aggregation of blastomeres is a promising method to improve the developmental competence of blastocysts and may be useful for the production of chimeric animals and the establishment of embryonic stem cell lines by increasing inner cell masses. Here, we determined the optimal conditions for blastomere aggregation using phytohemagglutinin-L (PHA-L) and examined PHA-L efficiency by comparing it with Well of the Well (WOW), a general blastomere aggregation method. As a result, we confirmed that treatment with 15 μg/ml PHA-L for 144 h was effective for blastomere aggregation and embryonic development of three zona-free 2-cell stage embryos (TZ2Es) after parthenogenetic activation (PA). The TZ2Es cultured with PHA-L showed a significantly (p < 0.05) higher blastomere aggregation rate than the WOW method (93.5 ± 1.9% vs. 78.0 ± 8.5%). In addition, our results demonstrated that TZ2Es aggregation through PHA-L improved the quality of PA-derived blastocysts and improved porcine embryonic stem-like cell (pESLCs) seeding efficiency and quality of colonies. It was also observed that PHA-L-derived pESLC could remain undifferentiated and exhibit typical embryonic stem cell pluripotency markers, embryoid body (EB)-forming ability, and differentiation into cell lineages of three germ layers. Pig blastomere aggregation technology is expected to improve embryo quality and the efficiency of embryonic stem cell establishment and embryoid-body formation. It can also be used in blastocyst complementation systems and in the production of chimeric animals.

Effect of NANOG overexpression on porcine embryonic development and pluripotent embryonic stem cell formation in vitro

The efficiency of establishing pig pluripotent embryonic stem cell clones from blastocysts is still low. The transcription factor Nanog plays an important role in maintaining the pluripotency of mouse and human embryonic stem cells. Adequate activation of Nanog has been reported to increase the efficiency of establishing mouse embryonic stem cells from 3.5 day embryos. In mouse, Nanog starts to be strongly expressed as early as the morula stage, whereas in porcine NANOG starts to be strongly expressed by the late blastocyst stage. Therefore, here we investigated both the effect of expressing NANOG on porcine embryos early from the morula stage and the efficiency of porcine pluripotent embryonic stem cell clone formation. Compared with intact porcine embryos, NANOG overexpression induced a lower blastocyst rate, and did not show any advantages for embryo development and pluripotent embryonic stem cell line formation. These results indicated that, although NANOG is important pluripotent factor, NANOG overexpression is unnecessary for the initial formation of porcine pluripotent embryonic stem cell clones in vitro.

Generation of Trophoblast-Like Cells From Hypomethylated Porcine Adult Dermal Fibroblasts

The first differentiation event in mammalian embryos is the formation of the trophectoderm, which is the progenitor of the outer epithelial components of the placenta, and which supports the fetus during the intrauterine life. However, the epigenetic and paracrine controls at work in trophectoderm differentiation are still to be fully elucidated and the creation of dedicated in vitro models is desirable to increase our understanding. Here we propose a novel approach based on the epigenetic conversion of adult dermal fibroblasts into trophoblast-like cells. The method combines the use of epigenetic erasing with an ad hoc differentiation protocol. Dermal fibroblasts are erased with 5-azacytidine (5-aza-CR) that confers cells a transient high plasticity state. They are then readdressed toward the trophoblast (TR) phenotype, using MEF conditioned medium, supplemented with bone morphogenetic protein 4 (BMP4) and inhibitors of the Activin/Nodal and FGF2 signaling pathways in low O₂ conditions. The method here described allows the generation of TR-like cells from easily accessible material, such as dermal fibroblasts, that are very simply propagated in vitro. Furthermore, the strategy proposed is free of genetic modifications that make cells prone to instability and transformation. The TR model obtained may also find useful application in order to better characterize embryo implantation mechanisms and developmental disorders based on TR defects.

Porcine Primordial Germ Cell-Like Cells Generated from Induced Pluripotent Stem Cells Under Different Culture Conditions

Culture conditions regulate the process of pluripotency acquisition and self-renewal. This study aimed to analyse the influence of the in vitro environment on the induction of porcine induced pluripotent stem cell (piPSCs) differentiation into primordial germ cell-like cells (pPGCLCs). piPSC culture with different supplementation strategies (LIF, bFGF, or LIF plus bFGF) promoted heterogeneous phenotypic profiles. Continuous bFGF supplementation during piPSCs culture was beneficial to support a pluripotent state and the differentiation of piPSCs into pPGCLCs. The pPGCLCs were positive for the gene and protein expression of pluripotent and germinative markers. This study can provide a suitable in vitro model for use in translational studies and to help answer numerous remaining questions about germ cells.

