Characterisation of Wnt gene expression during the differentiation of murine embryonic stem cells in vitro: role of Wnt3 in enhancing haematopoietic differentiation

Analysis of key pathways and genes in nodal structure on rat skin surface using gene ontology and KEGG pathway

BACKGROUND

We have previously reported anatomical, histological, and gene expression characteristics of the nodal structure of rat skin surface and suggested its potential as an acupuncture point. However, the specific characteristics of the interactions among the genes expressed in this structure remain unclear.

OBJECTIVE

We aimed to determine gene expression changes by analyzing interaction networks of genes up-regulated in nodal structures and to explore relationships with acupuncture points.

METHODS

We investigated the relationship between the nodal structures and acupuncture points by analyzing the interactions of up-regulated genes, their Gene Ontology biological functions, and the characteristics of Kyoto Encyclopedia of Genes and Genomes pathways. RNA-seq and STRING analysis provided comprehensive information on these gene groups.

RESULTS

Interactions between up-regulated genes in nodal structures were classified into three groups. The first group, which includes Wnt7b, Wnt3, and Wnt16, showed significant interactions in pathways such as Wnt signaling, Alzheimer's disease, and regulation of stem cell pluripotency. The second group, composed of Fos, Dusp1, Pla2g4e, Pla2g4f, and Fgfr3, demonstrated a notable association with the MAPK signaling pathway. Lastly, the third group, consisting of Adcy1, Pla2g4e, Pla2g4f, and Dusp1 exhibited effective interactions with the inflammatory mediator regulation of TRP channels and serotonergic synapse.

CONCLUSION

Continued research on nodal structures where these genes are expressed is needed to improve our understanding of skin anatomy and physiology as well as their potential clinical utility as acupuncture points.

Exploring the formation mechanism of short-tailed phenotypes in animals using mutant mice with the TBXT gene c.G334T developed by CRISPR/Cas9

With the change in diet structure, individuals prefer to consume mutton with less fat. However, sheep tail has a lot of fat. We identified a breed of low-fat short-tailed sheep (i.e., Hulunbuir short-tailed sheep). It is necessary to develop an animal model that can promote research on the potential mechanisms of the short-tail phenotype in sheep, which results from the TBXT gene c.G334T mutation. To create animal models, we selected mice as experimental animals. Mouse embryos lacking the TBXT protein, which crucially regulates mouse embryonic development, cannot develop normally. We utilized CRISPR/Cas9 gene editing technology to generate site-specific mutation (c.G334T) in the TBXT gene of mice, and found that the mouse TBXT mutation (c.G334T) leads to a short-tail phenotype. Furthermore, we investigated the interaction between TBXT and Wnt signaling pathways. The expressions of TBXT, Axin2, Dkk1, Wnt3, Wnt3a, and Wnt5a were discovered to be significantly different between mutant embryos and wild embryos by obtaining mouse embryos at various developmental stages and examining the expression relationship between the TBXT and Wnt signaling pathway-related components in all of these embryos. Therefore, as a transcription factor, TBXT regulates the expression of the aforementioned Wnt signaling pathway components by forming a regulatory network for the normal development of mouse embryos. This study enriches the research on the functional role of the TBXT in the development of mouse embryos and the mechanism by which the short-tailed phenotype in sheep develops.

Wnt-5A/B Signaling in Hematopoiesis throughout Life

Wnt signaling is well-known to play major roles in the hematopoietic system, from embryogenesis to aging and disease. In addition to the main β-catenin-dependent pathway, it is now clear that Wnt5a and the structurally related Wnt5b are essential for hematopoiesis, bone marrow colonization and the final steps of hematopoietic stem cell (HSC) maturation via β-catenin-independent signaling. Wnt5a and Wnt5b ligands prevent hematopoietic exhaustion (by maintaining quiescent, long-term HSCs), induce the proliferation of progenitors, and guide myeloid development, in addition to being involved in the development of aging-related alterations. The aim of this review is to summarize the current knowledge on these roles of Wnt5a and Wn5b signaling in the hematopoietic field.

Divergent effects of Wnt5b on IL-3- and GM-CSF-induced myeloid differentiation

The multiple specialized cell types of the hematopoietic system originate from differentiation of hematopoietic stem cells and progenitors (HSPC), which can generate both lymphoid and myeloid lineages. The myeloid lineage is preferentially maintained during ageing, but the mechanisms that contribute to this process are incompletely understood. Here, we studied the roles of Wnt5a and Wnt5b, ligands that have previously been linked to hematopoietic stem cell ageing and that are abundantly expressed by both hematopoietic progenitors and bone-marrow derived niche cells. Whereas Wnt5a had no major effects on primitive cell differentiation, Wnt5b had profound and divergent effects on cytokine-induced myeloid differentiation. Remarkably, while IL-3- mediated myeloid differentiation was largely repressed by Wnt5b, GM-CSF-induced myeloid differentiation was augmented. Furthermore, in the presence of IL-3, Wnt5b enhanced HSPC self-renewal, whereas in the presence ofGM-CSF, Wnt5b accelerated differentiation, leading to progenitor cell exhaustion. Our results highlight discrepancies between IL-3 and GM-CSF, and reveal novel effects of Wnt5b on the hematopoietic system.

Construction of injectable, pH sensitive, antibacterial, mineralized amino acid yolk-shell microspheres for potential minimally invasive treatment of bone infection

INTRODUCTION

Treatment of infection within bone is difficult, and conventional surgical treatment brings intense pain to the patients physically and mentally. There is an urgent need to develop injectable nano- and/or micro-medicine for minimally invasive treatment of osteomyelitis.

METHODS

In this paper, amino acid (L-lysine [Lys]) was mineralized into yolk-shell structured CaCO3 microspheres (MSs). The morphologies of the obtained MSs were investigated by scanning electron microscopy and transmission electron microscopy. The composition of CaCO3 MSs was identified by using Fourier transform infrared spectroscopy. The as-prepared CaCO3 MSs were examined with power X-ray diffraction analysis to obtain the crystallographic structure of the MSs.

RESULTS

The as prepared Lys encapsulated CaCO3 MSs (Lys@CaCO3 MSs) were used as micro-drug to improve acidic environment of osteomyelitis caused by bacterial infection and promote osteoblast proliferation under oxidative stress. These pH responsive Lys@CaCO3 MSs have a drug loading efficiency of 89.8 wt % and drug loading content (DLC) of 22.3 wt %.

CONCLUSION

Our results demonstrated that Lys@CaCO3 MSs can effectively kill Staphylococcus aureus and promote proliferation and differentiation of osteoblasts under stimulation of H2O2 at pH = 5.5.

