Characterization of platelet-derived growth factor-A expression in mouse tissues using a lacZ knock-in approach

TAD border deletion at the Kit locus causes tissue-specific ectopic activation of a neighboring gene

Topologically associated domains (TADs) restrict promoter-enhancer interactions, thereby maintaining the spatiotemporal pattern of gene activity. However, rearrangements of the TADs boundaries do not always lead to significant changes in the activity pattern. Here, we investigated the consequences of the TAD boundaries deletion on the expression of developmentally important genes encoding tyrosine kinase receptors: Kit, Kdr, Pdgfra. We used genome editing in mice to delete the TADs boundaries at the Kit locus and characterized chromatin folding and gene expression in pure cultures of fibroblasts, mast cells, and melanocytes. We found that although Kit is highly active in both mast cells and melanocytes, deletion of the TAD boundary between the Kit and Kdr genes results in ectopic activation only in melanocytes. Thus, the epigenetic landscape, namely the mutual arrangement of enhancers and actively transcribing genes, is important for predicting the consequences of the TAD boundaries removal. We also found that mice without a TAD border between the Kit and Kdr genes have a phenotypic manifestation of the mutation - a lighter coloration. Thus, the data obtained shed light on the principles of interaction between the 3D chromatin organization and epigenetic marks in the regulation of gene activity.

Severe cerebellar malformations in mutant mice demonstrate a role for PDGF-C/PDGFRα signalling in cerebellar development

Formation of the mouse cerebellum is initiated in the embryo and continues for a few weeks after birth. Double mutant mice lacking platelet-derived growth factor-C and that are heterozygous for platelet-derived growth factor receptor alpha (Pdgfc-/-; PdgfraGFP/+) develop cerebellar hypoplasia and malformation with loss of cerebellar lobes in the posterior vermis. This phenotype is similar to those observed in Foxc1 mutant mice and in a human neuroimaging pattern called Dandy Walker malformation. Pdgfc-Pdgfra mutant mice also display ependymal denudation in the 4th ventricle and gene expression changes in cerebellar meninges, which coincide with the first visible signs of cerebellar malformation. Here we show that PDGF-C/PDGFRα signalling is a critical component in the network of molecular and cellular interactions that take place between the developing meninges and neural tissues, and which are required to build a fully functioning cerebellum.

Acquisition of cellular properties during alveolar formation requires differential activity and distribution of mitochondria

Alveolar formation requires coordinated movement and interaction between alveolar epithelial cells, mesenchymal myofibroblasts, and endothelial cells/pericytes to produce secondary septa. These processes rely on the acquisition of distinct cellular properties to enable ligand secretion for cell-cell signaling and initiate morphogenesis through cellular contraction, cell migration, and cell shape change. In this study, we showed that mitochondrial activity and distribution play a key role in bestowing cellular functions on both alveolar epithelial cells and mesenchymal myofibroblasts for generating secondary septa to form alveoli in mice. These results suggest that mitochondrial function is tightly regulated to empower cellular machineries in a spatially specific manner. Indeed, such regulation via mitochondria is required for secretion of ligands, such as platelet-derived growth factor, from alveolar epithelial cells to influence myofibroblast proliferation and contraction/migration. Moreover, mitochondrial function enables myofibroblast contraction/migration during alveolar formation. Together, these findings yield novel mechanistic insights into how mitochondria regulate pivotal steps of alveologenesis. They highlight selective utilization of energy in cells and diverse energy demands in different cellular processes during development. Our work serves as a paradigm for studying how mitochondria control tissue patterning.

Assessment of Plasma Vitronectin as Diagnostic and Prognostic Marker of Hepatocellular Carcinoma in Patients with Hepatitis C Virus Cirrhosis

