What guides early embryonic blood vessel formation?

Anatomy and development of the pectoral fin vascular network in the zebrafish

The pectoral fins of teleost fish are analogous structures to human forelimbs, and the developmental mechanisms directing their initial growth and patterning are conserved between fish and tetrapods. The forelimb vasculature is crucial for limb function, and it appears to play important roles during development by promoting development of other limb structures, but the steps leading to its formation are poorly understood. In this study, we use high-resolution imaging to document the stepwise assembly of the zebrafish pectoral fin vasculature. We show that fin vascular network formation is a stereotyped, choreographed process that begins with the growth of an initial vascular loop around the pectoral fin. This loop connects to the dorsal aorta to initiate pectoral vascular circulation. Pectoral fin vascular development continues with concurrent formation of three elaborate vascular plexuses, one in the distal fin that develops into the fin-ray vasculature and two near the base of the fin in association with the developing fin musculature. Our findings detail a complex, yet highly choreographed, series of steps involved in the development of a complete, functional, organ-specific vascular network.

Effect of biochemical and biomechanical factors on vascularization of kidney organoid-on-a-chip

Kidney organoids derived from the human pluripotent stem cells (hPSCs) recapitulating human kidney are the attractive tool for kidney regeneration, disease modeling, and drug screening. However, the kidney organoids cultured by static conditions have the limited vascular networks and immature nephron-like structures unlike human kidney. Here, we developed a kidney organoid-on-a-chip system providing fluidic flow mimicking shear stress with optimized extracellular matrix (ECM) conditions. We demonstrated that the kidney organoids cultured in our microfluidic system showed more matured podocytes and vascular structures as compared to the static culture condition. Additionally, the kidney organoids cultured in microfluidic systems showed higher sensitivity to nephrotoxic drugs as compared with those cultured in static conditions. We also demonstrated that the physiological flow played an important role in maintaining a number of physiological functions of kidney organoids. Therefore, our kidney organoid-on-a-chip system could provide an organoid culture platform for in vitro vascularization in formation of functional three-dimensional (3D) tissues.

Upper limb arterial pattern: clinical correlation and embryological perspective

Background

Variations in the upper limb arterial pattern are commonplace and necessitate complete familiarity for successful surgical and interventional procedures. Variance in the vascular tree may involve any part of the axis artery of the upper limb, including the axillary artery and brachial artery or its branches, in the form of radial and ulnar arteries, which eventually supply the hand via anastomosing arches.

Objectives

To study the peculiarities of the arterial pattern of the upper limb and to correlate them with embryological development.

Methods

The entire arterial branching of forty-two upper limbs of formalin fixed adult human cadavers was examined during routine dissection for educational purposes, conducted over a 3-year period in the Department of Anatomy, Lady Hardinge Medical College, New Delhi.

Results

The study found: 1) One case in which a common trunk arose from the third part of the axillary artery, which immediately splayed into four branches (2.4%); 2) High division of the brachial artery into ulnar and radial arteries, in 3 cases (7.1%); 3) Pentafurcation of the brachial artery into ulnar, interosseus, radial, and radial recurrent arteries and a muscular twig to the brachioradialis in 1/42 cases (2.4%); 4) Incomplete Superficial Palmar arch in 3/42 cases (7.1%); and 5) Presence of a median artery in 2/42 case(4.8%)

Conclusions

This study observed and described the varied arterial patterns of the upper limb and identified the various anomalous patterns, supplementing the surgeon’s armamentarium in various surgical procedures, thereby helping to prevent complications or failures of reconstructive surgeries, bypass angiography, and many similar procedures.

Organoids-on-a-chip

Recent studies have demonstrated an array of stem cell-derived, self-organizing miniature organs, termed organoids, that replicate the key structural and functional characteristics of their in vivo counterparts. As organoid technology opens up new frontiers of research in biomedicine, there is an emerging need for innovative engineering approaches for the production, control, and analysis of organoids and their microenvironment. In this Review, we explore organ-on-a-chip technology as a platform to fulfill this need and examine how this technology may be leveraged to address major technical challenges in organoid research. We also discuss emerging opportunities and future obstacles for the development and application of organoid-on-a-chip technology.

Soluble VEGFR1 signaling guides vascular patterns into dense branching morphologies

Vascular patterning is a key process during development and disease. The diffusive decoy receptor sVEGFR1 (sFlt1) is a known regulator of endothelial cell behavior, yet the mechanism by which it controls vascular structure is little understood. We propose computational models to shed light on how vascular patterning is guided by self-organized gradients of the VEGF/sVEGFR1 factors. We demonstrate that a diffusive inhibitor can generate structures with a dense branching morphology in models where the activator elicits directed growth. Inadequate presence of the inhibitor leads to compact growth, while excessive production of the inhibitor blocks expansion and stabilizes existing structures. Model predictions were compared with time-resolved experimental data obtained from endothelial sprout kinetics in fibrin gels. In the presence of inhibitory antibodies against VEGFR1 vascular sprout density increases while the speed of sprout expansion remains unchanged. Thus, the rate of secretion and stability of extracellular sVEGFR1 can modulate vascular sprout density.

Evolution of the muscular system in tetrapod limbs

While skeletal evolution has been extensively studied, the evolution of limb muscles and brachial plexus has received less attention. In this review, we focus on the tempo and mode of evolution of forelimb muscles in the vertebrate history, and on the developmental mechanisms that have affected the evolution of their morphology. Tetrapod limb muscles develop from diffuse migrating cells derived from dermomyotomes, and the limb-innervating nerves lose their segmental patterns to form the brachial plexus distally. Despite such seemingly disorganized developmental processes, limb muscle homology has been highly conserved in tetrapod evolution, with the apparent exception of the mammalian diaphragm. The limb mesenchyme of lateral plate mesoderm likely plays a pivotal role in the subdivision of the myogenic cell population into individual muscles through the formation of interstitial muscle connective tissues. Interactions with tendons and motoneuron axons are involved in the early and late phases of limb muscle morphogenesis, respectively. The mechanism underlying the recurrent generation of limb muscle homology likely resides in these developmental processes, which should be studied from an evolutionary perspective in the future.

