Differentiation of mouse embryonic stem cells in vitro: III. Morphological evaluation of tissues developed after implantation of differentiated mouse embryoid bodies

Induction of inner ear hair cell-like cells from Math1-transfected mouse ES cells

Math1, a basic helix-loop-helix transcription factor homolog of the Drosophila atonal gene, is considered to be a key factor for induction of sensory hair cells (HCs) during development of the organ of Corti or cochlea. Although embryonic stem (ES) cells are able to produce HC-like cells, the role of Math1 in induction of those cells has not been thoroughly elucidated. In the present study, we introduced Math1 into ES cells in order to achieve efficient generation of HC-like cells. ES cells carrying Tet-inducible Math1, Math1-ES cells, were generated using a Tet-On gene expression system. Embryoid bodies (EBs) formed in the absence of doxycycline (Dox) for 4 days were allowed to grow for an additional 14 days in the dishes in the presence of 400 μg/ml of Dox. At the end of those 14-day cultures, approximately 10% of the cells in EB outgrowths expressed the HC-related markers myosin6, myosin7a, calretinin, α9AchR, and Brn3c (also known as Pou4f3) and showed formation of stereocilia-like structures, whereas few cells in EB outgrowths grown without Dox showed those markers. Reporter assays of Math1-ES cells using a Brn3c-promoter plasmid demonstrated positive regulation of Brn3c by Math1. Furthermore, such HC-related marker-positive cells derived from Math1-ES cells were found to be incorporated in the developing inner ear after transplantation into chick embryos. Math1-ES cells are considered to be an efficient source of ES-derived HC-like cells, and Math1 may be an important factor for induction of HC-like cells from differentiating ES cells.

Coculture strategies in bone tissue engineering: the impact of culture conditions on pluripotent stem cell populations

The use of pluripotent stem cell populations for bone tissue regeneration provides many opportunities and challenges within the bone tissue engineering field. For example, coculture strategies have been utilized to mimic embryological development of bone tissue, and particularly the critical intercellular signaling pathways. While research in bone biology over the last 20 years has expanded our understanding of these intercellular signaling pathways, we still do not fully understand the impact of the system's physical characteristics (orientation, geometry, and morphology). This review of coculture literature delineates the various forms of coculture systems and their respective outcomes when applied to bone tissue engineering. To understand fully the key differences between the different coculture methods, we must appreciate the underlying paradigms of physiological interactions. Recent advances have enabled us to extrapolate these techniques to larger dimensions and higher geometric resolutions. Finally, the contributions of bioreactors, micropatterned biomaterials, and biomaterial interaction platforms are evaluated to give a sense of the sophistication established by a combination of these concepts with coculture systems.

A plant-derived remedy for repair of infarcted heart

Background

Myocardial infarction (MI) due to coronary artery disease remains one of the leading causes of premature death. Replacement of infarcted heart tissue with regenerating myocardium from endogenous progenitor pools or exogenously introduced stem cells remains a therapeutic ideal. Their impracticality mainly lies in their low efficiency in cardiogenic differentiation (CD). Our recent studies with an acute MI animal model have already demonstrated the therapeutic effect of the MeOH extract of Geum japonicum (EGJ), providing clear evidence of myocardial regeneration.

Methods and Findings

The present study further isolated the active component contained in EGJ using bioassay-guided isolation and investigated its efficacy in the treatment of infarcted heart in animal MI models. We demonstrated that substantial repair of infarcted heart in animal MI models by EGJ can be mimicked by the isolated candidate compound (cardiogenin) in MI animal models. Clear evidence of newly regenerated endogenous mesenchymal stem cells (MSCs) derived cardiomyocytes was observed throughout the infarct zone, accompanied by significantly improved functional performance of the heart. Transplantation of MSCs pretreated with EGJ or cardiogenin into a MI animal model also resulted in substantial regeneration of functional myocardium, implying that the activated MSCs carry all the necessary blueprints for myocardial regeneration. Signaling pathways specific to cell survival, CD identified in embryonic heart induction and angiogenesis were activated in both cardiogenin-treated MSCs and cardiogenin-induced regenerating myocardium.

Conclusions

This study has demonstrated the therapeutic effects of cardiogenin in infarcted heart repair, and identified the associated signalling pathways for effective cardiogenic differentiation of MSCs, cell survival and angiogenesis. These findings should enable new treatment strategies for MI to be developed immediately.

Microporous membrane growth substrates for embryonic stem cell culture and differentiation

As the field of embryonic stem cell culture and differentiation advances, many diverse culturing techniques will ultimately be necessary in order to fully reproduce the various environments these cells normally encounter during development. Although most of the work to date has been performed on solid plastic supports, this growth support has several limitations in its representation of the in vivo environment. Impermeable substrates force the cells to exchange their gas and nutrients exclusively through the top side of the cultured cells. In contrast, cells growing in vivo are exposed from several directions to factors from the blood, other cells, soluble factors, and liquid-air interfaces. Additionally, solid plastic presents a smooth two-dimensional surface that is not experienced in vivo. Therefore, the use of traditional plastic presents limitations upon normal cellular morphology, function, and differentiation. An important alternative to growth on solid plastic is the growth of cells on microporous membranes. One of the many advantages to cell growth on porous membrane substrates is their ability to provide a surface that better mimics a three-dimensional in vivo setting. A porous membrane allows multidirectional exposure to nutrients and waste products. In addition, the membrane separation of dual chambers allows for the coculture of cells of different origin to study how cells interact through indirect signaling or through providing a conditioned niche for the proper growth and differentiation of cell types.