Background: hepatitis C is an inflammatory liver disease caused by the hepatitis C infection (HCV), and without treatment, almost 50% will progress to liver cirrhosis. Hepatocellular carcinoma (HCC) is the most frequent type of primary liver cancer and the fourth leading cause of cancer-related mortality. Aim of the study: the objective of this study was to evaluate the serum level of vitronectin (VTN) compared to AFP and determine their role as diagnostic and prognostic markers of HCV-related liver diseases. Subject and Methods: this study involved 52 HCV patients from which 26 patients were cirrhotic, and 26 patients had HCC (on top of hepatitis C virus-related cirrhosis) plus 10 healthy people as a control group. It was carried out in Gastroenterology and Hepatology Unit, Internal Medicine Department, Zagazig University Hospitals, Egypt. All individuals in this study were subjected to physical examination, full history taking, liver function tests, assessment of serum levels of Vitronectin (VTN) and alpha-fetoprotein (AFP) before and after the intervention within three months. Results: serum level of vitronectin increased significantly in cirrhosis patients and HCC patients than controls (p = 0.0041), (p < 0.001), respectively, and in HCC than cirrhosis patients (p < 0.001). Significant positive correlations were observed between levels of serum VTN and AFP in all HCV patients as well as cirrhotic patients (p < 0.001, p = 0.011, respectively). On the contrary, VTN and AFP didn’t show a significant correlation in HCC patients’ group. Moreover, the median serum level of VTN decreased significantly after treatment in patients with HCC (p < 0.001). At cut-off 38.5 ng/mL for AFP it shows sensitivity 80.8%, specificity 76.9% to differentiate HCC from cirrhosis cases. While VTN shows 84.6% sensitivity, 96.2% specificity at cut-off 26.5 μg/mL. Regarding clinicopathological characteristics and VTN levels, half of patients were stage B, 63.9% had tumor size >3 cm, 84.6% had more than one focal lesion. Conclusions: these results may allow one to speculate a potential role of Vitronectin in diagnosis and prognosis of HCC on top of cirrhosis related to HCV infection in addition to AFP and US and CT.

Role of PDGF-A/B Ligands in Cardiac Repair After Myocardial Infarction

Platelet-derived growth factors (PDGFs) are powerful inducers of cellular mitosis, migration, angiogenesis, and matrix modulation that play pivotal roles in the development, homeostasis, and healing of cardiac tissues. PDGFs are key signaling molecules and important drug targets in the treatment of cardiovascular disease as multiple researchers have shown that delivery of recombinant PDGF ligands during or after myocardial infarction can reduce mortality and improve cardiac function in both rodents and porcine models. The mechanism involved cannot be easily elucidated due to the complexity of PDGF regulatory activities, crosstalk with other protein tyrosine kinase activators, and diversity of the pathological milieu. This review outlines the possible roles of PDGF ligands A and B in the healing of cardiac tissues including reduced cell death, improved vascularization, and improved extracellular matrix remodeling to improve cardiac architecture and function after acute myocardial injury. This review may highlight the use of recombinant PDGF-A and PDGF-B as a potential therapeutic modality in the treatment of cardiac injury.

Identification of a Repair-Supportive Mesenchymal Cell Population during Airway Epithelial Regeneration

Tissue regeneration requires coordinated and dynamic remodeling of stem and progenitor cells and the surrounding niche. Although the plasticity of epithelial cells has been well explored in many tissues, the dynamic changes occurring in niche cells remain elusive. Here, we show that, during lung repair after naphthalene injury, a population of PDGFRα⁺ cells emerges in the non-cartilaginous conducting airway niche, which is normally populated by airway smooth muscle cells (ASMCs). This cell population, which we term “repair-supportive mesenchymal cells” (RSMCs), is distinct from conventional ASMCs, which have previously been shown to contribute to epithelial repair. Gene expression analysis on sorted lineage-labeled cells shows that RSMCs express low levels of ASMC markers, but high levels of the pro-regenerative marker Fgf10. Organoid co-cultures demonstrate an enhanced ability for RSMCs in supporting club-cell growth. Our study highlights the dynamics of mesenchymal cells in the airway niche and has implications for chronic airway-injury-associated diseases.

Moiseenko et al. explore the dynamics of mesenchymal cells in the peribronchial niche in response to airway injury. They identify a population of mesenchymal cells located in close proximity to airway smooth muscle cells (ASMCs). This population, termed “repair-supportive mesenchymal cells” (RSMCs), is recruited to facilitate airway epithelial regeneration.

