Loss of the extraembryonic ectoderm in Elf5 mutants leads to defects in embryonic patterning

The epigenetic modifier Fam208a is required to maintain epiblast cell fitness

Gastrulation initiates with the formation of the primitive streak, during which, cells of the epiblast delaminate to form the mesoderm and definitive endoderm. At this stage, the pluripotent cell population of the epiblast undergoes very rapid proliferation and extensive epigenetic programming. Here we show that Fam208a, a new epigenetic modifier, is essential for early post-implantation development. We show that Fam208a mutation leads to impaired primitive streak elongation and delayed epithelial-to-mesenchymal transition. Fam208a mutant epiblasts had increased expression of p53 pathway genes as well as several pluripotency-associated long non-coding RNAs. Fam208a mutants exhibited an increase in p53-driven apoptosis and complete removal of p53 could partially rescue their gastrulation block. This data demonstrates a new in vivo function of Fam208a in maintaining epiblast fitness, establishing it as an important factor at the onset of gastrulation when cells are exiting pluripotency.

Bovine trophectoderm cells induced from bovine fibroblasts with induced pluripotent stem cell reprogramming factors

Thirteen independent induced bovine trophectroderm (iBT) cell lines were established by reprogramming bovine fetal liver-derived fibroblasts after viral-vector transduction with either six or eight factors, including POU5F1 (OCT4), KLF4, SOX2, MYC, NANOG, LIN28, SV40 large T antigen, and hTERT. Light- and electron-microscopy analysis showed that the iBT cells had epithelial cell morphology typical of bovine trophectoderm cells. Reverse-transcription-PCR assays indicated that all of the cell lines expressed interferon-tau (IFNT) at passages 1 or 2. At later passages (≥ passage 8), however, immunoblot and antiviral activity assays revealed that more than half of the iBT cell lines had stopped expressing IFNT. Messenger RNAs specific to trophectoderm differentiation and function were found in the iBT cell lines, and 2-dimensional-gel analysis for cellular proteins showed an expression pattern similar to that of trophectoderm cell lines derived from bovine blastocysts. Integration of some of the human reprogramming factors, including POU5F1, KLF4, SOX2, MYC, NANOG, and LIN28, were detected by PCR, but their transcription was mostly absent in the iBT cell lines. Gene expression assessment of endogenous bovine reprogramming factor orthologs revealed endogenous bLIN28 and bMYC transcripts in all; bSOX2 and bNANOG in none; and bKLF4 and bPOU5F1 in less than half of the iBT cell lines. These results demonstrate that bovine trophectoderm can be induced via reprogramming factor expression from bovine liver-derived fibroblasts, although other fibroblast populations-e.g., derived from fetal thigh tissue-may produce similar results, albeit at lower frequencies.

EWSR1/ELF5 induces acute myeloid leukemia by inhibiting p53/p21 pathway

The Ewing sarcoma breakpoint region 1 (EWSR1) gene is known to fuse with various partner genes to promote the development of the Ewing sarcoma family of tumors and other sarcomas. In contrast, the association of EWSR1 chimeric fusion genes with leukemia has rarely been reported. We identified a novel EWSR1‐associated chimeric fusion gene in a patient with acute myeloid leukemia harboring 46, XY, t (11; 22) (p13; q12) karyotype abnormality. The patient was refractory to intensified chemotherapy including hematopoietic stem cell transplantation. Total RNA paired‐end sequencing identified a novel chimeric fusion gene as EWSR1/ELF5, a member of the E26 transformation‐specific transcription factor family. Transduction of EWSR1/ELF5 to NIH3T3 cells induced transformation by attenuating with the p53/p21‐dependent pathway. The injection of EWSR1/ELF5‐transduced NIH3T3 cells into NSG‐SCID mice systematically induced the development of tumors in vivo. These results revealed the oncogenic potency of EWSR1/ELF5.

What Is Trophoblast? A Combination of Criteria Define Human First-Trimester Trophoblast

Controversy surrounds reports describing the derivation of human trophoblast cells from placentas and embryonic stem cells (ESC), partly due to the difficulty in identifying markers that define cells as belonging to the trophoblast lineage. We have selected criteria that are characteristic of primary first-trimester trophoblast: a set of protein markers, HLA class I profile, methylation of ELF5, and expression of microRNAs (miRNAs) from the chromosome 19 miRNA cluster (C19MC). We tested these criteria on cells previously reported to show some phenotypic characteristics of trophoblast: bone morphogenetic protein (BMP)-treated human ESC and 2102Ep, an embryonal carcinoma cell line. Both cell types only show some, but not all, of the four trophoblast criteria. Thus, BMP-treated human ESC have not fully differentiated to trophoblast. Our study identifies a robust panel, including both protein and non-protein-coding markers that, in combination, can be used to reliably define cells as characteristic of early trophoblast.

Stem cell insights into human trophoblast lineage differentiation

BACKGROUND

The human placenta is vital for fetal development, yet little is understood about how it forms successfully to ensure a healthy pregnancy or why this process is inadequate in 1 in 10 pregnancies, leading to miscarriage, intrauterine growth restriction or preeclampsia. Trophoblasts are placenta-specific epithelial cells that maximize nutrient exchange. All trophoblast lineages are thought to arise from a population of trophoblast stem cells (TSCs). However, whilst the isolation of murine TSC has led to an explosion in understanding murine placentation, the isolation of an analogous human TSC has proved more difficult. Consequently, alternative methods of studying human trophoblast lineage development have been employed, including human embryonic stem cells (hESCs), induced pluripotent stem cells (iPS) and transformed cell lines; but what do these proxy models tell us about what is happening during early placental development?

OBJECTIVE AND RATIONALE

In this systematic review, we evaluate current approaches to understanding human trophoblast lineage development in order to collate and refine these models and inform future approaches aimed at establishing human TSC lines.

SEARCH METHODS

To ensure all relevant articles were analysed, an unfiltered search of Pubmed, Embase, Scopus and Web of Science was conducted for 25 key terms on the 13th May 2016. In total, 47 313 articles were retrieved and manually filtered based on non-human, non-English, non-full text, non-original article and off-topic subject matter. This resulted in a total of 71 articles deemed relevant for review in this article.

OUTCOMES

Candidate human TSC populations have been identified in, and isolated from, both the chorionic membrane and villous tissue of the placenta, but further investigation is required to validate these as 'true' human TSCs. Isolating human TSCs from blastocyst trophectoderm has not been successful in humans as it was in mice, although recently the first reported TSC line (USFB6) was isolated from an eight-cell morula. In lieu of human TSC lines, trophoblast-like cells have been induced to differentiate from hESCs and iPS. However, differentiation in these model systems is difficult to control, culture conditions employed are highly variable, and the extent to which they accurately convey the biology of 'true' human TSCs remains unclear, particularly as a consensus has not been met among the scientific community regarding which characteristics a human TSC must possess.