Fate of undifferentiated mouse embryonic stem cells within the rat heart: role of myocardial infarction and immune suppression

Abstract It has recently been suggested that the infarcted rat heart microenvironment could direct pluripotent mouse embryonic stem cells to differentiate into cardiomyocytes through an in situ paracrine action. To investigate whether the heart can function as a cardiogenic niche and confer an immune privilege to embryonic stem cells, we assessed the cardiac differentiation potential of undifferentiated mouse embryonic stem cells (mESC) injected into normal, acutely or chronically infarcted rat hearts. We found that mESC survival depended on immunosuppression both in normal and infarcted hearts. However, upon Cyclosporin A treatment, both normal and infarcted rat hearts failed to induce selective cardiac differentiation of implanted mESC. Instead, teratomas developed in normal and infarcted rat hearts 1 week and 4 weeks (50% and 100%, respectively) after cell injection. Tight control of ESC commitment into a specific cardiac lineage is mandatory to avoid the risk of uncontrolled growth and tumourigenesis following transplantation of highly plastic cells into a diseased myocardium.

Comparison of gene expression profiles in erythroid-like cells derived from mouse embryonic stem cells differentiated in simple and co-culture systems

The feeder layer and the presence of specific growth factors are thought to induce the differentiation of embryonic stem cells (ESCs) in culture. The aim of this study was to evaluate the effect of erythropoietin (EPO) on the differentiation of ESCs into erythroid colonies in simple and co-culture systems. Embryoid bodies were dissociated and replated in semisolid medium in simple culture or in a co-culture system with bone-marrow stromal cells (BMSCs), both in the presence or absence of EPO. Colony assays, benzidine staining, and ultrastructural studies were carried out until day 10 of culture. Expression of the epsilon globin, betaH1 globin, runt-related transcription factor 1 (RUNX1), betamajor globin, and erythropoietin receptor (EPOR) genes was evaluated using semi-quantitative RT-PCR. A comparison with the corresponding controls showed that colony size increased in both systems (P <or= 0.05). The number of benzidine-positive colonies in the co-culture system with EPO (86.6+/-17.86) was significantly different compared to the simple culture system with EPO (43.6+/-4.77; P <or= 0.05). The hemoglobin content of the differentiated cells was visualized in micrographs. Analysis of gene expression showed that all genes except betamajor globin were expressed in the simple culture system, whereas in the co-culture system all genes were expressed. These results confirmed that the presence of EPO in a BMSC co-culture system with ESCs improves the differentiation of ESCs to erythroid colonies. Moreover, evidence of primitive and definitive erythropoiesis was observed in this co-culture system.

Transplantation of undifferentiated murine embryonic stem cells in the heart: teratoma formation and immune response

Embryonic stem (ES) cells are promising for cardiac repair, but directing their differentiation toward cardiomyocytes remains challenging. We investigated whether the heart guides ES cells toward cardiomyocytes in vivo and whether allogeneic ES cells were immunologically tolerated. Undifferentiated mouse ES cells consistently formed cardiac teratomas in nude or immunocompetent syngeneic mice. Cardiac teratomas contained no more cardiomyocytes than hind-limb teratomas, suggesting lack of guided differentiation. ES cells also formed teratomas in infarcted hearts, indicating injury-related signals did not direct cardiac differentiation. Allogeneic ES cells also caused cardiac teratomas, but these were immunologically rejected after several weeks, in association with increased inflammation and up-regulation of class I and II histocompatibility antigens. Fusion between ES cells and cardiomyocytes occurred in vivo, but was rare. Infarct autofluorescence was identified as an artifact that might be mistaken for enhanced GFP expression and true regeneration. Hence, undifferentiated ES cells were not guided toward a cardiomyocyte fate in either normal or infarcted hearts, and there was no evidence for allogeneic immune tolerance of ES cell derivatives. Successful cardiac repair strategies involving ES cells will need to control cardiac differentiation, avoid introducing undifferentiated cells, and will likely require immune modulation to avoid rejection.

