Notch-mediated patterning and cell fate allocation of pancreatic progenitor cells

A perfect islet: reviewing recent protocol developments and proposing strategies for stem cell derived functional pancreatic islets

The search for an effective cell replacement therapy for diabetes has driven the development of "perfect" pancreatic islets from human pluripotent stem cells (hPSCs). These hPSC-derived pancreatic islet-like β cells can overcome the limitations for disease modelling, drug development and transplantation therapies in diabetes. Nevertheless, challenges remain in generating fully functional and mature β cells from hPSCs. This review underscores the significant efforts made by researchers to optimize various differentiation protocols aimed at enhancing the efficiency and quality of hPSC-derived pancreatic islets and proposes methods for their improvement. By emulating the natural developmental processes of pancreatic embryogenesis, specific growth factors, signaling molecules and culture conditions are employed to guide hPSCs towards the formation of mature β cells capable of secreting insulin in response to glucose. However, the efficiency of these protocols varies greatly among different human embryonic stem cell (hESC) and induced pluripotent stem cell (hiPSC) lines. This variability poses a particular challenge for generating patient-specific β cells. Despite recent advancements, the ultimate goal remains to develop a highly efficient directed differentiation protocol that is applicable across all genetic backgrounds of hPSCs. Although progress has been made, further research is required to optimize the protocols and characterization methods that could ensure the safety and efficacy of hPSC-derived pancreatic islets before they can be utilized in clinical settings.

The significance of ultradian oscillations in development

Genes regulating developmental processes have been identified, but the mechanisms underlying their expression with the correct timing are still under investigation. Several genes show oscillatory expression that regulates the timing of developmental processes, such as somitogenesis and neurogenesis. These oscillations are also important for other developmental processes, such as cell proliferation and differentiation. In this review, we discuss the significance of oscillatory gene expression in developmental time and other forms of regulation.

Regulation of multiple signaling pathways promotes the consistent expansion of human pancreatic progenitors in defined conditions

The unlimited expansion of human progenitor cells in vitro could unlock many prospects for regenerative medicine. However, it remains an important challenge as it requires the decoupling of the mechanisms supporting progenitor self-renewal and expansion from those mechanisms promoting their differentiation. This study focuses on the expansion of human pluripotent stem (hPS) cell-derived pancreatic progenitors (PP) to advance novel therapies for diabetes. We obtained mechanistic insights into PP expansion requirements and identified conditions for the robust and unlimited expansion of hPS cell-derived PP cells under GMP-compliant conditions through a hypothesis-driven iterative approach. We show that the combined stimulation of specific mitogenic pathways, suppression of retinoic acid signaling, and inhibition of selected branches of the TGFβ and Wnt signaling pathways are necessary for the effective decoupling of PP proliferation from differentiation. This enabled the reproducible, 2000-fold, over 10 passages and 40-45 d, expansion of PDX1+/SOX9+/NKX6-1+ PP cells. Transcriptome analyses confirmed the stabilization of PP identity and the effective suppression of differentiation. Using these conditions, PDX1+/SOX9+/NKX6-1+ PP cells, derived from different, both XY and XX, hPS cell lines, were enriched to nearly 90% homogeneity and expanded with very similar kinetics and efficiency. Furthermore, non-expanded and expanded PP cells, from different hPS cell lines, were differentiated in microwells into homogeneous islet-like clusters (SC-islets) with very similar efficiency. These clusters contained abundant β-cells of comparable functionality as assessed by glucose-stimulated insulin secretion assays. These findings established the signaling requirements to decouple PP proliferation from differentiation and allowed the consistent expansion of hPS cell-derived PP cells. They will enable the establishment of large banks of GMP-produced PP cells derived from diverse hPS cell lines. This approach will streamline SC-islet production for further development of the differentiation process, diabetes research, personalized medicine, and cell therapies.

The role of noncoding RNAs in pancreatic birth defects

Congenital defects in the pancreas can cause severe health issues such as pancreatic cancer and diabetes which require lifelong treatment. Regenerating healthy pancreatic cells to replace malfunctioning cells has been considered a promising cure for pancreatic diseases including birth defects. However, such therapies are currently unavailable in the clinic. The developmental gene regulatory network underlying pancreatic development must be reactivated for in vivo regeneration and recapitulated in vitro for cell replacement therapy. Thus, understanding the mechanisms driving pancreatic development will pave the way for regenerative therapies. Pancreatic progenitor cells are the precursors of all pancreatic cells which use epigenetic changes to control gene expression during differentiation to generate all of the distinct pancreatic cell types. Epigenetic changes involving DNA methylation and histone modifications can be controlled by noncoding RNAs (ncRNAs). Indeed, increasing evidence suggests that ncRNAs are indispensable for proper organogenesis. Here, we summarize recent insight into the role of ncRNAs in the epigenetic regulation of pancreatic development. We further discuss how disruptions in ncRNA biogenesis and expression lead to developmental defects and diseases. This review summarizes in vivo data from animal models and in vitro studies using stem cell differentiation as a model for pancreatic development.

The role of the Notch signalling pathway in regulating the balance between neuronal and nonneuronal cells in sympathetic ganglia and the adrenal gland

Sympathetic neurons and endocrine chromaffin cells of the adrenal medulla are catecholaminergic cells that derive from the neural crest. According to the classic model, they develop from a common sympathoadrenal (SA) progenitor that has the ability to differentiate into both sympathetic neurons and chromaffin cells depending on signals provided by their final environment. Our previous data revealed that a single premigratory neural crest cell can give rise to both sympathetic neurons and chromaffin cells, indicating that the fate decision between these cell types occurs after delamination. A more recent study demonstrated that at least half of chromaffin cells arise from a later contribution by Schwann cell precursors. Since Notch signalling is known to be implicated in the regulation of cell fate decisions, we investigated the early role of Notch signalling in regulating the development of neuronal and non-neuronal SA cells within sympathetic ganglia and the adrenal gland. To this end, we implemented both gain and loss of function approaches. Electroporation of premigratory neural crest cells with plasmids encoding Notch inhibitors revealed an elevation in the number of SA cells expressing the catecholaminergic enzyme tyrosine-hydroxylase, with a concomitant reduction in the number of cells expressing the glial marker P0 in both sympathetic ganglia and adrenal gland. As expected, gain of Notch function had the opposite effect. Numbers of neuronal and non-neuronal SA cells were affected differently by Notch inhibition depending on the time of its onset. Together our data show that Notch signalling can regulate the ratio of glial cells, neuronal SA cells and nonneuronal SA cells in both sympathetic ganglia and the adrenal gland.

