A Multipotent Progenitor Domain Guides Pancreatic Organogenesis

New hPSC SOX9 and INS Reporter Cell Lines Facilitate the Observation and Optimization of Differentiation into Insulin-Producing Cells

Differentiation of human pluripotent stem cells into insulin-producing stem cell-derived beta cells harbors great potential for research and therapy of diabetes. SOX9 plays a crucial role during development of the pancreas and particularly in the development of insulin-producing cells as SOX9+ cells form the source for NEUROG3+ endocrine progenitor cells. For the purpose of easy monitoring of differentiation efficiencies into pancreatic progenitors and insulin-producing cells, we generated new reporter lines by knocking in a P2A-H-2Kk-F2A-GFP2 reporter gene into the SOX9-locus and a P2A-mCherry reporter gene into the INS-locus mediated by CRISPR/CAS9-technology. The knock-ins enabled co-expression of the endogenous and reporter genes and report on the endogenous gene expression. Furthermore, FACS and MACS enabled the purification of pancreatic progenitors and insulin-producing cells. Using these cell lines, we established a new differentiation protocol geared towards SOX9+ cells to efficiently drive human pluripotent stem cells into glucose-responsive beta cells. Our new protocol offers an alternative route towards stem cell-derived beta cells, pointing out the importance of Wnt/beta-catenin inhibition and the efficacy of EGF for the development of pancreatic progenitors, as well as the significance of 3D culture for the functionality of the generated beta cells.

Microvessels support engraftment and functionality of human islets and hESC-derived pancreatic progenitors in diabetes models

Islet transplantation is a promising treatment for type 1 diabetes (T1D), yet the low donor pool, poor islet engraftment, and life-long immunosuppression prevent it from becoming the standard of care. Human embryonic stem cell (hESC)-derived pancreatic cells could eliminate donor shortages, but interventions to improve graft survival are needed. Here, we enhanced subcutaneous engraftment by employing a unique vascularization strategy based on ready-made microvessels (MVs) isolated from the adipose tissue. This resulted in improved cell survival and effective glucose response of both human islets and hESC-derived pancreatic cells, which ameliorated preexisting diabetes in three mouse models of T1D.

Hnf1b-CreER causes efficient recombination of a Rosa26-RFP reporter in duct and islet δ cells

The Hnf1b-CreER^T2 BAC transgenic (Tg(Hnf1b-cre/ERT2)1Jfer) has been used extensively to trace the progeny of pancreatic ducts in developmental, regeneration, or cancer models. Hnf1b-CreER^T2 transgenics have been used to show that the cells that form the embryonic pancreas duct-like plexus are bipotent duct-endocrine progenitors, whereas adult mouse duct cells are not a common source of β cells in various regenerative settings. The interpretation of such genetic lineage tracing studies is critically dependent on a correct understanding of the cell type specificity of recombinase activity with each reporter system. We have reexamined the performance of Hnf1b-CreER^T2 with a Rosa26-RFP reporter transgene. This showed inducible recombination of up to 96% adult duct cells, a much higher efficiency than previously used reporter transgenes. Despite this high duct-cell excision, recombination in α and β cells remained very low, similar to previously used reporters. However, nearly half of somatostatin-expressing δ cells showed reporter activation, which was due to Cre expression in δ cells rather than to duct to δ cell conversions. The high recombination efficiency in duct cells indicates that the Hnf1b-CreER^T2 model can be useful for both ductal fate mapping and genetic inactivation studies. The recombination in δ cells does not modify the interpretation of studies that failed to show duct conversions to other cell types, but needs to be considered if this model is used in studies that aim to modify the plasticity of pancreatic duct cells.

The Potential of Pancreatic Organoids for Diabetes Research and Therapy

The success of clinical transplantation of pancreas or isolated pancreatic islets supports the concept of cell-based cure for diabetes. One limitation is the shortage of cadaver human pancreata. The demand-supply gap could potentially be bridged by harnessing the self-renewal capacity of stem cells. Pluripotent stem cells and adult pancreatic stem cells have been explored as possible cell sources. Recently, a system for long-term culture of proposed adult pancreatic stem cells in a form of organoids was developed. Generated organoids partially mimic the architecture and cell-type composition of pancreatic tissue. Here, we review the attempts over the past decade, to utilize the organoid cell culture principles in order to identify, expand, and differentiate the adult pancreatic stem cells from different compartments of mouse and human pancreata. The development of the culture conditions, effects of specific growth factors and small molecules is discussed. The potential utility of the adult pancreatic stem cells is considered in the context of other cell sources.

Quantitative lineage analysis identifies a hepato-pancreato-biliary progenitor niche

Studies based on single cells have revealed vast cellular heterogeneity in stem cell and progenitor compartments, suggesting continuous differentiation trajectories with intermixing of cells at various states of lineage commitment and notable degrees of plasticity during organogenesis^1-5. The hepato-pancreato-biliary organ system relies on a small endoderm progenitor compartment that gives rise to a variety of different adult tissues, including the liver, pancreas, gall bladder and extra-hepatic bile ducts^6,7. Experimental manipulation of various developmental signals in the mouse embryo has underscored important cellular plasticity in this embryonic territory⁶. This is reflected in the existence of human genetic syndromes as well as congenital malformations featuring multi-organ phenotypes in liver, pancreas and gall bladder⁶. Nevertheless, the precise lineage hierarchy and succession of events leading to the segregation of an endoderm progenitor compartment into hepatic, biliary and pancreatic structures have not yet been established. Here we combine computational modelling approaches with genetic lineage tracing to accurately reconstruct the hepato-pancreato-biliary lineage tree. We show that a multipotent progenitor subpopulation persists in the pancreato-biliary organ rudiment, contributing cells not only to the pancreas and gall bladder but also to the liver. Moreover, using single-cell RNA sequencing and functional experiments we define a specialized niche that supports this subpopulation in a multipotent state for an extended time during development. Together these findings indicate sustained plasticity underlying hepato-pancreato-biliary development that might also explain the rapid expansion of the liver while attenuating pancreato-biliary growth.

MECOM permits pancreatic acinar cell dedifferentiation avoiding cell death under stress conditions

Maintenance of the pancreatic acinar cell phenotype suppresses tumor formation. Hence, repetitive acute or chronic pancreatitis, stress conditions in which the acinar cells dedifferentiate, predispose for cancer formation in the pancreas. Dedifferentiated acinar cells acquire a large panel of duct cell-specific markers. However, it remains unclear to what extent dedifferentiated acini differ from native duct cells and which genes are uniquely regulating acinar cell dedifferentiation. Moreover, most studies have been performed on mice since the availability of human cells is scarce. Here, we applied a non-genetic lineage tracing method of human pancreatic exocrine acinar and duct cells that allowed cell-type-specific gene expression profiling by RNA sequencing. Subsequent to this discovery analysis, one transcription factor that was unique for dedifferentiated acinar cells was functionally characterized. RNA sequencing analysis showed that human dedifferentiated acinar cells expressed genes in "Pathways of cancer" with a prominence of MECOM (EVI-1), a transcription factor that was not expressed by duct cells. During mouse embryonic development, pre-acinar cells also transiently expressed MECOM and in the adult mouse pancreas, MECOM was re-expressed when mice were subjected to acute and chronic pancreatitis, conditions in which acinar cells dedifferentiate. In human cells and in mice, MECOM expression correlated with and was directly regulated by SOX9. Mouse acinar cells that, by genetic manipulation, lose the ability to upregulate MECOM showed impaired cell adhesion, more prominent acinar cell death, and suppressed acinar cell dedifferentiation by limited ERK signaling. In conclusion, we transcriptionally profiled the two major human pancreatic exocrine cell types, acinar and duct cells, during experimental stress conditions. We provide insights that in dedifferentiated acinar cells, cancer pathways are upregulated in which MECOM is a critical regulator that suppresses acinar cell death by permitting cellular dedifferentiation.

