In vitro culture of embryonic mouse intestinal epithelium: cell differentiation and introduction of reporter genes

3D In Vitro Platform for Cell and Explant Culture in Liquid-like Solids

Existing 3D cell models and technologies have offered tools to elevate cell culture to a more physiologically relevant dimension. One mechanism to maintain cells cultured in 3D is by means of perfusion. However, existing perfusion technologies for cell culture require complex electronic components, intricate tubing networks, or specific laboratory protocols for each application. We have developed a cell culture platform that simply employs a pump-free suction device to enable controlled perfusion of cell culture media through a bed of granular microgels and removal of cell-secreted metabolic waste. We demonstrated the versatile application of the platform by culturing single cells and keeping tissue microexplants viable for an extended period. The human cardiomyocyte AC16 cell line cultured in our platform revealed rapid cellular spheroid formation after 48 h and ~90% viability by day 7. Notably, we were able to culture gut microexplants for more than 2 weeks as demonstrated by immunofluorescent viability assay and prolonged contractility.

Lysoptosis is an evolutionarily conserved cell death pathway moderated by intracellular serpins

Lysosomal membrane permeabilization (LMP) and cathepsin release typifies lysosome-dependent cell death (LDCD). However, LMP occurs in most regulated cell death programs suggesting LDCD is not an independent cell death pathway, but is conscripted to facilitate the final cellular demise by other cell death routines. Previously, we demonstrated that Caenorhabditis elegans (C. elegans) null for a cysteine protease inhibitor, srp-6, undergo a specific LDCD pathway characterized by LMP and cathepsin-dependent cytoplasmic proteolysis. We designated this cell death routine, lysoptosis, to distinguish it from other pathways employing LMP. In this study, mouse and human epithelial cells lacking srp-6 homologues, mSerpinb3a and SERPINB3, respectively, demonstrated a lysoptosis phenotype distinct from other cell death pathways. Like in C. elegans, this pathway depended on LMP and released cathepsins, predominantly cathepsin L. These studies suggested that lysoptosis is an evolutionarily-conserved eukaryotic LDCD that predominates in the absence of neutralizing endogenous inhibitors.

An Interphase Microfluidic Culture System for the Study of Ex Vivo Intestinal Tissue

Ex vivo explant culture models offer unique properties to study complex mechanisms underlying tissue growth, renewal, and disease. A major weakness is the short viability depending on the biopsy origin and preparation protocol. We describe an interphase microfluidic culture system to cultivate full thickness murine colon explants which keeps morphological structures of the tissue up to 192 h. The system was composed of a central well on top of a porous membrane supported by a microchannel structure. The microfluidic perfusion allowed bathing the serosal side while preventing immersion of the villi. After eight days, up to 33% of the samples displayed no histological abnormalities. Numerical simulation of the transport of oxygen and glucose provided technical solutions to improve the functionality of the microdevice.

Ex vivo gut culture for studying differentiation and migration of small intestinal epithelial cells

Epithelial cultures are commonly used for studying gut health. However, due to the absence of mesenchymal cells and gut structure, epithelial culture systems including recently developed three-dimensional organoid culture cannot accurately represent in vivo gut development, which requires intense cross-regulation of the epithelial layer with the underlying mesenchymal tissue. In addition, organoid culture is costly. To overcome this, a new culture system was developed using mouse embryonic small intestine. Cultured intestine showed spontaneous peristalsis, indicating the maintenance of the normal gut physiological structure. During 10 days of ex vivo culture, epithelial cells moved along the gut surface and differentiated into different epithelial cell types, including enterocytes, Paneth cells, goblet cells and enteroendocrine cells. We further used the established ex vivo system to examine the role of AMP-activated protein kinase (AMPK) on gut epithelial health. Tamoxifen-induced AMPKα1 knockout vastly impaired epithelial migration and differentiation of the developing ex vivo gut, showing the crucial regulatory function of AMPK α1 in intestinal health.