SOXE group transcription factors regulates the expression of FoxG1 during inner ear development

The transcription factor FOXG1 plays an important role in inner ear development; however, the cis-regulatory mechanisms controlling the inner-ear-specific expression of FOXG1 are poorly understood. In this study, we aimed to identify the element that specifically regulates FoxG1 expression in the otic vesicle, which develops into the inner ear, through comparative genome analysis between vertebrate species and chromatin immunoprecipitation. The cis-regulatory element (E2) identified showed high evolutionary conservation among vertebrates in the genomic DNA of FoxG1 spanning approximately 3 Mbp. We identified core sequences important for the activity of the otic-vesicle-specific enhancer through in vitro and in vivo reporter assays for various E2 enhancer mutants and determined the consensus sequence for SOX DNA binding. In addition, SoxE, a subfamily of the Sox family, was simultaneously expressed in the otic vesicles of developing embryos and showed a similar protein expression pattern as that of FoxG1. Furthermore, SOXE transcription factors induced specific transcriptional activity through the FoxG1 Otic enhancer (E2b). These findings suggest that the interaction between the otic enhancer of FoxG1 and SOXE transcription factor, in which the otic expression of FoxG1 is evolutionarily well-conserved, is important during early development of the inner ear, a sensory organ important for survival in nature.

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.

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.

Inhibition of Notch activity suppresses hyperglycemia-augmented polarization of macrophages to the M1 phenotype and alleviates acute pancreatitis

Acute pancreatitis (AP) is an acute inflammatory disorder characterized by acinar cell death and inflammation. Multiple factors cause hyperglycemia after AP. Macrophage polarization is involved in tissue injury and repair, and is regulated by Notch signaling during certain inflammatory diseases. The present study explores the relationship among hyperglycemia, macrophage polarization, and Notch signaling during AP and the related mechanisms. A cerulein-induced AP model was established in FVB/N mice, and AP with hyperglycemia was initiated by injection of 50% concentration glucose. Tissue damage, Notch activity, and macrophage polarization were assessed in pancreatic tissues. The role of Notch signaling in macrophage polarization during AP was also assessed in vitro by co-culturing primary macrophages and pancreatic acinar cells, and establishing a lipopolysaccharide (LPS)-induced inflammatory model in RAW264.7 cells. Pancreatic acinar cells were damaged and proinflammatory factor levels were increased in pancreatic tissues during AP. The hyperglycemic conditions aggravated pancreatic injury, increased macrophage infiltration, promoted macrophage polarization towards an M1 phenotype, and led to excessive up-regulation of Notch activity. Inhibition of Notch signaling by DAPT or Notch1 knockdown decreased the proportion of M1 macrophages and reduced the production of proinflammatory factors, thus mitigating pancreatic injury. These findings suggest that hyperglycemia induces excessive Notch signaling after AP and further aggravates AP by promoting pancreatic macrophage polarization towards the M1 phenotype. The Notch signaling pathway is a potential target for the prevention and treatment of AP.

SerpinB13 antibodies promote β cell development and resistance to type 1 diabetes

Pancreatic endocrine cell development is dependent on the rescue of the neurogenin3 (Ngn3) transcription factor from repression by Notch. The signals that prevent Notch signaling, thereby allowing the formation of pancreatic endocrine cells, remain unclear. We show that inhibiting serpinB13, a cathepsin L (CatL) protease inhibitor expressed in the pancreatic epithelium, caused in vitro and in vivo cleavage of the extracellular domain of Notch1. This was followed by a twofold increase in the Ngn3⁺ progenitor cell population and enhanced conversion of these cells to express insulin. Conversely, both recombinant serpinB13 protein and CatL deficiency down-regulated pancreatic Ngn3⁺ cell output. Mouse embryonic exposure to inhibitory anti-serpinB13 antibody resulted in increased islet cell mass and improved outcomes in streptozotocin-induced diabetes at 8 weeks of age. Moreover, anti-serpinB13 autoantibodies stimulated Ngn3⁺ endocrine progenitor formation in the pancreas and were associated with delayed progression to type 1 diabetes (T1D) in children. These data demonstrate long-term impact of serpinB13 activity on islet biology and suggest that promoting protease activity by blocking this serpin may have prophylactic potential in T1D.

Hippo Signaling Pathway in Pancreas Development

The Hippo signaling pathway is a vital regulator of pancreatic development and homeostasis, directing cell fate decisions, morphogenesis, and adult pancreatic cellular plasticity. Through loss-of-function research, Hippo signaling has been found to play key roles in maintaining the proper balance between progenitor cell renewal, proliferation, and differentiation in pancreatic organogenesis. Other studies suggest that overactivation of YAP, a downstream effector of the pathway, promotes ductal cell development and suppresses endocrine cell fate specification via repression of Ngn3. After birth, disruptions in Hippo signaling have been found to lead to de-differentiation of acinar cells and pancreatitis-like phenotype. Further, Hippo signaling directs pancreatic morphogenesis by ensuring proper cell polarization and branching. Despite these findings, the mechanisms through which Hippo governs cell differentiation and pancreatic architecture are yet to be fully understood. Here, we review recent studies of Hippo functions in pancreatic development, including its crosstalk with NOTCH, WNT/β-catenin, and PI3K/Akt/mTOR signaling pathways.

Aberrant development of pancreatic beta cells derived from human iPSCs with FOXA2 deficiency

FOXA2 has been identified as an essential factor for pancreas development and emerging evidence supports an association between FOXA2 and diabetes. Although the role of FOXA2 during pancreatic development is well-studied in animal models, its role during human islet cell development remains unclear. Here, we generated induced pluripotent stem cells (iPSCs) from a patient with FOXA2 haploinsufficiency (FOXA2^+/- iPSCs) followed by beta-cell differentiation to understand the role of FOXA2 during pancreatic beta-cell development. Our results showed that FOXA2 haploinsufficiency resulted in aberrant expression of genes essential for the differentiation and proper functioning of beta cells. At pancreatic progenitor (PP2) and endocrine progenitor (EPs) stages, transcriptome analysis showed downregulation in genes associated with pancreatic development and diabetes and upregulation in genes associated with nervous system development and WNT signaling pathway. Knockout of FOXA2 in control iPSCs (FOXA2^-/- iPSCs) led to severe phenotypes in EPs and beta-cell stages. The expression of NGN3 and its downstream targets at EPs as well as INSUILIN and GLUCAGON at the beta-cell stage, were almost absent in the cells derived from FOXA2^-/- iPSCs. These findings indicate that FOXA2 is crucial for human pancreatic endocrine development and its defect may lead to diabetes based on FOXA2 dosage.

