Correlation between Musashi-1 and c-hairy-1 expression and cell proliferation activity in the developing intestine and stomach of both chicken and mouse

MiMIC analysis reveals an isoform specific role for Drosophila Musashi in follicle stem cell maintenance and escort cell function

The Drosophila ovary is regenerated from germline and somatic stem cell populations that have provided fundamental conceptual understanding on how adult stem cells are regulated within their niches. Recent ovarian transcriptomic studies have failed to identify mRNAs that are specific to follicle stem cells (FSCs), suggesting that their fate may be regulated post-transcriptionally. We have identified that the RNA-binding protein, Musashi (Msi) is required for maintaining the stem cell state of FSCs. Loss of msi function results in stem cell loss, due to a change in differentiation state, indicated by upregulation of Lamin C in the stem cell population. In msi mutant ovaries, Lamin C upregulation was also observed in posterior escort cells that interact with newly formed germ cell cysts. Mutant somatic cells within this region were dysfunctional, as evidenced by the presence of germline cyst collisions, fused egg chambers and an increase in germ cell cyst apoptosis. The msi locus produces two classes of mRNAs (long and short). We show that FSC maintenance and escort cell function specifically requires the long transcripts, thus providing the first evidence of isoform-specific regulation in a population of Drosophila epithelial cells. We further demonstrate that although male germline stem cells have previously been shown to require Msi function to prevent differentiation this is not the case for female germline stem cells, indicating that these similar stem cell types have different requirements for Msi, in addition to the differential use of Msi isoforms between soma and germline. In summary, we show that different isoforms of the Msi RNA-binding protein are expressed in specific cell populations of the ovarian stem cell niche where Msi regulates stem cell differentiation, niche cell function and subsequent germ cell survival and differentiation.

Development and Functional Properties of Intestinal Mucus Layer in Poultry

Intestinal mucus plays important roles in protecting the epithelial surfaces against pathogens, supporting the colonization with commensal bacteria, maintaining an appropriate environment for digestion, as well as facilitating nutrient transport from the lumen to the underlying epithelium. The mucus layer in the poultry gut is produced and preserved by mucin-secreting goblet cells that rapidly develop and mature after hatch as a response to external stimuli including environmental factors, intestinal microbiota as well as dietary factors. The ontogenetic development of goblet cells affects the mucin composition and secretion, causing an alteration in the physicochemical properties of the mucus layer. The intestinal mucus prevents the invasion of pathogens to the epithelium by its antibacterial properties (e.g. β-defensin, lysozyme, avidin and IgA) and creates a physical barrier with the ability to protect the epithelium from pathogens. Mucosal barrier is the first line of innate defense in the gastrointestinal tract. This barrier has a selective permeability that allows small particles and nutrients passing through. The structural components and functional properties of mucins have been reviewed extensively in humans and rodents, but it seems to be neglected in poultry. This review discusses the impact of age on development of goblet cells and their mucus production with relevance for the functional characteristics of mucus layer and its protective mechanism in the chicken’s intestine. Dietary factors directly and indirectly (through modification of the gut bacteria and their metabolic activities) affect goblet cell proliferation and differentiation and can be used to manipulate mucosal integrity and dynamic. However, the mode of action and mechanisms behind these effects need to be studied further. As mucins resist to digestion processes, the sloughed mucins can be utilized by bacteria in the lower part of the gut and are considered as endogenous loss of protein and energy to animal. Hydrothermal processing of poultry feed may reduce this loss by reduction in mucus shedding into the lumen. Given the significance of this loss and the lack of precise data, this matter needs to be carefully investigated in the future and the nutritional strategies reducing this loss have to be defined better.

Cellular Composition and Differentiation Signaling in Chicken Small Intestinal Epithelium

The small intestine plays an important role for animals to digest and absorb nutrients. The epithelial lining of the intestine develops from the embryonic endoderm of the embryo. The mature intestinal epithelium is composed of different types of functional epithelial cells that are derived from stem cells, which are located in the crypts. Chickens have been widely used as an animal model for researching vertebrate embryonic development. However, little is known about the molecular basis of development and differentiation within the chicken small intestinal epithelium. This review introduces processes of development and growth in the chicken gut, and compares the cellular characteristics and signaling pathways between chicken and mammals, including Notch and Wnt signaling that control the differentiation in the small intestinal epithelium. There is evidence that the chicken intestinal epithelium has a distinct cellular architecture and proliferation zone compared to mammals. The establishment of an in vitro cell culture model for chickens will provide a novel tool to explore molecular regulation of the chicken intestinal development and differentiation.

