For reasons that are unclear the production of embryonic stem cells from ungulates has proved elusive. Here, we describe induced pluripotent stem cells (iPSC) derived from porcine fetal fibroblasts by lentiviral transduction of 4 human (h) genes, hOCT4, hSOX2, hKLF4, and hc-MYC, the combination commonly used to create iPSC in mouse and human. Cells were cultured on irradiated mouse embryonic fibroblasts (MEF) and in medium supplemented with knockout serum replacement and FGF2. Compact colonies of alkaline phosphatase-positive cells emerged after Ϸ22 days, providing an overall reprogramming efficiency of Ϸ0.1%. The cells expressed porcine OCT4, NANOG, and SOX2 and had high telomerase activity, but also continued to express the 4 human transgenes. Unlike human ESC, the porcine iPSC (piPSC) were positive for SSEA-1, but negative for SSEA-3 and -4. Transcriptional profiling on Affymetrix (porcine) microarrays and real time RT-PCR supported the conclusion that reprogramming to pluripotency was complete. One cell line, ID6, had a normal karyotype, a cell doubling time of Ϸ17 h, and has been maintained through >220 doublings. The ID6 line formed embryoid bodies, expressing genes representing all 3 germ layers when cultured under differentiating conditions, and teratomas containing tissues of ectoderm, mesoderm, and endoderm origin in nude mice. We conclude that porcine somatic cells can be reprogrammed to form piPSC. Such cell lines derived from individual animals could provide a means for testing the safety and efficacy of stem cell-derived tissue grafts when returned to the same pigs at a later age.iPS ͉ reprogramming ͉ OCT4

Human ES cells (hESC) exposed to bone morphogenic protein 4 (BMP4) in the absence of FGF2 have become widely used for studying trophoblast development, but the soundness of this model has been challenged by others, who concluded that differentiation was primarily toward mesoderm rather than trophoblast. Here we confirm that hESC grown under the standard conditions on a medium conditioned by mouse embryonic fibroblasts in the presence of BMP4 and absence of FGF2 on a Matrigel substratum rapidly convert to an epithelium that is largely KRT7+ within 48 h, with minimal expression of mesoderm markers, including T (Brachyury). Instead, they begin to express a series of trophoblast markers, including HLA-G, demonstrate invasive properties that are independent of the continued presence of BMP4 in the medium, and, over time, produce extensive amounts of human chorionic gonadotropin, progesterone, placental growth factor, and placental lactogen. This process of differentiation is not dependent on conditioning of the medium by mouse embryonic fibroblasts and is accelerated in the presence of inhibitors of Activin and FGF2 signaling, which at day 2 provide colonies that are entirely KRT7 + and in which the majority of cells are transiently CDX2 + . Colonies grown on two chemically defined media, including the one in which BMP4 was reported to drive mesoderm formation, also differentiate at least partially to trophoblast in response to BMP4. The experiments demonstrate that the in vitro BMP4/hESC model is valid for studying the emergence and differentiation of trophoblasts.A popular model for examining the early commitment of cells to the trophoblast (TR) lineage is based on the initial observation of Xu et al. (1), who noted that a group of related factors in the TGF-β family, especially bone morphogenic protein 4 (BMP4), was capable of causing human ES cells (hESC) to differentiate efficiently to TRs. This differentiation occurred without extensive generation of mesoderm, endoderm, and ectoderm derivatives, as judged by microarray analysis of transcribed genes, although a low level of expression of genes characteristic of mesoderm and endoderm did occur. This model has become widely used (2-13) to study an aspect of early human development that is not easily addressed otherwise because of lack of access to human embryos. Over the course of these studies it was demonstrated that the key to obtaining differentiation primarily to TR rather than to other lineages when using BMP4 as the triggering agent was to exclude FGF2, a factor required for maintenance of hESC (14-17). When BMP4 is provided simultaneously with FGF2, the morphological transition of the cells is altered (10), and the colonies begin to form a range of mesoderm and endoderm derivatives in addition to TR (18). This effect is probably achieved by FGF2 signaling through the MEK/ERK pathway, thereby preserving NANOG expression (19,20). This body of work suggests that optimal differentiation to TR can be achieved best by maximizing BMP4 signaling while simultaneous...