High-Dimensional Design-Of-Experiments Extracts Small-Molecule-Only Induction Conditions for Dorsal Pancreatic Endoderm from Pluripotency

The derivation of endoderm and descendant organs, such as pancreas, liver, and intestine, impacts disease modeling and regenerative medicine. Use of TGF-β signaling agonism is a common method for induction of definitive endoderm from pluripotency. By using a data-driven, High-Dimensional Design of Experiments (HD-DoE)-based methodology to address multifactorial problems in directed differentiation, we found instead that optimal conditions demanded BMP antagonism and retinoid input leading to induction of dorsal foregut endoderm (DFE). We demonstrate that pancreatic identity can be rapidly, and robustly, induced from DFE and that such cells are of dorsal pancreatic identity. The DFE population was highly competent to differentiate into both stomach organoids and pancreatic tissue types and able to generate fetal-type β cells through two subsequent differentiation steps using only small molecules. This alternative, rapid, and low-cost basis for generating pancreatic insulin-producing cells may have impact for the development of cell-based therapies for diabetes.

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Method development for addressing multifactorial problems in directed differentiation

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Generation of endodermal populations without the use of TGF-β agonism

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Small-molecule-based pancreatic differentiation protocol

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.

Distinctive properties of the interactions between Notch and Notch ligands

Although Notch signaling is known to be critical for the specification of cell fate in various developing organs, the particular roles of each Notch and Notch ligand (NotchL) have not yet been elucidated. The phenotypes found in loss-of-function experiments have varied, depending on the expression profiles of the receptors and ligands. However, in some cases, their significances differ from others, even with comparable levels of expression, suggesting a distinctive functional receptor-ligand interaction during the activation process of Notch signaling. In this review, the phenotypes observed in Notch/NotchL-deficient situations are introduced, and their distinct roles are accentuated. The distinctive features of the specific combinations of Notch/NotchL are also discussed. This review aims to highlight the unanswered questions in this field to help improve our understanding of the preferential functional interaction between Notch and NotchL.

Protein Methyltransferase Inhibition Decreases Endocrine Specification Through the Upregulation of Aldh1b1 Expression

Understanding the mechanisms that promote the specification of pancreas progenitors and regulate their self-renewal and differentiation will help to maintain and expand pancreas progenitor cells derived from human pluripotent stem (hPS) cells. This will improve the efficiency of current differentiation protocols of hPS cells into β-cells and bring such cells closer to clinical applications for the therapy of diabetes. Aldehyde dehydrogenase 1b1 (Aldh1b1) is a mitochondrial enzyme expressed specifically in progenitor cells during mouse pancreas development, and we have shown that its functional inactivation leads to accelerated differentiation and deficient β-cells. In this report, we aimed to identify small molecule inducers of Aldh1b1 expression taking advantage of a mouse embryonic stem (mES) cell Aldh1b1 lacZ reporter line and a pancreas differentiation protocol directing mES cells into pancreatic progenitors. We identified AMI-5, a protein methyltransferase inhibitor, as an Aldh1b1 inducer and showed that it can maintain Aldh1b1 expression in embryonic pancreas explants. This led to a selective reduction in endocrine specification. This effect was due to a downregulation of Ngn3, and it was mediated through Aldh1b1 since the effect was abolished in Aldh1b1 null pancreata. The findings implicated methyltransferase activity in the regulation of endocrine differentiation and showed that methyltransferases can act through specific regulators during pancreas differentiation. Stem Cells 2019;37:640-651.

Differentiation Potential of Mesenchymal Stem Cells into Pancreatic β-Cells

Stem cells having the capability to differentiate into other type of cells and renewing themselves, gained so much importance in recent years. Investigations in stem cells revealed that mesenchymal stem cells can successfully differentiate into other type of cells like adipocytes, hepatocytes, osteocytes, neurocytes and chondrocytes. In addition, these cells can also differentiate into insulin-producing beta cells. Insulin is a crucial hormone for glucose balance of the body. Insufficiency or unavailability of insulin is called diabetes. External insulin intake, as well as pancreas or islet transplantation, is the most basic treatment of diabetes. In vivo and in vitro studies demonstrate that stem cell therapy is also used in the cure of diabetes. Differentiation process of stem cells into beta cells releasing insulin is quite complicated. There are many different reports for the differentiation of stem cells in the literature. The success of differentiation of stem cells into beta cells depends on several factors like the source of stem cells, chemicals added into the differentiation medium and the duration of differentiation protocol. Distinct studies for the differentiation of stem cells into insulin-secreting cells are available in the literature. Moreover, thanks to the superior differentiation capacity of stem cells, they are being preferred in clinical studies. Stem cells were clinically used to heal diabetic ulcer, to increase c-peptide level and insulin secretion in both type 1 and type 2 diabetes. Mesenchymal stem cells having high differentiation potential to insulin-secreting cells are encouraging vehicles for both in vivo and in vitro studies together with clinical trials for diabetes mellitus.

ROCK-nmMyoII, Notch and Neurog3 gene-dosage link epithelial morphogenesis with cell fate in the pancreatic endocrine-progenitor niche

During mouse pancreas organogenesis, endocrine cells are born from progenitors residing in an epithelial plexus niche. After a period in a lineage-primed Neurog3^LO state, progenitors become endocrine committed via upregulation of Neurog3 We find that the Neurog3^LO to Neurog3^HI transition is associated with distinct stages of an epithelial egression process: narrowing the apical surface of the cell, basalward cell movement and eventual cell-rear detachment from the apical lumen surface to allow clustering as nascent islets under the basement membrane. Apical narrowing, basalward movement and Neurog3 transcriptional upregulation still occur without Neurog3 protein, suggesting that morphogenetic cues deployed within the plexus initiate endocrine commitment upstream or independently of Neurog3. Neurog3 is required for cell-rear detachment and complete endocrine-cell birth. The ROCK-nmMyoII pathway coordinates epithelial-cell morphogenesis and the progression through Neurog3-expressing states. NmMyoII is necessary for apical narrowing, basalward cell displacement and Neurog3 upregulation, but all three are limited by ROCK activity. We propose that ROCK-nmMyoII activity, Neurog3 gene-dose and Notch signaling integrate endocrine fate allocation with epithelial plexus growth and morphogenesis, representing a feedback control circuit that coordinates morphogenesis with lineage diversification in the endocrine-birth niche.

