Expression of homeobox genes, including an insulin promoting factor, in the murine yolk sac at the time of hematopoietic initiation

Single-cell joint detection of chromatin occupancy and transcriptome enables higher-dimensional epigenomic reconstructions

Deciphering mechanisms in cell-fate decisions requires single-cell holistic reconstructions of multidimensional epigenomic states in transcriptional regulation. Here we develop CoTECH, a combinatorial barcoding method allowing high-throughput single-cell joint detection of chromatin occupancy and transcriptome. We used CoTECH to examine bivalent histone marks (H3K4me3 and H3K27me3) with transcription from naive to primed mouse embryonic stem cells. We also derived concurrent bivalent marks in pseudosingle cells using transcriptome as an anchor for resolving pseudotemporal bivalency trajectories and disentangling a context-specific interplay between H3K4me3/H3K27me3 and transcription level. Next, we revealed the regulatory basis of endothelial-to-hematopoietic transition in two waves of hematopoietic cells and distinctive enhancer-gene-linking schemes guiding hemogenic endothelial cell emergence, indicating a unique epigenetic control of transcriptional regulation for hematopoietic stem cell priming. CoTECH provides an efficient framework for single-cell coassay of chromatin occupancy and transcription, thus enabling higher-dimensional epigenomic reconstructions.

Making HSCs in vitro: don't forget the hemogenic endothelium

Generating a hematopoietic stem cell (HSC) in vitro from nonhematopoietic tissue has been a goal of experimental hematologists for decades. Until recently, no in vitro-derived cell has closely demonstrated the full lineage potential and self-renewal capacity of a true HSC. Studies revealing stem cell ontogeny from embryonic mesoderm to hemogenic endothelium to HSC provided the key to inducing HSC-like cells in vitro from a variety of cell types. Here we review the path to this discovery and discuss the future of autologous transplantation with in vitro-derived HSCs as a therapeutic modality.

De novo generation of HSCs from somatic and pluripotent stem cell sources

Generating human hematopoietic stem cells (HSCs) from autologous tissues, when coupled with genome editing technologies, is a promising approach for cellular transplantation therapy and for in vitro disease modeling, drug discovery, and toxicology studies. Human pluripotent stem cells (hPSCs) represent a potentially inexhaustible supply of autologous tissue; however, to date, directed differentiation from hPSCs has yielded hematopoietic cells that lack robust and sustained multilineage potential. Cellular reprogramming technologies represent an alternative platform for the de novo generation of HSCs via direct conversion from heterologous cell types. In this review, we discuss the latest advancements in HSC generation by directed differentiation from hPSCs or direct conversion from somatic cells, and highlight their applications in research and prospects for therapy.

Mouse ES cell-derived hematopoietic progenitor cells

Future stem cell-based therapies will benefit from the new discoveries being made on pluripotent stem cells such as embryonic stem (ES) cells and induced pluripotent stem (IPS) cells. Understanding the genes regulating pluripotency has opened new opportunities to generate patient-tailored therapies. However, protocols for deriving progenitor cells of therapeutic grade from these pluripotent stem cells are not yet worked out. In particular the potential of these cells in treating diseases when compared to their adult progenitor counterparts is unknown. This is crucial work that needs to be studied in detail because we will need to determine engraftment potential of these cells and their ability for multi-lineage engraftment in the in vivo setting before any clinical applications. The ability of these cells to engraft is dependent on their expression of cell surface markers which guide their homing patterns. In this review, I discuss murine hematopoietic progenitor cells derived from mouse ES cells. Stem cells in the bone marrow are found in the bone marrow niches. Our knowledge of the bone marrow niches is growing and will ultimately lead to improved clinical transplantation of bone marrow cells. We are, however, a long way in appreciating how hematopoietic progenitor cells migrate and populate lymphoid tissues. One of the variables in generating hematopoietic progenitor cells is that different labs use different approaches in generating progenitor cells. In some cases, the ES cell lines used show some variability as well. The cell culture media used by the different investigators highly influence the maturation level of the cells and their homing patterns. Here, mouse ES cell-derived progenitor cells are discussed.