WIDER IMPLICATIONS

Human TSC models have the potential to revolutionize our understanding of trophoblast differentiation, allowing us to make significant gains in understanding the underlying pathology of pregnancy disorders and to test potential therapeutic interventions on cell function in vitro. In order to do this, a collaborative effort is required to establish the criteria that define a human TSC to confirm the presence of human TSCs in both primary isolates and to determine how accurately trophoblast-like cells derived from current model systems reflect trophoblast from primary tissue. The in vitro systems currently used to model early trophoblast lineage formation have provided insights into early human placental formation but it is unclear whether these trophoblast-like cells are truly representative of primary human trophoblast. Consequently, continued refinement of current models, and standardization of culture protocols is essential to aid our ability to identify, isolate and propagate 'true' human TSCs from primary tissue.

ELF5 transcription factor expression during gestation in humans and rats - an immunohistochemical analysis

OBJECTIVE

The purpose of this study was to measure immunohistochemically the expression of ELF5 protein in term human and rat placentas and in human placentas associated with gestational diabetes (GD) and intrauterine growth restriction (IUGR).

METHODS

The results were quantitated stereologically using the stereological variable of volume density. A semiquantitative analysis was performed independently by a certified pathologist.

RESULTS

Total expression of ELF5 protein was higher in pathological pregnancies than in corresponding control term placentas, with both methods of quantifications showing similar results. In addition, ELF5 expression was also higher in connective tissue and blood vessels in chorionic villi in IUGR placentas (but not in GD placentas) compared to healthy controls. ELF5 is higher in placenta as a whole and in most of its components in both pathologies. The two exceptions are chorionic plates in IUGR and decidua in GD, where its expression is lower than in healthy controls.

CONCLUSIONS

We have shown that IUGR and GD are associated with significantly increased levels of ELF5 protein in placentas, which suggests that ELF5 may play an important role in normal placentation. However, these are term placentas and to study ELF5 in premature births would give better insight into human placentation in health and disease.

Resolving early mesoderm diversification through single-cell expression profiling

In mammals, specification of the three major germ layers occurs during gastrulation, when cells ingressing through the primitive streak differentiate into the precursor cells of major organ systems. However, the molecular mechanisms underlying this process remain unclear, as numbers of gastrulating cells are very limited. In the mouse embryo at embryonic day 6.5, cells located at the junction between the extra-embryonic region and the epiblast on the posterior side of the embryo undergo an epithelial-to-mesenchymal transition and ingress through the primitive streak. Subsequently, cells migrate, either surrounding the prospective ectoderm contributing to the embryo proper, or into the extra-embryonic region to form the yolk sac, umbilical cord and placenta. Fate mapping has shown that mature tissues such as blood and heart originate from specific regions of the pre-gastrula epiblast, but the plasticity of cells within the embryo and the function of key cell-type-specific transcription factors remain unclear. Here we analyse 1,205 cells from the epiblast and nascent Flk1(+) mesoderm of gastrulating mouse embryos using single-cell RNA sequencing, representing the first transcriptome-wide in vivo view of early mesoderm formation during mammalian gastrulation. Additionally, using knockout mice, we study the function of Tal1, a key haematopoietic transcription factor, and demonstrate, contrary to previous studies performed using retrospective assays, that Tal1 knockout does not immediately bias precursor cells towards a cardiac fate.

Human pluripotent stem cells as a model of trophoblast differentiation in both normal development and disease

Trophoblast is the primary epithelial cell type in the placenta, a transient organ required for proper fetal growth and development. Different trophoblast subtypes are responsible for gas/nutrient exchange (syncytiotrophoblasts, STBs) and invasion and maternal vascular remodeling (extravillous trophoblasts, EVTs). Studies of early human placental development are severely hampered by the lack of a representative trophoblast stem cell (TSC) model with the capacity for self-renewal and the ability to differentiate into both STBs and EVTs. Primary cytotrophoblasts (CTBs) isolated from early-gestation (6-8 wk) human placentas are bipotential, a phenotype that is lost with increasing gestational age. We have identified a CDX2(+)/p63(+) CTB subpopulation in the early postimplantation human placenta that is significantly reduced later in gestation. We describe a reproducible protocol, using defined medium containing bone morphogenetic protein 4 by which human pluripotent stem cells (hPSCs) can be differentiated into CDX2(+)/p63(+) CTB stem-like cells. These cells can be replated and further differentiated into STB- and EVT-like cells, based on marker expression, hormone secretion, and invasive ability. As in primary CTBs, differentiation of hPSC-derived CTBs in low oxygen leads to reduced human chorionic gonadotropin secretion and STB-associated gene expression, instead promoting differentiation into HLA-G(+) EVTs in an hypoxia-inducible, factor-dependent manner. To validate further the utility of hPSC-derived CTBs, we demonstrated that differentiation of trisomy 21 (T21) hPSCs recapitulates the delayed CTB maturation and blunted STB differentiation seen in T21 placentae. Collectively, our data suggest that hPSCs are a valuable model of human placental development, enabling us to recapitulate processes that result in both normal and diseased pregnancies.

Plet1 is an epigenetically regulated cell surface protein that provides essential cues to direct trophoblast stem cell differentiation

Gene loci that are hypermethylated and repressed in embryonic (ESCs) but hypomethylated and expressed in trophoblast (TSCs) stem cells are very rare and may have particularly important roles in early developmental cell fate decisions, as previously shown for Elf5. Here, we assessed another member of this small group of genes, Placenta Expressed Transcript 1 (Plet1), for its function in establishing trophoblast lineage identity and modulating trophoblast differentiation. We find that Plet1 is tightly repressed by DNA methylation in ESCs but expressed on the cell surface of TSCs and trophoblast giant cells. In hypomethylated ESCs that are prone to acquire some trophoblast characteristics, Plet1 is required to confer a trophoblast-specific gene expression pattern, including up-regulation of Elf5. Plet1 displays an unusual biphasic expression profile during TSC differentiation and thus may be pivotal in balancing trophoblast self-renewal and differentiation. Furthermore, overexpression and CRISPR/Cas9-mediated knockout in TSCs showed that high Plet1 levels favour differentiation towards the trophoblast giant cell lineage, whereas lack of Plet1 preferentially induces syncytiotrophoblast formation. Thus, the endogenous dynamics of Plet1 expression establish important patterning cues within the trophoblast compartment by promoting differentiation towards the syncytiotrophoblast or giant cell pathway in Plet1-low and Plet1-high cells, respectively.

