Vezf1: A Zn finger transcription factor restricted to endothelial cells and their precursors

Epigenetic Regulation of Mammalian Cardiomyocyte Development

The heart is the first organ formed during mammalian development and functions to distribute nutrients and oxygen to other parts of the developing embryo. Cardiomyocytes are the major cell types of the heart and provide both structural support and contractile function to the heart. The successful differentiation of cardiomyocytes during early development is under tight regulation by physical and molecular factors. We have reviewed current studies on epigenetic factors critical for cardiomyocyte differentiation, including DNA methylation, histone modifications, chromatin remodelers, and noncoding RNAs. This review also provides comprehensive details on structural and morphological changes associated with the differentiation of fetal and postnatal cardiomyocytes and highlights their differences. A holistic understanding of all aspects of cardiomyocyte development is critical for the successful in vitro differentiation of cardiomyocytes for therapeutic purposes.

The tissue-specific transcriptional landscape underlines the involvement of endothelial cells in health and disease

Endothelial cells (ECs) that line vascular and lymphatic vessels are being increasingly recognized as important to organ function in health and disease. ECs participate not only in the trafficking of gases, metabolites, and cells between the bloodstream and tissues but also in the angiocrine-based induction of heterogeneous parenchymal cells, which are unique to their specific tissue functions. The molecular mechanisms regulating EC heterogeneity between and within different tissues are modeled during embryogenesis and become fully established in adults. Any changes in adult tissue homeostasis induced by aging, stress conditions, and various noxae may reshape EC heterogeneity and induce specific transcriptional features that condition a functional phenotype. Heterogeneity is sustained via specific genetic programs organized through the combinatory effects of a discrete number of transcription factors (TFs) that, at the single tissue-level, constitute dynamic networks that are post-transcriptionally and epigenetically regulated. This review is focused on outlining the TF-based networks involved in EC specialization and physiological and pathological stressors thought to modify their architecture.

ETV2 and VEZF1 interaction and regulation of the hematoendothelial lineage during embryogenesis

Ets variant 2 (Etv2), a member of the Ets factor family, has an essential role in the formation of endothelial and hematopoietic cell lineages during embryonic development. The functional role of ETS transcription factors is, in part, dependent on the interacting proteins. There are relatively few studies exploring the coordinated interplay between ETV2 and its interacting proteins that regulate mesodermal lineage determination. In order to identify novel ETV2 interacting partners, a yeast two-hybrid analysis was performed and the C2H2 zinc finger transcription factor VEZF1 (vascular endothelial zinc finger 1) was identified as a binding factor, which was specifically expressed within the endothelium during vascular development. To confirm this interaction, co-immunoprecipitation and GST pull down assays demonstrated the direct interaction between ETV2 and VEZF1. During embryoid body differentiation, Etv2 achieved its peak expression at day 3.0 followed by rapid downregulation, on the other hand Vezf1 expression increased through day 6 of EB differentiation. We have previously shown that ETV2 potently activated Flt1 gene transcription. Using a Flt1 promoter-luciferase reporter assay, we demonstrated that VEZF1 co-activated the Flt1 promoter. Electrophoretic mobility shift assay and Chromatin immunoprecipitation established VEZF1 binding to the Flt1 promoter. Vezf1 knockout embryonic stem cells had downregulation of hematoendothelial marker genes when undergoing embryoid body mediated mesodermal differentiation whereas overexpression of VEZF1 induced the expression of hematoendothelial genes during differentiation. These current studies provide insight into the co-regulation of the hemato-endothelial lineage development via a co-operative interaction between ETV2 and VEZF1.

MicroRNA-150-5p is upregulated in the brain microvasculature during prenatal alcohol exposure and inhibits the angiogenic factor Vezf1

BACKGROUND

Fetal alcohol spectrum disorders (FASD) occur in children who were exposed to alcohol in utero and are manifested in a wide range of neurocognitive deficits. These deficits could be caused by alterations to the cortical microvasculature that are controlled by post-transcriptional regulators such as microRNAs.

METHODS

Using an established mouse model of moderate prenatal alcohol exposure (PAE), we isolated cortices (CTX) and brain microvascular endothelial cells (BMVECs) at embryonic day 18 (E18) and examined the expression of miR-150-5p and potential downstream targets. Cellular transfections and intrauterine injections with LNA™ mimics or inhibitors were used to test miR-150-5p regulation of novel target vascular endothelial zinc finger 1 (Vezf1). Dual-luciferase assays were used to assess the direct binding of miR-150-5p to the Vezf1 3'UTR. The effects of miR-150-5p and Vezf1 on endothelial cell function were determined by in vitro migration and tube formation assays.

RESULTS

We found that miR-150-5p was upregulated and Vezf1 was downregulated during PAE in the E18 CTX and BMVECs. Transfection with miR-150-5p mimics resulted in decreased Vezf1 expression in BMVECs, while miR-150-5p inhibition did the opposite. Dual-luciferase assays revealed direct binding of miR-150-5p with the Vezf1 3'UTR. Intrauterine injections showed that miR-150-5p regulates the expression of Vezf1 in vivo during PAE. miR-150-5p overexpression decreased BMVEC migration and tube formation, while miR-150-5p inhibition enhanced migration and tube formation. Vezf1 overexpression rescued the effects of the miR-150-5p mimic. Alcohol treatment of BMVECs increased miR-150-5p expression and inhibited migration and tube formation. Finally, miR-150-5p inhibition and Vezf1 overexpression rescued the negative effects of alcohol on migration and tube formation.

CONCLUSIONS

miR-150-5p regulation of Vezf1 results in altered endothelial cell function during alcohol exposure. Further, miR-150-5p inhibition of Vezf1 may adversely alter the development of the cortical microvasculature during PAE and contribute to deficits seen in patients with FASD.

Identification of Key Immune-Related Genes in the Progression of Septic Shock

Objective: Septic shock is the severe complication of sepsis, with a high mortality. The inflammatory response regulates the immune status and mediates the progression of septic shock. In this study, we aim to identify the key immune-related genes (IRGs) of septic shock and explore their potential mechanism. Methods: Gene expression profiles of septic shock blood samples and normal whole blood samples were retrieved from the Gene Expression Omnibus (GEO) and Genotype-Tissue Expression Portal (GTEx). The differential expression genes (DEGs) and septic shock-specific immune-related genes (SSSIRGs) were evaluated and identified, along with the immune components by "cell type identification by estimating relative subsets of RNA transcripts (CIBERSORT, version x)" algorithm. Additionally, in order to explore the key regulatory network, the relationship among SSSIRGs, upstream transcription factors (TFs), and downstream signaling pathways were also identified by Gene Set Variation Analysis (GSVA) and co-expression analysis. Moreover, the Connectivity Map (CMap) analysis was applied to find bioactive small molecules against the members of regulation network while Chromatin Immunoprecipitation sequencing (ChIP-seq) and Assay for Targeting Accessible-Chromatin with high-throughput sequencing (ATAC-seq) data were used to validate the regulation mechanism of the network. Results: A total of 14,843 DEGs were found between 63 septic shock blood samples and 337 normal whole blood samples. Then, we identified septic shock-specific 839 IRGs as the intersection of DEGs and IRGs. Moreover, we uncovered the regulatory networks based on co-expression analysis and found 28 co-expression interaction pairs. In the regulation network, protein phosphatase 3, catalytic subunit, alpha isozyme (PPP3CA) may regulate late estrogen response, glycolysis and TNFα signaling via NFκB and HLA; Kirsten rat sarcoma viral oncogene homolog (KRAS) may be related to late estrogen response and HLA; and Toll-like receptor 8 (TLR8) may be associated with TNFα signaling via NFκB. And the regulation mechanisms between TFs and IRGs (TLR8, PPP3CA, and KRAS) were validated by ChIP-seq and ATAC-seq. Conclusion: Our data identify three SSSIRGs (TLR8, PPP3CA, and KRAS) as candidate therapeutic targets for septic shock and provide constructed regulatory networks in septic shock to explore its potential mechanism.