Development and evaluation of a porcine in vitro colon organ culture technique

The intestinal mucosa comprises a complex assemblage of specialized tissues that interact in numerous ways. In vitro cell culture models are generally focused on recreating a specific characteristic of this organ and do not account for the many interactions between the different tissues. In vitro organ culture (IVOC) methods offer a way to overcome these limitations, but prolonging cell viability is essential. This study aimed to determine the feasibility and optimal conditions for in vitro culture of swine colonic mucosa for use as an enteric pathogen infection model. Explants (n = 168) from commercial pigs (n = 12), aged 5 to 10 wk, were used to assess the impact of various culture protocols on explant viability. Explants were cultured for up to 5 d and formalin fixed at 24-h intervals. Following establishment of the culture protocol, explants (n = 208) from 13 pigs were evaluated at Day 0 and 5 of culture. Assessment of viability was based on histological changes (tissue architecture evaluated by H&E, immunostaining of cell proliferation marker Ki-67) and expression of genes encoding IL-1α, IL-8, TNF-α, IFN-γ, and e-cadherin. After 5 d in culture, 20% of explants displayed over 80% of epithelial coverage, whereas 31% of explants had more than 50% of their surface covered by columnar epithelium, and 81% had crypts but with a decreased number of Ki-67-positive cells when compared to Day 0. Notably, large variability in explant quality was observed between donor pigs. Best possible explants were obtained from the distal colon of pigs, processed immediately after euthanasia, cultured at the liquid-tissue-gas interface in media supplemented with a mixture of antibiotics and antifungals and an oxygen-rich gas mix.

Organotypical Tissue Cultures from Fetal and Neonatal Murine Colon

The complex functions of the gastrointestinal tract rely on the coordinated interplay of several cell and tissue types involving epithelium, connective tissue, smooth muscles as well as cells of the immune and nervous system. It is therefore obvious, that these functions can hardly be investigated sufficiently using cell lines or two-dimensional cell cultures.Here, we describe an easy to produce three-dimensional organotypical explants culture from fetal and neonatal murine colon. This model is suitable for in vitro testing of intestinal function or the evaluation of developmental or pathological processes.

Bridging the gap: functional healing of embryonic small intestine ex vivo

The ability to grow embryonic organs ex vivo provides an opportunity to follow their differentiation in a controlled environment, with resulting insights into normal development. Additionally, similar strategies can be used to assess effects on organogenesis of physical and chemical manipulations. This study aimed to create an organ culture model with which to test physical manipulations to enhance healing of gut segments, thus generating a single functional organ. Embryonic mouse jejunum was isolated and cut into 2–3 mm tubes, which were placed in pairs, separated by a small gap, on semi‐permeable supports. Each pair was linked by a nylon suture threaded through their lumens. After 3 days in organ culture fed by defined serum‐free media, the rudiments differentiated to form tubes of smooth muscle surrounding a core of rudimentary villi. Of 34 such pairs, 74% had touching and well aligned proximate ends. Of these joined structures, 80% (59% of the total pairs) had a continuous lumen, as assessed by observing the trajectories of fluorescent dextrans injected into their distal ends. Fused organ pairs formed a single functional unit, as assessed by spontaneous contraction waves propagated along their lengths. In these healed intestines, peripherin⁺ neurons formed a nexus in the zone of fusion, linking the rudiment pairs. In future, this system could be used to test whether growth factors enhance fusion. Such results should in turn inform the design of novel treatments for short bowel syndrome, a potentially fatal condition with a currently limited and imperfect range of therapies. ©2015. The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons, Ltd

Role of TGF-β1/p38 MAPK pathway in hepatitis B virus-induced tubular epithelial-myofibroblast transdifferentiation

OBJECTIVE

This study is to investigate the hepatitis B virus (HBV)-induced tubular epithelial-myofibroblast transdifferentiation (TEMT) in human renal tubular epithelial HK-2 cells.

METHODS

Human proximal tubular epithelial HK-2 cells were cultured. These HK-2 cells were divided into 4 groups: the blank control group, the vector control group, the HBV-transfected group, and the inhibitor-treated group. Transfection was performed with lipofectamine. Measurements of hepatitis B e antigen (HBeAg) and hepatitis B surface antigen (HBsAg) in culture supernatant were determined by electrochemiluminescence immunoassay. Immunocytochemical staining, reverse transcription PCR (RT-PCR), and Western blot analysis were performed to detect the mRNA and protein expression levels, respectively.

