Epithelial cells within the human pancreas do not coexpress mesenchymal antigens: epithelial-mesenchymal transition is an artifact of cell culture

Canine amniotic membrane-derived mesenchymal stem cells ameliorate atopic dermatitis through regeneration and immunomodulation

Mesenchymal stem cells (MSCs) are a promising tool for treating immune disorders. However, the immunomodulatory effects of canine MSCs compared with other commercialized biologics for treating immune disorders have not been well studied. In this study we investigated the characteristics and immunomodulatory effects of canine amnion membrane (cAM)-MSCs. We examined gene expression of immune modulation and T lymphocytes from activated canine peripheral blood mononuclear cell (PBMC) proliferation. As a result, we confirmed that cAM-MSCs upregulated immune modulation genes (TGF-β1, IDO1 and PTGES2) and suppressed the proliferation capacity of T cells. Moreover, we confirmed the therapeutic effect of cAM-MSCs compared with oclacitinib (OCL), the most commonly used Janus kinase (JAK) inhibitor, as a treatment for canine atopic dermatitis (AD) using a mouse AD model. As a result, we confirmed that cAM-MSCs with PBS treatment groups (passage 4, 6 and 8) compared with PBS only (PBS) though scores of dermatologic signs, tissue pathologic changes and inflammatory cytokines were significantly reduced. In particular, cAM-MSCs were more effective than OCL in the recovery of wound dysfunction, regulation of mast cell activity and expression level of immune modulation protein. Interestingly, subcutaneous injection of cAM-MSCs induced weight recovery, but oral administration of oclacitinib induced weight loss as a side effect. In conclusion, this study suggests that cAM-MSCs can be developed as a safe canine treatment for atopic dermatitis without side effects through effective regeneration and immunomodulation.

Overview and Future Perspectives on Tumor-Targeted Positron Emission Tomography and Fluorescence Imaging of Pancreatic Cancer in the Era of Neoadjuvant Therapy

BACKGROUND

Despite recent advances in the multimodal treatment of pancreatic ductal adenocarcinoma (PDAC), overall survival remains poor with a 5-year cumulative survival of approximately 10%. Neoadjuvant (chemo- and/or radio-) therapy is increasingly incorporated in treatment strategies for patients with (borderline) resectable and locally advanced disease. Neoadjuvant therapy aims to improve radical resection rates by reducing tumor mass and (partial) encasement of important vascular structures, as well as eradicating occult micrometastases. Results from recent multicenter clinical trials evaluating this approach demonstrate prolonged survival and increased complete surgical resection rates (R0). Currently, tumor response to neoadjuvant therapy is monitored using computed tomography (CT) following the RECIST 1.1 criteria. Accurate assessment of neoadjuvant treatment response and tumor resectability is considered a major challenge, as current conventional imaging modalities provide limited accuracy and specificity for discrimination between necrosis, fibrosis, and remaining vital tumor tissue. As a consequence, resections with tumor-positive margins and subsequent early locoregional tumor recurrences are observed in a substantial number of patients following surgical resection with curative intent. Of these patients, up to 80% are diagnosed with recurrent disease after a median disease-free interval of merely 8 months. These numbers underline the urgent need to improve imaging modalities for more accurate assessment of therapy response and subsequent re-staging of disease, thereby aiming to optimize individual patient's treatment strategy. In cases of curative intent resection, additional intra-operative real-time guidance could aid surgeons during complex procedures and potentially reduce the rate of incomplete resections and early (locoregional) tumor recurrences. In recent years intraoperative imaging in cancer has made a shift towards tumor-specific molecular targeting. Several important molecular targets have been identified that show overexpression in PDAC, for example: CA19.9, CEA, EGFR, VEGFR/VEGF-A, uPA/uPAR, and various integrins. Tumor-targeted PET/CT combined with intraoperative fluorescence imaging, could provide valuable information for tumor detection and staging, therapy response evaluation with re-staging of disease and intraoperative guidance during surgical resection of PDAC.

METHODS

A literature search in the PubMed database and (inter)national trial registers was conducted, focusing on studies published over the last 15 years. Data and information of eligible articles regarding PET/CT as well as fluorescence imaging in PDAC were reviewed. Areas covered: This review covers the current strategies, obstacles, challenges, and developments in targeted tumor imaging, focusing on the feasibility and value of PET/CT and fluorescence imaging for integration in the work-up and treatment of PDAC. An overview is given of identified targets and their characteristics, as well as the available literature of conducted and ongoing clinical and preclinical trials evaluating PDAC-targeted nuclear and fluorescent tracers.