Gut-like structures from mouse embryonic stem cells as an in vitro model for gut organogenesis preserving developmental potential after transplantation

Recently, we reported the formation of gut-like structures from mouse ESCs in vitro. To determine whether ESCs provide an in vitro model of gastrointestinal (GI) tracts and their organogenesis, we investigated the morphological features, formation process, cellular development, and regional location within the GI tract by immunohistochemistry, electron microscopy, and reverse transcription-polymerase chain reaction. We also examined the developmental potential by transplantation into kidney capsules. The results demonstrated that Id2-expressing epithelium developed first, alpha-smooth muscle actin appeared around the periphery, and finally, the gut-like structures were formed into a three-layer organ with well-differentiated epithelium. A connective tissue layer and musculature with interstitial cells of Cajal developed, similar to organogenesis of the embryonic gut. Enteric neurons appeared underdeveloped, and blood vessels were absent. Many structures expressed intestinal markers Cdx2 and 5-hydroxytryptamine but not the stomach marker H(+)/K(+) ATPase. Transplants obtained blood vessels and extrinsic nerve growth from the host to prolong life, and even grafts of premature structures did not form teratoma. In conclusion, gut-like structures were provided with prototypical tissue components of the GI tract and are inherent in the intestine rather than the stomach. The formation process was basically same as in gut organogenesis. They maintain their developmental potential after transplantation. Therefore, gut-like structures provide a unique and useful in vitro system for development and stem cell studies of the GI tract, including transplantation experiments.

Wnt4-transformed mouse embryonic stem cells differentiate into renal tubular cells

Embryonic stem (ES) cells have the potential to differentiate into various progenitor cells. Here we investigated the capacity of mouse ES cells to differentiate into renal tubular cells both in vitro and in vivo. After stably transfecting Wnt4 cDNA to mouse ES cells (Wnt4-ES cells), undifferentiated ES cells were incubated by the hanging drop culture method to induce differentiation to embryoid bodies (EBs). During culturing of the EBs derived from the Wnt4-ES cells, aquaporin-2 (AQP2) mRNA and protein were expressed within 15-20 days. The expression of AQP2 in Wnt4-EBs was enhanced in the presence of hepatocyte growth factor (HGF) and activin A. We next performed in vivo experiments by transplanting the Wnt4-EBs into the mouse renal cortex. Four weeks after transplantation, some portions of the EB-derived cells expressing AQP2 in the kidney assembled into tubular-like formations. In conclusion, our in vitro and in vivo experiments revealed two new findings: first, that cultured Wnt4-EBs have an ability to differentiate into renal tubular cells; and second, that Wnt4, HGF, and activin A may promote the differentiation of ES cells to renal tubular cells.

Establishment of new murine embryonic stem cell lines for the generation of mouse models of human genetic diseases

Embryonic stem cells are totipotent cells derived from the inner cell mass of blastocysts. Recently, the development of appropriate culture conditions for the differentiation of these cells into specific cell types has permitted their use as potential therapeutic agents for several diseases. In addition, manipulation of their genome in vitro allows the creation of animal models of human genetic diseases and for the study of gene function in vivo. We report the establishment of new lines of murine embryonic stem cells from preimplantation stage embryos of 129/Sv mice. Most of these cells had a normal karyotype and an XY sex chromosome composition. The pluripotent properties of the cell lines obtained were analyzed on the basis of their alkaline phosphatase activity and their capacity to form complex embryoid bodies with rhythmically contracting cardiomyocytes. Two lines, USP-1 and USP-3, with the best in vitro characteristics of pluripotency were used in chimera-generating experiments. The capacity to contribute to the germ line was demonstrated by the USP-1 cell line. This cell line is currently being used to generate mouse models of human diseases.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Human placental alkaline phosphatase as a histochemical marker of gene expression in transgenic mice

The human placental alkaline phosphatase (PLAP) gene was analysed for its utility as a histochemically detectable reporter gene in transgenic mice. A reporter gene was made by linking the PLAP structural gene to an enhancer-promoter element from the human beta-actin gene. This gene was inserted into the mouse genome by transfection of embryonic stem cells, and by microinjection of fertilized eggs. Histochemical staining showed that the transgene was uniformly expressed in four of four stable ES cell lines, and in all ten tissues examined from adult animals from five lines of transgenic mice. Non-transgenic cells did not stain. These results suggest that the human PLAP gene will be of utility in studies requiring phenotypic marking of cells in tissues of mice.

A gene trap strategy for identifying the gene expressed in the embryonic nervous system

An efficient gene trap strategy was devised for identifying the genes that are expressed in the mouse developing nervous system. Mouse embryonic stem (ES) cell lines that carried independent integrations of a gene trap vector, pSneolN/acZA, were allowed to differentiate in a suspension culture system. To select cells containing neurons, astrocytes or neuron-glia precursors, cell lines were immunohistochemically examined with antibodies against neuron-specific proteins (neurofilament protein 150 kD and microtubule associated protein 2), glial fibrillary acidic protein or nestin. Three cell clones (GT3-8, 11 and 12) were immunoreactive to either of the antibodies employed and at the same time positive for beta-galactosidase activity. When chimeric embryos were generated by the use of the above 3 cell lines, some cells in their nervous system showed X-gal staining. Thus the major advantage of the present gene trap method lies in its prescreening step of manipulated ES cells prior to generation of chimeric animals. This method holds promise as a useful tool for investigating the genes involved in the development of the nervous system.