Clonality and life cycles of intestinal crypts explained by a state dependent stochastic model of epithelial stem cell organization

A mixed-effects stochastic model reveals clonal dominance in gene therapy safety studies

BACKGROUND

Mathematical models of haematopoiesis can provide insights on abnormal cell expansions (clonal dominance), and in turn can guide safety monitoring in gene therapy clinical applications. Clonal tracking is a recent high-throughput technology that can be used to quantify cells arising from a single haematopoietic stem cell ancestor after a gene therapy treatment. Thus, clonal tracking data can be used to calibrate the stochastic differential equations describing clonal population dynamics and hierarchical relationships in vivo.

RESULTS

In this work we propose a random-effects stochastic framework that allows to investigate the presence of events of clonal dominance from high-dimensional clonal tracking data. Our framework is based on the combination between stochastic reaction networks and mixed-effects generalized linear models. Starting from the Kramers-Moyal approximated Master equation, the dynamics of cells duplication, death and differentiation at clonal level, can be described by a local linear approximation. The parameters of this formulation, which are inferred using a maximum likelihood approach, are assumed to be shared across the clones and are not sufficient to describe situation in which clones exhibit heterogeneity in their fitness that can lead to clonal dominance. In order to overcome this limitation, we extend the base model by introducing random-effects for the clonal parameters. This extended formulation is calibrated to the clonal data using a tailor-made expectation-maximization algorithm. We also provide the companion  package RestoreNet, publicly available for download at https://cran.r-project.org/package=RestoreNet .

CONCLUSIONS

Simulation studies show that our proposed method outperforms the state-of-the-art. The application of our method in two in-vivo studies unveils the dynamics of clonal dominance. Our tool can provide statistical support to biologists in gene therapy safety analyses.

Shape-specific characterization of colorectal adenoma growth and transition to cancer with stochastic cell-based models

Colorectal adenoma are precursor lesions on the pathway to cancer. Their removal in screening colonoscopies has markedly reduced rates of cancer incidence and death. Generic models of adenoma growth and transition to cancer can guide the implementation of screening strategies. But adenoma shape has rarely featured as a relevant risk factor. Against this backdrop we aim to demonstrate that shape influences growth dynamics and cancer risk. Stochastic cell-based models are applied to a data set of 197,347 Bavarian outpatients who had colonoscopies from 2006-2009, 50,649 patients were reported with adenoma and 296 patients had cancer. For multi-stage clonal expansion (MSCE) models with up to three initiating stages parameters were estimated by fits to data sets of all shapes combined, and of sessile (70% of all adenoma), peduncular (17%) and flat (13%) adenoma separately for both sexes. Pertinent features of adenoma growth present themselves in contrast to previous assumptions. Stem cells with initial molecular changes residing in early adenoma predominantly multiply within two-dimensional structures such as crypts. For these cells mutation and division rates decrease with age. The absolute number of initiated cells in an adenoma of size 1 cm is small around 103, related to all bulk cells they constitute a share of about 10-5. The notion of very few proliferating stem cells with age-decreasing division rates is supported by cell marker experiments. The probability for adenoma transiting to cancer increases with squared linear size and shows a shape dependence. Compared to peduncular and flat adenoma, it is twice as high for sessile adenoma of the same size. We present a simple mathematical expression for the hazard ratio of interval cancers which provides a mechanistic understanding of this important quality indicator. We conclude that adenoma shape deserves closer consideration in screening strategies and as risk factor for transition to cancer.

Developing a reproducible protocol for culturing functional confluent monolayers of differentiated equine oviduct epithelial cells

We describe the development of two methods for obtaining confluent monolayers of polarized, differentiated equine oviduct epithelial cells (EOEC) in Transwell inserts and microfluidic chips. EOECs from the ampulla were isolated post-mortem and seeded either (1) directly onto a microporous membrane as differentiated EOECs (direct seeding protocol) or (2) first cultured to a confluent de-differentiated monolayer in conventional wells, then trypsinized and seeded onto a microporous membrane (re-differentiation protocol). Maintenance or induction of EOEC differentiation in these systems was achieved by air-liquid interface introduction. Monolayers cultured via both protocols were characterized by columnar, cytokeratin 19-positive EOECs in Transwell inserts. However, only the re-differentiation protocol could be transferred successfully to the microfluidic chips. Integrity of the monolayers was confirmed by transepithelial resistance measurements, tracer flux and the demonstration of an intimate network of tight junctions. Using the direct protocol, 28% of EOECs showed secondary cilia at the apical surface in a diffuse pattern. In contrast, re-differentiated polarized EOECs rarely showed secondary cilia in either culture system (>90% of the monolayers showed <1% ciliated EOECs). Occasionally (5-10%), re-differentiated monolayers with 11-27% EOECs with secondary cilia in a diffuse pattern were obtained. Additionally, nuclear progesterone receptor expression was found to be inhibited by simulated luteal phase hormone concentrations, and sperm binding to cilia was higher for re-differentiated EOEC monolayers exposed to estrogen-progesterone concentrations mimicking the follicular rather than luteal phase. Overall, a functional equine oviduct model was established with close morphological resemblance to in vivo oviduct epithelium.

The evolution of metapopulation dynamics and the number of stem cells in intestinal crypts and other tissue structures in multicellular bodies

Carcinogenesis is a process of somatic evolution. Previous models of stem and transient amplifying cells in epithelial proliferating units like colonic crypts showed that intermediate numbers of stem cells in a crypt should optimally prevent progression to cancer. If a stem cell population is too small, it is easy for a mutator mutation to drift to fixation. If it is too large, it is easy for selection to drive cell fitness enhancing carcinogenic mutations to fixation. Here, we show that a multiscale microsimulation, that captures both within-crypt and between-crypt evolutionary dynamics, leads to a different conclusion. Epithelial tissues are metapopulations of crypts. We measured time to initiation of a neoplasm, implemented as inactivation of both alleles of a tumor suppressor gene. In our model, time to initiation is dependent on the spread of mutator clones in the crypts. The proportion of selectively beneficial and deleterious mutations in somatic cells is unknown and so was explored with a parameter. When the majority of non-neutral mutations are deleterious, the fitness of mutator clones tends to decline. When crypts are maintained by few stem cells, intercrypt competition tends to remove crypts with fixed mutators. When there are many stem cells within a crypt, there is virtually no crypt turnover, but mutator clones are suppressed by within-crypt competition. If the majority of non-neutral mutations are beneficial to the clone, then these results are reversed and intermediate-sized crypts provide the most protection against initiation. These results highlight the need to understand the dynamics of turnover and the mechanisms that control homeostasis, both at the level of stem cells within proliferative units and at the tissue level of competing proliferative units. Determining the distribution of fitness effects of somatic mutations will also be crucial to understanding the dynamics of tumor initiation and progression.

From Colitis to Cancer: An Evolutionary Trajectory That Merges Maths and Biology

Patients with inflammatory bowel disease have an increased risk of developing colorectal cancer, and this risk is related to disease duration, extent, and cumulative inflammation burden. Carcinogenesis follows the principles of Darwinian evolution, whereby somatic cells acquire genomic alterations that provide them with a survival and/or growth advantage. Colitis represents a unique situation whereby routine surveillance endoscopy provides a serendipitous opportunity to observe somatic evolution over space and time in vivo in a human organ. Moreover, somatic evolution in colitis is evolution in the ‘fast lane': the repeated rounds of inflammation and mucosal healing that are characteristic of the disease accelerate the evolutionary process and likely provide a strong selective pressure for inflammation-adapted phenotypic traits. In this review, we discuss the evolutionary dynamics of pre-neoplastic clones in colitis with a focus on how measuring their evolutionary trajectories could deliver a powerful way to predict future cancer occurrence. Measurements of somatic evolution require an interdisciplinary approach that combines quantitative measurement of the genotype, phenotype and the microenvironment of somatic cells–paying particular attention to spatial heterogeneity across the colon–together with mathematical modeling to interpret these data within an evolutionary framework. Here we take a practical approach in discussing how and why the different “evolutionary ingredients” can and should be measured, together with our viewpoint on subsequent translation into clinical practice. We highlight the open questions in the evolution of colitis-associated cancer as a stimulus for future work.