Neurog3-dependent pancreas dysgenesis causes ectopic pancreas in Hes1 mutant mice

Mutations in Hes1, a target gene of the Notch signalling pathway, lead to ectopic pancreas by a poorly described mechanism. Here, we use genetic inactivation of Hes1 combined with lineage tracing and live imaging to reveal an endodermal requirement for Hes1, and show that ectopic pancreas tissue is derived from the dorsal pancreas primordium. RNA-seq analysis of sorted E10.5 Hes1^+/+ and Hes1^-/- Pdx1-GFP⁺ cells suggested that upregulation of endocrine lineage genes in Hes1^-/- embryos was the major defect and, accordingly, early pancreas morphogenesis was normalized, and the ectopic pancreas phenotype suppressed, in Hes1^-/-Neurog3^-/- embryos. In Mib1 mutants, we found a near total depletion of dorsal progenitors, which was replaced by an anterior Gcg⁺ extension. Together, our results demonstrate that aberrant morphogenesis is the cause of ectopic pancreas and that a part of the endocrine differentiation program is mechanistically involved in the dysgenesis. Our results suggest that the ratio of endocrine lineage to progenitor cells is important for morphogenesis and that a strong endocrinogenic phenotype without complete progenitor depletion, as seen in Hes1 mutants, provokes an extreme dysgenesis that causes ectopic pancreas.

Mesodermal induction of pancreatic fate commitment

The pancreas is a compound gland comprised of both exocrine acinar and duct cells as well as endocrine islet cells. Most notable amongst the latter are the insulin-synthesizing β-cells, loss or dysfunction of which manifests in diabetes mellitus. All exocrine and endocrine cells derive from multipotent pancreatic progenitor cells arising from the primitive gut epithelium via inductive interactions with adjacent mesodermal tissues. Research in the last two decades has revealed the identity of many of these extrinsic cues and they include signaling molecules used in many other developmental contexts such as retinoic acid, fibroblast growth factors, and members of the TGF-β superfamily. As important as these inductive cues is the absence of other signaling molecules such as hedgehog family members. Much has been learned about the interactions of extrinsic factors with fate regulators intrinsic to the pancreatic endoderm. This new knowledge has had tremendous impact on the development of directed differentiation protocols for converting pluripotent stem cells to β-cells in vitro.

Cellular and molecular mechanisms coordinating pancreas development

The pancreas is an endoderm-derived glandular organ that participates in the regulation of systemic glucose metabolism and food digestion through the function of its endocrine and exocrine compartments, respectively. While intensive research has explored the signaling pathways and transcriptional programs that govern pancreas development, much remains to be discovered regarding the cellular processes that orchestrate pancreas morphogenesis. Here, we discuss the developmental mechanisms and principles that are known to underlie pancreas development, from induction and lineage formation to morphogenesis and organogenesis. Elucidating such principles will help to identify novel candidate disease genes and unravel the pathogenesis of pancreas-related diseases, such as diabetes, pancreatitis and cancer.

A radial axis defined by semaphorin-to-neuropilin signaling controls pancreatic islet morphogenesis

The islets of Langerhans are endocrine organs characteristically dispersed throughout the pancreas. During development, endocrine progenitors delaminate, migrate radially and cluster to form islets. Despite the distinctive distribution of islets, spatially localized signals that control islet morphogenesis have not been discovered. Here, we identify a radial signaling axis that instructs developing islet cells to disperse throughout the pancreas. A screen of pancreatic extracellular signals identified factors that stimulated islet cell development. These included semaphorin 3a, a guidance cue in neural development without known functions in the pancreas. In the fetal pancreas, peripheral mesenchymal cells expressed Sema3a, while central nascent islet cells produced the semaphorin receptor neuropilin 2 (Nrp2). Nrp2 mutant islet cells developed in proper numbers, but had defects in migration and were unresponsive to purified Sema3a. Mutant Nrp2 islets aggregated centrally and failed to disperse radially. Thus, Sema3a-Nrp2 signaling along an unrecognized pancreatic developmental axis constitutes a chemoattractant system essential for generating the hallmark morphogenetic properties of pancreatic islets. Unexpectedly, Sema3a- and Nrp2-mediated control of islet morphogenesis is strikingly homologous to mechanisms that regulate radial neuronal migration and cortical lamination in the developing mammalian brain.

Lacrimal Gland Repair after Short-term Obstruction of Excretory Duct in Rabbits

Aqueous tear-deficient dry eye is a multifactorial chronic disorder in which the lacrimal glands fail to produce enough tears to maintain a healthy ocular surface. The existence of lacrimal gland stem/progenitor cells was proposed in several species, yet their origin and characteristics are not very clear. Here, we investigated the presence of resident progenitor cells and their regenerative potential in a rabbit model with lacrimal gland main excretory duct ligation-induced injury. The ligation-injured lacrimal glands temporarily decreased in weight and had impaired tear secretion. Protein expression profiles and transcriptional profiles were obtained from injured tissue. Isolated lacrimal gland progenitor cells were tested and characterized by stem cell-related marker evaluation, single cell clonal assay and three-dimensional (3-D) culture. The results of our study indicate that lacrimal glands are capable of tissue repair after duct ligation-induced injury, likely involving resident stem/progenitor cells and epithelial-mesenchymal transitions. Lacrimal gland progenitor cells isolated from ligated tissue can differentiate in 3-D culture. The results provide further insights into lacrimal gland stem/progenitor cell physiology and their potential for treating severe cases of tear deficiency.

Pancreas lineage allocation and specification are regulated by sphingosine-1-phosphate signalling

During development, progenitor expansion, lineage allocation, and implementation of differentiation programs need to be tightly coordinated so that different cell types are generated in the correct numbers for appropriate tissue size and function. Pancreatic dysfunction results in some of the most debilitating and fatal diseases, including pancreatic cancer and diabetes. Several transcription factors regulating pancreas lineage specification have been identified, and Notch signalling has been implicated in lineage allocation, but it remains unclear how these processes are coordinated. Using a combination of genetic approaches, organotypic cultures of embryonic pancreata, and genomics, we found that sphingosine-1-phosphate (S1p), signalling through the G protein coupled receptor (GPCR) S1pr2, plays a key role in pancreas development linking lineage allocation and specification. S1pr2 signalling promotes progenitor survival as well as acinar and endocrine specification. S1pr2-mediated stabilisation of the yes-associated protein (YAP) is essential for endocrine specification, thus linking a regulator of progenitor growth with specification. YAP stabilisation and endocrine cell specification rely on Gαi subunits, revealing an unexpected specificity of selected GPCR intracellular signalling components. Finally, we found that S1pr2 signalling posttranscriptionally attenuates Notch signalling levels, thus regulating lineage allocation. Both S1pr2-mediated YAP stabilisation and Notch attenuation are necessary for the specification of the endocrine lineage. These findings identify S1p signalling as a novel key pathway coordinating cell survival, lineage allocation, and specification and linking these processes by regulating YAP levels and Notch signalling. Understanding lineage allocation and specification in the pancreas will shed light in the origins of pancreatic diseases and may suggest novel therapeutic approaches.

