Pancreas organogenesis: from bud to plexus to gland

Emerging diabetes therapies: Bringing back the β-cells

BACKGROUND

Stem cell therapies are finally coming of age as a viable alternative to pancreatic islet transplantation for the treatment of insulin-dependent diabetes. Several clinical trials using human embryonic stem cell (hESC)-derived β-like cells are currently underway, with encouraging preliminary results. Remaining challenges notwithstanding, these strategies are widely expected to reduce our reliance on human isolated islets for transplantation procedures, making cell therapies available to millions of diabetic patients. At the same time, advances in our understanding of pancreatic cell plasticity and the molecular mechanisms behind β-cell replication and regeneration have spawned a multitude of translational efforts aimed at inducing β-cell replenishment in situ through pharmacological means, thus circumventing the need for transplantation.

SCOPE OF REVIEW

We discuss here the current state of the art in hESC transplantation, as well as the parallel quest to discover agents capable of either preserving the residual mass of β-cells or inducing their proliferation, transdifferentiation or differentiation from progenitor cells.

MAJOR CONCLUSIONS

Stem cell-based replacement therapies in the mold of islet transplantation are already around the corner, but a permanent cure for type 1 diabetes will likely require the endogenous regeneration of β-cells aided by interventions to restore the immune balance. The promise of current research avenues and a strong pipeline of clinical trials designed to tackle these challenges bode well for the realization of this goal.

Pancreatic β-Cell Development and Regeneration

The pancreatic β-cells are essential for regulating glucose homeostasis through the coordinated release of the insulin hormone. Dysfunction of the highly specialized β-cells results in diabetes mellitus, a growing global health epidemic. In this review, we describe the development and function of β-cells the emerging concept of heterogeneity within insulin-producing cells, and the potential of other cell types to assume β-cell functionality via transdifferentiation. We also discuss emerging routes to design cells with minimal β-cell properties and human stem cell differentiation efforts that carry the promise to restore normoglycemia in patients suffering from diabetes.

Signaling oscillations in embryonic development

Tight spatiotemporal control of cellular behavior and cell fate decisions is paramount to the formation of multicellular organisms during embryonic development. Intercellular communication via signaling pathways mediates this control. Interestingly, these signaling pathways are not static, but dynamic and change in activity over time. Signaling oscillations as a specific type of dynamics are found in various signaling pathways and model systems. Functions of oscillations include the regulation of periodic events or the transmission of information by encoding signals in the dynamic properties of a signaling pathway. For instance, signaling oscillations in neural or pancreatic progenitor cells modulate their proliferation and differentiation. Oscillations between neighboring cells can also be synchronized, leading to the emergence of waves traveling through the tissue. Such population-wide signaling oscillations regulate for example the consecutive segmentation of vertebrate embryos, a process called somitogenesis. Here, we outline our current understanding of signaling oscillations in embryonic development, how signaling oscillations are generated, how they are studied and how they contribute to the regulation of embryonic development.

Pancreatic Organoids for Regenerative Medicine and Cancer Research

In recent years, the development of ex vivo organoid cultures has gained substantial attention as a model to study regenerative medicine and diseases in several tissues. Diabetes and pancreatic ductal adenocarcinoma (PDAC) are the two major devastating diseases affecting the pancreas. Suitable models for regenerative medicine in diabetes and to accurately study PDAC biology and treatment response are essential in the pancreatic field. Pancreatic organoids can be generated from healthy pancreas or pancreatic tumors and constitute an important translational bridge between in vitro and in vivo models. Here, we review the rapidly emerging field of pancreatic organoids and summarize the current applications of the technology to tissue regeneration, disease modelling, and drug screening.

Isolation of mouse pancreatic islet Procr+ progenitors and long-term expansion of islet organoids in vitro

Insulin production is required for glucose homeostasis. Pancreatic islet β cells are the only cells that produce insulin in humans; however, generation of functional β cells in vitro from embryonic or adult tissues has been challenging. Here, we describe isolation of pancreatic islet progenitors from adult mice, which enables the efficient generation and long-term expansion of functional islet organoids in vitro. This protocol starts with purification of protein C receptor (Procr)-expressing islet progenitors. Coculture with endothelial cells generates islet organoids in vitro that can be expanded by passage. Functional maturation is achieved as a consequence of a prolonged culture period and cyclic glucose stimulation. Primary islet organoids form in 7-10 days. Subsequently, each passage takes 1 week, with the final maturation step requiring 3 weeks of additional culture. The resulting organoids are predominantly composed of β cells but also contain small proportions of α, δ and pancreatic polypeptide cells. The organoids sense glucose and secrete insulin. This approach thus provides a strategy for β cell generation in vitro and an organoid system to study islet regeneration and diseases.

MNX1-HNF1B Axis Is Indispensable for Intraductal Papillary Mucinous Neoplasm Lineages

BACKGROUND & AIMS

Chromatin architecture governs cell lineages by regulating the specific gene expression; however, its role in the diversity of cancer development remains unknown. Among pancreatic cancers, pancreatic ductal adenocarcinoma (PDAC) and intraductal papillary mucinous neoplasms (IPMN) with an associated invasive carcinoma (IPMNinv) arise from 2 distinct precursors, and their fundamental differences remain obscure. Here, we aimed to assess the difference of chromatin architecture regulating the transcriptional signatures or biological features in pancreatic cancers.

METHODS

We established 28 human organoids from distinct subtypes of pancreatic tumors, including IPMN, IPMNinv, and PDAC. We performed exome sequencing (seq), RNA-seq, assay for transposase-accessible chromatin-seq, chromatin immunoprecipitation-seq, high-throughput chromosome conformation capture, and phenotypic analyses with short hairpin RNA or clustered regularly interspaced short palindromic repeats interference.

