Dosage-dependent requirement for mouse Vezf1 in vascular system development

Functional variant at 19q13.3 confers nonsyndromic cleft palate susceptibility by regulating HIF3A

This study investigates the genetic factors associated with nonsyndromic cleft palate only (NSCPO) through a two-stage genome-wide association study (GWAS) and functional experiments. A total of 311 NSCPO cases and 1,136 controls were included, and we identified rs3826795 in HIF3A significantly associated with NSCPO risk (p = 4.27E-09). Functional assays showed that the A allele of rs3826795 reduced VEZF1 binding to the HIF3A promoter, thereby enhancing HIF3A expression. Additionally, we demonstrated that HIF3A significantly influenced cellular processes, including apoptosis, proliferation, and migration, in both in vitro and in vivo models. Pathway enrichment analysis indicated that HIF3A suppressed the GABAergic synapse pathway, which plays a crucial role in embryonic development. These findings provide valuable insights into the genetic mechanisms underlying NSCPO susceptibility and suggest potential targets for future therapeutic interventions.

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.

VEZF1, destabilized by STUB1, affects cellular growth and metastasis of hepatocellular carcinoma by transcriptionally regulating PAQR4

Hepatocellular carcinoma (HCC) is an aggressive solid malignancy, and recurrence and metastasis are major incentives contributing to its poor outcome. Vascular endothelial zinc finger 1 (VEZF1) has been recognized as an oncoprotein in certain types of cancer, but the expression pattern and regulatory mechanism in HCC remains unclear. This study focused on the functional effect and regulatory basis of VEZF1 in HCC. Microarray analysis identified the differentially expressed VEZF1 in HCC, and we validated its raised expression in HCC clinical samples. Artificial modulation of VEZF1 (knockdown and overexpression) was conducted to explore its role in HCC progression both in vitro and in vivo. It was shown that silencing of VEZF1 suppressed, whereas its overexpression promoted HCC cellular proliferation and metastasis abilities. Mechanistically, VEZF1 transcriptionally activated progestin and adipoQ receptor 4 (PAQR4) to accelerate HCC progression. Furthermore, VEZF1 is confirmed as a substrate of stress-inducible phosphoprotein 1 homology and U-box containing protein 1 (STUB1), and its stability is impacted by STUB1-mediated ubiquitination degradation. Conjointly, our work suggested that VEZF1, destabilized by STUB1, participates in HCC progression by regulating PAQR4. The STUB1/VEZF1/PAQR4 mechanism might provide novel insights on guiding early diagnosis and therapy in HCC patients.

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.

Fetal nuchal edema and developmental anomalies caused by gene mutations in mice

Fetal nuchal edema, a subcutaneous accumulation of extracellular fluid in the fetal neck, is detected as increased nuchal translucency (NT) by ultrasonography in the first trimester of pregnancy. It has been demonstrated that increased NT is associated with chromosomal anomalies and genetic syndromes accompanied with fetal malformations such as defective lymphatic vascular development, cardiac anomalies, anemia, and a wide range of other fetal anomalies. However, in many clinical cases of increased NT, causative genes, pathogenesis and prognosis have not been elucidated in humans. On the other hand, a large number of gene mutations have been reported to induce fetal nuchal edema in mouse models. Here, we review the relationship between the gene mutants causing fetal nuchal edema with defective lymphatic vascular development, cardiac anomalies, anemia and blood vascular endothelial barrier anomalies in mice. Moreover, we discuss how studies using gene mutant mouse models will be useful in developing diagnostic method and predicting prognosis.

Circ_0006768 upregulation attenuates oxygen-glucose deprivation/reoxygenation-induced human brain microvascular endothelial cell injuries by upregulating VEZF1 via miR-222-3p inhibition