The molecular and morphogenetic basis of pancreas organogenesis

The pancreas is an essential endoderm-derived organ that ensures nutrient metabolism via its endocrine and exocrine functions. Here we review the essential processes governing the embryonic and early postnatal development of the pancreas discussing both the mechanisms and molecules controlling progenitor specification, expansion and differentiation. We elaborate on how these processes are orchestrated in space and coordinated with morphogenesis. We draw mainly from experiments conducted in the mouse model but also from investigations in other model organisms, complementing a recent comprehensive review of human pancreas development (Jennings et al., 2015) [1]. The understanding of pancreas development in model organisms provides a framework to interpret how human mutations lead to neonatal diabetes and may contribute to other forms of diabetes and to guide the production of desired pancreatic cell types from pluripotent stem cells for therapeutic purposes.

Regulation of Cellular Identity in Cancer

Neoplastic transformation requires changes in cellular identity. Emerging evidence increasingly points to cellular reprogramming, a process during which fully differentiated and functional cells lose aspects of their identity while gaining progenitor characteristics, as a critical early step during cancer initiation. This cell identity crisis persists even at the malignant stage in certain cancers, suggesting that reactivation of progenitor functions supports tumorigenicity. Here, we review recent findings that establish the essential role of cellular reprogramming during neoplastic transformation and the major players involved in it with a special emphasis on pancreatic cancer.

Regulation of Cellular Identity in Cancer

Neoplastic transformation requires changes in cellular identity. Emerging evidence increasingly points to cellular reprogramming, a process during which fully differentiated and functional cells lose aspects of their identity while gaining progenitor characteristics, as a critical early step during cancer initiation. This cell identity crisis persists even at the malignant stage in certain cancers, suggesting that reactivation of progenitor functions supports tumorigenicity. Here, we review recent findings that establish the essential role of cellular reprogramming during neoplastic transformation and the major players involved in it with a special emphasis on pancreatic cancer.

Centroacinar cells: At the center of pancreas regeneration

The process of regeneration serves to heal injury by replacing missing cells. Understanding regeneration can help us replace cell populations lost during disease, such as the insulin-producing β cells lost in diabetic patients. Centroacinar cells (CACs) are a specialized ductal pancreatic cell type that act as progenitors to replace β cells in the zebrafish. However, whether CACs contribute to β-cell regeneration in adult mammals remains controversial. Here we review the current understanding of the role of CACs as endocrine progenitors during regeneration in zebrafish and mammals.

Endocrine Pancreas Development and Regeneration: Noncanonical Ideas From Neural Stem Cell Biology

Loss of insulin-producing pancreatic islet β-cells is a hallmark of type 1 diabetes. Several experimental paradigms demonstrate that these cells can, in principle, be regenerated from multiple endogenous sources using signaling pathways that are also used during pancreas development. A thorough understanding of these pathways will provide improved opportunities for therapeutic intervention. It is now appreciated that signaling pathways should not be seen as "on" or "off" but that the degree of activity may result in wildly different cellular outcomes. In addition to the degree of operation of a signaling pathway, noncanonical branches also play important roles. Thus, a pathway, once considered as "off" or "low" may actually be highly operational but may be using noncanonical branches. Such branches are only now revealing themselves as new tools to assay them are being generated. A formidable source of noncanonical signal transduction concepts is neural stem cells because these cells appear to have acquired unusual signaling interpretations to allow them to maintain their unique dual properties (self-renewal and multipotency). We discuss how such findings from the neural field can provide a blueprint for the identification of new molecular mechanisms regulating pancreatic biology, with a focus on Notch, Hes/Hey, and hedgehog pathways.

Feedback control of growth, differentiation, and morphogenesis of pancreatic endocrine progenitors in an epithelial plexus niche

In the mammalian pancreas, endocrine cells undergo lineage allocation upon emergence from a bipotent duct/endocrine progenitor pool, which resides in the "trunk epithelium." Major questions remain regarding how niche environments are organized within this epithelium to coordinate endocrine differentiation with programs of epithelial growth, maturation, and morphogenesis. We used EdU pulse-chase and tissue-reconstruction approaches to analyze how endocrine progenitors and their differentiating progeny are assembled within the trunk as it undergoes remodeling from an irregular plexus of tubules to form the eventual mature, branched ductal arbor. The bulk of endocrine progenitors is maintained in an epithelial "plexus state," which is a transient intermediate during epithelial maturation within which endocrine cell differentiation is continually robust and surprisingly long-lived. Within the plexus, local feedback effects derived from the differentiating and delaminating endocrine cells nonautonomously regulate the flux of endocrine cell birth as well as proliferative growth of the bipotent cell population using Notch-dependent and Notch-independent influences, respectively. These feedback effects in turn maintain the plexus state to ensure prolonged allocation of endocrine cells late into gestation. These findings begin to define a niche-like environment guiding the genesis of the endocrine pancreas and advance current models for how differentiation is coordinated with the growth and morphogenesis of the developing pancreatic epithelium.

Notch Signaling in Pancreatic Development

The Notch signaling pathway plays a significant role in embryonic cell fate determination and adult tissue homeostasis. Various studies have demonstrated the deep involvement of Notch signaling in the development of the pancreas and the lateral inhibition of Notch signaling in pancreatic progenitor differentiation and maintenance. The targeted inactivation of the Notch pathway components promotes premature differentiation of the endocrine pancreas. However, there is still the contrary opinion that Notch signaling specifies the endocrine lineage. Here, we review the current knowledge of the Notch signaling pathway in pancreatic development and its crosstalk with the Wingless and INT-1 (Wnt) and fibroblast growth factor (FGF) pathways.

Three-Dimensional Culture of Functional Adult Rabbit Lacrimal Gland Epithelial Cells on Decellularized Scaffold

Aqueous tear-deficient dry eye disease is a multifactorial chronic disorder, in which the lacrimal gland fails to produce enough tears to maintain a healthy ocular surface. Some severe cases may develop corneal damage and significant vision loss. Treatment primarily involves palliation using ocular surface lubricants, but can only provide temporary relief. Construction of a bioengineered lacrimal gland having functional secretory epithelial cells is a potentially promising option for providing long-term relief to severe dry eye patients. Using sphere-forming culture techniques, we cultured adult rabbit lacrimal gland progenitor cells and prepared a lacrimal gland scaffold by decellularization. When progenitor cells were seeded onto the decellularized scaffold, they formed duct- and acinar-like structures in the three-dimensional culture system. Lacrimal gland epithelial cells showed good cell viability, cell differentiation, and secretory function in decellularized lacrimal gland matrix, as indicated by morphology, immunostaining, and β-hexosaminidase secretion assay. This study demonstrated the potential suitability of utilizing tissue-specific progenitor cells and a tissue-derived bioscaffold for lacrimal gland restoration.