Microfluidic assay of the deformability of primitive erythroblasts

Primitive erythroblasts (precursors of red blood cells) enter vascular circulation during the embryonic period and mature while circulating. As a result, primitive erythroblasts constantly experience significant hemodynamic shear stress. Shear-induced deformation of primitive erythroblasts however, is poorly studied. In this work, we examined the deformability of primitive erythroblasts at physiologically relevant flow conditions in microfluidic channels and identified the regulatory roles of the maturation stage of primitive erythroblasts and cytoskeletal protein 4.1 R in shear-induced cell deformation. The results showed that the maturation stage affected the deformability of primitive erythroblasts significantly and that primitive erythroblasts at later maturational stages exhibited a better deformability due to a matured cytoskeletal structure in the cell membrane.

Brachyury drives formation of a distinct vascular branchpoint critical for fetal-placental arterial union in the mouse gastrula

How the fetal-placental arterial connection is made and positioned relative to the embryonic body axis, thereby ensuring efficient and directed blood flow to and from the mother during gestation, is not known. Here we use a combination of genetics, timed pharmacological inhibition in living mouse embryos, and three-dimensional modeling to link two novel architectural features that, at present, have no status in embryological atlases. The allantoic core domain (ACD) is the extraembryonic extension of the primitive streak into the allantois, or pre-umbilical tissue; the vessel of confluence (VOC), situated adjacent to the ACD, is an extraembryonic vessel that marks the site of fetal-placental arterial union. We show that genesis of the fetal-placental connection involves the ACD and VOC in a series of steps, each one dependent upon the last. In the first, Brachyury (T) ensures adequate extension of the primitive streak into the allantois, which in turn designates the allantoic-yolk sac junction. Next, the streak-derived ACD organizes allantoic angioblasts to the axial junction; upon signaling from Fibroblast Growth Factor Receptor-1 (FGFR1), these endothelialize and branch, forming a sprouting VOC that unites the umbilical and omphalomesenteric arteries with the fetal dorsal aortae. Arterial union is followed by the appearance of the medial umbilical roots within the VOC, which in turn designate the correct axial placement of the lateral umbilical roots/common iliac arteries. In addition, we show that the ACD and VOC are conserved across Placentalia, including humans, underscoring their fundamental importance in mammalian biology. We conclude that T is required for correct axial positioning of the VOC via the primitive streak/ACD, while FGFR1, through its role in endothelialization and branching, further patterns it. Together, these genetic, molecular and structural elements safeguard the fetus against adverse outcomes that can result from vascular mispatterning of the fetal-placental arterial connection.

Using Zebrafish for High-Throughput Screening of Novel Cardiovascular Drugs

Cardiovascular diseases remain a major challenge for modern drug discovery. The diseases are chronic, complex, and the result of sophisticated interactions between genetics and environment involving multiple cell types and a host of systemic factors. The clinical events are often abrupt, and the diseases may be asymptomatic until a highly morbid event. Target selection is often based on limited information, and though highly specific agents are often identified in screening, their final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index, or substantial toxicities. Our understanding of complexity of cardiovascular disease has grown dramatically over the past 2 decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in cardiac or vascular disease. Despite these insights, the majority of active cardiovascular agents derive from a remarkably small number of classes of agents and target a very limited number of pathways. These agents have often been used initially for particular indications and then discovered serendipitously to have efficacy in other cardiac disorders or in a manner unrelated to their original mechanism of action. In this review, the rationale for in vivo screening is described, and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. An overview is provided of the complex mechanisms underlying most clinical cardiovascular diseases, and insight is offered into the limits of single downstream pathways as drug targets. The zebrafish is introduced as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology are discussed, including in vivo screening of zebrafish genetic disease models.

Intra-laboratory validated human cell-based in vitro vasculogenesis/angiogenesis test with serum-free medium

Vasculogenesis and angiogenesis are the processes by which new blood vessels are formed. We have developed a serum-free human adipose stromal cell and umbilical cord vein endothelial cell based vasculogenesis/angiogenesis test. In this study, the test was validated in our GLP laboratory following the OECD Guidance Document 34 [1] using erlotinib, acetylic salicylic acid, levamisole, 2-methoxyestradiol, anti-VEGF, methimazole, and D-mannitol to show its reproducibility, repeatability, and predictivity for humans. The results were obtained from immunostained tubule structures and cytotoxicity assessment. The performance of the test was evaluated using 26 suspected teratogens and non-teratogens. The positive predictive value was 71.4% and the negative predictive value was 50.0%, indicating that inhibition of vasculogenesis is a significant mechanism behind teratogenesis. In conclusion, this test has great potential to be a screening test for prioritization purposes of chemicals and to be a test in a battery to predict developmental hazards in a regulatory context.

Limb ischemia and vessel regeneration: Is there a role for VEGF?

Vascular endothelial growth factor (VEGF), as an endothelial cell-specific mitogen, is crucial for new blood vessels formation. Atherosclerosis affecting the cardiovascular system causes ischemia and functio laesa in tissues supplied by the occluded vessels. When such a situation occurs in the lower extremities, it causes critical limb ischemia (CLI) often requiring leg amputation. Low oxygen tension leads to upregulation of hypoxia-regulated genes (i.e. VEGF), that should help to restore the impaired blood flow. In CLI these rescue mechanisms are, however, often inefficient. Moreover, there are many contradictory reports showing either induction, no changes or even down-regulation of VEGF in specimens taken from patients with CLI, as well as in samples collected from animals subjected to hindlimb ischemia. Additionally, taking into account numerous experimental and clinical data demonstrating rather insufficient therapeutic potential of VEGF, we called into question the role of this protein in limb ischemia and vessel regeneration. In this review we are also summarizing several aspects which can influence VEGF expression and its measurement in the ischemic tissues.

