Pancreas organogenesis: from lineage determination to morphogenesis.

The pancreas is an essential organ for proper nutrient metabolism and has both endocrine and exocrine function. In the past two decades, knowledge of how the pancreas develops during embryogenesis has significantly increased, largely from developmental studies in model organisms. Specifically, the molecular basis of pancreatic lineage decisions and cell differentiation is well studied. Still not well understood are the mechanisms governing three-dimensional morphogenesis of the organ. Strategies to derive transplantable ß-cells in vitro for diabetes treatment have benefited from the accumulated knowledge of pancreas development. In this review, we provide an overview of the current understanding of pancreatic lineage determination and organogenesis, and we examine future implications of these findings for treatment of diabetes mellitus through cell replacement.

Colony-forming cells in the adult mouse pancreas are expandable in Matrigel and form endocrine/acinar colonies in laminin hydrogel.

The study of hematopoietic colony-forming units using semisolid culture media has greatly advanced the knowledge of hematopoiesis. Here we report that similar methods can be used to study pancreatic colony-forming units. We have developed two pancreatic colony assays that enable quantitative and functional analyses of progenitor-like cells isolated from dissociated adult (2-4 mo old) murine pancreas. We find that a methylcellulose-based semisolid medium containing Matrigel allows growth of duct-like "Ring/Dense" colonies from a rare (∼1%) population of total pancreatic single cells. With the addition of roof plate-specific spondin 1, a wingless-int agonist, Ring/Dense colony-forming cells can be expanded more than 100,000-fold when serially dissociated and replated in the presence of Matrigel. When cells grown in Matrigel are then transferred to a Matrigel-free semisolid medium with a unique laminin-based hydrogel, some cells grow and differentiate into another type of colony, which we name "Endocrine/Acinar." These Endocrine/Acinar colonies are comprised mostly of endocrine- and acinar-like cells, as ascertained by RNA expression analysis, immunohistochemistry, and electron microscopy. Most Endocrine/Acinar colonies contain beta-like cells that secrete insulin/C-peptide in response to D-glucose and theophylline. These results demonstrate robust self-renewal and differentiation of adult Ring/Dense colony-forming units in vitro and suggest an approach to producing beta-like cells for cell replacement of type 1 diabetes. The methods described, which include microfluidic expression analysis of single cells and colonies, should also advance study of pancreas development and pancreatic progenitor cells.

Sox9 plays multiple roles in the lung epithelium during branching morphogenesis.

Lung branching morphogenesis is a highly orchestrated process that gives rise to the complex network of gas-exchanging units in the adult lung. Intricate regulation of signaling pathways, transcription factors, and epithelial-mesenchymal cross-talk are critical to ensuring branching morphogenesis occurs properly. Here, we describe a role for the transcription factor Sox9 during lung branching morphogenesis. Sox9 is expressed at the distal tips of the branching epithelium in a highly dynamic manner as branching occurs and is down-regulated starting at embryonic day 16.5, concurrent with the onset of terminal differentiation of type 1 and type 2 alveolar cells. Using epithelial-specific genetic loss- and gain-of-function approaches, our results demonstrate that Sox9 controls multiple aspects of lung branching. Fine regulation of Sox9 levels is required to balance proliferation and differentiation of epithelial tip progenitor cells, and loss of Sox9 leads to direct and indirect cellular defects including extracellular matrix defects, cytoskeletal disorganization, and aberrant epithelial movement. Our evidence shows that unlike other endoderm-derived epithelial tissues, such as the intestine, Wnt/ß-catenin signaling does not regulate Sox9 expression in the lung. We conclude that Sox9 collectively promotes proper branching morphogenesis by controlling the balance between proliferation and differentiation and regulating the extracellular matrix.

A Sox9/Fgf feed-forward loop maintains pancreatic organ identity.