RESULTS

The immunocytochemical staining showed that, the expression level of E-cadherin was dramatically decreased, while the α-SMA expression level was significantly elevated, in HBV-transfected HK-2 cells. The mRNA level of TGF-β1 and the protein level of p-p38 mitogen-activated protein kinase (MAPK) were elevated in HK-2 cells transfected with HBV. When treated with the p38 MAPK-specific inhibitor, the activation of p38 MAPK was eliminated in HBV-transfected HK-2 cells. In addition, the altered expression levels of E-cadherin and α-SMA, the increased contents of HBeAg and HBsAg in the culture supernatant, as well as the morphological changes of TEMT in HBV-transfected HK-2 cells, were all reversed by the inhibiter treatment.

CONCLUSION

HBV transfection could induce TEMT in HK-2 cells, which was mediated by the TGF-β1/p38 MAPK pathway. These findings provide new insights into the prevention and treatment of HBV-associated glomerulonephritis.

Abnormal differentiation of intestinal epithelium and intestinal barrier dysfunction in diabetic mice associated with depressed Notch/NICD transduction in Notch/Hes1 signal pathway

Proliferative change and intestinal barrier dysfunction in intestinal mucosa of diabetes have been described, but the differentiation characteristics of intestinal epithelial cells (IECs) and the mechanisms in the IECs development remain unclear. To explore the intestinal epithelial constitution patterns and barrier function, the diabetic mouse model was induced by streptozotocin. Tight junctions between IECs were significantly damaged and the serum level of D-lactate was raised in diabetic mice (P < 0.05). The expression of Zo1 and Ocln in the small intestine of diabetic mice were lower, while the markers for absorptive cell (SI) and Paneth cell (Lyz1) were significantly higher than in control mice (P < 0.05). The expression of Msi1, Notch1, and Dll1 in small intestine gradually increased throughout the course of hyperglycemia in diabetic mice (P < 0.05). However, the expression of NICD, RBP-jκ, Math1, and Hes1 had a reverse trend compared with Msi1 and Notch1. Intestinal absorptive cells and Paneth cells had a high proliferation rate in diabetic mice. However, the intestinal barrier dysfunction associated with the decreased expressions of Zo1 and Ocln was detected throughout hyperglycemia. In conclusion, downregulation of Notch/Hes1 signal pathway caused by depressed Notch/NICD transduction is associated with the abnormal differentiation of IECs and intestinal barrier dysfunction in diabetic mice.

Morphine induces bacterial translocation in mice by compromising intestinal barrier function in a TLR-dependent manner

Opiates are among the most prescribed drugs for pain management. However, morphine use or abuse results in significant gut bacterial translocation and predisposes patients to serious infections with gut origin. The mechanism underlying this defect is still unknown. In this report, we investigated the mechanisms underlying compromised gut immune function and bacterial translocation following morphine treatment. We demonstrate significant bacterial translocation to mesenteric lymph node (MLN) and liver following morphine treatment in wild-type (WT) animals that was dramatically and significantly attenuated in Toll-like receptor (TLR2 and 4) knockout mice. We further observed significant disruption of tight junction protein organization only in the ileum but not in the colon of morphine treated WT animals. Inhibition of myosin light chain kinase (MLCK) blocked the effects of both morphine and TLR ligands, suggesting the role of MLCK in tight junction modulation by TLR. This study conclusively demonstrates that morphine induced gut epithelial barrier dysfunction and subsequent bacteria translocation are mediated by TLR signaling and thus TLRs can be exploited as potential therapeutic targets for alleviating infections and even sepsis in morphine-using or abusing populations.

Serum levels of alpha-smooth muscle actin and c-Met as biomarkers of the degree of severity of Henoch-Schonlein purpura nephritis

Approximately 40% of patients with Henoch-Schonlein purpura (HSP) develop Henoch-Schonlein purpura nephritis (HSPN) after 4 to 6 weeks of subcutaneous hemorrhaging. Immunoglobulin-A nephropathy (IgAN) and HSPN have numerous similarities, which can cause difficulty in correctly diagnosing the disorder during a differential diagnosis. The pathogenesis of the 2 diseases is not clear. We enrolled 137 patients with HSPN, 107 patients with IgAN, and 28 healthy (control) patients in our study. The levels of alpha-smooth muscle actin (α-SMA), c-Met, and Gal-deficient IgA1 (Gd-IgA1) in the 3 patient groups were determined and compared. The α-SMA, c-Met, and Gd-IgA1 levels and the clinical data from the patients with HSPN were analyzed for any correlations. The α-SMA and c-Met levels of the HSPN group were significantly higher than those of the IgAN and healthy control groups (P < 0.01). The Gd-IgA1 levels of the HSPN and IgAN groups were significantly different from the Gd-IgA1 level of the healthy control group (P < 0.01). The α-SMA levels of the HSPN group were positively correlated with blood urea nitrogen levels, serum creatinine levels, hematuria index, and proteinuria levels (P < 0.01). The c-Met levels of the HSPN group were positively correlated with the blood urea nitrogen and serum creatinine levels (P < 0.01). There were no significant differences among the α-SMA, c-Met, and Gd-IgA1 levels or the clinical data for the child and adult patients with HSPN. The serum levels of α-SMA and c-Met in patients with HSPN may be associated with the degree of disease severity. Gd-IgA1 is involved in the common immunologic pathogenesis of HSPN and IgAN.