Current Advances in 3D Tissue and Organ Reconstruction

Bi-dimensional culture systems have represented the most used method to study cell biology outside the body for over a century. Although they convey useful information, such systems may lose tissue-specific architecture, biomechanical effectors, and biochemical cues deriving from the native extracellular matrix, with significant alterations in several cellular functions and processes. Notably, the introduction of three-dimensional (3D) platforms that are able to re-create in vitro the structures of the native tissue, have overcome some of these issues, since they better mimic the in vivo milieu and reduce the gap between the cell culture ambient and the tissue environment. 3D culture systems are currently used in a broad range of studies, from cancer and stem cell biology, to drug testing and discovery. Here, we describe the mechanisms used by cells to perceive and respond to biomechanical cues and the main signaling pathways involved. We provide an overall perspective of the most recent 3D technologies. Given the breadth of the subject, we concentrate on the use of hydrogels, bioreactors, 3D printing and bioprinting, nanofiber-based scaffolds, and preparation of a decellularized bio-matrix. In addition, we report the possibility to combine the use of 3D cultures with functionalized nanoparticles to obtain highly predictive in vitro models for use in the nanomedicine field.

A 3D approach to reproduction

For over a century, 2D cell culture has been extensively used for all the different research fields. However, this in vitro system does not allow to reproduce the natural structures of the original tissue, causing several changes and, in most cases, the loss of cell-to-cell communications and cell-to-extracellular matrix interactions. Based on this, during the last years, novel 3D platforms, able to mimic the in vivo milieu, are being developed. The advantages of the use of 3D models are: the reduction of the gap between cell culture and physiological environment; imitation of the specific architecture; partially maintenance of the mechanical and biochemical cues of the original tissue. Currently, 3D systems are used in a broad range of studies, including the field of reproduction, where they have been applied to promote maturation of follicles and oocytes and embryo culture. Here, we review 2D and 3D cell culture methods, discussing advantages and limitations of these techniques. We report the fundamental mechanisms involved in cell ability to perceive and respond to mechanical cues and their role in transmitting signals to and between cells and in regulating intracellular signaling pathways. In particular, we focus on the main effectors of the Hippo pathway, Yes-associated protein (YAP) and WW domain-containing transcription regulator protein 1 (TAZ), describing their behavior and function in oocytes and embryos. Lastly, we provide an overall perspective of the most recent 3D technologies developed in the field of reproduction, describing how their use may revolutionize the understanding of cellular behavior and provide novel tools, useful in reproductive technologies and livestock production.

Cellular reprogramming by single-cell fusion with mouse embryonic stem cells in pig

Fusion of differentiated somatic cells with pluripotent stem cells can be used for cellular reprogramming, but the efficiency to obtain hybrid cells is extremely low. Here, we explored a novel cell fusion system, termed single-cell fusion, the efficiency was significantly improved verified by fusion of mouse embryonic stem cells (mESCs), comparing to traditional polyethylene glycol fusion. Then, we employed the optimized system to perform cell fusion of porcine embryonic fibroblasts (PEFs) and porcine pluripotent stem cells (pPSCs) with mESCs. The hybrid cells showed both red and green fluorescence and expressed species-specific genes of mouse and pig to evidence that the fusion was successful. The hybrid cells displayed characteristics similar with mESCs, including colony morphology, alkaline phosphatase positive and formation of embryoid body, and the expressions of core pluripotent factors OCT4, NANOG, and SOX2 of the pig were induced in the mESC/PEF hybrid cells. The results indicate PEFs and pPSCs could be reprogrammed by mESCs via the single-cell fusion. Taking advantage of the hybrid cells to investigate the signaling pathways depended on the pluripotency of pig, we suggest the transforming growth factor-β signaling pathways may play important roles. In summary, the single-cell fusion is highly efficient, and we believe in the future it will be widely used in the application and fundamental research.