A mammalian Wnt5a-Ror2-Vangl2 axis controls the cytoskeleton and confers cellular properties required for alveologenesis

Alveolar formation increases the surface area for gas-exchange and is key to the physiological function of the lung. Alveolar epithelial cells, myofibroblasts and endothelial cells undergo coordinated morphogenesis to generate epithelial folds (secondary septa) to form alveoli. A mechanistic understanding of alveologenesis remains incomplete. We found that the planar cell polarity (PCP) pathway is required in alveolar epithelial cells and myofibroblasts for alveologenesis in mammals. Our studies uncovered a Wnt5a-Ror2-Vangl2 cascade that endows cellular properties and novel mechanisms of alveologenesis. This includes PDGF secretion from alveolar type I and type II cells, cell shape changes of type I cells and migration of myofibroblasts. All these cellular properties are conferred by changes in the cytoskeleton and represent a new facet of PCP function. These results extend our current model of PCP signaling from polarizing a field of epithelial cells to conferring new properties at subcellular levels to regulate collective cell behavior.

Lung developmental arrest caused by PDGF-A deletion: consequences for the adult mouse lung

PDGF-A is a key contributor to lung development in mice. Its expression is needed for secondary septation of the alveoli and deletion of the gene leads to abnormally enlarged alveolar air spaces in mice. In humans, the same phenotype is the hallmark of bronchopulmonary dysplasia (BPD), a disease that affects premature babies and may have long lasting consequences in adulthood. So far, the knowledge regarding adult effects of developmental arrest in the lung is limited. This is attributable to few follow-up studies of BPD survivors and lack of good experimental models that could help predict the outcomes of this early age disease for the adult individual. In this study, we used the constitutive lung-specific Pdgfa deletion mouse model to analyze the consequences of developmental lung defects in adult mice. We assessed lung morphology, physiology, cellular content, ECM composition and proteomics data in mature mice, that perinatally exhibited lungs with a BPD-like morphology. Histological and physiological analyses both revealed that enlarged alveolar air spaces remained until adulthood, resulting in higher lung compliance and higher respiratory volume in knockout mice. Still, no or only small differences were seen in cellular, ECM and protein content when comparing knockout and control mice. Taken together, our results indicate that Pdgfa deletion-induced lung developmental arrest has consequences for the adult lung at the morphological and functional level. In addition, these mice can reach adulthood with a BPD-like phenotype, which makes them a robust model to further investigate the pathophysiological progression of the disease and test putative regenerative therapies.

Platelet-derived growth factor receptor-α is essential for cardiac fibroblast survival

Platelet-derived growth factor receptor α (PDGFRα), a receptor tyrosine kinase required for cardiac fibroblast development, is uniquely expressed by fibroblasts in the adult heart. Despite the consensus that PDGFRα is expressed in adult cardiac fibroblasts, we know little about its function when these cells are at rest. Here, we demonstrate that loss of PDGFRα in cardiac fibroblasts resulted in a rapid reduction of resident fibroblasts. Furthermore, we observe that phosphatidylinositol 3-kinase signaling was required for PDGFRα-dependent fibroblast maintenance. Interestingly, this reduced number of fibroblasts was maintained long-term, suggesting that there is no homeostatic mechanism to monitor fibroblast numbers and restore hearts to wild-type levels. Although we did not observe any systolic functional changes in hearts with depleted fibroblasts, the basement membrane and microvasculature of these hearts were perturbed. Through in vitro analyses, we showed that PDGFRα signaling inhibition resulted in an increase in fibroblast cell death, and PDGFRα stimulation led to increased levels of the cell survival factor activating transcription factor 3. Our data reveal a unique role for PDGFRα signaling in fibroblast maintenance and illustrate that a 50% loss in cardiac fibroblasts does not result in lethality.NEW & NOTEWORTHY Platelet-derived growth factor receptor α (PDGFRα) is required in developing cardiac fibroblasts, but a functional role in adult, quiescent fibroblasts has not been identified. Here, we demonstrate that PDGFRα signaling is essential for cardiac fibroblast maintenance and that there are no homeostatic mechanisms to regulate fibroblast numbers in the heart. PDGFR signaling is generally considered mitogenic in fibroblasts, but these data suggest that this receptor may direct different cellular processes depending on the cell's maturation and activation status.