Single-cell-resolved differentiation of human induced pluripotent stem cells into pancreatic duct-like organoids on a microwell chip

Creating in vitro models of diseases of the pancreatic ductal compartment requires a comprehensive understanding of the developmental trajectories of pancreas-specific cell types. Here we report the single-cell characterization of the differentiation of pancreatic duct-like organoids (PDLOs) from human induced pluripotent stem cells (hiPSCs) on a microwell chip that facilitates the uniform aggregation and chemical induction of hiPSC-derived pancreatic progenitors. Using time-resolved single-cell transcriptional profiling and immunofluorescence imaging of the forming PDLOs, we identified differentiation routes from pancreatic progenitors through ductal intermediates to two types of mature duct-like cells and a few non-ductal cell types. PDLO subpopulations expressed either mucins or the cystic fibrosis transmembrane conductance regulator, and resembled human adult duct cells. We also used the chip to uncover ductal markers relevant to pancreatic carcinogenesis, and to establish PDLO co-cultures with stellate cells, which allowed for the study of epithelial-mesenchymal signalling. The PDLO microsystem could be used to establish patient-specific pancreatic duct models.

Continuous clonal labeling reveals uniform progenitor potential in the adult exocrine pancreas

The tissue dynamics that govern maintenance and regeneration of the pancreas remain largely unknown. In particular, the presence and nature of a cellular hierarchy remains a topic of debate. Previous lineage tracing strategies in the pancreas relied on specific marker genes for clonal labeling, which left other populations untested and failed to account for potential widespread phenotypical plasticity. Here we employed a tracing system that depends on replication-induced clonal marks. We found that, in homeostasis, steady acinar replacement events characterize tissue dynamics, to which all acinar cells have an equal ability to contribute. Similarly, regeneration following pancreatitis was best characterized by an acinar self-replication model because no evidence of a cellular hierarchy was detected. In particular, rapid regeneration in the pancreas was found to be driven by an accelerated rate of acinar fission-like events. These results provide a comprehensive and quantitative model of cell dynamics in the exocrine pancreas.

Stem/progenitor cells in fetuses and newborns: overview of immunohistochemical markers

Microanatomy of the vast majority of human organs at birth is characterized by marked differences as compared to adult organs, regarding their architecture and the cell types detectable at histology. In preterm neonates, these differences are even more evident, due to the lower level of organ maturation and to ongoing cell differentiation. One of the most remarkable finding in preterm tissues is the presence of huge amounts of stem/progenitor cells in multiple organs, including kidney, brain, heart, adrenals, and lungs. In other organs, such as liver, the completely different burden of cell types in preterm infants is mainly related to the different function of the liver during gestation, mainly focused on hematopoiesis, a function that is taken by bone marrow after birth. Our preliminary studies showed that the antigens expressed by stem/progenitors differ significantly from one organ to the next. Moreover, within each developing human tissue, reactivity for different stem cell markers also changes during gestation, according with the multiple differentiation steps encountered by each progenitor during development. A better knowledge of stem/progenitor cells of preterms will allow neonatologists to boost preterm organ maturation, favoring the differentiation of the multiple cells types that characterize each organ in at term neonates.

Shaping the thyroid: From peninsula to de novo lumen formation

A challenging and stimulating question in biology deals with the formation of organs from groups of undifferentiated progenitor cells. Most epithelial organs indeed derive from the endodermal monolayer and evolve into various shape and tridimensional organization adapted to their specialized adult function. Thyroid organogenesis is no exception. In most mammals, it follows a complex and sequential process initiated from the endoderm and leading to the development of a multitude of independent closed spheres equipped and optimized for the synthesis, storage and production of thyroid hormones. The first sign of thyroid organogenesis is visible as a thickening of the anterior foregut endoderm. This group of thyroid progenitors then buds and detaches from the foregut to migrate caudally and then laterally. Upon reaching their final destination in the upper neck region on both sides of the trachea, thyroid progenitors mix with C cell progenitors and finally organize into hormone-producing thyroid follicles. Intrinsic and extrinsic factors controlling thyroid organogenesis have been identified in several species, but the fundamental cellular processes are not sufficiently considered. This review focuses on the cellular aspects of the key morphogenetic steps during thyroid organogenesis and highlights similarities and common mechanisms with developmental steps elucidated in other endoderm-derived organs, despite different final architecture and functions.

Stem Cells in the Exocrine Pancreas during Homeostasis, Injury, and Cancer

Simple Summary

Pancreatic cancer is one of the most lethal malignancies. Hence, improved therapies are urgently needed. Recent research indicates that pancreatic cancers depend on cancer stem cells (CSCs) for tumor expansion, metastasis, and therapy resistance. However, the exact functionality of pancreatic CSCs is still unclear. CSCs have much in common with normal pancreatic stem cells that have been better, albeit still incompletely, characterized. In this literature review, we address how pancreatic stem cells influence growth, homeostasis, regeneration, and cancer. Furthermore, we outline which intrinsic and extrinsic factors regulate stem cell functionality during these different processes to explore potential novel targets for treating pancreatic cancer.

Abstract

Cell generation and renewal are essential processes to develop, maintain, and regenerate tissues. New cells can be generated from immature cell types, such as stem-like cells, or originate from more differentiated pre-existing cells that self-renew or transdifferentiate. The adult pancreas is a dormant organ with limited regeneration capacity, which complicates studying these processes. As a result, there is still discussion about the existence of stem cells in the adult pancreas. Interestingly, in contrast to the classical stem cell concept, stem cell properties seem to be plastic, and, in circumstances of injury, differentiated cells can revert back to a more immature cellular state. Importantly, deregulation of the balance between cellular proliferation and differentiation can lead to disease initiation, in particular to cancer formation. Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a 5-year survival rate of only ~9%. Unfortunately, metastasis formation often occurs prior to diagnosis, and most tumors are resistant to current treatment strategies. It has been proposed that a specific subpopulation of cells, i.e., cancer stem cells (CSCs), are responsible for tumor expansion, metastasis formation, and therapy resistance. Understanding the underlying mechanisms of pancreatic stem cells during homeostasis and injury might lead to new insights to understand the role of CSCs in PDAC. Therefore, in this review, we present an overview of the current literature regarding the stem cell dynamics in the pancreas during health and disease. Furthermore, we highlight the influence of the tumor microenvironment on the growth behavior of PDAC.