Clonal evolution of colorectal cancer in IBD

Optimizing the management of colorectal cancer (CRC) risk in IBD requires a fundamental understanding of the evolutionary process underpinning tumorigenesis. In IBD, clonal evolution begins long before the development of overt neoplasia, and is probably accelerated by the repeated cycles of epithelial wounding and repair that are characteristic of the condition. Here, we review the biological drivers of mutant clone selection in IBD with particular reference to the unique histological architecture of the intestinal epithelium coupled with the inflammatory microenvironment in IBD, and the unique mutation patterns seen in IBD-driven neoplasia when compared with sporadic adenomas and CRC. How these data can be leveraged as evolutionary-based biomarkers to predict cancer risk is discussed, as well as how the efficacy of CRC surveillance programmes and the management of dysplasia can be improved. From a research perspective, the longitudinal surveillance of patients with IBD provides an under-exploited opportunity to investigate the biology of the human gastrointestinal tract over space and time.

Notch as a Driver of Gastric Epithelial Cell Proliferation

The gastric epithelium is sustained by a population of stem cells that replenish the various mature epithelial lineages throughout adulthood. Regulation of stem and progenitor cell proliferation occurs via basic developmental signaling pathways, including the Notch pathway, which recently was described to promote gastric stem cell proliferation in both mice and human beings. Current cancer theory proposes that adult stem cells that maintain gastrointestinal tissues accumulate mutations that promote cancerous growth, and that basic signaling pathways, such as Notch, which stimulate stem cell proliferation, can promote tumorigenesis. Accordingly, constitutive Notch activation leads to unchecked cellular proliferation and gastric tumors in genetic mouse models. Furthermore, there is emerging evidence suggesting that the Notch pathway may be activated in some human gastric cancers, supporting a potential role for Notch in gastric tumorigenesis. In this review, we first summarize the current understanding of gastric stem cells defined by genetic mouse studies, followed by discussion of the literature regarding Notch pathway regulation of gastric stem cell function in the mouse and human beings. Notch action to maintain gastric epithelial cell homeostasis and the cellular consequences of dysregulated signaling to promote tumorigenesis are discussed, including studies associating Notch activation with human gastric cancer. Finally, we compare and contrast Notch function in the stomach with other gastrointestinal tissues, including the intestine, to highlight the sensitivity of the stomach to Notch-induced tumors.

An individual based computational model of intestinal crypt fission and its application to predicting unrestrictive growth of the intestinal epithelium

Intestinal crypt fission is a homeostatic phenomenon, observable in healthy adult mucosa, but which also plays a pathological role as the main mode of growth of some intestinal polyps. Building on our previous individual based model for the small intestinal crypt and on in vitro cultured intestinal organoids, we here model crypt fission as a budding process based on fluid mechanics at the individual cell level and extrapolated predictions for growth of the intestinal epithelium. Budding was always observed in regions of organoids with abundant Paneth cells. Our data support a model in which buds are biomechanically initiated by single stem cells surrounded by Paneth cells which exhibit greater resistance to viscoelastic deformation, a hypothesis supported by atomic force measurements of single cells. Time intervals between consecutive budding events, as simulated by the model and observed in vitro, were 2.84 and 2.62 days, respectively. Predicted cell dynamics was unaffected within the original crypt which retained its full capability of providing cells to the epithelium throughout fission. Mitotic pressure in simulated primary crypts forced upward migration of buds, which simultaneously grew into new protruding crypts at a rate equal to 1.03 days(-1) in simulations and 0.99 days(-1) in cultured organoids. Simulated crypts reached their final size in 4.6 days, and required 6.2 days to migrate to the top of the primary crypt. The growth of the secondary crypt is independent of its migration along the original crypt. Assuming unrestricted crypt fission and multiple budding events, a maximal growth rate of the intestinal epithelium of 0.10 days(-1) is predicted and thus approximately 22 days are required for a 10-fold increase of polyp size. These predictions are in agreement with the time reported to develop macroscopic adenomas in mice after loss of Apc in intestinal stem cells.

The Viral Mimetic Polyinosinic:Polycytidylic Acid Alters the Growth Characteristics of Small Intestinal and Colonic Crypt Cultures

Background & Aims

The intestinal epithelium is the first line of defense against enteric pathogens. We investigated the response of small intestinal and colonic crypt cultures to a panel of toll-like receptor ligands to assess the impact of microbial pattern recognition on epithelial growth.

Methods

Primary murine jejunal enteroids and colonoids were cultured with lipopeptide Pam3CSK4, lipopolysaccharide (LPS) or polyinosinic:polycytidylic acid (Poly I:C) for 4 to 6 days. Surface area, budding and survival were assessed. Proliferation and numbers of lysozyme positive cells were quantified by flow cytometry. Gene expression was assessed by Nanostring and qRT-PCR.

Results

Exposure to Pam3CSK4 and LPS had minimal impact on either enteroids or colonoids. In contrast, Poly I:C increased the surface area of enteroids, while colonoids demonstrated decreased budding. Survival was decreased by Poly I:C in enteroids but not in colonoids. Both enteroids and colonoids exhibited upregulated gene expression of chemokines, but these were increased in magnitude in enteroids. Decreases in gene expression associated with epithelial differentiation and lysozyme positive cells were more apparent in enteroids than in colonoids. Baseline gene expression between enteroids and colonoids differed markedly in levels of stem cell and inflammatory markers. The changes in morphology induced by Poly I:C were mediated by the toll-like receptor adaptor molecule 1 (Ticam1) in enteroids but not in colonoids.

Conclusions

Poly I:C alters the molecular program of epithelial cells and shifts from absorption and digestion towards defense and inflammation. Diversity of responses to microbial patterns in enteroids and colonoids may underlie differences in susceptibility to infection along the intestinal tract.

Notch signaling regulates gastric antral LGR5 stem cell function

The major signaling pathways regulating gastric stem cells are unknown. Here we report that Notch signaling is essential for homeostasis of LGR5(+) antral stem cells. Pathway inhibition reduced proliferation of gastric stem and progenitor cells, while activation increased proliferation. Notch dysregulation also altered differentiation, with inhibition inducing mucous and endocrine cell differentiation while activation reduced differentiation. Analysis of gastric organoids demonstrated that Notch signaling was intrinsic to the epithelium and regulated growth. Furthermore, in vivo Notch manipulation affected the efficiency of organoid initiation from glands and single Lgr5-GFP stem cells, suggesting regulation of stem cell function. Strikingly, constitutive Notch activation in LGR5(+) stem cells induced tissue expansion via antral gland fission. Lineage tracing using a multi-colored reporter demonstrated that Notch-activated stem cells rapidly generate monoclonal glands, suggesting a competitive advantage over unmanipulated stem cells. Notch activation was associated with increased mTOR signaling, and mTORC1 inhibition normalized NICD-induced increases in proliferation and gland fission. Chronic Notch activation induced undifferentiated, hyper-proliferative polyps, suggesting that aberrant activation of Notch in gastric stem cells may contribute to gastric tumorigenesis.