Molecular signatures of epithelial oviduct cells of a laying hen (Gallus gallus domesticus) and quail (Coturnix japonica)

Background

In this work we have determined molecular signatures of oviduct epithelial and progenitor cells. We have proposed a panel of selected marker genes, which correspond with the phenotype of oviduct cells of a laying hen (Gallus gallus domesticus) and quail (Coturnix japonica). We demonstrated differences in characteristics of those cells, in tissue and in vitro, with respect to different anatomical and functional parts of the oviduct (infundibulum (INF), distal magnum (DM, and proximal magnum (PM)). The following gene expression signatures were studied: (1) oviduct markers (estrogen receptor 1, ovalbumin, and SPINK7 - ovomucoid), (2) epithelial markers (keratin 5, keratin 14, and occludin) and (3) stem-like/progenitor markers (CD44 glycoprotein, LGR5, Musashi-1, and sex determining region Y-box 9, Nanog homebox, OCT4/cPOUV gene encoding transcription factor POU5F3).

Results

In chicken, the expression of oviduct markers increased toward the proximal oviduct. Epithelial markers keratin14 and occludin were high in distal oviduct and decreased toward the proximal magnum. In quail oviduct tissue, the gene expression pattern of oviduct/epithelial markers was similar to chicken. The markers of progenitors/stemness in hen oviduct (Musashi-1 and CD44 glycoprotein) had the highest relative expression in the infundibulum and decreased toward the proximal magnum. In quail, we found significant expression of four progenitor markers (LGR5 gene, SRY sex determining region Y-box 9, OCT4/cPOUV gene, and CD44 glycoprotein) that were largely present in the distal oviduct. After in vitro culture of oviduct cells, the gene expression pattern has changed. High secretive potential of magnum-derived cells diminished by using decreased abundance of mRNA. On the other hand, chicken oviduct cells originating from the infundibulum gained ability to express OVM and OVAL. Epithelial character of the cells was maintained in vitro. Among progenitor markers, both hen and quail cells expressed high level of SOX9, LGR5 and Musashi-1.

Conclusion

Analysis of tissue material revealed gradual increase/decrease pattern in majority of the oviduct markers in both species. This pattern changed after the oviductal cells have been cultured in vitro. The results can provide molecular tools to validate the phenotype of in vitro biological models from reproductive tissue.

Electronic supplementary material

The online version of this article (10.1186/s12861-018-0168-2) contains supplementary material, which is available to authorized users.

Knockout of RNA Binding Protein MSI2 Impairs Follicle Development in the Mouse Ovary: Characterization of MSI1 and MSI2 during Folliculogenesis

Characterizing the mechanisms underlying follicle development in the ovary is crucial to understanding female fertility and is an area of increasing research interest. The RNA binding protein Musashi is essential for post-transcriptional regulation of oocyte maturation in Xenopus and is expressed during ovarian development in Drosophila. In mammals Musashi is important for spermatogenesis and male fertility, but its role in the ovary has yet to be characterized. In this study we determined the expression of mammalian Musashi proteins MSI1 and MSI2 during mouse folliculogenesis, and through the use of a MSI2-specific knockout mouse model we identified that MSI2 is essential for normal follicle development. Time-course characterization of MSI1 and MSI2 revealed distinct differences in steady-state mRNA levels and protein expression/localization at important developmental time-points during folliculogenesis. Using a gene-trap mouse model that inactivates Msi2, we observed a significant decrease in ovarian mass, and change in follicle-stage composition due to developmental blocking of antral stage follicles and pre-antral follicle loss through atresia. We also confirmed that hormonally stimulated Msi2-deficient mice produce significantly fewer MII oocytes (60.9% less than controls, p < 0.05). Furthermore, the majority of these oocytes are of poor viability (62.2% non-viable/apoptotic, p < 0.05), which causes a reduction in female fertility evidenced by decreased litter size in Msi2-deficient animals (33.1% reduction to controls, p < 0.05). Our findings indicate that MSI1 and MSI2 display distinct expression profiles during mammalian folliculogenesis and that MSI2 is required for pre-antral follicle development.

The Musashi family RNA-binding proteins in stem cells

The Musashi family is an evolutionarily conserved group of RNA-binding proteins. In mammal, two members of the group, Msi1 and Msi2, have been identified to date. Msi1 is considered to play roles in maintaining the stem cell status (stemness) of neural stem/progenitor cells in adults and in the development of central nervous system through translational regulation of its target mRNAs, which encode regulators of signal transduction and the cell cycle. Recently, strong expression of Msi1 in various somatic stem/progenitor cells of adult tissues, such as eye, gut, stomach, breast, and hair follicle, has been reported. The protein is also expressed in various cancer cells, and ectopically emerging cells have been found in neural tissues of patients with diseases involving neural disorder, including epilepsy. Many novel target mRNAs and regulatory pathways of Msi1 have been reported in recent years. Here, we present a review of the functions and action mechanisms of Msi1 protein and discuss possible directions for further study.