Differential effects of high and low strength magnetic fields on mouse embryonic development and vasculogenesis of embryonic stem cells

Man-made magnetic fields (MFs) may exert adverse effects on mammalian embryonic development. Herein, we analysed the effect of 10mT 50Hz sinusoidal (AC) or static (DC) MFs versus 1mT MFs on embryonic development of mice. Exposure for 20days during gestation to 10mT MFs increased resorptions and dead fetuses, decreased crown-rump length and fresh weight, reduced blood vessel differentiation and caused histological changes, accompanied with diminished vascular endothelial growth factor (VEGF) protein expression in several organs. In embryonic stem (ES) cell-derived embryoid bodies exposure towards 10mT MFs increased reactive oxygen species (ROS), decreased vascular marker as well as VEGF expression and enhanced apoptosis. In conclusion, our combined data from in vivo and in vitro experiments identified VEGF as an important mediator during embryonic development that can be influenced by high strength MFs, which in consequence leads to severe abnormalities in fetus organs and blood vessel formation.

Endocardial tip cells in the human embryo - facts and hypotheses

Experimental studies regarding coronary embryogenesis suggest that the endocardium is a source of endothelial cells for the myocardial networks. As this was not previously documented in human embryos, we aimed to study whether or not endothelial tip cells could be correlated with endocardial-dependent mechanisms of sprouting angiogenesis. Six human embryos (43–56 days) were obtained and processed in accordance with ethical regulations; immunohistochemistry was performed for CD105 (endoglin), CD31, CD34, α-smooth muscle actin, desmin and vimentin antibodies. Primitive main vessels were found deriving from both the sinus venosus and aorta, and were sought to be the primordia of the venous and arterial ends of cardiac microcirculation. Subepicardial vessels were found branching into the outer ventricular myocardium, with a pattern of recruiting α-SMA+/desmin+ vascular smooth muscle cells and pericytes. Endothelial sprouts were guided by CD31+/CD34+/CD105+/vimentin+ endothelial tip cells. Within the inner myocardium, we found endothelial networks rooted from endocardium, guided by filopodia-projecting CD31+/CD34+/CD105+/ vimentin+ endocardial tip cells. The myocardial microcirculatory bed in the atria was mostly originated from endocardium, as well. Nevertheless, endocardial tip cells were also found in cardiac cushions, but they were not related to cushion endothelial networks. A general anatomical pattern of cardiac microvascular embryogenesis was thus hypothesized; the arterial and venous ends being linked, respectively, to the aorta and sinus venosus. Further elongation of the vessels may be related to the epicardium and subepicardial stroma and the intramyocardial network, depending on either endothelial and endocardial filopodia-guided tip cells in ventricles, or mostly on endocardium, in atria.

Heterogeneity in the Segmental Development of the Aortic Tree: Impact on Management of Genetically Triggered Aortic Aneurysms

An extensive search of the medical literature examining the development of the thoracic aortic tree reveals that the thoracic aorta does not develop as one unit or in one stage: the oldest part of the thoracic aorta is the descending aorta with the aortic arch being the second oldest, developing under influence from the neural crest cell. Following in chronological order are the proximal ascending aorta and aortic root, which develop from a conotruncal origin. Different areas of the thoracic aorta develop under the influence of different gene sets. These parts develop from different cell lineages: the aortic root (the conotruncus), developing from the mesoderm; the ascending aorta and aortic arch, developing from the neural crest cells; and the descending aorta from the mesoderm. Findings illustrate that the thoracic aorta is not a single entity, in developmental terms. It develops from three or four distinct areas, at different stages of embryonic life, and under different sets of genes and signaling pathways. Genetically triggered thoracic aortic aneurysms are not a monolithic group but rather share a multi-genetic origin. Identification of therapeutic targets should be based on the predilection of certain genes to cause aneurysmal disease in specific aortic segments.

Microfluidic techniques for development of 3D vascularized tissue

Development of a vascularized tissue is one of the key challenges for the successful clinical application of tissue engineered constructs. Despite the significant efforts over the last few decades, establishing a gold standard to develop three dimensional (3D) vascularized tissues has still remained far from reality. Recent advances in the application of microfluidic platforms to the field of tissue engineering have greatly accelerated the progress toward the development of viable vascularized tissue constructs. Numerous techniques have emerged to induce the formation of vascular structure within tissues which can be broadly classified into two distinct categories, namely (1) prevascularization-based techniques and (2) vasculogenesis and angiogenesis-based techniques. This review presents an overview of the recent advancements in the vascularization techniques using both approaches for generating 3D vascular structure on microfluidic platforms.

Endothelial cell motility, coordination and pattern formation during vasculogenesis

How vascular networks assemble is a fundamental problem of developmental biology that also has medical importance. To explain the organizational principles behind vascular patterning, we must understand how can tissue level structures be controlled through cell behavior patterns like motility and adhesion that, in turn, are determined by biochemical signal transduction processes? We discuss the various ideas that have been proposed as mechanisms for vascular network assembly: cell motility guided by extracellular matrix alignment (contact guidance), chemotaxis guided by paracrine and autocrine morphogens, and multicellular sprouting guided by cell-cell contacts. All of these processes yield emergent patterns, thus endothelial cells can form an interconnected structure autonomously, without guidance from an external pre-pattern.

