Life Sciences Research for Lifelong Health

Publications myriam-hemberger

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From the stem of the placental tree: trophoblast stem cells and their progeny.
Latos PA, Hemberger M

Trophoblast stem cells (TSCs) retain the capacity to self-renew indefinitely and harbour the potential to differentiate into all trophoblast subtypes of the placenta. Recent studies have shown how signalling cascades integrate with transcription factor circuits to govern the fine balance between TSC self-renewal and differentiation. In addition, breakthroughs in reprogramming strategies have enabled the generation of TSCs from fibroblasts, opening up exciting new avenues that may allow the isolation of this stem cell type from other species, notably humans. Here, we review these recent advances in light of their importance for understanding placental pathologies and developing personalised medicine approaches for pregnancy complications.

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Development (Cambridge, England), 143, 1477-9129, 3650-3660, 2016

PMID: 27802134

Plet1 is an epigenetically regulated cell surface protein that provides essential cues to direct trophoblast stem cell differentiation.
Murray A, Sienerth AR, Hemberger M

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.

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Scientific reports, 6, 2045-2322, 25112, 2016

PMID: 27121762

Open Access

What Is Trophoblast? A Combination of Criteria Define Human First-Trimester Trophoblast.
Lee CQ, Gardner L, Turco M, Zhao N, Murray MJ, Coleman N, Rossant J, Hemberger M, Moffett A

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.

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Stem cell reports, 6, 2213-6711, 257-72, 2016

PMID: 26862703

Open Access

Maternal DNA Methylation Regulates Early Trophoblast Development.
Branco MR, King M, Perez-Garcia V, Bogutz AB, Caley M, Fineberg E, Lefebvre L, Cook SJ, Dean W, Hemberger M, Reik W

Critical roles for DNA methylation in embryonic development are well established, but less is known about its roles during trophoblast development, the extraembryonic lineage that gives rise to the placenta. We dissected the role of DNA methylation in trophoblast development by performing mRNA and DNA methylation profiling of Dnmt3a/3b mutants. We find that oocyte-derived methylation plays a major role in regulating trophoblast development but that imprinting of the key placental regulator Ascl2 is only partially responsible for these effects. We have identified several methylation-regulated genes associated with trophoblast differentiation that are involved in cell adhesion and migration, potentially affecting trophoblast invasion. Specifically, trophoblast-specific DNA methylation is linked to the silencing of Scml2, a Polycomb Repressive Complex 1 protein that drives loss of cell adhesion in methylation-deficient trophoblast. Our results reveal that maternal DNA methylation controls multiple differentiation-related and physiological processes in trophoblast via both imprinting-dependent and -independent mechanisms.

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Developmental cell, 36, 1878-1551, 152-63, 2016

PMID: 26812015

Open Access

Elf5-centered transcription factor hub controls trophoblast stem cell self-renewal and differentiation through stoichiometry-sensitive shifts in target gene networks.
Latos PA, Sienerth AR, Murray A, Senner CE, Muto M, Ikawa M, Oxley D, Burge S, Cox BJ, Hemberger M

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.

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Genes & development, , 1549-5477, , 2015

PMID: 26584622

Open Access

Direct Induction of Trophoblast Stem Cells from Murine Fibroblasts.
Kubaczka C, Senner CE, Cierlitza M, Araúzo-Bravo MJ, Kuckenberg P, Peitz M, Hemberger M, Schorle H