Transformation of the intestinal epithelium by the MSI2 RNA-binding protein

The MSI2 RNA binding protein is a potent oncogene playing key roles in hematopoietic stem cell homeostasis and malignant hematopoiesis. Here we demonstrate that MSI2 is expressed in the intestinal stem cell compartment, that its expression is elevated in colorectal adenocarcinomas, and that MSI2 loss of function abrogates colorectal cancer cell growth. MSI2 gain of function in the intestinal epithelium in a drug inducible mouse model is sufficient to phenocopy many of the morphological and molecular consequences of acute loss of the APC tumor suppressor in the intestinal epithelium in a Wnt-independent manner. Transcriptome-wide RNA-binding analysis indicates that MSI2 acts as a pleiotropic inhibitor of known intestinal tumor suppressors including Lrig1, Bmpr1a, Cdkn1a, and Pten. Finally, we demonstrate that inhibition of the PDK-AKT-mTORC1 axis rescues oncogenic consequences of MSI2 induction. Taken together, our findings identify MSI2 as a central component in an unappreciated oncogenic pathway promoting intestinal transformation.

Enriched Intestinal Stem Cell Seeding Improves the Architecture of Tissue-Engineered Intestine

OBJECTIVE

To develop a methodology to separate intestinal stem cell (ISC)-enriched crypts from differentiated epithelial cell (DEC)-containing villi to improve the morphology of tissue-engineered intestine (TEI).

METHODS

Small intestinal tissues from 5- to 7-day-old transgenic Lgr5-EGFP mice (with fluorescently labeled ISCs) were used to measure the height of villi and the depth of crypts. Based on the significant size difference between crypts and villi, a novel cell filtration system was developed. Filtration of mixed organoid units from full-thickness intestine of transgenic Lgr5-EGFP mice allowed determination of the percentage of ISCs in the different size-based filtration fractions obtained. In vivo, 5-7-day-old Lewis rat pups were used as cell donors to obtain purified crypts and villi, and the dams of the pups served as recipients. Flat and tubular polyglycolic acid (PGA) scaffolds were seeded with either ISC-enriched crypts or DEC-containing villi and implanted intra-abdominally on the anterior abdominal wall. After 1, 3, 7, 14, 21, and 28 days of in vivo incubation, explants were processed for histologic evaluation.

RESULTS

Small intestine from transgenic Lgr5-EGFP mice contained villi with an average height of 134.89±41.91 μm and crypts with an average depth of 49.59±8.95 μm. After filtration, we found that the 100-200 μm fractions contained relatively pure villi in which DECs were located, whereas the 25-70 μm range fractions contained concentrated crypts in which ISCs were located. In vivo, flat PGA scaffolds implanted with purified crypts formed well-developed mucosa by day 14 postimplantation, whereas flat scaffolds seeded with villi were replaced with fibrous tissue. Tubular scaffolds seeded with the crypt fraction developed a well-formed mucosal layer on the interior surface, with 80.9% circumferential mucosal engraftment and an average villous height of 478±65 μm, which was very close to native intestine (512±98 μm), whereas tubular scaffolds seeded with the villous fraction only had 21.7% circumferential mucosal engraftment and an average villous height of 243±78 μm.

CONCLUSION

The novel filtration system described can effectively and efficiently isolate ISC-containing crypts. TEI produced from ISC-containing crypts has an improved morphology that is similar to native intestine.

A conserved three-nucleotide core motif defines Musashi RNA binding specificity

Musashi (MSI) family proteins control cell proliferation and differentiation in many biological systems. They are overexpressed in tumors of several origins, and their expression level correlates with poor prognosis. MSI proteins control gene expression by binding RNA and regulating its translation. They contain two RNA recognition motif (RRM) domains, which recognize a defined sequence element. The relative contribution of each nucleotide to the binding affinity and specificity is unknown. We analyzed the binding specificity of three MSI family RRM domains using a quantitative fluorescence anisotropy assay. We found that the core element driving recognition is the sequence UAG. Nucleotides outside of this motif have a limited contribution to binding free energy. For mouse MSI1, recognition is determined by the first of the two RRM domains. The second RRM adds affinity but does not contribute to binding specificity. In contrast, the recognition element for Drosophila MSI is more extensive than the mouse homolog, suggesting functional divergence. The short nature of the binding determinant suggests that protein-RNA affinity alone is insufficient to drive target selection by MSI family proteins.