RESULTS

Established organoids successfully reproduced the histology of primary tumors. IPMN and IPMNinv organoids harbored GNAS, RNF43, or KLF4 mutations and showed the distinct expression profiles compared with PDAC. Chromatin accessibility profiles revealed the gain of stomach-specific open regions in IPMN and the pattern of diverse gastrointestinal tissues in IPMNinv. In contrast, PDAC presented an impressive loss of accessible regions compared with normal pancreatic ducts. Transcription factor footprint analysis and functional assays identified that MNX1 and HNF1B were biologically indispensable for IPMN lineages. The upregulation of MNX1 was specifically marked in the human IPMN lineage tissues. The MNX1-HNF1B axis governed a set of genes, including MYC, SOX9, and OLFM4, which are known to be essential for gastrointestinal stem cells. High-throughput chromosome conformation capture analysis suggested the HNF1B target genes to be 3-dimensionally connected in the genome of IPMNinv.

CONCLUSIONS

Our organoid analyses identified the MNX1-HNF1B axis to be biologically significant in IPMN lineages.

Pancreatic-Like Cells Derived From Mouse Embryonic Stem Cells Are Regulated by Pdx1 Involving the Notch Pathway

OBJECTIVES

Embryonic stem cells (ESCs)-derived pancreatic precursor cells have great potential for pancreas repair. Expression of pancreatic duodenal homeobox 1 (Pdx1) in definitive endoderm (DE) cells is the premise that DE cells differentiate into pancreatic cells. To achieve the required number of Pdx1-expressing DE cells for cell transplantation therapy, a valid model must be established. Using this model, researchers investigated how Pdx1 regulates ESC differentiation into pancreatic cells.

METHODS

Tet-On inducible lentiviral vector encoding Pdx1 or mock vector was transduced into mouse ESC (ES-E14TG2a). The mouse ESCs were divided into 3 groups: control (ESC), mock vector (Pdx1 - -ESC), and vector encoding Pdx1 (Pdx1 + -ESC). All groups were separately cocultured with the DE cells sorted by immune beads containing CXCR-4 + (C-X-C chemokine receptor type-4) antibody. Doxycycline induced the expression of Pdx1 on the Pdx1 + -ESC cells. The markers of cell differentiation and Notch pathway were examined.

RESULTS

Significantly increased expression levels of Ptf1a, CK19, and amylase on day (d) 3 and d7, Neuro-D1 on d10 and d14, Pax6 and insulin on d14, as well as Notch1, Notch2, Hes1, and Hes5 on d3 and thereafter declined on d14 were observed in Pdx1 + -ESC group.

CONCLUSIONS

Pdx1 + -ESC could differentiate into pancreatic-like cells with involvement of the Notch pathway.

Molecular signaling in pancreatic ductal metaplasia: emerging biomarkers for detection and intervention of early pancreatic cancer

Pancreatic ductal metaplasia (PDM) is the transformation of potentially various types of cells in the pancreas into ductal or ductal-like cells, which eventually replace the existing differentiated somatic cell type(s). PDM is usually triggered by and manifests its ability to adapt to environmental stimuli and genetic insults. The development of PDM to atypical hyperplasia or dysplasia is an important risk factor for pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDA). Recent studies using genetically engineered mouse models, cell lineage tracing, single-cell sequencing and others have unraveled novel cellular and molecular insights in PDM formation and evolution. Those novel findings help better understand the cellular origins and functional significance of PDM and its regulation at cellular and molecular levels. Given that PDM represents the earliest pathological changes in PDA initiation and development, translational studies are beginning to define PDM-associated cell and molecular biomarkers that can be used to screen and detect early PDA and to enable its effective intervention, thereby truly and significantly reducing the dreadful mortality rate of PDA. This review will describe recent advances in the understanding of PDM biology with a focus on its underlying cellular and molecular mechanisms, and in biomarker discovery with clinical implications for the management of pancreatic regeneration and tumorigenesis.

Characterization and reduction of non-endocrine cells accompanying islet-like endocrine cells differentiated from human iPSC

The differentiation of pancreatic endocrine cells from human pluripotent stem cells has been thoroughly investigated for their application in cell therapy against diabetes. Although non-endocrine cells are inevitable contaminating by-products of the differentiation process, a comprehensive profile of such cells is lacking. Therefore, we characterized non-endocrine cells in iPSC-derived pancreatic islet cells (iPIC) using single-cell transcriptomic analysis. We found that non-endocrine cells consist of (1) heterogeneous proliferating cells, and (2) cells with not only pancreatic traits but also liver or intestinal traits marked by FGB or AGR2. Non-endocrine cells specifically expressed FGFR2, PLK1, and LDHB. We demonstrated that inhibition of pathways involving these genes selectively reduced the number of non-endocrine cells in the differentiation process. These findings provide useful insights into cell purification approaches and contribute to the improvement of the mass production of endocrine cells for stem cell-derived cell therapy for diabetes.

Development of a 3D atlas of the embryonic pancreas for topological and quantitative analysis of heterologous cell interactions

Generating comprehensive image maps, while preserving spatial three-dimensional (3D) context, is essential in order to locate and assess quantitatively specific cellular features and cell-cell interactions during organ development. Despite recent advances in 3D imaging approaches, our current knowledge of the spatial organization of distinct cell types in the embryonic pancreatic tissue is still largely based on two-dimensional histological sections. Here, we present a light-sheet fluorescence microscopy approach to image the pancreas in three dimensions and map tissue interactions at key time points in the mouse embryo. We demonstrate the utility of the approach by providing volumetric data, 3D distribution of three main cellular components (epithelial, mesenchymal and endothelial cells) within the developing pancreas, and quantification of their relative cellular abundance within the tissue. Interestingly, our 3D images show that endocrine cells are constantly and increasingly in contact with endothelial cells forming small vessels, whereas the interactions with mesenchymal cells decrease over time. These findings suggest distinct cell-cell interaction requirements for early endocrine cell specification and late differentiation. Lastly, we combine our image data in an open-source online repository (referred to as the Pancreas Embryonic Cell Atlas).