Cellular Dynamics of Mouse Trophoblast Stem Cells: Identification of a Persistent Stem Cell Type

Mouse trophoblast stem cells (TSCs) proliferate indefinitely in vitro, despite their highly heterogeneous nature. In this study, we sought to characterize TSC colony types by using methods based on cell biology and biochemistry for a better understanding of how TSCs are maintained over multiple passages. Colonies of TSCs could be classified into four major types: type 1 is compact and dome-shaped, type 4 is flattened but with a large multilayered cell cluster, and types 2 and 3 are their intermediates. A time-lapse analysis indicated that type 1 colonies predominantly appeared after passaging, and a single type 1 colony gave rise to all other types. These colony transitions were irreversible, but at least some type 1 colonies persisted throughout culture. The typical cells comprising type 1 colonies were small and highly motile, and they aggregated together to form primary colonies. A hierarchical clustering based on global gene expression profiles suggested that a TSC line containing more type 1 colony cells was similar to in vivo extraembryonic tissues. Among the known TSC genes examined, Elf5 showed a differential expression pattern according to colony type, indicating that this gene might be a reliable marker of undifferentiated TSCs. When aggregated with fertilized embryos, cells from types 1 and 2, but not from type 4, distributed to the polar trophectoderm in blastocysts. These findings indicate that cells typically found in type 1 colonies can persist indefinitely as stem cells and are responsible for the maintenance of TSC lines. They may provide key information for future improvements in the quality of TSC lines.

Selection of accurate reference genes in mouse trophoblast stem cells for reverse transcription-quantitative polymerase chain reaction

Mouse trophoblast stem cells (TSCs) form colonies of different sizes and morphologies, which might reflect their degrees of differentiation. Therefore, each colony type can have a characteristic gene expression profile; however, the expression levels of internal reference genes may also change, causing fluctuations in their estimated gene expression levels. In this study, we validated seven housekeeping genes by using a geometric averaging method and identified Gapdh as the most stable gene across different colony types. Indeed, when Gapdh was used as the reference, expression levels of Elf5, a TSC marker gene, stringently classified TSC colonies into two groups: a high expression groups consisting of type 1 and 2 colonies, and a lower expression group consisting of type 3 and 4 colonies. This clustering was consistent with our putative classification of undifferentiated/differentiated colonies based on their time-dependent colony transitions. By contrast, use of an unstable reference gene (Rn18s) allowed no such clear classification. Cdx2, another TSC marker, did not show any significant colony type-specific expression pattern irrespective of the reference gene. Selection of stable reference genes for quantitative gene expression analysis might be critical, especially when cell lines consisting of heterogeneous cell populations are used.

Epigenesis and plasticity of mouse trophoblast stem cells

The critical role of the placenta in supporting a healthy pregnancy is mostly ensured by the extraembryonic trophoblast lineage that acts as the interface between the maternal and the foetal compartments. The diverse trophoblast cell subtypes that form the placenta originate from a single layer of stem cells that emerge from the embryo when the earliest cell fate decisions are occurring. Recent studies show that these trophoblast stem cells exhibit extensive plasticity as they are capable of differentiating down multiple pathways and are easily converted into embryonic stem cells in vitro. In this review, we discuss current knowledge of the mechanisms and control of the epigenesis of mouse trophoblast stem cells through a comparison with the corresponding mechanisms in pluripotent embryonic stem cells. To illustrate some of the more striking manifestations of the epigenetic plasticity of mouse trophoblast stem cells, we discuss them within the context of two paradigms of epigenetic regulation of gene expression: the imprinted gene expression of specific loci and the process of X-chromosome inactivation.

A Resource for the Transcriptional Signature of Bona Fide Trophoblast Stem Cells and Analysis of Their Embryonic Persistence

Trophoblast stem cells (TSCs) represent the multipotent progenitors that give rise to the different cells of the embryonic portion of the placenta. Here, we analysed the expression of key TSC transcription factors Cdx2, Eomes, and Elf5 in the early developing placenta of mouse embryos and in cultured TSCs and reveal surprising heterogeneity in protein levels. We analysed persistence of TSCs in the early placenta and find that TSCs remain in the chorionic hinge until E9.5 and are lost shortly afterwards. To define the transcriptional signature of bona fide TSCs, we used inducible gain- and loss-of-function alleles of Eomes or Cdx2, and Eomes^GFP, to manipulate and monitor the core maintenance factors of TSCs, followed by genome-wide expression profiling. Combinatorial analysis of resulting expression profiles allowed for defining novel TSC marker genes that might functionally contribute to the maintenance of the TSC state. Analyses by qRT-PCR and in situ hybridisation validated novel TSC- and chorion-specific marker genes, such as Bok/Mtd, Cldn26, Duox2, Duoxa2, Nr0b1, and Sox21. Thus, these expression data provide a valuable resource for the transcriptional signature of bona fide and early differentiating TSCs and may contribute to an increased understanding of the transcriptional circuitries that maintain and/or establish stemness of TSCs.

ELF5 isoform expression is tissue-specific and significantly altered in cancer

Background

E74-like factor 5 (ELF5) is an epithelial-specific member of the E26 transforming sequence (ETS) transcription factor family and a critical regulator of cell fate in the placenta, pulmonary bronchi, and milk-producing alveoli of the mammary gland. ELF5 also plays key roles in malignancy, particularly in basal-like and endocrine-resistant forms of breast cancer. Almost all genes undergo alternative transcription or splicing, which increases the diversity of protein structure and function. Although ELF5 has multiple isoforms, this has not been considered in previous studies of ELF5 function.

Methods

RNA-sequencing data for 6757 samples from The Cancer Genome Atlas were analyzed to characterize ELF5 isoform expression in multiple normal tissues and cancers. Extensive in vitro analysis of ELF5 isoforms, including a 116-gene quantitative polymerase chain reaction panel, was performed in breast cancer cell lines.

Results

ELF5 isoform expression was found to be tissue-specific due to alternative promoter use but altered in multiple cancer types. The normal breast expressed one main isoform, while in breast cancer there were subtype-specific alterations in expression. Expression of other ETS factors was also significantly altered in breast cancer, with the basal-like subtype demonstrating a distinct ETS expression profile. In vitro inducible expression of the full-length isoforms 1 and 2, as well as isoform 3 (lacking the Pointed domain) had similar phenotypic and transcriptional effects.

Conclusions

Alternative promoter use, conferring differential regulatory responses, is the main mechanism governing ELF5 action rather than differential transcriptional activity of the isoforms. This understanding of expression and function at the isoform level is a vital first step in realizing the potential of transcription factors such as ELF5 as prognostic markers or therapeutic targets in cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0666-0) contains supplementary material, which is available to authorized users.

PC7 and the related proteases Furin and Pace4 regulate E-cadherin function during blastocyst formation

Targeted deletion of PC7 and the related proprotein convertases Furin and Pace4, combined with live imaging of their activities, unmasks their overlapping and complementary functions in morula compaction and ICM formation in mouse blastocysts and in E-cadherin precursor processing.