Circular RNAs (circRNAs) have been widely implicated in multiple diseases, including ischemic stroke. This study aimed to explore the function and functional mechanism of circ_0006768 in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced brain injury models of ischemic stroke. Human brain microvascular endothelial cells (HBMECs) were induced by OGD/R to mimic ischemic stroke models in vitro. The expression of circ_0006768, microRNA-222-3p (miR-222-3p) and vascular endothelial zinc finger 1 (VEZF1) was detected by quantitative real-time PCR (qPCR). Cell viability, angiogenesis ability and cell migration were assessed by cell counting kit-8 (CCK-8) assay, tube formation assay and wound healing assay, respectively. The releases of pro-inflammatory factors were determined by commercial enzyme-linked immunosorbent assay (ELISA) kits. The protein levels of vascular endothelial growth factor A (VEGFA), N-cadherin and VEZF1 were detected by western blot. The putative relationship between miR-222-3p and circ_0006768 or VEZF1 was validated by dual-luciferase reporter assay, RNA Immunoprecipitation (RIP) assay and pull-down assay. Circ_0006768 was poorly expressed in ischemic stroke plasma and OGD/R-induced HBMECs. OGD/R inhibited cell viability, angiogenesis and cell migration and promoted the releases of pro-inflammatory factors, while circ_0006768 overexpression or miR-222-3p inhibition partially abolished the effects of OGD/R. MiR-222-3p was targeted by circ_0006768, and VEZF1 was a target of miR-222-3p. Circ_0006768 enriched the expression of VEZF1 via mediating miR-222-3p inhibition. Rescue experiments presented that the effects of circ_0006768 overexpression were reversed by miR-222-3p restoration or VEZF1 knockdown. Circ_0006768 overexpression attenuates OGD/R-induced HBMEC injuries by upregulating VEZF1 via miR-222-3p inhibition.

Regulation of breast cancer metastasis signaling by miRNAs

Despite the decline in death rate from breast cancer and recent advances in targeted therapies and combinations for the treatment of metastatic disease, metastatic breast cancer remains the second leading cause of cancer-associated death in U.S. women. The invasion-metastasis cascade involves a number of steps and multitudes of proteins and signaling molecules. The pathways include invasion, intravasation, circulation, extravasation, infiltration into a distant site to form a metastatic niche, and micrometastasis formation in a new environment. Each of these processes is regulated by changes in gene expression. Noncoding RNAs including microRNAs (miRNAs) are involved in breast cancer tumorigenesis, progression, and metastasis by post-transcriptional regulation of target gene expression. miRNAs can stimulate oncogenesis (oncomiRs), inhibit tumor growth (tumor suppressors or miRsupps), and regulate gene targets in metastasis (metastamiRs). The goal of this review is to summarize some of the key miRNAs that regulate genes and pathways involved in metastatic breast cancer with an emphasis on estrogen receptor α (ERα+) breast cancer. We reviewed the identity, regulation, human breast tumor expression, and reported prognostic significance of miRNAs that have been documented to directly target key genes in pathways, including epithelial-to-mesenchymal transition (EMT) contributing to the metastatic cascade. We critically evaluated the evidence for metastamiRs and their targets and miRNA regulation of metastasis suppressor genes in breast cancer progression and metastasis. It is clear that our understanding of miRNA regulation of targets in metastasis is incomplete.

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.

Increased Expression of miR-483-3p Impairs the Vascular Response to Injury in Type 2 Diabetes

Aggravated endothelial injury and impaired endothelial repair capacity contribute to the high cardiovascular risk in patients with type 2 diabetes (T2D), but the underlying mechanisms are still incompletely understood. Here we describe the functional role of a mature form of miRNA (miR) 483-3p, which limits endothelial repair capacity in patients with T2D. Expression of human (hsa)-miR-483-3p was higher in endothelial-supportive M2-type macrophages (M2MΦs) and in the aortic wall of patients with T2D than in control subjects without diabetes. Likewise, the murine (mmu)-miR-483* was higher in T2D than in nondiabetic murine carotid samples. Overexpression of miR-483-3p increased endothelial and macrophage apoptosis and impaired reendothelialization in vitro. The inhibition of hsa-miR-483-3p in human T2D M2MΦs transplanted to athymic nude mice (NMRI-Foxn1^ν/Foxn1^ν ) or systemic inhibition of mmu-miR-483* in B6.BKS(D)-Lepr^db /J diabetic mice rescued diabetes-associated impairment of reendothelialization in the murine carotid-injury model. We identified the endothelial transcription factor vascular endothelial zinc finger 1 (VEZF1) as a direct target of miR-483-3p. VEZF1 expression was reduced in aortae of diabetic mice and upregulated in diabetic murine aortae upon systemic inhibition of mmu-483*. The miRNA miR-483-3p is a critical regulator of endothelial integrity in patients with T2D and may represent a therapeutic target to rescue endothelial regeneration after injury in patients with T2D.