Summary: A light-sheet fluorescence microscopy approach is used for 3D imaging of the pancreas and to quantitatively map its interactions with surrounding tissues at key development time points in the mouse embryo.

The cell cortex as mediator of pancreatic epithelial development and endocrine differentiation

Organogenesis is the complex process of cells coordinating their own proliferation with changes to their shape, cell migration and cell-cell signaling, so that they transform into a three dimensional functional tissue, with its own custom range of differentiated cell types. Understanding when and where critical signals emanate from, and how those signals are transduced and interpreted, is the fundamental challenge of developmental biology. Here, we review recent findings regarding how progenitor cells interpret cues during pancreatic morphogenesis and how they coordinate cell fate determination. Recent evidence suggests that molecules located in the cell cortex play a crticial role in determining cellular behavior during pancreatic morphogenesis. Specifically, we find that control of cell adhesion, polarity, and constriction are all integral to both initiation of epithelial development and to later cell differentiation. Here, we review key molecules that coordinate these processes and suggest that the cell cortex acts as a signaling center that relays cues during pancreas development.

Windows of sensitivity to toxic chemicals in the development of the endocrine system: an analysis of ATSDR's toxicological profile database

This review utilizes the robust database of literature contained in toxicological profiles developed by the Agency for Toxic Substances and Disease Registry. The aim was to use this database to identify developmental toxicity studies reporting alterations in hormone levels in the developing fetus and offspring and identify windows of sensitivity. We identified 74 oral exposure studies in rats that provided relevant information on 30 chemicals from 21 profiles. Most studies located provided information on thyroid hormones, with fewer studies on anterior pituitary, adrenal medulla, ovaries, and testes. No studies pertaining to hormones of the posterior pituitary, pancreas, or adrenal cortex were located. The results demonstrate that development of the endocrine system may be affected by exposure to environmental contaminants at many different points, including gestational and/or lactational exposure. Moreover, this review demonstrates the need for more developmental toxicity studies focused on the endocrine system and specifically alterations in hormone levels.

Axon Guidance Molecules in the Islets of Langerhans

The islets of Langerhans, responsible for regulating blood glucose in vertebrates, are clusters of endocrine cells distributed throughout the exocrine pancreas. The spatial architecture of the different cell types within the islets controls cell-cell communication and impacts their ability to collectively regulate glucose. Islets rely on a range of chemotactic and adhesive cues to establish and manage intercellular relationships. Growing evidence indicates that axon guidance molecules such as Slit-Robo, Semaphorin-Neuropilin, Ephrin-Eph, and Netrins, influence endocrine progenitors' cell migration to establish correct architecture during islet morphogenesis, as well as directly regulating physical cell-cell communication in the mature islet to coordinate hormone secretion. In this mini-review, we discuss what is known and not yet known about how axon guidance molecules contribute to islet morphogenesis and function.

Pleiotrophin Expression and Actions in Pancreatic β-Cells

Pleiotrophin (PTN) is a heparin-binding cytokine that is widely expressed during early development and increases in maternal circulation during pregnancy.Aged PTN-deficient mice exhibit insulin resistance, suggesting a role in metabolic control. The objectives of this study were to determine if PTN is expressed in mouse pancreatic β-cells in young vs. adult animals, and its effects on DNA synthesis, β-cell gene expression and glucose-stimulated insulin secretion (GSIS). The Ptn gene was expressed in isolated fractions of young mouse β-cells, especially within immature β-cells with low glucose transporter 2 expression. Expression was retained in the adult pancreas but did not significantly change during pregnancy. PTN and its receptor, phosphotyrosine phosphatase-β/ζ, were also expressed in the proliferative INS1E β-cell line. Fluorescence immunohistochemistry showed that PTN peptide was present in islets of Langerhans in adult mice, associated predominantly with β-cells. The percentage of β-cells staining for PTN did not alter during mouse pregnancy, but intense staining was seen during β-cell regeneration in young mice following depletion of β-cells with streptozotocin. Incubation of INS1E cells with PTN resulted in an increased DNA synthesis as measured by Ki67 localization and increased expression of Pdx1 and insulin. However, both DNA synthesis and GSIS were not altered by PTN in isolated adult mouse islets. The findings show that Ptn is expressed in mouse β-cells in young and adult life and could potentially contribute to adaptive increases in β-cell mass during early life or pregnancy.

Leveraging the strengths of mice, human stem cells, and organoids to model pancreas development and diabetes

Diabetes is an epidemic with increasing incidence across the world. Most individuals who are afflicted by this disease have type 2 diabetes, but there are many who suffer from type 1, an autoimmune disorder. Both types of diabetes have complex genetic underpinnings that are further complicated by epigenetic and environmental factors. A less prevalent and often under diagnosed subset of diabetes cases are characterized by single genetic mutations and include Maturity Onset Diabetes of the Young (MODY) and Neonatal Diabetes Mellitus (NDM). While the mode of action and courses of treatment for all forms of diabetes are distinct, the diseases all eventually result in the dysfunction and/or death of the pancreatic β cell - the body's source of insulin. With loss of β cell function, blood glucose homeostasis is disrupted, and life-threatening complications arise. In this review, we focus on how model systems provide substantial insights into understanding β cell biology to inform our understanding of all forms of diabetes. The strengths and weaknesses of animal, hPSC derived β-like cell, and organoid models are considered along with discussion of GATA6, a critical transcription factor frequently implicated in pancreatic dysfunction with developmental origins; experimental studies of GATA6 have highlighted the advantages and disadvantages of how each of these model systems can be used to inform our understanding of β cell specification and function in health and disease.