The first cell differentiation in mammalian embryos segregates polarized trophectoderm cells from an apolar inner cell mass (ICM). This lineage decision is specified in compacted morulae by cell polarization and adhesion acting on the Yes-associated protein in the Hippo signaling pathway, but the regulatory mechanisms are unclear. We show that morula compaction and ICM formation depend on PC7 and the related proprotein convertases (PCs) Furin and Pace4 and that these proteases jointly regulate cell–cell adhesion mediated by E-cadherin processing. We also mapped the spatiotemporal activity profiles of these proteases by live imaging of a transgenic reporter substrate in wild-type and PC mutant embryos. Differential inhibition by a common inhibitor revealed that all three PCs are active in inner and outer cells, but in partially nonoverlapping compartments. E-cadherin processing by multiple PCs emerges as a novel mechanism to modulate cell–cell adhesion and fate allocation.

Elf5-centered transcription factor hub controls trophoblast stem cell self-renewal and differentiation through stoichiometry-sensitive shifts in target gene networks

Latos et al. demonstrate that precise levels of Elf5 are critical for normal expansion of the trophoblast stem cell (TSC) compartment and embryonic survival. Their data place Elf5 at the center of a stoichiometry-sensitive transcriptional network, where it acts as a molecular switch governing the balance between TSC proliferation and differentiation.

Elf5 is a transcription factor with pivotal roles in the trophoblast compartment, where it reinforces a trophoblast stem cell (TSC)-specific transcriptional circuit. However, Elf5 is also present in differentiating trophoblast cells that have ceased to express other TSC genes such as Cdx2 and Eomes. In the present study, we aimed to elucidate the context-dependent role of Elf5 at the interface between TSC self-renewal and the onset of differentiation. We demonstrate that precise levels of Elf5 are critical for normal expansion of the TSC compartment and embryonic survival, as Elf5 overexpression triggers precocious trophoblast differentiation. Through integration of protein interactome, transcriptome, and genome-wide chromatin immunoprecipitation data, we reveal that this abundance-dependent function is mediated through a shift in preferred Elf5-binding partners; in TSCs, Elf5 interaction with Eomes recruits Tfap2c to triply occupied sites at TSC-specific genes, driving their expression. In contrast, the Elf5 and Tfap2c interaction becomes predominant as their protein levels increase. This triggers binding to double- and single-occupancy sites that harbor the cognate Tfap2c motif, causing activation of the associated differentiation-promoting genes. These data place Elf5 at the center of a stoichiometry-sensitive transcriptional network, where it acts as a molecular switch governing the balance between TSC proliferation and differentiation.

The Efficient Derivation of Trophoblast Cells from Porcine In Vitro Fertilized and Parthenogenetic Blastocysts and Culture with ROCK Inhibitor Y-27632

Trophoblasts (TR) are specialized cells of the placenta and play an important role in embryo implantation. The in vitro culture of trophoblasts provided an important tool to investigate the mechanisms of implantation. In the present study, porcine trophoblast cells were derived from pig in vitro fertilized (IVF) and parthenogenetically activated (PA) blastocysts via culturing in medium supplemented with KnockOut serum replacement (KOSR) and basic fibroblast growth factor (bFGF) on STO feeder layers, and the effect of ROCK (Rho-associated coiled-coil protein kinases) inhibiter Y-27632 on the cell lines culture was tested. 5 PA blastocyst derived cell lines and 2 IVF blastocyst derived cell lines have been cultured more than 20 passages; one PA cell lines reached 110 passages without obvious morphological alteration. The derived trophoblast cells exhibited epithelium-like morphology, rich in lipid droplets, and had obvious defined boundaries with the feeder cells. The cells were histochemically stained positive for alkaline phosphatase. The expression of TR lineage markers, such as CDX2, KRT7, KRT18, TEAD4, ELF5 and HAND1, imprinted genes such as IGF2, PEG1 and PEG10, and telomerase activity related genes TERC and TERF2 were detected by immunofluorescence staining, reverse transcription PCR and quantitative real-time PCR analyses. Both PA and IVF blastocysts derived trophoblast cells possessed the ability to differentiate into mature trophoblast cells in vitro. The addition of Y-27632 improved the growth of both PA and IVF blastocyst derived cell lines and increased the expression of trophoblast genes. This study has provided an alternative highly efficient method to establish trophoblast for research focused on peri-implantation and placenta development in IVF and PA embryos.

Gene Expression Profiling Reveals a Novel Regulatory Role for Sox21 Protein in Mouse Trophoblast Stem Cell Differentiation

Appropriate self-renewal and differentiation of trophoblast stem cells (TSCs) are key factors for proper placental development and function and, in turn, for appropriate in utero fetal growth. To identify novel TSC-specific genes, we performed genome-wide expression profiling of TSCs, embryonic stem cells, epiblast stem cells, and mouse embryo fibroblasts, derived from mice of the same genetic background. Our analysis revealed a high expression of Sox21 in TSCs compared with other cell types. Sox21 levels were high in undifferentiated TSCs and were dramatically reduced upon differentiation. In addition, modulation of Sox21 expression in TSCs affected lineage-specific differentiation, based on both marker analysis and functional assessment. Our results implicate Sox21 specifically in the promotion of spongiotrophoblast and giant cell differentiation and establish a new mechanism through which trophoblast sublineages are specified.

Placenta: the forgotten organ

The placenta sits at the interface between the maternal and fetal vascular beds where it mediates nutrient and waste exchange to enable in utero existence. Placental cells (trophoblasts) accomplish this via invading and remodeling the uterine vasculature. Amazingly, despite being of fetal origin, trophoblasts do not trigger a significant maternal immune response. Additionally, they maintain a highly reliable hemostasis in this extremely vascular interface. Decades of research into how the placenta differentiates itself from embryonic tissues to accomplish these and other feats have revealed a previously unappreciated level of complexity with respect to the placenta's cellular composition. Additionally, novel insights with respect to roles played by the placenta in guiding fetal development and metabolism have sparked a renewed interest in understanding the interrelationship between fetal and placental well-being. Here, we present an overview of emerging research in placental biology that highlights these themes and the importance of the placenta to fetal and adult health.

Fgf and Esrrb integrate epigenetic and transcriptional networks that regulate self-renewal of trophoblast stem cells

Esrrb (oestrogen-related receptor beta) is a transcription factor implicated in embryonic stem (ES) cell self-renewal, yet its knockout causes intrauterine lethality due to defects in trophoblast development. Here we show that in trophoblast stem (TS) cells, Esrrb is a downstream target of fibroblast growth factor (Fgf) signalling and is critical to drive TS cell self-renewal. In contrast to its occupancy of pluripotency-associated loci in ES cells, Esrrb sustains the stemness of TS cells by direct binding and regulation of TS cell-specific transcription factors including Elf5 and Eomes. To elucidate the mechanisms whereby Esrrb controls the expression of its targets, we characterized its TS cell-specific interactome using mass spectrometry. Unlike in ES cells, Esrrb interacts in TS cells with the histone demethylase Lsd1 and with the RNA Polymerase II-associated Integrator complex. Our findings provide new insights into both the general and context-dependent wiring of transcription factor networks in stem cells by master transcription factors.