Characterization of Small Molecules Inhibiting the Pro-Angiogenic Activity of the Zinc Finger Transcription Factor Vezf1

Discovery of inhibitors for endothelial-related transcription factors can contribute to the development of anti-angiogenic therapies that treat various diseases, including cancer. The role of transcription factor Vezf1 in vascular development and regulation of angiogenesis has been defined by several earlier studies. Through construction of a computational model for Vezf1, work here has identified a novel small molecule drug capable of inhibiting Vezf1 from binding to its cognate DNA binding site. Using structure-based design and virtual screening of the NCI Diversity Compound Library, 12 shortlisted compounds were tested for their ability to interfere with the binding of Vezf1 to DNA using electrophoretic gel mobility shift assays. We identified one compound, T4, which has an IC50 of 20 μM. Using murine endothelial cells, MSS31, we tested the effect of T4 on endothelial cell viability and angiogenesis by using tube formation assay. Our data show that addition of T4 in cell culture medium does not affect cell viability at concentrations lower or equal to its IC 50 but strongly inhibits the network formation by MSS31 in the tube formation assays. Given its potential efficacy, this inhibitor has significant therapeutic potential in several human diseases.

Synergistic potential of fenvalerate and triadimefon on endocrine disruption and oxidative stress during rare minnow embryo development

Pyrethroids have been reported to interact synergistically when co-exposed with azoles fungicides in different organisms. In the present study, we investigated the mixture toxicity of fenvalerate (FEN) and triadimefon (TDF) toward embryos of Gobiocypris rarus after 96 h exposure. Results demonstrated that TDF enhanced the acute toxicity of FEN. Exposure to binary mixtures of FEN and TDF resulted in synergistic responses of endocrine disruption by inducing the transcripts of several genes including vtg, erα, erβ1, erβ2, cyp19a, cyp1a, cyp4, cyp11a, gnrh3, gnrhr1a, star, and dmrt1. Furthermore, FEN and TDF mixture increased the VTG level and aromatase activity in rare minnow embryos. FEN and TDF co-exposure also regulated the mRNA of vezf, hsp70, p53, gadd45α, induced the synthesis of ROS and activity of GST, suggesting the synergistic potential of oxidative stress induced by FEN and TDF co-exposure. The results indicated that binary mixtures of FEN and TDF could simultaneously induce endocrine disruption and oxidative stress in a synergistic manner during rare minnow embryo development.

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.

Inhibition of microRNA-495 Enhances Therapeutic Angiogenesis of Human Induced Pluripotent Stem Cells

Therapeutic angiogenesis has emerged as a promising strategy to regenerate the damaged blood vessels resulting from ischemic diseases such as myocardial infarction (MI). However, the functional integration of implanted endothelial cells (ECs) in infarcted heart remains challenging. We herein develop an EC generation approach by inhibiting microRNA-495 (miR-495) in human induced pluripotent stem cells (hiPSCs) and assess the angiogenic potential for MI treatment. The anti-angiogenic miR-495 belonging to Dlk1-Dio3 miR cluster was identified through expression profiling and computational analysis. Loss-of-function experiments for miR-495 were performed using a lentiviral transfer of antisense sequence in hiPSCs. The pluripotency of hiPSCs was not impacted by the genetic modification. Induced with differentiation medium, miR-495 inhibition enhanced the expression of EC genes of hiPSCs, as well as the yield of ECs. Newly derived ECs displayed prominent angiogenic characteristics including tube formation, cell migration, and proliferation. Mechanistically, miR-495 mediated the expression of endothelial or angiogenic genes by directly targeting vascular endothelial zinc finger 1. After transplantation in immunodeficient MI mice, the derived ECs significantly increased neovascularization in the infarcted heart, prevented functional worsening, and attenuated expansion of infarct size. The functional integration of the implanted ECs into coronary networks was also enhanced by inhibiting miR-495. miR-495 represents a new target not only for promoting EC generation from hiPSCs but also for enhancing angiogenesis and engraftment of hiPSC-derived ECs in ischemic heart.

