Developmental aspects of the endocrine pancreas

NADPH Oxidase-Dependent Reactive Oxygen Species Stimulate β-Cell Regeneration Through Differentiation of Endocrine Progenitors in Murine Pancreas

AIMS

Reactive oxygen species (ROS) act as second messengers for redox modification of transcription factors essential for differentiation. The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a major source of ROS, has been shown to regulate differentiation of various progenitor cells, while its role in pancreatic endocrine cell differentiation is unclear. This study was aimed at this knowledge gap.

RESULTS

Our results showed that ROS levels were dynamically changed during pancreas development concomitant with endocrine cell differentiation induced by modest exogenous ROS in rudiment cultures. NOX4, but not NOX2, the member of NADPH oxidase, was expressed persistently in endocrine lineage and showed high activity in critical pancreas development phase. Inhibition of NADPH oxidase activity impeded the differentiation of endocrine progenitors in vitro, and exogenous ROS reversed this effect. Studies performed in streptozotocin (STZ)-injected neonatal rats showed that diphenyleneiodonium (DPI) obstructed β-cell regeneration through the suppression of neurogenin 3 (NGN3) expression, but not Ki67-labeling β-cells, indicating that ROS stimulation promoted differentiation beyond proliferation of β-cells. Inhibition of NADPH oxidase also reduced expression of SRY (sex-determining region Y)-box 9 (SOX9), a transcriptional regulator of Ngn3, in endocrine precursor cells, both in vivo and in vitro. Overexpression of SOX9 attenuated the reduction of NGN3 induced by suppression of NADPH oxidase.

INNOVATION AND CONCLUSION

This is the first study to demonstrate NADPH oxidase, especially NOX4-dependent ROS that promotes pancreatic progenitor cell differentiation into endocrine cells both in vitro and in vivo, probably through the regulation of SOX9. We provide evidence that NADPH oxidase-dependent ROS-mediated signaling is necessary for endocrine cell differentiation, which provides a potential strategy for efficient generation of insulin-producing cells in clinical application.

Analysis of gene expression on ngn3 gene signaling pathway in endocrine pancreatic cancer

In order to define the undifferentiated transcriptional factors present in neurogenesis of pancreatic β-islet cells, we studied the effect of Pdx1 in embryonic stem cell derived endocrine lineage. There are undifferentiated transcriptional progenitors Pdx1+/Ptf1a+/Cpa1+ tracking the growth of acini, ducts, α and β-islet cells. The upregulated transcriptional factors Pdx1 and ngn3 specify consequences of cell cycle regulation in early gut endocrine cells. The undifferentiated transcriptional factors basic helix loop helix (bHLH) protein regulate Ptf1a+/Cpa1+ in acini, ducts and it also regulate ngn3 to decrease expression of insulin and other pancreas secretions. The Pdx1+ and other unknown gene mutations show abnormal growth of neurogenesis in endocrine lineages. Using microarray based gene expression analysis to determine undifferential gene ontology in tissue specific gene regulation and disease progression that common in both metabolic and biological signaling pathways. The data expression profiles of ngn3 of wild- type pancreatic islet and islet derived tumor stem cells provide information on endocrine specific ngn3 genes. Therefore, 3755 genes were significantly regulated by Ngn3 induced pancreatic islet cell development. Moreover 317 upregulated and 175 downregulated, 757 genes deemed as undifferential expressions in endocrine cell. Furthermore to predict signaling pathways that associates with diabetes is highlighted.