Preserving self-renewal of porcine pluripotent stem cells in serum-free 3i culture condition and independent of LIF and b-FGF cytokines

Derivation of bona fide porcine pluripotent stem cells is still a critical issue because porcine embryonic stem cells (ESCs) are not available yet, and most of the culture conditions to maintain porcine induced pluripotent stem cells (piPSCs) are based on conditions for mouse and human iPS cells. In this study, we generated a doxycycline-inducible porcine iPS cell line (DOX-iPSCs) and used it to screen the optimal culture condition to sustain the self-renewal of piPSCs. We found that LIF and b-FGF were required for porcine cell reprogramming, but were not essential cytokines for maintaining the self-renewal and pluripotency of piPSCs. A serum-free 3i medium, which includes three inhibitors CHIR99021, SB431542, and PD0325901, three cytokines BMP4, SCF, and IL-6, and human platelet lysates (PL), was made through serious selections. In 3i condition, the doxycycline-inducible iPSCs could be passaged for a long term without the addition of doxycycline, and the flattened morphology of intermediate state piPSCs could convert to the naïve-like morphology with the increase in endogenous pluripotent gene expressions. Additionally, pPSC cell line isolated from 5.5 days blastocysts could be sustained in 3i medium and the expression of endogenous pluripotent genes OCT4, ESRRB, and STELLA was significantly increased. Our finding directed a new reprogramming strategy by using 3i condition to maintain and convert primed piPSCs into naïve-like pluripotent state. A combination of traditional LIF/b-FGF conditions and 3i condition may help us to find out an appropriate reprogramming approach to generate the naïve state of porcine iPSCs.

EpCAM Intracellular Domain Promotes Porcine Cell Reprogramming by Upregulation of Pluripotent Gene Expression via Beta-catenin Signaling

Previous study showed that expression of epithelial cell adhesion molecule (EpCAM) was significantly upregulated in porcine induced pluripotent stem cells (piPSCs). However, the regulatory mechanism and the downstream target genes of EpCAM were not well investigated. In this study, we found that EpCAM was undetectable in fibroblasts, but highly expressed in piPSCs. Promoter of EpCAM was upregulated by zygotic activated factors LIN28, and ESRRB, but repressed by maternal factors OCT4 and SOX2. Knocking down EpCAM by shRNA significantly reduced the pluripotent gene expression. Conversely, overexpression of EpCAM significantly increased the number of alkaline phosphatase positive colonies and elevated the expression of endogenous pluripotent genes. As a key surface-to-nucleus factor, EpCAM releases its intercellular domain (EpICD) by a two-step proteolytic processing sequentially. Blocking the proteolytic processing by inhibitors TAPI-1 and DAPT could reduce the intracellular level of EpICD and lower expressions of OCT4, SOX2, LIN28, and ESRRB. We noticed that increasing intracellular EpICD only was unable to improve activity of EpCAM targeted genes, but by blocking GSK-3 signaling and stabilizing beta-catenin signaling, EpICD could then significantly stimulate the promoter activity. These results showed that EpCAM intracellular domain required beta-catenin signaling to enhance porcine cell reprogramming.

Activin-SMAD signaling is required for maintenance of porcine iPS cell self-renewal through upregulation of NANOG and OCT4 expression

Porcine induced pluripotent stem cells (piPSCs) retain the enormous potential for farm animal reproduction and translational medicine, and have been reported by many laboratories worldwide. Some piPSC lines were bFGF-dependence and showed mouse EpiSC-like morphology; other lines were LIF-dependence and showed mouse ESC-like morphology. Metastable state of piPSC line that required both LIF and bFGF was also reported. Because bona fide pig embryonic stem cells were not available, uncovering piPSC state-specific regulatory circuitries was the most important task. In this study, we explored the function of Activin-SMAD signaling pathway and its downstream activated target genes in piPSCs. Transcriptome analysis showed that genes involved in Activin-SMAD signaling pathway were evidently activated during porcine somatic cell reprogramming, regardless piPSCs were LIF- or bFGF-dependent. Addition of Activin A and overexpression of SMAD2/3 significantly promoted expressions of porcine NANOG and OCT4, whereas inhibition of Activin-SMAD signaling by SB431542 and SMAD7 reduced NANOG and OCT4 expressions, and induced piPSCs differentiation exiting from pluripotent state. Our data demonstrate that activation of Activin-SMAD signaling pathway by addition of Activin A in culture medium is necessary for maintenance of self-renewal in porcine pluripotent stem cells.