Theoretical Analysis of S, M and N Structural Proteins by the Protein-RNA Recognition Code Leads to Genes/proteins that Are Relevant to the SARS-CoV-2 Life Cycle and Pathogenesis

In this conceptual review, based on the protein-RNA recognition code, some theoretical sequences were detected in the spike (S), membrane (M) and capsid (N) proteins that may post-transcriptionally regulate the host genes/proteins in immune homeostasis, pulmonary epithelial tissue homeostasis, and lipid homeostasis. According to the review of literature, the spectrum of identified genes/proteins shows that the virus promotes IL1α/β-IL1R1 signaling (type 1 immunity) and immunity defense against helminths and venoms (type 2 immunity). In the alteration of homeostasis in the pulmonary epithelial tissue, the virus blocks the function of cilia and the molecular programs that are involved in wound healing (EMT and MET). Additionally, the protein-RNA recognition method described here identifies compatible sequences in the S1A-domain for the post-transcriptional promotion of PIKFYVE, which is one of the critical factors for SARS-CoV-2 entry to the host cell, and for the post-transcriptional repression of xylulokinase XYLB. A decrease in XYLB product (Xu5P) in plasma was proposed as one of the potential metabolomics biomarkers of COVID-19. In summary, the protein-RNA recognition code leads to protein genes relevant to the SARS-CoV-2 life cycle and pathogenesis.

EWSR1-PATZ1-rearranged sarcoma: a report of nine cases of spindle and round cell neoplasms with predilection for thoracoabdominal soft tissues and frequent expression of neural and skeletal muscle markers

The knowledge of clinical features and, particularly, histopathological spectrum of EWSR1-PATZ1-rearranged spindle and round cell sarcomas (EPS) remains limited. For this reason, we report the largest clinicopathological study of EPS to date. Nine cases were collected, consisting of four males and five females ranging in age from 10 to 81 years (average: 49 years). Five tumors occurred in abdominal wall soft tissues, three in the thorax, and one in the back of the neck. Tumor sizes ranged from 2.5 to 18 cm (average 6.6 cm). Five patients had follow-up with an average of 38 months (range: 18-60 months). Two patients had no recurrence or metastasis 19 months after diagnosis. Four patients developed multifocal pleural or pulmonary metastasis and were treated variably by surgery, radiotherapy, and chemotherapy. The latter seemed to have little to no clinical benefit. One of the four patients was free of disease 60 months after diagnosis, two patients were alive with disease at 18 and 60 months, respectively. Morphologically, low, intermediate, and high-grade sarcomas composed of a variable mixture of spindled, ovoid, epithelioid, and round cells were seen. The architectural and stromal features also varied, resulting in a broad morphologic spectrum. Immunohistochemically, the following markers were most consistently expressed: S100-protein (7/9 cases), GFAP (7/8), MyoD1 (8/9), Pax-7 (4/5), desmin (7/9), and AE1/3 (4/9). By next-generation sequencing, all cases revealed EWSR1-PATZ1 gene fusion. In addition, 3/6 cases tested harbored CDKN2A deletion, while CDKN2B deletion and TP53 mutation were detected in one case each. Our findings confirm that EPS is a clinicopathologic entity, albeit with a broad morphologic spectrum. The uneventful outcome in some of our cases indicates that a subset of EPS might follow a more indolent clinical course than previously appreciated. Additional studies are needed to validate whether any morphological and/or molecular attributes have a prognostic impact.

VEZF1-guanine quadruplex DNA interaction regulates alternative polyadenylation and detyrosinase activity of VASH1

Vascular endothelial zinc finger 1 (VEZF1) plays important roles in endothelial lineage definition and angiogenesis. Vasohibins 1 and 2 (VASH1 and VASH2) can form heterodimers with small vasohibin-binding protein (SVBP) and were recently shown to regulate angiogenesis by acting as tubulin detyrosinases. Here, we showed that VEZF1 binds directly with DNA guanine quadruplex (G quadruplex, G4) structures in vitro and in cells, which modulates the levels of the two isoforms of VASH1 mRNA. Disruption of this interaction, through genetic depletion of VEZF1 or treatment of cells with G4-stabilizing small molecules, led to increased production of the long over short isoform of VASH1 (i.e. VASH1A and VASH1B, respectively) mRNA and elevated tubulin detyrosinase activity in cells. Moreover, disruption of VEZF1-G4 interactions in human umbilical vein endothelial cells resulted in diminished angiogenesis. These results suggest that the interaction between VEZF1 and G4 structures assumes a crucial role in angiogenesis, which occurs through regulating the relative levels of the two isoforms of VASH1 mRNA and the detyrosinase activity of the VASH1-SVBP complex. Together, our work revealed VEZF1 as a G4-binding protein, identified a novel regulatory mechanism for tubulin detyrosinase, and illustrated that the VEZF1- and VASH1-mediated angiogenesis pathways are functionally connected.

Vezf1 regulates cardiac structure and contractile function

Background

Vascular endothelial zinc finger 1 (Vezf1) is a transcription factor previously shown to regulate vasculogenesis and angiogenesis. We aimed to investigate the role of Vezf1 in the postnatal heart.

Methods

The role of Vezf1 in regulating cardiac growth and contractile function was studied in zebrafish and in primary cardiomyocytes.

Findings

We find that expression of Vezf1 is decreased in diseased human myocardium and mouse hearts. Our experimental data shows that knockdown of zebrafish Vezf1 reduces cardiac growth and results in impaired ventricular contractile response to β-adrenergic stimuli. However, Vezf1 knockdown is not associated with dysregulation of cardiomyocyte Ca²⁺ transient kinetics. Gene ontology enrichment analysis indicates that Vezf1 regulates cardiac muscle contraction and dilated cardiomyopathy related genes and we identify cardiomyocyte Myh7/β-MHC as key target for Vezf1. We further identify a key role for an MCAT binding site in the Myh7 promoter regulating the response to Vezf1 knockdown and show that TEAD-1 is a binding partner of Vezf1.

Interpretation

We demonstrate a role for Vezf1 in regulation of compensatory cardiac growth and cardiomyocyte contractile function, which may be relevant in human cardiac disease.

MiR-191 inhibit angiogenesis after acute ischemic stroke targeting VEZF1

Acute ischemic stroke (AIS) is a major public health problem in China. Impaired angiogenesis plays crucial roles in the development of ischemic cerebral injury. Recent studies have identified that microRNAs (miRNAs) are important regulators of angiogenesis, but little is known the exact effects of angiogenesis-associated miRNAs in AIS. In the present study, we detected the expression levels of angiogenesis-associated miRNAs in AIS patients, middle cerebral artery occlusion (MCAO) rats, and oxygen-glucose deprivation/reoxygenation (OGD/R) human umbilical vein endothelial cells (HUVECs). MiR-191 was increased in the plasma of AIS patients, OGD/R HUVECs, and the plasma and brain of MCAO rats. Over-expression of miR-191 promoted apoptosis, but reduced the proliferation, migration, tube-forming and spheroid sprouting activity in HUVECs OGD/R model. Mechanically, vascular endothelial zinc finger 1 (VEZF1) was identified as the direct target of miR-191, and could be regulated by miR-191 at post-translational level. In vivo studies applying miR-191 antagomir demonstrated that inhibition of miR-191 reduced infarction volume in MCAO rats. In conclusion, our data reveal a novel role of miR-191 in promoting ischemic brain injury through inhibiting angiogenesis via targeting VEZF1. Therefore, miR-191 may serve as a biomarker or a therapeutic target for AIS.