Brief report: musashi1-eGFP mice, a new tool for differential isolation of the intestinal stem cell populations

The intestinal epithelium self-renews rapidly and continuously throughout life, due to the presence of crypt stem cells. Two pools of these cells have been identified in the small intestine, which differ in position ("+4" or the bottom of the crypts), expression of specific markers (Bmi1/mTert or Lgr5/Ascl2), and cell cycle characteristics. Interestingly, the RNA-binding protein Musashi1 is expressed in both populations and therefore a potential marker for both stem cell types. In order to locate, isolate, and study Musashi1-expressing cells within the intestinal epithelium, we generated transgenic mice expressing GFP fluorescent protein under the control of a 7-kb Msi1 promoter. The expression pattern of GFP in the intestinal crypts of both small and large intestines completely overlapped that of Musashi1, validating our model. By using fluorescence-activated cell sorting, cellular, and molecular analyses, we showed that GFP-positive Msi1-expressing cells are divided into two major pools corresponding to the Lgr5- and mTert-expressing stem cells. Interestingly, monitoring the cell cycle activity of the two sorted populations reveals that they are both actively cycling, although differences in cell cycle length were confirmed. Altogether, our new reporter mouse model based upon Musashi1 expression is a useful tool to isolate and study stem cells of the intestinal epithelium. Moreover, these mice uniquely enable the concomitant study of two pools of intestinal stem cells within the same animal model.

Stem cells and biopharmaceuticals: vital roles in the growth of tissue-engineered small intestine

Tissue engineering currently constitutes a complex, multidisciplinary field exploring ideal sources of cells in combination with scaffolds or delivery systems in order to form a new, functional organ to replace native organ lack or loss. Short bowel syndrome (SBS) is a life-threatening condition with high morbidity and mortality rates in children. Current therapeutic strategies consist of costly and risky allotransplants that demand lifelong immunosuppression. A promising alternative is the implantation of autologous organoid units (OU) to create a tissue-engineered small intestine (TESI). This strategy is proven to be stem cell and mesenchyme dependent. Intestinal stem cells (ISCs) are located at the base of the crypt and are responsible for repopulating the cycling mucosa up to the villus tip. The stem cell niche governs the biology of ISCs and, together with the rest of the epithelium, communicates with the underlying mesenchyme to sustain intestinal homeostasis. Biopharmaceuticals are broadly used in the clinic to activate or enhance known signaling pathways and may greatly contribute to the development of a full-thickness intestine by increasing mucosal surface area, improving blood supply, and determining stem cell fate. This review will focus on tissue engineering as a means of building the new small intestine, highlighting the importance of stem cells and recombinant peptide growth factors as biopharmaceuticals.

Tissue engineering: a promising therapeutic approach to necrotizing enterocolitis

Tissue engineering is a promising potential candidate for treating intestinal failure resulting from necrotizing enterocolitis. This requires the acquisition, preparation and implantation of autologous organoid units. This may be affected by the complexities of periods of storage of viable donor tissue and delayed implantation. This chapter addresses the development, methodology, and application of tissue-engineered intestine in the experimental and clinical setting. Tissue engineering has the potential of avoiding the inherent toxicities of intestinal transplantation and prolonged immunosuppression.

Tissue engineering the small intestine

Short bowel syndrome (SBS) results from the loss of a highly specialized organ, the small intestine. SBS and its current treatments are associated with high morbidity and mortality. Production of tissue-engineered small intestine (TESI) from the patient's own cells could restore normal intestinal function via autologous transplantation. Improved understanding of intestinal stem cells and their niche have been coupled with advances in tissue engineering techniques. Originally described by Vacanti et al of Massachusetts General Hospital, TESI has been produced by in vivo implantation of organoid units. Organoid units are multicellular clusters of epithelium and mesenchyme that may be harvested from native intestine. These clusters are loaded onto a scaffold and implanted into the host omentum. The scaffold provides physical support that permits angiogenesis and vasculogenesis of the developing tissue. After a period of 4 weeks, histologic analyses confirm the similarity of TESI to native intestine. TESI contains a differentiated epithelium, mesenchyme, blood vessels, muscle, and nerve components. To date, similar experiments have proved successful in rat, mouse, and pig models. Additional experiments have shown clinical improvement and rescue of SBS rats after implantation of TESI. In comparison with the group that underwent massive enterectomy alone, rats that had surgical anastomosis of TESI to their shortened intestine showed improvement in postoperative weight gain and serum B12 values. Recently, organoid units have been harvested from human intestinal samples and successfully grown into TESI by using an immunodeficient mouse host. Current TESI production yields approximately 3 times the number of cells initially implanted, but improvements in the scaffold and blood supply are being developed in efforts to increase TESI size. Exciting new techniques in stem cell biology and directed cellular differentiation may generate additional sources of autologous intestinal tissue for direct translation to human therapy.