Genomic instability and radiation risk in molecular pathways to colon cancer

Colon cancer is caused by multiple genomic alterations which lead to genomic instability (GI). GI appears in molecular pathways of microsatellite instability (MSI) and chromosomal instability (CIN) with clinically observed case shares of about 15–20% and 80–85%. Radiation enhances the colon cancer risk by inducing GI, but little is known about different outcomes for MSI and CIN. Computer-based modelling can facilitate the understanding of the phenomena named above. Comprehensive biological models, which combine the two main molecular pathways to colon cancer, are fitted to incidence data of Japanese a-bomb survivors. The preferred model is selected according to statistical criteria and biological plausibility. Imprints of cell-based processes in the succession from adenoma to carcinoma are identified by the model from age dependences and secular trends of the incidence data. Model parameters show remarkable compliance with mutation rates and growth rates for adenoma, which has been reported over the last fifteen years. Model results suggest that CIN begins during fission of intestinal crypts. Chromosomal aberrations are generated at a markedly elevated rate which favors the accelerated growth of premalignant adenoma. Possibly driven by a trend of Westernization in the Japanese diet, incidence rates for the CIN pathway increased notably in subsequent birth cohorts, whereas rates pertaining to MSI remained constant. An imbalance between number of CIN and MSI cases began to emerge in the 1980s, whereas in previous decades the number of cases was almost equal. The CIN pathway exhibits a strong radio-sensitivity, probably more intensive in men. Among young birth cohorts of both sexes the excess absolute radiation risk related to CIN is larger by an order of magnitude compared to the MSI-related risk. Observance of pathway-specific risks improves the determination of the probability of causation for radiation-induced colon cancer in individual patients, if their exposure histories are known.

Senescence in adipose-derived stem cells and its implications in nerve regeneration

Adult mesenchymal stem cells, specifically adipose-derived stem cells have self-renewal and multiple differentiation potentials and have shown to be the ideal candidate for therapeutic applications in regenerative medicine, particularly in peripheral nerve regeneration. Adipose-derived stem cells are easily harvested, although they may show the effects of aging, hence their potential in nerve repair may be limited by cellular senescence or donor age. Cellular senescence is a complex process whereby stem cells grow old as consequence of intrinsic events (e.g., DNA damage) or environmental cues (e.g., stressful stimuli or diseases), which determine a permanent growth arrest. Several mechanisms are implicated in stem cell senescence, although no one is exclusive of the others. In this review we report some of the most important factors modulating the senescence process, which can influence adipose-derived stem cell morphology and function, and compromise their clinical application for peripheral nerve regenerative cell therapy.

Polarized cells, polarized views: asymmetric cell division in hematopoietic cells

It has long been recognized that alterations in cell shape and polarity play important roles in coordinating lymphocyte functions. In the last decade, a new aspect of lymphocyte polarity has attracted much attention, termed asymmetric cell division (ACD). ACD has previously been shown to dictate or influence many aspects of development in model organisms such as the worm and the fly, and to be disrupted in disease. Recent observations that ACD also occurs in lymphocytes led to exciting speculations that ACD might influence lymphocyte differentiation and function, and leukemia. Dissecting the role that ACD might play in these activities has not been straightforward, and the evidence to date for a functional role in lymphocyte fate determination has been controversial. In this review, we discuss the evidence to date for ACD in lymphocytes, and how it might influence lymphocyte fate. We also discuss current gaps in our knowledge, and suggest approaches to definitively test the physiological role of ACD in lymphocytes.

A calibrated agent-based computer model of stochastic cell dynamics in normal human colon crypts useful for in silico experiments

BACKGROUND

Normal colon crypts consist of stem cells, proliferating cells, and differentiated cells. Abnormal rates of proliferation and differentiation can initiate colon cancer. We have measured the variation in the number of each of these cell types in multiple crypts in normal human biopsy specimens. This has provided the opportunity to produce a calibrated computational model that simulates cell dynamics in normal human crypts, and by changing model parameter values, to simulate the initiation and treatment of colon cancer.

RESULTS

An agent-based model of stochastic cell dynamics in human colon crypts was developed in the multi-platform open-source application NetLogo. It was assumed that each cell's probability of proliferation and probability of death is determined by its position in two gradients along the crypt axis, a divide gradient and in a die gradient. A cell's type is not intrinsic, but rather is determined by its position in the divide gradient. Cell types are dynamic, plastic, and inter-convertible. Parameter values were determined for the shape of each of the gradients, and for a cell's response to the gradients. This was done by parameter sweeps that indicated the values that reproduced the measured number and variation of each cell type, and produced quasi-stationary stochastic dynamics. The behavior of the model was verified by its ability to reproduce the experimentally observed monocolonal conversion by neutral drift, the formation of adenomas resulting from mutations either at the top or bottom of the crypt, and by the robust ability of crypts to recover from perturbation by cytotoxic agents. One use of the virtual crypt model was demonstrated by evaluating different cancer chemotherapy and radiation scheduling protocols.

CONCLUSIONS

A virtual crypt has been developed that simulates the quasi-stationary stochastic cell dynamics of normal human colon crypts. It is unique in that it has been calibrated with measurements of human biopsy specimens, and it can simulate the variation of cell types in addition to the average number of each cell type. The utility of the model was demonstrated with in silico experiments that evaluated cancer therapy protocols. The model is available for others to conduct additional experiments.

Skin stem cell hypotheses and long term clone survival--explored using agent-based modelling

Epithelial renewal in skin is achieved by the constant turnover and differentiation of keratinocytes. Three popular hypotheses have been proposed to explain basal keratinocyte regeneration and epidermal homeostasis: 1) asymmetric division (stem-transit amplifying cell); 2) populational asymmetry (progenitor cell with stochastic fate); and 3) populational asymmetry with stem cells. In this study, we investigated lineage dynamics using these hypotheses with a 3D agent-based model of the epidermis. The model simulated the growth and maintenance of the epidermis over three years. The offspring of each proliferative cell was traced. While all lineages were preserved in asymmetric division, the vast majority were lost when assuming populational asymmetry. The third hypothesis provided the most reliable mechanism for self-renewal by preserving genetic heterogeneity in quiescent stem cells, and also inherent mechanisms for skin ageing and the accumulation of genetic mutation.

Wnt blockade with dickkopf reduces intestinal crypt fission and intestinal growth in infant rats

OBJECTIVES

Intestinal crypt fission peaks during infancy. In human and experimental familial polyposis coli, increased crypt fission is due to activation of Wnt/β-catenin signalling, but the molecular basis of crypt fission during intestinal growth has not been examined. The aim of this project was to investigate whether crypt fission and intestinal growth are affected by experimental blockade of the Wnt/β-catenin signalling pathway.

METHODS

Hooded Wistar rats were given either the Wnt inhibitor, dickkopf (30 and 100 ng), daily or vehicle control intraperitoneally from days 11 to 15 and were killed at day 16. Intestinal morphometry was used to measure villous area, crypt area, percentage of crypt fission, and crypt mitotic count. Intestinal stem cells were assessed by expression of real time-polymerase chain reaction for Lgr5 (a stem cell marker), and the number of β-catenin-expressing crypts by immunostaining was determined after 100-ng dickkopf treatment.

RESULTS

Dickkopf at 30 and 100 ng/day reduced villous area to 71% (P = 0.013) and 29% (P < 0.0001), crypt area to 42% (P = 0.0026) and 30% (P = 0.0067), and crypt fission to 51% (P = 0.006) and 29% (P < 0.0001), respectively, of control values. Mitotic count per crypt did not change. Lgr5 RNA expression and the number of β-catenin-expressing crypts decreased in dickkopf-treated animals.

CONCLUSIONS

We conclude that intestinal crypt fission during infancy is mediated by Wnt signalling. It is possible that local treatment with Wnt agonists could be used to increase intestinal growth.

Mathematical modeling of monoclonal conversion in the colonic crypt

A novel spatial multiscale model of a colonic crypt is described, which couples the cell cycle (including cell division) with the mechanics of cell movement. The model is used to investigate the process of monoclonal conversion under two hypotheses concerning stem cell behavior. Under the first hypothesis, 'stem-ness' is an intrinsic cell property, and the stem cell population is maintained through asymmetric division. Under the second hypothesis, the proliferative behavior of each cell is governed by its microenvironment through a biochemical signalling cue, and all cell division is symmetric. Under each hypothesis, the model is used to run virtual experiments, in which a harmless labeling mutation is bestowed upon a single cell in the crypt and the mutant clonal population is tracked over time to check if and when the crypt becomes monoclonal. It is shown that under the first hypothesis, a stable structured cell population is not possible without some form of population-dependent feedback; in contrast, under the second hypothesis, a stable crypt architecture arises naturally. Through comparison with an existing spatial crypt model and a non-spatial stochastic population model, it is shown that the spatial structure of the crypt has a significant effect on the time scale over which a crypt becomes monoclonal.