The transcription factor Vezf1 represses the expression of the antiangiogenic factor Cited2 in endothelial cells

Formation of the vasculature by angiogenesis is critical for proper development, but angiogenesis also contributes to the pathogenesis of various disorders, including cancer and cardiovascular diseases. Vascular endothelial zinc finger 1 (Vezf1), is a Krüppel-like zinc finger protein that plays a vital role in vascular development. However, the mechanism by which Vezf1 regulates this process is not fully understood. Here, we show that Vezf1^−/− mouse embryonic stem cells (ESC) have significantly increased expression of a stem cell factor, Cbp/p300-interacting transactivator 2 (Cited2). Compared with WT ESCs, Vezf1^−/− ESCs inefficiently differentiated into endothelial cells (ECs), which exhibited defects in the tube-formation assay. These defects were due to reduced activation of EC-specific genes concomitant with lower enrichment of histone 3 acetylation at Lys²⁷ (H3K27) at their promoters. We hypothesized that overexpression of Cited2 in Vezf1^−/− cells sequesters P300/CBP away from the promoters of proangiogenic genes and thereby contributes to defective angiogenesis in these cells. This idea was supported by the observation that shRNA-mediated depletion of Cited2 significantly reduces the angiogenic defects in the Vezf1^−/− ECs. In contrast to previous studies that have focused on the role of Vezf1 as a transcriptional activator of proangiogenic genes, our findings have revealed a role for Vezf1 in modulating the expression of the antiangiogenic factor Cited2. Vezf1 previously has been characterized as an insulator protein, and our results now provide insights into the mechanism, indicating that Vezf1 can block inappropriate, nonspecific interactions of promoters with cis-located enhancers, preventing aberrant promoter activation.

Developmental Toxicity of Carbon Quantum Dots to the Embryos/Larvae of Rare Minnow (Gobiocypris rarus)

The toxic effects of CDs on rare minnow (Gobiocypris rarus) embryos at different developmental stages were investigated. The results showed that rare minnow embryos had decreased spontaneous movements, body length, increased heart rate, pericardial edema, yolk sac edema, tail/spinal curvature, various morphological malformations, and decreased hatching rate. Biochemical analysis showed the CDs exposure significantly inhibited the activity of Na⁺/K⁺-ATPase and Ca²⁺-ATPase and increased the MDA contents and the activity of SOD, CAT, and GPX. Further examination suggested that the CDs exposure induced serious embryonic cellular DNA damage. Moreover, the CDs exposure induced upregulation of development related genes (Wnt8a and Mstn) along with the downregulation of Vezf1. Overall, the present study revealed that the CDs exposure has significant development toxicity on rare minnow embryos/larvae. Mechanistically, this toxicity might result from the pressure of induced oxidative stress coordinate with the dysregulated development related gene expression mediated by the CDs exposure.

Infantile Hemangioma Originates From A Dysregulated But Not Fully Transformed Multipotent Stem Cell

Infantile hemangioma (IH) is the most common tumor of infancy. Its cellular origin and biological signals for uncontrolled growth are poorly understood, and specific pharmacological treatment is unavailable. To understand the process of hemangioma-genesis we characterized the progenitor hemangioma-derived stem cell (HemSC) and its lineage and non-lineage derivatives. For this purpose we performed a high-throughput (HT) phenotypic and gene expression analysis of HemSCs, and analyzed HemSC-derived tumorspheres. We found that IH is characterized by high expression of genes involved in vasculogenesis, angiogenesis, tumorigenesis and associated signaling pathways. These results show that IH derives from a dysregulated stem cell that remains in an immature, arrested stage of development. The potential biomarkers we identified can afford the development of diagnostic tools and precision-medicine therapies to "rewire" or redirect cellular transitions at an early stage, such as signaling pathways or immune response modifiers.

Developmental toxicity in rare minnow (Gobiocypris rarus) embryos exposed to Cu, Zn and Cd

Using rare minnow (Gobiocypris rarus) embryos as experimental model, the developmental toxicity of Cu, Zn and Cd were investigated following exposure to 0.001-1.000mg/L for 72h, and the toxicity effects were evaluated by larval malformation rate, heart rate, pericardial area, spontaneous movements, tail length, enzyme activities and biomarker genes. Our results revealed that increased malformation rate provide a gradual dose-response relationship, and the most pronounced morphological alteration was heart and body malformations. Values of 72h EC50 with their 95 percent confidence intervals on G. rarus embryos were 0.103 (0.072-0.149)mg/L for Cu, 0.531 (0.330-1.060)mg/L for Zn, 0.219 (0.147-0.351)mg/L for Cd. Enzyme activities can be regard as a type of low-dose stimulation and high-dose inhibition. Stress and metabolism-related genes (hsp70, cyp1a and mt) were significantly up-regulated, development-related genes (wnt8a, vezf1 and mstn) were significantly down-regulated after the treatment by Cu, Zn and Cd. Overall, the present study points out Cu, Zn and Cd are highly toxic to G. rarus embryos. The information presented in this study will be helpful in fully understanding the toxicity induced by Cu, Zn and Cd in fish embryos.

[Regulation of endothelial cell-specific Robo4 gene expression by DNA methylation and non-lineage specific transcription factors]

Studies of tissue-specific gene expression have suggested that tissue-specific transcription factors or tissue-specific combinations of non-cell-type-specific transcription factors regulate tissue-specific gene expression. Although the studies of endothelial cell (EC)-specific gene expression has identified several transcriptional activators such as SP1, ETS family proteins, and GATA proteins, their expression and combinations are not likely to be EC-specific. To investigate the mechanism of EC-specific gene expression, we analyzed the regulation mechanism of an EC-specific gene, Roundabout4 (Robo4). We identified the 3-kb Robo4 promoter and several transcription factors including SP1 and GABP that bind to the Robo4 promoter and promote Robo4 gene expression. However, we could not explain the mechanism for EC-specific Robo4 gene expression with only those factors because their expression and combination are not EC-specific. Therefore, we hypothesized the contribution of other mechanisms, especially epigenetic control, to Robo4 gene regulation and demonstrated the importance of DNA methylation for EC-specific Robo4 expression. In this review, we summarize our recent studies and discuss the novel regulation model of Robo4 gene expression by transcription factors and DNA methylation.

Role of HOXA9 and VEZF1 in endothelial biology

Proper development of the vascular system as one of the earliest and most critical steps during vertebrate embryogenesis is ensured by the exact spatial and temporal control of gene expression in cells forming the vessel network. Whereas the regulation of vascular system development is well elucidated on the level of ligand-receptor signaling, the processes on the transcriptional level are much less understood. As the signaling mechanisms in embryogenesis and pathological conditions are similar, the study of embryonic blood vessel development is of great interest for the treatment of cardiovascular diseases and cancer. This review discusses two transcription factors, HOXA9 and VEZF1, which are relevant for endothelial biology but are excluded in the bulk of transcription factor references discussing endothelial biology. To our knowledge, there is no comprehensive overview of these two transcription factors available to date. Here, we summarize the current knowledge of human HOXA9 and VEZF1 biology and function, we detail their target genes and roles in endothelial biology and propose that HOXA9 and VEZF1 also deserve consideration as relevant transcriptional regulators of endothelial biology. Due to their broad role in multiple aspects of endothelial biology, they might potentially become interesting targets for therapeutic manipulation of pathological blood vessel growth.