All mature pancreatic cell types arise from organ-specific multipotent progenitor cells. Although previous studies have identified cell-intrinsic and -extrinsic cues for progenitor cell expansion, it is unclear how these cues are integrated within the niche of the developing organ. Here, we present genetic evidence in mice that the transcription factor Sox9 forms the centerpiece of a gene regulatory network that is crucial for proper organ growth and maintenance of organ identity. We show that pancreatic progenitor-specific ablation of Sox9 during early pancreas development causes pancreas-to-liver cell fate conversion. Sox9 deficiency results in cell-autonomous loss of the fibroblast growth factor receptor (Fgfr) 2b, which is required for transducing mesenchymal Fgf10 signals. Likewise, Fgf10 is required to maintain expression of Sox9 and Fgfr2 in epithelial progenitors, showing that Sox9, Fgfr2 and Fgf10 form a feed-forward expression loop in the early pancreatic organ niche. Mirroring Sox9 deficiency, perturbation of Fgfr signaling in pancreatic explants or genetic inactivation of Fgf10 also result in hepatic cell fate conversion. Combined with previous findings that Fgfr2b or Fgf10 are necessary for pancreatic progenitor cell proliferation, our results demonstrate that organ fate commitment and progenitor cell expansion are coordinately controlled by the activity of a Sox9/Fgf10/Fgfr2b feed-forward loop in the pancreatic niche. This self-promoting Sox9/Fgf10/Fgfr2b loop may regulate cell identity and organ size in a broad spectrum of developmental and regenerative contexts.

A Notch-dependent molecular circuitry initiates pancreatic endocrine and ductal cell differentiation.

In the pancreas, Notch signaling is thought to prevent cell differentiation, thereby maintaining progenitors in an undifferentiated state. Here, we show that Notch renders progenitors competent to differentiate into ductal and endocrine cells by inducing activators of cell differentiation. Notch signaling promotes the expression of Sox9, which cell-autonomously activates the pro-endocrine gene Ngn3. However, at high Notch activity endocrine differentiation is blocked, as Notch also induces expression of the Ngn3 repressor Hes1. At the transition from high to intermediate Notch activity, only Sox9, but not Hes1, is maintained, thus de-repressing Ngn3 and initiating endocrine differentiation. In the absence of Sox9 activity, endocrine and ductal cells fail to differentiate, resulting in polycystic ducts devoid of primary cilia. Although Sox9 is required for Ngn3 induction, endocrine differentiation necessitates subsequent Sox9 downregulation and evasion from Notch activity via cell-autonomous repression of Sox9 by Ngn3. If high Notch levels are maintained, endocrine progenitors retain Sox9 and undergo ductal fate conversion. Taken together, our findings establish a novel role for Notch in initiating both ductal and endocrine development and reveal that Notch does not function in an on-off mode, but that a gradient of Notch activity produces distinct cellular states during pancreas development.

Sox9+ ductal cells are multipotent progenitors throughout development but do not produce new endocrine cells in the normal or injured adult pancreas.

One major unresolved question in the field of pancreas biology is whether ductal cells have the ability to generate insulin-producing ß-cells. Conclusive examination of this question has been limited by the lack of appropriate tools to efficiently and specifically label ductal cells in vivo. We generated Sox9CreER(T2) mice, which, during adulthood, allow for labeling of an average of 70% of pancreatic ductal cells, including terminal duct/centroacinar cells. Fate-mapping studies of the Sox9(+) domain revealed endocrine and acinar cell neogenesis from Sox9(+) cells throughout embryogenesis. Very small numbers of non-ß endocrine cells continue to arise from Sox9(+) cells in early postnatal life, but no endocrine or acinar cell neogenesis from Sox9(+) cells occurs during adulthood. In the adult pancreas, pancreatic injury by partial duct ligation (PDL) has been suggested to induce ß-cell regeneration from a transient Ngn3(+) endocrine progenitor cell population. Here, we identify ductal cells as a cell of origin for PDL-induced Ngn3(+) cells, but fail to observe ß-cell neogenesis from duct-derived cells. Therefore, although PDL leads to activation of Ngn3 expression in ducts, PDL does not induce appropriate cues to allow for completion of the entire ß-cell neogenesis program. In conclusion, although endocrine cells arise from the Sox9(+) ductal domain throughout embryogenesis and the early postnatal period, Sox9(+) ductal cells of the adult pancreas no longer give rise to endocrine cells under both normal conditions and in response to PDL.

Nanofiber-microwell cell culture system for spatially patterned differentiation of pluripotent stem cells in 3D.