Deregulation of Transcription Factor Networks Driving Cell Plasticity and Metastasis in Pancreatic Cancer

Pancreatic cancer is a very aggressive disease with 5-year survival rates of less than 10%. The constantly increasing incidence and stagnant patient outcomes despite changes in treatment regimens emphasize the requirement of a better understanding of the disease mechanisms. Challenges in treating pancreatic cancer include diagnosis at already progressed disease states due to the lack of early detection methods, rapid acquisition of therapy resistance, and high metastatic competence. Pancreatic ductal adenocarcinoma, the most prevalent type of pancreatic cancer, frequently shows dominant-active mutations in KRAS and TP53 as well as inactivation of genes involved in differentiation and cell-cycle regulation (e.g. SMAD4 and CDKN2A). Besides somatic mutations, deregulated transcription factor activities strongly contribute to disease progression. Specifically, transcriptional regulatory networks essential for proper lineage specification and differentiation during pancreas development are reactivated or become deregulated in the context of cancer and exacerbate progression towards an aggressive phenotype. This review summarizes the recent literature on transcription factor networks and epigenetic gene regulation that play a crucial role during tumorigenesis.

GLIS3: A Critical Transcription Factor in Islet β-Cell Generation

Understanding of pancreatic islet biology has greatly increased over the past few decades based in part on an increased understanding of the transcription factors that guide this process. One such transcription factor that has been increasingly tied to both β-cell development and the development of diabetes in humans is GLIS3. Genetic deletion of GLIS3 in mice and humans induces neonatal diabetes, while single nucleotide polymorphisms (SNPs) in GLIS3 have been associated with both Type 1 and Type 2 diabetes. As a significant progress has been made in understanding some of GLIS3’s roles in pancreas development and diabetes, we sought to compare current knowledge on GLIS3 within the pancreas to that of other islet enriched transcription factors. While GLIS3 appears to regulate similar genes and pathways to other transcription factors, its unique roles in β-cell development and maturation make it a key target for future studies and therapy.

Recent advances in tissue stem cells

Stem cells are undifferentiated cells capable of self-renewal and differentiation, giving rise to specialized functional cells. Stem cells are of pivotal importance for organ and tissue development, homeostasis, and injury and disease repair. Tissue-specific stem cells are a rare population residing in specific tissues and present powerful potential for regeneration when required. They are usually named based on the resident tissue, such as hematopoietic stem cells and germline stem cells. This review discusses the recent advances in stem cells of various tissues, including neural stem cells, muscle stem cells, liver progenitors, pancreatic islet stem/progenitor cells, intestinal stem cells, and prostate stem cells, and the future perspectives for tissue stem cell research.

On the Origin of Pancreatic Cancer: Molecular Tumor Subtypes in Perspective of Exocrine Cell Plasticity

Pancreatic ductal adenocarcinoma (PDAC) is a devastating type of cancer. While many studies have shed light into the pathobiology of PDAC, the nature of PDAC's cell of origin remains under debate. Studies in adult pancreatic tissue have unveiled a remarkable exocrine cell plasticity including transitional states, mostly exemplified by acinar to ductal cell metaplasia, but also with recent evidence hinting at duct to basal cell transitions. Single-cell RNA sequencing has further revealed intrapopulation heterogeneity among acinar and duct cells. Transcriptomic and epigenomic relationships between these exocrine cell differentiation states and PDAC molecular subtypes have started to emerge, suggesting different ontogenies for different tumor subtypes. This review sheds light on these diverse aspects with particular focus on studies with human cells. Understanding the "masked ball" of exocrine cells at origin of PDAC and leaving behind the binary acinar vs duct cell classification may significantly advance our insights in PDAC biology.

Cell Lineage Infidelity in PDAC Progression and Therapy Resistance

Infidelity to cell fate occurs when differentiated cells lose their original identity and either revert to a more multipotent state or transdifferentiate into a different cell type, either within the same embryonic lineage or in an entirely different one. Whilst in certain circumstances, such as in wound repair, this process is beneficial, it can be hijacked by cancer cells to drive disease initiation and progression. Cell phenotype switching has been shown to also serve as a mechanism of drug resistance in some epithelial cancers. In pancreatic ductal adenocarcinoma (PDAC), the role of lineage infidelity and phenotype switching is still unclear. Two consensus molecular subtypes of PDAC have been proposed that mainly reflect the existence of cell lineages with different degrees of fidelity to pancreatic endodermal precursors. Indeed, the classical subtype of PDAC is characterised by the expression of endodermal lineage specifying transcription factors, while the more aggressive basal-like/squamous subtype is defined by epigenetic downregulation of endodermal genes and alterations in chromatin modifiers. Here, we summarise the current knowledge of mechanisms (genetic and epigenetic) of cell fate switching in PDAC and discuss how pancreatic organoids might help increase our understanding of both cell-intrinsic and cell-extrinsic factors governing lineage infidelity during the distinct phases of PDAC evolution.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

Cell therapy research for Diabetes: Pancreatic β cell differentiation from pluripotent stem cells

Human pluripotent stem cells (PSCs), both embryonic and induced pluripotent stem cells (iPSCs), have been differentiated into pancreatic β isletsin vitrofor more than a decade. The idea is to get enough β cells for cell transplantation for diabetics. Finding a standard cell therapy for diabetes is essential because of the logarithmic increase in the global population of people with diabetes and the insufficient availability of the human cadaveric pancreas. Moreover, with better insights into developmental biology, thein vitroβ cell differentiation protocols have depended on thein vivoβ cell organogenesis. Various protocols for pancreatic β cell differentiation have been developed. Such protocols are based on the modulation of cell signalling pathways with growth factors, small molecules, RNAi approaches, directed differentiation using transcription factors, genome editing. Growth factor free differentiation protocols, epigenetic modulations, 3D differentiation approaches, and encapsulation strategies have also been reported for better glycemic control and endocrine modulations. Here, we have reviewed various aforementionedin vitroβ cell differentiation protocols from human PSCs, their respective comparisons, challenges, past, present, and future. The literature has been reviewed primarily from PubMed from the year 2000 till date using the mentioned keywords.