Wnt3 and Gata4 regulate axon regeneration in adult mouse DRG neurons

Neurons in the adult central nervous system (CNS) have a poor intrinsic axon growth potential after injury, but the underlying mechanisms are largely unknown. Wingless-related mouse mammary tumor virus integration site (WNT) family members regulate neural stem cell proliferation, axon tract and forebrain development in the nervous system. Here we report that Wnt3 is an important modulator of axon regeneration. Downregulation or overexpression of Wnt3 in adult dorsal root ganglion (DRG) neurons enhances or inhibits their axon regeneration ability respectively in vitro and in vivo. Especially, we show that Wnt3 modulates axon regeneration by repressing mRNA translation of the important transcription factor Gata4 via binding to the three prime untranslated region (3'UTR). Downregulation of Gata4 could restore the phenotype exhibited by Wnt3 downregulation in DRG neurons. Taken together, these data indicate that Wnt3 is a key intrinsic regulator of axon growth ability of the nervous system.

Editor's Highlight: Identification and Characterization of Teratogenic Chemicals Using Embryonic Stem Cells Isolated From a Wnt/β-Catenin-Reporter Transgenic Mouse Line

Embryonic stem cells (ESCs) are commonly used for the analysis of gene function in embryonic development and provide valuable models for human diseases. In recent years, ESCs have also become an attractive tool for toxicological testing, in particular for the identification of teratogenic compounds. We have recently described a Bmp-reporter ESC line as a new tool to identify teratogenic compounds and to characterize the molecular mechanisms mediating embryonic toxicity. Here we describe the use of a Wnt/β-Catenin-reporter ESC line isolated from a previously described mouse line that carries the LacZ reporter gene under the control of a β-Catenin responsive promoter. The reporter ESC line stably differentiates into cardiomyocytes within 12 days. The reporter was endogenously induced between day 3-5 of differentiation reminiscent of its expression in vivo, in which strong LacZ activity is detected around gastrulation. Subsequently its expression becomes restricted to mesodermal cells and cells undergoing an epithelial to mesenchymal transition. The Wnt/β-Catenin-dependent expression of the reporter protein allowed quantification of dose- and time-dependent effects of teratogenic chemicals. In particular, valproic acid reduced reporter activity on day 7 whereas retinoic acid induced reporter activity on day 5 at concentrations comparable to the ones inhibiting the formation of functional cardiomyocytes, the classical read-out of the embryonic stem cell test (EST). In addition, we were also able to show distinct effects of teratogenic chemicals on the Wnt/β-Catenin-reporter compared with the previously described Bmp-reporter ESCs. Thus, different reporter cell lines provide complementary tools for the identification and analysis of potentially teratogenic compounds.

Molecular etiology of an indolent lymphoproliferative disorder determined by whole-genome sequencing

In an attempt to assess potential treatment options, whole-genome and transcriptome sequencing were performed on a patient with an unclassifiable small lymphoproliferative disorder. Variants from genome sequencing were prioritized using a combination of comparative variant distributions in a spectrum of lymphomas, and meta-analyses of gene expression profiling. In this patient, the molecular variants that we believe to be most relevant to the disease presentation most strongly resemble a diffuse large B-cell lymphoma (DLBCL), whereas the gene expression data are most consistent with a low-grade chronic lymphocytic leukemia (CLL). The variant of greatest interest was a predicted NOTCH2-truncating mutation, which has been recently reported in various lymphomas.

Endogenous WNT signals mediate BMP-induced and spontaneous differentiation of epiblast stem cells and human embryonic stem cells

Therapeutic application of human embryonic stem cells (hESCs) requires precise control over their differentiation. However, spontaneous differentiation is prevalent, and growth factors induce multiple cell types; e.g., the mesoderm inducer BMP4 generates both mesoderm and trophoblast. Here we identify endogenous WNT signals as BMP targets that are required and sufficient for mesoderm induction, while trophoblast induction is WNT independent, enabling the exclusive differentiation toward either lineage. Furthermore, endogenous WNT signals induce loss of pluripotency in hESCs and their murine counterparts, epiblast stem cells (EpiSCs). WNT inhibition obviates the need to manually remove differentiated cells to maintain cultures and improves the efficiency of directed differentiation. In EpiSCs, WNT inhibition stabilizes a pregastrula epiblast state with novel characteristics, including the ability to contribute to blastocyst chimeras. Our findings show that endogenous WNT signals function as hidden mediators of growth factor-induced differentiation and play critical roles in the self-renewal of hESCs and EpiSCs.

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BMP induces WNT-dependent and -independent differentiation pathways in hESCs

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Modulating WNT and BMP directs differentiation toward mesoderm or trophoblast

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WNT inhibition returns epiblast stem cells to a chimera-competent pregastrula state

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WNT inhibition prevents spontaneous differentiation of hESCs and epiblast stem cells

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

The Wnt signaling pathway and mitotic regulators in the initiation and evolution of mantle cell lymphoma: Gene expression analysis

For an accurate understanding of mantle cell lymphoma (MCL), molecular behavior could be staged into two major events: lymphomagenesis with the t(11;14) translocation (initiation), and evolution into a more aggressive form (transformation). Unfortunately, it is still unknown which genes contribute to each event. In this study, we performed cDNA microarray experiments designed based on the concept that morphologically heterogeneous MCL samples would provide insights into the role of aberrant gene expression for both events. A total of 15 MCLs were collected from the files, which include a total of 237 MCL patients confirmed by histology as CCND1-positive. We posited four stepwise morphological grades for MCL: MCL in situ, MCL with classical form (cMCL), MCL with aggressive form (aMCL), and MCL with intermediate morphology between classical and aggressive forms at the same site (iMCL). To identify genes involved in initiation, we compared the tumor cells of MCL in situ (n=4) with normal mantle zone B lymphocytes (n=4), which were selected by laser microdissection (LMD). To identify genes contributing to transformation, we selected the overlapping genes differentially expressed between both cMCL (n=4) vs. aMCL (n=5) and classical vs. aggressive areas in iMCL (n=2) obtained by LMD. A significant number of genes (n=23, p=0.016) belonging to the Wnt signaling pathway were differentially expressed in initiation. This specific activation was confirmed by immuno-histochemistry, as MCL in situ had nuclear localization of phosphorylated-β-catenin with high levels of cytoplasmic Wnt3 staining. For transformation, identified 60 overlapping genes included a number of members of the p53 interaction network (CDC2, BIRC5 and FOXM1), which is known to mediate cell cycle progression during the G2/M transition. Thus, we observe that the Wnt signaling pathway may play an important role in initial lymphomagenesis in addition to t(11;14) translocations, and that specific mitotic regulators facilitate transformation into more aggressive forms.

WNT3A promotes hematopoietic or mesenchymal differentiation from hESCs depending on the time of exposure

We investigated the role of canonical WNT signaling in mesoderm and hematopoietic development from human embryonic stem cells (hESCs) using a recombinant human protein-based differentiation medium (APEL). In contrast to prior studies using less defined culture conditions, we found that WNT3A alone was a poor inducer of mesoderm. However, WNT3A synergized with BMP4 to accelerate mesoderm formation, increase embryoid body size, and increase the number of hematopoietic blast colonies. Interestingly, inclusion of WNT3A or a GSK3 inhibitor in methylcellulose colony-forming assays at 4 days of differentiation abrogated blast colony formation but supported the generation of mesospheres that expressed genes associated with mesenchymal lineages. Mesospheres differentiated into cells with characteristics of bone, fat, and smooth muscle. These studies identify distinct effects for WNT3A, supporting the formation of hematopoietic or mesenchymal lineages from human embryonic stem cells, depending upon differentiation stage at the time of exposure.