Long-Term Engraftment Promotes Differentiation of Alveolar Epithelial Cells from Human Embryonic Stem Cell Derived Lung Organoids

Human embryonic stem cell (hESC) derived 3D human lung organoids (HLOs) provide a promising model to study human lung development and disease. HLOs containing proximal or/and immature distal airway epithelial cells have been successfully generated in vitro, such as early staged alveolar type 2 (AT2) cells (SPC⁺/SOX9⁺) and immature alveolar type 1 (AT1) cells (HOPX⁺/SOX9⁺). When HLOs were transplanted into immunocompromised mice for further differentiation in vivo, only few distal epithelial cells could be observed. In this study, we transplanted different stages of HLOs into immunocompromised mice to assess whether HLOs could expand and mature in vivo. We found that short-term transplanted HLOs contained lung progenitor cells (NKX2.1⁺, SOX9⁺, and P63⁺), but not SPC⁺ AT2 cells or AQP5⁺ AT1 cells. Meanwhile, long-term engrafted HLOs could differentiate into lung distal bipotent progenitor cells (PDPN⁺/SPC⁺/SOX9⁺), AT2 cells (SPC⁺, SPB⁺), and immature AT1 cells (PDPN⁺, AQP5^-). However, HLOs at late in vitro stage turned into mature AT1-like cells (AQP5⁺/SPB^-/SOX9^-) in vivo. Immunofluorescence staining and transmission electron microscopy (TEM) results revealed that transplanted HLOs contained mesenchymal cells (collagen I⁺), vasculature (ACTA2⁺), neuroendocrine-like cells (PGP9.5⁺), and nerve fiber structures (myelin sheath structure). Together, these data reveal that hESC-derived HLOs would be useful for human lung development modeling, and transplanted HLOs could mimic lung organ-like structures in vivo by possessing vascular network and neuronal network.

Understanding alveolarization to induce lung regeneration

Background

Gas exchange represents the key physiological function of the lung, and is dependent upon proper formation of the delicate alveolar structure. Malformation or destruction of the alveolar gas-exchange regions are key histopathological hallmarks of diseases such as bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis; all of which are characterized by perturbations to the alveolo-capillary barrier structure. Impaired gas-exchange is the primary initial consequence of these perturbations, resulting in severe clinical symptoms, reduced quality of life, and death. The pronounced morbidity and mortality associated with malformation or destruction of alveoli underscores a pressing need for new therapeutic concepts. The re-induction of alveolarization in diseased lungs is a new and exciting concept in a regenerative medicine approach to manage pulmonary diseases that are characterized by an absence of alveoli.

Main text

Mechanisms of alveolarization first need to be understood, to identify pathways and mediators that may be exploited to drive the induction of alveolarization in the diseased lung. With this in mind, a variety of candidate cell-types, pathways, and molecular mediators have recently been identified. Using lineage tracing approaches and lung injury models, new progenitor cells for epithelial and mesenchymal cell types – as well as cell lineages which are able to acquire stem cell properties – have been discovered. However, the underlying mechanisms that orchestrate the complex process of lung alveolar septation remain largely unknown.

Conclusion

While important progress has been made, further characterization of the contributing cell-types, the cell type-specific molecular signatures, and the time-dependent chemical and mechanical processes in the developing, adult and diseased lung is needed in order to implement a regenerative therapeutic approach for pulmonary diseases.

PDGF-A signaling is required for secondary alveolar septation and controls epithelial proliferation in the developing lung

Platelet-derived growth factor A (PDGF-A) signaling through PDGF receptor α is essential for alveogenesis. Previous studies have shown that Pdgfa−/− mouse lungs have enlarged alveolar airspace with absence of secondary septation, both distinctive features of bronchopulmonary dysplasia. To study how PDGF-A signaling is involved in alveogenesis, we generated lung-specific Pdgfa knockout mice (Pdgfafl/−; Spc-cre) and characterized their phenotype postnatally. Histological differences between mutant mice and littermate controls were visible after the onset of alveogenesis and maintained until adulthood. Additionally, we generated Pdgfafl/−; Spc-cre; PdgfraGFP/+ mice in which Pdgfra+ cells exhibit nuclear GFP expression. In the absence of PDGF-A, the number of PdgfraGFP+ cells was significantly decreased. In addition, proliferation of PdgfraGFP+ cells was reduced. During alveogenesis, PdgfraGFP+ myofibroblasts failed to form the α-smooth muscle actin rings necessary for alveolar secondary septation. These results indicate that PDGF-A signaling is involved in myofibroblast proliferation and migration. In addition, we show an increase in both the number and proliferation of alveolar type II cells in Pdgfafl/−; Spc-cre lungs, suggesting that the increased alveolar airspace is not caused solely by deficient myofibroblast function.