SETD4-expressing cells contribute to pancreatic development and response to cerulein induced pancreatitis injury

In the adult pancreas, the presence of progenitor or stem cells and their potential involvement in homeostasis and regeneration remains unclear. Here, we identify that SET domain-containing protein 4 (SETD4), a histone lysine methyltransferase, is expressed in a small cell population in the adult mouse pancreas. Genetic lineage tracing shows that during pancreatic development, descendants of SETD4⁺ cells make up over 70% of pancreatic cells and then contribute to each pancreatic lineage during pancreatic homeostasis. SETD4⁺ cells generate newborn acinar cells in response to cerulein-induced pancreatitis in acinar compartments. Ablation of SETD4⁺ cells compromises regeneration of acinar cells, in contrast to controls. Our findings provide a new cellular narrative for pancreatic development, homeostasis and response to injury via a small SETD4⁺ cell population. Potential applications may act to preserve pancreatic function in case of pancreatic disease and/or damage.

Pancreas morphogenesis and homeostasis depends on tightly regulated Zeb1 levels in epithelial cells

The pancreas is comprised of exocrine and endocrine compartments releasing digestive enzymes into the duodenum and regulating blood glucose levels by insulin and glucagon release. Tissue homeostasis is depending on transcription factor networks, involving Ptf1α, Ngn3, Nkx6.1, and Sox9, which are already activated during organogenesis. However, proper organ function is challenged by diets of high sugar and fat content, increasing the risk of type 2 diabetes and other disorders. A detailed understanding of processes that are important for homeostasis and are impaired during type 2 diabetes is lacking. Here, we show that Zeb1—a transcription factor known for its pivotal role in epithelial-mesenchymal transition, cell plasticity, and metastasis in cancer—is expressed at low levels in epithelial cells of the pancreas and is crucial for organogenesis and pancreas function. Loss of Zeb1 in these cells result in an increase of islet mass, impaired glucose tolerance, and sensitizes to develop liver and pancreas steatosis during diabetes and obesity. Interestingly, moderate overexpression of Zeb1 results in severe pancreas agenesis and lethality after birth, due to islet insufficiency and lack of acinar structures. We show that Zeb1 induction interferes with proper differentiation, cell survival, and proliferation during pancreas formation, due to deregulated expression of endocrine-specific transcription factors. In summary, our analysis suggests a novel role of Zeb1 for homeostasis in epithelial cells that is indispensable for pancreas morphogenesis and proper organ function involving a tight regulation of Zeb1 expression.

A 3D system to model human pancreas development and its reference single-cell transcriptome atlas identify signaling pathways required for progenitor expansion

Human organogenesis remains relatively unexplored for ethical and practical reasons. Here, we report the establishment of a single-cell transcriptome atlas of the human fetal pancreas between 7 and 10 post-conceptional weeks of development. To interrogate cell–cell interactions, we describe InterCom, an R-Package we developed for identifying receptor–ligand pairs and their downstream effects. We further report the establishment of a human pancreas culture system starting from fetal tissue or human pluripotent stem cells, enabling the long-term maintenance of pancreas progenitors in a minimal, defined medium in three-dimensions. Benchmarking the cells produced in 2-dimensions and those expanded in 3-dimensions to fetal tissue identifies that progenitors expanded in 3-dimensions are transcriptionally closer to the fetal pancreas. We further demonstrate the potential of this system as a screening platform and identify the importance of the EGF and FGF pathways controlling human pancreas progenitor expansion.

From single-cell transcriptome analyses to defining culture media for spheroids, the authors provide a census of information to understand the development of human pancreatic progenitors. This approach identifies signalling pathways (EGF and FGF) regulating progenitor proliferation.

Single-cell transcriptome analysis defines heterogeneity of the murine pancreatic ductal tree

To study disease development, an inventory of an organ's cell types and understanding of physiologic function is paramount. Here, we performed single-cell RNA-sequencing to examine heterogeneity of murine pancreatic duct cells, pancreatobiliary cells, and intrapancreatic bile duct cells. We describe an epithelial-mesenchymal transitory axis in our three pancreatic duct subpopulations and identify osteopontin as a regulator of this fate decision as well as human duct cell dedifferentiation. Our results further identify functional heterogeneity within pancreatic duct subpopulations by elucidating a role for geminin in accumulation of DNA damage in the setting of chronic pancreatitis. Our findings implicate diverse functional roles for subpopulations of pancreatic duct cells in maintenance of duct cell identity and disease progression and establish a comprehensive road map of murine pancreatic duct cell, pancreatobiliary cell, and intrapancreatic bile duct cell homeostasis.

Sonic hedgehog signals hinder the transcriptional network necessary for pancreatic endoderm formation from human embryonic stem cells

Hedgehog morphogens govern multiple aspects of pancreas organogenesis and functioning with diverse outcomes across species. Although most current differentiation protocols repress Sonic hedgehog (SHH) signals during in vitro endocrine specification, the role and mechanisms through which the SHH pathway antagonizes pancreas development during in vitro human embryonic stem (hES) cell differentiation remain unclear. We modulated SHH signaling at transitory stages of hES cell-derived pancreatic progenitors and analyzed the effect on cellular fate decisions. We identify the Hedgehog pathway as a negative regulator of pancreatic endoderm formation through up-regulation of a set of pancreatobiliary markers required for ductal specification, including SOX17, FOXA2, HNF1β, HNF6, PDX1, and SOX9. Surprisingly, active Hedgehog signals impeded a group of pancreatic epithelium markers, including HNF4α, HHEX, PAX6, and PTF1α. To understand how SHH signals repress the transcription of these specific markers, we analyzed Polycomb group proteins. We found differential expression of Polycomb Repressive Complex 1 subunit, BMI1 upon Shh pathway modulation in the pancreatic progenitors. Ectopic activation of Sonic hedgehog results in over-expression of BMI1 and its associated repressive histone mark, H2AK119Ub1, in the multipotent progenitors. Our data suggest that Sonic hedgehog restricts the pancreatic differentiation program by limiting progenitor cells acquiring pancreatic epithelial fates and instead promotes pancreatobiliary differentiation. We further provide mechanistic cues of an association between Hedgehog signaling and epigenetic silencers during pancreatic lineage decisions.

Endocrine Pancreas Development and Dysfunction Through the Lens of Single-Cell RNA-Sequencing

A chronic inability to maintain blood glucose homeostasis leads to diabetes, which can damage multiple organs. The pancreatic islets regulate blood glucose levels through the coordinated action of islet cell-secreted hormones, with the insulin released by β-cells playing a crucial role in this process. Diabetes is caused by insufficient insulin secretion due to β-cell loss, or a pancreatic dysfunction. The restoration of a functional β-cell mass might, therefore, offer a cure. To this end, major efforts are underway to generate human β-cells de novo, in vitro, or in vivo. The efficient generation of functional β-cells requires a comprehensive knowledge of pancreas development, including the mechanisms driving cell fate decisions or endocrine cell maturation. Rapid progress in single-cell RNA sequencing (scRNA-Seq) technologies has brought a new dimension to pancreas development research. These methods can capture the transcriptomes of thousands of individual cells, including rare cell types, subtypes, and transient states. With such massive datasets, it is possible to infer the developmental trajectories of cell transitions and gene regulatory pathways. Here, we summarize recent advances in our understanding of endocrine pancreas development and function from scRNA-Seq studies on developing and adult pancreas and human endocrine differentiation models. We also discuss recent scRNA-Seq findings for the pathological pancreas in diabetes, and their implications for better treatment.