Mechanism of action of HOXB4 on the hematopoietic differentiation of embryonic stem cells

Pluripotent stem cells can be differentiated into hematopoietic lineages in vitro and hold promise for the future treatment of hematological disease. Differentiation strategies involving defined factors in serum-free conditions have been successful in producing hematopoietic progenitors and some mature cell types from mouse and human embryonic stem cells and induced pluripotent cells. However, these precisely defined protocols are relatively inefficient and have not been used successfully to produce hematopoietic stem cells capable of multilineage long-term reconstitution of the hematopoietic system. More complex differentiation induction strategies including coculture with stromal cells derived from sites of hematopoietic activity in vivo and enforced expression of reprogramming transcription factors, such as HOXB4, have been required to increase the efficiency of the differentiation procedure and to produce these most potent hematopoietic stem cells. We review the studies that have used HOXB4 to improve hematopoietic differentiation from pluripotent cells focusing on studies that have provided some insight into its mechanism of action. A better understanding of the molecular pathways involved in the action of HOXB4 might lead to more defined culture systems and safer protocols for clinical translation.

Safety evaluation of stem cells used for clinical cell therapy in chronic liver diseases; with emphasize on biochemical markers

There are several issues to be considered to reduce the risk of rejection and minimize side effects associated with liver cell transplantation in chronic liver diseases. The source and the condition of stem cell proliferation and differentiation ex vivo and the transplantation protocols are important safety considerations for cell based therapy. The biochemical and molecular markers are important tools for safety evaluation of different processes of cell expansion and transplantation. Studies show that hepatocytes differentiated from adult and embryonic stem cells exhibit biochemical and metabolic properties resembling mature hepatocytes. Therefore these assays can help to assess the biological and metabolic performance of hepatocytes and progenitor stem cells. The assays also help in testing the contribution of transplanted hepatocytes in improving the repair and function of damaged liver in the recipient. Here we review the biochemical and metabolic markers, which are implicated in evaluation of safety issues of stem cells used for therapeutic purposes in chronic liver diseases and regeneration of damaged liver. We also highlight application of biochemical tests for assessment of liver cell transplantation.

What does it take to make a heart?

Ever increasing advances are being made in our quest to understand what it takes to direct pluripotent precursor cells to adopt a specific developmental fate. Eventually, the obvious goal is that targeted manipulation of these precursor cells will result in an efficient and reliable production of tissue-specific cells, which can be safely employed for therapeutic purposes. We have gained an incredible insight as to which molecular pathways are involved in governing neural, skeletal and cardiac muscle fate decisions. However, we still face the challenge of how to direct, for example, a cardiac fate in stem cells in the amounts needed to be employed for regenerative means. Equally importantly, we need to resolve critical questions such as: can the in vitro generated cardiomyocytes actually functionally replace damaged heart tissue? Here I will provide an overview of the molecules and signalling pathways that have first been demonstrated in embryological studies to function in cardiogenesis, and summarize how this knowledge is being applied to differentiate mouse and human embryonic stem cells into cardiomyocytes.

Challenges and strategies for generating therapeutic patient-specific hemangioblasts and hematopoietic stem cells from human pluripotent stem cells

Recent characterization of hemangioblasts differentiated from human embryonic stem cells (hESC) has further confirmed evidence from murine, zebrafish and avian experimental systems that hematopoietic and endothelial lineages arise from a common progenitor. Such progenitors may provide a valuable resource for delineating the initial developmental steps of human hemato-endotheliogenesis, which is a process normally difficult to study due to the very limited accessibility of early human embryonic/fetal tissues. Moreover, efficient hemangioblast and hematopoietic stem cell (HSC) generation from patient-specific pluripotent stem cells has enormous potential for regenerative medicine, since it could lead to strategies for treating a multitude of hematologic and vascular disorders. However, significant scientific challenges remain in achieving these goals, and the generation of transplantable hemangioblasts and HSC derived from hESC currently remains elusive. Our previous work has suggested that the failure to derive engraftable HSC from hESC is due to the fact that current methodologies for differentiating hESC produce hematopoietic progenitors developmentally similar to those found in the human yolk sac, and are therefore too immature to provide adult-type hematopoietic reconstitution. Herein, we outline the nature of this challenge and propose targeted strategies for generating engraftable human pluripotent stem cell-derived HSC from primitive hemangioblasts using a developmental approach. We also focus on methods by which reprogrammed somatic cells could be used to derive autologous pluripotent stem cells, which in turn could provide unlimited sources of patient-specific hemangioblasts and HSC.

Differential Hox expression in murine embryonic stem cell models of normal and malignant hematopoiesis

The Hox family are master transcriptional regulators of developmental processes, including hematopoiesis. The Hox regulators, caudal homeobox factors (Cdx1-4), and Meis1, along with several individual Hox proteins, are implicated in stem cell expansion during embryonic development, with gene dosage playing a significant role in the overall function of the integrated Hox network. To investigate the role of this network in normal and aberrant, early hematopoiesis, we employed an in vitro embryonic stem cell differentiation system, which recapitulates mouse developmental hematopoiesis. Expression profiles of Hox, Pbx1, and Meis1 genes were quantified at distinct stages during the hematopoietic differentiation process and compared with the effects of expressing the leukemic oncogene Tel/PDGFRβ. During normal differentiation the Hoxa cluster, Pbx1 and Meis1 predominated, with a marked reduction in the majority of Hox genes (27/39) and Meis1 occurring during hematopoietic commitment. Only the posterior Hoxa cluster genes (a9, a10, a11, and a13) maintained or increased expression at the hematopoietic colony stage. Cdx4, Meis1, and a subset of Hox genes, including a7 and a9, were differentially expressed after short-term oncogenic (Tel/PDGFRβ) induction. Whereas Hoxa4-10, b1, b2, b4, and b9 were upregulated during oncogenic driven myelomonocytic differentiation. Heterodimers between Hoxa7/Hoxa9, Meis1, and Pbx have previously been implicated in regulating target genes involved in hematopoietic stem cell (HSC) expansion and leukemic progression. These results provide direct evidence that transcriptional flux through the Hox network occurs at very early stages during hematopoietic differentiation and validates embryonic stem cell models for gaining insights into the genetic regulation of normal and malignant hematopoiesis.

Functional diversity of ESC-derived motor neuron subtypes revealed through intraspinal transplantation

Cultured ESCs can form different classes of neurons, but whether these neurons can acquire specialized subtype features typical of neurons in vivo remains unclear. We show here that mouse ESCs can be directed to form highly specific motor neuron subtypes in the absence of added factors, through a differentiation program that relies on endogenous Wnts, FGFs, and Hh-mimicking the normal program of motor neuron subtype differentiation. Molecular markers that characterize motor neuron subtypes anticipate the functional properties of these neurons in vivo: ESC-derived motor neurons grafted isochronically into chick spinal cord settle in appropriate columnar domains and select axonal trajectories with a fidelity that matches that of their in vivo generated counterparts. ESC-derived motor neurons can therefore be programmed in a predictive manner to acquire molecular and functional properties that characterize one of the many dozens of specialized motor neuron subtypes that exist in vivo.