Trophoblast stem cells (TSCs) arise from the first cell fate decision in the developing embryo and generate extra-embryonic lineages, giving rise to the fetal portion of the placenta. Mouse embryonic and extra-embryonic lineages are strictly separated by a distinct epigenetic barrier, which is not fully overcome following expression of TSC-determining factors in embryonic stem cells. Here, we show that transient expression of Tfap2c, Gata3, Eomes, and Ets2 is sufficient to reprogram mouse embryonic fibroblasts and post-natal tail-tip-derived fibroblasts into induced TSCs (iTSCs) and surmount the epigenetic barrier separating somatic from extra-embryonic lineages. iTSCs share nearly identical morphological characteristics, gene expression profiles, and DNA methylation patterns with blastocyst-derived TSCs. Furthermore, iTSCs display transgene-independent self-renewal, differentiate along extra-embryonic lineages, and chimerize host placentas following blastocyst injection. These findings provide insights into the transcription factor networks governing TSC identity and opportunities for studying the epigenetic barriers underlying embryonic and extra-embryonic lineage segregation.

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Cell stem cell, 17, 1875-9777, 557-68, 2015

PMID: 26412560

Fgf and Esrrb integrate epigenetic and transcriptional networks that regulate self-renewal of trophoblast stem cells.
Latos PA, Goncalves A, Oxley D, Mohammed H, Turro E, Hemberger M

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.

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Nature communications, 6, 2041-1723, 7776, 2015

PMID: 26206133

Open Access

Epigenetic memory of the first cell fate decision prevents complete ES cell reprogramming into trophoblast.
F Cambuli, A Murray, W Dean, D Dudzinska, F Krueger, S Andrews, CE Senner, S Cook, M Hemberger

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.

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Nat Commun., 26, 5, 5538, 2014

PMID: 25423963

Open Access

ADP-ribosyltransferases Parp1 and Parp7 safeguard pluripotency of ES cells.
Roper SJ, Chrysanthou S, Senner CE, Sienerth A, Gnan S, Murray A, Masutani M, Latos P, M Hemberger

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.

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Nucleic acids research, 42, 1362-4962, 8914-27, 2014

PMID: 25034692

Open Access

Derivation and maintenance of murine trophoblast stem cells under defined conditions.
Kubaczka C,Senner C,Arauzo-Bravo MJ,Sharma N,Kuckenberg P,Becker A,Zimmer A,Brustle O,Peitz M, M Hemberger,Schorle H

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.

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Stem cell reports, 2, 2213-6711, 232-42, 2014

PMID: 24527396

Open Access

Review: The transcriptional and signalling networks of mouse trophoblast stem cells.
PA Latos, M Hemberger

Trophoblast stem cells (TSCs) are a self-renewing stem cell population derived from the early trophoblast lineage, analogous to embryonic stem cells (ESCs) that can be generated from the inner cell mass (ICM) of the mouse blastocyst. In that sense TSCs and ESCs reflect the earliest lineage differentiation event after fertilization. TSCs are characterized by an indefinite proliferation potential and by multipotency, i.e. the ability to differentiate into all the various trophoblast cell types of the placenta. These properties are driven by specific signalling pathways orchestrating characteristic transcriptional outputs. Here we review the recent advances in studying the signalling cascades and the transcriptional regulatory networks that define specification and maintenance of TSCs, and provide a future outlook of TSC research.

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Placenta, , , , 2013

PMID: 24220516
DOI: 10.1016/j.placenta.2013.10.013

The H19 induction triggers trophoblast lineage commitment in mouse ES cells.
H Fujimori, H Mukai, Y Murakami, M Hemberger, Y Hippo, M Masutani