From blastocyst to gastrula: gene regulatory networks of embryonic stem cells and early mouse embryogenesis

To date, many regulatory genes and signalling events coordinating mammalian development from blastocyst to gastrulation stages have been identified by mutational analyses and reverse-genetic approaches, typically on a gene-by-gene basis. More recent studies have applied bioinformatic approaches to generate regulatory network models of gene interactions on a genome-wide scale. Such models have provided insights into the gene networks regulating pluripotency in embryonic and epiblast stem cells, as well as cell-lineage determination in vivo. Here, we review how regulatory networks constructed for different stem cell types relate to corresponding networks in vivo and provide insights into understanding the molecular regulation of the blastocyst-gastrula transition.

Developmental plasticity, cell fate specification and morphogenesis in the early mouse embryo

A critical point in mammalian development is when the early embryo implants into its mother's uterus. This event has historically been difficult to study due to the fact that it occurs within the maternal tissue and therefore is hidden from view. In this review, we discuss how the mouse embryo is prepared for implantation and the molecular mechanisms involved in directing and coordinating this crucial event. Prior to implantation, the cells of the embryo are specified as precursors of future embryonic and extra-embryonic lineages. These preimplantation cell fate decisions rely on a combination of factors including cell polarity, position and cell–cell signalling and are influenced by the heterogeneity between early embryo cells. At the point of implantation, signalling events between the embryo and mother, and between the embryonic and extraembryonic compartments of the embryo itself, orchestrate a total reorganization of the embryo, coupled with a burst of cell proliferation. New developments in embryo culture and imaging techniques have recently revealed the growth and morphogenesis of the embryo at the time of implantation, leading to a new model for the blastocyst to egg cylinder transition. In this model, pluripotent cells that will give rise to the fetus self-organize into a polarized three-dimensional rosette-like structure that initiates egg cylinder formation.

Reduced Gene Dosage of Tfap2c Impairs Trophoblast Lineage Differentiation and Alters Maternal Blood Spaces in the Mouse Placenta

Tfap2c is required for placental development and trophoblast stem cell maintenance. Deletion of Tfap2c results in early embryonic loss because of failure in placental development. We evaluated the effect of reduced Tfap2c expression on fetal outcome and placental development. Sixty percent of the heterozygous mice were lost directly after birth. Labyrinthine differentiation was impaired, as indicated by enhanced proliferation and inclusions of cobblestone-shaped cell clusters characterized by expression of Tfap2c and glycogen stores. Moreover, expression of marker genes such as Cdx2, Eomes, Gata3, and Ascl2 are decreased in the spongiotrophoblast and indicate a lowered stem cell potential. On Day 18.5 postcoitum, the labyrinth layer of Tfap2c(+/-) placentas exhibited massive hemorrhages in the maternal blood spaces; these hemorrhages might have contributed to the significantly reduced number of live-born pups. These morphological alterations were accompanied by a shift toward sinusoidal trophoblast giant cells as the cell subpopulation lining the maternal sinusoids and toward reduction in expression of the prolactin gene family member Prl2c2, a finding characteristic of the spiral arteries lining trophoblast cells. The trophoblast stem cells heterozygous for Tfap2c exhibited a reduction in the expression level of stem cell markers and in their proliferation and differentiation capacity but did not exhibit changes in marker genes of the trophoblast giant cell lineage. Taken together, these findings indicate that a reduction in the gene dosage of placental Tfap2c leads to morphological changes in the labyrinth at midgestation and in the maternal blood spaces during late pregnancy.

E74-like factor inhibition induces reacquisition of hormone sensitiveness decreasing period circadian protein homolog 1 expression in prostate cancer cells

Purpose

Initiating as an androgen-dependent adenocarcinoma, prostate cancer (PCa) gradually progresses to a castrate-resistant disease following androgen deprivation therapy with a propensity to metastasize.

Methods

In order to resolve the mechanism of castrate-resistant PCa, we performed a cDNA-microarray assay of two PCa cell lines, LNCaP (androgen dependent) and C4-2 (androgen independent). Among them, we focused on a novel Ets transcription factor, E74-like factor 5 (ELF5), the expression level of which was extremely high in C4-2 in comparison with LNCaP both in the microarray analysis and real-time polymerase chain reaction analysis, and investigated the biological role in acquisition of androgen-refractory PCa growth.

Results

Western blot analysis and morphological analysis using confocal immunofluorescence microscopy demonstrated that ELF5 was expressed mainly in cytosol both in LNCaP and C4-2. Inhibition of ELF5 expression using ELF5-small interfering RNA in C4-2 induced decreased expression of androgen receptor corepressor, period circadian protein homolog 1, and MTT assay of C4-2 after ELF5 small interfering RNA transfection showed the same cell growth pattern of LNCaP.

Conclusions

Our in vitro experiments of cell growth and microarray analysis have demonstrated for the first time that decreased expression of period circadian protein homolog 1 due to ELF5 inhibition may induce the possibility of reacquisition of hormone sensitiveness of PCa cells. We suggest that ELF5 could be a novel potential target for the treatment of hormone-refractory PCa patients.

Epigenetic memory of the first cell fate decision prevents complete ES cell reprogramming into trophoblast

Embryonic (ES) and trophoblast (TS) stem cells reflect the first, irrevocable cell fate decision in development that is reinforced by distinct epigenetic lineage barriers. Nonetheless, ES cells can seemingly acquire TS-like characteristics upon manipulation of lineage-determining transcription factors or activation of the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway. Here we have interrogated the progression of reprogramming in ES cell models with regulatable Oct4 and Cdx2 transgenes or conditional Erk1/2 activation. Although trans-differentiation into TS-like cells is initiated, lineage conversion remains incomplete in all models, underpinned by the failure to demethylate a small group of TS cell genes. Forced expression of these non-reprogrammed genes improves trans-differentiation efficiency, but still fails to confer a stable TS cell phenotype. Thus, even ES cells in ground-state pluripotency cannot fully overcome the boundaries that separate the first cell lineages but retain an epigenetic memory of their ES cell origin.

Elf5 and Ets2 maintain the mouse extraembryonic ectoderm in a dosage dependent synergistic manner

The ETS superfamily transcription factors Elf5 and Ets2 have both been implicated in the maintenance of the extraembryonic ectoderm (ExE) of the mouse embryo. While homozygous mutants of either gene result in various degrees of ExE tissue loss, heterozygotes are without phenotype. We show here that compound heterozygous mutants exhibit a phenotype intermediate to that of the more severe Elf5-/- and the milder Ets2-/- mutants. Functional redundancy is shown via commonalities in expression patterns, in target gene expression, and by partial rescue of Elf5-/- mutants through overexpressing Ets2 in an Elf5-like fashion. A model is presented suggesting the functional division of the ExE region into a proximal and distal domain based on gene expression patterns and the proximal to distal increasing sensitivity to threshold levels of combined Elf5 and Ets2 activity.