The intricate interplay between biochemical and physical cues dictates pluripotent stem cell (PSC) differentiation to form various tissues. While biochemical modulation has been extensively studied, the role of biophysical microenvironments in early lineage commitment remains elusive. Here, we introduce a novel 3D cell culture system combining electrospun nanofibers with microfabricated polydimethylsiloxane (PDMS) patterns. This system enables the controlled formation of semispherical human induced pluripotent stem cell (hiPSC) colonies, facilitating the investigation of local mechanical stem cell niches on mechano-responsive signaling and lineage specification. Our system unveiled spatially organized RhoA activity coupled with actin-myosin cable formation, suggesting mechano-dependent hiPSC behaviors. Nodal network analysis of RNA-seq data revealed RhoA downstream regulation of YAP signaling, DNA histone modifications, and patterned germ layer specification. Notably, altering colony morphology through controlled PDMS microwell shaping effectively modulated the spatial distribution of mechano-sensitive mediators and subsequent differentiation. This study provides a cell culture platform to decipher the role of biophysical cues in early embryogenesis, offering valuable insights for material design in tissue engineering and regenerative medicine applications.

A matrigel-free method for culture of pancreatic endocrine-like cells in defined protein-based hydrogels.

The transplantation of pancreatic endocrine islet cells from cadaveric donors is a promising treatment for type 1 diabetes (T1D), which is a chronic autoimmune disease that affects approximately nine million people worldwide. However, the demand for donor islets outstrips supply. This problem could be solved by differentiating stem and progenitor cells to islet cells. However, many current culture methods used to coax stem and progenitor cells to differentiate into pancreatic endocrine islet cells require Matrigel, a matrix composed of many extracellular matrix (ECM) proteins secreted from a mouse sarcoma cell line. The undefined nature of Matrigel makes it difficult to determine which factors drive stem and progenitor cell differentiation and maturation. Additionally, it is difficult to control the mechanical properties of Matrigel without altering its chemical composition. To address these shortcomings of Matrigel, we engineered defined recombinant proteins roughly 41 kDa in size, which contain cell-binding ECM peptides derived from fibronectin (ELYAVTGRGDSPASSAPIA) or laminin alpha 3 (PPFLMLLKGSTR). The engineered proteins form hydrogels through association of terminal leucine zipper domains derived from rat cartilage oligomeric matrix protein. The zipper domains flank elastin-like polypeptides whose lower critical solution temperature (LCST) behavior enables protein purification through thermal cycling. Rheological measurements show that a 2% w/v gel of the engineered proteins display material behavior comparable to a Matrigel/methylcellulose-based culture system previously reported by our group to support the growth of pancreatic ductal progenitor cells. We tested whether our protein hydrogels in 3D culture could derive endocrine and endocrine progenitor cells from dissociated pancreatic cells of young (1-week-old) mice. We found that both protein hydrogels favored growth of endocrine and endocrine progenitor cells, in contrast to Matrigel-based culture. Because the protein hydrogels described here can be further tuned with respect to mechanical and chemical properties, they provide new tools for mechanistic study of endocrine cell differentiation and maturation.

Coordination between ECM and cell-cell adhesion regulates the development of islet aggregation, architecture, and functional maturation.

Pancreatic islets are three-dimensional cell aggregates consisting of unique cellular composition, cell-to-cell contacts, and interactions with blood vessels. Cell aggregation is essential for islet endocrine function; however, it remains unclear how developing islets establish aggregation. By combining genetic animal models, imaging tools, and gene expression profiling, we demonstrate that islet aggregation is regulated by extracellular matrix signaling and cell-cell adhesion. Islet endocrine cell-specific inactivation of extracellular matrix receptor integrin ß1 disrupted blood vessel interactions but promoted cell-cell adhesion and the formation of larger islets. In contrast, ablation of cell-cell adhesion molecule α-catenin promoted blood vessel interactions yet compromised islet clustering. Simultaneous removal of integrin ß1 and α-catenin disrupts islet aggregation and the endocrine cell maturation process, demonstrating that establishment of islet aggregates is essential for functional maturation. Our study provides new insights into understanding the fundamental self-organizing mechanism for islet aggregation, architecture, and functional maturation.

DNA Methylation-Dependent Restriction of Tyrosine Hydroxylase Contributes to Pancreatic ß-Cell Heterogeneity.

The molecular and functional heterogeneity of pancreatic ß-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of ß-cells that co-express tyrosine hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ ß-cells within islets is essential for appropriate function in mice, such that a higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of ß-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ ß-cells and show differences in their developmental restriction in mice and humans. We show that TH expression in ß-cells is restricted by DNA methylation during ß-cell differentiation. Ablation of de novo DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ ß-cells, whereas ß-cell-specific ablation of Dnmt3a does not. We demonstrate that maintenance of Th promoter methylation is essential for its continued restriction in postnatal ß-cells. Loss of Th promoter methylation in response to chronic overnutrition increases the number of TH+ ß-cells, corresponding to impaired ß-cell function. These results reveal a regulatory role of DNA methylation in determining ß-cell heterogeneity.