Trophoblast lineage differentiation is properly regulated to support embryogenesis. Besides normal developmental process, during germ cell tumor formation or development of other reproductive system diseases, unregulated trophoblast differentiation is also observed and affects the pathogenesis of the diseases. During normal embryogenesis, cell fate of late-stage blastcyst is regulated by a reciprocal repression of the key transcriptional factors; Oct3/4 dominancy inhibits Cdx2 expression in inner cell mass (ICM) and leads them to epiblast/primitive ectoderm but Cdx2 dominancy in trophectoderm (TE) leads them to trophoblast lineage. In contrast during early blastcyst stage, the Cdx2 expression is restricted in TE and not present in ICM, although Oct3/4 signaling does not inhibit the Cdx2 expression in ICM, implying that some factors could be inactivated leading to the suppressed Cdx2 expression in ICM of early blastcyst. ES cells (ESCs), which are derived from ICM, could be a unique model to study trophoblast differentiation in an ectopic context. We previously showed that poly(ADP-ribose) polymerase-1 (Parp-1) deficient ESCs highly expressed non-coding RNA H19 and could differentiate into trophoblast lineage. The expression of H19 is known to start at pre-blastcyst stage during mouse development, and the gene shows high expression only in trophoectoderm (TE) at blastcyst stage. However, its role in trophoblast differentiation has not been clarified yet. Thus, we hypothesized that the H19 activation may act as a trigger for induction of trophoblast differentiation cascade in mouse ESCs. To investigate this issue, we asked whether a forced H19 expression drives ESCs into trophoblast lineage or not. We demonstrated that the H19 induction leads to trophoblast lineage commitment through induction of the Cdx2 expression. We also showed that the expression of Cdx2 is induced in ESCs by forced H19 expression even under a high level of Oct3/4, which could act as a suppressor for Cdx2 expression. It is thus suggested that the H19 induction promotes trophoblast lineage commitment against the repression pressure by Oct3/4 in differentiating ESCs. Taken together, this study suggests that the H19 expression is able to function as a cascade activator of trophoblast lineage commitment possibly by overriding the Oct3/4 action in ESCs.

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Biochemical and biophysical research communications, 436, 2, 313-8, 2013

PMID: 23743205
DOI: 10.1016/j.bbrc.2013.05.100

Deciphering the Mechanisms of Developmental Disorders (DMDD): a new programme for phenotyping embryonic lethal mice.
T Mohun, DJ Adams, R Baldock, S Bhattacharya, AJ Copp, M Hemberger, C Houart, ME Hurles, E Robertson, JC Smith, T Weaver, W Weninger

International efforts to test gene function in the mouse by the systematic knockout of each gene are creating many lines in which embryonic development is compromised. These homozygous lethal mutants represent a potential treasure trove for the biomedical community. Developmental biologists could exploit them in their studies of tissue differentiation and organogenesis; for clinical researchers they offer a powerful resource for investigating the origins of developmental diseases that affect newborns. Here, we outline a new programme of research in the UK aiming to kick-start research with embryonic lethal mouse lines. The 'Deciphering the Mechanisms of Developmental Disorders' (DMDD) programme has the ambitious goal of identifying all embryonic lethal knockout lines made in the UK over the next 5 years, and will use a combination of comprehensive imaging and transcriptomics to identify abnormalities in embryo structure and development. All data will be made freely available, enabling individual researchers to identify lines relevant to their research. The DMDD programme will coordinate its work with similar international efforts through the umbrella of the International Mouse Phenotyping Consortium [see accompanying Special Article (Adams et al., 2013)] and, together, these programmes will provide a novel database for embryonic development, linking gene identity with molecular profiles and morphology phenotypes.

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Disease models & mechanisms, 6, 3, 562-6, 2013

PMID: 23519034
DOI: 10.1242/dmm.011957

Open Access

Immune balance at the foeto-maternal interface as the fulcrum of reproductive success.
M Hemberger