Hematopoietic specification from human pluripotent stem cells: current advances and challenges toward de novo generation of hematopoietic stem cells

Significant advances in cellular reprogramming technologies and hematopoietic differentiation from human pluripotent stem cells (hPSCs) have already enabled the routine production of multiple lineages of blood cells in vitro and opened novel opportunities to study hematopoietic development, model genetic blood diseases, and manufacture immunologically matched cells for transfusion and cancer immunotherapy. However, the generation of hematopoietic cells with robust and sustained multilineage engraftment has not been achieved. Here, we highlight the recent advances in understanding the molecular and cellular pathways leading to blood development from hPSCs and discuss potential approaches that can be taken to facilitate the development of technologies for de novo production of hematopoietic stem cells.

Transient gene delivery for functional enrichment of differentiating embryonic stem cells

There is a critical need for new sources of hepatocytes, both clinically to provide support for patients with liver failure and in drug discovery for toxicity, metabolic and pharmacokinetic screening of new drug entities. We have reported previously a variety of methods for differentiating murine embryonic stem (ES) cells into hepatocyte-like cells. One major challenge of our work and others in the field has been the ability to selectively purify and enrich these cells from a heterogeneous population. Traditional approaches for inserting new genes (e.g., stable transfection, knock-in, retroviral transduction) involve permanent alterations in the genome. These approaches can lead to mutations and involve the extra costs and time of developing, validating and maintaining new cell lines. We have developed a transient gene delivery system that uses fluorescent gene reporters for purification of the cells. Following a transient transfection, the cells are purified through a fluorescence-activated cell sorter (FACS), re-plated in secondary culture and subsequent phenotypic analysis is performed. In an effort to test the ability of the reporters to work in a transient environment for our differentiation system, we engineered two non-viral plasmid reporters, the first driven by the mouse albumin enhancer/promoter and the second by the mouse cytochrome P450 7A1 (Cyp7A1) promoter. We optimized the transfection efficiency of delivering these genes into spontaneously differentiated ES cells and sorted independent fractions positive for each reporter 17 days after inducing differentiation. We found that cells sorted based on the Cyp7A1 promoter showed significant enrichment in terms of albumin secretion, urea secretion and cytochrome P450 1A2 detoxification activity as compared to enrichment garnered by the albumin promoter-based cell sort. Development of gene reporter systems that allow us to identify, purify and assess homogeneous populations of cells is important in better understanding stem cell differentiation pathways. And engineering cellular systems without making permanent gene changes will be critical for the generation of clinically acceptable cellular material in the future.

An illustrated review of early pancreas development in the mouse

Pancreas morphogenesis and cell differentiation are highly conserved among vertebrates during fetal development. The pancreas develops through simple budlike structures on the primitive gut tube to a highly branched organ containing many specialized cell types. This review presents an overview of key molecular components and important signaling sources illustrated by an extensive three-dimensional (3D) imaging of the developing mouse pancreas at single cell resolution. The 3D documentation covers the time window between embryonic days 8.5 and 14.5 in which all the pancreatic cell types become specified and therefore includes gene expression patterns of pancreatic endocrine hormones, exocrine gene products, and essential transcription factors. The 3D perspective provides valuable insight into how a complex organ like the pancreas is formed and a perception of ventral and dorsal pancreatic growth that is otherwise difficult to uncover. We further discuss how this global analysis of the developing pancreas confirms and extends previous studies, and we envisage that this type of analysis can be instrumental for evaluating mutant phenotypes in the future.