Pattern formation during vasculogenesis

Vasculogenesis, the assembly of the first vascular network, is an intriguing developmental process that yields the first functional organ system of the embryo. In addition to being a fundamental part of embryonic development, vasculogenic processes also have medical importance. To explain the organizational principles behind vascular patterning, we must understand how morphogenesis of tissue level structures can be controlled through cell behavior patterns that, in turn, are determined by biochemical signal transduction processes. Mathematical analyses and computer simulations can help conceptualize how to bridge organizational levels and thus help in evaluating hypotheses regarding the formation of vascular networks. Here, we discuss the ideas that have been proposed to explain the formation of the first vascular pattern: cell motility guided by extracellular matrix alignment (contact guidance), chemotaxis guided by paracrine and autocrine morphogens, and sprouting guided by cell-cell contacts.

Vascular Network Formation in Expanding versus Static Tissues: Embryos and Tumors

In this perspectives article, we review scientific literature regarding de novo formation of vascular networks within tissues undergoing a significant degree of motion. Next, we contrast dynamic pattern formation in embryos to the vascularization of relatively static tissues, such as the retina. We argue that formation of primary polygonal vascular networks is an emergent process, which is regulated by biophysical mechanisms. Dynamic empirical data, derived from quail embryos, show that vascular beds readily form within a moving extracellular matrix (ECM) microenvironment-which we analogize to the de novo vascularization of small rapidly growing tumors. Our perspective is that the biophysical rules, which govern cell motion during vasculogenesis, may hold important clues to understanding how the first vessels form in certain malignancies.

The adaptor protein Shc integrates growth factor and ECM signaling during postnatal angiogenesis

Angiogenesis requires integration of cues from growth factors, extracellular matrix (ECM) proteins, and their receptors in endothelial cells. In the present study, we show that the adaptor protein Shc is required for angiogenesis in zebrafish, mice, and cell-culture models. Shc knockdown zebrafish embryos show defects in intersegmental vessel sprouting in the trunk. Shc flox/flox; Tie2-Cre mice display reduced angiogenesis in the retinal neovascularization model and in response to VEGF in the Matrigel plug assay in vivo. Functional studies reveal a model in which Shc is required for integrin-mediated spreading and migration specifically on fibronectin, as well as endothelial cell survival in response to VEGF. Mechanistically, Shc is required for activation of the Akt pathway downstream of both integrin and VEGF signaling, as well as for integration of signals from these 2 receptors when cells are grown on fibronectin. Therefore, we have identified a unique mechanism in which signals from 2 critical angiogenic signaling axes, integrins and VEGFR-2, converge at Shc to regulate postnatal angiogenesis.

Diverse functions for the semaphorin receptor PlexinD1 in development and disease

Plexins are a family of single-pass transmembrane proteins that serve as cell surface receptors for Semaphorins during the embryonic development of animals. Semaphorin-Plexin signaling is critical for many cellular aspects of organogenesis, including cell migration, proliferation and survival. Until recently, little was known about the function of PlexinD1, the sole member of the vertebrate-specific PlexinD (PlxnD1) subfamily. Here we review novel findings about PlxnD1's roles in the development of the cardiovascular, nervous and immune systems and salivary gland branching morphogenesis and discuss new insights concerning the molecular mechanisms of PlxnD1 activity.

An anteroposterior wave of vascular inhibitor downregulation signals aortae fusion along the embryonic midline axis

Paracrine signals, both positive and negative, regulate the positioning and remodeling of embryonic blood vessels. In the embryos of mammals and birds, the first major remodeling event is the fusion of bilateral dorsal aortae at the midline to form the dorsal aorta. Although the original bilaterality of the dorsal aortae occurs as the result of inhibitory factors (antagonists of BMP signaling) secreted from the midline by the notochord, it is unknown how fusion is later signaled. Here, we report that dorsal aortae fusion is tightly regulated by a change in signaling by the notochord along the anteroposterior axis. During aortae fusion, the notochord ceases to exert its negative influence on vessel formation. This is achieved by a transcriptional downregulation of negative regulators while positive regulators are maintained at pre-fusion levels. In particular, Chordin, the most abundant BMP antagonist expressed in the notochord prior to fusion, undergoes a dramatic downregulation in an anterior to posterior wave. With inhibitory signals diminished and sustained expression of the positive factors SHH and VEGF at the midline, fusion of the dorsal aortae is signaled. These results demonstrate a novel mechanism by which major modifications of the vascular pattern can occur through modulation of vascular inhibitors without changes in the levels of positive vascular regulators.

Arteries provide essential guidance cues for lymphatic endothelial cells in the zebrafish trunk

The endothelial cells of the vertebrate lymphatic system assemble into complex networks, but local cues that guide the migration of this distinct set of cells are currently unknown. As a model for lymphatic patterning, we have studied the simple vascular network of the zebrafish trunk consisting of three types of lymphatic vessels that develop in close connection with the blood vasculature. We have generated transgenic lines that allow us to distinguish between arterial, venous and lymphatic endothelial cells (LECs) within a single zebrafish embryo. We found that LECs migrate exclusively along arteries in a manner that suggests that arterial endothelial cells serve as the LEC migratory substrate. In the absence of intersegmental arteries, LEC migration in the trunk is blocked. Our data therefore demonstrate a crucial role for arteries in LEC guidance.