Viviparity has many evolutionary advantages but brings with it the problem of the semi-allogeneic foetus having to coexist with the mother for the duration of pregnancy. In species with haemochorial placentation this problem is particularly evident as foetal trophoblast cells are extensively intermingled with maternal tissue and are directly exposed to maternal blood. Fascinating adaptations on both the foetal and maternal side have allowed for this interaction to be re-directed away from an immune rejection response not only towards immunotolerance, but in fact towards actively supporting reproductive success. Recent data have shown that some of these remarkable adaptations are conserved between mice and humans. Thus, a subset of trophoblast cells that is directly exposed to the maternal uterine environment shares the feature of expressing an unusual antigen repertoire on their surface. Paternal antigens can be recognized by maternal immune cells, in particular uterine natural killer cells that express cognate receptors, to regulate the extensive remodelling events that take place at the implantation site. Detailed genetic dissection experiments in the mouse have further demonstrated the direct impact of antigenic dissimilarity on foetal growth. With the availability of inbred strains, in vitro culture systems of trophoblast stem cells, and in-depth genetic, genomic and epigenomic data the mouse will be a valuable model system to study the intricate immune crosstalk at the foeto-maternal boundary. These insights will pave the way towards unravelling the mutual and synergistic interactions between trophoblast and its surrounding maternal environment, and in doing so help understand pregnancy pathologies.

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Journal of reproductive immunology, 97, 1, 36-42, 2013

PMID: 23432870
DOI: 10.1016/j.jri.2012.10.006

Zoonoses: a potential obstacle to the growing wildlife industry of Namibia.
Magwedere K, Hemberger MY, Hoffman LC, Dziva F

Zoonoses, which account for approximately 75% of emerging human infectious diseases worldwide, pose a re-emerging threat to public health. With an ever-increasing interrelationship between humans, livestock and wildlife species, the threat to human health will rise to unprecedented levels. Wildlife species contribute to the majority of emerging diseases; therefore, there is an urgent need to define control systems of zoonoses of wildlife origin but very little information exists. In this review, we examine prevalent zoonotic infections reported in Namibia between 1990 and 2009 and assess their potential impact on the growing wildlife industry. A wide spectrum of zoonotic diseases was confirmed in both livestock and wildlife species, with rabies and anthrax cases being over-represented and also showing the widest species distribution. Whilst vaccination and ante-mortem inspection against these diseases may curb infected livestock species from entering the human food chain, such practices are difficult to implement in free-ranging wildlife species. In this context, there is a need to improve existing control measures and/or develop novel and better interventional strategies to reduce the threat of this re-emerging global problem. This review provides the basis for initiating a multidisciplinary evidence-based approach to control zoonoses in countries with thriving wildlife and game farming.

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Infection ecology & epidemiology, 2, 2000-8686, , 2012

PMID: 23077724

Open Access

DNA methylation profiles define stem cell identity and reveal a tight embryonic-extraembryonic lineage boundary.
CE Senner, F Krueger, D Oxley, S Andrews, M Hemberger

Embryonic (ES) and epiblast (EpiSC) stem cells are pluripotent but committed to an embryonic lineage fate. Conversely, trophoblast (TS) and extraembryonic endoderm (XEN) stem cells contribute predominantly to tissues of the placenta and yolk sac, respectively. Here we show that each of these four stem cell types is defined by a unique DNA methylation profile. Despite their distinct developmental origin, TS and XEN cells share key epigenomic hallmarks, chiefly characterized by robust DNA methylation of embryo-specific developmental regulators, as well as a subordinate role of 5-hydroxymethylation. We also observe a substantial methylation reinforcement of pre-existing epigenetic repressive marks that specifically occurs in extraembryonic stem cells compared to in vivo tissue, presumably due to continued high Dnmt3b expression levels. These differences establish a major epigenetic barrier between the embryonic and extraembryonic stem cell types. In addition, epigenetic lineage boundaries also separate the two extraembryonic stem cell types by mutual repression of key lineage-specific transcription factors. Thus, global DNA methylation patterns are a defining feature of each stem cell type that underpin lineage commitment and differentiative potency of early embryo-derived stem cells. Our detailed methylation profiles identify a cohort of developmentally regulated sequence elements, such as orphan CpG islands, that will be most valuable to uncover novel transcriptional regulators and pivotal "gatekeeper" genes in pluripotency and lineage differentiation.