Wnt-3 and Wnt-3a play different region-specific roles in neural crest development in avians

Wnt signalling regulates cell proliferation and cell fate determination during embryogenesis. However, little is known about the developmental role of one Wnt family member, Wnt-3, during avian development. To investigate the possible functions of Wnt-3, its expression pattern was determined using whole-mount in situ hybridization. Wnt-3 is expressed in important signalling centres, including the dorsal neural tube, Hensen's node and the AER (apical ectodermal ridge). Most interestingly, Wnt-3 is expressed in the dorsal neural tube as a gradient, with the strongest expression anterior in the trunk. Furthermore, this study showed that Wnt-3 and Wnt-3a play a different role in neural crest lineages derived from different axial level of neural tube. Wnt-3 might be involved in proliferation of neural crest lineages, whereas Wnt-3a plays an important role in melanogenesis in vagal. However, both Wnt-3 and Wnt-3a cause a significant increase in melanogenesis in the trunk neural crest lineage.

Wnt and Notch signaling pathways selectively regulating hematopoiesis

Hematopoietic stem and progenitor cells (HSPCs) are the source of all blood cells in the adult body. The pool of HSPCs is formed during embryogenesis process through a well-characterized succession of intra-embryonic regions and organs. The spatial and temporal restrictions in definitive hematopoietic development and the signaling molecules involved are of great interest as these may prove useful for generating and expanding these clinically important cell populations ex vivo. To elucidate the mechanism by which definitive HSPCs expand during this limited developmental time frame, we analyzed the spatial and temporal programmed gene expression patterns of Wnt and Notch signaling members during hematopoietic development. Genes related to the Wnt signaling pathway were up-regulated in E10.5 aorta-gonad-mesonephros (AGM) and E14.5 fetal liver corresponding to the inherent proliferation potential of hematopoietic progenitors, whereas genes related to the Notch signaling pathway were identified as up-regulated in E10.5 AGM, and bone marrow coincides with the maintenance of undifferentiation state of hematopoietic progenitors. Our findings suggest that Wnt and Notch signalings are integrated and are selectively regulating hematopoiesis. The spatial and temporal balance between Wnt and Notch signaling orchestrates the precise progression of hematopoietic progenitors.

Chemical induction of cardiac differentiation in p19 embryonal carcinoma stem cells

P19 cells, a pluripotent cell line derived from a teratocarcinoma induced in C3H/HeHa mice, have been widely used as a model system to study cardiac differentiation. We have used these cells to evaluate the extent to which exposure to DMSO and/or cardiogenol C for 4 days in suspension culture enhanced their differentiation into cardiomyocytes. Cardiac differentiation was assessed by observing beating clusters and further confirmed using immunocytochemical, biochemical, and pharmacological approaches. The presence of functional gap junctions in differentiated P19 cells was identified through calcium wave analyses. Proliferation rate and cell death were analyzed by BrdU incorporation and activated caspase-3 immunodetection, respectively. Beating clusters of differentiated P19 cells were only found in cultures treated with DMSO. In addition, groups treated with DMSO up-regulated cardiac troponin-T expression. However, when DMSO was used together with cardiogenol C the up-regulation was less than that with DMSO alone, approximately 1.5 times. Moreover, P19 cells cultured in DMSO or DMSO plus 0.25 microM cardiogenol C had lower proliferation rates and higher numbers of activated caspase-3-positive cells. In summary, using several methodological approaches we have demonstrated that DMSO can induce cardiac differentiation of P19 cells but that cardiogenol C does not.

Hepatic stem cells and liver development

The liver consists of many cell types with specialized functions. Hepatocytes are one of the main players in the organ and therefore are the most vulnerable cells to damage. Since they are not everlasting cells, they need to be replenished throughout life. Although the capacity of hepatocytes to contribute to their own maintenance has long been recognized, recent studies have indicated the presence of both intrahepatic and extrahepatic stem/progenitor cell populations that serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults.The intrahepatic compartment most likely derives primarily from the biliary tree, particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extrahepatic compartment is at least in part derived from diverse populations of cells from the bone marrow. Embryonic stem cells (ES's) are considered as a part of the extrahepatic compartment. Due to their pluripotent capabilities, ES cell-derived cells form a potential future source of hepatocytes, to replace or restore hepatic tissues that have been damaged by disease or injury. Progressing knowledge about stem cells in the liver would allow a better understanding of the mechanisms of hepatic homeostasis and regeneration. Although a human stem cell-derived cell type equivalent to primary hepatocytes does not yet exist, the promising results obtained with extrahepatic stem cells would open the way to cell-based therapy for liver diseases.

Biphasic glucocorticoid-dependent regulation of Wnt expression and its inhibitors in mature osteoblastic cells

Glucocorticoids exert both anabolic and catabolic effects on bone. Previously, we reported that endogenous glucocorticoids control mesenchymal lineage commitment and osteoblastogenesis through regulation of Wnt signaling in osteoblasts. Here, we investigated the effects of glucocorticoids on Wnt expression in mature osteoblasts. Mature osteoblasts and their immature progenitors were separately isolated from Col2.3-GFP transgenic mice in which mature osteoblasts are identifiable through GFP expression. mRNA levels of Wnt2, Wnt2b, Wnt4, Wnt5a, Wnt10b, and Wnt11 were 4- to 12-fold higher in osteoblasts compared to their progenitors (P < 0.05). Expression of Wnt7b and Wnt10b in osteoblasts was modulated by corticosterone (CS), in a biphasic fashion with 3- to 3.5-fold upregulation at 10 nM CS (P < 0.01) and 50% downregulation at 100 nM CS (P < 0.05). CS 100 nM also increased expression of the Wnt inhibitors sFRP-1 and DKK-1 two- to threefold (P < 0.05). We conclude that the contrasting anabolic and catabolic effects of glucocorticoids on bone are, at least in part, mediated through the regulation of Wnt expression and its inhibitors in mature osteoblasts.

The Wnt receptor, Lrp5, is expressed by mouse mammary stem cells and is required to maintain the basal lineage

BACKGROUND

Ectopic Wnt signaling induces increased stem/progenitor cell activity in the mouse mammary gland, followed by tumor development. The Wnt signaling receptors, Lrp5/6, are uniquely required for canonical Wnt activity. Previous data has shown that the absence of Lrp5 confers resistance to Wnt1-induced tumor development.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we show that all basal mammary cells express Lrp5, and co-express Lrp6 in a similar fashion. Though Wnt dependent transcription of key target genes is relatively unchanged in mammary epithelial cell cultures, the absence of Lrp5 specifically depletes adult regenerative stem cell activity (to less than 1%). Stem cell activity can be enriched by >200 fold (over 80% of activity), based on high Lrp5 expression alone. Though Lrp5 null glands have apparent normal function, the basal lineage is relatively reduced (from 42% basal/total epithelial cells to 22%) and Lrp5-/- mammary epithelial cells show enhanced expression of senescence-associated markers in vitro, as measured by expression of p16(Ink4a) and TA-p63.