Modeling plasticity and dysplasia of pancreatic ductal organoids derived from human pluripotent stem cells

Personalized in vitro models for dysplasia and carcinogenesis in the pancreas have been constrained by insufficient differentiation of human pluripotent stem cells (hPSCs) into the exocrine pancreatic lineage. Here, we differentiate hPSCs into pancreatic duct-like organoids (PDLOs) with morphological, transcriptional, proteomic, and functional characteristics of human pancreatic ducts, further maturing upon transplantation into mice. PDLOs are generated from hPSCs inducibly expressing oncogenic GNAS, KRAS, or KRAS with genetic covariance of lost CDKN2A and from induced hPSCs derived from a McCune-Albright patient. Each oncogene causes a specific growth, structural, and molecular phenotype in vitro. While transplanted PDLOs with oncogenic KRAS alone form heterogenous dysplastic lesions or cancer, KRAS with CDKN2A loss develop dedifferentiated pancreatic ductal adenocarcinomas. In contrast, transplanted PDLOs with mutant GNAS lead to intraductal papillary mucinous neoplasia-like structures. Conclusively, PDLOs enable in vitro and in vivo studies of pancreatic plasticity, dysplasia, and cancer formation from a genetically defined background.

Insulin-positive ductal cells do not migrate into preexisting islets during pregnancy

The adult pancreatic ductal system was suggested to harbor facultative beta-cell progenitors similar to the embryonic pancreas, and the appearance of insulin-positive duct cells has been used as evidence for natural duct-to-beta-cell reprogramming. Nevertheless, the phenotype and fate of these insulin-positive cells in ducts have not been determined. Here, we used a cell-tagging dye, CFDA-SE, to permanently label pancreatic duct cells through an intraductal infusion technique. Representing a time when significant increases in beta-cell mass occur, pregnancy was later induced in these CFDA-SE-treated mice to assess the phenotype and fate of the insulin-positive cells in ducts. We found that a small portion of CFDA-SE-labeled duct cells became insulin-positive, but they were not fully functional beta-cells based on the in vitro glucose response and the expression levels of key beta-cell genes. Moreover, these insulin-positive cells in ducts expressed significantly lower levels of genes associated with extracellular matrix degradation and cell migration, which may thus prevent their budding and migration into preexisting islets. A similar conclusion was reached through analysis of the Gene Expression Omnibus database for both mice and humans. Together, our data suggest that the contribution of duct cells to normal beta-cells in adult islets is minimal at best.

Generation of a Novel Nkx6-1 Venus Fusion Reporter Mouse Line

Nkx6-1 is a member of the Nkx family of homeodomain transcription factors (TFs) that regulates motor neuron development, neuron specification and pancreatic endocrine and β-cell differentiation. To facilitate the isolation and tracking of Nkx6-1-expressing cells, we have generated a novel Nkx6-1 Venus fusion (Nkx6-1-VF) reporter allele. The Nkx6-1-VF knock-in reporter is regulated by endogenous cis-regulatory elements of Nkx6-1 and the fluorescent protein fusion does not interfere with the TF function, as homozygous mice are viable and fertile. The nuclear localization of Nkx6-1-VF protein reflects the endogenous Nkx6-1 protein distribution. During embryonic pancreas development, the reporter protein marks the pancreatic ductal progenitors and the endocrine lineage, but is absent in the exocrine compartment. As expected, the levels of Nkx6-1-VF reporter are upregulated upon β-cell differentiation during the major wave of endocrinogenesis. In the adult islets of Langerhans, the reporter protein is exclusively found in insulin-secreting β-cells. Importantly, the Venus reporter activities allow successful tracking of β-cells in live-cell imaging and their specific isolation by flow sorting. In summary, the generation of the Nkx6-1-VF reporter line reflects the expression pattern and dynamics of the endogenous protein and thus provides a unique tool to study the spatio-temporal expression pattern of this TF during organ development and enables isolation and tracking of Nkx6-1-expressing cells such as pancreatic β-cells, but also neurons and motor neurons in health and disease.

TGF-β Signaling in Pancreatic Islet β Cell Development and Function

Pancreatic islet beta cells (β-cells) synthesize and secrete insulin in response to rising glucose levels and thus are a prime target in both major forms of diabetes. Type 1 diabetes ensues due to autoimmune destruction of β-cells. On the other hand, the prevailing insulin resistance and hyperglycemia in type 2 diabetes (T2D) elicits a compensatory response from β-cells that involves increases in β-cell mass and function. However, the sustained metabolic stress results in β-cell failure, characterized by severe β-cell dysfunction and loss of β-cell mass. Dynamic changes to β-cell mass also occur during pancreatic development that involves extensive growth and morphogenesis. These orchestrated events are triggered by multiple signaling pathways, including those representing the transforming growth factor β (TGF-β) superfamily. TGF-β pathway ligands play important roles during endocrine pancreas development, β-cell proliferation, differentiation, and apoptosis. Furthermore, new findings are suggestive of TGF-β's role in regulation of adult β-cell mass and function. Collectively, these findings support the therapeutic utility of targeting TGF-β in diabetes. Summarizing the role of the various TGF-β pathway ligands in β-cell development, growth and function in normal physiology, and during diabetes pathogenesis is the topic of this mini-review.

Pre-existing beta cells but not progenitors contribute to new beta cells in the adult pancreas

It has been suggested that new beta cells can arise from specific populations of adult pancreatic progenitors or facultative stem cells. However, their existence remains controversial, and the conditions under which they would contribute to new beta-cell formation are not clear. Here, we use a suite of mouse models enabling dual-recombinase-mediated genetic tracing to simultaneously fate map insulin-positive and insulin-negative cells in the adult pancreas. We find that the insulin-negative cells, of both endocrine and exocrine origin, do not generate new beta cells in the adult pancreas during homeostasis, pregnancy or injury, including partial pancreatectomy, pancreatic duct ligation or beta-cell ablation with streptozotocin. However, non-beta cells can give rise to insulin-positive cells after extreme genetic ablation of beta cells, consistent with transdifferentiation. Together, our data indicate that pancreatic endocrine and exocrine progenitor cells do not contribute to new beta-cell formation in the adult mouse pancreas under physiological conditions.

The Role of Mesenchymal Stem Cells with Ascorbic Acid and N-Acetylcysteine on TNF-α, IL 1β, and NF-κβ Expressions in Acute Pancreatitis in Albino Rats

Severe acute pancreatitis (SAP) is a necrotic pancreatic inflammation associated with high mortality rate (up to 70%). Bone marrow (BM) mesenchymal stem cells (MSCs) have been investigated in pancreatic cellular regeneration, but still their effects are controversial. Therefore, the present study is aimed at examining the enrichment of the stem cells with ascorbic acid (AA) and N-acetylcysteine (NAC) and explore their combined action on the expression of the inflammatory cytokines: interleukin 1β (IL 1β), tumor necrosis factor-α (TNF-α), and nuclear factor-κβ (NF-κβ). A total of twenty adult male Sprague-Dawley albino rats were divided into four groups: the control group, cerulein group (to induce acute pancreatitis), BM-MSCs group, and combined BM-MSCs with AA and NAC group. Homing and proliferation of stem cells were revealed by the appearance of PKH26-labelled BM-MSCs in the islets of Langerhans. AA and NAC combination with BM-MSCs (group IV) was demonstrated to affect the expression of the inflammatory cytokines: IL 1β, TNF-α, and NF-κβ. In addition, improvement of the biochemical and histological parameters is represented in increasing body weight, normal blood glucose, and insulin levels and regeneration of the islet cells. Immunohistochemical studies showed an increase in proliferating cell nuclear antigen (PCNA) and decrease in caspase-3 reactions, detected markedly in group IV, after the marked distortion of the classic pancreatic lobular architecture was induced by cerulein. It could be concluded that treatment with BM-MSCs combined with antioxidants could provide a promising therapy for acute pancreatitis and improve the degeneration, apoptosis, necrosis, and inflammatory processes of the islets of Langerhans. TNF-α, IL 1β, and NF-κβ are essential biomarkers for the evaluation of MSC regenerative effectiveness.