Differentiation of intestinal absorptive cells derived from mouse embryonic bodies can be promoted by inducing the differentiation of definitive endoderm in vivo

AIM: To investigate the effect of inducing the differentiation of definitive endoderm derived from mouse embryonic bodies (EBs) cultured by the hanging drop method in promoting the differentiation of intestinal absorptive cells in vivo.

METHODS: The differentiation of definitive endoderm during EBs formation derived from mouse ES-E14TG2a embryonic stem cells (ESC) and the role of Activin A in promoting its differentiation were monitored by detecting its markers by RT-PCR and fluorescence-activated cell sorting. Subsequently, the EBs with high proportion of definitive endoderm were hypodermically engrafted into the back of NOD/SCID mice to form grafts. The markers for small intestinal absorptive cells, including SI, LPH, and Fabp2, were detected in these grafts by quantitative RT-PCR and immunohistochemistry.

RESULTS: The marker genes for definitive endoderm were more highly expressed in the 5-day EBs than in other stages of EBs (Gsc: 0.9809 ± 0.1001 vs 0.5435 ± 0.0821, 0.5525 ± 0.0786, 0.2234 ± 0.0425; Tm4sf2: 0.9231 ± 0.1121 vs 0.0017 ± 0.0007, 0.0176 ± 0.0058, 0.6542 ± 0.0742; Gpc1: 0.8639 ± 0.1098 vs 0.5882 ± 0.1027, 0.7112 ± 0.0956, 0.4239 ± 0.0874, all P < 0.05). The percentage of definitive endoderm cells in the 5-day EBs induced with 50 μg/L Activin A (SF-A group) was significantly higher than that in controls (all P < 0.05). SI and LPH mRNA expression in the grafts from the SF-A group was significantly higher than that in control groups (all P < 0.05). Immunohistochemical analysis revealed that Fabp2 was expressed in some immature cells without specific structure or adenoid structures in the grafts from the SF-A group.

CONCLUSION: The differentiation of definitive endoderm derived from mouse ESC could be induced with 50 ng/ml Activin A in EBs cultured by the hanging drop method. Increasing the proportion of definitive endoderm in EBs promotes the differentiation of intestinal absorptive cells in vivo.

Musashi1 and hairy and enhancer of split 1 high expression cells derived from embryonic stem cells enhance the repair of small-intestinal injury in the mouse

BACKGROUND

Embryonic stem cells have great plasticity. In this study, we repaired impaired small intestine by transplanting putative intestinal epithelial stem cells (Musashi1 and hairy and enhancer of split 1 high expression cells) derived from embryonic stem cells.

METHODS

The differentiation of definitive endoderm in embryoid bodies, derived from male ES-E14TG2a cells by the hanging-drop method, was monitored to define a time point for maximal induction of putative intestinal epithelial stem cells by epidermal growth factor. Furthermore, to evaluate the regenerative potential of intestinal epithelium, these putative stem cells were engrafted into NOD/SCID mice and female mice with enteritis. Donor cells were located by SRY DNA in situ hybridization.

RESULTS

The results revealed that definitive endodermal markers were highly expressed in 5-day embryoid bodies. These embryoid body cells were induced into putative intestinal epithelial stem cells on the 5th day of epidermal growth factor administration. Grafts from these cells consisted of adenoid structures and nonspecific structural cells with strong expression of small-intestinal epithelial cell markers. In situ hybridization revealed that the donor cells could specifically locate in damaged intestinal epithelium, contribute to epithelial structures, and enhance regeneration.