H3K4 Trimethylation Is Required for Postnatal Pancreatic Endocrine Cell Functional Maturation

During pancreas development, endocrine progenitors differentiate into the islet cell subtypes, which undergo further functional maturation in postnatal islet development. In islet β-cells, genes involved in glucose-stimulated insulin secretion are activated, and glucose exposure increases the insulin response as β-cells mature. We investigated the role of H3K4 trimethylation in endocrine cell differentiation and functional maturation by disrupting TrxG complex histone methyltransferase activity in mouse endocrine progenitors. In the embryo, genetic inactivation of TrxG component Dpy30 in NEUROG3⁺ cells did not affect the number of endocrine progenitors or endocrine cell differentiation. H3K4 trimethylation was progressively lost in postnatal islets, and the mice displayed elevated nonfasting and fasting glycemia as well as impaired glucose tolerance by postnatal day 24. Although postnatal endocrine cell proportions were equivalent to controls, islet RNA sequencing revealed a downregulation of genes involved in glucose-stimulated insulin secretion and an upregulation of immature β-cell genes. Comparison of histone modification enrichment profiles in NEUROG3⁺ endocrine progenitors and mature islets suggested that genes downregulated by loss of H3K4 trimethylation more frequently acquire active histone modifications during maturation. Taken together, these findings suggest that H3K4 trimethylation is required for the activation of genes involved in the functional maturation of pancreatic islet endocrine cells.

Gfi1 Loss Protects against Two Models of Induced Diabetes

Background: Although several approaches have revealed much about individual factors that regulate pancreatic development, we have yet to fully understand their complicated interplay during pancreas morphogenesis. Gfi1 is transcription factor specifically expressed in pancreatic acinar cells, whose role in pancreas cells fate identity and specification is still elusive. Methods: In order to gain further insight into the function of this factor in the pancreas, we generated animals deficient for Gfi1 specifically in the pancreas. Gfi1 conditional knockout animals were phenotypically characterized by immunohistochemistry, RT-qPCR, and RNA scope. To assess the role of Gfi1 in the pathogenesis of diabetes, we challenged Gfi1-deficient mice with two models of induced hyperglycemia: long-term high-fat/high-sugar feeding and streptozotocin injections. Results: Interestingly, mutant mice did not show any obvious deleterious phenotype. However, in depth analyses demonstrated a significant decrease in pancreatic amylase expression, leading to a diminution in intestinal carbohydrates processing and thus glucose absorption. In fact, Gfi1-deficient mice were found resistant to diet-induced hyperglycemia, appearing normoglycemic even after long-term high-fat/high-sugar diet. Another feature observed in mutant acinar cells was the misexpression of ghrelin, a hormone previously suggested to exhibit anti-apoptotic effects on β-cells in vitro. Impressively, Gfi1 mutant mice were found to be resistant to the cytotoxic and diabetogenic effects of high-dose streptozotocin administrations, displaying a negligible loss of β-cells and an imperturbable normoglycemia. Conclusions: Together, these results demonstrate that Gfi1 could turn to be extremely valuable for the development of new therapies and could thus open new research avenues in the context of diabetes research.

Sex-biased islet β cell dysfunction is caused by the MODY MAFA S64F variant by inducing premature aging and senescence in males

A heterozygous missense mutation of the islet β cell-enriched MAFA transcription factor (p.Ser64Phe [S64F]) is found in patients with adult-onset β cell dysfunction (diabetes or insulinomatosis), with men more prone to diabetes than women. This mutation engenders increased stability to the unstable MAFA protein. Here, we develop a S64F MafA mouse model to determine how β cell function is affected and find sex-dependent phenotypes. Heterozygous mutant males (MafAS64F/+) display impaired glucose tolerance, while females are slightly hypoglycemic with improved blood glucose clearance. Only MafAS64F/+ males show transiently higher MafA protein levels preceding glucose intolerance and sex-dependent changes to genes involved in Ca2+ signaling, DNA damage, aging, and senescence. MAFAS64F production in male human β cells also accelerate cellular senescence and increase senescence-associated secretory proteins compared to cells expressing MAFAWT. These results implicate a conserved mechanism of accelerated islet aging and senescence in promoting diabetes in MAFAS64F carriers in a sex-biased manner.

Combinatorial transcription factor profiles predict mature and functional human islet α and β cells

Islet-enriched transcription factors (TFs) exert broad control over cellular processes in pancreatic α and β cells, and changes in their expression are associated with developmental state and diabetes. However, the implications of heterogeneity in TF expression across islet cell populations are not well understood. To define this TF heterogeneity and its consequences for cellular function, we profiled more than 40,000 cells from normal human islets by single-cell RNA-Seq and stratified α and β cells based on combinatorial TF expression. Subpopulations of islet cells coexpressing ARX/MAFB (α cells) and MAFA/MAFB (β cells) exhibited greater expression of key genes related to glucose sensing and hormone secretion relative to subpopulations expressing only one or neither TF. Moreover, all subpopulations were identified in native pancreatic tissue from multiple donors. By Patch-Seq, MAFA/MAFB-coexpressing β cells showed enhanced electrophysiological activity. Thus, these results indicate that combinatorial TF expression in islet α and β cells predicts highly functional, mature subpopulations.

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.