Cardiac Arrhythmia: In vivo screening in the zebrafish to overcome complexity in drug discovery

IMPORTANCE OF THE FIELD: Cardiac arrhythmias remain a major challenge for modern drug discovery. Clinical events are paroxysmal, often rare and may be asymptomatic until a highly morbid complication. Target selection is often based on limited information and though highly specific agents are identified in screening, the final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index and substantial toxicities. AREAS COVERED IN THIS REVIEW: Our understanding of complexity of arrhythmogenesis has grown dramatically over the last two decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in arrhythmia. This review surveys the literature on arrhythmia mechanisms from 1965 to the present day, outlines the complex biology underlying potentially each and every rhythm disturbance, and highlights the problems for rational target identification. The rationale for in vivo screening is described and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. WHAT THE READER WILL GAIN: An overview of the complex mechanisms underlying most clinical arrhythmias, and insight into the limits of ion channel conductances as drug targets. An introduction to the zebrafish as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology including in vivo screening of zebrafish genetic disease models. TAKE HOME MESSAGE: In vivo screening in faithful disease models allows the effects of drugs on integrative physiology and disease biology to be captured during the screening process, in a manner agnostic to potential drug target or targets. This systematic strategy bypasses current gaps in our understanding of disease biology, but emphasizes the importance of the rigor of the disease model.

Fetal and maternal angiogenic/anti-angiogenic factors in normal and preeclamptic pregnancy

Few studies evaluated angiogenic/anti-angiogenic factors and endothelial (dys)function in both maternal and umbilical cord blood (UCB) in preeclampsia (PE). We aimed to clarify the role of placental growth factor (PlGF), vascular endothelial growth factor (VEGF), soluble vascular endothelial growth factor receptor 1 (VEGFR-1) and tissue plasminogen activator (tPA), by evaluating them in maternal and UCB in 42 normal and 46 preeclamptic (PEc) cases. In PE, maternal and UCB PlGF were significantly lower; maternal VEGF, sVEGFR-1 and tPA were significantly higher. In UCB, sVEGFR-1 and tPA were significantly higher in PEc cases, while VEGF and PlGF were significantly lower. A significant correlation between maternal and UCB sVEGFR-1, and between sVEGFR-1 and tPA both in maternal and UCB, was observed in PEc cases. In maternal and UCB circulation in PE, a close interaction seems to exist between endothelial dysfunction and angiogenesis disturbance, and sVEGFR-1 seems to play a central role in those disturbances.

Genetic control of cell morphogenesis during Drosophila melanogaster cardiac tube formation

Tubulogenesis is an essential component of organ development, yet the underlying cellular mechanisms are poorly understood. We analyze here the formation of the Drosophila melanogaster cardiac lumen that arises from the migration and subsequent coalescence of bilateral rows of cardioblasts. Our study of cell behavior using three-dimensional and time-lapse imaging and the distribution of cell polarity markers reveals a new mechanism of tubulogenesis in which repulsion of prepatterned luminal domains with basal membrane properties and cell shape remodeling constitute the main driving forces. Furthermore, we identify a genetic pathway in which roundabout, slit, held out wings, and dystroglycan control cardiac lumen formation by establishing nonadherent luminal membranes and regulating cell shape changes. From these data we propose a model for D. melanogaster cardiac lumen formation, which differs, both at a cellular and molecular level, from current models of epithelial tubulogenesis. We suggest that this new example of tube formation may be helpful in studying vertebrate heart tube formation and primary vasculogenesis.

How to create the vascular tree? (Latest) help from the zebrafish

The cardiovascular system provides oxygen, nutrients and hormones to organs, it directs traffic of metabolites and it maintains tissue homeostasis. It is one of the first organs assembled during vertebrate development and it is essential to life from early stages to adult. For these reasons, the process of vessel formation has being studied for more than a century, but it is only in the late eighties that there has been an explosion of research in the field with the employment of various in vitro and in vivo model systems. The zebrafish (Danio rerio) offers several advantages for in vivo studies; it played a fundamental role in new discoveries and helped to refine our knowledge of the vascular system. This review recapitulates the zebrafish data on vasculogenesis and angiogenesis, including the specification of the haemangioblasts from the mesoderm, their migration to form the vascular cord followed by axial vessels specification, the primary and secondary sprouting of intersomitic vessels, the formation of the lumen, the arterial versus venous specification and patterning. To emphasize the strengths of the zebrafish system in the vascular field, we summarize main tools, such as gene expression and mutagenesis screens, knock down technologies, transgenic lines and imaging, which played a major role in the development of the field and allowed significant discoveries, for instance the recent visualization of the lymphatic system in zebrafish. This information contributes to the prospective of drug discovery to cure human diseases linked to angiogenesis, not last tumours.

Multicellular sprouting during vasculogenesis

Living organisms, from bacteria to vertebrates, are well known to generate sophisticated multicellular patterns. Numerous recent interdisciplinary studies have focused on the formation and regulation of these structures. Advances in automatized microscopy allow the time-resolved tracking of embryonic development at cellular resolution over an extended area covering most of the embryo. The resulting images yield simultaneous information on the motion of multiple tissue components-both cells and extracellular matrix (ECM) fibers. Recent studies on ECM displacements in bird embryos resulted in a method to distinguish tissue deformation and cell-autonomous motion. Patterning of the primary vascular plexus results from a collective action of primordial endothelial cells. The emerging "polygonal" vascular structure is shown to be formed by cell-cell and cell-ECM interactions: adhesion and protrusive activity (sprouting). Utilizing avb3 integrins, multicellular sprouts invade rapidly into avascular areas. Sprout elongation, in turn, depends on a continuous supply of endothelial cells. Endothelial cells migrate along the sprout, towards its tip, in a vascular endothelial (VE) cadherin-dependent process. The observed abundance of multicellular sprout formation in various in vitro and in vivo systems can be explained by a general mechanism based on preferential attraction to elongated structures. Our interacting particle model exhibits robust sprouting dynamics and results in patterns with morphometry similar to native primordial vascular plexuses--without ancillary assumptions involving chemotaxis or mechanochemical signaling.