Deriving and identifying hepatocytes from embryonic stem cells

The generation of hepatocytes from embryonic stem cells (ESCs) holds considerable promise for basic and applied research. However, the unequivocal identification of hepatocytes in ESC differentiation strategies has been hampered by a lack of hepatocyte-specific markers. Recent studies are beginning to address this issue with the identification of hepatocyte-specific genes and the production of hepatocytes from intermediate cell types like definitive endoderm. Assuming the successful identification of ESC-derived hepatocytes, the next challenge will be in balancing the proliferation and differentiation of these cells in order to generate usable numbers of functional hepatocytes in vitro.

Possibility of insulin-producing cells derived from mouse embryonic stem cells for diabetes treatment

Insulin injection therapy is the principal current treatment of type 1 diabetes. Patients, however, suffer from various complications generated by insufficient control of blood glucose levels over a long period. Therefore, a method which can infuse insulin in response to changes of blood glucose levels is eagerly desired. Transplantation of insulin releasing cells derived from embryonic stem (ES) cells has been expected to be one of promising approaches to realize this requirement. In this study, ES cell progeny which were derived in culture media with/without fetal calf serum contained two distinct kinds of cells immunostained by anti-insulin and anti-C-peptide antibodies. The cytoplasm and nuclei of one type of cell were immunoreactive against antibodies for insulin, while the other kind of cell only had the cytoplasm stained by the anti-insulin antibody. The first cell type was the major population of insulin-positive cells in serum-free medium, while the latter kind of cells was the major population in medium containing serum. Interestingly, the latter insulin-positive cells could be also immunostained by anti-C-peptide antibodies, and was observed even after nine subcultures in medium containing serum. Although there still remain many issues to be addressed in order to definitely demonstrate that insulin-positive cells derived from ES cells to be truly beta cells in the islets, these properties of the obtained cells are believed to promising cells for treatment of type 1 diabetes.

Definitive endoderm from embryonic stem cells

Evaluation of: D'Amour KA, Agulnick AD, Eliazer S, Kelly OG, Kroon E, Baetge EE. Efficient differentiation of human embryonic stem cells to definitive endoderm. Nat. Biotechnol. 23(12), 1534–1541(2005) [1] and Yasunaga M, Tada S, Torikai-Nishikawa S et al. Induction and monitoring of definitive and visceral endoderm differentiation of mouse ES cells. Nat. Biotechnol. 23(12),1542–1550 (2005) [2] .

Hematopoietic Cells

Murine embryonic stem cells (mESC) readily form embryoid bodies (EBs) that exhibit hematopoietic differentiation. Methods based on EB formation or ESC coculture with murine bone marrow stromal cell lines have revealed pathways of both primitive and definitive hematopoietic differentiation progressing from primitive mesoderm via hemangioblasts to endothelium and hematopoietic stem and progenitor cells. The addition of specific hematopoietic growth factors and morphogens to these cultures enhances the generation of neutrophils, macrophages, megakaryocyte/platelets, and hemoglobinized mature red cells. In addition, selective culture systems have been developed to support differentiation into mature T lymphocytes, natural killer cells, B cells, and dendritic cells. In most cases, culture systems have been developed that support equivalent differentiation of various human ESC (hESC). The major obstacle to translation of ESC hematopoietic cultures to clinical relevance has been the general inability to produce hematopoietic stem cells (HSC) that can engraft adult, irradiated recipients. In this context, the pattern of ES hematopoietic development mirrors the yolk sac phase of hematopoiesis that precedes the appearance of engraftable HSC in the aorta-gonad-mesonephros region. Genetic manipulation of mESC hematopoietic progeny by upregulation of HOXB4 or STAT5 has led to greatly enhanced long- or short-term multilineage hematopoietic engraftment, suggesting that genetic or epigenetic manipulation of these pathways may lead to functional HSC generation from hESC.