Isolation of adult stem cells and their differentiation to Schwann cells

Peripheral nerve injuries are an economic burden for society in general and despite advanced microsurgical reconstruction of the damaged nerves the functional result is unsatisfactory with poor sensory recovery and reduced motor functions (Wiberg and Terenghi, Surg Technol Int 11:303-310, 2003). In the treatment of nerve injuries transplantation of a nerve graft is often necessary, especially in nerve gap injuries.Schwann cells (SC) are the key facilitators of peripheral nerve regeneration and are responsible for the formation and maintenance of the myelin sheath around axons in peripheral nerve fibers. They are essential for nerve regeneration after nerve injuries as they produce extracellular matrix molecules, integrins, and trophic factors providing guidance and trophic support for regenerating axons (Wiberg and Terenghi, Surg Technol Int 11:303-310, 2003; Bunge, J Neurol 242:S19-21, 1994; Ide, Neurosci Res 25:101-121, 1996; Mahanthappa et al. J Neurosci 16:4673-4683, 1996). However, the use of ex vivo cultured SC within conduits is limited in its clinical application because of the concomitant donor site morbidity and the slow growth of these cells in vitro (Tohill et al. Tissue Eng 10:1359-1367, 2004).Mesenchymal stem cells (MSC or bone marrow stromal cells) and adipose-derived stem cells (ASC) are easily accessible non-hematopoietic stem cells that have proven essential for research purposes due to their plasticity and ability to differentiate into several functional cell types. This alternative source of cells is relatively simple to isolate and expand in culture. We have demonstrated that MSC and ASC can trans-differentiate along a SC lineage with functional properties and growth factor synthesis activities similar to those of native SC and could provide nerve fiber support and guidance during nerve regeneration.

Field cancerization in the GI tract

The widely accepted paradigm for tumorigenesis begins with rate-limiting mutations in a key growth control gene resulting in immediate lesion growth. Tumor progression occurs as cells within the tumor acquire additional carcinogenic mutations. However, there is clear evidence that the road to cancer can begin long before the growth of a clinically detectable lesion - indeed, long before any of the usual morphological correlates of preneoplasia are recognizable. Field cancerization, the replacement of the normal cell population by a histologically nondysplastic but protumorigenic mutant cell clone, underlies the development of many cancer types, and in this article we review field cancerization in the GI tract. We present the evidence that field cancerization can underpin tumorigenesis in all gastrointestinal compartments, discuss the homeostatic mechanisms that could permit clone spread and highlight how an understanding of the mechanisms driving field cancerization is a means to study human stem cell biology. Finally, we discuss how appropriate recognition of the role of field cancerization in tumorigenesis could impact patient care.

Role of heterozygous APC mutation in niche succession and initiation of colorectal cancer--a computational study

Mutations in the adenomatous polyposis coli (APC) gene are found in most colorectal cancers. They cause constitutive activation of proliferative pathways when both alleles of the gene are mutated. However studies on individuals with familial adenomatous polyposis (FAP) have shown that a single mutated APC allele can also create changes in the precancerous colon crypt, like increased number of stem cells, increased crypt fission, greater variability of DNA methylation patterns, and higher somatic mutation rates. In this paper, using a computational model of colon crypt dynamics, we evolve and investigate a hypothesis on the effect of heterozygous APC mutation that explains these different observations. Based on previous reports and the results from the computational model we propose the hypothesis that heterozygous APC mutation has the effect of increasing the chances for a stem cell to divide symmetrically, producing two stem cell daughters. We incorporate this hypothesis into the model and perform simulation experiments to investigate the consequences of the hypothesis. Simulations show that this hypothesis links together the changes in FAP crypts observed in previous studies. The simulations also show that an APC(+/-) stem cell gets selective advantages for dominating the crypt and progressing to cancer. This explains why most colon cancers are initiated by APC mutation. The results could have implications for preventing or retarding the onset of colon cancer in people with inherited or acquired mutation of one APC allele. Experimental validation of the hypothesis as well as investigation into the molecular mechanisms of this effect may therefore be worth undertaking.

Ets2 regulates colonic stem cells and sensitivity to tumorigenesis

Ets2 has both tumor repressive and supportive functions for different types of cancer. We have investigated the role of Ets2 within intestinal epithelial cells in postnatal mouse colon development and tumorigenesis. Conditional inactivation of Ets2 within intestinal epithelial cells results in over representation of Ets2-deficient colon crypts within young and adult animals. This preferential representation is associated with an increased number of proliferative cells within the stem cell region and an increased rate of crypt fission in young mice that result in larger patches of Ets2-deficient crypts. These effects are consistent with a selective advantage of Ets2-deficient intestinal stem cells in colonizing colonic crypts and driving crypt fission. Ets2-deficient colon crypts have an increased mucosal thickness, an increased number of goblet cells, and an increased density. Mice with Ets2-deficient intestinal cells develop more colon tumors in response to treatment with azoxymethane and dextran sulfate sodium. The selective population of colon crypts, the altered differentiation state and increased sensitivity to carcinogen-induced tumors all indicate that Ets2 deficiency alters colon stem cell number or behavior. Ets2-dependent, epithelial cell-autonomous repression of intestinal tumors may contribute to protection from colon cancer of persons with increased dosage of chromosome 21.

Ets2 regulates colonic stem cells and sensitivity to tumorigenesis

Ets2 has both tumor repressive and supportive functions for different types of cancer. We have investigated the role of Ets2 within intestinal epithelial cells in postnatal mouse colon development and tumorigenesis. Conditional inactivation of Ets2 within intestinal epithelial cells results in over representation of Ets2-deficient colon crypts within young and adult animals. This preferential representation is associated with an increased number of proliferative cells within the stem cell region and an increased rate of crypt fission in young mice that result in larger patches of Ets2-deficient crypts. These effects are consistent with a selective advantage of Ets2-deficient intestinal stem cells in colonizing colonic crypts and driving crypt fission. Ets2-deficient colon crypts have an increased mucosal thickness, an increased number of goblet cells, and an increased density. Mice with Ets2-deficient intestinal cells develop more colon tumors in response to treatment with azoxymethane and dextran sulfate sodium. The selective population of colon crypts, the altered differentiation state and increased sensitivity to carcinogen-induced tumors all indicate that Ets2 deficiency alters colon stem cell number or behavior. Ets2-dependent, epithelial cell-autonomous repression of intestinal tumors may contribute to protection from colon cancer of persons with increased dosage of chromosome 21.

Towards predictive models of stem cell fate

Quantitative approaches are essential for the advancement of strategies to manipulate stem cells or their derivatives for therapeutic applications. Predictive models of stem cell systems would provide the means to pose and validate non-intuitive hypotheses and could thus serve as an important tool for discerning underlying regulatory mechanisms governing stem cell fate decisions. In this paper we review the development of computational models that attempt to describe mammalian adult and embryonic stem (ES) cell responses. Early stochastic models that relied exclusively on statistical distributions to describe the in vitro or in vivo output of stem cells are being revised to incorporate the contributions of exogenous and endogenous parameters on specific stem cell fate processes. Recent models utilize cell specific data (for example, cell-surface receptor distributions, transcription factor half-lives, cell-cycle status, etc.) to provide mechanistic descriptions that are consistent with biologically observed phenomena. Ultimately, the goal of these computational models is to, a priori, predict stem cell output given an initial set of conditions. Our efforts to develop a predictive model of ES cell fate are discussed. The quantitative studies presented in this review represent an important step in developing bioengineering approaches to characterize and predict stem cell behavior. Ongoing efforts to incorporate genetic and signaling network data into computational models should accelerate our understanding of fundamental principles governing stem cell fate decisions.