Developmental toxicity of 3,4-dichloroaniline on rare minnow (Gobiocypris rarus) embryos and larvae

Gobiocypris rarus is a freshwater cyprinid, which possesses lots of attractive features (short life cycle, high fecundity, and especially the transparent trait during early life stage) that make it a suitable model in aquatic toxicity tests. In this study, the effects of 3,4-dichloroaniline (3,4-DCA) on the early life stages of G. rarus were measured. As endpoints, normal developmental parameters (survival rate, malformation rate, total body length and average heart rate) as well as biomarker genes (stress response (hsp70), organizer function and axis formation (wnt8a), vascular system development (vezf1), detoxification (cyp1a) and endocrine disruption (erα)) in the developing embryos and larvae were recorded during a 72 h exposure. The results revealed that reduced survival rate, increased malformation, changes in heart rate and total body length provide a gradual dose-response relationship, values of 72 h LC(50) were 4.146 (3.665-4.713) mg L(-1) for embryos and 1.088 (0.832-1.432) mg L(-1) for larvae. The developmental biochemical biomarkers are very promising tools to determine the severity of toxicants in the growing G. rarus embryos and larvae, even at a concentration of 1% for LC(50). Gene expressions of wnt8a and cyp1a in embryos were highly up-regulated (more than 100-fold) after exposure to 3,4-DCA. Overall, the present study points out that 3,4-DCA is high toxic to the early development of G. rarus, and offers a practicable and highly sensitive bioassay for the general assessment of chemical toxicity.

Vezf1 protein binding sites genome-wide are associated with pausing of elongating RNA polymerase II

The protein Vezf1 plays multiple roles important for embryonic development. In Vezf1(-/-) mouse embryonic stem (mES) cells, our earlier data showed widespread changes in gene-expression profiles, including decreased expression of the full-length active isoform of Dnmt3b methyltransferase and concomitant genome-wide reduction in DNA methylation. Here we show that in HeLaS3 cells there is a strong genome-wide correlation between Vezf1 binding and peaks of elongating Ser2-P RNA polymerase (Pol) ll, reflecting Vezf1-dependent slowing of elongation. In WT mES cells, the elongating form of RNA pol II accumulates near Vezf1 binding sites within the dnmt3b gene and at several other Vezf1 sites, and this accumulation is significantly reduced at these sites in Vezf1(-/-) mES cells. Depending upon genomic location, Vezf1-mediated Pol II pausing can have different regulatory roles in transcription and splicing. We find examples of genes in which Vezf1 binding sites are located near cassette exons, and in which loss of Vezf1 leads to a change in the relative abundance of alternatively spliced messages. We further show that Vezf1 interacts with Mrg15/Mrgbp, a protein that recognizes H3K36 trimethylation, consistent with the role of histone modifications at alternatively spliced sites.

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin-1 (ET-1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue-specific production of ET-1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET-1 bioavailability is the rate of transcription from the ET-1 gene (edn1). Studies conducted on a variety of cell types have identified key transcription factors that govern edn1 expression. With few exceptions, the cis-acting elements bound by these factors have been mapped in the edn1 regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate edn1 in a tissue or hormone-specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated edn1 expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern edn1 activity at the molecular level.

Complete biallelic insulation at the H19/Igf2 imprinting control region position results in fetal growth retardation and perinatal lethality

Background

The H19/Igf2 imprinting control region (ICR) functions as an insulator exclusively in the unmethylated maternal allele, where enhancer-blocking by CTCF protein prevents the interaction between the Igf2 promoter and the distant enhancers. DNA methylation inhibits CTCF binding in the paternal ICR allele. Two copies of the chicken β-globin insulator (ChβGI)₂ are capable of substituting for the enhancer blocking function of the ICR. Insulation, however, now also occurs upon paternal inheritance, because unlike the H19 ICR, the (ChβGI)₂ does not become methylated in fetal male germ cells. The (ChβGI)₂ is a composite insulator, exhibiting enhancer blocking by CTCF and chromatin barrier functions by USF1 and VEZF1. We asked the question whether these barrier proteins protected the (ChβGI)₂ sequences from methylation in the male germ line.

Methodology/Principal Findings

We genetically dissected the ChβGI in the mouse by deleting the binding sites USF1 and VEZF1. The methylation of the mutant versus normal (ChβGI)₂ significantly increased from 11% to 32% in perinatal male germ cells, suggesting that the barrier proteins did have a role in protecting the (ChβGI)₂ from methylation in the male germ line. Contrary to the H19 ICR, however, the mutant (mChβGI)₂ lacked the potential to attain full de novo methylation in the germ line and to maintain methylation in the paternal allele in the soma, where it consequently functioned as a biallelic insulator. Unexpectedly, a stricter enhancer blocking was achieved by CTCF alone than by a combination of the CTCF, USF1 and VEZF1 sites, illustrated by undetectable Igf2 expression upon paternal transmission.

Conclusions/Significance

In this in vivo model, hypomethylation at the ICR position together with fetal growth retardation mimicked the human Silver-Russell syndrome. Importantly, late fetal/perinatal death occurred arguing that strict biallelic insulation at the H19/Igf2 ICR position is not tolerated in development.

Vascular potential of human pluripotent stem cells

Cardiovascular disease is the number one cause of death and disability in the US. Understanding the biological activity of stem and progenitor cells, and their ability to contribute to the repair, regeneration and remodeling of the heart and blood vessels affected by pathological processes is an essential part of the paradigm in enabling us to achieve a reduction in related deaths. Both human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are promising sources of cells for clinical cardiovascular therapies. Additional in vitro studies are needed, however, to understand their relative phenotypes and molecular regulation toward cardiovascular cell fates. Further studies in translational animal models are also needed to gain insights into the potential and function of both human ES- and iPS-derived cardiovascular cells, and enable translation from experimental and preclinical studies to human trials.

Targeted Vezf1-null mutation impairs vascular structure formation during embryonic stem cell differentiation

OBJECTIVE

Vezf1 encodes an early zinc finger transcription factor that is essential for normal vascular development and functions in a dose-dependent manner. Here, we investigated the role of Vezf1 during processes of endothelial cell differentiation and maturation by studying mutant Vezf1 embryonic stem (ES) cells using the in vitro embryoid body differentiation model and the in vivo teratocarcinoma model.

METHODS AND RESULTS

Vezf1-/- ES cell-derived embryoid bodies failed to form a well-organized vascular network and showed dramatic vascular sprouting defects. Our results indicate that the retinol pathway is an important mediator of Vezf1 function and that loss of Vezf1 results in reduced retinol/vitamin A signaling and aberrant extracellular matrix (ECM) formation. Unexpectedly, we also uncovered defects during in vitro differentiation of Vezf1-/- ES cells along hematopoietic cell lineages. Vezf1-/- ES cell-derived teratocarcinomas were able to spontaneously differentiate into cell types of all 3 germ layers. However, histological and immunohistochemical examination of these tumors showed decreased cell proliferation, delayed differentiation, and large foci of cells with extensive deposition of ECM. Embryoid bodies and teratocarcinomas derived from heterozygous ES cells displayed an intermediate phenotype.

CONCLUSIONS

Together, these results suggest that Vezf1 is involved in early differentiation processes of the vasculature by regulating cell differentiation, proliferation, and ECM distribution and deposition.