Nonadditive effects of PAHs on Early Vertebrate Development: mechanisms and implications for risk assessment

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants. Traditionally, much of the research has focused on the carcinogenic potential of specific PAHs, such as benzo(a)pyrene, but recent studies using sensitive fish models have shown that exposure to PAHs alters normal fish development. Some PAHs can induce a teratogenic phenotype similar to that caused by planar halogenated aromatic hydrocarbons, such as dioxin. Consequently, mechanism of action is often equated between the two classes of compounds. Unlike dioxins, however, the developmental toxicity of PAH mixtures is not necessarily additive. This is likely related to their multiple mechanisms of toxicity and their rapid biotransformation by CYP1 enzymes to metabolites with a wide array of structures and potential toxicities. This has important implications for risk assessment and management as the current approach for complex mixtures of PAHs usually assumes concentration addition. In this review we discuss our current knowledge of teratogenicity caused by single PAH compounds and by mixtures and the importance of these latest findings for adequately assessing risk of PAHs to humans and wildlife. Throughout, we place particular emphasis on research on the early life stages of fish, which has proven to be a sensitive and rapid developmental model to elucidate effects of hydrocarbon mixtures.

Critical role for NF-kappaB-induced JunB in VEGF regulation and tumor angiogenesis

Regulation of vascular endothelial growth factor (VEGF) expression is a complex process involving a plethora of transcriptional regulators. The AP-1 transcription factor is considered as facilitator of hypoxia-induced VEGF expression through interaction with hypoxia-inducible factor (HIF) which plays a major role in mediating the cellular hypoxia response. As yet, both the decisive AP-1 subunit leading to VEGF induction and the molecular mechanism by which this subunit is activated have not been deciphered. Here, we demonstrate that the AP-1 subunit junB is a target gene of hypoxia-induced signaling via NF-kappaB. Loss of JunB in various cell types results in severely impaired hypoxia-induced VEGF expression, although HIF is present and becomes stabilized. Thus, we identify JunB as a critical independent regulator of VEGF transcription and provide a mechanistic explanation for the inherent vascular phenotypes seen in JunB-deficient embryos, ex vivo allantois explants and in vitro differentiated embryoid bodies. In support of these findings, tumor angiogenesis was impaired in junB(-/-) teratocarcinomas because of severely impaired paracrine-acting VEGF and the subsequent inability to efficiently recruit host-derived vessels.

HIF-dependent hematopoietic factors regulate the development of the embryonic vasculature

Hypoxia inducible factors (HIFs) regulate adaptive responses to changes in oxygen (O(2)) tension during embryogenesis, tissue ischemia, and tumorigenesis. Because HIF-deficient embryos exhibit a number of developmental defects, the precise role of HIF in early vascular morphogenesis has been uncertain. Using para-aortic splanchnopleural (P-Sp) explant cultures, we show that deletion of the HIF-beta subunit (ARNT) results in defective hematopoiesis and the inhibition of both vasculogenesis and angiogenesis. These defects are rescued upon the addition of wild-type Sca-1(+) hematopoietic cells or recombinant VEGF. Arnt(-/-) embryos exhibit reduced levels of VEGF protein and increased numbers of apoptotic hematopoietic cells. These results suggest that HIF coordinates early endothelial cell emergence and vessel development by promoting hematopoietic cell survival and paracrine growth factor production.

Vascular anatomy of the developing medaka, Oryzias latipes: a complementary fish model for cardiovascular research on vertebrates

The zebrafish has become a very useful vertebrate model for cardiovascular research, but detailed morphogenetic studies have revealed that it differs from mammals in certain aspects of the primary circulatory system, in particular, the early vitelline circulation. We searched for another teleost species that might serve as a complementary model for the formation of these early primary vessels. Here (and online at http://www.shigen.nig.ac.jp/medaka/atlas/), we present a detailed characterization of the vascular anatomy of the developing medaka embryo from the stage 24 (1 day 20 hr) through stage 30 (3 days 10 hr). Three-dimensional images using confocal microangiography show that the medaka, Oryzias latipes, follows the common embryonic circulatory pattern consisting of ventral aorta, aortic arches, dorsal aorta, transverse vessels, vitelline capillary plexus, and marginal veins. The medaka, thus, may serve as a valuable model system for genetic analysis of the primary vasculature of vertebrates.

Cadherin2 (N-cadherin) plays an essential role in zebrafish cardiovascular development

BACKGROUND

Cadherins are cell surface adhesion molecules that play important roles in development of vertebrate tissues and organs. We studied cadherin2 expression in developing zebrafish heart using in situ hybridization and immunocytochemical methods, and we found that cadherin2 was strongly expressed by the myocardium of the embryonic zebrafish. To gain insight into cadherin2 role in the formation and function of the heart, we analyzed cardiac differentiation and performance in a cadherin2 mutant, glass onion (glo).

RESULTS

We found that the cadherin2 mutant had enlarged pericardial cavity, disorganized atrium and ventricle, and reduced expression of a ventricular specific marker vmhc. Individual myocardiocytes in the glo mutant embryos became round shaped and loosely aggregated. In vivo measurements of cardiac performance revealed that the mutant heart had significantly reduced heart rate, stroke volume and cardiac output compared to control embryos. Formation of the embryonic vascular system in the glo mutants was also affected.

CONCLUSION

Our results suggest that cadherin2 plays an essential role in zebrafish cardiovascular development. Although the exact mechanisms remain unknown as to the formation of the enlarged pericardium and reduced peripheral blood flow, it is clear that myocardiocyte differentiation and physiological cardiovascular performance is impaired when cadherin2 function is disrupted.