Angiotensin II type 2 receptor is critical for the development of human fetal pancreatic progenitor cells into islet-like cell clusters and their potential for transplantation

Local renin-angiotensin systems (RASs) regulate the differentiation of tissue progenitors. However, it is not known whether such systems can regulate the development of pancreatic progenitor cells (PPCs). To address this issue, we characterized the expression profile of major RAS components in human fetal PPC preparations and examined their effects on the differentiation of PPCs into functional islet-like cell clusters (ICCs). We found that expression of RAS components was highly regulated throughout PPC differentiation and that locally generated angiotensin II (Ang II) maintained PPC growth and differentiation via Ang II type 1 and type 2 (AT(1) and AT(2)) receptors. In addition, we observed colocalization of AT(2) receptors with critical β-cell phenotype markers in PPCs/ICCs, as well as AT(2) receptor upregulation during differentiation, suggesting that these receptors may regulate β-cell development. In fact, we found that AT(2) , but not AT(1) , receptor was a key mediator of Ang II-induced upregulation of transcription factors important in β-cell development. Furthermore, lentivirus-mediated knockdown of AT(2) receptor suppressed the expression of these transcription factors in ICCs. Transplantation of AT(2) receptor-depleted ICCs into immune-privileged diabetic mice failed to ameliorate hyperglycemia, implying that AT(2) receptors are indispensable during ICC maturation in vivo. These data strongly indicate that a local RAS is involved in governing the functional maturation of pancreatic progenitors toward the endocrine lineage.

The Cdk4-E2f1 pathway regulates early pancreas development by targeting Pdx1+ progenitors and Ngn3+ endocrine precursors

Cell division and cell differentiation are intricately regulated processes vital to organ development. Cyclin-dependent kinases (Cdks) are master regulators of the cell cycle that orchestrate the cell division and differentiation programs. Cdk1 is essential to drive cell division and is required for the first embryonic divisions, whereas Cdks 2, 4 and 6 are dispensable for organogenesis but vital for tissue-specific cell development. Here, we illustrate an important role for Cdk4 in regulating early pancreas development. Pancreatic development involves extensive morphogenesis, proliferation and differentiation of the epithelium to give rise to the distinct cell lineages of the adult pancreas. The cell cycle molecules that specify lineage commitment within the early pancreas are unknown. We show that Cdk4 and its downstream transcription factor E2f1 regulate mouse pancreas development prior to and during the secondary transition. Cdk4 deficiency reduces embryonic pancreas size owing to impaired mesenchyme development and fewer Pdx1(+) pancreatic progenitor cells. Expression of activated Cdk4(R24C) kinase leads to increased Nkx2.2(+) and Nkx6.1(+) cells and a rise in the number and proliferation of Ngn3(+) endocrine precursors, resulting in expansion of the β cell lineage. We show that E2f1 binds and activates the Ngn3 promoter to modulate Ngn3 expression levels in the embryonic pancreas in a Cdk4-dependent manner. These results suggest that Cdk4 promotes β cell development by directing E2f1-mediated activation of Ngn3 and increasing the pool of endocrine precursors, and identify Cdk4 as an important regulator of early pancreas development that modulates the proliferation potential of pancreatic progenitors and endocrine precursors.

In vitro insulin production and analysis of pancreatic transcription factors in induced human hepatic progenitor cells

BACKGROUND

beta-Cell destruction and/or insufficient insulin production are the hallmarks of diabetes mellitus (type 1 diabetes). A hepatic progenitor from developing liver is sought to be one of the surrogate sources of insulin production as the pancreas and the liver share a common precursor and signals from the cardiac mesoderm. Production of insulin is possible by transfecting pancreatic transcription factors that play important roles in development of the pancreatic beta-cell. But, there is always the fear of using genetically manipulated cells for therapeutics. Hence, the present study was designed to analyze the feasibility of using primary human fetal hepatic progenitors as a potential source for insulin production.

METHODS

Human fetal hepatic progenitors were enriched using CD-326 magnetic cell sorting. The sorted cells were cultured with different concentrations of glucose (5-30 mM) in Dulbecco's modified Eagle's medium. The amount of insulin production was estimated in the cultured cells by the chemiluminescence method. Total RNA isolated from sorted epithelial cell adhesion molecule (EpCAM)-positive cells was reverse-transcribed, and the expression of different beta-cell-producing transcriptions factors was analyzed by polymerase chain reaction (PCR). Immunocytochemical analysis was performed in cultured cells using specific insulin antibodies.