Modelling of Epithelial Growth, Fission and Lumen Formation During Embryonic Thyroid Development: A Combination of Computational and Experimental Approaches

Organogenesis is the phase of embryonic development leading to the formation of fully functional organs. In the case of the thyroid, organogenesis starts from the endoderm and generates a multitude of closely packed independent spherical follicular units surrounded by a dense network of capillaries. Follicular organisation is unique and essential for thyroid function, i.e. thyroid hormone production. Previous in vivo studies showed that, besides their nutritive function, endothelial cells play a central role during thyroid gland morphogenesis. However, the precise mechanisms and biological parameters controlling the transformation of the multi-layered thyroid epithelial primordium into a multitude of single-layered follicles are mostly unknown. Animal studies used to improve understanding of organogenesis are costly and time-consuming, with recognised limitations. Here, we developed and used a 2-D vertex model of thyroid growth, angiogenesis and folliculogenesis, within the open-source Chaste framework. Our in silico model, based on in vivo images, correctly simulates the differential growth and proliferation of central and peripheral epithelial cells, as well as the morphogen-driven migration of endothelial cells, consistently with our experimental data. Our simulations further showed that reduced epithelial cell adhesion was critical to allow endothelial invasion and fission of the multi-layered epithelial mass. Finally, our model also allowed epithelial cell polarisation and follicular lumen formation by endothelial cell abundance and proximity. Our study illustrates how constant discussion between theoretical and experimental approaches can help us to better understand the roles of cellular movement, adhesion and polarisation during thyroid embryonic development. We anticipate that the use of in silico models like the one we describe can push forward the fields of developmental biology and regenerative medicine.

Pancreas development and the Polycomb group protein complexes

The dual nature of pancreatic tissue permits both endocrine and exocrine functions. Enzymatic secretions by the exocrine pancreas help digestive processes while the pancreatic hormones regulate glucose homeostasis and energy metabolism. Pancreas organogenesis is defined by a conserved array of signaling pathways that act on common gut progenitors to bring about the generation of diverse cell types. Multiple cellular processes characterize development of the mature organ. These processes are mediated by signaling pathways that regulate lineage-specific transcription factors and chromatin modifications guiding long-term gene expression programs. The chromatin landscape is altered chiefly by DNA or histone modifications, chromatin remodelers, and non-coding RNAs. Amongst histone modifiers, several studies have identified Polycomb group (PcG) proteins as crucial determinants mediating transcriptional repression of genes involved in developmental processes. Although PcG-mediated chromatin modifications define cellular transitions and influence cell identity of multipotent progenitors, much remains to be understood regarding coordination between extracellular signals and their impact on Polycomb functions during the pancreas lineage progression. In this review, we discuss interactions between sequence-specific DNA binding proteins and chromatin regulators underlying pancreas development and insulin producing β-cells, with particular focus on Polycomb group proteins. Understanding such basic molecular mechanisms would improve current strategies for stem cell-based differentiation while also help elucidate the pathogenesis of several pancreas-related maladies, including diabetes and pancreatic cancer.

Pancreas morphogenesis: Branching in and then out

The pancreas of adult mammals displays a branched structure which transports digestive enzymes produced in the distal acini through a tree-like network of ducts into the duodenum. In contrast to several other branched organs, its branching patterns are not stereotypic. Moreover, the branches do not grow from dichotomic splitting of an initial stem but rather from the formation of microlumen in a mass of cells. These lumen progressively assemble into a hyperconnected network that refines into a tree by the time of birth. We review the cell remodeling events and the molecular mechanisms governing pancreas branching, as well as the role of the surrounding tissues in this process. Furthermore, we draw parallels with other branched organs such as the salivary and mammary gland.

Biological functions and theranostic potential of HMGB family members in human cancers

The high mobility group box (HMGB) protein family consists of four members: HMGB1, 2, 3, and 4. They share similar amino acid sequences and identical functional regions, especially HMGB1, 2, and 3. The homology in structure may lead to similarity in function. In fact, though their targets may be different, they all possess the fundamental function of binding and distorting target DNAs. However, further research confirmed they are distributed differently in tissues and involved in various distinct physiological and pathological cellular processes, including cell proliferation, division, migration, and differentiation. Recently, the roles of HMGB family members in carcinogenesis has been widely investigated; however, systematic discussion on their functions and clinical values in malignant tumors is limited. In this review, we mainly review and summarize recent advances in knowledge of HMGB family members in terms of structure, distribution, biochemical cascades, and specific mechanisms regarding tumor progression. Importantly, the diagnostic, prognostic, and therapeutic value of these proteins in cancers is discussed. Finally, we envisage the orientation and challenges of this field in further studies.

NKX6.1 transcription factor: a crucial regulator of pancreatic β cell development, identity, and proliferation

Understanding the biology underlying the mechanisms and pathways regulating pancreatic β cell development is necessary to understand the pathology of diabetes mellitus (DM), which is characterized by the progressive reduction in insulin-producing β cell mass. Pluripotent stem cells (PSCs) can potentially offer an unlimited supply of functional β cells for cellular therapy and disease modeling of DM. Homeobox protein NKX6.1 is a transcription factor (TF) that plays a critical role in pancreatic β cell function and proliferation. In human pancreatic islet, NKX6.1 expression is exclusive to β cells and is undetectable in other islet cells. Several reports showed that activation of NKX6.1 in PSC-derived pancreatic progenitors (MPCs), expressing PDX1 (PDX1⁺/NKX6.1⁺), warrants their future commitment to monohormonal β cells. However, further differentiation of MPCs lacking NKX6.1 expression (PDX1⁺/NKX6.1⁻) results in an undesirable generation of non-functional polyhormonal β cells. The importance of NKX6.1 as a crucial regulator in MPC specification into functional β cells directs attentions to further investigating its mechanism and enhancing NKX6.1 expression as a means to increase β cell function and mass. Here, we shed light on the role of NKX6.1 during pancreatic β cell development and in directing the MPCs to functional monohormonal lineage. Furthermore, we address the transcriptional mechanisms and targets of NKX6.1 as well as its association with diabetes.

Tracing the cellular basis of islet specification in mouse pancreas

Pancreatic islets play an essential role in regulating blood glucose level. Although the molecular pathways underlying islet cell differentiation are beginning to be resolved, the cellular basis of islet morphogenesis and fate allocation remain unclear. By combining unbiased and targeted lineage tracing, we address the events leading to islet formation in the mouse. From the statistical analysis of clones induced at multiple embryonic timepoints, here we show that, during the secondary transition, islet formation involves the aggregation of multiple equipotent endocrine progenitors that transition from a phase of stochastic amplification by cell division into a phase of sublineage restriction and limited islet fission. Together, these results explain quantitatively the heterogeneous size distribution and degree of polyclonality of maturing islets, as well as dispersion of progenitors within and between islets. Further, our results show that, during the secondary transition, α- and β-cells are generated in a contemporary manner. Together, these findings provide insight into the cellular basis of islet development.