Efficient differentiation of human embryonic stem cells to definitive endoderm

The potential of human embryonic stem (hES) cells to differentiate into cell types of a variety of organs has generated much excitement over the possible use of hES cells in therapeutic applications. Of great interest are organs derived from definitive endoderm, such as the pancreas. We have focused on directing hES cells to the definitive endoderm lineage as this step is a prerequisite for efficient differentiation to mature endoderm derivatives. Differentiation of hES cells in the presence of activin A and low serum produced cultures consisting of up to 80% definitive endoderm cells. This population was further enriched to near homogeneity using the cell-surface receptor CXCR4. The process of definitive endoderm formation in differentiating hES cell cultures includes an apparent epithelial-to-mesenchymal transition and a dynamic gene expression profile that are reminiscent of vertebrate gastrulation. These findings may facilitate the use of hES cells for therapeutic purposes and as in vitro models of development.

Signals from the embryonic mouse pancreas induce differentiation of human embryonic stem cells into insulin-producing beta-cell-like cells

The recent success in restoring normoglycemia in type 1 diabetes by islet cell transplantation indicates that cell replacement therapy of this severe disease is achievable. However, the severe lack of donor islets has increased the demand for alternative sources of beta-cells, such as adult and embryonic stem cells. Here, we investigate the potential of human embryonic stem cells (hESCs) to differentiate into beta-cells. Spontaneous differentiation of hESCs under two-dimensional growth conditions resulted in differentiation of Pdx1(+)/Foxa2(+) pancreatic progenitors and Pdx1(+)/Isl1(+) endocrine progenitors but no insulin-producing cells. However, cotransplantation of differentiated hESCs with the dorsal pancreas, but not with the liver or telencephalon, from mouse embryos resulted in differentiation of beta-cell-like cell clusters. Comparative analysis of the basic characteristics of hESC-derived insulin(+) cell clusters with human adult islets demonstrated that the insulin(+) cells share important features with normal beta-cells, such as synthesis (proinsulin) and processing (C-peptide) of insulin and nuclear localization of key beta-cell transcription factors, including Foxa2, Pdx1, and Isl1.

Expression of the liver-specific gene Cyp7a1 reveals hepatic differentiation in embryoid bodies derived from mouse embryonic stem cells

Hepatic differentiation from mouse embryonic stem (ES) cells via the formation of embryoid bodies (EBs) has been revealed by the expression of hepatocyte-related genes such as alpha-fetoprotein and albumin. It is known, however, that the visceral endoderm differentiates in early EBs and expresses these hepatocyte-related genes. Thus, it remains unclear whether ES cells are capable of differentiating into hepatocytes derived from definitive endoderm in vitro. In the present study, yolk sac tissues isolated from the foetal mouse were found to express many hepatocyte-related genes. Among the hepatocyte-related genes examined, cytochrome P450 7A1 (Cyp7a1) was identified as a liver-specific gene that was not expressed in the yolk sac. Cyp7a1 was induced in developing EBs, and hepatic differentiation was preferentially observed in the developing EBs in attached culture as compared to those in suspension culture. Leukaemia inhibitory factor permitted the differentiation of visceral endoderm, but inhibited the expression of gastrulation-related genes and the hepatic differentiation in cultured EBs. ES cells expressing green fluorescent protein (GFP) under the control of the Cyp7a1 enhancer/promoter showed that cultured EBs contained GFP-positive epithelial-like cells. These results demonstrate that ES cells can differentiate in vitro into hepatocytes derived from definitive endoderm.

Embryonic stem cell differentiation: emergence of a new era in biology and medicine

The discovery of mouse embryonic stem (ES) cells >20 years ago represented a major advance in biology and experimental medicine, as it enabled the routine manipulation of the mouse genome. Along with the capacity to induce genetic modifications, ES cells provided the basis for establishing an in vitro model of early mammalian development and represented a putative new source of differentiated cell types for cell replacement therapy. While ES cells have been used extensively for creating mouse mutants for more than a decade, their application as a model for developmental biology has been limited and their use in cell replacement therapy remains a goal for many in the field. Recent advances in our understanding of ES cell differentiation, detailed in this review, have provided new insights essential for establishing ES cell-based developmental models and for the generation of clinically relevant populations for cell therapy.