RESULTS

The viability of the total liver cells isolated was found to be 95%. The average number of EpCAM-positive cells in the total liver was found to be approximately 15%. An insulin kinetics study using glucose induction with different concentrations showed increased insulin secretion in response to glucose concentrations up to 20 mM. Furthermore, results of immunocytochemical analysis demonstrated intense insulin expression in EpCAM-positive cultured cells. Expression studies of the cultured EpCAM-positive cells using reverse transcription-PCR showed positive expression of the pancreatic transcription factors essential for insulin production.

CONCLUSIONS

The present study demonstrates that in vitro differentiation of induced human hepatic progenitors into insulin-producing cells without genetic manipulations may promote strategies for the treatment of type 1 diabetes.

PDZ-domain containing-2 (PDZD2) drives the maturity of human fetal pancreatic progenitor-derived islet-like cell clusters with functional responsiveness against membrane depolarization

We recently reported the isolation and characterization of a population of pancreatic progenitor cells (PPCs) from early trimester human fetal pancreata. The PPCs, being the forerunners of adult pancreatic cell lineages, were amenable to growth and differentiation into insulin-secreting islet-like cell clusters (ICCs) upon stimulation by adequate morphogens. Of note, a novel morphogenic factor, PDZ-domain containing-2 (PDZD2) and its secreted form (sPDZD2) were ubiquitously expressed in the PPCs. Our goals for this study were to evaluate the potential role of sPDZD2 in stimulating PPC differentiation and to establish the optimal concentration for such stimulation. We found that 10(-9)M sPDZD2 promoted PPC differentiation, as evidenced by the upregulation of the pancreatic endocrine markers (PDX-1, NGN3, NEURO-D, ISL-1, NKX 2.2, NKX 6.1) and INSULIN mRNA. Inhibited endogenous production of sPDZD2 suppressed expression of these factors. Secreted PDZD2 treatment significantly elevated the C-peptide content of the ICCs and increased the basal rate of insulin secretion. However, they remained unresponsive to glucose stimulation, reflected by a minimal increase in GLUT-2 and GLUCOKINASE mRNA expression. Interestingly, sPDZD2 treatment induced increased expression of the L-type voltage-gated calcium channel (Ca(v)1.2) in the ICCs, triggering calcium ion influx under KCl stimulation and conferring an ability to secrete insulin in response to KCl. Pancreatic progenitor cells from 10- and 13-week fetal pancreata showed peak expression of endogenous sPDZD2, implying that sPDZD2 has a specific role in islet development during the first trimester. In conclusion, our data suggest that sPDZD2 promotes functional maturation of human fetal PPC-derived ICCs, thus enhancing its transplanting potentials.

Transcription factor Glis3, a novel critical player in the regulation of pancreatic beta-cell development and insulin gene expression

In this study, we report that the Krüppel-like zinc finger transcription factor Gli-similar 3 (Glis3) is induced during the secondary transition of pancreatic development, a stage of cell lineage specification and extensive patterning, and that Glis3(zf/zf) mutant mice develop neonatal diabetes, evidenced by hyperglycemia and hypoinsulinemia. The Glis3(zf/zf) mutant mouse pancreas shows a dramatic loss of beta and delta cells, contrasting a smaller relative loss of alpha, PP, and epsilon cells. In addition, Glis3(zf/zf) mutant mice develop ductal cysts, while no significant changes were observed in acini. Gene expression profiling and immunofluorescent staining demonstrated that the expression of pancreatic hormones and several transcription factors important in endocrine cell development, including Ngn3, MafA, and Pdx1, were significantly decreased in the developing pancreata of Glis3(zf/zf) mutant mice. The population of pancreatic progenitors appears not to be greatly affected in Glis3(zf/zf) mutant mice; however, the number of neurogenin 3 (Ngn3)-positive endocrine cell progenitors is significantly reduced. Our study indicates that Glis3 plays a key role in cell lineage specification, particularly in the development of mature pancreatic beta cells. In addition, we provide evidence that Glis3 regulates insulin gene expression through two Glis-binding sites in its proximal promoter, indicating that Glis3 also regulates beta-cell function.