The RNA-Binding Protein Musashi1: A Major Player in Intestinal Epithelium Renewal and Colon Cancer Development

Aberrant gene expression is the cause and the consequence of tumorigenesis. A major component of gene expression is translation regulation; a process whose main players are RNA-binding-proteins (RBPs). More than 800 RBPs have been identified in the human genome and several of them have been shown to control gene networks associated with relevant cancer processes. A more systematic characterization of RBPs starts to reveal that similar to transcription factors, they can function as tumor suppressors or oncogenes. A relevant example is Musashi1 (Msi1), which is emerging as a critical regulator of tumorigenesis in multiple cancer types, including colon cancer. Msi1 is a stem marker in several tissues and is critical in maintaining the balance between self-renewal and differentiation. However, a boost in Msi1 expression can most likely lead cells towards an oncogenic pathway. In this article, we discuss the parallels between Msi1 function in normal renewal of intestinal epithelium and in colon cancer.

Tissue-engineering of the gastrointestinal tract

PURPOSE OF REVIEW

The purpose of this review is to describe recent advancements in tissue-engineering of the gastrointestinal system. For some patients, a congenital or acquired defect in the alimentary system results in digestive or nutritional deficiencies requiring intervention. Unfortunately, these treatments are associated with morbid complications. Advances in the growth of tissue-engineered esophagus, stomach, small intestine, colon and anus have been made in recent years. The progress reviewed here hopefully will someday benefit patients with gastrointestinal organ loss by providing a tissue replacement with morphology and function similar to native tissue.

RECENT FINDINGS

In native gastrointestinal tissue, epithelial homeostasis is governed largely by the interaction of the stem cell and its surrounding cellular niche. In particular, the small intestinal stem cell populations identified as the crypt base columnar cell (CBCC) and at cell position 4 (cp4) are responsible for mucosal maintenance and response to injury. This work influences efforts to generate bioengineered tissues for both in-vitro mucosal models and full-thickness in-vivo tissue-engineered esophagus, stomach, intestine and colon.

SUMMARY

Gastrointestinal organ loss is a challenge to manage. Current therapy can be life-saving, but is associated with morbid complications. Tissue-engineering will someday restore normal gastrointestinal function and eliminate the need for nutritional supplementation or transplant.

Generating intestinal tissue from stem cells: potential for research and therapy

Intestinal resection and malformations in adult and pediatric patients result in devastating consequences. Unfortunately, allogeneic transplantation of intestinal tissue into patients has not been met with the same measure of success as the transplantation of other organs. Attempts to engineer intestinal tissue in vitro include disaggregation of adult rat intestine into subunits called organoids, harvesting native adult stem cells from mouse intestine and spontaneous generation of intestinal tissue from embryoid bodies. Recently, by utilizing principles gained from the study of developmental biology, human pluripotent stem cells have been demonstrated to be capable of directed differentiation into intestinal tissue in vitro. Pluripotent stem cells offer a unique and promising means to generate intestinal tissue for the purposes of modeling intestinal disease, understanding embryonic development and providing a source of material for therapeutic transplantation.

Characterization of the RNA-binding protein Musashi1 in zebrafish

Musashi (Msi) is an evolutionarily conserved gene family of RNA-binding proteins (RBPs) that is preferentially expressed in the nervous system. The first member of the Msi family was identified in Drosophila. Drosophila Msi plays an important role in regulating asymmetric cell division of the sensory organ precursor cells. The mammalian orthologs, including human and mouse Musashi1 (Msi1), are neural RBPs that are strongly expressed in fetal and adult neural stem/progenitor cells (NS/PCs). Mammalian Msi1 contributes to self renewal of NS/PCs through translational regulation of several target mRNAs. In this study, the zebrafish Msi ortholog zMsi1 was identified and characterized. The normal spatial and temporal expression profiles for both protein and mRNA were determined. A series of splice variants were detected. Overall, zMsi1 was strongly expressed in neural tissue in early stages of development and exhibited similarity to mammalian Msi1 expression patterns. To reveal the in vivo function of zMsi1, morpholinos against Msi1 were introduced into one-cell stage zebrafish embryos. Knock down of zmsi1 frequently resulted in aberrant formation of the Central Nervous System (CNS). These results suggest that Msi1 plays roles in CNS development in vertebrates. This article is part of a Special Issue entitled "RNA-Binding Proteins".