Metallothionein 1 is a Downstream Target of Vascular Endothelial Zinc Finger 1 (VEZF1) in Endothelial Cells and Participates in the Regulation of Angiogenesis

Vascular endothelial zinc finger 1 (VEZF1) is a transcription factor that is expressed in endothelial cells and plays a requisite role in the regulation of angiogenesis. The authors' previous microarray analysis revealed that the down-regulation of VEZF1 gene resulted in the decrease of metallothionein 1 (MT1) gene in endothelial cells. Here the authors showed by Northern blotting that the down-regulation of VEZF1 decreased, whereas up-regulation of VEZF1 increased, the expression of MT1 in endothelial cells. Moreover, MT1 was expressed in endothelial cells at the site of angiogenesis in vivo. The authors therefore examined whether MT1 played any role in the regulation of angiogenesis. Down-regulation of MT1 in endothelial cells inhibited proliferation, migration, and network formation in vitro, as well as angiogenesis in vivo. Moreover, down-regulation of MT1 resulted in the cell cycle arrest at G1 phase. These results indicate that MT1 is a downstream target of VEZF1 in endothelial cells and is involved in the regulation of angiogenesis.

Vezf1 regulates genomic DNA methylation through its effects on expression of DNA methyltransferase Dnmt3b

The zinc finger protein vascular endothelial zinc finger 1 (Vezf1) has been implicated in the development of the blood vascular and lymphatic system in mice, and has been characterized as a transcriptional activator in some systems. The chicken homolog, BGP1, has binding sites in the beta-globin locus, including the upstream insulator element. We report that in a mouse embryonic stem cell line deletion of both copies of Vezf1 results in loss of DNA methylation at widespread sites in the genome, including Line1 elements and minor satellite repeats, some imprinted genes, and several CpG islands. Loss of methylation appears to arise from a substantial decrease in the abundance of the de novo DNA methyltransferase, Dnmt3b. These results suggest that naturally occurring mutations in Vezf1/BGP1 might have widespread effects on DNA methylation patterns and therefore on epigenetic regulation of gene expression.

Neurotrophin p75 receptor (p75NTR) promotes endothelial cell apoptosis and inhibits angiogenesis: implications for diabetes-induced impaired neovascularization in ischemic limb muscles

Diabetes impairs endothelial function and reparative neovascularization. The p75 receptor of neurotrophins (p75(NTR)), which is scarcely present in healthy endothelial cells (ECs), becomes strongly expressed by capillary ECs after induction of peripheral ischemia in type-1 diabetic mice. Here, we show that gene transfer-induced p75(NTR) expression impairs the survival, proliferation, migration, and adhesion capacities of cultured ECs and endothelial progenitor cells (EPCs) and inhibits angiogenesis in vitro. Moreover, intramuscular p75(NTR) gene delivery impairs neovascularization and blood flow recovery in a mouse model of limb ischemia. These disturbed functions are associated with suppression of signaling mechanisms implicated in EC survival and angiogenesis. In fact, p75(NTR) depresses the VEGF-A/Akt/eNOS/NO pathway and additionally reduces the mRNA levels of ITGB1 [beta (1) integrin], BIRC5 (survivin), PTTG1 (securin) and VEZF1. Diabetic mice, which typically show impaired postischemic muscular neovascularization and blood perfusion recovery, have these defects corrected by intramuscular gene transfer of a dominant negative mutant form of p75(NTR). Collectively, our data newly demonstrate the antiangiogenic action of p75(NTR) and open new avenues for the therapeutic use of p75(NTR) inhibition to combat diabetes-induced microvascular liabilities.

Embryonic cardiomyocyte expression of endothelial genes

Vertebrate precardiac mesoderm contains cells destined to become cardiomyocyte or endothelial cells. To determine the stability of these phenotypes freshly isolated embryonic day (E) 2.5-E6 chicken hearts were immunostained for myosin heavy chain (MyHC) to identify cardiomyocytes, and von Willebrand factor (vWF) and Flk-1 to identify endothelial cells. At E2.5-E3, 90% of cells express only MyHC and 6% express only vWF/Flk-1. However, 2% MyHC+ cells in E2.5-E3 hearts and 0.3% in E4-E6 hearts, also express vWF/Flk-1; and when cultured 3 days, >40% of the MyHC+ cells express vWF/Flk-1, but they do not express Vezf1, vascular endothelial cadherin, or Tie2. Thus, only a subset of endothelial genes are induced in cultured cardiomyocytes. While the subsequent developmental fate of embryonic heart cells exhibiting a vWF+/MyHC+ phenotype is unknown, analysis of this phenotype may provide information pertinent to mechanisms of cell phenotype stability, cellular transdifferentiation, and induction of stable cell types from embryonic stem cells.

Transcriptional regulators of angiogenesis

Angiogenesis, the process by which new blood vessels develop from a pre-existing vascular network, is essential for normal development and in certain physiological states. Inadequate or excessive angiogenesis has been incriminated in a number of pathologic states. For example, vaso-occlusive disease arising from atherosclerosis can lead to ischemia, a situation in which enhanced angiogenesis would be beneficial. Conversely, overzealous angiogenesis can contribute to tumor development and in this case inhibition of angiogenesis is desirable. Thus, strategies to induce or inhibit angiogenesis are of considerable therapeutic interest.

Dosage-dependent requirement for mouse Vezf1 in vascular system development

Vezf1 is an early development gene that encodes a zinc finger transcription factor. In the developing embryo, Vezf1 is expressed in the yolk sac mesoderm and the endothelium of the developing vasculature and, in addition, in mesodermal and neuronal tissues. Targeted inactivation of Vezf1 in mice reveals that it acts in a closely regulated, dose-dependent fashion on the development of the blood vascular and lymphatic system. Homozygous mutant embryos display vascular remodeling defects and loss of vascular integrity leading to localized hemorrhaging. Ultrastructural analysis shows defective endothelial cell adhesion and tight junction formation in the mutant vessels. Moreover, in heterozygous embryos, haploinsufficiency is observed that is characterized by lymphatic hypervascularization associated with hemorrhaging and edema in the jugular region; a phenotype reminiscent of the human congenital lymphatic malformation syndrome cystic hygroma.

Shb promotes blood vessel formation in embryoid bodies by augmenting vascular endothelial growth factor receptor-2 and platelet-derived growth factor receptor-β signaling

The mechanisms controlling blood vessel formation during early embryonal development have only partly been elucidated. Shb is an adaptor protein previously implicated in the angiogenic response to vascular endothelial growth factor (VEGF). To elucidate a possible role of Shb in embryonic vascular development, wild-type and SH2 domain mutated (R522K) Shb were overexpressed in murine embryonic stem (ES) cells. Embryoid bodies (EBs) differentiating from Shb-overexpressing ES cells in vitro were stained for CD31 or VEGFR-2 to visualize the formation of vascular structures. We found that Shb promotes the outgrowth of blood vessels in EBs both in the absence and presence of growth factors. This response may be the consequence of an increased number of VEGFR-2 positive cells at an early stage of EB development, a finding corroborated by both immunostaining and real-time RT-PCR. In addition, Shb overexpression upregulated the expression of PDGFR-beta, CD31, CD41 and Tal1. Cells co-expressing VEGFR-2 and PDGFR-beta were commonly observed when Shb was overexpressed and inhibition of PDGF-BB signaling reduced the amount of VEGFR-2 mRNA under these conditions. EBs expressing the Shb R522K-mutant did not form vascular structures. Microarray analysis of VEGFR-2/CD31 positive cells after 6 days of differentiation revealed numerous changes of expression of genes relating to an endothelial/hematopoietic phenotype in response to Shb overexpression. The findings suggest that Shb may play a crucial role during early ES cell differentiation to vascular structures by transducing VEGFR-2 and PDGFR-beta signals.