Acinar cell reprogramming: a clinically important target in pancreatic disease

Acinar cells of the pancreas produce the majority of enzymes required for digestion and make up >90% of the cells within the pancreas. Due to a common developmental origin and the plastic nature of the acinar cell phenotype, these cells have been identified as a possible source of β cells as a therapeutic option for Type I diabetes. However, recent evidence indicates that acinar cells are the main source of pancreatic intraepithelial neoplasias (PanINs), the predecessor of pancreatic ductal adenocarcinoma (PDAC). The conversion of acinar cells to either β cells or precursors to PDAC is dependent on reprogramming of the cells to a more primitive, progenitor-like phenotype, which involves changes in transcription factor expression and activity, and changes in their epigenetic program. This review will focus on the mechanisms that promote acinar cell reprogramming, as well as the factors that may affect these mechanisms.

Progenitor potential of nkx6.1-expressing cells throughout zebrafish life and during beta cell regeneration

Background

In contrast to mammals, the zebrafish has the remarkable capacity to regenerate its pancreatic beta cells very efficiently. Understanding the mechanisms of regeneration in the zebrafish and the differences with mammals will be fundamental to discovering molecules able to stimulate the regeneration process in mammals. To identify the pancreatic cells able to give rise to new beta cells in the zebrafish, we generated new transgenic lines allowing the tracing of multipotent pancreatic progenitors and endocrine precursors.

Results

Using novel bacterial artificial chromosome transgenic nkx6.1 and ascl1b reporter lines, we established that nkx6.1-positive cells give rise to all the pancreatic cell types and ascl1b-positive cells give rise to all the endocrine cell types in the zebrafish embryo. These two genes are initially co-expressed in the pancreatic primordium and their domains segregate, not as a result of mutual repression, but through the opposite effects of Notch signaling, maintaining nkx6.1 expression while repressing ascl1b in progenitors. In the adult zebrafish, nkx6.1 expression persists exclusively in the ductal tree at the tip of which its expression coincides with Notch active signaling in centroacinar/terminal end duct cells. Tracing these cells reveals that they are able to differentiate into other ductal cells and into insulin-expressing cells in normal (non-diabetic) animals. This capacity of ductal cells to generate endocrine cells is supported by the detection of ascl1b in the nkx6.1:GFP ductal cell transcriptome. This transcriptome also reveals, besides actors of the Notch and Wnt pathways, several novel markers such as id2a. Finally, we show that beta cell ablation in the adult zebrafish triggers proliferation of ductal cells and their differentiation into insulin-expressing cells.

Conclusions

We have shown that, in the zebrafish embryo, nkx6.1+ cells are bona fide multipotent pancreatic progenitors, while ascl1b+ cells represent committed endocrine precursors. In contrast to the mouse, pancreatic progenitor markers nkx6.1 and pdx1 continue to be expressed in adult ductal cells, a subset of which we show are still able to proliferate and undergo ductal and endocrine differentiation, providing robust evidence of the existence of pancreatic progenitor/stem cells in the adult zebrafish. Our findings support the hypothesis that nkx6.1+ pancreatic progenitors contribute to beta cell regeneration. Further characterization of these cells will open up new perspectives for anti-diabetic therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0179-4) contains supplementary material, which is available to authorized users.

Neurogenin 3 Expressing Cells in the Human Exocrine Pancreas Have the Capacity for Endocrine Cell Fate

Neurogenin 3 (NGN3) is necessary and sufficient for endocrine differentiation during pancreatic development and is expressed by a population of progenitor cells that give rise exclusively to hormone-secreting cells within islets. NGN3 protein can be detected in the adult rodent pancreas only following certain types of injury, when it is transiently expressed by exocrine cells undergoing reprogramming to an endocrine cell fate. Here, NGN3 protein can be detected in 2% of acinar and duct cells in living biopsies of histologically normal adult human pancreata and 10% in cadaveric biopsies of organ donor pancreata. The percentage and total number of NGN3+ cells increase during culture without evidence of proliferation or selective cell death. Isolation of highly purified and viable NGN3+ cell populations can be achieved based on coexpression of the cell surface glycoprotein CD133. Transcriptome and targeted expression analyses of isolated CD133+ / NGN3+ cells indicate that they are distinct from surrounding exocrine tissue with respect to expression phenotype and Notch signaling activity, but retain high level mRNA expression of genes indicative of acinar and duct cell function. NGN3+ cells have an mRNA expression profile that resembles that of mouse early endocrine progenitor cells. During in vitro differentiation, NGN3+ cells express genes in a pattern characteristic of endocrine development and result in cells that resemble beta cells on the basis of coexpression of insulin C-peptide, chromogranin A and pancreatic and duodenal homeobox 1. NGN3 expression in the adult human exocrine pancreas marks a dedifferentiating cell population with the capacity to take on an endocrine cell fate. These cells represent a potential source for the treatment of diabetes either through ex vivo manipulation, or in vivo by targeting mechanisms controlling their population size and endocrine cell fate commitment.

Progenitor Epithelium: Sorting Out Pancreatic Lineages

Insulin-producing β cells within the vertebrate fetal pancreas acquire their fate in a step-wise manner. Whereas the intrinsic factors dictating the transcriptional or epigenetic status of pancreatic lineages have been intensely examined, less is known about cell-cell interactions that might constitute a niche for the developing β cell lineage. It is becoming increasingly clear that understanding and recapitulating these steps may instruct in vitro differentiation of embryonic stem cells and/or therapeutic regeneration. Indeed, directed differentiation techniques have improved since transitioning from 2D to 3D cultures, suggesting that the 3D microenvironment in which β cells are born is critical. However, to date, it remains unknown whether the changing architecture of the pancreatic epithelium impacts the fate of cells therein. An emerging challenge in the field is to elucidate how progenitors are allocated during key events, such as the stratification and subsequent resolution of the pre-pancreatic epithelium, as well as the formation of lumens and branches. Here, we assess the progenitor epithelium and examine how it might influence the emergence of pancreatic multipotent progenitors (MPCs), which give rise to β cells and other pancreatic lineages.