Modeling endodermal organ development and diseases using human pluripotent stem cell-derived organoids

Recent advances in development of protocols for directed differentiation from human pluripotent stem cells (hPSCs) to defined lineages, in combination with 3D organoid technology, have facilitated the generation of various endoderm-derived organoids for in vitro modeling of human gastrointestinal development and associated diseases. In this review, we discuss current state-of-the-art strategies for generating hPSC-derived endodermal organoids including stomach, liver, pancreatic, small intestine, and colonic organoids. We also review the advantages of using this system to model various human diseases and evaluate the shortcomings of this technology. Finally, we emphasize how other technologies, such as genome editing and bioengineering, can be incorporated into the 3D hPSC-organoid models to generate even more robust and powerful platforms for understanding human organ development and disease modeling.

Recent Advances in the Generation of β-Cells from Induced Pluripotent Stem Cells as a Potential Cure for Diabetes Mellitus

Diabetes mellitus (DM) is a group of metabolic disorders characterized by high blood glucose levels due to insufficient insulin secretion, insulin action, or both. The present-day solution to diabetes mellitus includes regular administration of insulin, which brings about many medical complications in diabetic patients. Although islet transplantation from cadaveric subjects was proposed to be a permanent cure, the increased risk of infections, the need for immunosuppressive drugs, and their unavailability had restricted its use. To overcome this, the generation of renewable and transplantable β-cells derived from autologous induced pluripotent stem cells (iPSCs) has gained enormous interest as a potential therapeutic strategy to treat diabetes mellitus permanently. To date, extensive research has been undertaken to derive transplantable insulin-producing β-cells (iβ-cells) from iPSCs in vitro by recapitulating the in vivo developmental process of the pancreas. This in vivo developmental process relies on transcription factors, signaling molecules, growth factors, and culture microenvironment. This review highlights the various factors facilitating the generation of mature β-cells from iPSCs. Moreover, this review also describes the generation of pancreatic progenitors and β-cells from diabetic patient-specific iPSCs, exploring the potential of the diabetes disease model and drug discovery. In addition, the applications of genome editing strategies have also been discussed to achieve patient-specific diabetes cell therapy. Last, we have discussed the current challenges and prospects of iPSC-derived β-cells to improve the relative efficacy of the available treatment of diabetes mellitus.

Stage-specific transcriptomic changes in pancreatic α-cells after massive β-cell loss

Background

Loss of pancreatic insulin-secreting β-cells due to metabolic or autoimmune damage leads to the development of diabetes. The discovery that α-cells can be efficiently reprogrammed into insulin-secreting cells in mice and humans has opened promising avenues for innovative diabetes therapies. β-cell loss triggers spontaneous reprogramming of only 1–2% of α-cells, limiting the extent of regeneration. Most α-cells are refractory to conversion and their global transcriptomic response to severe β-cell loss as well as the mechanisms opposing their reprogramming into insulin producers are largely unknown. Here, we performed RNA-seq on FAC-sorted α-cells to characterize their global transcriptional responses at different time points after massive β-cell ablation.

Results

Our results show that α-cells undergo stage-specific transcriptional changes 5- and 15-days post-diphtheria toxin (DT)-mediated β-cell ablation. At 5 days, α-cells transiently upregulate various genes associated with interferon signaling and proliferation, including Interferon Induced Protein with Tetratricopeptide Repeats 3 (Ifit3). Subsequently, at 15 days post β-cell ablation, α-cells undergo a transient downregulation of genes from several pathways including Insulin receptor, mTOR and MET signaling.

Conclusions

The results presented here pinpoint novel markers discriminating α-cells at different stages after acute β-cell loss, and highlight additional signaling pathways that are modulated in α-cells in this context.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07812-x.

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.

Spatio-temporal expression pattern and role of the tight junction protein MarvelD3 in pancreas development and function

Tight junction complexes are involved in the establishment and maintenance of cell polarity and the regulation of signalling pathways, controlling biological processes such as cell differentiation and cell proliferation. MarvelD3 is a tight junction protein expressed in adult epithelial and endothelial cells. In Xenopus laevis, MarvelD3 morphants present differentiation defects of several ectodermal derivatives. In vitro experiments further revealed that MarvelD3 couples tight junctions to the MEKK1-JNK pathway to regulate cell behaviour and survival. In this work, we found that MarvelD3 is expressed from early developmental stages in the exocrine and endocrine compartments of the pancreas, as well as in endothelial cells of this organ. We thoroughly characterized MarvelD3 expression pattern in developing pancreas and evaluated its function by genetic ablation. Surprisingly, inactivation of MarvelD3 in mice did not alter development and differentiation of the pancreatic tissue. Moreover, tight junction formation and organization, cell polarization, and activity of the JNK-pathway were not impacted by the deletion of MarvelD3.

Monogenic Diabetes Modeling: In Vitro Pancreatic Differentiation From Human Pluripotent Stem Cells Gains Momentum

The occurrence of diabetes mellitus is characterized by pancreatic β cell loss and chronic hyperglycemia. While Type 1 and Type 2 diabetes are the most common types, rarer forms involve mutations affecting a single gene. This characteristic has made monogenic diabetes an interesting disease group to model in vitro using human pluripotent stem cells (hPSCs). By altering the genotype of the original hPSCs or by deriving human induced pluripotent stem cells (hiPSCs) from patients with monogenic diabetes, changes in the outcome of the in vitro differentiation protocol can be analyzed in detail to infer the regulatory mechanisms affected by the disease-associated genes. This approach has been so far applied to a diversity of genes/diseases and uncovered new mechanisms. The focus of the present review is to discuss the latest findings obtained by modeling monogenic diabetes using hPSC-derived pancreatic cells generated in vitro. We will specifically focus on the interpretation of these studies, the advantages and limitations of the models used, and the future perspectives for improvement.

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.