Therapeutic Use of Mesenchymal Stromal Cells: The Need for Inclusive Characterization Guidelines to Accommodate All Tissue Sources and Species

Following their discovery over 50 years ago, mesenchymal stromal cells (MSCs) have become one of the most studied cellular therapeutic products by both academia and industry due to their regenerative potential and immunomodulatory properties. The promise of MSCs as a therapeutic modality has been demonstrated by preclinical data yet has not translated to consistent, successful clinical trial results in humans. Despite the disparities across the field, MSC shareholders are unified under one common goal-to use MSCs as a therapeutic modality to improve the quality of life for those suffering from a malady in which the standard of care is suboptimal or no longer effective. Currently, there is no Food and Drug Administration (FDA)-approved MSC therapy on the market in the United States although several MSC products have been granted regulatory approval in other countries. In this review, we intend to identify hurdles that are impeding therapeutic progress and discuss strategies that may aid in accomplishing this universal goal of widespread therapeutic use.

scCATCH: Automatic Annotation on Cell Types of Clusters from Single-Cell RNA Sequencing Data

Recent advancements in single-cell RNA sequencing (scRNA-seq) have facilitated the classification of thousands of cells through transcriptome profiling, wherein accurate cell type identification is critical for mechanistic studies. In most current analysis protocols, cell type-based cluster annotation is manually performed and heavily relies on prior knowledge, resulting in poor replicability of cell type annotation. This study aimed to introduce a single-cell Cluster-based Automatic Annotation Toolkit for Cellular Heterogeneity (scCATCH, https://github.com/ZJUFanLab/scCATCH). Using three benchmark datasets, the feasibility of evidence-based scoring and tissue-specific cellular annotation strategies were demonstrated by high concordance among cell types, and scCATCH outperformed Seurat, a popular method for marker genes identification, and cell-based annotation methods. Furthermore, scCATCH accurately annotated 67%–100% (average, 83%) clusters in six published scRNA-seq datasets originating from various tissues. The present results show that scCATCH accurately revealed cell identities with high reproducibility, thus potentially providing insights into mechanisms underlying disease pathogenesis and progression.

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Construction of a comprehensive tissue-specific reference database of cell markers

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Paired comparisons to identify potential marker genes for clusters to ensure accuracy

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Evidence-based scoring and annotation for clustered cells from scRNA-seq data

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Accurate and replicable annotation on cell types of clusters without prior knowledge

Characterization of a Vimentinhigh /Nestinhigh proteome and tissue regenerative secretome generated by human pancreas-derived mesenchymal stromal cells

Multipotent/mesenchymal stromal cells (MSCs) exist within a variety of postnatal tissues; however, global proteomic analyses comparing tissue-specific MSC are limited. Using human bone marrow (BM)-derived MSCs as a gold standard, we used label-free mass spectrometry and functional assays to characterize the proteome, secretome, and corresponding function of human pancreas-derived MSCs (Panc-MSCs) with a classical phenotype (CD90+/CD73+/CD105+/CD45-/CD31-). Both MSC subtypes expressed mesenchymal markers vimentin, α-SMA, and STRO-1; however, expression of nestin was increased in Panc-MSCs. Accordingly, these Vimentin^high /Nestin^high cells were isolated from fresh human pancreatic islet and non-islet tissues. Next, we identified expression of >60 CD markers shared between Panc-MSCs and BM-MSCs, including validated expression of CD14. An additional 19 CD markers were differentially expressed, including reduced pericyte-marker CD146 expression on Panc-MSCs. Panc-MSCs also showed reduced expression of proteins involved in lipid and retinoid metabolism. Accordingly, Panc-MSCs showed restricted responses to adipogenic stimuli in vitro, although both MSC types demonstrated trilineage differentiation. In contrast, Panc-MSCs demonstrated accelerated growth kinetics and competency to pro-neurogenic stimuli in vitro. The secretome of Panc-MSCs was highly enriched for proteins associated with vascular development, wound healing and chemotaxis. Similar to BM-MSCs, Panc-MSCs conditioned media augmented endothelial cell survival, proliferation, and tubule formation in vitro. Importantly, the secretome of both MSC types was capable of stimulating chemotactic infiltration of murine endothelial cells in vivo and reduced hyperglycemia in STZ-treated mice following intrapancreatic injection. Overall, this study provides foundational knowledge to develop Panc-MSCs as a unique MSC subtype with functional properties beneficial in regenerative medicine for diabetes and vascular disease.