Endothelial Cell Gene Regulation

Endothelial cells (ECs) display phenotypic heterogeneity. Endothelial cell heterogeneity is mediated, at least in part, by site-specific and time-dependent differences in gene transcription. The goal of this review is to provide a conceptual framework for approaching EC gene regulation in the adult vasculature. We summarize data from cell culture studies that provide insight into the transcription factors involved in mediating gene expression in ECs. Next, we review the results of in vivo studies relating to gene regulation in the intact endothelium. Finally, we draw on both the in vitro and in vivo results to propose a model of gene regulation that emphasizes the importance of the extracellular environment in controlling site- and time-specific vascular gene expression.

Molecular determinants of NOTCH4 transcription in vascular endothelium

The process whereby the primitive vascular network develops into the mature vasculature, known as angiogenic vascular remodeling, is controlled by the Notch signaling pathway. Of the two mammalian Notch receptors expressed in vascular endothelium, Notch1 is broadly expressed in diverse cell types, whereas Notch4 is preferentially expressed in endothelial cells. As mechanisms that confer Notch4 expression were unknown, we investigated how NOTCH4 transcription is regulated in human endothelial cells and in transgenic mice. The NOTCH4 promoter and the 5' portion of NOTCH4 assembled into an endothelial cell-specific histone modification pattern. Analysis of NOTCH4 primary transcripts in human umbilical vein endothelial cells by RNA fluorescence in situ hybridization revealed that 36% of the cells transcribed one or both NOTCH4 alleles. The NOTCH4 promoter was sufficient to confer endothelial cell-specific transcription in transfection assays, but intron 1 or upstream sequences were required for expression in the vasculature of transgenic mouse embryos. Cell-type-specific activator protein 1 (AP-1) complexes occupied NOTCH4 chromatin and conferred endothelial cell-specific transcription. Vascular angiogenic factors activated AP-1 and reprogrammed the endogenous NOTCH4 gene in HeLa cells from a repressed to a transcriptionally active state. These results reveal an AP-1-Notch4 pathway, which we propose to be crucial for transducing angiogenic signals and to be deregulated upon aberrant signal transduction in cancer.

Egfl7, a novel epidermal growth factor-domain gene expressed in endothelial cells

We report the cloning and characterization of a novel epidermal growth factor (EGF) domain gene that was identified in a retroviral gene entrapment screen and is expressed in endothelial cells. This gene encodes a protein of 278 amino acids with an amino-terminal signal peptide and two centrally located EGF-like domains. We have named this novel gene in accordance with the guidelines of the Mouse Genome Informatics group Egfl7, for EGF-like domain 7. Egfl7 mRNA is expressed in highly vascularized adult tissues such as the lung, heart, uterus, and ovary. In addition, Egfl7 is expressed early during mouse embryogenesis and in undifferentiated murine embryonic stem cells. The analysis of Egfl7 expression in embryonic day 9.5 embryos by in situ hybridization indicates that Egfl7 is expressed in vascular structures in both the embryo proper and the yolk sac and at sites of mesodermal precursors of angioblasts. Within the cell, EGFL7 protein is localized to the endoplasmic reticulum and Golgi apparatus, suggesting that the protein is targeted for secretion. Indeed, recombinant EGFL7 is readily detectable in the supernatant media of transiently transfected HEK293 cells. We also report the identification of an Egfl7 paralog, Egfl8, and show that EGFL8 protein shares similar domains and molecular weight with EGFL7.

Serial analysis of gene expression in sinusoidal endothelial cells from normal and injured mouse liver

Here we describe gene expression profiles of mouse liver sinusoidal endothelial cells (LSECs) revealed by serial analysis of gene expression (SAGE). We prepared SAGE libraries of LSECs from normal and injured liver by CCl(4) administration, and we obtained 32,867 tags from normal and 37,493 tags from injured liver, representing 6011 unique transcripts. CCl(4) administration upregulated several genes related to cell growth and differentiation (Cdkn1a, Irf1, Il4ra, etc.), whereas it downregulated genes related to cell growth or protein transport (Kdr, Igfbp4, Ap1b1, etc.). To identify genes preferentially expressed in LSEC, we compared our SAGE libraries with 77 publicly available libraries generated from various mouse tissues and cell lines. We identified 23 genes, including Stab2 and uncharacterized genes, as possible markers for LSEC, which will be useful to analyze the specific role for LSECs in normal as well as regenerating liver.

Hematopoietic stem cell repopulating ability can be maintained in vitro by some primary endothelial cells

OBJECTIVE

Murine hematopoietic stem cells (HSC) reside primarily in bone marrow but freely circulate throughout the systemic circulation with retention of transplantable hematopoietic repopulating ability. The mechanisms maintaining HSC potential during systemic circulation remain elusive. We hypothesized that vascular endothelial cells (EC) play an important role in maintaining circulating HSC repopulating ability.

METHODS

Using Tie2-green fluorescence protein transgenic mice, we have isolated primary EC populations derived from several nonhematopoietic organs and cocultured bone marrow Sca1+c-Kit+lin- cells for 7 days in the presence or absence of growth factors.

RESULTS

All cocultures promoted the growth of hematopoietic progenitor cells at day 7 of coculture in the presence of added growth factors. Compared to fresh sorted cells, brain and heart EC monolayers significantly increased, lung and liver EC monolayers maintained, and kidney EC monolayer markedly decreased the number of colony-forming unit-spleen day-8 colonies in the 7-day cocultures. HSC competitive repopulating unit activity was maintained during the heart and liver EC 7-day cocultures but was lost in the kidney EC coculture in vitro.

CONCLUSION

These results demonstrate that some but not all primary EC isolated from nonhematopoietic organs support HSC function ex vivo.

Gene-trap expression screening to identify endothelial-specific genes

The endothelial cell is a key cellular component for blood vessel formation. Many signaling receptors expressed in endothelial cells play critical roles in vascular development during embryogenesis. However, downstream response genes required for vascular differentiation are still not clearly identified. Here we describe the development of a protocol for gene-trap expression screening in embryonic stem (ES) cells for endothelial-specific genes. ES cells were differentiated into endothelial cells on an OP9 feeder cell layer in 96-well plates. In a pilot screen, 5 gene-trapped ES cell lines showed an up-regulated expression of the gene trap lacZ reporter out of 864 ES clones screened. One of the trapped genes was endoglin, an endothelial-specific transforming growth factor-beta type III receptor, and another was ASPP1, a p53-binding protein. In vivo expression analysis of the lacZ reporter confirmed that both genes are specifically expressed in endothelial cells during early mouse embryogenesis. Gene-trap expression screening can thus be used to identify early endothelial-specific genes and analyze their function in mice.

p68RacGAP Is a Novel GTPase-activating Protein That Interacts with Vascular Endothelial Zinc Finger-1 and Modulates Endothelial Cell Capillary Formation

The endothelium is required for maintenance of vascular integrity and homeostasis during vascular development and in adulthood. However, little is known about the coordinated interplay between transcription factors and signaling molecules that regulate endothelial cell-dependent transcriptional events. Vascular endothelial zinc finger-1 (Vezf1) is a zinc finger-containing transcription factor that is specifically expressed within the endothelium during vascular development. We have previously shown that Vezf1 potently activates transcription of the endothelin-1 promoter. We now report the identification of p68RacGAP, a novel Vezf1-interacting 68-kDa RhoGAP domain-containing protein. p68RacGAP mRNA is highly expressed in vascular endothelial cells by Northern blot analysis, and immunohistochemical staining of adult mouse tissues identified p68RacGAP in endothelial cells, vascular smooth muscle cells, and epithelial cells in vivo. Rac1 and Vezf1 both bind avidly to p68RacGAP, suggesting that p68RacGAP is not only a GTPase-activating protein for Rac1 but that p68RacGAP may also be part of the protein complex that binds to and modulates Vezf1 transcriptional activity. Functionally p68RacGAP specifically activates the GTPase activity of Rac1 in vivo but not Cdc42 or RhoA. In addition, p68RacGAP potently inhibits Vezf1/DB1-mediated transcriptional activation of the human endothelin-1 promoter and modulates endothelial cell capillary tube formation. Taken together, these data suggest that p68RacGAP is a multifunctional regulatory protein that has a Rac1-specific GTPase-activating activity, regulates transcriptional activity of the endothelin-1 promoter, and is involved in the signal transduction pathway that regulates endothelial cell capillary tube formation during angiogenesis.