CONCLUSIONS/SIGNIFICANCE

This is the first single biomarker that has been demonstrated to be functionally involved in stem cell maintenance. Together, these results demonstrate that Wnt signaling through Lrp5 is an important component of normal mammary stem cell function.

BMP inhibition stimulates WNT-dependent generation of chondrogenic mesoderm from embryonic stem cells

WNT and bone morphogenetic protein (BMP) signaling are known to stimulate hemogenesis from pluripotent embryonic stem (ES) cells. However, osteochondrogenic mesoderm was generated effectively when BMP signaling is kept to a low level, while WNT signaling was strongly activated. When mesoderm specification from ES cells was exogenous factor dependent, WNT3a addition supported the generation of cardiomyogenic cells expressing lateral plate/extraembryonic mesoderm genes, and this process involved endogenous BMP activities. Exogenous BMP4 showed a similar effect that depended on endogenous WNT activities. However, neither factor induced robust chondrogenic activity. In support, ES cell differentiation in the presence of either WNT3a or BMP4 was associated with elevated levels of both Bmp and Wnt mRNAs, which appeared to provide sufficient levels of active BMPs and WNTs to promote the nonchondrogenic mesoderm specification. The osteochondrogenic mesoderm expressed PDGFRalpha, which also expressed genes that mark somite and rostral presomitic mesoderm. A strong WNT signaling was required for generating the mesodermal progeny, while approximately 50- to 100-fold lower concentration of WNT3a was sufficient for specifying axial mes(end)oderm. Thus, depending on the dose and cofactor (BMP), WNT signaling stimulates the generation of different biological activities and specification of different types of mesodermal progeny from ES cells.

Patterns of Wnt/Fzd/LRP gene expression during embryonic hematopoiesis

Wnt signaling plays several roles in hematopoiesis, promoting hemopoietic stem cell (HSC) self-renewal, providing proliferative signals for immature progenitors and regulating lineage commitment. To ascertain which Wnt proteins and receptors are important during hematopoietic development, we used two systems; in vitro hematopoietic differentiation of embryonic stem (ES) cells and tissues isolated from sites specific for hematopoiesis during mouse embryogenesis. Initially genes involved in hematopoiesis were profiled and indicate differentiating ES cells undergo a wave of primitive hematopoiesis (Day 3.75) similar to the mouse yolk sac, followed by a wave of more definitive hematopoiesis (Day 7.75) comparable to the aorta-gonad-mesonephros (AGM) and E15.5 liver with lineage commitment by Day 15. A similar biphasic expression pattern occurred for Wnt/Fzd/LRP genes with Wnt 3, 5a, 8a, Fzd4, and LRP5 becoming upregulated during primitive hematopoiesis, followed by Wnt3a, 6, 7b, 10b, and 16 during more definitive hematopoiesis. High expression of Wnt5a, Fzd4, and LRP5 during the first phase of hematopoiesis suggests these genes are involved in early hematopoietic regulation. Wnt3a and 16 were also expressed at specific stages, with Wnt16 detected when the earliest lymphoid progenitors are formed (AGM and 2 degrees BC of ES differentiation). Wnt3a expression corresponded with the induction of definitive hematopoiesis a period, which involves rapid expansion of HSC (Day 7.75 of ES differentiation, AGM and E15.5 liver). Supplementation with Wnt3a during ES hematopoietic differentiation increased proliferation and appeared to promote stem cell expansion. Overall this study provides valuable information on the Wnt/Fzd/LRP involved in supporting embryonic hematopoiesis.

Wnt-related molecules and signaling pathway equilibrium in hematopoiesis

There is near consensus that Wnt family molecules establish important gradients within niches where hematopoietic stem cells (HSC) reside. We review recent papers suggesting that a delicate balance is required between competing Wnt ligands and corresponding signaling pathways to maintain HSC integrity. Some steps in the transitions from HSC to lymphoid progenitor seem to be partially reversible and under the influence of Wnts. In addition, it has been recently suggested that HSC can oscillate between dormant versus active or lineage-biased states. We speculate that Wnts control a reflux process that may sustain stem cell self-renewal and differentiation potential.

Dissection of sets of genes that control the character of wnt5a-deficient mouse calvarial cells

Wnts (wingless and int-related proteins) are a family of secreted cysteine-rich glycoproteins, expressed in a variety of tissues in developing embryos, thought to be involved in cell fate specification and stem cell commitment. To identify the specific Wnts involved in osteoblastic differentiation of human mesenchymal stem cells (hMSCs), we performed degenerative RT-PCR cloning method to amplify Wnt-encoding cDNAs expressed during osteoblastic differentiation of hMSCs in vitro and during hMSC-directed ectopic osteogenesis in the severe combined immunodeficient (SCID) mouse host. WNT5A was found to be the dominant Wnt expressed during osteoblastic differentiation of hMSCs both in vitro and in vivo. RT-PCR further revealed that hWNT5A and its receptor Frizzled family member 5 (hFZD5) was up-regulated during osteoblastic differentiation compared to uncommitted hMSCs. To evaluate the function of Wnt5a, calvarial cells were obtained from Wnt5a(-/-), Wnt5a(+/-), and wild type mice. Wnt5a(-/-) cells showed significantly slower growth when compared to Wnt5a(+/-) and wild type cells. Gene expression profiles of the Wnt5a(-/-) calvarial cells as compared to wild type cells were evaluated using microarray analysis. 255 genes exhibited at least 2-fold changes in expression. Clusters of genes regulating cell cycle, cell proliferation and cell growth, and gene transcription were altered with absence of Wnt5a expression. In addition, genes regulating osteoblastic differentiation including Runx2, osterix, and alkaline phosphatase (ALP) were shown to be down-regulated in Wnt5a(-/-) cells. In conclusion, Wnt5a is highly expressed during osteoblastic differentiation. Its function during mesenchymal stem cell differentiation as well as cell growth was suggested by comparing the gene expression profile of calvarial cells from the Wnt5a(-/-) and wild type mice.

Expression profiles of Wnt genes during neural differentiation of mouse embryonic stem cells

The Wnt family of secreted signaling proteins regulates many aspects of animal development and the behavior of several types of stem cells, including embryonic stem (ES) cells. Activation of canonical Wnt signaling has been shown to either inhibit or promote the differentiation of ES cells into neurons, depending on the stage of differentiation. Here, we describe the expression of all 19 mouse Wnt genes during this process. Using the well-established retinoic acid induction protocol we found that all Wnt genes except Wnt8b are expressed as ES cells differentiate into neurons, many of them in dynamic patterns. The expression pattern of 12 Wnt genes was analyzed quantitatively at 2-day intervals throughout neural differentiation, showing that multiple Wnt genes are expressed at each stage. A large proportion of these, including both canonical and noncanonical Wnts, are expressed at highest levels during later stages of differentiation. The complexity of the patterns observed indicates that disentangling specific roles for individual Wnt genes in the differentiation process will be a significant challenge.