EMT and Stemness-Key Players in Pancreatic Cancer Stem Cells

Metastasis and tumor progression are the major cause of death in patients suffering from pancreatic ductal adenocarcinoma. Tumor growth and especially dissemination are typically associated with activation of an epithelial-to-mesenchymal transition (EMT) program. This phenotypic transition from an epithelial to a mesenchymal state promotes migration and survival both during development and in cancer progression. When re-activated in pathological contexts such as cancer, this type of developmental process confers additional stemness properties to specific subsets of cells. Cancer stem cells (CSCs) are a subpopulation of cancer cells with stem-like features that are responsible for the propagation of the tumor as well as therapy resistance and cancer relapse, but also for circulating tumor cell release and metastasis. In support of this concept, EMT transcription factors generate cells with stem cell properties and mediate chemoresistance. However, their role in pancreatic ductal adenocarcinoma metastasis remains controversial. As such, a better characterization of CSC populations will be crucial in future development of therapies targeting these cells. In this review, we will discuss the latest updates on the mechanisms common to pancreas development and CSC-mediated tumor progression.

β-cell replacement sources for type 1 diabetes: a focus on pancreatic ductal cells

Thorough research on the capacity of human islet transplantation to cure type 1 diabetes led to the achievement of 3- to 5-year-long insulin independence in nearly half of transplanted patients. Yet, translation of this technique to clinical routine is limited by organ shortage and the need for long-term immunosuppression, restricting its use to adults with unstable disease. The production of new bona fide β cells in vitro was thus investigated and finally achieved with human pluripotent stem cells (PSCs). Besides ethical concerns about the use of human embryos, studies are now evaluating the possibility of circumventing the spontaneous tumor formation associated with transplantation of PSCs. These issues fueled the search for cell candidates for β-cell engineering with safe profiles for clinical translation. In vivo studies revealed the regeneration capacity of the exocrine pancreas after injury that depends at least partially on facultative progenitors in the ductal compartment. These stimulated subpopulations of pancreatic ductal cells (PDCs) underwent β-cell transdifferentiation through reactivation of embryonic signaling pathways. In vitro models for expansion and differentiation of purified PDCs toward insulin-producing cells were described using cocktails of growth factors, extracellular-matrix proteins and transcription factor overexpression. In this review, we will describe the latest findings in pancreatic β-cell mass regeneration due to adult ductal progenitor cells. We will further describe recent advances in human PDC transdifferentiation to insulin-producing cells with potential for clinical translational studies.

Identification and differentiation of PDX1 β-cell progenitors within the human pancreatic epithelium

AIM: To minimize the expansion of pancreatic mesenchymal cells in vitro and confirm that β-cell progenitors reside within the pancreatic epithelium.

METHODS: Due to mesenchymal stem cell (MSC) expansion and overgrowth, progenitor cells within the pancreatic epithelium cannot be characterized in vitro, though β-cell dedifferentiation and expansion of MSC intermediates via epithelial-mesenchymal transition (EMT) may generate β-cell progenitors. Pancreatic epithelial cells from endocrine and non-endocrine tissue were expanded and differentiated in a novel pancreatic epithelial expansion medium supplemented with growth factors known to support epithelial cell growth (dexamethasone, epidermal growth factor, 3,5,3’-triiodo-l-thyronine, bovine brain extract). Cells were also infected with a single and dual lentiviral reporter prior to cell differentiation. Enhanced green fluorescent protein was controlled by the rat Insulin 1 promoter and the monomeric red fluorescent protein was controlled by the mouse PDX1 promoter. In combination with lentiviral tracing, cells expanded and differentiated in the pancreatic medium were characterized by flow cytometry (BD fluorescence activated cell sorting), immunostaining and real-time polymerase chain reaction (PCR) (7900HT Fast Realtime PCR System).