Infection of pregnant women by Asian lineage strains of Zika virus (ZIKV) has been linked to brain abnormalities in their infants, yet it is uncertain when during pregnancy the human conceptus is most vulnerable to the virus. We have examined two models to study susceptibility of human placental trophoblast to ZIKV: cytotrophoblast and syncytiotrophoblast derived from placental villi at term and colonies of trophoblast differentiated from embryonic stem cells (ESC). The latter appear to be analogous to the primitive placenta formed during implantation. The cells from term placentas, which resist infection, do not express genes encoding most attachment factors implicated in ZIKV entry but do express many genes associated with antiviral defense. By contrast, the ESC-derived trophoblasts possess a wide range of attachment factors for ZIKV entry and lack components of a robust antiviral response system. These cells, particularly areas of syncytiotrophoblast within the colonies, quickly become infected, produce infectious virus and undergo lysis within 48 h after exposure to low titers (multiplicity of infection > 0.07) of an African lineage strain (MR766 Uganda: ZIKVU) considered to be benign with regards to effects on fetal development. Unexpectedly, lytic effects required significantly higher titers of the presumed more virulent FSS13025 Cambodia (ZIKVC). Our data suggest that the developing fetus might be most vulnerable to ZIKV early in the first trimester before a protective zone of mature villous trophoblast has been established. Additionally, MR766 is highly trophic toward primitive trophoblast, which may put the early conceptus of an infected mother at high risk for destruction.

Human embryonic stem cells (ESCs) readily commit to the trophoblast lineage after exposure to bone morphogenetic protein-4 (BMP-4) and two small compounds, an activin A signaling inhibitor and a FGF2 signaling inhibitor (BMP4/A83-01/PD173074; BAP treatment). During differentiation, areas emerge within the colonies with the biochemical and morphological features of syncytiotrophoblast (STB). Relatively pure fractions of mononucleated cytotrophoblast (CTB) and larger syncytial sheets displaying the expected markers of STB can be obtained by differential filtration of dispersed colonies through nylon strainers. RNA-seq analysis of these fractions has allowed them to be compared with cytotrophoblasts isolated from term placentas before and after such cells had formed syncytia. Although it is clear from extensive gene marker analysis that both ESC-and placenta-derived syncytial cells are trophoblast, each with the potential to transport a wide range of solutes and synthesize placental hormones, their transcriptome profiles are sufficiently dissimilar to suggest that the two cell types have distinct pedigrees and represent functionally different kinds of STB. We propose that the STB generated from human ESCs represents the primitive syncytium encountered in early pregnancy soon after the human trophoblast invades into the uterine wall.is encountered during at least two stages of human placental development (1-3). The first coincides with early implantation when a multinucleated syncytium forms, presumably by cell fusion events, ahead of proliferating, mononucleated, cytotrophoblast (CTB) cells originating from polar trophectoderm (3,4). This invasive syncytium emerges either during or soon after the trophoblast passes through the breached uterine epithelium and into the decidualized stromal layer beneath and appears to be responsible for hollowing out regions within the stroma to form lacunae (5), which become filled with fluid and cells from maternal blood and uterine glands and presumably provide a source of nutrients for the conceptus (3, 6). By about 12 d of gestation, soon after the blastocyst has sunk below the endometrial surface, strands of cytotrophoblast begin to form and penetrate through the primitive syncytium to form primary chorionic villi, which are subsequently invaded by extraembryonic mesoderm to form secondary and tertiary villi (villous trees) (2-4). The cytotrophoblast cells associated with the villi continue to divide and provide a progenitor cell population for the villous STB, which is the cell layer that covers the outer surface of the villi and forms the definitive interface involved in exchange of gases, nutrients, and excretory materials between the fetal placenta and maternal blood. Villous STB is also the major site for production of placental hormones. Cytotrophoblast cells at the tips of the anchoring villi proliferate and colonize the endometrium, thus expanding the placental bed and simultaneously remodeling maternal spiral arteries. The extent to which extravillous trophoblast becom...