Dynamic proteomic profiles of in vivo- and in vitro-produced mouse postimplantation extraembryonic tissues and placentas

As the interface between the mother and the developing fetus, the placenta is believed to play an important role in assisted reproductive technology (ART)-induced aberrant intrauterine and postnatal development. However, the mechanisms underlying aberrant placentation remain unclear, especially during extraembryonic tissue development and early stages of placental formation. Using a mouse model, this investigation provides the first comparative proteomic analysis of in vivo (IVO) and in vitro-produced (IVP) extraembryonic tissues and placentas after IVO fertilization and development, or in vitro fertilization and culture, respectively. We identified 165 and 178 differentially expressed proteins (DEPs) between IVO and IVP extraembryonic tissues and placentas on Embryonic Day 7.5 (E7.5) and E10.5, respectively. Many DEPs were functionally associated with genetic information processing, such as impaired de novo DNA methylation, as well as posttranscriptional, translational and posttranslational dysregulation. These novel findings were further confirmed by global hypomethylation, and a lower level of correlation was found between the transcriptome and proteome in the IVP groups. In addition, numerous DEPs were involved in energy and amino acid metabolism, cytoskeleton organization and transport, and vasculogenesis and angiogenesis. These disturbed processes and pathways are likely to be associated with embryonic intrauterine growth restriction, an enlarged placenta, and impaired labyrinth morphogenesis. This study provides a direct and comprehensive reference for the further exploration of the placental mechanisms that underlie ART-induced developmental aberrations.

Transcriptional regulators of the trophoblast lineage in mammals with hemochorial placentation

Mammalian reproduction is critically dependent on the trophoblast cell lineage, which assures proper establishment of maternal-fetal interactions during pregnancy. Specification of trophoblast cell lineage begins with the development of the trophectoderm (TE) in preimplantation embryos. Subsequently, other trophoblast cell types arise with the progression of pregnancy. Studies with transgenic animal models as well as trophoblast stem/progenitor cells have implicated distinct transcriptional and epigenetic regulators in trophoblast lineage development. This review focuses on our current understanding of transcriptional and epigenetic mechanisms regulating specification, determination, maintenance and differentiation of trophoblast cells.

ADP-ribosyltransferases Parp1 and Parp7 safeguard pluripotency of ES cells

Embryonic stem (ES) cells are in a dynamic equilibrium of distinct functional states, characterized by the heterogeneous expression of critical pluripotency factors and regulated by a spectrum of reversible histone modifications. Maintenance of this equilibrium is a hallmark of pluripotency. Here we find that the ADP-ribosyltransferases Parp1 and Parp7 play a critical role in safeguarding this state by occupying key pluripotency genes, notably Nanog, Pou5f1, Sox2, Stella, Tet1 and Zfp42, thereby protecting them from progressive epigenetic repression. In the absence of either Parp1 or Parp7, or upon inhibition of the ADP-ribosylating activity, ES cells exhibit a decrease in ground state pluripotency as they cannot maintain the typical heterogeneity characteristic of the metastable state. As a consequence, they display a higher propensity to differentiate. These findings place Parp1 and Parp7 at the genetic-epigenetic interface of pluripotency networks, fine-tuning the transcriptional heterogeneity and thereby determining the developmental plasticity of ES cells.

The Dynamics of Morphogenesis in the Early Mouse Embryo

SUMMARYOver the past two decades, our understanding of mouse development from implantation to gastrulation has grown exponentially with an upsurge of genetic, molecular, cellular, and morphogenetic information. New discoveries have exalted the role of extraembryonic tissues in orchestrating embryonic patterning and axial specification. At the same time, the identification of unexpected morphogenetic processes occurring during mouse gastrulation has challenged established dogmas and brought new insights into the mechanisms driving germ layer formation. In this article, we summarize the key findings that have reinvigorated the contemporary view of early postimplantation mammalian development.

Elf5 counteracts precocious trophoblast differentiation by maintaining Sox2 and 3 and inhibiting Hand1 expression

In mice the transcription factor Elf5 is necessary for correct trophoblast development. Upon knockdown of Elf5, TS cells display neither a decrease in proliferation nor an increase in cell death but rather an increased propensity to differentiate. Such cells rapidly lose Sox2 and 3 expression, while transiently upregulating the giant cell differentiation determinant gene Hand1. Other genes affected within 24h of Elf5 knock-down, many of which have not previously been implicated in trophoblast development, exhibited in vivo expression domains and in vitro expression responses consistent with Elf5 having a role in counteracting trophoblast differentiation. In an ES to TS differentiation assay using Cdx2 overexpression with Elf5 loss of function cell lines, it was shown that Elf5 is necessary to prevent terminal trophoblast differentiation. This data thus suggest that Elf5 is a gatekeeper for the TS to differentiated trophoblast transition thereby preventing the precocious differentiation of the undifferentiated extraembryonic ectoderm.

Specific epiblast loss and hypoblast impairment in cattle embryos sensitized to survival signalling by ubiquitous overexpression of the proapoptotic gene BAD

Early embryonic lethality is common, particularly in dairy cattle. We made cattle embryos more sensitive to environmental stressors by raising the threshold of embryo survival signaling required to overcome the deleterious effects of overexpressing the proapoptotic protein BAD. Two primary fibroblast cell lines expressing BAD and exhibiting increased sensitivity to stress-induced apoptosis were used to generate transgenic Day13/14 BAD embryos. Transgenic embryos were normal in terms of retrieval rates, average embryo length or expression levels of the trophectoderm marker ASCL2. However both lines of BAD-tg embryos lost the embryonic disc and thus the entire epiblast lineage at significantly greater frequencies than either co-transferrred IVP controls or LacZ-tg embryos. Embryos without epiblast still contained the second ICM-derived lineage, the hypopblast, albeit frequently in an impaired state, as shown by reduced expression of the hypoblast markers GATA4 and FIBRONECTIN. This indicates a gradient of sensitivity (epiblast > hypoblast > TE) to BAD overexpression. We postulate that the greater sensitivity of specifically the epiblast lineage that we have seen in our transgenic model, reflects an inherent greater susceptibility of this lineage to environmental stress and may underlie the epiblast-specific death seen in phantom pregnancies.

Epigenetic choreography of stem cells: the DNA demethylation episode of development

Reversible DNA methylation is a fundamental epigenetic manipulator of the genomic information in eukaryotes. DNA demethylation plays a very significant role during embryonic development and stands out for its contribution in molecular reconfiguration during cellular differentiation for determining stem cell fate. DNA demethylation arbitrated extensive make-over of the genome via reprogramming in the early embryo results in stem cell plasticity followed by commitment to the principal cell lineages. This article attempts to highlight the sequential phases and hierarchical mode of DNA demethylation events during enactment of the molecular strategy for developmental transition. A comprehensive knowledge regarding the pattern of DNA demethylation during embryogenesis and organogenesis and study of the related lacunae will offer exciting avenues for future biomedical research and stem cell-based regenerative therapy.