RESULTS: In the presence of 10% serum MSCs rapidly expand in vitro while the epithelial cell population declines. The percentage of vimentin⁺ cells increased from 22% ± 5.83% to 80.43% ± 3.24% (14 d) and 99.00% ± 0.0% (21 d), and the percentage of epithelial cells decreased from 74.71% ± 8.34% to 26.57% ± 9.75% (14 d) and 4.00% ± 1.53% (21 d), P < 0.01 for all time points. Our novel pancreatic epithelial expansion medium preserved the epithelial cell phenotype and minimized epithelial cell dedifferentiation and EMT. Cells expanded in our epithelial medium contained significantly less mesenchymal cells (vimentin⁺) compared to controls (44.87% ± 4.93% vs 95.67% ± 1.36%; P < 0.01). During cell differentiation lentiviral reporting demonstrated that, PDX1⁺ and insulin⁺ cells were localized within adherent epithelial cell aggregates compared to controls. Compared to starting islets differentiated cells had at least two fold higher gene expression of PDX1, insulin, PAX4 and RFX (P < 0.05).

CONCLUSION: PDX1⁺ cells were confined to adherent epithelial cell aggregates and not vimentin⁺ cells (mesenchymal), suggesting that EMT is not a mechanism for generating pancreatic progenitor cells.

Functional plasticity of the human infant β-cell exocytotic phenotype

Our understanding of adult human β-cells is advancing, but we know little about the function and plasticity of β-cells from infants. We therefore characterized islets and single islet cells from human infants after isolation and culture. Although islet morphology in pancreas biopsies was similar to that in adults, infant islets after isolation and 24-48 hours of culture had less insulin staining, content, and secretion. The cultured infant islets expressed pancreatic and duodenal homeobox 1 and several (Glut1, Cav1.3, Kir6.2) but not all (syntaxin 1A and synaptosomal-associated protein 25) markers of functional islets, suggesting a loss of secretory phenotype in culture. The activity of key ion channels was maintained in isolated infant β-cells, whereas exocytosis was much lower than in adults. We examined whether a functional exocytotic phenotype could be reestablished under conditions thought to promote β-cell differentiation. After a 24- to 28-day expansion and maturation protocol, we found preservation of endocrine markers and hormone expression, an increased proportion of insulin-positive cells, elevated expression of syntaxin 1A and synaptosomal-associated protein 25, and restoration of exocytosis to levels comparable with that in adult β-cells. Thus, human infant islets are prone to loss of their exocytotic phenotype in culture but amenable to experimental approaches aimed at promoting expansion and functional maturation. Control of exocytotic protein expression may be an important mechanism underlying the plasticity of the secretory machinery, an increased understanding of which may lead to improved regenerative approaches to treat diabetes.

β-Cell Generation: Can Rodent Studies Be Translated to Humans?

β-cell replacement by allogeneic islet transplantation is a promising approach for patients with type 1 diabetes, but the shortage of organ donors requires new sources of β cells. Islet regeneration in vivo and generation of β-cells ex vivo followed by transplantation represent attractive therapeutic alternatives to restore the β-cell mass. In this paper, we discuss different postnatal cell types that have been envisaged as potential sources for future β-cell replacement therapy. The ultimate goal being translation to the clinic, a particular attention is given to the discrepancies between findings from studies performed in rodents (both ex vivo on primary cells and in vivo on animal models), when compared with clinical data and studies performed on human cells.

Transforming growth factor-β induces epithelial to mesenchymal transition and suppresses the proliferation and transdifferentiation of cultured human pancreatic duct cells

Pancreatic duct cells are considered a potential source of β-cell regeneration, and transforming growth factor-β (TGF-β) has been suggested to perform an important role in these processes, but the underlying mechanism of the signal pathways, especially in humans, remains poorly understood. To evaluate the role of TGF-β1, pancreatic duct cells were isolated from three brain-dead organ donors. Pancreatic cell clusters harvested after islet isolation were dispersed to single cells and cultured in monolayers, then treated with TGF-β1. We analyzed the characteristics of the cultured cells, the TGF-β1 intracellular signaling pathway, the proliferation, and transdifferentiation rates of the duct cells. We also evaluated the genes and protein expression patterns after TGF-β1 treatment. After TGF-β1 treatment, typical morphologic changes representative of EMT were observed and Erk1/2, JNK, and AKT phosphorylation, Ras downstream effectors, were increased. β cell-specific transcription factors including PDX-1, Beta2/NeuroD, Ist-1, and NGN3 were markedly suppressed and the rate of transdifferentiation into β cells was also suppressed. Genomic and proteomic analyses suggested that TGF-β1 induces marked changes in a variety of structural genes and proteins associated with EMT. In conclusion, TGF-β1 induces EMT in cultured human pancreatic duct cells, but suppresses its proliferation and transdifferentiation into β cells. Our results are the first report of TGF-β1 effects for EMT and ductal cell transdifferentiation and proliferation at the protein level in human pancreatic duct cells.