The cellular basis of islet morphogenesis and fate allocation remain unclear. Here, the authors use a R26-CreER-R26R-Confetti mouse line to follow quantitatively the clonal dynamics of islet formation showing how, during the secondary transition, islet progenitors amplify through rounds of stochastic cell division before becoming restricted to α and β cell sublineages.

TrxG Complex Catalytic and Non-catalytic Activity Play Distinct Roles in Pancreas Progenitor Specification and Differentiation

Appropriate regulation of genes that coordinate pancreas progenitor proliferation and differentiation is required for pancreas development. Here, we explore the role of H3K4 methylation and the Trithorax group (TrxG) complexes in mediating gene expression during pancreas development. Disruption of TrxG complex assembly, but not catalytic activity, prevented endocrine cell differentiation in pancreas progenitor spheroids. In vivo loss of TrxG catalytic activity in PDX1⁺ cells increased apoptosis and the fraction of progenitors in the G1 phase of the cell cycle. Pancreas progenitors were reallocated to the acinar lineage, primarily at the expense of NEUROG3⁺ endocrine progenitors. Later in development, acinar and endocrine cell numbers were decreased, and increased gene expression variance and reduced terminal marker activation in acinar cells led to their incomplete differentiation. These findings demonstrate that TrxG co-activator activity is required for gene induction, whereas TrxG catalytic activity and H3K4 methylation help maintain transcriptional stability.

Wnt Signaling Separates the Progenitor and Endocrine Compartments during Pancreas Development

In vitro differentiation of pluripotent cells into β cells is a promising alternative to cadaveric-islet transplantation as a cure for type 1 diabetes (T1D). During the directed differentiation of human embryonic stem cells (hESCS) by exogenous factors, numerous genes that affect the differentiation process are turned on and off autonomously. Manipulating these reactions could increase the efficiency of differentiation and provide a more complete control over the final composition of cell populations. To uncover in vitro autonomous responses, we performed single-cell RNA sequencing on hESCs as they differentiate in spherical clusters. We observed that endocrine cells and their progenitors exist beside one another in separate compartments that activate distinct genetic pathways. WNT pathway inhibition in the endocrine domain of the differentiating clusters reveals a necessary role for the WNT inhibitor APC during islet formation in vivo. Accordingly, WNT inhibition in vitro causes an increase in the proportion of differentiated endocrine cells.

Stem cell therapy: a potential for the perils of pancreatitis

Acute and chronic pancreatitis carry a significant disease burden and there is no definite treatment that exists for either. They are associated with local and systemic inflammation and lead to numerous complications. Stem cell therapy has been explored for other disease processes and is a topic of research that has gained momentum with regards to implications for acute and chronic pancreatitis. They not only carry the potential to aid in regeneration but also prevent pancreatic injury as well as injury of other organs and hence the resultant complications. Stem cells appear to have immunomodulatory properties and clinical potential as evidenced by numerous studies in animal models. This review article discusses the types of stem cells commonly used and the properties that show promise in the field of pancreatitis.

Adult Pancreatic Acinar Progenitor-like Populations in Regeneration and Cancer

The bulk of the pancreas primarily comprises long-lived acinar cells that are not considered a bona fide source for stem cells. However, certain acinar subpopulations have a repopulating capacity during regeneration, raising the hypothesis as to the presence of regenerative progenitor-like populations in the adult pancreas. Here, we describe recent discoveries based on fate-mapping techniques that support the existence of progenitor-like acinar subpopulations, including active progenitor-like cells that maintain tissue homeostasis and facultative progenitor-like cells that drive tissue regeneration. A possible link between progenitor-like acinar cells and cancer initiators is proposed. Further analysis of these cellular components is needed, because it would help uncover possible cellular sources for regeneration and cancer, as well as potential targets for therapy.

MYC Instructs and Maintains Pancreatic Adenocarcinoma Phenotype

The signature features of pancreatic ductal adenocarcinoma (PDAC) are its fibroinflammatory stroma, poor immune activity, and dismal prognosis. We show that acute activation of Myc in indolent pancreatic intraepithelial neoplasm (PanIN) epithelial cells in vivo is, alone, sufficient to trigger immediate release of instructive signals that together coordinate changes in multiple stromal and immune-cell types and drive transition to pancreatic adenocarcinomas that share all the characteristic stromal features of their spontaneous human counterpart. We also demonstrate that this Myc-driven PDAC switch is completely and immediately reversible: Myc deactivation/inhibition triggers meticulous disassembly of advanced PDAC tumor and stroma and concomitant death of tumor cells. Hence, both the formation and deconstruction of the complex PDAC phenotype are continuously dependent on a single, reversible Myc switch. SIGNIFICANCE: We show that Myc activation in indolent Kras G12D-induced PanIN epithelium acts as an immediate pleiotropic switch, triggering tissue-specific signals that instruct all the diverse signature stromal features of spontaneous human PDAC. Subsequent Myc deactivation or inhibition immediately triggers a program that coordinately disassembles PDAC back to PanIN.See related commentary by English and Sears, p. 495.

Small Molecule-Induced Pancreatic β-Like Cell Development: Mechanistic Approaches and Available Strategies

Diabetes is a metabolic disease which affects not only glucose metabolism but also lipid and protein metabolism. It encompasses two major types: type 1 and 2 diabetes. Despite the different etiologies of type 1 and 2 diabetes mellitus (T1DM and T2DM, respectively), the defining features of the two forms are insulin deficiency and resistance, respectively. Stem cell therapy is an efficient method for the treatment of diabetes, which can be achieved by differentiating pancreatic β-like cells. The consistent generation of glucose-responsive insulin releasing cells remains challenging. In this review article, we present basic concepts of pancreatic organogenesis, which intermittently provides a basis for engineering differentiation procedures, mainly based on the use of small molecules. Small molecules are more auspicious than any other growth factors, as they have unique, valuable properties like cell-permeability, as well as a nonimmunogenic nature; furthermore, they offer immense benefits in terms of generating efficient functional beta-like cells. We also summarize advances in the generation of stem cell-derived pancreatic cell lineages, especially endocrine β-like cells or islet organoids. The successful induction of stem cells depends on the quantity and quality of available stem cells and the efficient use of small molecules.

Jag1 Modulates an Oscillatory Dll1-Notch-Hes1 Signaling Module to Coordinate Growth and Fate of Pancreatic Progenitors

Notch signaling controls proliferation of multipotent pancreatic progenitor cells (MPCs) and their segregation into bipotent progenitors (BPs) and unipotent pro-acinar cells (PACs). Here, we showed that fast ultradian oscillations of the ligand Dll1 and the transcriptional effector Hes1 were crucial for MPC expansion, and changes in Hes1 oscillation parameters were associated with selective adoption of BP or PAC fate. Conversely, Jag1, a uniformly expressed ligand, restrained MPC growth. However, when its expression later segregated to PACs, Jag1 became critical for the specification of all but the most proximal BPs, and BPs were entirely lost in Jag1; Dll1 double mutants. Anatomically, ductal morphogenesis and organ architecture are minimally perturbed in Jag1 mutants until later stages, when ductal remodeling fails, and signs of acinar-to-ductal metaplasia appear. Our study thus uncovers that oscillating Notch activity in the developing pancreas, modulated by Jag1, is required to coordinate MPC growth and fate.