Committing embryonic stem cells to early endocrine pancreas in vitro

A panel of genetic markers was used to assess the in vitro commitment of murine embryonic stem (ES) cells toward the endoderm-derived pancreas and to distinguish insulin-expressing cells of this lineage from other lineages such as neuron, liver, and yolk sac. There are two nonallelic insulin genes in mice. Neuronal cells express only insulin II, whereas the pancreas expresses both insulin I and II. Yolk sac and fetal liver express predominately insulin II, small amounts of insulin I, and no glucagon. We found that ES-derived embryoid bodies cultured in the presence of stage-specific concentrations of monothio-glycerol and 15% fetal calf serum, followed by serum-free conditions, give rise to a population that expresses insulin I, insulin II, pdx-1 (a pancreas marker), and Sox17 (an endoderm marker). Immunohistochemical staining shows intracellular insulin particles, and its de novo production was confirmed by staining for C-peptide. Most, but not all, of the insulin+ or C-peptide+ cells coexpress glucagon, demonstrating a differentiation pathway to pancreas rather than yolk sac or fetal liver. Addition of beta-cell specification and differentiation factors activin beta B, nicotinamide, and exendin-4 to later-stage culture increased insulin-positive cells to 2.73% of the total population, compared with the control culture, which gave rise to less than 1% insulin-staining cells. These findings suggest that stepwise culture manipulations can direct ES cells to become early endocrine pancreas.

Generation of insulin-expressing cells from mouse embryonic stem cells

The therapeutic potential of transplantation of insulin-secreting pancreatic beta-cells has stimulated interest in using pluripotent embryonic stem (ES) cells as a starting material from which to generate insulin secreting cells in vitro. Mature beta-cells are endodermal in origin so most reported differentiation protocols rely on the identification of endoderm-specific markers. However, endoderm development is an early event in embryogenesis that produces cells destined for the gut and associated organs in the embryo, and for the development of extra-embryonic structures such as the yolk sac. We have demonstrated that mouse ES cells readily differentiate into extra-embryonic endoderm in vitro, and that these cell populations express the insulin gene and other functional elements associated with beta-cells. We suggest that the insulin-expressing cells generated in this and other studies are not authentic pancreatic beta-cells, but may be of extra-embryonic endodermal origin.

Definitive Hematopoiesis Requires the Mixed-Lineage Leukemia Gene

The Mixed-Lineage Leukemia (MLL) gene encodes a Trithorax-related chromatin-modifying protooncogene that positively regulates Hox genes. In addition to their well-characterized roles in axial patterning, Trithorax and Polycomb family proteins perform less-understood functions in vertebrate hematopoiesis. To define the role of MLL in the development of the hematopoietic system, we examined the potential of cells lacking MLL. Mll-deficient cells could not develop into lymphocytes in adult RAG-2 chimeric animals. Similarly, in vitro differentiation of B cells required MLL. In chimeric embryos, Mll-deficient cells failed to contribute to fetal liver hematopoietic stem cell/progenitor populations. Moreover, we show that aorta-gonad-mesonephros (AGM) cells from Mll-deficient embryos lacked hematopoietic stem cell (HSC) activity despite their ability to generate hematopoietic progeny in vitro. These results demonstrate an intrinsic requirement for MLL in definitive hematopoiesis, where it is essential for the generation of HSCs in the embryo.