Ubiquitous Luciferase Expression in "Firefly Rats" Does Not Alter the Pancreatic Islet Morphology, Metabolism, and Function.

"Firefly rats" ubiquitously express the luciferase reporter gene under the control of constitutively active ROSA26 promoter in inbred Lewis rats. Due to the minimal immunogenicity of luciferase, wide applications of Firefly rats have been reported in solid organ/cell transplantation studies for in vivo imaging, permitting quantitative and non-invasive tracking of the transplanted graft. ROSA26 is a non-coding gene and generally does not affect the expression of other endogenous genes. However, the effect of ubiquitous luciferase expression on islet morphology and function has not been thoroughly investigated, which is critical for the use of Firefly rats as islet donors in islet transplantation studies. Accordingly, in vivo glucose homeostasis (i.e., islet function in the native pancreas) was compared between age-matched luciferase-expressing Firefly rats and non-luciferase-expressing rats. In vivo assessments demonstrated no statistical difference between these rats in non-fasting blood glucose levels, intraperitoneal glucose tolerance tests, and glucose-stimulated serum C-peptide levels. Furthermore, islets were isolated from both rats to compare the morphology, function, and metabolism in vitro. Isolated islets from both rats exhibited similar in vitro characteristics in post-isolation islet yield, islet size, beta cell populations, insulin content per islet, oxygen consumption rate, and glucose-stimulated insulin secretion. In conclusion, ubiquitous luciferase expression in Firefly rats does not affect their islet morphology, metabolism, and function; this finding is critical and enables the use of isolated islets from Firefly rats for the dual assessment of islet graft function and bioluminescence imaging of islet grafts.

Painting the Pancreas in Three Dimensions: Whole-Mount Immunofluorescence Method.

The pancreas is composed of different cellular populations, organized into distinct functional units, including acinar clusters, islets of Langerhans, and the ductal system. As a result of research into diabetes, several optical techniques have been developed for the three-dimensional visualization of islet populations, so as to better understand their anatomical characteristics. These approaches are largely reliant on three-dimensional whole-mount immunofluorescence staining. In this chapter, we review a revised whole mount immunofluorescence staining method for studying adult pancreatic islet morphology. This method uses smaller samples and combines the blocking and permeabilization steps. This reduces the time needed, relative to existing protocols; the method is compatible with regular confocal microscopy as well.

LSD1-mediated enhancer silencing attenuates retinoic acid signalling during pancreatic endocrine cell development.

Developmental progression depends on temporally defined changes in gene expression mediated by transient exposure of lineage intermediates to signals in the progenitor niche. To determine whether cell-intrinsic epigenetic mechanisms contribute to signal-induced transcriptional responses, here we manipulate the signalling environment and activity of the histone demethylase LSD1 during differentiation of hESC-gut tube intermediates into pancreatic endocrine cells. We identify a transient requirement for LSD1 in endocrine cell differentiation spanning a short time-window early in pancreas development, a phenotype we reproduced in mice. Examination of enhancer and transcriptome landscapes revealed that LSD1 silences transiently active retinoic acid (RA)-induced enhancers and their target genes. Furthermore, prolonged RA exposure phenocopies LSD1 inhibition, suggesting that LSD1 regulates endocrine cell differentiation by limiting the duration of RA signalling. Our findings identify LSD1-mediated enhancer silencing as a cell-intrinsic epigenetic feedback mechanism by which the duration of the transcriptional response to a developmental signal is limited.

A dosage-dependent requirement for Sox9 in pancreatic endocrine cell formation.