bFGF signaling-mediated reprogramming of porcine primordial germ cells

Primordial germ cells (PGCs) have the ability to be reprogrammed into embryonic germ cells (EGCs) in vitro and are an alternative source of embryonic stem cells. Other than for the mouse, the systematic characterization of mammalian PGCs is still lacking, especially the process by which PGCs convert to pluripotency. This hampers the understanding of germ cell development and the derivation of authenticated EGCs from other species. We observed the morphological development of the genital ridge from Bama miniature pigs and found primary sexual differentiation in the E28 porcine embryo, coinciding with Blimp1 nuclear exclusion in PGCs. To explore molecular events involved in porcine PGC reprogramming, transcriptome data of porcine EGCs and fetal fibroblasts (FFs) were assembled and 1169 differentially expressed genes were used for Gene Ontology analysis. These genes were significantly enriched in cell-surface receptor-linked signal transduction, in agreement with the activation of LIF/Stat3 signaling and FGF signaling during the derivation of porcine EG-like cells. Using a growth-factor-defined culture system, we explored the effects of bFGF on the process and found that bFGF not only functioned at the very beginning of PGC dedifferentiation by impeding Blimp1 nuclear expression via a PI3K/AKT-dependent pathway but also maintained the viability of cultured PGCs thereafter. These results provide further insights into the development of germ cells from livestock and the mechanism of porcine PGC reprogramming.

From "ES-like" cells to induced pluripotent stem cells: a historical perspective in domestic animals

Pluripotent stem cells such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) provide great potential as cell sources for gene editing to generate genetically modified animals, as well as in the field of regenerative medicine. Stable, long-term ESCs have been established in laboratory mouse and rat; however, isolation of true pluripotent ESCs in domesticated animals such as pigs and dogs have been less successful. Initially, domesticated animal pluripotent cell lines were referred to as "embryonic stem-like" cells owing to their similar morphologic characteristics to mouse ESCs, but accompanied by a limited ability to proliferate in vitro in an undifferentiated state. That is, they shared some but not all the characteristics of true ESCs. More recently, advances in reprogramming using exogenous transcription factors, combined with the utilization of small chemical inhibitors of key biochemical pathways, have led to the isolation of iPSCs. In this review, we provide a historical perspective of the isolation of various types of pluripotent stem cells in domesticated animals. In addition, we summarize the latest progress and limitations in the derivation and application of iPSCs.

Establishment of bovine trophoblast stem-like cells from in vitro-produced blastocyst-stage embryos using two inhibitors

The trophoblast (TR) is the first to differentiate during mammalian embryogenesis and play a pivotal role in the development of the placenta. We used a dual inhibitor system (PD0325901 and CHIR99021) with mixed feeders to successfully obtain bovine trophoblast stem-like (bTS) cells, which were similar in phenotype to mouse trophoblast stem cells (TSCs). The bTS cells that were generated using this system continually proliferated, displayed a normal diploid karyotype, and had no signs of altered morphology or differentiation even after 150 passages. These cells exhibited alkaline phosphatase (AP) activity and expressed pluripotency markers, such as OCT4, NANOG, SOX2, SSEA-1, SSEA-4, TRA-1-60, and TRA-1-81, and TR lineage markers such as CDX2, as determined by both immunofluorescence and reverse transcription-polymerase chain reaction (RT-PCR). Additionally, these cells generated dome-like structures, formed teratomas when injected into NOD-SCID mice, and differentiated into placenta TR cells in vitro. The microarray analysis of bTS cells showed high expression levels of many TR markers, such as TEAD4, EOMES, GATA3, ETS2, TFAP2A, ELF5, SMARCA4 (BRG1), CDH3, MASH2, HSD17B1, CYP11A1, PPARG, ID2, GCM1, HAND1, TDK, PAG, IFN-τ, and THAP11. The expression of many pluripotency markers, such as OCT4, SOX2, NANOG, and GDF3, was lower in bTS cells compared with in vitro-produced blastocysts; however, compared with bovine fetal fibroblasts, the expression of these pluripotency markers was elevated in bTS cells. The DNA methylation status of the promoter regions of OCT4, NANOG, and SOX2 was investigated, which were significantly higher in bTS cells (OCT4 23.90%, NANOG 74.40%, and SOX2 8.50%) compared with blastocysts (OCT4 8.90%, NANOG 34.4%, and SOX2 3.80%). In contrast, two promoter regions of CDX2 were hypomethylated in bTS cells (13.80% and 3.90%) compared with blastocysts (18.80% and 9.10%). The TSC lines that were established in this study may be used either for basic research that is focused on peri-implantation and placenta development or as donor cells for transgenic animal production.