From embryos to embryoid bodies: generating blood from embryonic stem cells

Differentiation of embryonic stem (ES) cells in vitro yields abundant hematopoietic progenitors, but achieving stable hematopoietic engraftment of irradiated mice has proven difficult, begging the question of whether ES cells give rise to hematopoietic stem cells in vitro, and limiting the application of ES cells as experimental and therapeutic models. We have employed a number of hematopoietic regulatory genes to probe the nature and developmental potential of ES-derived blood precursors. The chronic myeloid leukemia-associated BCR/ABL oncoprotein transforms a novel class of ES-derived embryonic hematopoietic stem cell that represents a common progenitor of primitive erythropoiesis and definitive lymphoid-myeloid blood development. Expression of the homeobox gene HoxB4 generated normal, non-leukemic hematopoietic progenitors that enabled long-term, multilineage hematopoietic engraftment in primary and secondary mouse recipients. We have used these repopulating hematopoietic stem cells to model therapeutic transplantation from ES cells. We treated an immunodeficient Rag2(-/-) mouse by therapeutic cloning, that is, isogenic ES cell generation by somatic cell nuclear transfer, gene correction, and cell replacement therapy. Comparable approaches with human ES cells are being developed to lay the foundation for cellular therapies in patients with a variety of bone marrow diseases.

HNF-6-independent differentiation of mouse embryonic stem cells into insulin-producing cells

AIMS/HYPOTHESIS

Embryonic stem cells, when grown as embryoid bodies, spontaneously generate insulin-producing cells which could be used in therapy of diabetes mellitus, provided that their selection and differentiation are optimized. To achieve such optimization, one needs to know whether the differentiation of cells in embryoid bodies mimicks that of pancreatic beta cells in embryos. To address this question we verified if the differentiation of the insulin-producing cells in embryoid bodies requires Hepatocyte Nuclear Factor-6 (HNF-6), a transcription factor known to control pancreatic endocrine differentiation in embryos.

METHODS

We generated mouse Hnf6-/- embryonic stem cells and grew them as embryoid bodies. The expression of HNF-6, insulin, and transcription factors that are regulated by HNF-6 in developing pancreas was compared in wild-type and Hnf6-/- embryoid bodies.

RESULTS

No difference was observed in the expression of insulin between wild-type and Hnf6-/-embryoid bodies. In both cases insulin was expressed in the outer layer of cells, which is similar to the visceral endoderm. In wild-type embryoid bodies HNF-6 was transiently expressed in the outer layer of cells, but was not co-expressed with insulin. The expression of genes that are targets of HNF-6 in developing pancreas was unaffected in Hnf6-/-embryoid bodies.

CONCLUSION/INTERPRETATION

In contrast to the development of pancreatic beta cells, the differentiation of insulin-producing cells in embryoid bodies did not require HNF-6. Thus, the differentiation mechanism of insulin-producing cells in embryoid bodies differs from that of the beta cells and it is likely to resemble that of insulin-producing cells in the visceral endoderm.

beta-cell neogenesis induced by adenovirus-mediated gene delivery of transcription factor pdx-1 into mouse pancreas

beta-cell neogenesis is expected to provide a new therapy for diabetes. Numerous studies have demonstrated that transcriptional regulation involving pdx-1 is essential for endocrine neogenesis in vivo and in vitro. Therefore, it is possible that ectopic expression of pdx-1 in the pancreas could induce endocrine neogenesis. To test this possibility, we performed safe and efficient gene delivery of the pdx-1 gene into the mouse pancreas through the common bile duct using adenoviral vectors, and examined the effects of the ectopic expression of pdx-1. Here we show that adenovirus-mediated expression of pdx-1 can activate the endogenous pdx-1 gene, leading to beta-cell neogenesis and ductal proliferation. This technique is similar to the endoscopic retrograde cholangiopancreatography, which has been already established as a safe procedure for humans. Thus, beta-cell neogenesis induced by adenovirus-mediated expression of pdx-1 provides a novel strategy for gene therapy for a cure for diabetes mellitus.

HoxB4 confers definitive lymphoid-myeloid engraftment potential on embryonic stem cell and yolk sac hematopoietic progenitors

The extent to which primitive embryonic blood progenitors contribute to definitive lymphoid-myeloid hematopoiesis in the adult remains uncertain. In an effort to characterize factors that distinguish the definitive adult hematopoietic stem cell (HSC) and primitive progenitors derived from yolk sac or embryonic stem (ES) cells, we examined the effect of ectopic expression of HoxB4, a homeotic selector gene implicated in self-renewal of definitive HSCs. Expression of HoxB4 in primitive progenitors combined with culture on hematopoietic stroma induces a switch to the definitive HSC phenotype. These progenitors engraft lethally irradiated adults and contribute to long-term, multilineage hematopoiesis in primary and secondary recipients. Our results suggest that primitive HSCs are poised to become definitive HSCs and that this transition can be promoted by HoxB4 expression. This strategy for blood engraftment enables modeling of hematopoietic transplantation from ES cells.