Assessment of trifloxystrobin uptake kinetics, developmental toxicity and mRNA expression in rare minnow embryos

Trifloxystrobin (TFS) is the widely used strobilurin fungicide. However, little information is so far available regarding the uptake kinetics and developmental toxicity of TFS to fish. The present study was conducted to investigate the uptake kinetics, potential environment risk and toxicity of TFS on Gobiocypris rarus embryos. Results revealed that increased malformation, decreased body length and heart rate, affected spontaneous movement and swimming speed provide a gradual concentration-dependent manner; values of 144 h LC50 (median lethal concentration) and EC50 (median effective concentration) were 1.11 and 0.86 μg L(-1). Continuous exposure to TFS resulted in a steady accumulation with no evidence of elimination. Enzyme activities were significantly changed; reactive oxygen species and DNA damage were significantly induced after TFS treatment. Certain genes related to cell apoptosis (p53), metabolism (cyp1a), stress response (hsp70) and blood vessels (vezf1) development were all significantly up-regulated. This is the first study to define uptake kinetics and to focus on behavioral consequences, physiological changes and mRNA expression following TFS exposure in the early life stages of fish. Our results suggest that TFS is highly toxic to fish embryos.

Triazole-induced toxicity in developing rare minnow (Gobiocypris rarus) embryos

Using rare minnow (Gobiocypris rarus) at early-life stages as experimental models, the developmental toxicity of five widely used triazole fungicides (myclobutanil, fluconazole, flusilazole, triflumizole, and epoxiconazole) were investigated following exposure to 1-15 mg/L for 72 h. Meanwhile, morphological parameters (body length, body weight, and heart rate), enzyme activities (superoxide dismutase (SOD), glutathione S-transferase (GST), adenosine triphosphatase (ATPase), and acetyl cholinesterase (AChE)), and mRNA levels (hsp70, mstn, mt, apaf1, vezf1, and cyp1a) were also recorded following exposure to 0.2, 1.0, and 5.0 mg/L for 72 h. Results indicated that increased malformation and mortality, decreased body length, body weight, and heart rate provide a concentration-dependent pattern; values of 72 h LC50 (median lethal concentration) and EC50 (median effective concentration) ranged from 3 to 12 mg/L. Most importantly, the results of the present study suggest that even at the lowest concentration, 0.2 mg/L, five triazole fungicides also caused notable changes in enzyme activities and mRNA levels. Overall, the present study points out that those five triazole fungicides are highly toxic to the early development of G. rarus embryos. The information presented in this study will be helpful in better understanding the toxicity induced by triazole fungicides in fish embryos.

Toxic effects of triazophos on rare minnow (Gobiocypris rarus) embryos and larvae

Triazophos (TAP) has been widely used in agriculture for controlling insect pests and is a known organophosphorus pesticide. Due to TAP characteristics, such as high chemical and photochemical stability, its potential toxicity to aquatic organisms has gained great interest. To explore the potential developmental toxicity of TAP, Gobiocypris rarus embryos and larvae were exposed to various concentrations of TAP (0.1-15 mg L(-1)) until 72 h. Results showed that values of 72 h LC50 and EC50 were 7.44 and 5.60 mg L(-1) for embryos, 2.52 and 1.37 mg L(-1) for larvae. Increased malformation, decreased heart rate and body length provide a gradual concentration-dependent pattern. Enzyme activities and mRNA levels were significantly changed even at low concentration (0.05 mg L(-1) for embryos and 0.01 mg L(-(1) for larvae). Overall, the present study points out that TAP is likely a risk to the early development of G. rarus. The information presented in this study will be helpful in better understanding the toxicity induced by TAP in fish embryos and larvae.

RhoB controls coordination of adult angiogenesis and lymphangiogenesis following injury by regulating VEZF1-mediated transcription

Mechanisms governing the distinct temporal dynamics that characterize post-natal angiogenesis and lymphangiogenesis elicited by cutaneous wounds and inflammation remain unclear. RhoB, a stress-induced small GTPase, modulates cellular responses to growth factors, genotoxic stress and neoplastic transformation. Here we show, using RhoB null mice, that loss of RhoB decreases pathological angiogenesis in the ischaemic retina and reduces angiogenesis in response to cutaneous wounding, but enhances lymphangiogenesis following both dermal wounding and inflammatory challenge. We link these unique and opposing roles of RhoB in blood versus lymphatic vasculatures to the RhoB-mediated differential regulation of sprouting and proliferation in primary human blood versus lymphatic endothelial cells. We demonstrate that nuclear RhoB-GTP controls expression of distinct gene sets in each endothelial lineage by regulating VEZF1-mediated transcription. Finally, we identify a small-molecule inhibitor of VEZF1-DNA interaction that recapitulates RhoB loss in ischaemic retinopathy. Our findings establish the first intra-endothelial molecular pathway governing the phased response of angiogenesis and lymphangiogenesis following injury.