Islet formation in mice and men: lessons for the generation of functional insulin-producing β-cells from human pluripotent stem cells

The Islets of Langerhans are crucial 'micro-organs' embedded in the glandular exocrine pancreas that regulate nutrient metabolism. They not only synthesize, but also secrete endocrine hormones in a modulated fashion in response to physiologic metabolic demand. These highly sophisticated structures with intricate organization of multiple cell types, namely endocrine, vascular, neuronal and mesenchymal cells, have evolved to perform this task to perfection over time. Not surprisingly, islet architecture and function are dissimilar between humans and typically studied model organisms, such as rodents and zebrafish. Further, recent findings also suggest noteworthy differences in human islet development from that in mouse, including delayed appearance and gradual resolution of key differentiation markers, a single-phase of endocrine differentiation, and prenatal association of developing islets with neurovascular milieu. In light of these findings, it is imperative that a systematic study is undertaken to compare islet development between human and mouse. Illuminating inter-species differences in islet development will likely be critical in furthering our pursuit to generate an unlimited supply of truly functional and fully mature β-cells from human pluripotent stem cell (hPSC) sources for therapeutic purposes.

Growth Factor Independence-1 (Gfi1) Is Required for Pancreatic Acinar Unit Formation and Centroacinar Cell Differentiation

BACKGROUND & AIMS

The genetic specification of the compartmentalized pancreatic acinar/centroacinar unit is poorly understood. Growth factor independence-1 (Gfi1) is a zinc finger transcriptional repressor that regulates hematopoietic stem cell maintenance, pre-T-cell differentiation, formation of granulocytes, inner ear hair cells, and the development of secretory cell types in the intestine. As GFI1/Gfi1 is expressed in human and rodent pancreas, we characterized the potential function of Gfi1 in mouse pancreatic development.

METHODS

Gfi1 knockout mice were analyzed at histological and molecular levels, including qRT-PCR, in situ hybridization, immunohistochemistry, and electron microscopy.

RESULTS

Loss of Gfi1 impacted formation and structure of the pancreatic acinar/centroacinar unit. Histologic and ultrastructural analysis of Gfi1-null pancreas revealed specific defects at the level of pancreatic acinar cells as well as the centroacinar cells (CACs) in Gfi1^-/- mice when compared with wild-type littermates. Pancreatic endocrine differentiation, islet architecture, and function were unaffected. Organ domain patterning and the formation of ductal cells occurred normally during the murine secondary transition (E13.5-E14.5) in the Gfi1^-/- pancreas. However, at later gestational time points (E18.5), expression of cellular markers for CACs was substantially reduced in Gfi1^-/- mice, corroborated by electron microscopy imaging of the acinar/centroacinar unit. The reduction in CACs was correlated with an exocrine organ defect. Postnatally, Gfi1 deficiency resulted in severe pancreatic acinar dysplasia, including loss of granulation, autolytic vacuolation, and a proliferative and apoptotic response.

CONCLUSIONS

Gfi1 plays an important role in regulating the development of pancreatic CACs and the function of pancreatic acinar cells.

Epithelial Notch signaling is a limiting step for pancreatic carcinogenesis

Background

Pancreatic cancer is one of the deadliest human malignancies, with few therapeutic options. Re-activation of embryonic signaling pathways is commonly in human pancreatic cancer and provided rationale to explore inhibition of these pathways therapeutically. Notch signaling is important during pancreatic development, and it is re-activated in pancreatic cancer. The functional role of Notch signaling during pancreatic carcinogenesis has been previously characterized using both genetic and drug-based approaches. However, contrasting findings were reported based on the study design. In fact, Notch signaling has been proposed to act as tumor-promoter or tumor-suppressor. Given the availability of Notch inhibitors in the clinic, understanding how this signaling pathway contributes to pancreatic carcinogenesis has important therapeutic implications. Here, we interrogated the role of Notch signaling specifically in the epithelial compartment of the pancreas, in the context of a genetically engineered mouse model of pancreatic cancer.

Methods

To inhibit Notch signaling in the pancreas epithelium, we crossed a mouse model of pancreatic cancer based on pancreas-specific expression of mutant Kras with a transgenic mouse that conditionally expresses a dominant negative form of the Mastermind-like 1 gene. MAML is an essential co-activator of the canonical Notch signaling-mediated transcription. DNMAML encodes a truncated MAML protein that represses all canonical Notch mediated transcription in a cell autonomous manner, independent of which Notch receptor is activated. As a result, in mice co-expressing mutant Kras and DNMAML, Notch signaling is inhibited specifically in the epithelium upon Cre-mediated recombination. We explored the effect of epithelial-specific DNMAML expression on Kras-driven carcinogenesis both during normal aging and following the induction of acute pancreatitis.

Results

We find that DNMAML expression efficiently inhibits epithelial Notch signaling and delays PanIN formation. However, over time, loss of Notch inhibition allows PanIN formation and progression.

Conclusions

Epithelial-specific Notch signaling is important for PanIN initiation. Our findings indicate that PanIN formation can only occur upon loss of epithelial Notch inhibition, thus supporting an essential role of this signaling pathway during pancreatic carcinogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-862) contains supplementary material, which is available to authorized users.

Non-neural tyrosine hydroxylase, via modulation of endocrine pancreatic precursors, is required for normal development of beta cells in the mouse pancreas

AIMS/HYPOTHESIS

Apart from transcription factors, little is known about the molecules that modulate the proliferation and differentiation of pancreatic endocrine cells. The early expression of tyrosine hydroxylase (TH) in a subset of glucagon(+) cells led us to investigate whether catecholamines have a role in beta cell development.

METHODS

We studied the immunohistochemical characteristics of TH-expressing cells in wild-type (Th (+/+) ) mice during early pancreas development, and analysed the endocrine pancreas phenotype of TH-deficient (Th (-/-) ) mice. We also studied the effect of dopamine addition and TH-inhibition on insulin-producing cells in explant cultures.

RESULTS

In the mouse pancreas at embryonic day (E)12.5-E13.5, the ∼10% of early glucagon(+) cells that co-expressed TH rarely proliferated and did not express the precursor marker neurogenin 3 at E13.5. The number of insulin(+) cells in the Th (-/-) embryonic pancreas was decreased as compared with wild-type embryos at E13.5. While no changes in pancreatic and duodenal homeobox 1 (PDX1)(+)-progenitor cell number were observed between groups at E12.5, the number of neurogenin 3 and NK2 homeobox 2 (NKX2.2)-expressing cells was reduced in Th (-/-) embryonic pancreas, an effect that occurred in parallel with increased expression of the transcriptional repressor Hes1. The potential role of dopamine as a pro-beta cell stimulus was tested by treating pancreas explants with this catecholamine, which resulted in an increase in total insulin content and insulin(+) cells relative to control explants.