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Stem cells (Dayton, Ohio), 30, 12, 2732-45, 2012

PMID: 23034951
DOI: 10.1002/stem.1249

Open Access

Endoplasmic reticulum stress disrupts placental morphogenesis: implications for human intrauterine growth restriction.
HW Yung, M Hemberger, ED Watson, CE Senner, CP Jones, RJ Kaufman, DS Charnock-Jones, GJ Burton

We recently reported the first evidence of placental endoplasmic reticulum (ER) stress in the pathophysiology of human intrauterine growth restriction. Here, we used a mouse model to investigate potential underlying mechanisms. Eif2s1(tm1RjK) mice, in which Ser51 of eukaryotic initiation factor 2 subunit alpha (eIF2α) is mutated, display a 30% increase in basal translation. In Eif2s1(tm1RjK) placentas, we observed increased ER stress and anomalous accumulation of glycoproteins in the endocrine junctional zone (Jz), but not in the labyrinthine zone where physiological exchange occurs. Placental and fetal weights were reduced by 15% (97 mg to 82 mg, p < 0.001) and 20% (1009 mg to 798 mg, p < 0.001), respectively. To investigate whether ER stress affects bioactivity of secreted proteins, mouse embryonic fibroblasts (MEFs) were derived from Eif2s1(tm1RjK) mutants. These MEFs exhibited ER stress, grew 50% slower, and showed reduced Akt-mTOR signalling compared to wild-type cells. Conditioned medium (CM) derived from Eif2s1(tm1RjK) MEFs failed to maintain trophoblast stem cells in a progenitor state, but the effect could be rescued by exogenous application of FGF4 and heparin. In addition, ER stress promoted accumulation of pro-Igf2 with altered glycosylation in the CM without affecting cellular levels, indicating that the protein failed to be processed after release. Igf2 is the major growth factor for placental development; indeed, activity in the Pdk1-Akt-mTOR pathways was decreased in Eif2s1(tm1RjK) placentas, indicating loss of Igf2 signalling. Furthermore, we observed premature differentiation of trophoblast progenitors at E9.5 in mutant placentas, consistent with the in vitro results and with the disproportionate development of the labyrinth and Jz seen in placentas at E18.5. Similar disproportion has been reported in the Igf2-null mouse. These results demonstrate that ER stress adversely affects placental development, and that modulation of post-translational processing, and hence bioactivity, of secreted growth factors contributes to this effect. Placental dysmorphogenesis potentially affects fetal growth through reduced exchange capacity. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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The Journal of pathology, , , , 2012

PMID: 22733590
DOI: 10.1002/path.4068

Open Access

A placenta for life.
R John, M Hemberger

The chorioallantoic placenta is the defining organ of eutherians that has enabled prolonged intrauterine gestation. As such, normal placental development and function are essential for mammalian reproductive success. Reflecting the key role of this organ in providing nutrients to the embryo, the characteristic cell type that forms substantial parts of the placenta is called 'trophoblast' (from Greek trephein 'to feed' and blastos 'germinator'). However, in addition to regulating nutrient supply, the placenta also exerts a number of other pivotal functions that highlight the importance of normal trophoblast differentiation for a successful pregnancy. In this guest symposium, 'Trophoblast Development', several contributors summarize insights gained from recent studies in the mouse that have advanced our understanding of trophoblast biology. This includes how the earliest trophoblast cells are set aside to expand in a stem- or progenitor-cell compartment under tight genetic and epigenetic control and how subsequent differentiation into the various placental cell types is controlled to ensure normal placentation. The relevance of these contributions range from early developmental cell fate decisions, stem cell biology and placental development for healthy pregnancy to the impact of placental failures on long-term health, with important clinical implications for assisted reproductive technology procedures and pregnancy-associated complications.