We have previously shown the transcription factor SOX9 to be required for the maintenance of multipotential pancreatic progenitor cells in the early embryonic pancreas. However, the association of pancreatic endocrine defects with the Sox9-haploinsufficiency syndrome campomelic dysplasia (CD) implies additional later roles for Sox9 in endocrine development. Using short-term lineage tracing in mice, we demonstrate here that SOX9 marks a pool of multipotential pancreatic progenitors throughout the window of major cell differentiation. During mid-pancreogenesis, both endocrine and exocrine cells simultaneously arise from the SOX9(+) epithelial cords. Our analysis of mice with 50%-reduced Sox9 gene dosage in pancreatic progenitors reveals endocrine-specific defects phenocopying CD. By birth, these mice display a specific reduction in endocrine cell mass, while their exocrine compartment and total organ size is normal. The decrease in endocrine cells is caused by reduced generation of endocrine progenitors from the SOX9(+) epithelium. Conversely, formation of exocrine progenitors is insensitive to reduced Sox9 gene dosage, thus explaining the normal organ size at birth. Our results show that not only is SOX9 required for the maintenance of early pancreatic progenitors, but also governs their adoption of an endocrine fate. Our findings therefore suggest that defective endocrine specification might underlie the pancreatic phenotype of individuals with CD.

Analysis of mPygo2 mutant mice suggests a requirement for mesenchymal Wnt signaling in pancreatic growth and differentiation.

Pygopus has recently been identified in Drosophila as an essential component of the nuclear complex required for canonical Wnt signaling. Here, we have investigated the role of the mammalian pygopus ortholog, mPygo2, in pancreas development. We show that a null mutation of mPygo2 in mice causes pancreas hypoplasia due to decreased progenitor cell proliferation after embryonic day (e) 12.5. During the same time window, mPygo2-deficient embryos begin to display a reduction in endocrine progenitors and consequently a decrease in islet endocrine cell mass. Consistent with its function after e12.5, late-developing endocrine cell types, such as beta, delta and PP cells, are specifically reduced, while the earlier-forming alpha cells develop normally. We find canonical Wnt signaling to be predominantly active in the mesenchyme at the time when mPygo2 is required and demonstrate the dependence of Wnt signal transduction on mPygo2. Furthermore, conditional deletion of mPygo2(flox) allele in the pancreatic epithelium does not phenocopy the defects in mPygo2-null mutants. Since mPygo2 is expressed in the pancreatic mesenchyme and the role of the mesenchyme in epithelial progenitor cell expansion is well documented, our findings suggest an indirect role for mPygo2 in epithelial growth and differentiation through regulation of mesenchymal signals. Together, our data suggest a previously unappreciated role for mesenchymal Wnt signaling in regulating pancreatic organ growth and cell differentiation.

Desmoplasia and oncogene driven acinar-to-ductal metaplasia are concurrent events during acinar cell-derived pancreatic cancer initiation in young adult mice.

The five-year survival rate of patients diagnosed with advanced pancreatic ductal adenocarcinoma (PDAC) has remained static at <5% despite decades of research. With the exception of erlotinib, clinical trials have failed to demonstrate the benefit of any targeted therapy for PDAC despite promising results in preclinical animal studies. The development of more refined mouse models of PDAC which recapitulate the carcinogenic progression from non-neoplastic, adult exocrine subsets of pancreatic cells to invasive carcinoma in humans are needed to facilitate the accurate translation of therapies to the clinic. To study acinar cell-derived PDAC initiation, we developed a genetically engineered mouse model of PDAC, called KPT, utilizing a tamoxifen-inducible Cre recombinase/estrogen receptor (ESR1) fusion protein knocked into the Ptf1a locus to activate the expression of oncogenic KrasG12D and Trp53R270H alleles in mature pancreatic acinar cells. Oncogene-expressing acinar cells underwent acinar-to-ductal metaplasia, and formed pancreatic intraepithelial neoplasia lesions following the induction of oncogene expression. After a defined latency period, oncogene-expressing acinar cells initiated the formation of highly differentiated and fibrotic tumors, which metastasized to the lungs and liver. Whole-transcriptome analysis of microdissected regions of acinar-to-ductal metaplasia and histological validation experiments demonstrated that regions of acinar-to-ductal metaplasia are characterized by the deposition of the extracellular matrix component hyaluronan. These results indicate that acinar cells expressing KrasG12D and Trp53R270H can initiate PDAC development in young adult mice and implicate hyaluronan deposition in the formation of the earliest characterized PDAC precursor lesions (and the progression of pancreatic cancer). Further studies are necessary to provide a comprehensive characterization of PDAC progression and treatment response in KPT mice and to investigate whether the KPT model could be used as a tool to study translational aspects of acinar cell-derived PDAC tumorigenesis.

A Network of microRNAs Acts to Promote Cell Cycle Exit and Differentiation of Human Pancreatic Endocrine Cells.