CONCLUSIONS/INTERPRETATION

A non-neural catecholaminergic pathway appears to modulate the pancreatic endocrine precursor and insulin producing cell neogenesis. This finding may have important implications for approaches seeking to promote the generation of beta cells to treat diabetes.

Segregation of striated and smooth muscle lineages by a Notch-dependent regulatory network

Background

Lineage segregation from multipotent epithelia is a central theme in development and in adult stem cell plasticity. Previously, we demonstrated that striated and smooth muscle cells share a common progenitor within their epithelium of origin, the lateral domain of the somite-derived dermomyotome. However, what controls the segregation of these muscle subtypes remains unknown. We use this in vivo bifurcation of fates as an experimental model to uncover the underlying mechanisms of lineage diversification from bipotent progenitors.

Results

Using the strength of spatio-temporally controlled gene missexpression in avian embryos, we report that Notch harbors distinct pro-smooth muscle activities depending on the duration of the signal; short periods prevent striated muscle development and extended periods, through Snail1, promote cell emigration from the dermomyotome towards a smooth muscle fate. Furthermore, we define a Muscle Regulatory Network, consisting of Id2, Id3, FoxC2 and Snail1, which acts in concert to promote smooth muscle by antagonizing the pro-myogenic activities of Myf5 and Pax7, which induce striated muscle fate. Notch and BMP closely regulate the network and reciprocally reinforce each other’s signal. In turn, components of the network strengthen Notch signaling, while Pax7 silences this signaling. These feedbacks augment the robustness and flexibility of the network regulating muscle subtype segregation.

Conclusions

Our results demarcate the details of the Muscle Regulatory Network, underlying the segregation of muscle sublineages from the lateral dermomyotome, and exhibit how factors within the network promote the smooth muscle at the expense of the striated muscle fate. This network acts as an exemplar demonstrating how lineage segregation occurs within epithelial primordia by integrating inputs from competing factors.

Transcriptional control of mammalian pancreas organogenesis

The field of pancreas development has markedly expanded over the last decade, significantly advancing our understanding of the molecular mechanisms that control pancreas organogenesis. This growth has been fueled, in part, by the need to generate new therapeutic approaches for the treatment of diabetes. The creation of sophisticated genetic tools in mice has been instrumental in this progress. Genetic manipulation involving activation or inactivation of genes within specific cell types has allowed the identification of many transcription factors (TFs) that play critical roles in the organogenesis of the pancreas. Interestingly, many of these TFs act at multiple stages of pancreatic development, and adult organ function or repair. Interaction with other TFs, extrinsic signals, and epigenetic regulation are among the mechanisms by which TFs may play context-dependent roles during pancreas organogenesis. Many of the pancreatic TFs directly regulate each other and their own expression. These combinatorial interactions generate very specific gene regulatory networks that can define the different cell lineages and types in the developing pancreas. Here, we review recent progress made in understanding the role of pancreatic TFs in mouse pancreas formation. We also summarize our current knowledge of human pancreas development and discuss developmental pancreatic TFs that have been associated with human pancreatic diseases.

Sox9: a master regulator of the pancreatic program

Over the last decade, it has been discovered that the transcription factor Sox9 plays several critical roles in governing the development of the embryonic pancreas and the homeostasis of the mature organ. While analysis of pancreata from patients affected by the Sox9 haploinsufficiency syndrome campomelic dysplasia initially alluded to a functional role of Sox9 in pancreatic morphogenesis, transgenic mouse models have been instrumental in mechanistically dissecting such roles. Although initially defined as a marker and maintenance factor for pancreatic progenitors, Sox9 is now considered to fulfill additional indispensable functions during pancreogenesis and in the postnatal organ through its interactions with other transcription factors and signaling pathways such as Fgf and Notch. In addition to maintaining both multipotent and bipotent pancreatic progenitors, Sox9 is also required for initiating endocrine differentiation and maintaining pancreatic ductal identity, and it has recently been unveiled as a key player in the initiation of pancreatic cancer. These functions of Sox9 are discussed in this article, with special emphasis on the knowledge gained from various loss-of-function and lineage tracing mouse models. Also, current controversies regarding Sox9 function in healthy and injured adult pancreas and unanswered questions and avenues of future study are discussed.

Distinct requirements for beta-catenin in pancreatic epithelial growth and patterning

Pancreatic exocrine and endocrine lineages arise from multipotent pancreatic progenitor cells (MPCs). Exploiting the mechanisms that govern expansion and differentiation of these cells could enhance efforts to generate β-cells from stem cells. Although our prior work indicates that the canonical Wnt signaling component β-catenin is required qualitatively for exocrine acinar but not endocrine development, precisely how this requirement plays out at the level of MPCs and their lineage-restricted progeny is unknown. In addition, the contribution of β-catenin function to β-cell development remains controversial. To resolve the potential roles of β-catenin in development of MPCs and β-cells, we generated pancreas- and pre-endocrine-specific β-catenin knockout mice. Pancreas-specific loss of β-catenin produced not only a dramatic reduction in acinar cell numbers, but also a significant reduction in β-cell mass. The loss of β-cells is due not to a defect in the differentiation of endocrine precursors, but instead correlates with an early and specific loss of MPCs. In turn, this reflects a novel role for β-catenin in maintaining proximal-distal patterning of the early epithelium, such that distal MPCs resort to a proximal, endocrine-competent "trunk" fate when β-catenin is deleted. Moreover, β-catenin maintains proximal-distal patterning, in part, by inhibiting Notch signaling. Subsequently, β-catenin is required for proliferation of both distal and proximal cells, driving overall organ growth. In distinguishing two distinct roles for β-catenin along the route of β-cell development, we suggest that temporally appropriate positive and negative manipulation of this molecule could enhance expansion and differentiation of stem cell-derived MPCs.

An unusual presentation of diabetic ketoacidosis in familial hajdu-cheney syndrome: a case report

A 21-year-old man with diabetic ketoacidosis (DKA) displayed short and clubbed fingers and marked eyebrow, which are typical of Hajdu-Cheney Syndrome (HCS). Laboratory findings confirmed type 1 diabetes mellitus (DM). After conservative care with hydration and insulin supply, metabolic impairment was improved. Examinations of bone and metabolism revealed osteoporosis and craniofacial abnormalities. The mutation (c.6443T>G) of the NOTCH2 gene was found. The patient was diagnosed with HCS and DM. There may be a relationship between HCS and DM, with development of pancreatic symptoms related to the NOTCH2 gene mutation.