CONCLUSIONS

In conclusion, the Musashi1 and hairy and enhancer of split 1 high expression cells, derived from mouse embryonic stem cells, locate predominantly in impaired small-intestinal epithelium after transplantation and contribute to epithelial regeneration.

Explant culture of gastrointestinal tissue: a review of methods and applications

The gastrointestinal (GI) tract is an important target organ for the toxicity of xenobiotics. The toxic effects of xenobiotics on this complex, heterogeneous structure have been difficult to model in vitro and have traditionally been assessed in vivo. The explant culture of GI tissue offers an alternative approach. Historically, the organotypic culture of the GI tract proved far more challenging than the culture of other tissues, and it was not until the late 1960s that Browning and Trier described the means by which intestinal tissues could be successfully cultured. This breakthrough provided a tool researchers could utilise, and adapt, to investigate topics such as the pathogenesis of inflammatory intestinal diseases, the effect of growth factors and cytokines on intestinal proliferation and differentiation, and the testing of novel xenobiotics for efficacy and safety. This review considers that intestinal explant culture shows much potential for the application of a relatively under-used procedure in future biomedical research. Furthermore, there appear to be many instances where the technique may provide experimental solutions where both cell culture and in vivo models have been unable to deliver conclusive and convincing findings.

Dexamethasone treatment induces the reprogramming of pancreatic acinar cells to hepatocytes and ductal cells

Background

The pancreatic exocrine cell line AR42J-B13 can be reprogrammed to hepatocytes following treatment with dexamethasone. The question arises whether dexamethasone also has the capacity to induce ductal cells as well as hepatocytes.

Methodology/Principal Findings

AR42J-B13 cells were treated with and without dexamethasone and analyzed for the expression of pancreatic exocrine, hepatocyte and ductal markers. Addition of dexamethasone inhibited pancreatic amylase expression, induced expression of the hepatocyte marker transferrin as well as markers typical of ductal cells: cytokeratin 7 and 19 and the lectin peanut agglutinin. However, the number of ductal cells was low compared to hepatocytes. The proportion of ductal cells was enhanced by culture with dexamethasone and epidermal growth factor (EGF). We established several features of the mechanism underlying the transdifferentiation of pancreatic exocrine cells to ductal cells. Using a CK19 promoter reporter, we show that a proportion of the ductal cells arise from differentiated pancreatic exocrine-like cells. We also examined whether C/EBPβ (a transcription factor important in the conversion of pancreatic cells to hepatocytes) could alter the conversion from acinar cells to a ductal phenotype. Overexpression of an activated form of C/EBPβ in dexamethasone/EGF-treated cells provoked the expression of hepatocyte markers and inhibited the expression of ductal markers. Conversely, ectopic expression of a dominant-negative form of C/EBPβ, liver inhibitory protein, inhibited hepatocyte formation in dexamethasone-treated cultures and enhanced the ductal phenotype.

Conclusions/Significance

These results indicate that hepatocytes and ductal cells may be induced from pancreatic exocrine AR42J-B13 cells following treatment with dexamethasone. The conversion from pancreatic to hepatocyte or ductal cells is dependent upon the expression of C/EBPβ.

Barrett's metaplasia: molecular mechanisms and nutritional influences

Barrett's metaplasia is discussed in the context of a general theory for the formation of metaplasias based on developmental biology. The phenotype of a particular tissue type becomes established during embryonic development by the expression of a specific set of transcription factors. If this combination becomes altered, then the tissue type can be altered. Such events may occur by mutation or by environmental effects on gene expression, normally within the stem cell population of the tissue. A macroscopic patch of metaplastic tissue will arise only if the new gene activity state is self-sustaining in the absence of its original causes, and if the new tissue type can outgrow the parent tissue type. An important candidate gene for the causation of Barrett's metaplasia is Cdx2 (Caudal-type homeobox 2). In normal development, this is expressed in the future intestine, but not the future foregut. Mouse knockout studies have shown that it is needed for intestinal development, and that its loss from adult intestine can lead to squamous transformations. It is also expressed in Barrett's metaplasia and can be activated in oesophageal cell cultures by treatment with bile acids. We have investigated the ability of Cdx2 to bring about intestinal transformations in oesophageal epithelium. Our results show that Cdx2 can activate a programme of intestinal gene expression when overexpressed in HET-1A cells, or in fetal epithelium, but not in the adult epithelium. This suggests that Cdx2, although necessary for formation of intestinal tissue, is not sufficient to provoke Barrett's metaplasia in adult life and that overexpression of additional transcription factors is necessary. In terms of diet and nutrition, there is a known association of Barrett's metaplasia with obesity. This may work through an increased risk of gastro-oesophageal reflux. Acid and bile are known to activate Cdx2 expression in oesophageal cells. It may also increase circulating levels of TNFalpha (tumour necrosis factor alpha), which activates Cdx2. In addition, there may be effects of diet on the composition of the bile.