Expression analysis of platelet-derived growth factor receptor alpha and its ligands in the developing mouse lung

Activation of the platelet-derived growth factor receptor-α (PDGFRα) signaling pathway is critically important during lung alveogenesis, the process in lung development during which alveoli are formed from the terminal alveolar sacs. Several studies have aimed to characterize the expression patterns of PDGFRα and its two ligands (PDGF-A and -C) in the lung, but published analyses have been limited to embryonic and/or perinatal time points, and no attempts have been made to characterize both receptor and ligand expression simultaneously. In this study, we present a detailed map of the expression patterns of PDGFRα, PDGF-A and PDGF-C during the entire period of lung development, that is, from early embryogenesis until adulthood. Three different reporter mice were analyzed (Pdgfa^{ex4-COIN-INV-lacZ} , Pdgfc^tm1Nagy , and Pdgfra^{tm11(EGFP)Sor} ), in which either lacZ or H2B-GFP were expressed under the respective promoter in gene-targeted alleles. A spatiotemporal dynamic expression was identified for both ligands and receptor. PDGF-A and PDGF-C were located to distinct populations of epithelial and smooth muscle cells, whereas PDGFRα expression was located to different mesenchymal cell populations. The detailed characterization of gene expression provides a comprehensive map of PDGFRα signaling in lung cells, opening up for a better understanding of the role of PDGF signaling during lung development.

PDGF in organ fibrosis

Fibrosis is part of a tissue repair response to injury, defined as increased deposition of extracellular matrix. In some instances, fibrosis is beneficial; however, in the majority of diseases fibrosis is detrimental. Virtually all chronic progressive diseases are associated with fibrosis, representing a huge number of patients worldwide. Fibrosis occurs in all organs and tissues, becomes irreversible with time and further drives loss of tissue function. Various cells types initiate and perpetuate pathological fibrosis by paracrine activation of the principal cellular executors of fibrosis, i.e. stromal mesenchymal cells like fibroblasts, pericytes and myofibroblasts. Multiple pathways are involved in fibrosis, platelet-derived growth factor (PDGF)-signaling being one of the central mediators. Stromal mesenchymal cells express both PDGF receptors (PDGFR) α and β, activation of which drives proliferation, migration and production of extracellular matrix, i.e. the principal processes of fibrosis. Here, we review the role of PDGF signaling in organ fibrosis, with particular focus on the more recently described ligands PDGF-C and -D. We discuss the potential challenges, opportunities and open questions in using PDGF as a potential target for anti-fibrotic therapies.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

Skin Adipocyte Stem Cell Self-Renewal Is Regulated by a PDGFA/AKT-Signaling Axis

Tissue growth and maintenance requires stem cell populations that self-renew, proliferate, and differentiate. Maintenance of white adipose tissue (WAT) requires the proliferation and differentiation of adipocyte stem cells (ASCs) to form postmitotic, lipid-filled mature adipocytes. Here we use the dynamic adipogenic program that occurs during hair growth to uncover an unrecognized regulator of ASC self-renewal and proliferation, PDGFA, which activates AKT signaling to drive and maintain the adipogenic program in the skin. Pdgfa expression is reduced in aged ASCs and is required for ASC proliferation and maintenance in the dermis, but not in other WATs. Our molecular and genetic studies uncover PI3K/AKT2 as a direct PDGFA target that is activated in ASCs during WAT hyperplasia and is functionally required for dermal ASC proliferation. Our data therefore reveal active mechanisms that regulate ASC self-renewal in the skin and show that distinct regulatory mechanisms operate in different WAT depots.