Dkk1andWnt3interact to control head morphogenesis in the mouse

Loss of Dkk1 results in ectopic WNT/β-catenin signalling activity in the anterior germ layer tissues and impairs cell movement in the endoderm of the mouse gastrula. The juxtaposition of the expression domains of Dkk1 and Wnt3 is suggestive of an antagonist-agonist interaction. The downregulation of Dkk1 when Wnt3 activity is reduced reveals a feedback mechanism for regulating WNT signalling. Compound Dkk1;Wnt3 heterozygous mutant embryos display head truncation and trunk malformation, which are not found in either Dkk1+/- or Wnt3+/- embryos. Reducing the dose of Wnt3 gene in Dkk1-/- embryos partially rescues the truncated head phenotype. These findings highlight that head development is sensitive to the level of WNT3 signalling and that DKK1 is the key antagonist that modulates WNT3 activity during anterior morphogenesis.

Pluripotency of embryonic stem cells

Embryonic stem (ES) cells derived from pre-implantation embryos have the potential to differentiate into any cell type derived from the three germ layers of ectoderm (epidermal tissues and nerves), mesoderm (muscle, bone, blood), and endoderm (liver, pancreas, gastrointestinal tract, lungs), including fetal and adult cells. Alone, these cells do not develop into a viable fetus or adult animal because they do not retain the potential to contribute to extraembryonic tissue, and in vitro, they lack spatial and temporal signaling cues essential to normal in vivo development. The basis of pluripotentiality resides in conserved regulatory networks composed of numerous transcription factors and multiple signaling cascades. Together, these regulatory networks maintain ES cells in a pluripotent and undifferentiated form; however, alterations in the stoichiometry of these signals promote differentiation. By taking advantage of this differentiation capacity in vitro, ES cells have clearly been shown to possess the potential to generate multipotent stem and progenitor cells capable of differentiating into a limited number of cell fates. These latter types of cells may prove to be therapeutically viable, but perhaps more importantly, the studies of these cells have led to a greater understanding of mammalian development.

Wnt signaling promotes hematoendothelial cell development from human embryonic stem cells

Human embryonic stem cells (hESCs) provide an important means to effectively study soluble and cell-bound mediators that regulate development of early blood and endothelial cells in a human model system. Here, several complementary methods are used to demonstrate canonical Wnt signaling is important for development of hESC-derived cells with both hematopoietic and endothelial potential. Analyses using both standard flow cy-tometry, as well the more detailed high-throughput image scanning flow cytometry, characterizes sequential development of distinct early developing CD34(bright)CD31(+)Flk1(+) cells and a later population of CD34(dim)CD45(+) cells. While the CD34(bright)CD31(+)Flk1(+) have a more complex morphology and can develop into both endothelial cells and hematopoietic cells, the CD34(dim)CD45(+) cells have a simpler morphology and give rise to only hematopoietic cells. Treatment with dickkopf1 to inhibit Wnt signaling results in a dramatic decrease in development of cells with hematoendothelial potential. In addition, activation of the canonical Wnt signaling pathway in hESCs by coculture with stromal cells that express Wnt1, but not use of noncanonical Wnt5-expressing stromal cells, results in an accelerated differentiation and higher percentage of CD34(bright)CD31(+)Flk1(+) cells at earlier stages of differentiation. These studies effectively demonstrate the importance of canonical Wnt signaling to mediate development of early hematoendothelial progenitors during human development.

Mouse lysocardiolipin acyltransferase controls the development of hematopoietic and endothelial lineages during in vitro embryonic stem-cell differentiation

The blast colony-forming cell (BL-CFC) was identified as an equivalent to the hemangioblast during in vitro embryonic stem (ES) cell differentiation. However, the molecular mechanisms underlying the generation of the BL-CFC remain largely unknown. Here we report the isolation of mouse lysocardiolipin acyltransferase (Lycat) based on homology to zebrafish lycat, a candidate gene for the cloche locus. Mouse Lycat is expressed in hematopoietic organs and is enriched in the Lin(-)C-Kit(+)Sca-1(+) hematopoietic stem cells in bone marrow and in the Flk1(+)/hCD4(+)(Scl(+)) hemangioblast population in embryoid bodies. The forced Lycat transgene leads to increased messenger RNA expression of hematopoietic and endothelial genes as well as increased blast colonies and their progenies, endothelial and hematopoietic lineages. The Lycat small interfering RNA transgene leads to a decrease expression of hematopoietic and endothelial genes. An unbiased genomewide microarray analysis further substantiates that the forced Lycat transgene specifically up-regulates a set of genes related to hemangioblasts and hematopoietic and endothelial lineages. Therefore, mouse Lycat plays an important role in the early specification of hematopoietic and endothelial cells, probably acting at the level of the hemangioblast.

The role of microtubule actin cross-linking factor 1 (MACF1) in the Wnt signaling pathway

MACF1 (microtubule actin cross-linking factor 1) is a multidomain protein that can associate with microfilaments and microtubules. We found that MACF1 was highly expressed in neuronal tissues and the foregut of embryonic day 8.5 (E8.5) embryos and the head fold and primitive streak of E7.5 embryos. MACF1(-/-) mice died at the gastrulation stage and displayed developmental retardation at E7.5 with defects in the formation of the primitive streak, node, and mesoderm. This phenotype was similar to Wnt-3(-/-) and LRP5/6 double-knockout embryos. In the absence of Wnt, MACF1 associated with a complex that contained Axin, beta-catenin, GSK3beta, and APC. Upon Wnt stimulation, MACF1 appeared to be involved in the translocation and subsequent binding of the Axin complex to LRP6 at the cell membrane. Reduction of MACF1 with small interfering RNA decreased the amount of beta-catenin in the nucleus, and led to an inhibition of Wnt-induced TCF/beta-catenin-dependent transcriptional activation. Similar results were obtained with a dominant-negative MACF1 construct that contained the Axin-binding region. Reduction of MACF1 in Wnt-1-expressing P19 cells resulted in decreased T (Brachyury) gene expression, a DNA-binding transcription factor that is a direct target of Wnt/beta-catenin signaling and required for mesoderm formation. These results suggest a new role of MACF1 in the Wnt signaling pathway.

(Re)defining stem cells

Stem-cell nomenclature is in a muddle! So-called stem cells may be self-renewing or emergent, oligopotent (uni- and multipotent) or pluri- and totipotent, cells with perpetual embryonic features or cells that have changed irreversibly. Ambiguity probably seeped into stem cells from common usage, flukes in biology's history beginning with Weismann's divide between germ and soma and Haeckel's biogenic law and ending with contemporary issues over the therapeutic efficacy of adult versus embryonic cells. Confusion centers on tissue dynamics, whether stem cells are properly members of emerging or steady-state populations. Clarity might yet be achieved by codifying differences between cells in emergent populations, including embryonic stem and embryonic germ (ES and EG) cells in tissue culture as opposed to self-renewing (SR) cells in steady-state populations.