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.

Development of the mammalian lymphatic vasculature

The two vascular systems of our body are the blood and lymphatic vasculature. Our understanding of the cellular and molecular processes controlling the development of the lymphatic vasculature has progressed significantly in the last decade. In mammals, this is a stepwise process that starts in the embryonic veins, where lymphatic EC (LEC) progenitors are initially specified. The differentiation and maturation of these progenitors continues as they bud from the veins to produce scattered primitive lymph sacs, from which most of the lymphatic vasculature is derived. Here, we summarize our current understanding of the key steps leading to the formation of a functional lymphatic vasculature.

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.

Genome-wide profiling of in vivo LPS-responsive genes in splenic myeloid cells

Lipopolysaccharide (LPS), the major causative agent of bacterial sepsis, has been used by many laboratories in genome-wide expression profiling of the LPS response. However, these studies have predominantly used in vitro cultured macrophages (Macs), which may not accurately reflect the LPS response of these innate immune cells in vivo. To overcome this limitation and to identify inflammatory genes in vivo, we have profiled genome-wide expression patterns in non-lymphoid, splenic myeloid cells extracted directly from LPS-treated mice. Genes encoding factors known to be involved in mediating or regulating inflammatory processes, such as cytokines and chemokines, as well as many genes whose immunological functions are not well known, were strongly induced by LPS after 3 h or 8 h of treatment. Most of the highly LPS-responsive genes that we randomly selected from the microarray data were independently confirmed by quantitative RT-PCR, implying that our microarray data are quite reliable. When our in vivo data were compared to previously reported microarray data for in vitro LPS-treated Macs, a significant proportion (∼20%) of the in vivo LPS-responsive genes defined in this study were specific to cells exposed to LPS in vivo, but a larger proportion of them (∼60%) were influenced by LPS in both in vitro and in vivo settings. This result indicates that our in vivo LPS-responsive gene set includes not only previously identified in vitro LPS-responsive genes but also novel LPS-responsive genes. Both types of genes would be a valuable resource in the future for understanding inflammatory responses in vivo.

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.

Endothelial cells require related transcription enhancer factor-1 for cell-cell connections through the induction of gap junction proteins

OBJECTIVE

Capillary network formation represents a specialized endothelial cell function and is a prerequisite to establish a continuous vessel lumen. Formation of endothelial cell connections that form the vascular structure is regulated, at least in part, at the transcriptional level. We report here that related transcription enhancer factor-1 (RTEF-1) plays an important role in vascular structure formation.

METHODS AND RESULTS

Knockdown of RTEF-1 by small interfering RNA or blockage of RTEF-1 function by the transcription enhancer activators domain decreased endothelial connections in a Matrigel assay, whereas overexpression of RTEF-1 in endothelial cells resulted in a significant increase in cell connections and aggregation. In a model of oxygen-induced retinopathy, endothelial-specific RTEF-1 overexpressing mice had enhanced angiogenic sprouting and vascular structure remodeling, resulting in the formation of a denser and more highly interconnected superficial capillary plexus. Mechanistic studies revealed that RTEF-1 induced the expression of functional gap junction proteins including connexin 43, connexin 40, and connexin 37. Blocking connexin 43 function inhibited RTEF-1-induced endothelial cell connections and aggregation.

CONCLUSIONS

These findings provide novel insights into the transcriptional control of endothelial function in the coordination of cell-cell connections.

Chromatin domains, insulators, and the regulation of gene expression

The DNA sequence elements called insulators have two basic kinds of properties. Barrier elements block the propagation of heterochromatic structures into adjacent euchromatin. Enhancer blocking elements interfere with interaction between an enhancer and promoter when placed between them. We have dissected a compound insulator element found at the 5' end of the chicken β-globin locus, which possesses both activities. Barrier insulation is mediated by two kinds of DNA binding proteins: USF1/USF2, a heterodimer which recruits multiple enzyme complexes capable of marking histone on adjacent nucleosomes with 'activating' marks, and Vezf1, which protects against DNA methylation. We have found that the heterochromatic region upstream of the insulator element is maintained in its silent state by a dicer-dependent mechanism, suggesting a mechanism for Vezf1 function in the insulator. Enhancer blocking function in the β-globin insulator element is conferred by a binding site for CTCF. Consistent with this property, CTCF binding was found some years ago to be essential for imprinted expression at the Igf2/H19 locus. Work in many laboratories has since demonstrated that CTCF helps stabilize long-range interactions in the nucleus. We have recently shown that in the case of the human insulin locus such an interaction, over a distance of ~300kb, can result in stimulation of a target gene which itself is important for insulin secretion. This article is part of a Special Issue entitled: Chromatin in time and space.