Cooperative transcriptional regulation of the essential pancreatic islet gene NeuroD1 (beta2) by Nkx2.2 and neurogenin 3

Nkx2.2 and NeuroD1 are two critical regulators of pancreatic beta cell development. Nkx2.2 is a homeodomain transcription factor that is essential for islet cell type specification and mature beta cell function. NeuroD1 is a basic helix-loop-helix transcription factor that is critical for islet beta cell maturation and maintenance. Although both proteins influence beta cell development directly downstream of the endocrine progenitor factor, neurogenin3 (Ngn3), a connection between the two proteins in the regulation of beta cell fate and function has yet to be established. In this study, we demonstrate that Nkx2.2 transcriptional activity is required to facilitate the activation of NeuroD1 by Ngn3. Furthermore, Nkx2.2 is necessary to maintain high levels of NeuroD1 expression in developing mouse and zebrafish islets and in mature beta cells. Interestingly, Nkx2.2 regulates NeuroD1 through two independent promoter elements, one that is bound and activated directly by Nkx2.2 and one that appears to be regulated by Nkx2.2 through an indirect mechanism. Together, these findings suggest that Nkx2.2 coordinately activates NeuroD1 with Ngn3 within the endocrine progenitor cell and also plays a role in the maintenance of NeuroD1 expression to regulate beta cell function in the mature islet. Collectively, these findings further define the conserved regulatory networks involved in islet beta cell formation and function.

Beneficial effects of intercellular interactions between pancreatic islet cells in blood glucose regulation

Glucose homeostasis is controlled by the islets of Langerhans which are equipped with alpha-cells increasing the blood glucose level, beta-cells decreasing it, and delta-cells the precise role of which still needs identifying. Although intercellular communications between these endocrine cells have recently been observed, their roles in glucose homeostasis have not been clearly understood. In this study, we construct a mathematical model for an islet consisting of two-state alpha-, beta-, and delta-cells, and analyze effects of known chemical interactions between them with emphasis on the combined effects of those interactions. In particular, such features as paracrine signals of neighboring cells and cell-to-cell variations in response to external glucose concentrations as well as glucose dynamics, depending on insulin and glucagon hormone, are considered explicitly. Our model predicts three possible benefits of the cell-to-cell interactions: First, the asymmetric interaction between alpha- and beta-cells contributes to the dynamic stability while the perturbed glucose level recovers to the normal level. Second, the inhibitory interactions of delta-cells for glucagon and insulin secretion prevent the wasteful co-secretion of them at the normal glucose level. Finally, the glucose dose-responses of insulin secretion is modified to become more pronounced at high glucose levels due to the inhibition by delta-cells. It is thus concluded that the intercellular communications in islets of Langerhans should contribute to the effective control of glucose homeostasis.

Characterization of pancreatic transcription factor Pdx-1 binding sites using promoter microarray and serial analysis of chromatin occupancy

The homeobox transcription factor Pdx-1 is necessary for pancreas organogenesis and beta cell function, however, most Pdx-1-regulated genes are unknown. To further the understanding of Pdx-1 in beta cell biology, we have characterized its genomic targets in NIT-1 cells, a mouse insulinoma cell line. To identify novel targets, we developed a microarray that includes traditional promoters as well as non-coding conserved elements, micro-RNAs, and elements identified through an unbiased approach termed serial analysis of chromatin occupancy. In total, 583 new Pdx-1 target genes were identified, many of which contribute to energy sensing and insulin release in pancreatic beta cells. By analyzing 31 of the protein-coding Pdx-1 target genes, we show that 29 are expressed in beta cells and, of these, 68% are down- or up-regulated in cells expressing a dominant negative mutant of Pdx-1. We additionally show that many Pdx-1 targets also interact with NeuroD1/BETA2, including the micro-RNA miR-375, a known regulator of insulin secretion.

Defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly in the Goto-Kakizaki rat model of type 2 diabetes

AIMS/HYPOTHESIS

The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes. Defective beta cell mass detectable in late fetal age precedes the onset of hyperglycaemia. Our hypothesis was that an embryonic IGF production deficiency might be involved in beta cell mass anomaly in the diabetic GK rat. To test this, we evaluated during pancreatic organogenesis: (1) the beta cell development in GK rats on embryonic day (E) 13.5 and E18.5; (2) IGF2 and IGF1 receptor (IGF1R) pancreatic protein production on E13.5 and E18.5; (3) the in vitro development of GK pancreatic rudiment on E13.5; and (4) the in vitro effect of IGF2 addition on beta cell mass.

MATERIALS AND METHODS

Beta cell quantitative analyses were determined by immunohistochemistry and morphometry. IGF2 and IGF1R pancreatic protein production was evaluated using western blot analyses. Dorsal pancreatic rudiments were dissected on E13.5, separated from surrounding mesenchyme and cultured for 7 days without or with recombinant IGF2.

RESULTS

While beta cell mass was already decreased on E18.5, the differentiation of the first beta cells was in fact normal in E13.5 GK pancreas. Moreover, defective IGF2 and IGF1R protein production was detected in GK pancreatic rudiment as early as E13.5. The isolated GK pancreatic rudiment as maintained in vitro mimics the GK beta cell deficiency observed in vivo. This last approach enabled us to show that GK beta cells were fully responsive to IGF2 as far as their net growth is concerned.

CONCLUSIONS/INTERPRETATION

In diabetic GK rat, defective IGF2 and IGF1R protein production in embryonic pancreas precedes beta cell mass anomaly. IGF2 supplementation expands the pool of beta cells.

Sonic Hedgehog and Other Soluble Factors from Differentiating Embryoid Bodies Inhibit Pancreas Development

Success of cell-replacement therapy for diabetes will largely depend on the establishment of alternative sources of pancreatic islet grafts. Embryonic stem (ES) cell differentiation toward pancreatic insulin-producing cells offers such perspectives, but there are still many challenges to overcome. Our previous studies suggested that the limited amount of insulin-positive cells derived from ES cells is related to the activation of pancreas inhibitory signals. To confirm this hypothesis, we report here that exposure of mouse embryonic pancreas explants to soluble factors from embryoid bodies (EBs) inhibits growth, morphogenesis, and endocrine and exocrine differentiation as evaluated by explant size and mRNA and protein expression. Sonic Hedgehog (Shh), an established pancreas repressor both at early and late developmental stages, was produced and secreted by EBs, and participated in the inhibitory effect by inducing its target Gli1 in the explants. Inhibition of Hedgehog pathway rescued the differentiation of Insulin-positive cells in the explants. In contrast to pancreatic cells, hepatic progenitors exposed to EB-conditioned medium showed improved differentiation of albumin-positive cells. In a model system of ES cell differentiation in vitro, we found that definitive endoderm induction by serum removal or activin A treatment further increased Hedgehog production and activity in EBs. Concomitantly, downregulation of the pancreas marker Pdx1 was recorded in activin-treated EBs, a phenomenon that was prevented by antagonizing Hedgehog signaling with Hedgehog interacting protein. These data strongly suggest that Hedgehog production in EBs limits pancreatic fate acquisition and forms a major obstacle in the specification of pancreatic cells from ES-derived definitive endoderm. Disclosure of potential conflicts of interest is found at the end of this article.