Derivation and maintenance of murine trophoblast stem cells under defined conditions

Trophoblast stem cells (TSCs) are in vitro equivalents to the precursor cells of the placenta. TSCs are cultured in serum-rich medium with fibroblast growth factor 4, heparin, and embryonic-fibroblast-conditioned medium. Here, we developed a simple medium consisting of ten chemically defined ingredients for culture of TSCs on Matrigel or synthetic substrates, named TX medium. Gene expression and DNA methylation profiling demonstrated the faithful propagation of expression profiles and epigenomic characteristics of TSCs cultured in TX. Further, TX medium supported the de novo derivation of TSC lines. Finally, TSCs cultured in TX differentiate into all derivatives of the trophectodermal lineage in vitro, give rise to hemorrhagic lesions in nude mice, and chimerize the placenta, indicating that they retained all hallmarks of TSCs. TX media formulation no longer requires fetal bovine serum and conditioned medium, which facilitates and standardizes the culture of this extraembryonic lineage.

Paracrine effects of embryo-derived FGF4 and BMP4 during pig trophoblast elongation

The crosstalk between the epiblast and the trophoblast is critical in supporting the early stages of conceptus development. FGF4 and BMP4 are inductive signals that participate in the communication between the epiblast and the extraembryonic ectoderm (ExE) of the developing mouse embryo. Importantly, however, it is unknown whether a similar crosstalk operates in species that lack a discernible ExE and develop a mammotypical embryonic disc (ED). Here we investigated the crosstalk between the epiblast and the trophectoderm (TE) during pig embryo elongation. FGF4 ligand and FGFR2 were detected primarily on the plasma membrane of TE cells of peri-elongation embryos. The binding of this growth factor to its receptor triggered a signal transduction response evidenced by an increase in phosphorylated MAPK/ERK. Particular enrichment was detected in the periphery of the ED in early ovoid embryos, indicating that active FGF signalling was operating during this stage. Gene expression analysis shows that CDX2 and ELF5, two genes expressed in the mouse ExE, are only co-expressed in the Rauber's layer, but not in the pig mural TE. Interestingly, these genes were detected in the nascent mesoderm of early gastrulating embryos. Analysis of BMP4 expression by in situ hybridisation shows that this growth factor is produced by nascent mesoderm cells. A functional test in differentiating epiblast shows that CDX2 and ELF5 are activated in response to BMP4. Furthermore, the effects of BMP4 were also demonstrated in the neighbouring TE cells, as demonstrated by an increase in phosphorylated SMAD1/5/8. These results show that BMP4 produced in the extraembryonic mesoderm is directly influencing the SMAD response in the TE of elongating embryos. These results demonstrate that paracrine signals from the embryo, represented by FGF4 and BMP4, induce a response in the TE prior to the extensive elongation. The study also confirms that expression of CDX2 and ELF5 is not conserved in the mural TE, indicating that although the signals that coordinate conceptus growth are similar between rodents and pigs, the gene regulatory network of the trophoblast lineage is not conserved in these species.

Transcriptional reprogramming and chromatin remodeling accompanies Oct4 and Nanog silencing in mouse trophoblast lineage

In mouse blastocysts, CDX2 plays a key role in silencing Oct4 and Nanog expression in the trophectoderm (TE) lineage. However, the underlying transcriptional and chromatin-based changes that are associated with CDX2-mediated repression are poorly understood. To address this, a Cdx2-inducible mouse embryonic stem (ES) cell line was utilized as a model system. Induction of Cdx2 expression resulted in a decrease in Oct4/Nanog expression, an increase in TE markers, and differentiation into trophoblast-like stem (TS-like) cells within 48 to 120 h. Consistent with the down-regulation of Oct4 and Nanog transcripts, a time-dependent increase in CDX2 binding and a decrease in RNA polymerase II (RNAPII) and OCT4 binding was observed within 48 h (P<0.05). To test whether transcriptionally active epigenetic marks were erased during differentiation, histone H3K9/14 acetylation and two of its epigenetic modifiers were evaluated. Accordingly, a significant decrease in histone H3K9/14 acetylation and loss of p300 and HDAC1 binding at the Oct4 and Nanog regulatory elements was observed by 48 h. Accompanying these changes, there was a significant increase in total histone H3 and a loss of chromatin accessibility at both the Oct4 and Nanog regulatory elements (P<0.05), indicative of chromatin remodeling. Lastly, DNA methylation analysis revealed that methylation did not occur at Oct4 and Nanog until 96 to 120 h after induction of CDX2. In conclusion, our results show that silencing of Oct4 and Nanog is facilitated by sequential changes in transcription factor binding, histone acetylation, chromatin remodeling, and DNA methylation at core regulatory elements.

ELF5, normal mammary development and the heterogeneous phenotypes of breast cancer

SUMMARY The ETS transcription factor ELF5 specifies the formation of the secretory cell lineage of the mammary gland during pregnancy, by directing cell fate decisions of the mammary progenitor cells. The decision-making activity continues in breast cancer, where in luminal breast cancer cells forced ELF5 expression suppresses estrogen sensitivity and shifts gene expression toward the basal molecular subtype. The development of anti-estrogen resistance in luminal breast cancer is accompanied by increased expression of ELF5 and acquired dependence on ELF5 for continued proliferation, providing a potential new therapeutic target or prognostic marker to improve the treatment of this stage of the disease. Forced ELF5 expression suppresses the mesenchymal phenotype, making cells more epithelial and producing lower rates of invasion and motility. Conversely, loss of ELF5 promotes metastasis, with a clear corollary in the claudin-low subtype of breast cancer, which does not express ELF5 and is highly metastatic, or during the final stages of tumor progression, where loss of ELF5 expression may be involved in the acquisition of the lethal phenotype. In circumstances where ELF5 expression increases in parallel with metastatic potential, such as anti-estrogen resistant luminal breast cancers and basal breast cancer, there is much more to be understood about ELF5 and metastasis.

Somatic donor cell type correlates with embryonic, but not extra-embryonic, gene expression in postimplantation cloned embryos

The great majority of embryos generated by somatic cell nuclear transfer (SCNT) display defined abnormal phenotypes after implantation, such as an increased likelihood of death and abnormal placentation. To gain better insight into the underlying mechanisms, we analyzed genome-wide gene expression profiles of day 6.5 postimplantation mouse embryos cloned from three different cell types (cumulus cells, neonatal Sertoli cells and fibroblasts). The embryos retrieved from the uteri were separated into embryonic (epiblast) and extraembryonic (extraembryonic ectoderm and ectoplacental cone) tissues and were subjected to gene microarray analysis. Genotype- and sex-matched embryos produced by in vitro fertilization were used as controls. Principal component analysis revealed that whereas the gene expression patterns in the embryonic tissues varied according to the donor cell type, those in extraembryonic tissues were relatively consistent across all groups. Within each group, the embryonic tissues had more differentially expressed genes (DEGs) (>2-fold vs. controls) than did the extraembryonic tissues (P<1.0×10^–26). In the embryonic tissues, one of the common abnormalities was upregulation of Dlk1, a paternally imprinted gene. This might be a potential cause of the occasional placenta-only conceptuses seen in SCNT-generated mouse embryos (1–5% per embryos transferred in our laboratory), because dysregulation of the same gene is known to cause developmental failure of embryos derived from induced pluripotent stem cells. There were also some DEGs in the extraembryonic tissues, which might explain the poor development of SCNT-derived placentas at early stages. These findings suggest that SCNT affects the embryonic and extraembryonic development differentially and might cause further deterioration in the embryonic lineage in a donor cell-specific manner. This could explain donor cell-dependent variations in cloning efficiency using SCNT.