Lymphatic vascular morphogenesis in development, physiology, and disease

The lymphatic vasculature constitutes a highly specialized part of the vascular system that is essential for the maintenance of interstitial fluid balance, uptake of dietary fat, and immune response. Recently, there has been an increased awareness of the importance of lymphatic vessels in many common pathological conditions, such as tumor cell dissemination and chronic inflammation. Studies of embryonic development and genetically engineered animal models coupled with the discovery of mutations underlying human lymphedema syndromes have contributed to our understanding of mechanisms regulating normal and pathological lymphatic morphogenesis. It is now crucial to use this knowledge for the development of novel therapies for human diseases.

Regulation of mammalian Notch signaling and embryonic development by the protein O-glucosyltransferase Rumi

Protein O-glucosylation is a conserved post-translational modification that occurs on epidermal growth factor-like (EGF) repeats harboring the C(1)-X-S-X-P-C(2) consensus sequence. The Drosophila protein O-glucosyltransferase (Poglut) Rumi regulates Notch signaling, but the contribution of protein O-glucosylation to mammalian Notch signaling and embryonic development is not known. Here, we show that mouse Rumi encodes a Poglut, and that Rumi(-/-) mouse embryos die before embryonic day 9.5 with posterior axis truncation and severe defects in neural tube development, somitogenesis, cardiogenesis and vascular remodeling. Rumi knockdown in mouse cell lines results in cellular and molecular phenotypes of loss of Notch signaling without affecting Notch ligand binding. Biochemical, cell culture and cross-species transgenic experiments indicate that a decrease in Rumi levels results in reduced O-glucosylation of Notch EGF repeats, and that the enzymatic activity of Rumi is key to its regulatory role in the Notch pathway. Genetic interaction studies show that removing one copy of Rumi in a Jag1(+/-) (jagged 1) background results in severe bile duct morphogenesis defects. Altogether, our data indicate that addition of O-glucose to EGF repeats is essential for mouse embryonic development and Notch signaling, and that Jag1-induced signaling is sensitive to the gene dosage of the protein O-glucosyltransferase Rumi. Given that Rumi(-/-) embryos show more severe phenotypes compared to those displayed by other global regulators of canonical Notch signaling, Rumi is likely to have additional important targets during mammalian development.

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.

Abnormal embryonic lymphatic vessel development in Tie1 hypomorphic mice

Tie1 is an endothelial receptor tyrosine kinase that is essential for development and maintenance of the vascular system; however, the role of Tie1 in development of the lymphatic vasculature is unknown. To address this question, we first documented that Tie1 is expressed at the earliest stages of lymphangiogenesis in Prox1-positive venous lymphatic endothelial cell (LEC) progenitors. LEC Tie1 expression is maintained throughout embryonic development and persists in postnatal mice. We then generated two lines of Tie1 mutant mice: a hypomorphic allele, which has reduced expression of Tie1, and a conditional allele. Reduction of Tie1 levels resulted in abnormal lymphatic patterning and in dilated and disorganized lymphatic vessels in all tissues examined and in impaired lymphatic drainage in embryonic skin. Homozygous hypomorphic mice also exhibited abnormally dilated jugular lymphatic vessels due to increased production of Prox1-positive LECs during initial lymphangiogenesis, indicating that Tie1 is required for the early stages of normal lymphangiogenesis. During later stages of lymphatic development, we observed an increase in LEC apoptosis in the hypomorphic embryos after mid-gestation that was associated with abnormal regression of the lymphatic vasculature. Therefore, Tie1 is required for early LEC proliferation and subsequent survival of developing LECs. The severity of the phenotypes observed correlated with the expression levels of Tie1, confirming a dosage dependence for Tie1 in LEC integrity and survival. No defects were observed in the arterial or venous vasculature. These results suggest that the developing lymphatic vasculature is particularly sensitive to alterations in Tie1 expression.