Vascular endothelial zinc finger 1 is involved in the regulation of angiogenesis: possible contribution of stathmin/OP18 as a downstream target gene

OBJECTIVE

Vascular endothelial zinc finger 1 (Vezf1) is a recently identified zinc finger transcription factor that is expressed in endothelial cells (ECs) during vascular development in mouse embryo. Here, we present that Vezf1 was expressed in ECs at the site of postnatal angiogenesis. We therefore examined whether Vezf1 was involved in the regulation of angiogenesis.

METHODS AND RESULTS

The specific downregulation of Vezf1 by antisense oligodeoxynucleotide (AS-ODN) significantly inhibited the proliferation, migration, and network formation of cultured ECs as well as angiogenesis in vivo. Vezf1 AS-ODN downregulated the expression of stathmin/oncoprotein18 (OP18), a microtubule-destabilizing protein, in ECs, whereas transient transfection of Vezf1 cDNA increased the expression of stathmin/OP18 in ECs. To explore the relationship between Vezf1 and stathmin/OP18, we specifically downregulated stathmin/OP18. We found that stathmin/OP18 AS-ODN inhibited the proliferation, migration, and network formation of ECs as Vezf1 AS-ODN did. Moreover, Vezf1 AS-ODN decreased G2/M population of ECs and increased apoptosis, which reproduced the characteristic feature of stathmin/OP18 inhibition.

CONCLUSIONS

These results suggest that Vezf1 is involved in the regulation of angiogenesis, at least in part, through the expression of stathmin/OP18 in ECs.

VE-statin, an endothelial repressor of smooth muscle cell migration

The recruitment and proliferation of smooth muscle cells and pericytes are two key events for the stabilization of newly formed capillaries during angiogenesis and, when out of control in the adult, are the main causes of arteriosclerosis. We have identified a novel gene, named VE-statin for vascular endothelial-statin, which is expressed specifically by endothelial cells of the developing mouse embryo and in the adult, and in early endothelial progenitors. The mouse and human VE-statin genes have been located on chromosome 2 and 9, respectively, they span >10 kbp and are transcribed in two major variants arising from independent initiation sites. The VE-statin transcripts code for a unique protein of 30 kDa that contains a signal peptide and two epidermal growth factor (EGF)-like modules. VE-statin is found in the cellular endoplasmic reticulum and secreted in the cell supernatant. Secreted VE-statin inhibits platelet-derived growth factor (PDGF)-BB-induced smooth muscle cell migration, but has no effects on endothelial cell migration. VE-statin is the first identified inhibitor of mural cell migration specifically produced by endothelial cells.

Primary endothelial cells isolated from the yolk sac and para-aortic splanchnopleura support the expansion of adult marrow stem cells in vitro

The embryonic origin and development of hematopoietic and endothelial cells is highly interdependent. We hypothesized that primary endothelial cells from murine yolk sac and para-aortic splanchnopleura (P-Sp) may possess the capacity to expand hematopoietic stem cells (HSCs) and progenitor cells ex vivo. Using Tie2-GFP transgenic mice in combination with fluorochrome-conjugated monoclonal antibodies to vascular endothelial growth factor receptor-2 (Flk1) and CD41, we have successfully isolated pure populations of primary endothelial cells from 9.5-days after coitus (dpc) yolk sac and P-Sp. Adult murine bone marrow Sca-1+c-Kit+lin- cells were cocultured with yolk sac or P-Sp Tie2-GFP+Flk-1+CD41- endothelial cell monolayers for 7 days and the total number of nonadherent cells increased 47- and 295-fold, respectively, and hematopoietic progenitor counts increased 9.4- and 11.4-fold, respectively. Both the yolk sac and P-Sp endothelial cell cocultures facilitated long-term (> 6 months) HSC competitive repopulating ability (2.8- to 9.8-fold increases, respectively). These data suggest that 9.5-dpc yolk sac- and P-Sp-derived primary Tie2-GFP+Flk-1+CD41- endothelial cells possess the capacity to expand adult bone marrow hematopoietic progenitor cell and HSC repopulating ability ex vivo.

Mouse matriptase-2: identification, characterization and comparative mRNA expression analysis with mouse hepsin in adult and embryonic tissues

We report the identification and characterization of mouse matriptase-2 (m-matriptase-2), an 811-amino-acid protein composed of an N-terminal cytoplasmic domain, a membrane-spanning domain, two CUB (complement protein subcomponents C1r/C1s, urchin embryonic growth factor and bone morphogenetic protein 1) domains, three LDLR (low-density-lipoprotein receptor class A) domains and a C-terminal serine-protease domain. All m-matriptase-2 protein domain boundaries corresponded with intron/exon junctions of the encoding gene, which spans approx. 29 kb and comprises 18 exons. Matriptase-2 is highly conserved in human, mouse and rat, with the rat matriptase-2 gene ( r-maltriptase-2 ) predicted to encode transmembrane and soluble isoforms. Western-blot analysis indicated that m-matriptase-2 migrates close to its theoretical molecular mass of 91 kDa, and immunofluorescence analysis was consistent with the proposed surface membrane localization of this protein. Reverse-transcription PCR and in-situ -hybridization analysis indicated that m-matriptase-2 expression overlaps with the distribution of mouse hepsin (m-hepsin, a cell-surface serine protease identified in hepatoma cells) in adult tissues and during embryonic development. In adult tissues both are expressed at highest levels in liver, kidney and uterus. During embryogenesis m-matriptase-2 expression peaked between days 12.5 and 15.5. m-hepsin expression was biphasic, with peaks at day 7.5 to 8.5 and again between days 12.5 and 15.5. In situ hybridization of embryonic tissues indicated abundant expression of both m-matriptase-2 and m-hepsin in the developing liver and at lower levels in developing pharyngo-tympanic tubes. While m-hepsin was detected in the residual embryonic yolk sac and with lower intensity in lung, heart, gastrointestinal tract, developing kidney tubules and epithelium of the oral cavity, m-matriptase-2 was absent in these tissues, but strongly expressed within the nasal cavity by olfactory epithelial cells. Mechanistic insight into the potential role of this new transmembrane serine protease is provided by its novel expression profile in embryonic and adult mouse.