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Reproductive biomedicine online, 25, 1, 5-11, 2012

PMID: 22578825
DOI: 10.1016/j.rbmo.2012.03.018

Health during pregnancy and beyond: Fetal trophoblast cells as chief co-ordinators of intrauterine growth and reproductive success.
M Hemberger

Abstract Differentiation of extra-embryonic tissues and organs, notably the placenta, is vital for embryonic development and growth throughout gestation, starting from a few days after fertilization when the trophoblast cell lineage arises until parturition. In utero metabolic programming events may even extend the impact of placental function well into adulthood as they may predispose the offspring to common pathologies such as diabetes and cardiovascular disease. This review summarizes key steps that lead up to formation of a functional placenta. It highlights recent insights that have advanced our view of how early trophoblast expansion is achieved and how sufficient maternal blood supply to the developing fetus is secured. Exciting cumulative data have revealed the importance of a close cross-talk between the embryo proper and extra-embryonic trophoblast cells that involves extracellular matrix components in the establishment of a stem cell-like niche and proliferation compartment. Remarkably, placental function also relies on beneficial interactions between trophoblast cells and maternal immune cells at the implantation site. Our growing knowledge of the molecular mechanisms involved in trophoblast differentiation and function will help to devise informed approaches aimed at deciphering how placentation is controlled in humans as an essential process for reproductive success and long-term health.

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Annals of medicine, 44, 4, 325-37, 2012

PMID: 22409432
DOI: 10.3109/07853890.2012.663930

Pluripotency factor binding and Tsix expression act synergistically to repress Xist in undifferentiated embryonic stem cells.
TB Nesterova, CE Senner, J Schneider, T Alcayna-Stevens, A Tattermusch, M Hemberger, N Brockdorff

Expression of Xist, the master regulator of X chromosome inactivation, is extinguished in pluripotent cells, a process that has been linked to programmed X chromosome reactivation. The key pluripotency transcription factors Nanog, Oct4 and Sox2 are implicated in Xist gene extinction, at least in part through binding to an element located in Xist intron 1. Other pathways, notably repression by the antisense RNA Tsix, may also be involved.

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Epigenetics & chromatin, 4, 1, 17, 2011

PMID: 21982142
DOI: 10.1186/1756-8935-4-17

Open Access

Lineage-specific function of the noncoding Tsix RNA for Xist repression and Xi reactivation in mice.
T Ohhata, CE Senner, M Hemberger, A Wutz

The noncoding Tsix RNA is an antisense repressor of Xist and regulates X inactivation in mice. Tsix is essential for preventing the inactivation of the maternally inherited X chromosome in extraembryonic lineages where imprinted X-chromosome inactivation (XCI) occurs. Here we establish an inducible Tsix expression system for investigating Tsix function in development. We show that Tsix has a clear functional window in extraembryonic development. Within this window, Tsix can repress Xist, which is accompanied by DNA methylation of the Xist promoter. As a consequence of Xist repression, reactivation of the inactive X chromosome (Xi) is widely observed. In the parietal endoderm, Tsix represses Xist and causes reactivation of an Xi-linked GFP transgene throughout development, whereas Tsix progressively loses its Xist-repressing function from embryonic day 9.5 (E9.5) onward in trophoblast giant cells and spongiotrophoblast, suggesting that Tsix function depends on a lineage-specific environment. Our data also demonstrate that the maintenance of imprinted XCI requires Xist expression in specific extraembryonic tissues throughout development. This finding shows that reversible XCI is not exclusive to pluripotent cells, and that in some lineages cell differentiation is not accompanied by a stabilization of the Xi.