Secreted PDZD2 exerts concentration-dependent effects on the proliferation of INS-1E cells

PDZD2 (PDZ domain containing 2) is a multi-PDZ protein expressed in pancreas and many other tissues. PDZD2 shows extensive homology to pro-interleukin-16 (pro-IL-16) and is localized mainly to the endoplasmic reticulum. We have recently demonstrated that PDZD2, like pro-IL-16, is proteolytically cleaved at its C-terminus to generate a secreted protein, sPDZD2 (for secreted PDZD2). To understand the possible functional role of PDZD2 in pancreas, we investigated the cellular distribution of PDZD2 in adult pancreas using an antiserum that recognizes both the full-length and secreted forms of PDZD2. Immunohistochemical analysis revealed a strong expression of PDZD2 in pancreatic islet beta cells but not alpha cells. Consistent with the beta-cell-enriched expression of PDZD2, immunoblot analysis indicated expression of both full-length PDZD2 and sPDZD2 in the insulinoma cell line INS-1E. A recombinant sPDZD2 protein was synthesized for study of its functional effect on INS-1E cells. In culture media with limiting serum, co-incubation with sPDZD2 stimulated the proliferation of INS-1E cells. The mitogenic effect of sPDZD2 was concentration-dependent, and was associated with a slight inhibition of the insulin promoter activity at high sPDZD2 concentrations. As a potential mitogen of beta-like cells, sPDZD2 may be useful for the optimization of beta-cell growth and differentiation in vitro.

The classification of diabetes mellitus: a conceptual framework

Diabetes is the extreme manifestation of a spectrum conditions in which the balance of insulin secretion and insulin action (or insulin resistance) has been altered. Loss of euglycemia is caused by relative insulin deficiency in the presence of insulin resistance, or by absolute insulin deficiency. There are related conditions in which an alteration of insulin resistance or beta-cell dysfunction exists, but because of compensation glucose homeostasis has not been lost. The elucidation of the causes of insulin resistance and -cell failure and the attention to the different degrees of insulin deficiency and insulin resistance allow for better diagnosis, treatment, and prevention of diabetes and its related conditions.

Neonatal diabetes mellitus: from understudy to center stage

PURPOSE OF REVIEW

Although neonatal diabetes mellitus is rare, its molecular basis has far-reaching implications for understanding the regulation of beta cell function, a prerequisite for understanding and treating type1 and type 2 diabetes mellitus especially by the manipulation of stem cells. The purpose of this review is to highlight the recent exciting discoveries concerning the genetic and molecular basis of the spectrum of disorders constituting neonatal diabetes mellitus.

RECENT FINDINGS

Recent reports in the literature, all in the past year, have identified activating mutations in the KATP channel that prevent its closure and hence insulin secretion as the major cause of permanent neonatal diabetes mellitus. Concurrently, a transgenic mouse model of transient neonatal diabetes mellitus due to mutations in ZAC/HYMAI provides an exquisite tool to study its human counterpart. Already, mutations in KATP and ZAC/HYMAI have been shown to be associated with type 1 and type 2 diabetes mellitus in later life; some mutations in KATP are amenable to treatment with sulfonylureas.

SUMMARY

The discoveries of the genes responsible for rarely occurring transient and permanent neonatal diabetes mellitus, and transgenic animal models to study them, are exciting milestones on the road to understanding and treating the common forms of type 1 and type 2 diabetes mellitus in children and adolescents.

Cell-replacement therapy for diabetes: Generating functional insulin-producing tissue from adult human liver cells

Shortage in tissue availability from cadaver donors and the need for life-long immunosuppression severely restrict the large-scale application of cell-replacement therapy for diabetic patients. This study suggests the potential use of adult human liver as alternate tissue for autologous beta-cell-replacement therapy. By using pancreatic and duodenal homeobox gene 1 (PDX-1) and soluble factors, we induced a comprehensive developmental shift of adult human liver cells into functional insulin-producing cells. PDX-1-treated human liver cells express insulin, store it in defined granules, and secrete the hormone in a glucose-regulated manner. When transplanted under the renal capsule of diabetic, immunodeficient mice, the cells ameliorated hyperglycemia for prolonged periods of time. Inducing developmental redirection of adult liver offers the potential of a cell-replacement therapy for diabetics by allowing the patient to be the donor of his own insulin-producing tissue.