Context-dependent wiring of Sox2 regulatory networks for self-renewal of embryonic and trophoblast stem cells

Sox2 is a transcription factor required for the maintenance of pluripotency. It also plays an essential role in different types of multipotent stem cells, raising the possibility that Sox2 governs the common stemness phenotype. Here we show that Sox2 is a critical downstream target of fibroblast growth factor (FGF) signaling, which mediates self-renewal of trophoblast stem cells (TSCs). Sustained expression of Sox2 together with Esrrb or Tfap2c can replace FGF dependency. By comparing genome-wide binding sites of Sox2 in embryonic stem cells (ESCs) and TSCs combined with inducible knockout systems, we found that, despite the common role in safeguarding the stem cell state, Sox2 regulates distinct sets of genes with unique functions in these two different yet developmentally related types of stem cells. Our findings provide insights into the functional versatility of transcription factors during embryogenesis, during which they can be recursively utilized in a variable manner within discrete network structures.

CTR9/PAF1c regulates molecular lineage identity, histone H3K36 trimethylation and genomic imprinting during preimplantation development

Genome-wide epigenetic reprogramming is required for successful preimplantation development. Inappropriate or deficient chromatin regulation can result in defective lineage specification and loss of genomic imprinting, compromising normal development. Here we report that two members of the RNA polymerase II associated factor, homolog (Saccharomyces cerevisiae) complex (PAF1 complex) components, Ctr9 and Rtf1, are required during mammalian preimplantation development. We demonstrate that Ctr9-deficient embryos fail to correctly specify lineages at the blastocyst stage. Expression of some lineage specific factors is markedly reduced in Ctr9 knockdown embryos, including Eomes, Elf5 and Sox2, while others are inappropriately expressed (Oct4, Nanog, Gata6, Fgf4 and Sox17). We also show that several imprinted genes (Mest, Peg3, Snrpn and Meg3) are aberrantly expressed although allele specific DNA methylation is not altered. We document a loss of histone H3 lysine 36 trimethylation (H3K36me3) in Ctr9-deficient embryos and confirm that knockdown of either Setd2 or Rtf1 results in similar phenotypes. These findings show that the PAF1 complex is required for mammalian development, likely through regulation of H3K36me3, and indicate functional conservation of the PAF1 complex from yeast to mammals in vivo.

BMP4-directed trophoblast differentiation of human embryonic stem cells is mediated through a ΔNp63+ cytotrophoblast stem cell state

The placenta is a transient organ that is necessary for proper fetal development. Its main functional component is the trophoblast, which is derived from extra-embryonic ectoderm. Little is known about early trophoblast differentiation in the human embryo, owing to lack of a proper in vitro model system. Human embryonic stem cells (hESCs) differentiate into functional trophoblast following BMP4 treatment in the presence of feeder-conditioned media; however, this model has not been widely accepted, in part owing to a lack of proof for a trophoblast progenitor population. We have previously shown that p63, a member of the p53 family of nuclear proteins, is expressed in proliferative cytotrophoblast (CTB), precursors to terminally differentiated syncytiotrophoblast (STB) in chorionic villi and extravillous trophoblast (EVT) at the implantation site. Here, we show that BMP4-treated hESCs differentiate into bona fide CTB by direct comparison with primary human placental tissues and isolated CTB through gene expression profiling. We show that, in primary CTB, p63 levels are reduced as cells differentiate into STB, and that forced expression of p63 maintains cyclin B1 and inhibits STB differentiation. We also establish that, similar to in vivo events, hESC differentiation into trophoblast is characterized by a p63(+)/KRT7(+) CTB stem cell state, followed by formation of functional KLF4(+) STB and HLA-G(+) EVT. Finally, we illustrate that downregulation of p63 by shRNA inhibits differentiation of hESCs into functional trophoblast. Taken together, our results establish that BMP4-treated hESCs are an excellent model of human trophoblast differentiation, closely mimicking the in vivo progression from p63(+) CTB stem cells to terminally differentiated trophoblast subtypes.

CDX2 regulates multiple trophoblast genes in bovine trophectoderm CT-1 cells

The bovine trophectoderm (TE) undergoes a dramatic morphogenetic transition prior to uterine endometrial attachment. Many studies have documented trophoblast-specific gene expression profiles at various pre-attachment stages, yet genetic interactions within the transitioning TE gene regulatory network are not well characterized. During bovine embryogenesis, transcription factors OCT4 and CDX2 are co-expressed during early trophoblast elongation. In this study, the bovine trophectoderm-derived CT-1 cell line was utilized as a genetic model to examine the roles of CDX2 and OCT4 within the bovine trophoblast gene regulatory network. An RT-PCR screen for TE-lineage transcription factors identified expression of CDX2, ERRB, ID2, SOX15, ELF5, HAND1, and ASCL2. CT-1 cells also express a nuclear-localized, 360 amino acid OCT4 ortholog of the pluripotency-specific human OCT4A. To delineate the roles of CDX2 and OCT4 within the CT-1 gene network, CDX2 and OCT4 levels were manipulated via overexpression and siRNA-mediated knockdown. An increase in CDX2 negatively regulated OCT4 expression, but increased expression of IFNT, HAND1, ASCL2, SOX15, and ELF5. A reduction of CDX2 levels exhibited a reciprocal effect, resulting in decreased expression of IFNT, HAND1, ASCL2, and SOX15. Both overexpression and knockdown of CDX2 increased ETS2 transcription. In contrast to CDX2, manipulation of OCT4 levels only revealed a positive autoregulatory mechanism and upregulation of ASCL2. Together, these results suggest that CDX2 is a core regulator of multiple trophoblast genes within CT-1 cells.

Elf5 - breast cancer's little helper

A variety of transcription factors has been shown to regulate lineage commitment in the mammary gland and to be associated with different molecular subtypes of breast cancer. E74-like factor 5 (Elf5) has now been identified as a marker of oestrogen receptor status, and high expression correlates with more aggressive basal cancers and resistance to anti-oestrogens. Manipulation of Elf5 transcript levels perturbs the molecular profiles of luminal and basal subtypes, highlighting the possibility that targeting Elf5 could provide a new approach for the treatment of basal cancers.