HoxB5 is an upstream transcriptional switch for differentiation of the vascular endothelium from precursor cells

Endothelial cells differentiate from mesoderm-derived precursors to initiate the earliest events in vascular development. Although the signaling events that regulate the successive steps of vascular development are known in some detail, the transcriptional processes that regulate the first steps in vasculogenesis are not well defined. We have studied the regulatory mechanisms of flk1 expression as a model to understand the upstream events in endothelial cell differentiation, since flk1 is the earliest marker of endothelial precursors. Using a variety of biochemical approaches, we identified a cis-acting element in the first intron of the flk1 gene that is required for endothelium-dependent expression in transgenic reporter gene assays. Using the yeast one-hybrid system, we identified HoxB5 as the transcription factor that binds this cis-acting element, the HoxB5-binding element (HBE). HoxB5 mRNA colocalized with flk1 expression in differentiating embryoid bodies, and HoxB5 potently transactivated the flk1 promoter in an HBE-dependent fashion in transient-transfection assays. Overexpression of HoxB5 led to expansion of flk1(+) angioblasts in differentiating embryoid bodies and increased the number of PECAM (platelet-endothelial cell adhesion molecule)-positive primitive blood vessels. HoxB5 is necessary and sufficient to activate the cell-intrinsic events that regulate the differentiation of angioblasts and mature endothelial cells from their mesoderm-derived precursors.

Evaluation of cadmium-induced transcriptome alterations by three color cDNA labeling microarray analysis on a T-cell line

Beside heavy metals, cadmium (Cd(2+)) is a ubiquitous toxic metal with a well established apoptotic and genotoxic effect, chronic exposure of which has been involved in a variety of pathological conditions. In the present study, we investigated by 1455 genes cDNA microarrays the toxic and apoptotic effect of Cd(2+), on the T-cell line CCRF-CEM, applying a three laser differential analysis, on the same microarray slide. The cells were cultured for 6 and 24 h in the absence (control) or presence of Cd(2+) (10 or 20 microM), RNAs were extracted and the produced cDNAs were labeled with rhodamine derivatives fluorescent dyes. A microarray slide was simultaneously hybridized by the labeled cDNAs and analyzed. We found that, in relation to control, treatment of the cells for 6 h with 10 and 20 microM Cd(2+), induces up-regulation in 20 and 34 genes, respectively. Treatment for 24 h with 10 and 20 microM Cd(2+) induces up-regulation in 22 and 84 genes, respectively. Twenty-eight genes were found down-regulated only after treatment for 24 h with Cd(2+) 10 microM. These data suggest that Cd(2+) produces a time- and dose-dependent molecular cascade, induces disturbances in different subcellular compartments, influencing thereafter the normal cellular functions, the differentiation process, the malignant transformation and the cell death.

Insufficient VEGFA activity in yolk sac endoderm compromises haematopoietic and endothelial differentiation

Vascular endothelial growth factor A (VEGFA) plays a pivotal role in the first steps of endothelial and haematopoietic development in the yolk sac, as well as in the establishment of the cardiovascular system of the embryo. At the onset of gastrulation, VEGFA is primarily expressed in the yolk sac visceral endoderm and in the yolk sac mesothelium. We report the generation and analysis of a Vegf hypomorphic allele, Vegflo. Animals heterozygous for the targeted mutation are viable. Homozygous embryos, however, die at 9.0 dpc because of severe abnormalities in the yolk sac vasculature and deficiencies in the development of the dorsal aortae. We find that providing ‘Vegf wild-type’ visceral endoderm to the hypomorphic embryos restores normal blood and endothelial differentiation in the yolk sac, but does not rescue the phenotype in the embryo proper. In the opposite situation, however, when Vegf hypomorphic visceral endoderm is provided to a wild-type embryo, the ‘Vegf wild-type’ yolk sac mesoderm is not sufficient to support proper vessel formation and haematopoietic differentiation in this extra-embryonic membrane. These findings demonstrate that VEGFA expression in the visceral endoderm is absolutely required for the normal expansion and organisation of both the endothelial and haematopoietic lineages in the early sites of vessel and blood formation. However, normal VEGFA expression in the yolk sac mesoderm alone is not sufficient for supporting the proper development of the early vascular and haematopoietic system.

Vezf1/DB1 is an endothelial cell-specific transcription factor that regulates expression of the endothelin-1 promoter

Coordinated gene regulation within the vascular endothelium is required for normal cardiovascular patterning during development and for vascular homeostasis during adulthood, yet little is known about the mechanisms that regulate endothelial transcriptional events. Vascular endothelial zinc finger 1 (Vezf1)/DB1 is a recently identified zinc finger-containing protein that is expressed specifically within endothelial cells during development. In this report, we demonstrate that Vezf1/DB1 is a nuclear localizing protein that potently and specifically activates transcription mediated by the human endothelin-1 promoter, in a Tax-independent manner, in transient transfection assays. Using a combination of deletion mutagenesis and electrophoretic mobility shift assays, a novel Vezf1/DB1-responsive element was localized to a 6-base pair (bp) motif, ACCCCC, located 47 bp upstream of the endothelin-1 transcription start site. Recombinant Vezf1/DB1 also bound to this sequence, and a 2-bp mutation in this element abolished Vezf1/DB1 responsiveness by the endothelin-1 promoter. Vezf1/DB1 could be identified with a specific antibody in nuclear complexes from endothelial cells that bound to this element. Regulation of endothelin-1 promoter activity by Vezf1/DB1 provides a mechanism for endothelin-1 expression in the vascular endothelium during development and to maintain vascular tone; Vezf1/DB1 itself is a candidate transcription factor for modifying endothelial cell phenotypes in order to appropriately assemble and maintain the cardiovascular system.

Gene profiling techniques and their application in angiogenesis and vascular development

The analysis of gene expression in specific tissues and physiological processes has evolved over the last 20 years from the painstaking identification of selected genes to the relatively efficient and open-ended surveying of potentially all genes expressed in a tissue. Current art for gene discovery includes the use of large-scale arrays of cDNA sequences or oligonucleotides, and molecular 'tagging' techniques such as GeneCalling and SAGE. Common to each of these techniques is a reliance on the increasingly comprehensive databases of human and mouse EST and full-length gene sequences. Early efforts to characterize candidate genes were limited by their narrow scope, while current efforts are confounded by the enormous volume of data returned. Sophisticated software tools are an integral part of the analysis, helping to organize information into coherent groups with temporal or functional similarity. These techniques, in conjunction with the continued analysis of human genetic syndromes, transgenic, and knockout mice, have driven genetic analysis of angiogenesis and vascular development from describing which individual genes are involved to defining the outlines of regulatory networks.

Transcriptional regulation of vascular development

Vascular development is a highly organized sequence of events that requires the correct spatial and temporal expression of specific sets of genes leading to the development of a primary vascular network. The first step in this process is the differentiation of pluripotent stem cells into endothelial cells. This is followed by endothelial proliferation, migration, and eventual formation of endothelial tubes. Maturation of these primitive tubes into fully developed blood vessels requires the recruitment of surrounding pericytes and their differentiation into vascular smooth muscle cells. Many of the events that occur during vasculogenesis are recapitulated during angiogenesis. Transcription factors have been shown to serve as master switches for regulating a number of developmental processes. Using a candidate gene approach, the genomic regulatory regions required to direct vascular-specific gene expression of several receptor tyrosine kinases that are critical for vasculogenesis have been characterized and some of the transcription factors that are involved in the regulation of these genes have recently been identified. Many of these factors are also involved in the regulation of hematopoiesis and may have overlapping functions in determining hematopoietic and endothelial differentiation. Targeted disruption of other transcription factors that were not previously thought to be involved in vascular development have also been recently shown to play a role in blood vessel development. The purpose of this review is to provide an update on the progress that has been made in our understanding of the transcriptional regulation of vascular development over the past few years.