Evidence for mesenchymal-epithelial transition associated with mouse hepatic stem cell differentiation

Mesenchymal−epithelial transition events are related to embryonic development, tissue construction, and wound healing. Stem cells are involved in all of these processes, at least in part. However, the direct evidence of mesenchymal−epithelial transition associated with stem cells is unclear. To determine whether mesenchymal−epithelial transition occurs in liver development and/or the differentiation process of hepatic stem cells in vitro, we analyzed a variety of murine liver tissues from embryonic day 11.5 to adults and the colonies derived from hepatic stem/progenitor cells isolated with flow cytometry. The results of gene expression, immunohistochemistry and Western blot showed that as liver develops, the expression of epithelial markers such as Cytokeratin18 and E-cadherin increase, while expression of mesenchymal markers such as vimentin and N-cadherin decreased. On the other hand, in freshly isolated hepatic stem cells, the majority of cells (65.0%) co-express epithelial and mesenchymal markers; this proportion is significantly higher than observed in hematopoietic cells, non-hematopoietic cells and non-stem cell fractions. Likewise, in stem cell-derived colonies cultured over time, upregulation of epithelial genes (Cytokeratin-18 and E-cadherin) occurred simultaneously with downregulation of mesenchymal genes (vimentin and Snail1). Furthermore, in the fetal liver, vimentin-positive cells in the non-hematopoietic fraction had distinct proliferative activity and expressed early the hepatic lineage marker alpha-fetoprotein.

Isolation and culture of human multipotent stromal cells from the pancreas

Mesenchymal stem cells, also termed multipotent mesenchymal stromal cells (MSCs), can be isolated from most adult tissues. Although the exact origin of MSCs expanded from the human pancreas has not been resolved, we have developed protocols to isolate and expand MSCs from human pancreatic tissue that remains after islet procurement. Similar to techniques used to isolate MSCs from bone marrow, pancreatic MSCs are isolated based on their cell adherence, expression of several cell surface antigens, and multilineage differentiation. The protocols for isolating, characterizing, and differentiating MSCs from the pancreas are presented in this chapter.

Evidence for epithelial-mesenchymal transition in adult human pancreatic exocrine cells

It has been shown that adult pancreatic ductal cells can dedifferentiate and act as pancreatic progenitors. Dedifferentiation of epithelial cells is often associated with the epithelial-mesenchymal transition (EMT). In this study, we investigated the occurrence of EMT in adult human exocrine pancreatic cells both in vitro and in vivo. Cells of exocrine fraction isolated from the pancreas of brain-dead donors were first cultured in suspension for eight days. This led to the formation of spheroids, composed of a principal population of cells with duct-like phenotype. When cultivated in tissue culture-treated flasks, spheroid cells exhibited a proliferative capacity and coexpressed epithelial (cytokeratin7 and cytokeratin19) and mesenchymal (vimentin and alpha-smooth muscle actin) markers as well as marker of progenitor pancreatic cells (pancreatic duodenal homeobox factor-1) and surface markers of mesenchymal stem cells. The switch from E-cadherin to N-cadherin associated with Snail1 expression suggested that these cells underwent EMT. In addition, we showed coexpression of epithelial and mesenchymal markers in ductal cells of one normal adult pancreas and three type 2 diabetic pancreases. Some of the vimentin-positive cells were found to coexpress glucagon or amylase. These results point to the occurrence of EMT, which may take place on dedifferentiation of ductal cells during the regeneration or renewal of human pancreatic tissues.

Different responses in transformation of MDCK cells in 2D and 3D culture by v-Src as revealed by microarray techniques, RT-PCR and functional assays