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Genes & development, 25, 16, 1702-15, 2011

PMID: 21852535
DOI: 10.1101/gad.16997911

Open Access

BRACHYURY and CDX2 mediate BMP-induced differentiation of human and mouse pluripotent stem cells into embryonic and extraembryonic lineages.
AS Bernardo, T Faial, L Gardner, KK Niakan, D Ortmann, CE Senner, EM Callery, MW Trotter, M Hemberger, JC Smith, L Bardwell, A Moffett, RA Pedersen

BMP is thought to induce hESC differentiation toward multiple lineages including mesoderm and trophoblast. The BMP-induced trophoblast phenotype is a long-standing paradox in stem cell biology. Here we readdressed BMP function in hESCs and mouse epiblast-derived cells. We found that BMP4 cooperates with FGF2 (via ERK) to induce mesoderm and to inhibit endoderm differentiation. These conditions induced cells with high levels of BRACHYURY (BRA) that coexpressed CDX2. BRA was necessary for and preceded CDX2 expression; both genes were essential for expression not only of mesodermal genes but also of trophoblast-associated genes. Maximal expression of the latter was seen in the absence of FGF but these cells coexpressed mesodermal genes and moreover they differed in cell surface and epigenetic properties from placental trophoblast. We conclude that BMP induces human and mouse pluripotent stem cells primarily to form mesoderm, rather than trophoblast, acting through BRA and CDX2.

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Cell stem cell, 9, 2, 144-55, 2011

PMID: 21816365
DOI: 10.1016/j.stem.2011.06.015

Open Access

Paternal MHC expression on mouse trophoblast affects uterine vascularization and fetal growth.
Z Madeja, H Yadi, R Apps, S Boulenouar, SJ Roper, L Gardner, A Moffett, F Colucci, M Hemberger

The mammalian fetus represents a semiallograft within the maternal uterus yet is not rejected. This situation is particularly pronounced in species with a hemochorial type of placentation, such as humans and rodents, where maternal tissues and blood are in direct contact with fetal trophoblast and thus potentially with paternal antigens. The main polymorphic antigens responsible for graft rejection are MHC antigens. In humans the trophoblast cells invading into the decidua have a unique pattern of MHC class I expression characterized by both classical (HLA-C) and nonclassical (HLA-G and HLA-E) molecules. Whether such an unusual MHC repertoire on the surface of trophoblast is a conserved feature between species with hemochorial placentation has not been resolved. Here we demonstrate, using a range of methods, that C57BL/6 mouse trophoblast predominantly expresses only one MHC class I antigen, H2-K, at the cell surface of giant cells but lacks expression of nonclassical MHC molecules. Antigenic disparity between parental MHCs affects trophoblast-induced transformation of the uterine vasculature and, consequently, placental and fetal gowth. Maternal uterine blood vessels were more dilated, allowing for increased blood supply, in certain combinations of maternal and paternal MHC haplotypes, and these allogeneic fetuses and placentas were heavier at term compared with syngeneic controls. Thus, maternal-fetal immune interactions are instrumental to optimize reproductive success. This cross-talk has important implications for human disorders of pregnancy, such as preeclampsia and fetal growth restriction.

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Proceedings of the National Academy of Sciences of the United States of America, 108, 10, 4012-7, 2011

PMID: 21300875
DOI: 10.1073/pnas.1005342108

Open Access

Utility of dried blood spot sampling and storage for increased stability of photosensitive compounds.
Bowen CL, Hemberger MD, Kehler JR, Evans CA

Compound stability remains a major point of concern within pharmaceutical development. In attempts to minimize degradation, scientists may utilize acidification of samples prior to storage, dark chambers, decreased freezer temperatures and a variety of other stabilization techniques. All of these steps require additional procedures, increased costs and increased validation steps. Dried blood spots (DBS) are becoming a popular alternative to plasma sampling in many small- and even large-molecule applications. An investigation was performed in order to establish if DBS would provide storage advantages over liquid-based matrices for two light-sensitive compounds, nifedipine and omeprazole, to prevent or minimize photodegradation.

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Bioanalysis, 2, 1757-6199, 1823-8, 2010

PMID: 21083490

Stem cells. Epigenome disruptors.
M Hemberger, R Pedersen

Science (New York, N.Y.), 330, 6004, 598-9, 2010

PMID: 21030637
DOI: 10.1126/science.1199006