Intestinal stem cell replacement follows a pattern of neutral drift

With the capacity for rapid self-renewal and regeneration, the intestinal epithelium is stereotypical of stem cell-supported tissues. Yet the pattern of stem cell turnover remains in question. Applying analytical methods from population dynamics and statistical physics to an inducible genetic labeling system, we showed that clone size distributions conform to a distinctive scaling behavior at short times. This result demonstrates that intestinal stem cells form an equipotent population in which the loss of a stem cell is compensated by the multiplication of a neighbor, leading to neutral drift dynamics in which clones expand and contract at random until they either take over the crypt or they are lost. Combined with long-term clonal fate data, we show that the rate of stem cell replacement is comparable to the cell division rate, implying that neutral drift and symmetrical cell divisions are central to stem cell homeostasis.

New models of neoplastic progression in Barrett's oesophagus

Research in Barrett's oesophagus, and neoplastic progression to OAC (oesophageal adenocarcinoma), is hobbled by the lack of good pre-clinical models that capture the evolutionary dynamics of Barrett's cell populations. Current models trade off tractability for realism. Computational models are perhaps the most tractable and can be used both to interpret data and to develop intuitions and hypotheses for neoplastic progression. Tissue culture models include squamous cell lines, Barrett's oesophagus cell lines and OAC cell lines, although it was recognized recently that BIC-1, SEG-1 and TE-7 are not true OAC cell lines. Some of the unrealistic aspects of the micro-environment in two-dimensional tissue culture may be overcome with the development of three-dimensional organotypic cultures of Barrett's oesophagus. The most realistic, but least tractable, model is a canine surgical model that generates reflux and leads to an intestinal metaplasia. Alternatively, rat surgical models have gained popularity and should be tested for the common genetic features of Barrett's oesophagus neoplastic progression in humans including loss of CDKN2A (cyclin-dependent kinase inhibitor 2A) and TP53 (tumour protein 53), generation of aneuploidy and realistic levels of genetic diversity. This last feature will be important for studying the effects of cancer-prevention interventions. In order to study the dynamics of progression and the effects of an experimental intervention, there is a need to follow animals longitudinally, with periodic endoscopic biopsies. This is now possible and represents an exciting opportunity for the future.

New models of neoplastic progression in Barrett's oesophagus

Research in Barrett's oesophagus, and neoplastic progression to OAC (oesophageal adenocarcinoma), is hobbled by the lack of good pre-clinical models that capture the evolutionary dynamics of Barrett's cell populations. Current models trade off tractability for realism. Computational models are perhaps the most tractable and can be used both to interpret data and to develop intuitions and hypotheses for neoplastic progression. Tissue culture models include squamous cell lines, Barrett's oesophagus cell lines and OAC cell lines, although it was recognized recently that BIC-1, SEG-1 and TE-7 are not true OAC cell lines. Some of the unrealistic aspects of the micro-environment in two-dimensional tissue culture may be overcome with the development of three-dimensional organotypic cultures of Barrett's oesophagus. The most realistic, but least tractable, model is a canine surgical model that generates reflux and leads to an intestinal metaplasia. Alternatively, rat surgical models have gained popularity and should be tested for the common genetic features of Barrett's oesophagus neoplastic progression in humans including loss of CDKN2A (cyclin-dependent kinase inhibitor 2A) and TP53 (tumour protein 53), generation of aneuploidy and realistic levels of genetic diversity. This last feature will be important for studying the effects of cancer-prevention interventions. In order to study the dynamics of progression and the effects of an experimental intervention, there is a need to follow animals longitudinally, with periodic endoscopic biopsies. This is now possible and represents an exciting opportunity for the future.

The stem cells of small intestinal crypts: where are they?

Recently, there has been resurgence of interest in the question of small intestinal stem cells, their precise location and numbers in the crypts. In this article, we attempt to re-assess the data, including historical information often omitted in recent studies on the subject. The conclusion we draw is that the evidence supports the concept that active murine small intestinal stem cells in steady state are few in number and are proliferative. There are two evolving, but divergent views on their location (which may be more related to scope of capability and reversibility than to location) several lineage labelling and stem cell self-renewing studies (based on Lgr5 expression) suggest a location intercalated between the Paneth cells (crypt base columnar cells (CBCCs)), or classical cell kinetic, label-retention and radiobiological evidence plus other recent studies, pointing to a location four cell positions luminally from the base of the crypt The latter is supported by recent lineage labelling of Bmi-1-expressing cells and by studies on expression of Wip-1 phosphatase. The situation in the human small intestine remains unclear, but recent mtDNA mutation studies suggest that the stem cells in humans are also located above the Paneth cell zone. There could be a distinct and as yet undiscovered relationship between these observed traits, with stem cell properties both in cells of the crypt base and those at cell position 4.

Investigating the fixation and spread of mutations in the gastrointestinal epithelium

Tissue-specific stem cells are responsible for the maintenance of the epithelium throughout the gastrointestinal tract. The accumulation of mutations in these stem cells is the likely cause of most gastrointestinal cancers. Clonal analysis of these stem cell populations has revealed how normal homeostatic processes work and how neoplastic growth occurs. In this review, we consider the clonal dynamics of stem cells in the gastrointestinal tract. We focus on mechanisms of clonal expansion, and discuss the novel methods that have been developed to study these processes in humans. Particular consideration is given to the role of clonal analysis in understanding dysplasia and neoplasia. We consider how improvements in sequencing technology may shape future research and clinical practice.

Early but not late administration of glucagon-like peptide-2 following ileo-cecal resection augments putative intestinal stem cell expansion

Expansion of intestinal progenitors and putative stem cells (pISC) occurs early and transiently following ileo-cecal resection (ICR). The mechanism controlling this process is not defined. We hypothesized that glucagon-like peptide-2 (GLP-2) would augment jejunal pISC expansion only when administered to mice immediately after ICR. Since recent reports demonstrated increases in intestinal insulin-like growth factor (IGF)-I following GLP-2 administration, we further hypothesized that increased intestinal IGF-I expression would correlate with pISC expansion following ICR. To assess this, GLP-2 or vehicle was administered to mice either immediately after resection (early) or before tissue harvest 6 wk following ICR (late). Histological analysis quantified proliferation and intestinal morphometrics. Serum levels of GLP-2 were measured by ELISA and jejunal IGF-I mRNA by qRT-PCR. Expansion of jejunal pISC was assessed by fluorescent-activated cell sorting of side population cells, immunohistochemistry for phosphorylated beta-catenin at serine 552 (a pISC marker), percent of crypt fission, and total numbers of crypts per jejunal circumference. We found that early but not late GLP-2 treatment after ICR significantly augmented pISC expansion. Increases in jejunal IGF-I mRNA correlated temporally with early pISC expansion and effects of GLP-2. Early GLP-2 increased crypt fission and accelerated adaptive increases in crypt number and intestinal caliber. GLP-2 increased proliferation and intestinal morphometrics in all groups. This study shows that, in mice, GLP-2 promotes jejunal pISC expansion only in the period immediately following ICR. This is associated with increased IGF-I and accelerated adaptive increases in mucosal mass. These data provide clinical rationale relevant to the optimal timing of GLP-2 in patients with intestinal failure.

Inferring human stem cell behaviour from epigenetic drift

Although conventional experimental manipulations are impractical, it may be possible to infer human stem cell fates by 'reading' histories recorded within their genomes. Genomes are almost perfect copies of copies, and ancestries may be surreptitiously recorded by replication errors that inevitably accumulate. The greater the number of divisions, the greater the number of replication errors ('a molecular clock hypothesis'). Mutations rarely occur during a lifetime, but DNA methylation patterns are also copied after DNA replication and measurably drift with ageing at certain CpG sites in mitotic tissues, such as the colon. Such passenger methylation pattern variation may effectively function as 'epigenetic' somatic cell mitotic clocks. Replication errors can only accumulate in long-lived stem cell lineages, so methylation pattern drift largely records stem cell behaviour. How methylation patterns may encode stem cell ancestries is illustrated with two types of small reproductive units--colon crypt niches with continuous genealogies, and hair follicles with punctuated genealogies. Potentially, the genealogy of any human cell may be inferred by 'reading' its genome.