Musashi1 expression cells derived from mouse embryonic stem cells can be enriched in side population isolated by fluorescence activated cell sorter

Background

Purifying stem cells is an inevitable process for further investigation and cell-therapy. Sorting side population (SP) cells is generally regarded as an effective method to enrich for progenitor cells. This study was to explore whether sorting SP could enrich for the Musashi1 (Msi1) positive cells from Msi1 high expression cells (Msi1^high cells) derived from mouse embryonic stem cells (ESCs) in vitro.

Results

In this study, Msi1^high cell population derived from ESCs were stained by Hoechst 33342, and then the SP and non-SP (NSP) fractions were analyzed and sorted by fluorescence activated cell sorter. Subsequently, the expressions of Msi1 and other markers for neural and intestinal stem cells in SP and NSP were respectively detected. SP and NSP cells were hypodermically engrafted into the backs of NOD/SCID mice to form grafts. The developments of neural and intestinal epithelial cells in these grafts were investigated. SP fraction was identified and isolated from Msi1^high cell population. The expression of Msi1 in SP fraction was significantly higher than that in NSP fraction and unsorted Msi1^high cells (P< 0.05). Furthermore, the markers for neural cells and intestinal epithelial cells were more highly expressed in the grafts from SP fraction than those from NSP fraction (P< 0.05).

Conclusions

SP fraction, isolated from Msi1^high cells, contains almost all the Msi1-positive cells and has the potential to differentiate into neural and intestinal epithelial cells in vivo. Sorting SP fraction could be a convenient and practical method to enrich for Msi1-positive cells from the differentiated cell population derived from ESCs.

Translational control in germ cell development: A role for the RNA-binding proteins Musashi-1 and Musashi-2

Mammalian gametogenesis is a complex process involving specialised cell cycle progression and differentiation. As part of their differentiation, germ cells experience periods of transcriptional inactivation and chromatin inaccessibility whilst continuing to coordinate the correct temporal and spatial expression of genes required for continued development. To overcome these obstacles, mammalian germ cells express a wide variety of sequence-specific RNA-binding proteins, which assist in the translational control of many mRNA transcripts which are produced and stored during periods of high mRNA synthesis. In this review we focus on the Musashi family of RNA-binding proteins, a highly conserved family of translational regulatory proteins whose recent identification in germ cells of Drosophila and Xenopus, as well as their well described role in processes such as cell cycle progression and stem cell identity, has led us to investigate the role of these proteins in mammalian germ cell development.

Diversity counts. Visualizing pretumor progression in the gastrointestinal tract

Tumor progression is critically dependent on the selection of genetic alterations. This clonal evolution can be traced to the stage preceding visible tumor formation called pretumor progression, in which genetic change occurs without visible change. Recently, the identification of intestinal stem cell markers in animal models has made visualization of stem cells possible in vivo. Translating this work to the clinical setting by visualizing stem cells in patient material may allow us to understand differences in patients' vulnerability to cancer development and target preventive measures to high-risk groups. In this review article, we examine some of the analytic methods currently used in research settings tracing stem cell dynamics.

A multicellular approach forms a significant amount of tissue-engineered small intestine in the mouse

Tissue-engineered small intestine (TESI) has successfully been used to rescue Lewis rats after massive small bowel resection. In this study, we transitioned the technique to a mouse model, allowing investigation of the processes involved during TESI formation through the transgenic tools available in this species. This is a necessary step toward applying the technique to human therapy. Multicellular organoid units were derived from small intestines of transgenic mice and transplanted within the abdomen on biodegradable polymers. Immunofluorescence staining was used to characterize the cellular processes during TESI formation. We demonstrate the preservation of Lgr5- and DcamKl1-positive cells, two putative intestinal stem cell populations, in proximity to their niche mesenchymal cells, the intestinal subepithelial myofibroblasts (ISEMFs), at the time of implantation. Maintenance of the relationship between ISEMF and crypt epithelium is observed during the growth of TESI. The engineered small intestine has an epithelium containing a differentiated epithelium next to an innervated muscularis. Lineage tracing demonstrates that all the essential components, including epithelium, muscularis, nerves, and some of the blood vessels, are of donor origin. This multicellular approach provides the necessary cell population to regenerate large amounts of intestinal tissue that could be used to treat short bowel syndrome.

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.