Experimental hypoxia and embryonic angiogenesis

We examined the role of hypoxia and HIF factors in embryonic angiogenesis and correlated the degree of hypoxia with the level of HIF and VEGF expression and blood vessel formation. Quail eggs were incubated in normoxic and hypoxic (16% O(2)) conditions. Tissue hypoxia marker, pimonidazol hydrochloride, was applied in vivo for 1 hr and detected in sections with Hypoxyprobe-1 Ab. VEGF and HIF expression was detected by in situ hybridization. HIF-1alpha protein was detected in sections and by Western blot. Endothelial cells were visualized with QH-1 antibody. Hypoxic regions were detected even in normoxic control embryos, mainly in brain, neural tube, branchial arches, limb primordia, and mesonephros. The expression patterns of HIF-1alpha and HIF-1beta factors followed, in general, the Hypoxyprobe-1 marked regions. HIF-2alpha was predominantly expressed in endothelial cells. Diffuse VEGF expression was detected in hypoxic areas of neural tube, myocardium, digestive tube, and most prominently in mesonephros. Growing capillaries were directed to areas of VEGF positivity. Hypoxic regions in hypoxic embryos were larger and stained more intensely. VEGF and HIF-1 factors were proportionately elevated in Hypoxyprobe-1 marked regions without being expressed at new sites and were followed by increased angiogenesis. Our results demonstrate that normal embryonic vascular development involves the HIF-VEGF regulatory cascade. Experimentally increasing the level of hypoxia to a moderate level resulted in over-expression of HIF-1 factors and VEGF followed by an increase in the density of developing vessels. These data indicate that embryonic angiogenesis is responsive to environmental oxygen tension and, therefore, is not entirely genetically controlled.

The blood/vascular system in a phylogenetic perspective

The genetically and experimentally accessible organs of Drosophila, such as the heart or blood-forming tissues, have become a fertile ground for systematic projects of gene discovery and for functional studies of gene networks and signaling pathways. One argument justifying this approach is the often-tacit assumption that clear-cut homologies can be established between the Drosophila organs and their vertebrate counterparts. Here we investigate this assumption by surveying pertinent aspects of vascular structure and development in different invertebrate phyla, in the hope that this information will help to reveal the ancestral condition of the vascular system. Evolutionary scenarios that derive the structure of the cardiovascular system of extant animal taxa from the ancestral condition will be used to qualify hypotheses regarding homologies that are based on molecular similarities.

Formation of the coronary vasculature during development

The formation of the coronary vasculature involves a series of carefully regulated temporal events that include vasculogenesis, angiogenesis, arteriogenesis and remodeling. This review explores these events, which begin with the migration of proepicardial cells to form the epicardium and end with postnatal growth and remodeling. Coronary endothelial, smooth muscle and fibroblast cells differentiate via epithelial-mesenchymal transformation; these cells delaminate from the epicardium. Following the formation of a tubular network by endothelial cells, an aortic ring of endothelial cells penetrates the aorta at the left and right aortic cusps to form the two ostia. Smooth muscle cell recruitment occurs rapidly and the coronary artery network begins forming as blood flow is established. Recent studies have identified a number of regulatory molecules that play key roles in epicardial formation and the transformation of its component cells into mesenchyme. Moreover, we are finally gaining some understanding regarding the interplay of angiogenic growth factors in the complex process of establishing the coronary vascular tree. Understanding coronary embryogenesis is important for interventions regarding adult cardiovascular diseases as well as those necessary to correct congenital defects.

A three-dimensional functional assessment of heart and vessel development in the larva of the zebrafish (Danio rerio)

There has been considerable recent interest in the development of the circulation in the zebrafish. Optical techniques typically used to visualize changes in heart size allow measurement of stroke volume during early vertebrate development, but this approach is complicated in zebrafish larvae because of the heart's irregular shape and its significant change in morphology during the first 6 d of development. By use of a three-dimensional integration of the early zebrafish heart and vessels, we have greatly reduced measurement error of stroke volume and cardiac output and have determined the cross-sectional growth of major vessels in the developing zebrafish larvae. A dramatic 500%-600% increase in cardiac output (from 10 to 50-60 nL min(-1)) occurs on days 5 and 6 postfertilization in Danio rerio. Cross-sectional area of key vessels (dorsal artery, caudal artery, dorsal vein) as well as between-individual variation significantly decreased over the first 6 d of development. Associated with the decrease in cross-sectional area is a significant increase in red blood cell velocity on days 5 and 6 postfertilization. Together, the three-dimensional data of the cardiac and vascular systems have shown that the most profound physiological and developmental changes occur in days 5 and 6, which corresponds with the appearance of the adult form of the heart and the transition from diffusive to convective O2 supply to internal tissues.

NO as a mediator during the early development of the cardiovascular system in the zebrafish

As a general pattern innervation of the cardiovascular system appears late during development in vertebrate embryos, and cardiovascular control may be achieved by hormonal activity in early stages. However, very little is known about the onset of NO-responsiveness during development, which in adult vertebrates is known to play a key function in many physiological processes such as control of vascular tone, neurotransmission, macrophage activity, and angiogenesis. Analysis of the effect of NO on the cardiovascular system in zebrafish (Danio rerio) embryos and larvae revealed almost no effect on cardiac activity during chronic exposure to NO-producing chemicals, whereas vascular reactivity was observed in veins and arteries of the zebrafish in early developmental stages (5-6 days post fertilization). Chronic exposure also modified the development of the vascular system. The presence of an NO donor (sodium nitroprusside) did not change the patterning of the vascular bed, but it induced an earlier appearance of some blood vessels in the trunk region of the zebrafish larvae. The data reveal that NO plays an important role in the development of the cardiovascular system and in the ontogeny of the cardiovascular control system in fish.