NEUROD1 Is Required for the Early α and β Endocrine Differentiation in the Pancreas

Diabetes is a metabolic disease that involves the death or dysfunction of the insulin-secreting β cells in the pancreas. Consequently, most diabetes research is aimed at understanding the molecular and cellular bases of pancreatic development, islet formation, β-cell survival, and insulin secretion. Complex interactions of signaling pathways and transcription factor networks regulate the specification, growth, and differentiation of cell types in the developing pancreas. Many of the same regulators continue to modulate gene expression and cell fate of the adult pancreas. The transcription factor NEUROD1 is essential for the maturation of β cells and the expansion of the pancreatic islet cell mass. Mutations of the Neurod1 gene cause diabetes in humans and mice. However, the different aspects of the requirement of NEUROD1 for pancreas development are not fully understood. In this study, we investigated the role of NEUROD1 during the primary and secondary transitions of mouse pancreas development. We determined that the elimination of Neurod1 impairs the expression of key transcription factors for α- and β-cell differentiation, β-cell proliferation, insulin production, and islets of Langerhans formation. These findings demonstrate that the Neurod1 deletion altered the properties of α and β endocrine cells, resulting in severe neonatal diabetes, and thus, NEUROD1 is required for proper activation of the transcriptional network and differentiation of functional α and β cells.

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.

Pancreatic cell fate specification: insights into developmental mechanisms and their application for lineage reprogramming

Diabetes is a group of metabolic disorders, which results from insufficient functional pancreatic β-cell mass either due to the autoimmune destruction of insulin producing β-cells, or their death or de-differentiation as compensation for insulin resistance. The ability to reprogram cell types within close developmental proximity to β-cells offers a strategy to replenish β-cell mass and a future possible treatment of diabetes. Here, we review recent advances in the fields of pancreas development and lineage reprogramming. We also probe the possibility of using reprogrammed cells as an approach by which to further understand developmental mechanisms, in particular roadblocks to changing cell identity. Finally, we highlight fundamental challenges that need to be overcome to advance lineage reprogramming for generating pancreatic cells.

Apical Restriction of the Planar Cell Polarity Component VANGL in Pancreatic Ducts Is Required to Maintain Epithelial Integrity

Cell polarity is essential for the architecture and function of numerous epithelial tissues. Here, we show that apical restriction of planar cell polarity (PCP) components is necessary for the maintenance of epithelial integrity. Using the mammalian pancreas as a model, we find that components of the core PCP pathway, such as the transmembrane protein Van Gogh-like (VANGL), become apically restricted over a period of several days. Expansion of VANGL localization to the basolateral membranes of progenitors leads to their death and disruption of the epithelial integrity. VANGL basolateral expansion does not affect apico-basal polarity but acts in the cells where Vangl is mislocalized by reducing Dishevelled and its downstream target ROCK. This reduction in ROCK activity culminates in progenitor cell egression, death, and eventually pancreatic hypoplasia. Thus, precise spatiotemporal modulation of VANGL-dependent PCP signaling is crucial for proper pancreatic morphogenesis.

Deoxyhypusine synthase, an essential enzyme for hypusine biosynthesis, is required for proper exocrine pancreas development

Pancreatic diseases including diabetes and exocrine insufficiency would benefit from therapies that reverse cellular loss and/or restore cellular mass. The identification of molecular pathways that influence cellular growth is therefore critical for future therapeutic generation. Deoxyhypusine synthase (DHPS) is an enzyme that post-translationally modifies and activates the mRNA translation factor eukaryotic initiation factor 5A (eIF5A). Previous work demonstrated that the inhibition of DHPS impairs zebrafish exocrine pancreas development; however, the link between DHPS, eIF5A, and regulation of pancreatic organogenesis remains unknown. Herein we identified that the conditional deletion of either Dhps or Eif5a in the murine pancreas results in the absence of acinar cells. Because DHPS catalyzes the activation of eIF5A, we evaluated and uncovered a defect in mRNA translation concomitant with defective production of proteins that influence cellular development. Our studies reveal a heretofore unappreciated role for DHPS and eIF5A in the synthesis of proteins required for cellular development and function.

Maternal obesity as a risk factor for developing diabetes in offspring: An epigenetic point of view

According to the developmental origin of health and disease concept, the risk of many age-related diseases is not only determined by genetic and adult lifestyle factors but also by factors acting during early development. In particular, maternal obesity and neonatal accelerated growth predispose offspring to overweight and type 2 diabetes (T2D) in adulthood. This concept mainly relies on the developmental plasticity of adipose tissue and pancreatic β-cell programming in response to suboptimal milieu during the perinatal period. These changes result in unhealthy hypertrophic adipocytes with decreased capacity to store fat, low-grade inflammation and loss of insulin-producing pancreatic β-cells. Over the past years, many efforts have been made to understand how maternal obesity induces long-lasting adipose tissue and pancreatic β-cell dysfunction in offspring and what are the molecular basis of the transgenerational inheritance of T2D. In particular, rodent studies have shed light on the role of epigenetic mechanisms in linking maternal nutritional manipulations to the risk for T2D in adulthood. In this review, we discuss epigenetic adipocyte and β-cell remodeling during development in the progeny of obese mothers and the persistence of these marks as a basis of obesity and T2D predisposition.

Cell Cycle Regulation of the Pdx1 Transcription Factor in Developing Pancreas and Insulin-Producing β-Cells

Current evidence indicates that proliferating β-cells express lower levels of some functional cell identity genes, suggesting that proliferating cells are not optimally functional. Pdx1 is important for β-cell specification, function, and proliferation and is mutated in monogenic forms of diabetes. However, its regulation during the cell cycle is unknown. Here we examined Pdx1 protein expression in immortalized β-cells, maternal mouse islets during pregnancy, and mouse embryonic pancreas. We demonstrate that Pdx1 localization and protein levels are highly dynamic. In nonmitotic cells, Pdx1 is not observed in constitutive heterochromatin, nucleoli, or most areas containing repressive epigenetic marks. At prophase, Pdx1 is enriched around the chromosomes before Ki67 coating of the chromosome surface. Pdx1 uniformly localizes in the cytoplasm at prometaphase and becomes enriched around the chromosomes again at the end of cell division, before nuclear envelope formation. Cells in S phase have lower Pdx1 levels than cells at earlier cell cycle stages, and overexpression of Pdx1 in INS-1 cells prevents progression toward G2, suggesting that cell cycle-dependent regulation of Pdx1 is required for completion of mitosis. Together, we find that Pdx1 localization and protein levels are tightly regulated throughout the cell cycle. This dynamic regulation has implications for the dichotomous role of Pdx1 in β-cell function and proliferation.