Isoform-Specific Modulation of Inflammation Induced by Adenoviral Mediated Delivery of Platelet-Derived Growth Factors in the Adult Mouse Heart

Platelet-derived growth factors (PDGFs) are key regulators of mesenchymal cells in vertebrate development. To what extent PDGFs also exert beneficial homeostatic or reparative roles in adult organs, as opposed to adverse fibrogenic responses in pathology, are unclear. PDGF signaling plays critical roles during heart development, during which forced overexpression of PDGFs induces detrimental cardiac fibrosis; other studies have implicated PDGF signaling in post-infarct myocardial repair. Different PDGFs may exert different effects mediated through the two PDGF receptors (PDGFRα and PDGFRβ) in different cell types. Here, we assessed responses induced by five known PDGF isoforms in the adult mouse heart in the context of adenovirus vector-mediated inflammation. Our results show that different PDGFs have different, in some cases even opposing, effects. Strikingly, whereas the major PDGFRα agonists (PDGF-A and -C) decreased the amount of scar tissue and increased the numbers of PDGFRα-positive fibroblasts, PDGFRβ agonists either induced large scars with extensive inflammation (PDGF-B) or dampened the adenovirus-induced inflammation and produced a small and dense scar (PDGF-D). These results provide evidence for PDGF isoform-specific inflammation-modulating functions that may have therapeutic implications. They also illustrate a surprising complexity in the PDGF-mediated pathophysiological responses.

A role for PDGF-C/PDGFRα signaling in the formation of the meningeal basement membranes surrounding the cerebral cortex

Platelet-derived growth factor-C (PDGF-C) is one of three known ligands for the tyrosine kinase receptor PDGFRα. Analysis ofPdgfcnull mice has demonstrated roles for PDGF-C in palate closure and the formation of cerebral ventricles, but redundancy with other PDGFRα ligands might obscure additional functions. In search of further developmental roles for PDGF-C, we generated mice that were double mutants forPdgfc(-/-)andPdgfra(GFP/+) These mice display a range of severe phenotypes including spina bifida, lung emphysema, abnormal meninges and neuronal over-migration in the cerebral cortex. We focused our analysis on the central nervous system (CNS), where PDGF-C was identified as a critical factor for the formation of meninges and assembly of the glia limitans basement membrane. We also present expression data onPdgfa,PdgfcandPdgfrain the cerebral cortex and microarray data on cerebral meninges.

GATA4 regulates epithelial cell proliferation to control intestinal growth and development in mice

BACKGROUND & AIMS

The embryonic small intestinal epithelium is highly proliferative, and although much is known about mechanisms regulating proliferation in the adult intestine, the mechanisms controlling epithelial cell proliferation in the developing intestine are less clear. GATA4, a transcription factor that regulates proliferation in other developing tissues, is first expressed early in the developing gut in midgut endoderm. GATA4 function within midgut endoderm and the early intestinal epithelium has not been investigated.

METHODS

Using Sonic Hedgehog Cre to eliminate GATA4 in the midgut endoderm of mouse embryos, we determined the impact of loss of GATA4 on intestinal development, including epithelial cell proliferation, between E9.5-E18.5.

RESULTS

We found that intestinal length and width were decreased in GATA4 mutants compared with controls. GATA4-deficient intestinal epithelium contained fewer cells, and epithelial girth was decreased. We further observed a decreased proportion of proliferating cells at E10.5 and E11.5 in GATA4 mutants. We demonstrated that GATA4 binds to chromatin containing GATA4 consensus binding sites within Cyclin D2 (Ccnd2), Cyclin dependent kinase 6 (Cdk6), and Frizzled 5 (Fzd5). Moreover, Ccnd2, Cdk6, and Fzd5 transcripts were reduced at E11.5 in GATA4 mutant tissue. Villus morphogenesis was delayed, and villus structure was abnormal in GATA4 mutant intestine.

CONCLUSIONS

Our data identify GATA4 as an essential regulator of early intestinal epithelial cell proliferation. We propose that GATA4 controls proliferation in part by directly regulating transcription of cell cycle mediators. Our data further suggest that GATA4 affects proliferation through transcriptional regulation of Fzd5, perhaps by influencing the response of the epithelium to WNT signaling.