Adaptive Landscape Shaped by Core Endogenous Network Coordinates Complex Early Progenitor Fate Commitments in Embryonic Pancreas

The classical development hierarchy of pancreatic cell fate commitments describes that multipotent progenitors (MPs) first bifurcate into tip cells and trunk cells, and then these cells give rise to acinar cells and endocrine/ductal cells separately. However, lineage tracings reveal that pancreatic progenitors are highly heterogeneous in tip and trunk domains in embryonic pancreas. The progenitor fate commitments from multipotency to unipotency during early pancreas development is insufficiently characterized. In pursuing a mechanistic understanding of the complexity in progenitor fate commitments, we construct a core endogenous network for pancreatic lineage decisions based on genetic regulations and quantified its intrinsic dynamic properties using dynamic modeling. The dynamics reveal a developmental landscape with high complexity that has not been clarified. Not only well-characterized pancreatic cells are reproduced, but also previously unrecognized progenitors-tip progenitor (TiP), trunk progenitor (TrP), later endocrine progenitor (LEP), and acinar progenitors (AciP/AciP2) are predicted. Further analyses show that TrP and LEP mediate endocrine lineage maturation, while TiP, AciP, AciP2 and TrP mediate acinar and ductal lineage maturation. The predicted cell fate commitments are validated by analyzing single-cell RNA sequencing (scRNA-seq) data. Significantly, this is the first time that a redefined hierarchy with detailed early pancreatic progenitor fate commitment is obtained.

SOX9+/PTF1A+ Cells Define the Tip Progenitor Cells of the Human Fetal Pancreas of the Second Trimester

Significant progress has been made in recent years in characterizing human multipotent progenitor cells (hMPCs) of the early pancreas; however, the identity and persistence of these cells during the second trimester, after the initiation of branching morphogenesis, remain elusive. Additionally, studies on hMPCs have been hindered by few isolation methods that allow for the recovery of live cells. Here, we investigated the tip progenitor domain in the branched epithelium of human fetal pancreas between 13.5 and 17.5 gestational weeks by immunohistological staining. We also used a novel RNA-based technology to isolate live cells followed by gene expression analyses. We identified cells co-expressing SOX9 and PTF1A, two transcription factors known to be important for pancreatic MPCs, within the tips of the epithelium and observed a decrease in their proportions over time. Pancreatic SOX9+/PTF1A+ cells were enriched for MPC markers, including MYC and GATA6. These cells were proliferative and appeared active in branching morphogenesis and matrix remodeling, as evidenced by gene set enrichment analysis. We identified a hub of genes pertaining to the expanding tip progenitor niche, such as FOXF1, GLI3, TBX3, FGFR1, TGFBR2, ITGAV, ITGA2, and ITGB3. YAP1 of the Hippo pathway emerged as a highly enriched component within the SOX9+/PTF1A+ cells. Single-cell RNA-sequencing further corroborated the findings by identifying a cluster of SOX9+/PTF1A+ cells with multipotent characteristics. Based on these results, we propose that the SOX9+/PTF1A+ cells in the human pancreas are uncommitted MPC-like cells that reside at the tips of the expanding pancreatic epithelium, directing self-renewal and inducing pancreatic organogenesis. Stem Cells Translational Medicine 2019;8:1249&1264.

Stem Cells, Self-Renewal, and Lineage Commitment in the Endocrine System

The endocrine system coordinates a wide array of body functions mainly through secretion of hormones and their actions on target tissues. Over the last decades, a collective effort between developmental biologists, geneticists, and stem cell biologists has generated a wealth of knowledge related to the contribution of stem/progenitor cells to both organogenesis and self-renewal of endocrine organs. This review provides an up-to-date and comprehensive overview of the role of tissue stem cells in the development and self-renewal of endocrine organs. Pathways governing crucial steps in both development and stemness maintenance, and that are known to be frequently altered in a wide array of endocrine disorders, including cancer, are also described. Crucially, this plethora of information is being channeled into the development of potential new cell-based treatment modalities for endocrine-related illnesses, some of which have made it through clinical trials.

Extensive Fatty Replacement of the Pancreas (Pancreatic Lipomatosis) in a Dog

A 12-year-old neutered female mixed-breed dog was referred for occasional vomiting that had increased progressively in frequency over the past 3 months. Palpation of the abdomen revealed a firm mass of unknown aetiology, located within the cranial to mid abdomen, while abdominal surgical exploration revealed a well-defined abdominal mass of pancreatic origin. The pancreatic mass caused lateral displacement of the duodenum as well as medial displacement of the pylorus, resulting in impairment of pyloric outflow. Further examination revealed a firm, poorly vascularized and coarsely lobulated structure. The histopathological findings were consistent with severe pancreatic lipomatosis and atrophy. Immunohistochemically, the remnant pancreatic cells were positive for cytokeratins AE1/AE3 and glucagon, and negative for insulin. Routine follow-up with the referring veterinarian showed no evidence of postoperative complications, but the dog continued to deteriorate further and died despite medical management. Pancreatic lipomatosis is a rare condition in small animal practice. The aetiology or predisposing factors have not been identified in animals.

Sufu- and Spop-mediated downregulation of Hedgehog signaling promotes beta cell differentiation through organ-specific niche signals

Human embryonic stem cell-derived beta cells offer a promising cell-based therapy for diabetes. However, efficient stem cell to beta cell differentiation has proven difficult, possibly due to the lack of cross-talk with the appropriate mesenchymal niche. To define organ-specific niche signals, we isolated pancreatic and gastrointestinal stromal cells, and analyzed their gene expression during development. Our genetic studies reveal the importance of tightly regulated Hedgehog signaling in the pancreatic mesenchyme: inactivation of mesenchymal signaling leads to annular pancreas, whereas stroma-specific activation of signaling via loss of Hedgehog regulators, Sufu and Spop, impairs pancreatic growth and beta cell genesis. Genetic rescue and transcriptome analyses show that these Sufu and Spop knockout defects occur through Gli2-mediated activation of gastrointestinal stromal signals such as Wnt ligands. Importantly, inhibition of Wnt signaling in organoid and human stem cell cultures significantly promotes insulin-producing cell generation, altogether revealing the requirement for organ-specific regulation of stromal niche signals.

GATA factors in pancreas development and disease

There is an urgent need for the development of novel therapeutics options for diabetic patients given the high prevalence of diabetes worldwide and that, currently, there is no cure for this disease. The transplantation of pancreatic islets that contain insulin-producing cells is a promising therapeutic alternative, particularly for type 1 diabetes. However, the shortage of organ donors constitutes a major limitation for this approach; thus, developing alternative sources of insulin-producing cells is of critical importance. In the last decade, our knowledge of the molecular mechanisms controlling embryonic pancreas development has significantly advanced. More importantly, this knowledge has provided the basis for the in vitro generation of insulin-producing cells from stem cells. Recent studies have revealed that GATA transcription factors are involved in various stages of pancreas formation and in the adult ß cell function. Here, we review the fundamental role of GATA transcription factors in pancreas morphogenesis and their association with congenital diseases associated with pancreas.