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.

Groucho co-repressor proteins regulate β cell development and proliferation by repressing Foxa1 in the developing mouse pancreas

Groucho-related genes (GRGs) are transcriptional co-repressors that are crucial for many developmental processes. Several essential pancreatic transcription factors are capable of interacting with GRGs; however, the in vivo role of GRG-mediated transcriptional repression in pancreas development is still not well understood. In this study, we used complex mouse genetics and transcriptomic analyses to determine that GRG3 is essential for β cell development, and in the absence of Grg3 there is compensatory upregulation of Grg4 Grg3/4 double mutant mice have severe dysregulation of the pancreas gene program with ectopic expression of canonical liver genes and Foxa1, a master regulator of the liver program. Neurod1, an essential β cell transcription factor and predicted target of Foxa1, becomes downregulated in Grg3/4 mutants, resulting in reduced β cell proliferation, hyperglycemia, and early lethality. These findings uncover novel functions of GRG-mediated repression during pancreas development.

Molecular mechanisms of β-cell dysfunction and death in monogenic forms of diabetes

Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic β-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired β-cell function and survival, and discuss the molecular mechanisms involved in β-cell demise.

A developmental lineage-based gene co-expression network for mouse pancreatic β-cells reveals a role for Zfp800 in pancreas development

To gain a deeper understanding of pancreatic β-cell development, we used iterative weighted gene correlation network analysis to calculate a gene co-expression network (GCN) from 11 temporally and genetically defined murine cell populations. The GCN, which contained 91 distinct modules, was then used to gain three new biological insights. First, we found that the clustered protocadherin genes are differentially expressed during pancreas development. Pcdhγ genes are preferentially expressed in pancreatic endoderm, Pcdhβ genes in nascent islets, and Pcdhα genes in mature β-cells. Second, after extracting sub-networks of transcriptional regulators for each developmental stage, we identified 81 zinc finger protein (ZFP) genes that are preferentially expressed during endocrine specification and β-cell maturation. Third, we used the GCN to select three ZFPs for further analysis by CRISPR mutagenesis of mice. Zfp800 null mice exhibited early postnatal lethality, and at E18.5 their pancreata exhibited a reduced number of pancreatic endocrine cells, alterations in exocrine cell morphology, and marked changes in expression of genes involved in protein translation, hormone secretion and developmental pathways in the pancreas. Together, our results suggest that developmentally oriented GCNs have utility for gaining new insights into gene regulation during organogenesis.

Sequential progenitor states mark the generation of pancreatic endocrine lineages in mice and humans

The pancreatic islet contains multiple hormone⁺ endocrine lineages (α, β, δ, PP and ε cells), but the developmental processes that underlie endocrinogenesis are poorly understood. Here, we generated novel mouse lines and combined them with various genetic tools to enrich all types of hormone⁺ cells for well-based deep single-cell RNA sequencing (scRNA-seq), and gene coexpression networks were extracted from the generated data for the optimization of high-throughput droplet-based scRNA-seq analyses. These analyses defined an entire endocrinogenesis pathway in which different states of endocrine progenitor (EP) cells sequentially differentiate into specific endocrine lineages in mice. Subpopulations of the EP cells at the final stage (EP4^early and EP4^late) show different potentials for distinct endocrine lineages. ε cells and an intermediate cell population were identified as distinct progenitors that independently generate both α and PP cells. Single-cell analyses were also performed to delineate the human pancreatic endocrinogenesis process. Although the developmental trajectory of pancreatic lineages is generally conserved between humans and mice, clear interspecies differences, including differences in the proportions of cell types and the regulatory networks associated with the differentiation of specific lineages, have been detected. Our findings support a model in which sequential transient progenitor cell states determine the differentiation of multiple cell lineages and provide a blueprint for directing the generation of pancreatic islets in vitro.

Culture, differentiation, and transduction of mouse E12.5 pancreatic spheres: an in vitro model for the secondary transition of pancreas development

During the secondary transition of rodent pancreatic development, mainly between E12.5 and E15.5 in mice, exocrine and endocrine populations differentiate from pancreatic progenitors. Here we describe an experimental system for its study in vitro. First, we show that spheres derived from dissociated E12.5 mouse pancreases differentiate within 7 days into most pancreatic exocrine and endocrine cell types, including beta cells. The proportion and spatial repartition of the different endocrine populations mirror those observed during normal development. Thus, dissociation and culture do not impair the developmental events affecting pancreatic progenitors during the secondary transition. Moreover, dissociated cells from mouse E12.5 pancreas were transduced with ecotropic MLV-based retroviral vectors or, though less efficiently, with a mixture of ALV(A)-based retroviral vectors and gesicles containing the TVA (Tumor Virus A) receptor. As an additional improvement, we also created a transgenic mouse line expressing TVA under the control of the 4.5 kB pdx1 promoter (pdx1-TVA). We demonstrate that pancreatic progenitors from dissociated pdx1-TVA pancreas can be specifically transduced by ALV(A)-based retroviral vectors. Using this model, we expressed an activated mutant of the YAP transcriptional co-activator in pancreatic progenitors. These experiments indicate that deregulated YAP activity reduces endocrine and exocrine differentiation in the resulting spheres, confirming and extending previously published data. Thus, our experimental model recapitulates in vitro the crucial developmental decisions arising at the secondary transition and provides a convenient tool to study their genetic control.