Minireview: transcriptional regulation in pancreatic development

Considerable progress has been made in the understanding of the sequential activation of signal transduction pathways and the expression of transcription factors during pancreas development. Much of this understanding has been obtained by analyses of the phenotypes of mice in which the expression of key genes has been disrupted (knockout mice). Knockout of the genes for Pdx1, Hlxb9, Isl1, or Hex results in an arrest of pancreas development at a very early stage (embryonic d 8-9). Disruption of genes encoding components of the Notch signaling pathway, e.g. Hes1 or neurogenin-3, abrogates development of the endocrine pancreas (islets of Langerhans). Disruption of transcription factor genes expressed more downstream in the developmental cascade (Beta2/NeuroD, Pax4, NKx2.2, and Nkx6.1) curtails the formation of insulin-producing beta-cells. An understanding of the importance of transcription factor genes during pancreas development has provided insights into the pathogenesis of diabetes, in which the mass of insulin-producing beta-cells is reduced.

Ghrelin cells replace insulin-producing beta cells in two mouse models of pancreas development

The pancreatic islet is necessary for maintaining glucose homeostasis. Within the pancreatic islet, the homeodomain protein Nkx2.2 is essential for the differentiation of all insulin-producing beta cells and a subset of glucagon-producing alpha cells (1). Mice lacking Nkx2.2 have relatively normal sized islets, but a large number of cells within the mutant islet fail to produce any of the four major islet hormones. In this study we demonstrate that Nkx2.2 mutant endocrine cells have been replaced by cells that produce ghrelin, an appetite-promoting peptide predominantly found in the stomach. Intriguingly, normal mouse pancreas also contains a small population of ghrelin-producing cells, defining a new islet "epsilon" cell population. The expansion of ghrelin-producing cells at the expense of beta cells may be a general phenomenon, because we demonstrate that Pax4 mutant mice display a similar phenotype. We propose that insulin and ghrelin cells share a common progenitor and that Nkx2.2 and Pax4 are required to specify or maintain differentiation of the beta cell fate. This finding also suggests that there is a genetic component underlying the balance between insulin and ghrelin in regulating glucose metabolism.

Regulation of Pax4 paired homeodomain gene by neuron-restrictive silencer factor

An elucidation of the key regulatory factors in pancreas development is critical for understanding the pathogenesis of diabetes mellitus. This study examined whether a specific regulatory mechanism that exists in neuronal development also plays a role in the pancreas. In non-neuronal cells, neuron-restrictive silencer factor (NSRF) actively represses gene transcription via a sequence-specific DNA motif known as the neuron-restrictive silencer element (NRSE). This DNA motif has been identified in many genes that are specific markers for cells of neuronal and neuroendocrine lineage. We identified several genes involved in pancreas development that also harbor NRSE-like motifs, including pdx-1, Beta2/NeuroD, and pax4. The paired homeodomain transcription factor Pax4 is implicated in the differentiation of the insulin-producing beta-cell lineage because disruption of the pax4 gene results in a severe deficiency of beta-cells and the manifestation of diabetes mellitus in mice. The NRSE-like motif identified in the upstream pax4 promoter is highly conserved throughout evolution, forms a DNA-protein complex with NRSF, and confers NRSF-dependent transcriptional repression in the context of a surrogate gene promoter. This cis-activating NRSE element also confers NRSF-dependent modulation in the context of the native pax4 gene promoter. Together with earlier reports, these new findings suggest an important functional role for NRSF in the expression of the pax4 gene and infer a role for NRSF in pancreatic islet development.