Canonical Wnt signaling negatively regulates branching morphogenesis of the lung and lacrimal gland

Key gene families such as FGFs and BMPs are important mediators of branching morphogenesis. To understand whether Wnt genes, and in particular, the canonical Wnt signaling pathway also function in the branching process, we have used a combination of experimental and genetic gain and loss of function approaches to perturb the levels of canonical Wnt signaling in two arborized structures, the lung and the lacrimal gland. Here, we show that the addition of Wnt3a conditioned medium or LiCl strongly represses growth and proliferation of the lung and lacrimal gland, a result that was confirmed in vivo using a dominant stable mutation of beta-catenin conditionally expressed in the lacrimal gland epithelium. In agreement with these data, knockdown of Wnt signaling with beta-catenin morpholinos results in a greater number of branches and increased cell proliferation. In addition, we show that canonical Wnt signaling is able to modulate the levels of Fgf10 and suppress BMP-induced proliferation in the lacrimal gland. Thus, canonical Wnt signaling negatively regulates branching morphogenesis providing a balance to FGFs and BMPs which positively regulate this process. This multilayered control of growth and proliferation ensures that branched structures attain the morphology required to function efficiently.

Cloning and characterization of mouse cullin4B/E3 ubiquitin ligase

Heat induced differentiation of mouse embryonal carcinoma cells PCC4 has been reported earlier. We have further characterized the phenotype of the differentiated cells and by DD-RT-PCR identified several partial cDNAs that are differentially expressed during differentiation. Nucleotide homology search revealed that the genes corresponding to some of the up-regulated partial cDNAs are indeed part of differentiation pathway. 5'extension of an EST that has homology to one of the partial cDNAs led to the identification of mouse cullin4B. Cullin4B is coded by a separate gene and has a unique and longer amino-terminal end with a putative nuclear localization signal sequence (NLS). We have cloned, expressed and raised antibodies against the amino and carboxy-terminal halves of cullin4B. Immuno staining of differentiated PCC4 cells with N-terminal Cul4B antibody showed enhanced expression of Cul4B and its translocation into the nucleus upon differentiation. Transient transfection of a chimeric gene encoding the N-terminal part of Cul4B fused to green fluorescent protein into PCC4 cells revealed that the protein was localized in the nucleus confirming the functional significance of the putative NLS. Since cullins are involved in recognition of specific proteins for degradation, based on the evidence presented here, we hypothesize that cullin4B is probably involved in differentiation specific degradation/modification of nuclear proteins.

Germ layer induction from embryonic stem cells

Embryonic stem (ES) cells have the potential to develop into all cell types of the adult body. This capability provides the basis for considering the ES cell system as a novel and unlimited source of cells for replacement therapies for the treatment of a wide range of diseases. Before the cell-based therapy potential of ES cells can be realized, a better understanding of the pathways regulating lineage-specific differentiation is required. Current studies suggest that the bone morphogenic protein, transforming growth factor-beta, Wnt, and fibroblast growth factor pathways that are required for gastrulation and germ layer induction in the embryo are also essential for differentiation of ES cells in culture. The current understanding of how these factors influence germ layer induction in both the embryo and in the ES cell differentiation system is addressed in this review.

Activation of Stem-Cell Specific Genes by HOXA9 and HOXA10 Homeodomain Proteins in CD34+Human Cord Blood Cells

There is growing evidence for a role of HOX homeodomain proteins in normal hematopoiesis. Several HOX genes, including HOXA9 and HOXA10, are expressed in primitive hematopoietic cells, implying a role in early hematopoietic differentiation. To identify potential target genes of these two closely related transcription factors, human CD34+ umbilical cord blood cells were transduced with vectors expressing either HOXA9 or HOXA10 and analyzed with cDNA micro-arrays. Statistical analysis using significance analysis of microarrays revealed a common signature of several hundred genes, demonstrating that the transcriptomes of HOXA9 and HOXA10 largely overlap in this cellular context. Seven genes that were upregulated by both HOX proteins were validated by real-time reverse transcription polymerase chain reaction. HOXA9 and HOXA10 showed positive regulation of genes in the Wnt pathway, including Wnt10B and two Wnt receptors Frizzled 1 and Frizzled 5, an important pathway for hematopoietic stem cell (HSC) self-renewal. Other validated genes included v-ets-related gene (ERG), Iroquois 3 (IRX3), aldehyde dehydrogenase 1 (ALDH1), and very long-chain acyl-CoA synthetase homolog 1 (VLCS-H1). GenMAPP (Gene Micro Array Pathway Profiler) analysis indicated that HOXA10 repressed expression of several genes involved in heme biosynthesis and three globin genes, indicating a general suppression of erythroid differentiation. A number of genes regulated by HOXA9 and HOXA10 are expressed in normal HSC populations.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

Maintenance and self-renewal of long-term reconstituting hematopoietic stem cells supported by amniotic fluid

The maintenance and self-renewal of hematopoietic stem cells (HSC) in culture is a central focus of hematopoietic stem cell research. In vivo, the balance between HSC differentiation, apoptosis, and self-renewal is regulated at the endosteal surface niche in the bone marrow (BM). In feeder-free cultures, the fate of HSC is affected by growth factors/interleukins and serum, which affect the balance between self-renewal, differentiation, and apoptosis and lead to the rapid loss of multipotent HSC. We report that substituting human amniotic fluid (AF) for serum in HSC cultures provides a growth milieu in which HSC differentiation and apoptosis are down-regulated and multipotent HSC are maintained. Murine BM cells were cultured in serum-free medium containing 25% amniotic fluid and stem cell factor (SCF) only, "AF/SCF" cultures. Compared with serum and multiple growth factor-containing medium, cells cultured for 4 weeks in AF/SCF medium displayed downregulation of differentiation markers while maintaining a high fraction of cells expressing Sca1 (51.8%) and c-kit (10.2%). Reconstitution of lethally irradiated C57BL/6 (Ly5.2) mice with cultured Ly5.1 BM cells resulted in high levels of (cultured) donor cells in primary (78 +/- 19.4% and 94.32 +/- 2.5%, 10(5) and 10(6) cells injected, respectively) and secondary (96.5%) recipients at 8 and 11 months post-transplantation. Hence, long-term repopulation with AF/SCF cultured BM cells was maintained. Addition to the cultures of 10% serum, interleukin (IL)-3, IL-6, granulocyte colony stimulating factor (G-CSF), or granulocyte-macrophage colony stimulating factor (GM-CSF), singly or in combination, resulted in rapid differentiation and apoptosis, leading to the total loss of HSC.

Wnt3 modulates the characteristics and cobblestone area-supporting activity of human stromal cells

OBJECTIVE

Our objective was to investigate the expression and significance of Wnt proteins in adult human hematopoietic-supporting stromal cells.

METHODS

Degenerate reverse transcription-polymerase chain reaction was performed to screen telomerized human stromal cells (hTERT-stromal cells) and multipotent mesenchymal cells (hTERT-MSCs) for expression of Wnt genes. We studied the actions of Wnt proteins by overexpressing them in stromal cells and MSCs by retrovirus-mediated gene transfer.