Musashi 1-positive cells derived from mouse embryonic stem cells can differentiate into neural and intestinal epithelial-like cells in vivo

Msi1 (Musashi 1) is regarded as a marker for neural and intestinal epithelial stem cells. However, it is still unclear whether Msi1-positive cells derived from mouse embryonic stem cells have the ability to differentiate into neural or intestinal epithelial cells. A pMsi1-GFP (green fluorescent protein) reporter plasmid was constructed in order to sort Msi1-positive cells out of the differentiated cell population. The GFP-positive cells (i.e. Msi1-positive cells) were sorted by FACS and were hypodermically engrafted into the backs of NOD/SCID (non-obese diabetic/severe combined immunodeficient) mice. The presence of neural and intestinal epithelial cells in the grafts was detected. Msi1 was highly expressed in the GFP-positive cells, but not in the GFP-negative cells. The markers for neural cells (Nestin and Tubulin β III) and intestinal epithelial cells [FABP2 (fatty acid binding protein 2), Lyz (lysozyme) and ChA (chromogranin A)] were more highly expressed in the grafts from Msi1-positive cells than those from Msi1-negative cells (P<0.05). The grafts from the Msi1-negative cells contained more mesodermal-like tissues than those from the Msi1-positive cells. The pMsi1-GFP vector can be used to sort Msi1-positive cells from a cell population derived from mouse embryonic stem cells. The Msi1-positive cells can differentiate into neural and intestinal epithelial-like cells in vivo.

Context-dependent regulation of Musashi-mediated mRNA translation and cell cycle regulation

Musashi-mediated mRNA translational control has been implicated in the promotion of physiological and pathological stem cell proliferation. During self-renewal of mammalian stem cells, Musashi has been proposed to act to repress the translation of mRNAs encoding inhibitors of cell cycle progression. By contrast, in maturing Xenopus oocytes Musashi activates translation of target mRNAs that encode proteins promoting cell cycle progression. The mechanisms directing Musashi to differentially control mRNA translation in mammalian stem cells and Xenopus oocytes is unknown. In this study, we demonstrate that the mechanisms defining Musashi function lie within the cellular context. Specifically, we show that murine Musashi acts as an activator of translation in maturing Xenopus oocytes while Xenopus Musashi functions as a repressor of target mRNA translation in mammalian cells. We further demonstrate that within the context of a primary mammalian neural stem/progenitor cell, Musashi can be converted from a repressor of mRNA translation to an activator of translation in response to extracellular stimuli. We present current models of Musashi-mediated mRNA translational control and discuss possible mechanisms for regulating Musashi function. An understanding of these mechanisms presents exciting possibilities for development of therapeutic targets to control physiological and pathological stem cell proliferation.

Intestinal epithelial cells in vitro

Recent advances in the biology of stem cells has resulted in significant interest in the development of normal epithelial cell lines from the intestinal mucosa, both to exploit the therapeutic potential of stem cells in tissue regeneration and to develop treatment models of degenerative disorders of the digestive tract. However, the difficulty of propagating cell lines of normal intestinal epithelium has impeded research into the molecular mechanisms underlying differentiation of stem/progenitor cells into the various intestinal lineages. Several short-term organ/organoid and epithelial cell culture models have been described. There is a dearth of long-term epithelial and/or stem cell cultures of intestine. With an expanding role of stem cells in the treatment of degenerative disorders, there is a critical need for additional efforts to develop in vitro models of stem/progenitor epithelial cells of intestine. The objective of this review is to recapitulate the current status of technologies and knowledge for in vitro propagation of intestinal epithelial cells, markers of the intestinal stem cells, and gene and protein expression profiles of the intestinal cellular differentiation.

The intestinal stem cell

The epithelium of the adult mammalian intestine is in a constant dialog with its underlying mesenchyme to direct progenitor proliferation, lineage commitment, terminal differentiation, and, ultimately, cell death. The epithelium is shaped into spatially distinct compartments that are dedicated to each of these events. While the intestinal epithelium represents the most vigorously renewing adult tissue in mammals, the stem cells that fuel this self-renewal process have been identified only recently. The unique epithelial anatomy makes the intestinal crypt one of the most accessible models for the study of adult stem cell biology. This review attempts to provide a comprehensive overview of four decades of research on crypt stem cells.

The expression of Msi-1 and its significance in small intestinal mucosa severely damaged by high-dose 5-FU

OBJECTIVE

The purpose was to investigate the expression of musashi-1 (msi-1) and its significances in small intestinal mucosa that was severely damaged by high-dose 5-FU.

METHODS

A total of 40 adult C57BL/6J mice were divided into two groups: the control group (n = 8, group A) and experimental group (n = 32). The mice in the control group were treated with PBS by intraperitoneal injection, and the other mice were treated with high-dose 5-FU (150 mg/kg body weight for 5 consecutive days) by intraperitoneal injection. At the 1st (group B), 3rd (group C) and 5th (group D) day after treatment with high-dose 5-FU, the dying mice were killed, HE staining and immunohistochemical techniques were used to detect the expression of the putative marker of intestinal epithelial stem cells, msi-1, in samples of the middle intestine from these mice, and the percentage of the msi-1-positive cells from the intestinal mucosal cells of the mice in group B was detected by FACS.