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The pig is important for agriculture and as an animal model in human and veterinary medicine, yet despite over 20 years of effort, there has been a failure to generate pluripotent stem cells analogous to those derived from mouse embryos. Here we report the production of leukemia inhibitory factor-dependent, so-called naive type, pluripotent stem cells from the inner cell mass of porcine blastocysts by up-regulating expression of KLF4 and POU5F1. The alkaline phosphatase-positive colonies resulting from reprogramming resemble mouse embryonic stem cells in colony morphology, cell cycle interval, transcriptome profile, and expression of pluripotent markers, such as POU5F1, SOX2, and surface marker SSEA1. They are dependent on leukemia inhibitory factor signaling for maintenance of pluripotency, can be cultured over extended passage, and have the ability to form teratomas. These cells derived from the inner cell mass of pig blastocysts are clearly distinct from the FGF2-dependent “primed” induced pluripotent stem cells described recently from porcine mesenchymal cells. The data are consistent with the hypothesis that the up-regulation of KLF4, as well as POU5F1, is required to create and stabilize the naive pluripotent state and may explain why the derivation of embryonic stem cells from pigs and other ungulates has proved so difficult.

Interferon-tau (IFN-tau) is the antiluteolytic factor released by concepti of ruminant ungulate species prior to implantation. All type I interferons, including IFN-tau, exert their action through a common receptor, which consists of two subunits, IFNAR1 and IFNAR2c, but the distribution of the two polypeptides in uterine endometrium has not been examined. In situ hybridization and immunohistochemistry on sections from pregnant and nonpregnant ovine uteri at Days 14 and 15 after estrus and mating showed that both IFNAR1 and IFNAR2 mRNA and protein were strongly expressed in endometrial luminal epithelium (LE), superficial glandular epithelium (GE), and stromal cells, within but not outside caruncles. Similar staining patterns were noted in pregnant and nonpregnant uteri for both subunits. Western blot analysis of membrane fractions from cell lines derived from endometrial LE, GE, and stromal cells, and affinity cross-linking experiments with radioactively labeled IFN-tau performed on crude endometrial membranes indicated the presence of both high ( approximately 110 kDa) and low (75-80 kDa) molecular mass forms of the two receptor subunits. To localize where IFN-tau binds when it is introduced into the uterine lumen, immunohistochemistry with an antiserum against IFN-tau was performed on sections of uteri from Day 14 nonpregnant ewes whose uteri had previously been infused with IFN-tau. Staining was concentrated on the LE and superficial GE cells, and was absent from the deeper regions of the glands and from the stromal tissues. These studies demonstrate the heavy concentration of IFNAR1 and IFNAR2 in cells of the LE and superficial GE, which appear to be the main targets for IFN-tau.

Human pluripotent stem cells (PSCs) show epiblast-type pluripotency that is maintained with ACTIVIN/FGF2 signaling. Here, we report the acquisition of a unique stem cell phenotype by both human ES cells (hESCs) and induced pluripotent stem cells (iPSCs) in response to transient (24-36 h) exposure to bone morphogenetic protein 4 (BMP4) plus inhibitors of ACTIVIN signaling (A83-01) and FGF2 (PD173074), followed by trypsin dissociation and recovery of colonies capable of growing on a gelatin substratum in standard medium for human PSCs at low but not high FGF2 concentrations. The self-renewing cell lines stain weakly for CDX2 and strongly for NANOG, can be propagated clonally on either Matrigel or gelatin, and are morphologically distinct from human PSC progenitors on either substratum but still meet standard in vitro criteria for pluripotency. They form well-differentiated teratomas in immune-compromised mice that secrete human chorionic gonadotropin (hCG) into the host mouse and include small areas of trophoblast-like cells. The cells have a distinct transcriptome profile from the human PSCs from which they were derived (including higher expression of NANOG, LEFTY1, and LEFTY2). In nonconditioned medium lacking FGF2, the colonies spontaneously differentiated along multiple lineages, including trophoblast. They responded to PD173074 in the absence of both FGF2 and BMP4 by conversion to trophoblast, and especially syncytiotrophoblast, whereas an A83-01/PD173074 combination favored increased expression of HLA-G, a marker of extravillous trophoblast. Together, these data suggest that the cell lines exhibit totipotent potential and that BMP4 can prime human PSCs to a self-renewing alternative state permissive for trophoblast development. The results may have implications for regulation of lineage decisions in the early embryo.biological sciences | developmental biology | pluripotent stem cells | totipotent | trophoblast