Mechanisms regulating the origins of the vertebrate vascular system

In order to sustain growth, differentiation, and organogenesis, vertebrate embryos must form a functional vascular system early in embryonic development. Intrinsic interest in this process as well as the promise of potential clinical applications has led to significant progress in understanding the mechanisms governing the formation of the vascular system, however the earliest stages of vascular development--the emergence of committed endothelial precursors from the mesoderm--remain unclear. A review of the current literature reveals an unexpected diversity and heterogeneity with respect to where vascular endothelial cells originate in the embryo, when they become committed and the mechanisms governing how endothelial cells acquire their identity. Spatially, a widespread region of the early mesoderm possesses the ability to give rise to vascular endothelial cells; temporally the process is not limited to a small window during embryogenesis, but rather, may continue throughout the lifespan of the organism. On the molecular level, recent findings point to several determinative pathways that regulate, modulate, and extend the scope of the Flk1/VEGF signaling system. An expanding array of novel gene products implicated in endothelial cell type determination appear to act synergistically, with different combinations of factors leading to diverse cellular responses, varying patterns of differentiation, and considerable heterogeneity of endothelial cell types during embryogenesis.

Semaphorin-plexin signaling guides patterning of the developing vasculature

Major vessels of the vertebrate circulatory system display evolutionarily conserved and reproducible anatomy, but the cues guiding this stereotypic patterning remain obscure. In the nervous system, axonal pathways are shaped by repulsive cues provided by ligands of the semaphorin family that are sensed by migrating neuronal growth cones through plexin receptors. We show that proper blood vessel pathfinding requires the endothelial receptor PlexinD1 and semaphorin signals, and we identify mutations in plexinD1 in the zebrafish vascular patterning mutant out of bounds. These results reveal the fundamental conservation of repulsive patterning mechanisms between axonal migration in the central nervous system and vascular endothelium during angiogenesis.

Vitamin a requirement for early cardiovascular morphogenesis specification in the vertebrate embryo: insights from the avian embryo

Vitamin A is required throughout the life cycle, including crucial stages of embryonic and fetal development. With the identification of retinoic acid-specific nuclear transcription factors, the retinoid receptors, considerable advances have been made in understanding the molecular function of vitamin A. The requirement for vitamin A during early embryogenesis has successfully been examined in the vitamin A-deficient avian embryo during neurulation, when in the vertebrates crucial developmental decisions take place. These studies revealed that retinoic acid is essential during these early stages of embryogenesis for the initiation of organogenesis (i.e., formation of the heart). If retinoic acid is not present at this time, abnormal development ensues, leading to early embryonic death. Though the initial insult of the absence of vitamin A appears to be on the specification of cardiovascular tissues, subsequently all development is adversely affected and the embryo dies. Molecular and functional studies revealed that retinoic acid regulates the expression of the cardiogenic transcription factor GATA-4 and several heart asymmetry genes, which explains why the heart position is random in vitamin A-deficient quail embryos. During the crucial retinoic acid-requiring developmental window, retinoic acid transduces its signals to genes for heart morphogenesis via the receptors RARalpha2, RARgamma, and RXRalpha. Elucidation of the function of vitamin A during early embryonic development may lead to a better understanding of the cardiovascular birth defects prevalent in the Western world.

Calcineurin signaling and NFAT activation in cardiovascular and skeletal muscle development

Calcineurin signaling has been implicated in a broad spectrum of developmental processes in a variety of organ systems. Calcineurin is a calmodulin-dependent, calcium-activated protein phosphatase composed of catalytic and regulatory subunits. The serine/threonine-specific phosphatase functions within a signal transduction pathway that regulates gene expression and biological responses in many developmentally important cell types. Calcineurin signaling was first defined in T lymphocytes as a regulator of nuclear factor of activated T cells (NFAT) transcription factor nuclear translocation and activation. Recent studies have demonstrated the vital nature of calcium/calcineurin/NFAT signaling in cardiovascular and skeletal muscle development in vertebrates. Inhibition, mutation, or forced expression of calcineurin pathway genes result in defects or alterations in cardiomyocyte maturation, heart valve formation, vascular development, skeletal muscle differentiation and fiber-type switching, and cardiac and skeletal muscle hypertrophy. Conserved calcineurin genes are found in invertebrates such as Drosophila and Caenorhabditis elegans, and genetic studies have demonstrated specific myogenic functions for the phosphatase in their development. The ability to investigate calcineurin signaling pathways in vertebrates and model genetic organisms provides a great potential to more fully comprehend the functions of calcineurin and its interacting genes in heart, blood vessel, and muscle development.

Robo4 is a vascular-specific receptor that inhibits endothelial migration

Guidance and patterning of axons are orchestrated by cell-surface receptors and ligands that provide directional cues. Interactions between the Robo receptor and Slit ligand families of proteins initiate signaling cascades that repel axonal outgrowth. Although the vascular and nervous systems grow as parallel networks, the mechanisms by which the vascular endothelial cells are guided to their appropriate positions remain obscure. We have identified a putative Robo homologue, Robo4, based on its differential expression in mutant mice with defects in vascular sprouting. In contrast to known neuronal Robo family members, the arrangement of the extracellular domains of Robo4 diverges significantly from that of all other Robo family members. Moreover, Robo4 is specifically expressed in the vascular endothelium during murine embryonic development. We show that Robo4 binds Slit and inhibits cellular migration in a heterologous expression system, analogous to the role of known Robo receptors in the nervous system. Immunoprecipitation studies indicate that Robo4 binds to Mena, a known effector of Robo-Slit signaling. Finally, we show that Robo4 is the only Robo family member expressed in primary endothelial cells and that application of Slit inhibits their migration. These data demonstrate that Robo4 is a bona fide member of the Robo family and may provide a repulsive cue to migrating endothelial cells during vascular development.