Induced endothelial differentiation of cells from a murine embryonic mesenchymal cell line C3H/10T1/2 by angiogenic factors in vitro

A murine embryonic mesenchymal cell line C3H/10T1/2 possesses the potential to differentiate into multiple cell phenotypes and has been recognized as multipotent mesenchymal stem cells, but no in vitro model of its endothelial differentiation has been established and the effect of angiogenic factors on the differentiation is unknown. The aim of the present study was to evaluate the role of angiogenic factors in inducing endothelial differentiation of C3H/10T1/2 cells in vitro. C3H/10T1/2 cells were treated with angiogenic factors, VEGF (10 ng/mL) and bFGF (5 ng/mL). At specified time points, cells were subjected to morphological study, immunofluorescence staining, RT-PCR, LDL-uptake tests and 3-D culture for the examination of the structural and functional characteristics of endothelial cells. Classic cobblestone-like growth pattern appeared at 6 day of the induced differentiation. Immunofluorescence staining and RT-PCR analyses revealed that the induced cells exhibited endothelial cell-specific markers such as CD31, von Willebrand factor, Flk1, Flt1, VE-cadherin, Tie2, EphrinB2 and Vezf1 at 9 day. The induced C3H/10T1/2 cells exhibited functional characteristics of the mature endothelial phenotype, such as uptake of acetylated low-density lipoproteins (Ac-LDL) and formation of capillary-like structures in three-dimensional culture. At 9 day, Weibel-Palade bodies were observed under a transmission electron microscope. This study demonstrates, for the first time, endothelial differentiation of C3H/10T1/2 cells induced by angiogenic factors, VEGF and bFGF, and confirms the multipotential differentiation ability. This in vitro model is useful for investigating the molecular events in endothelial differentiation of mesenchymal stem cells.

Human synovial sarcoma proto-oncogene Syt is essential for early embryonic development through the regulation of cell migration

SYT-SSX protein, resulted from chromosomal translocation, causes synovial sarcoma, which is a malignant tumor accounting for 10% of soft tissue sarcoma. However, biological functions of SYT (synovial sarcoma translocation), also known as SS18, are largely unclear, whereas it has been proven that Syt-null mice die at early stages of embryonic development. Here, we generated Syt-deficient mice and confirmed the reported phenotypes, including growth retardation, open neural tube and haplo-insufficient lethality, and therefore, there is no doubt that Syt is essential for embryonic development. However, placental defects, described in the earlier report, were rarely seen in our mice and we frequently observed cardiac defect in Syt-deficient mice. As the mechanisms responsible for embryonic lethality seem to be complicate, we performed additional experiments. By using primary cultured embryonic fibroblasts, we showed that Syt(-/-) MEFs deregulate actin organization and suppressed cell migration. These observations suggest that Syt may contribute to the signaling pathway important for various cellular functions in vivo and in vitro, and we propose that Syt-deficient MEFs would be a powerful means to understand the biological roles of SYT in vitro.

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.

Molecular biology and pathology of lymphangiogenesis

The lymphatic vasculature is essential for the maintenance of tissue fluid balance, immune surveillance, and adsorption fatty acids in the gut. The lymphatic vessels are also crucially involved in the pathogenesis of diseases such as tumor metastasis, lymphedema, and various inflammatory conditions. Attempts to control or treat these diseases have drawn a lot of interest to lymphatic vascular research during the past few years. Recently, several markers specific for lymphatic endothelium and models for lymphatic vascular research have been characterized, enabling great technical progress in lymphatic vascular biology, and many critical regulators of lymphatic vessel growth have been identified. Despite these significant achievements, our understanding of the lymphatic vessel development and pathogenesis is still rather limited. Several key questions remain to be resolved, including the relative contributions of different pathways targeting lymphatic vasculature, the molecular and cellular processes of lymphatic maturation, and the detailed mechanisms of tumor metastasis via the lymphatic system.

Lymphatic vasculature: a molecular perspective

The lymphatic vasculature comprises an intricate network of vessels critical for fluid homeostasis, immune surveillance and fat absorption. Recent studies have provided insights into the developmental processes and molecular mechanisms controlling the formation and remodelling of the lymphatic vessels. These studies have further demonstrated the essential and active role of the lymphatic vessels in various pathological conditions and advanced our understanding of the progression of human diseases, such as inflammation and tumorigenesis. In the context of the latest exciting findings, we review here the current understanding of the mechanisms of lymphatic development and contribution of lymphatic vessels to pathological conditions.