Culture of human intestinal epithelial cell using the dissociating enzyme thermolysin and endothelin-3

Epithelium, a highly dynamic system, plays a key role in the homeostasis of the intestine. However, thus far a human intestinal epithelial cell line has not been established in many countries. Fetal tissue was selected to generate viable cell cultures for its sterile condition, effective generation, and differentiated character. The purpose of the present study was to culture human intestinal epithelial cells by a relatively simple method. Thermolysin was added to improve the yield of epithelial cells, while endothelin-3 was added to stimulate their growth. By adding endothelin-3, the achievement ratio (viable cell cultures/total cultures) was enhanced to 60% of a total of 10 cultures (initiated from 8 distinct fetal small intestines), allowing the generation of viable epithelial cell cultures. Western blot, real-time PCR and immunofluorescent staining showed that cytokeratins 8, 18 and mouse intestinal mucosa-1/39 had high expression levels in human intestinal epithelial cells. Differentiated markers such as sucrase-isomaltase, aminopeptidase N and dipeptidylpeptidase IV also showed high expression levels in human intestinal epithelial cells. Differentiated human intestinal epithelial cells, with the expression of surface markers (cytokeratins 8, 18 and mouse intestinal mucosa-1/39) and secretion of cytokines (sucrase-isomaltase, aminopeptidase N and dipeptidylpeptidase IV), may be cultured by the thermolysin and endothelin-3 method and maintained for at least 20 passages. This is relatively simple, requiring no sophisticated techniques or instruments, and may have a number of varied applications.

3-D tissue culture systems for the evaluation and optimization of nanoparticle-based drug carriers

Nanoparticle carriers are attractive vehicles for a variety of drug delivery applications. In order to evaluate nanoparticle formulations for biological efficacy, monolayer cell cultures are typically used as in vitro testing platforms. However, these studies sometimes poorly predict the efficacy of the drug in vivo. The poor in vitro and in vivo correlation may be attributed in part to the inability of two-dimensional cultures to reproduce extracellular barriers, and may also be due to differences in cell phenotype between cells cultured as monolayers and cells in native tissue. In order to more accurately predict in vivo results, it is desirable to test nanoparticle therapeutics in cells cultured in three-dimensional (3-D) models that mimic in vivo conditions. In this review, we discuss some 3-D culture systems that have been used to assess nanoparticle delivery and highlight several implications for nanoparticle design garnered from studies using these systems. While our focus will be on nanoparticle drug formulations, many of the systems discussed here could, or have been, used for the assessment of small molecule or peptide/protein drugs. We also offer some examples of advancements in 3-D culture that could provide even more highly predictive data for designing nanoparticle therapeutics for in vivo applications.

Organotypical tissue cultures from adult murine colon as an in vitro model of intestinal mucosa

Together with animal experiments, organotypical cell cultures are important models for analyzing cellular interactions of the mucosal epithelium and pathogenic mechanisms in the gastrointestinal tract. Here, we introduce a three-dimensional culture model from the adult mouse colon for cell biological investigations in an in vivo-like environment. These explant cultures were cultured for up to 2 weeks and maintained typical characteristics of the intestinal mucosa, including a high-prismatic epithelium with specific epithelial cell-to-cell connections, a basal lamina and various connective tissue cell types, as analyzed with immunohistological and electron microscopic methods. The function of the epithelium was tested by treating the cultures with dexamethasone, which resulted in a strong upregulation of the serum- and glucocorticoid-inducible kinase 1 similar to that found in vivo. The culture system was investigated in infection experiments with the fungal pathogen Candida albicans. Wildtype but not Deltacph1/Deltaefg1-knockout Candida adhered to, penetrated and infiltrated the epithelial barrier. The results demonstrate the potential usefulness of this intestinal in vitro model for studying epithelial cell-cell interactions, cellular signaling and microbiological infections in a three-dimensional cell arrangement.