Differentiation and transformation of untransformed and ts-Src-transformed canine kidney MDCK cells in 2D and 3D environment were investigated using microarray technique, RT-PCR, confocal microscopy and functional assays. Activated Src induced epithelial-mesenchymal transition (EMT) in 2D environment followed by translocation of junctional proteins to the cytoplasm, without significant changes in protein expression. In 3D environment untransformed MDCK cells formed cell cysts with apical domain facing a lumen, E-cadherin delineating the lateral membranes, ZO-1 at tight junctions and caspase-3 in apoptotic cells captured within the lumen. This was accompanied by reduced expression of an apoptosis inhibitor, survivin and vesicle transport effectors, rab 7 and 8, whereas rab 5 expression increased. In 3D environment activated Src induced changes in expression of over 100 genes as revealed by microarray analysis, mostly involved in cell signaling, division and energy metabolism. Only response in cytoskeletal components was decreased expression of actin and Arp2/3 by v-Src, whereas two p120catenin binding proteins Kaiso and Nanos increased their expression. Concomitantly, apoptosis was inhibited by v-Src resulting in formation of a sphere with epitheloid cells facing extracellular matrix and undifferentiated cells captured within the cluster. This was accompanied by increased expression of apoptosis inhibitor survivin, as revealed by western blotting. Mitochondrial membrane potential in untransformed MDCK cells was lower than in ts-Src-MDCK cells in early days of cluster formation correlating with the induction of apoptosis. Hence, v-Src activation in 3D environment did not induce EMT, but brought about inhibition of apoptosis and increased proliferation where increased expression of survivin and inhibition of the mitochondrial permeability have a role.

{beta}-Cell mass dynamics and islet cell plasticity in human type 2 diabetes

Studies of long-standing type 2 diabetes (T2D) report a deficit in beta-cell mass due to increased apoptosis, whereas neogenesis and replication are unaffected. It is unclear whether these changes are a cause or a consequence of T2D. Moreover, whereas islet morphogenetic plasticity has been demonstrated in vitro, the in situ plasticity of islets, as well as the effect of T2D on endocrine differentiation, is unknown. We compared beta-cell volume, neogenesis, replication, and apoptosis in pancreata from lean and obese (body mass index > or = 27 kg/m(2)) diabetic (5 +/- 2 yr since diagnosis) and nondiabetic cadaveric donors. We also subjected isolated islets from diabetic (3 +/- 1 yr since diagnosis) and nondiabetic donors to an established in vitro model of islet plasticity. Differences in beta-cell volume between diabetic and nondiabetic donors were consistently less pronounced than those reported in long-standing T2D. A compensatory increase in beta-cell neogenesis appeared to mediate this effect. Studies of induced plasticity indicated that islets from diabetic donors were capable of epithelial dedifferentiation but did not demonstrate regenerative potential, as was seen in islets from nondiabetic donors. This deficiency was associated with the overexpression of Notch signaling molecules and a decreased neurogenin-3(+) cell frequency. One interpretation of these results would be that decreased beta-cell volume is a consequence, not a cause, of T2D, mediated by increased apoptosis and attenuated beta-cell (re)generation. However, other explanations are also possible. It remains to be seen whether the morphogenetic plasticity of human islets, deficient in vitro in islets from diabetic donors, is a component of normal beta-cell mass dynamics.

One process for pancreatic beta-cell coalescence into islets involves an epithelial-mesenchymal transition

Islet replacement is a promising therapy for treating diabetes mellitus, but the supply of donor tissue for transplantation is limited. To overcome this limitation, endocrine tissue can be expanded, but this requires an understanding of normal developmental processes that regulate islet formation. In this study, we compare pancreas development in sheep and human, and provide evidence that an epithelial-mesenchymal transition (EMT) is involved in beta-cell differentiation and islet formation. Transcription factors know to regulate pancreas formation, pancreatic duodenal homeobox factor 1, neurogenin 3, NKX2-2, and NKX6-1, which were expressed in the appropriate spatial and temporal pattern to coordinate pancreatic bud outgrowth and direct endocrine cell specification in sheep. Immunofluorescence staining of the developing pancreas was used to co-localize insulin and epithelial proteins (cytokeratin, E-cadherin, and beta-catenin) or insulin and a mesenchymal protein (vimentin). In sheep, individual beta-cells become insulin-positive in the progenitor epithelium, then lose epithelial characteristics, and migrate out of the epithelial layer to form islets. As beta-cells exit the epithelial progenitor cell layer, they acquire mesenchymal characteristics, shown by their acquisition of vimentin. In situ hybridization expression analysis of the SNAIL family members of transcriptional repressors (SNAIL1, -2, and -3; listed as SNAI1, -2, -3 in the HUGO Database) showed that each of the SNAIL genes was expressed in the ductal epithelium during development, and SNAIL-1 and -2 were co-expressed with insulin. Our findings provide strong evidence that the movement of beta-cells from the pancreatic ductal epithelium involves an EMT.