The Use of Genetically Engineered Mouse Models for Studying the Function of Mutated Driver Genes in Pancreatic Cancer

Pancreatic cancer is often treatment-resistant, with the emerging standard of care, gemcitabine, affording only a few months of incrementally-deteriorating survival. Reflecting on the history of failed clinical trials, genetically engineered mouse models (GEMMs) in oncology research provides the inspiration to discover new treatments for pancreatic cancer that come from better knowledge of pathogenesis mechanisms, not only of the derangements in and consequently acquired capabilities of the cancer cells, but also in the aberrant microenvironment that becomes established to support, sustain, and enhance neoplastic progression. On the other hand, the existing mutational profile of pancreatic cancer guides our understanding of the disease, but leaves many important questions of pancreatic cancer biology unanswered. Over the past decade, a series of transgenic and gene knockout mouse modes have been produced that develop pancreatic cancers with features reflective of metastatic pancreatic ductal adenocarcinoma (PDAC) in humans. Animal models of PDAC are likely to be essential to understanding the genetics and biology of the disease and may provide the foundation for advances in early diagnosis and treatment.

Wnt signaling: implications in endoderm development and pancreas organogenesis

The pancreas is derived from the foregut endoderm during embryonic development. After gastrulation and endoderm germ layer formation complex morphogenetic events coupled with cell differentiation programs pattern the gut tube and induce pancreas organogenesis. This results in formation of exocrine, ductal and hormone-producing endocrine cells. Among these, endocrine cells are responsible for blood glucose homeostasis and their malfunction leads to diabetes mellitus, which cannot be stopped or reversed by the current standard treatments. Thus, intense efforts to regenerate or replace the lost or dysfunctional insulin-producing β-cells are on the way. This depends on identifying the factors that coordinate pancreas organogenesis. Here, we highlight the contribution of canonical and non-canonical Wnt signaling branches in orchestrating endoderm formation, pancreatic morphogenesis as well as endocrine cell formation and function.

GLIS3 binds pancreatic beta cell regulatory regions alongside other islet transcription factors

The Krüppel-like zinc finger transcription factor Gli-similar 3 (GLIS3) plays a critical role in the regulation of pancreatic beta cells, with global Glis3 knockout mice suffering from severe hyperglycemia and dying by post-natal day 11. In addition, GLIS3 has been shown to directly regulate the early endocrine marker Ngn3, as well as Ins2 gene expression in mature beta cells. We hypothesize that GLIS3 regulates several other genes critical to beta cell function, in addition to Ins2, by directly binding to regulatory regions. We therefore generated a pancreas-specific Glis3 deletion mouse model (Glis3Δpanc) using a Pdx1-driven Cre mouse line. Roughly 20% of these mice develop hyperglycemia by 8-weeks and lose most of their insulin expression. However, this did not appear to be due to loss of the beta cells themselves, as no change in cell death was observed. Indeed, presumptive beta cells appeared to persist as PDX1+/INS-/MAFA-/GLUT2- cells. Islet RNA-seq analysis combined with GLIS3 ChIP-seq analysis revealed apparent direct regulation of a variety of diabetes related genes, including Slc2a2 and Mafa. GLIS3 binding near these genes coincided with binding for other islet-enriched transcription factors, indicating these are distinct regulatory hubs. Our data indicates that GLIS3 not only regulates insulin expression, but several additional genes critical for beta cell function.

LATS1/2 suppress NFκB and aberrant EMT initiation to permit pancreatic progenitor differentiation

The Hippo pathway directs cell differentiation during organogenesis, in part by restricting proliferation. How Hippo signaling maintains a proliferation-differentiation balance in developing tissues via distinct molecular targets is only beginning to be understood. Our study makes the unexpected finding that Hippo suppresses nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) signaling in pancreatic progenitors to permit cell differentiation and epithelial morphogenesis. We find that pancreas-specific deletion of the large tumor suppressor kinases 1 and 2 (Lats1/2PanKO) from mouse progenitor epithelia results in failure to differentiate key pancreatic lineages: acinar, ductal, and endocrine. We carried out an unbiased transcriptome analysis to query differentiation defects in Lats1/2PanKO. This analysis revealed increased expression of NFκB activators, including the pantetheinase vanin1 (Vnn1). Using in vivo and ex vivo studies, we show that VNN1 activates a detrimental cascade of processes in Lats1/2PanKO epithelium, including (1) NFκB activation and (2) aberrant initiation of epithelial-mesenchymal transition (EMT), which together disrupt normal differentiation. We show that exogenous stimulation of VNN1 or NFκB can trigger this cascade in wild-type (WT) pancreatic progenitors. These findings reveal an unexpected requirement for active suppression of NFκB by LATS1/2 during pancreas development, which restrains a cell-autonomous deleterious transcriptional program and thereby allows epithelial differentiation.

Defining multistep cell fate decision pathways during pancreatic development at single-cell resolution

The generation of terminally differentiated cell lineages during organogenesis requires multiple, coordinated cell fate choice steps. However, this process has not been clearly delineated, especially in complex solid organs such as the pancreas. Here, we performed single-cell RNA-sequencing in pancreatic cells sorted from multiple genetically modified reporter mouse strains at embryonic stages E9.5-E17.5. We deciphered the developmental trajectories and regulatory strategies of the exocrine and endocrine pancreatic lineages as well as intermediate progenitor populations along the developmental pathways. Notably, we discovered previously undefined programs representing the earliest events in islet α- and β-cell lineage allocation as well as the developmental pathway of the "first wave" of α-cell generation. Furthermore, we demonstrated that repressing ERK pathway activity is essential for inducing both α- and β-lineage differentiation. This study provides key insights into the regulatory mechanisms underlying cell fate choice and stepwise cell fate commitment and can be used as a resource to guide the induction of functional islet lineage cells from stem cells in vitro.

Bromodomain and Extra Terminal Protein Inhibitors Promote Pancreatic Endocrine Cell Fate

Bromodomain and extraterminal (BET) proteins are epigenetic readers that interact with acetylated lysines of histone tails. Recent studies have demonstrated their role in cancer progression because they recruit key components of the transcriptional machinery to modulate gene expression. However, their role during embryonic development of the pancreas has never been studied. Using mouse embryonic pancreatic explants and human induced pluripotent stem cells (hiPSCs), we show that BET protein inhibition with I-BET151 or JQ1 enhances the number of neurogenin3 (NEUROG3) endocrine progenitors. In mouse explants, BET protein inhibition further led to increased expression of β-cell markers but in the meantime, strongly downregulated Ins1 expression. Similarly, although acinar markers, such as Cpa1 and CelA, were upregulated, Amy expression was repressed. In hiPSCs, BET inhibitors strongly repressed C-peptide and glucagon during endocrine differentiation. Explants and hiPSCs were then pulsed with BET inhibitors to increase NEUROG3 expression and further chased without inhibitors. Endocrine development was enhanced in explants with higher expression of insulin and maturation markers, such as UCN3 and MAFA. In hiPSCs, the outcome was different because C-peptide expression remained lower than in controls, but ghrelin expression was increased. Altogether, by using two independent models of pancreatic development, we show that BET proteins regulate multiple aspects of pancreatic development.