Pancreatic endocrine cell differentiation is orchestrated by the action of transcription factors that operate in a gene regulatory network to activate endocrine lineage genes and repress lineage-inappropriate genes. MicroRNAs (miRNAs) are important modulators of gene expression, yet their role in endocrine cell differentiation has not been systematically explored. Here we characterize miRNA-regulatory networks active in human endocrine cell differentiation by combining small RNA sequencing, miRNA over-expression, and network modeling approaches. Our analysis identified Let-7g, Let-7a, miR-200a, miR-127, and miR-375 as endocrine-enriched miRNAs that drive endocrine cell differentiation-associated gene expression changes. These miRNAs are predicted to target different transcription factors, which converge on genes involved in cell cycle regulation. When expressed in human embryonic stem cell-derived pancreatic progenitors, these miRNAs induce cell cycle exit and promote endocrine cell differentiation. Our study delineates the role of miRNAs in human endocrine cell differentiation and identifies miRNAs that could facilitate endocrine cell reprogramming.

Muscle development: forming the head and trunk muscles.

The morphological events forming the body's musculature are sensitive to genetic and environmental perturbations with high incidence of congenital myopathies, muscular dystrophies and degenerations. Pattern formation generates branching series of states in the genetic regulatory network. Different states of the network specify pre-myogenic progenitor cells in the head and trunk. These progenitors reveal their myogenic nature by the subsequent onset of expression of the master switch gene MyoD and/or Myf5. Once initiated, the myogenic progression that ultimately forms mature muscle appears to be quite similar in head and trunk skeletal muscle. Several genes that are essential in specifying pre-myogenic progenitors in the trunk are known. Pax3, Lbx1, and a number of other homeobox transcription factors are essential in specifying pre-myogenic progenitors in the dermomyotome, from which the epaxial and hypaxial myoblasts, which express myogenic regulatory factors (MRFs), emerge. The proteins involved in specifying pre-myogenic progenitors in the head are just beginning to be discovered and appear to be distinct from those in the trunk. The homeobox gene Pitx2, the T-box gene Tbx1, and the bHLH genes Tcf21 and Msc encode transcription factors that play roles in specifying progenitor cells that will give rise to branchiomeric muscles of the head. Pitx2 is expressed well before the onset of myogenic progression in the first branchial arch (BA) mesodermal core and is essential for the formation of first BA derived muscle groups. Anterior-posterior patterning events that occur during gastrulation appear to initiate the Pitx2 expression domain in the cephalic and BA mesoderm. Pitx2 therefore contributes to the establishment of network states, or kernels, that specify pre-myogenic progenitors for extraocular and mastication muscles. A detailed understanding of the molecular mechanisms that regulate head muscle specification and formation provides the foundation for understanding congenital myopathies. Current technology and mouse model systems help to elucidate the molecular basis on etiology and repair of muscular degenerative diseases.

Pancreatic Exocrine Tissue Architecture and Integrity are Maintained by E-cadherin During Postnatal Development.

Cadherin-mediated cell-cell adhesion plays an important role in organ development and changes in cadherin expression are often linked to morphogenetic and pathogenic events. Cadherins interact with other intracellular components to form adherens junctions (AJs) and provide mechanical attachments between adjacent cells. E-cadherin (Cdh1) represents an integral component of these intercellular junctions. To elucidate the function of E-cadherin in the developing pancreas, we generated and studied pancreas-specific Cdh1-knockout (Cdh1ΔPan/ΔPan) mice. Cdh1ΔPan/ΔPan mice exhibit normal body size at birth, but fail to gain weight and become hypoglycemic soon afterward. We found that E-cadherin is not required for the establishment of apical-basal polarity or pancreatic exocrine cell identity at birth. However, four days after birth, the pancreata of Cdh1ΔPan/ΔPan mutants display progressive deterioration of exocrine architecture and dysregulation of Wnt and YAP signaling. At this time point, the acinar cells of Cdh1ΔPan/ΔPan mutants begin to exhibit ductal phenotypes, suggesting acinar-to-ductal metaplasia (ADM) in the E-cadherin-deficient pancreas. Our findings demonstrate that E-cadherin plays an integral role in the maintenance of exocrine architecture and regulation of homeostatic signaling. The present study provides insights into the involvement of cadherin-mediated cell-cell adhesion in pathogenic conditions such as pancreatitis or pancreatic cancer.