Advances in intestinal stem cells and cancer stem cells of colorectal cancer

Over the past decade, the advances in our understanding of stem cell biology and the role of stem cells in neoplasms, such as colorectal cancer, have been remarkable. The theory of cancer stem cells states that a subset of cancer cells within a tumor has the ability to self-renew and differentiate. More and more studies implicated that cancer stem cells may originate from adult stem cells. The adult stem cells in intestinal crypts, i.e., intestinal stem cells, may relate with the pathogenesis of colorectal cancer closely. This paper reviews the recent advances about intestinal stem cells and cancer stem cells of colorectal cancer.

Crypt fission peaks early during infancy and crypt hyperplasia broadly peaks during infancy and childhood in the small intestine of humans

BACKGROUND

Postnatal growth of the small intestine occurs by crypt hyperplasia and by the less recognised mechanism of crypt fission. How the small intestine grows is largely extrapolated from animals and is poorly described in humans.

AIM

To investigate crypt fission and crypt hyperplasia as mechanisms of intestinal growth in humans.

PATIENTS AND METHODS

Proximal intestinal samples were taken from 3 neonates at surgical anastomosis, and duodenal biopsies were taken at endoscopy from 16 infants (mean age 0.7, range 0.3-1.7 years), 14 children (mean age 7.9, range 2.4-16.2 years), and 39 adults. Morphometric measures of villous area, crypt length (measure of crypt hyperplasia), and percentage of bifid crypts (measure of crypt fission) were assessed by a microdissection technique.

RESULTS

Mean crypt fission rates in neonates, infants, children, and adults were 7.8%, 15%, 4.9%, and 1.7%, respectively. In particular, crypt fission peaked at 18% in 5 infants from 6 to 12 months of age. Mean crypt length was 123 microm in neonates, 287 microm in infants, 277 microm in children, and 209 microm in adults. Thus, crypt hyperplasia had a broad peak during infancy and childhood.

CONCLUSIONS

We conclude that crypt fission was present predominantly during infancy, and crypt hyperplasia occurred during both infancy and childhood.

Colonic crypt organization and tumorigenesis

An appreciation of colonic crypt organization has become essential to any understanding of tumorigenesis in the colon. Intestinal crypts house tissue-specific, multipotential stem cells, which are located in the niche at the base of the intestinal crypt and are capable of regenerating all intestinal cell types. Recent advances in our understanding of crypt biology, including how mutations in stem cells become fixed and expand within the epithelium, has led to new theories on the origins of colonic adenomas and cancers.

Prospective identification of a multilineage progenitor in murine stomach epithelium

BACKGROUND & AIMS

Epithelial stem cells in the stomach are responsible for constant renewal of the epithelium through generation of multiple gastric cell lineages that populate the gastric glands. However, gastric stem or progenitor cells have not been well-characterized because of the lack of specific markers that permit their prospective recognition. We identified an intestinal promoter that is active in a rare subpopulation of gastric epithelial cells and investigated whether these cells possess multilineage potential.

METHODS

A marked allele of the endogenous mouse villin locus was used to visualize single beta-galactosidase-positive cells located in the lower third of antral glands. A 12.4-kb villin promoter/enhancer fragment drives several transgenes (EGFP, beta-galactosidase, and Cre recombinase) in these cells in a pattern similar to that of the marked villin allele. Reporter gene activity was used to track these cells during development and to examine cell number in the context of inflammatory challenge while Cre activity allowed lineage tracing in vivo.

RESULTS

We show that these rare epithelial cells are normally quiescent, but multiply in response to interferon gamma. Lineage tracing studies confirm that these cells give rise to all gastric lineages of the antral glands. In the embryo, these cells are located basally in the stomach epithelium before completion of gastric gland morphogenesis.

CONCLUSIONS

We have identified a rare subpopulation of gastric progenitors with multilineage potential. The ability to prospectively identify and manipulate such progenitors in situ represents a major step forward in gastric stem cell biology and has potential implications for gastric cancer.

Insertional mutagenesis and clonal dominance: biological and statistical considerations

Improvements of (retroviral) gene transfer vectors, stem cell isolation and culture techniques as well as transduction protocols eventually resulted not only in the successful genetic modification of cells capable of reconstituting the haematopoietic system in various animal models, but also human beings. This was a conditio sine qua non for the successful application of gene therapy for inherited diseases as meanwhile achieved for severe combined immune deficiencies (SCID-X1, ADA-SCID) and chronic granulomatous disease (CGD). Unexpectedly, in long-term animal experiments as well as in the follow up of patients from the CGD trial, haematopoietic clones bearing insertions in certain gene loci became dominant, which was most apparent in the myeloid blood compartment. Accumulating data strongly suggest that this clonal dominance was due to some growth and/or survival advantage conferred by gene-activating or -suppressing effects of the integrated retroviral vector (insertional mutagenesis). Importantly, such induced clonal dominance seems not to lead to malignant transformation of affected cell clones inadvertently. The latter finding has become the basis for the concept of 'induced haematopoietic stem cells', a potentially powerful tool to investigate genes involved in the regulation of mechanisms underlying competitive advantages of stem cells, but also in the multi-step nature of malignant transformation. Here we discuss promises and open issues of this concept as well as the important question of common insertion sites statistics and its pitfalls.

Asymmetry of stem cell fate and the potential impact of the niche: observations, simulations, and interpretations

Asymmetric cell division is a common concept to explain the capability of stem cells to simultaneously produce a continuous output of differentiated cells and to maintain their own population of undifferentiated cells. Whereas for some stem cell systems, an asymmetry in the division process has explicitly been demonstrated, no evidence for such a functional asymmetry has been shown for hematopoietic stem cells (HSC) so far. This raises the question regarding whether asymmetry of cell division is a prerequisite to explain obvious heterogeneity in the cellular fate of HSC. Through the application of a mathematical model based on self-organizing principles, we demonstrate that the assumption of asymmetric stem cell division is not necessary to provide a consistent account for experimentally observed asymmetries in the development of HSC. Our simulation results show that asymmetric cell fate can alternatively be explained by a reversible expression of functional stem cell potentials, controlled by changing cell-cell and cell-microenvironment interactions. The proposed view on stem cell organization is pointing to the potential role of stem cell niches as specific signaling environments, which induce developmental asymmetries and therefore, generate cell fate heterogeneity. The self-organizing concept is fully consistent with the functional definition of tissue stem cells. It naturally includes plasticity phenomena without contradicting a hierarchical appearance of the stem cell population. The concept implies that stem cell fate is only predictable in a probabilistic sense and that retrospective categorization of stem cell potential, based on individual cellular fates, provides an incomplete picture.

Activation of beta-catenin in the stem cell region of crypts during growth of the small intestine in infant rats

The Wnt/beta-catenin pathway has been proposed as promoting intestinal stem cell division. Wnt ligands activate cytoplasmic beta-catenin and increase nuclear translocation of beta-catenin that binds to the Tcf-4 transcription factor. The aim of this study was to investigate beta-catenin expression in the stem cell region of crypts during intestinal growth in rats. Litters of DAxPVG/c rats were humanely killed at 7, 14, 21, 35, and 72 days of life. beta-Catenin and Tcf-4 were quantified by immunoperoxidase staining and image analysis with cumulative signal analysis. Cytoplasmic and nuclear expression of beta-catenin peaked nearly 2-fold at day 14 (versus day 7) of life in the stem cell region of intestinal crypts. Tcf-4 nuclear expression peaked earlier at 7 days and was lower thereafter with age. We conclude that the Wnt/beta-catenin pathway is activated in the stem cell region of intestinal crypts during growth of the small intestine.