Stimulation of endothelin-1 gene expression by insulin via phosphoinositide-3 kinase-glycogen synthase kinase-3beta signaling in endothelial cells

Insulin stimulates secretion of the potent vasoactive and mitogenic peptide endothelin-1 (ET-1) from endothelial cells. We sought to investigate whether phosphoinositide-3 kinase (PI3K)-dependent inactivation of glycogen synthase kinase-3beta (GSK3beta) by insulin leads to elevation of ET-1 gene expression in endothelial cells. Inhibition of GSK3beta activity by LiCl or siRNA technique mimicked insulin action to stimulate ET-1 gene expression. Luciferase reporter assay showed insulin stimulated-elevation of ET-1 promoter activity can be abolished by the PI3K inhibitor Wortmannin, but not by the mitogen activated protein kinase (MAPK) inhibitor PD-98059. To further investigate whether the transcription factor vascular endothelial zinc finger-1 (Vezf1) is involved in ET-1 regulation, site-mutated reporter plasmid was used in luciferase reporter assay. A 2-bp mutation in Vezf1 binding element abolished insulin-stimulated elevation of ET-1 promoter activity. Furthermore, siRNA inhibition of Vezf1 led to decline in the levels of ET-1 mRNA and ET-1 peptides. These observations indicate that PI3K-dependent inactivation of GSK3beta by insulin leads to upregulation of ET-1 gene expression and Vezf1 may be a target for ET-1 regulation by insulin. PI3K-GSK3beta signaling may be responsible for insulin stimulation of ET-1 production associated with insulin resistance and hyperinsulinemia.

A betaPix Pak2a signaling pathway regulates cerebral vascular stability in zebrafish

The vasculature tailors to the needs of different tissues and organs. Molecular, structural, and functional specializations are observed in different vascular beds, but few genetic models give insight into how these differences arise. We identify a unique cerebrovascular mutation in the zebrafish affecting the integrity of blood vessels supplying the brain. The zebrafish bubblehead (bbh) mutant exhibits hydrocephalus and severe cranial hemorrhage during early embryogenesis, whereas blood vessels in other regions of the embryo appear intact. Here we show that hemorrhages are associated with poor cerebral endothelial-mesenchymal contacts and an immature vascular pattern in the head. Positional cloning of bbh reveals a hypomorphic mutation in betaPix, a binding partner for the p21-activated kinase (Pak) and a guanine nucleotide exchange factor for Rac and Cdc42. betaPix is broadly expressed during embryonic development and is enriched in the brain and in large blood vessels. By knockdown of specific betaPix splice variants, we show that they play unique roles in embryonic vascular stabilization or hydrocephalus. Finally, we show that Pak2a signaling is downstream of betaPix. These data identify an essential in vivo role for betaPix and Pak2a during embryonic development and illuminate a previously unrecognized pathway specifically involved in cerebrovascular stabilization.

Novel lethal mouse mutants produced in balancer chromosome screens

Mutagenesis screens are a valuable method to identify genes that are required for normal development. Previous mouse mutagenesis screens for lethal mutations were targeted at specific time points or for developmental processes. Here we present the results of lethal mutant isolation from two mutagenesis screens that use balancer chromosomes. One screen was localized to mouse chromosome 4, between the STS markers D4Mit281 and D4Mit51. The second screen covered the region between Trp53 and Wnt3 on mouse chromosome 11. These screens identified all lethal mutations in the balancer regions, without bias towards any phenotype or stage of death. We have isolated 19 lethal lines on mouse chromosome 4, and 59 lethal lines on chromosome 11, many of which are distinct from previous mutants that map to these regions of the genome. We have characterized the mutant lines to determine the time of death, and performed a pair-wise complementation cross to determine if the mutations are allelic. Our data suggest that the majority of mouse lethal mutations die during mid-gestation, after uterine implantation, with a variety of defects in gastrulation, heart, neural tube, vascular, or placental development. This initial group of mutants provides a functional annotation of mouse chromosomes 4 and 11, and indicates that many novel developmental phenotypes can be quickly isolated in defined genomic intervals through balancer chromosome mutagenesis screens.