CDX-1 and CDX-2 are expressed in human colonic mucosa and are down-regulated in patients with Hirschsprung's disease associated enterocolitis

Caudal type homeobox gene-1 and -2 (CDX-1 and CDX-2), homologues of the Drosophila homeobox gene caudal, encode transcription factors in endoderm derived tissues of the intestine. CDX genes control proliferation and differentiation of intestinal mucosal cells and colon cancer cells. Hirschsprung's Disease (HD) or congenital intestinal aganglionosis, a major developmental anomaly of intestine, which causes functional intestinal obstruction, is frequently associated with enterocolitis. Aetiology of HD-associated enterocolitis (HDEC) remains obscure. Reduction of gut mucosal enteroendocrine cells, and inefficient transfer of the secretory immunoglobulin A across the gut mucosal cell were shown to be associated with enterocolitis in HD patients suggesting that mucosa may directly involve in the pathophysiology of HDEC. This study aims to ascertain whether the CDX-1 and CDX-2 genes, that control the proliferation and differentiation of mucosal cells, play a role in HDEC. Using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridisation, we analysed the expression of CDX-1 and CDX-2 genes in colon specimens of normal controls, necrotising enterocolitis (NEC) infants, and HD patients with and without enterocolitis. We showed for the first time that CDX-1 and CDX-2 genes were expressed in the colonic mucosal epithelium in normal, NEC and in HD infants. However, the expressions of both genes were reduced in patients with HDEC. Our findings suggest that reduced expression of CDX-1 and CDX-2 genes in mucosa may be associated with the development of HDEC.

Improved glucose tolerance and acinar dysmorphogenesis by targeted expression of transcription factor PDX-1 to the exocrine pancreas

The homeodomain protein PDX-1 is critical for pancreas development and is a key regulator of insulin gene expression. PDX-1 nullizygosity and haploinsufficiency in mice and humans results in pancreatic agenesis and diabetes, respectively. At embryonic day (e) 10.5, PDX-1 is expressed in all pluripotential gut-derived epithelial cells destined to differentiate into the exocrine and endocrine pancreas. At e15, PDX-1 expression is downregulated in exocrine cells, but remains high in endocrine cells. The aim of this study was to determine whether targeted overexpression of PDX-1 to the exocrine compartment of the developing pancreas at e15 would allow for respecification of the exocrine cells. Transgenic (TG) mice were generated in which PDX-1 was expressed in the exocrine pancreas using the exocrine-specific elastase-1 promoter. These mice exhibited a marked dysmorphogenesis of the exocrine pancreas, manifested by increased rates of replication and apoptosis in acinar cells and a progressive fatty infiltration of the exocrine pancreas with age. Interestingly, the TG mice exhibited improved glucose tolerance, but absolute beta-cell mass was not increased. These findings indicate that downregulation of PDX-1 is required for the proper maintenance of the exocrine cell phenotype and that upregulation of PDX-1 in acinar cells affects beta-cell function. The mechanisms underlying these observations remain to be elucidated.

The Cdx-1 and Cdx-2 homeobox genes in the intestine

The past years have witnessed an increasing number of reports relative to homeobox genes in endoderm-derived tissues. In this review, we focus on the caudal-related Cdx-1 and Cdx-2 homeobox genes to give an overview of the in vivo, in vitro, and ex vivo approaches that emphasize their primary role in intestinal development and in the control of intestinal cell proliferation, differentiation, and identity. The participation of these genes in colon tumorigenesis and their identification as important actors of the oncogenic process are also discussed.