Crypt dynamics and colorectal cancer: advances in mathematical modelling

Mathematical modelling forms a key component of systems biology, offering insights that complement and stimulate experimental studies. In this review, we illustrate the role of theoretical models in elucidating the mechanisms involved in normal intestinal crypt dynamics and colorectal cancer. We discuss a range of modelling approaches, including models that describe cell proliferation, migration, differentiation, crypt fission, genetic instability, APC inactivation and tumour heterogeneity. We focus on the model assumptions, limitations and applications, rather than on the technical details. We also present a new stochastic model for stem-cell dynamics, which predicts that, on average, APC inactivation occurs more quickly in the stem-cell pool in the absence of symmetric cell division. This suggests that natural niche succession may protect stem cells against malignant transformation in the gut. Finally, we explain how we aim to gain further understanding of the crypt system and of colorectal carcinogenesis with the aid of multiscale models that cover all levels of organization from the molecular to the whole organ.

Postnatal epithelial growth of the small intestine in the rat occurs by both crypt fission and crypt hyperplasia

Studies of growth of the small intestine have largely concentrated on crypt hyperplasia rather than crypt fission. The aim of this study was to investigate quantitatively both crypt fission and crypt hyperplasia. DAxPVG/c rats were killed at 7, 11, 14, 17, 19, 21, 25, 55, and 72-73 days of life. Samples of jejunum at one third of the intestinal length were taken for morphometry (villous area, crypt area, percentage of bifid crypts, and crypt mitotic count) by microdissection. Growth factors and their receptors were assessed by oligonucleotide microarray. Crypt fission was 10.5%, 5.2%, and 1.5% at days 11, 25, and 72-73 of life, respectively. Crypt hyperplasia increased from day 21. No conventional growth factor was identified during crypt fission. We conclude that crypt fission contributes to growth of the small intestine prior to weaning and crypt hyperplasia to growth after weaning.

Acid fibroblast growth factor reduces rat intestinal mucosal damage caused by ischemia-reperfusion insult

AIM: To detect the effects of acid fibroblast growth factor (aFGF) on apoptosis and proliferation of intestinal epithelial cells in differentiation or proliferation status to explore the protective mechanisms of aFGF.

METHODS: Wistar rats were randomly divided into sham-operated control group (C, n = 6), intestinal ischemia group (I, n = 6), aFGF treatment group (A, n = 48) and intestinal ischemia-reperfusion group (R, n = 48). Apoptosis of intestinal mucosal cells was determined with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) technique. Proliferating cell nuclear antigen (PCNA) protein expression and distribution were detected with immunohistochemical method. Plasma levels of D-lactate were determined with modified Brandts method.

RESULTS: In A group, administration of exogenous aFGF could improve intestinal histological structure and decrease plasma D-lactate levels at 2-12 h after the reperfusion compared with R group. The apoptotic rates and PCNA protein expressions were not increased until 2 h after reperfusion and were maximal at 12 h. After reperfusion for 2-12 h, the apoptotic rates were gradually augmented along the length of jejunal crypt-villus units. Administration of aFGF could significantly reduce the apoptotic response at 2-12 h after reperfusion (P<0.05). Apoptosis rates in villus and crypt epithelial cells in A group at 12 h after reperfusion were (62.5±5.5)% and (73.2±18.6)% of those in R group, respectively. Treatment of aFGF could apparently induce protein expression of PCNA in intestinal mucosal cells of A group compared with R group during 2-12 h after reperfusion (P<0.05). There were approximately 1.3- and 1.5-times increments of PCNA expression levels in villus and crypt cells in A group at 12 h after reperfusion compared with R group, respectively.

CONCLUSION: Intestinal I/R insult could lead to histological structure change and apoptotic rate increment. The protective effects of aFGF against ischemia/reperfusion in rat intestinal mucosa might be partially due to its ability to inhibit ischemia/reperfusion-induced apoptosis and to promote cell proliferation of crypt cells and villus epithelial cells.

Direct Single Gene Mutational Events Account for Radiation-Induced Intestinal Adenoma Yields inApcMin/+Mice

Data on the induction of small intestinal tumors, predominantly adenomas, by X radiation in Apc(Min/+) mice are reported. Comparison of these incidences with estimates of radiation-induced direct single gene mutation frequencies taken from the literature support the hypothesis that direct mutational loss of Apc+ is the sole requirement for initiation of adenoma. Furthermore, estimates of radiation-induced initiation of adenoma per target stem cell in this animal model are similar to or less than radiation-induced direct somatic gene mutation frequencies. Therefore, while the data reported here do not preclude a role for genomic instability in tumor progression, it is not necessary in this model to postulate the involvement of radiation-induced transmissible genomic instability in initiation of intestinal adenoma.

Isolated crypts form spheres prior to full intestinal differentiation when grown as xenografts: anin vivo model for the study of intestinal differentiation and crypt neogenesis, and for the abnormal crypt architecture of juvenile polyposis coli

We describe a model system in which single crypts, isolated from newborn rats, were embedded in a type I collagen gel and subcutaneously grafted to the flanks of nude mice, whereupon they underwent full intestinal morphogenesis. Small fragments of small intestine and colon were incubated with the divalent cation chelator EDTA, resulting in the release of crypts and villi. Released crypts were then suspended sparsely in type I collagen gel. Segments of gel containing a single crypt were grafted subcutaneously into a nude mouse. Grafts were harvested at weekly intervals. By 2 days, the mouth of the crypts had joined to seal the crypt and, within 1 week, the structure ballooned to form a spherical cystic structure lined by flattened epithelial cells showing no evidence of cytodifferentiation. After 2 weeks, host stromal cells had invaded the collagen and settled around this spherical crypt. At points where stromal cells appeared in contact with the crypt, the epithelium exhibited a more columnar phenotype. By 4 weeks, the 'crypt sphere' was surrounded by stroma expressing alpha-smooth muscle actin and, at this time, multiple buds appeared that gave rise to new crypts. By 5 weeks, villi had formed and cell lineages associated with the small intestine and colon were present; the original single crypt had transformed into a functional intestinal unit. Therefore, we have shown that a single crypt has the potential to grow, give rise to other crypts and dependent structures such as villi. This model has considerable potential for use in gene transfer experiments in the study of intestinal differentiation, and for the analysis of crypt neogenesis via crypt fission. Moreover, the appearances showed a close resemblance to those seen in juvenile polyposis syndrome (JPS), where the budding and fission of single crypts isolated by stromal overgrowth offers an alternative explanation for the histogenesis of JPS.

Fission of pancreatic islets during postnatal growth of the mouse

A cell composition analysis was made of the pancreatic islets in postnatal H253 mice. This line has a lacZ insertion on the X chromosome so that in female hemizygotes 50% of cells should be positive for beta-galactosidase and 50% negative. Immediately after birth, the islets were of a heterogeneous cell composition. However, by 4 weeks some islets have become homogeneous. This suggests that islets progress towards monoclonality in a similar way to the intestinal crypts and stomach gastric glands. Pancreatic islets may therefore represent 'structural proliferative units' in the overall histological organization of the pancreas. Reduction of genetic heterogeneity might arise from cell turnover, fission of islets or both. Analysis of the cell composition of the X-inactivation mosaic mice also provides the first clear evidence for islet fission in pancreatic development. Irregularly shaped islets resembling dumb-bells, with a characteristic neck of alpha-cells, were observed with decreasing frequency with increasing age. Three-dimensional reconstruction confirmed their resemblance to conjoined islets. The cell composition analysis showed: (1) the relatedness of the two sides of a dumb-bell islet is significantly higher than between two non-dumb-bell islets and (2) the relatedness of two randomly selected islets decreases as the distance between them increases. This suggests that dumb-bell islets are in a state of fission rather than fusion, and that islet fission is a mode of islet production in the postnatal pancreas.