RESULTS

After treatment with high-dose 5-FU, the intestinal mucosa suffered severe damage: the villi and crypts disappeared, the number of msi-1-positive cells increased greatly, the intestinal epithelial cells could be divided into two fractions by FACS, and the percentage of msi-1-positive cells was up to 67.75% in the fraction in which the value of FSC was higher.

CONCLUSIONS

After treatment with high-dose 5-FU, the percentage of intestinal stem cells had increased significantly, which was useful for the further isolation and enrichment of intestinal epithelial stem cells.

Molecular analysis of endoderm regionalization

We have engaged in a number of studies in our laboratory that have focused on the molecular mechanisms underlying gut formation, with particular attention being paid to the establishment of regional differences found in the entire gut and within each digestive organ. We have found from our analyses that the presumptive fate of the endoderm in the embryos of vertebrates is determined quite early during development, but the realization of this fate often requires molecular cues from the neighboring tissues such as the lateral plate mesoderm and the mesenchyme derived from it. The mesenchyme seems often to exert instructive or supportive induction effects and, in some cases, a completely inhibitory role during the differentiation of the endodermal epithelium. In addition, many reports on the formation of the stomach, intestine, liver and salivary gland in vertebrates, and of Drosophila gut, all indicate that the morphogenesis and cytodifferentiation of these organs are regulated by the regulated expression of genes encoding growth factors and transcription factors. We have further shown that the epithelium can regulate the differentiation of the mesenchyme into the connective tissue and the smooth muscle layers, thus demonstrating the occurrence of literally interactive processes in the development of the digestive organs.

Helicobacter pylori infection induces candidate stem cell marker Musashi-1 in the human gastric epithelium

Musashi-1 (Msi-1), a mammalian neural RNA-binding protein, has been found to play important roles in the maintenance of stem cell states and differentiation in neural stem cells and mouse intestinal cells. We explored Msi-1 expression and its potential implications in the human stomach. Reverse transcription-PCR revealed that Msi-1 levels were significantly higher in the corpus than in antrum in Helicobacter pylori (Hp)-infected patients (n = 49) (P < 0.00001) in paired biopsy samples, whereas they were low and comparable at these two sites in Hp-negative patients (n = 31). Msi-1 levels were significantly higher in the Hp-infected corpus (n = 107) than in the Hp-negative corpus (n = 69) (P < 0.00000001). Immunohistochemistry and in situ hybridization demonstrated that Msi-1 was expressed at the base and neck/isthmus region of the fundic glands and partly co-expressed in Ki-67-positive cells in the corpus and antrum. Msi-1 levels correlated with Hp density (P < 0.05). Based on these results, we conclude that Hp infection strongly induces Msi-1 in the corpus. Given its expression in dividing cells, Msi-1 may modulate the state of gastric progenitor cells.

PTEN-deficient intestinal stem cells initiate intestinal polyposis

Intestinal polyposis, a precancerous neoplasia, results primarily from an abnormal increase in the number of crypts, which contain intestinal stem cells (ISCs). In mice, widespread deletion of the tumor suppressor Phosphatase and tensin homolog (PTEN) generates hamartomatous intestinal polyps with epithelial and stromal involvement. Using this model, we have established the relationship between stem cells and polyp and tumor formation. PTEN helps govern the proliferation rate and number of ISCs and loss of PTEN results in an excess of ISCs. In PTEN-deficient mice, excess ISCs initiate de novo crypt formation and crypt fission, recapitulating crypt production in fetal and neonatal intestine. The PTEN-Akt pathway probably governs stem cell activation by helping control nuclear localization of the Wnt pathway effector beta-catenin. Akt phosphorylates beta-catenin at Ser552, resulting in a nuclear-localized form in ISCs. Our observations show that intestinal polyposis is initiated by PTEN-deficient ISCs that undergo excessive proliferation driven by Akt activation and nuclear localization of beta-catenin.

Intestinal epithelial stem cells and progenitors

The adult intestinal epithelium contains a relatively simple, highly organized, and readily accessible stem cell system. Excellent methods exist for the isolation of intestinal epithelium from adults, and as a result collecting large quantities of intestinal stem and progenitor cells for study or culture and subsequent clinical applications should be routine. It is not, however, for two reasons: (1) adult intestinal epithelial cells rapidly initiate apoptosis on detachment from the basement membrane, and (2) in vitro conditions necessary for survival, proliferation, and differentiation are poorly understood. Thus to date the study of intestinal stem and progenitor cells has been largely dependent on in vivo approaches. We discuss existing in vivo assays for stem and progenitor cell behavior as well as current methods for isolating and culturing the intestinal epithelium.