Gene transfer to pre-hematopoietic and committed hematopoietic precursors in the early mouse yolk sac: a comparative study between in situ electroporation and retroviral transduction

BACKGROUND

Hematopoietic development in vertebrate embryos results from the sequential contribution of two pools of precursors independently generated. While intra-embryonic precursors harbour the features of hematopoietic stem cells (HSC), precursors formed earlier in the yolk sac (YS) display limited differentiation and self-renewal potentials. The mechanisms leading to the generation of the precursors in both sites are still largely unknown, as are the molecular basis underlying their different potential. A possible approach to assess the role of candidate genes is to transfer or modulate their expression/activity in both sites. We thus designed and compared transduction protocols to target either native extra-embryonic precursors, or hematopoietic precursors.

RESULTS

One transduction protocol involves transient modification of gene expression through in situ electroporation of the prospective blood islands, which allows the evolution of transfected mesodermal cells in their "normal" environment, upon organ culture. Following in situ electroporation of a GFP reporter construct into the YS cavity of embryos at post-streak (mesodermal/pre-hematopoietic precursors) or early somite (hematopoietic precursors) stages, high GFP expression levels as well as a good preservation of cell viability is observed in YS explants. Moreover, the erythro-myeloid progeny typical of the YS arises from GFP+ mesodermal cells or hematopoietic precursors, even if the number of targeted precursors is low. The second approach, based on retroviral transduction allows a very efficient transduction of large precursor numbers, but may only be used to target 8 dpc YS hematopoietic precursors. Again, transduced cells generate a progeny quantitatively and qualitatively similar to that of control YS.

CONCLUSION

We thus provide two protocols whose combination may allow a thorough study of both early and late events of hematopoietic development in the murine YS. In situ electroporation constitutes the only possible gene transfer method to transduce mesodermal/pre-hematopoietic precursors and analyze the earliest steps of hematopoietic development. Both in situ electroporation and retroviral transduction may be used to target early hematopoietic precursors, but the latter appears more convenient if a large pool of stably transduced cells is required. We discuss the assets and limitation of both methods, which may be alternatively chosen depending on scientific constraints.

In vitro models of intestinal epithelial cell differentiation

The intestinal epithelium is a particularly interesting tissue as (1) it is in a constant cell renewal from a stem cell pool located in the crypts which form, with the underlying fibroblasts, a stem cell niche and (2) the pluripotent stem cells give rise to four main cell types: enterocytes, mucus, endocrine, and Paneth cells. The mechanisms leading to the determination of phenotype commitment and cell-specific expressions are still poorly understood. Although transgenic mouse models are powerful tools for elucidating the molecular cascades implicated in these processes, cell culture approaches bring easy and elegant ways to study cellular behavior, cell interactions, and cell signaling pathways for example. In the present review, we will describe the major tissue culture technologies that allow differentiation of epithelial cells from undifferentiated embryonic or crypt cells. We will point to the necessity of the re-creation of a complex microenvironment that allows full differentiation process to occur. We will also summarize the characteristics and interesting properties of the cell lines established from human colorectal tumors.

Three-dimensional slice cultures from murine fetal gut for investigations of the enteric nervous system

Three-dimensional intestinal cultures offer new possibilities for the examination of growth potential, analysis of time specific gene expression, and spatial cellular arrangement of enteric nervous system in an organotypical environment. We present an easy to produce in vitro model of the enteric nervous system for analysis and manipulation of cellular differentiation processes. Slice cultures of murine fetal colon were cultured on membrane inserts for up to 2 weeks without loss of autonomous contractility. After slice preparation, cultured tissue reorganized within the first days in vitro. Afterward, the culture possessed more than 35 cell layers, including high prismatic epithelial cells, smooth muscle cells, glial cells, and neurons analyzed by immunohistochemistry. The contraction frequency of intestinal slice culture could be modulated by the neurotransmitter serotonin and the sodium channel blocker tetrodotoxin. Coculture experiments with cultured neurospheres isolated from enhanced green fluorescent protein (eGFP) transgenic mice demonstrated that differentiating eGFP-positive neurons were integrated into the intestinal tissue culture. This slice culture model of enteric nervous system proved to be useful for studying cell-cell interactions, cellular signaling, and cell differentiation processes in a three-dimensional cell arrangement.