The gastrointestinal stem cell

The longevity of adult stem cells, and their potential for vast tissue regeneration, makes them a focal point of current research and debate, with future aspirations for the use of stem cells in the treatment of a number of human pathological conditions. Due to the rapid rate of cell turnover in the gastrointestinal tract, the stem cells of this tissue are amongst the most assiduous in the body, although they remain unidentified to this day due to their immature, undifferentiated phenotype. However, our knowledge of the mechanisms regulating gastrointestinal stem cell function is evolving, with the identification of putative cellular markers and the elucidation of signalling pathways which regulate cell behaviour in the normal and neoplastic gastrointestinal tract. This review describes the fundamental properties of the gastrointestinal stem cell including: (i) their number, location and origins, (ii) their primary function of deriving gastrointestinal cell lineages and maintaining tissue homeostasis, (iii) the acquisition of gastrointestinal cell lineages from adult stem cells of extraneous tissues and the consequences of this in a therapeutic context, and (iv) the genetic and morphological phenomena surrounding neoplastic transformation in the gastrointestinal tract.

Enterophilin-1 Interacts with Focal Adhesion Kinase and Decreases β1 Integrins in Intestinal Caco-2 Cells

Intestinal cell growth and differentiation are tightly regulated by growth factors and extracellular matrix components along the crypt-villus axis. We previously described enterophilin-1 (Ent-1) as a new intestinal protein associated with growth arrest and enterocyte differentiation. Ent-1 interacted with sorting nexin 1 and decreased cell surface epidermal growth factor receptor. Because beta(1) integrins are mostly found in vivo in the proliferative crypt cells, we investigated the role of Ent-1 in the fate of beta(1) integrin subunits. In undifferentiated intestinal Caco-2 cells, overexpression of Ent-1 induces a marked decrease of alpha(5)beta(1) integrin pools, whereas alpha(2)beta(1) integrin is weakly affected. Conversely, overexpression of sorting nexin 1 has no effect on integrin levels despite its ability to interact with Ent-1. Interestingly, we identified focal adhesion kinase as a new Ent-1 partner using yeast two-hybrid screening and co-precipitation experiments. Furthermore by confocal microscopy, we observed that Ent-1 and beta(1) integrins partly co-localize on vesicular structures, suggesting a role for Ent-1 in integrin trafficking. Because focal adhesion kinase is able to bind both Ent-1 and beta(1) integrins, the kinase might act as a molecular bridge between the two proteins. Altogether, these results support a role of Ent-1 in regulating beta(1) integrin expression that could favor intestinal differentiation.

Enterophilin-1, a new partner of sorting nexin 1, decreases cell surface epidermal growth factor receptor

We previously described enterophilin-1 (Ent-1), a new intestinal protein bearing an extended leucine zipper and a B30.2 domain. Ent-1 expression is associated with growth arrest and enterocyte differentiation. To investigate the importance of Ent-1 in the differentiation, we performed a yeast two-hybrid screening. We identified sorting nexin 1 (SNX1) as a novel partner of Ent-1 and confirmed the specificity of interaction by co-immunoprecipitation experiments in mammalian cells. SNX1 is associated with endosomal membranes and triggers the endosome-to-lysosome pathway of epidermal growth factor receptor (EGFR). We observe by immunofluorescence microscopy that Ent-1 and SNX1 are co-localized on vesicular and tubulovesicular structures, which are different from early endosome antigen 1-containing endosomes. By gel filtration chromatography, we show that Ent-1 and SNX1 co-eluted in macromolecular complexes containing part of EGFR. Furthermore, overexpressed Ent-1 decreases cell surface EGFR. Ent-1 and SNX1 co-overexpression strongly extends EGFR diminution, indicating a synergetic effect of both proteins on cell surface EGFR removal. Interestingly, the increase of endogenous Ent-1 expression correlates with the decrease of EGFR during spontaneous differentiation of Caco-2 cells. We thus propose a role of Ent-1 in the trafficking of EGFR to down-regulate intestinal mitogenic signals, highlighting the mechanisms of cell growth arrest associated with enterocytic differentiation.

Structural-proliferative units and organ growth: effects of insulin-like growth factor 2 on the growth of colon and skin

Many epithelial renewal tissues in vertebrates are organised into structural-proliferative units. We have examined the effect of IGF2 dose on the structure of structural-proliferative units in skin and colon. The mouse strains used were the Igf2 knockout, wild type and K:Igf2, a transgenic in which Igf2 is overexpressed under control of a keratin promoter. For both skin and colon, the histological organisation of structural-proliferative units was unaltered with increasing IGF2 dose, although there was a higher fraction of dividing cells in the proliferative compartment. In the colon an increase in IGF2 dose increases the overall area of the epithelium. This is due to an increase in the number of crypts with no change of cell size or of crypt area. Growth stimulation appears to be due to a reduction in the duration of crypt fission. The conclusion is that the IGF2 pathway can stimulate the multiplication of colonic crypts independently of stimulating increased cell proliferation. The results for the skin are consistent with this. An increase of IGF2 dose increases the proportion of dividing cells in the basal layer, the thickness of the epidermis and the total area of the epidermis. By comparison with Drosophila, these results show no effects on cell size, but do show the possibility of inducing disproportionate growth. These differences may represent properties of the SPU organisation that is characteristic of vertebrate tissues.

Mammalian intestinal epithelial cells in primary culture: a mini-review

Epithelial cells lining the digestive tract represent a highly organized system built up by multipotent stem cells. A process of asymmetric mitosis produces a population of proliferative cells that are rapidly renewed and migrate along the crypt-villus axis, differentiating into functional mature cells before dying and exfoliating into the intestinal lumen. Isolated crypts or epithelial cells retaining high viability can be prepared within a few h after tissue sampling. After cells are cultured in serum-free media, short-term studies (16-48 h) can be conducted for endocrinology, energy metabolism, or programmed cell death. However, long-term primary culture of intestinal cells (up to 10 d) is still difficult despite progress in isolation methodologies and manipulation of the cell microenvironment. The main problem in developing primary culture is the lack of structural markers specific to the stem cell compartment. The design of a microscopic multidimensional analytic system to record the expression profiles of biomarkers all along the living intestinal crypt should improve basic knowledge of the survival and growth of adult crypt stem cells, and the selection of totipotent embryonic stem cells capable of differentiating into intestinal tissues should facilitate studies of the genomic basis of endodermal tissue differentiation.

Generation of a complete thymic microenvironment by MTS24(+) thymic epithelial cells

The epithelial component of the thymic microenvironment is indispensable for the generation of T lymphocytes. Although the heterogeneity of this epithelium is well documented, little is known about precursor-progeny relationships between distinct thymic epithelial lineages. Here we characterized a thymic epithelial cell subpopulation identified by the cell surface glycoprotein MTS24. These cells contained epithelial progenitor cells that were competent and sufficient to fully reconstitute the complex thymic epithelial microenvironment that supported normal T cell development.

Emx2regulates the proliferation of stem cells of the adult mammalian central nervous system

The appropriate control of proliferation of neural precursors has fundamental implications for the development of the central nervous system and for cell homeostasis/replacement within specific brain regions throughout adulthood. The role of genetic determinants in this process is largely unknown.

We report the expression of the homeobox transcription factor Emx2 within the periventricular region of the adult telencephalon. This neurogenetic area displays a large number of multipotent stem cells. Adult neural stem cells isolated from this region do express Emx2 and down-regulate it significantly upon differentiation into neurons and glia. Abolishing or, increasing Emx2 expression in adult neural stem cells greatly enhances or reduces their rate of proliferation, respectively. We determined that altering the expression of Emx2 affects neither the cell cycle length of adult neural stem cells nor their ability to generate neurons and glia. Rather, when Emx2 expression is abolished, the frequency of symmetric divisions that generate two stem cells increases, whereas it decreases when Emx2 expression is enhanced.