RESULTS

The hTERT-stromal and primary stromal cells expressed Wnt5A, while hTERT-MSCs and primary MSCs expressed Wnt3 and Wnt5A. Gene transfer of Wnt5A slightly reduced the growth rate of hTERT-stromal cells, but did not affect their morphology. In contrast, gene transfer of Wnt3 into both hTERT-stromal cells and hTERT-MSCs enhanced Wnt-betacatenin signaling, and caused remarkable morphological changes and growth retardation. Upon 2-week co-culture, expansion of clonogenic cells on Wnt5A-stromal cells was superior to that on control stromal cells. However, expansion of CD34+ cells on Wnt3-stromal cells did not differ from that on control stromal cells. Moreover, there was a drastic reduction in the formation of cobblestone area (CA) underneath Wnt3-stromal cells compared with that underneath control stromal cells.

CONCLUSION

These results suggest that Wnt3 plays an important role in regulating characteristics and CA support activity of stromal cells.

Commitment of embryonic stem cells to an epidermal cell fate and differentiation in vitro

The epidermis develops from a stem cell population in the surface ectoderm that feeds a single vertical terminal differentiation pathway. To date, however, the limited capacity for the isolation or purification of epidermal stem or precursor cells has hampered studies on early commitment and differentiation events. We have developed a two-step culture scheme in which pluripotent mouse embryonic stem (ES) cells are induced first to a surface ectoderm phenotype and then are positively selected for putative epidermal stem cells. We show that the earliest stages of epidermal development follow an ordered sequence that is similar to that observed in vivo (expression of keratin 8, keratin 19, keratin 17, and keratin 14), suggesting that ES cell-derived surface ectoderm-like cells can be induced to follow the epidermal developmental pathway. At a low frequency, keratin 14-positive early epidermal cells progressed to keratin 1-positive and terminally differentiated cells producing a cornified envelope. This culturing protocol provides an invaluable system in which to study both the mechanisms that direct stem cells along the epidermal pathway as well as those that influence their subsequent epidermal differentiation.

Detection of tissue-specific effects by methotrexate on differentiating mouse embryonic stem cells

BACKGROUND

Pluripotent embryonic stem (ES) cells offer a unique possibility to monitor the differentiation of several cell types in vitro. This study attempts to identify marker genes during in vitro cell differentiation of murine ES cells and allow a prediction of chemical effects on cell differentiation of specific target tissues. The study focused on the expression pattern of key genes involved in cardiomyocyte and osteoblast differentiation: Oct-4, Brachyury, Nkx2.5, alpha myosin heavy chain, Cbfa1, and Osteocalcin.

METHODS

Methotrexate was selected due to its well-characterized teratogenic effects. Several in vivo studies have demonstrated the specific interactions of methotrexate with bone formation whereas the cardiovascular system is not specifically affected after exposure to low concentration. The capability of murine ES cells to differentiate in vitro into cardiomyocytes as well as into osteoblasts have been used to demonstrate the target cell specificity in vitro, at non-cytotoxic concentration.

RESULTS

Exposure of differentiating ES cells did not result in any gene profile modification of the selected cardiomyocyte specific genes, whereas the expression of osteoblast specific key genes, Cbfa1 and Osteocalcin, decreased. At the latter stages of skeletal differentiation we observed a 30% decrease in gene expression for Cbfa1 and a 60% decrease for Osteocalcin, with reference to the control. Early marker genes for undifferentiated cells and mesodermal cells were not modified after methotrexate treatment.

CONCLUSIONS

These results show the possibility to integrate specific in vitro tests for teratogenicity in a test strategy for developmental toxicity.

Self-renewal of teratocarcinoma and embryonic stem cells

Pluripotent stem cells derived from preimplantation embryos, primordial germ cells or teratocarcinomas are currently unique in undergoing prolonged symmetrical self-renewal in culture. For mouse embryonic stem (ES) cells, self-renewal is dependent on signals from the cytokine leukaemia inhibitory factor (LIF) and from either serum or bone morphogenetic proteins (BMPs). In addition to the extrinsic regulation of gene expression, intrinsic transcriptional determinants are also required for maintenance of the undifferentiated state. These include Oct4, a member of the POU family of homeodomain proteins and a second recently identified homeodomain protein, Nanog. When overexpressed, Nanog allows ES cells to self-renew in the absence of the otherwise obligatory LIF and BMP signals. Although Nanog can act independent of the LIF signal, a contribution of both pathways provides maximal self-renewal efficiency. Nanog function also requires Oct4. Here, we review recent progress in ES cell self-renewal, relate this to the biology of teratocarcinomas and offer testable hypotheses to expose the mechanics of ES cell self-renewal.

Monitoring of teratogenic effects in vitro by analysing a selected gene expression pattern

The development of in vitro methods for regulatory embryotoxicity testing is challenging since the understanding of chemical effects on the mammalian development is still poor. The aim of the project is to identify marker genes during in vitro cell differentiation of murine embryonic stem cells, in order to predict chemical effects on cell differentiation of specific target tissues. The present study is focusing on the expression pattern by using semi-quantitative reverse transcriptase (RT)-PCR of key genes involved in cardiomyocytes development; i.e. Oct-4, Brachyury, Nkx2.5 and alpha myosin heavy chain (alpha-MHC). Two reference chemicals with well-known in vivo data have been analysed by using this approach: retinoic acid and lithium chloride. Retinoic acid has been selected as a teratogen affecting several target tissues, whereas lithium chloride has been described to affect the development of the cardiovascular system. We demonstrate that retinoic acid already affects in the early stage of germ layer formation, which was demonstrated by a change of Oct-4 and Brachyury gene expression. As we expected, the expression of cardiac specific genes (Nkx2.5, alpha-MHC) has been also modified. In contrary, the Oct-4 and Brachyury expression was not changed by lithium treatment. In this case, we observed a modification in the normal gene expression pattern, for alpha-MHC and Nkx2.5, demonstrating that lithium chloride affects the later stage of heart development. These data suggest that the inclusion of selective target organ genes in an established embryotoxicity test allows to predict effects of chemicals and drugs to the heart development.

Newly expressed proteins of mouse embryonic fibroblasts irradiated to be inactive

It has been found that post-radiation mouse embryonic fibroblasts can well maintain the pluripotency in human embryonic stem cells. However, the molecular mechanism remains unclear. In the present study, the new protein expression profile of post-radiation mouse embryonic fibroblasts was analyzed by immobilized pH gradient 2-dimensional polyacrylamide gel electrophoresis. Image analysis following silver staining revealed (969+/-57) vs. (1085+/-107) spots from post-radiation mouse embryonic fibroblasts and pre-radiation ones, respectively. Some newly expressed proteins, which were only abundantly present after irradiation, were subjected to peptide mass fingerprint analysis and identified using MALDI-TOF-MS, SWISS-PROT database, and RT-PCR. Several of those proteins were preliminarily identified to participate in cytokine secretion, cell signal transduction, transcriptional regulation, and apoptosis, etc., which suggested that inactive post-radiation mouse embryonic fibroblasts expressed some new proteins that may underlie the molecular mechanisms to maintain the pluripotency in human embryonic stem cells.