Zika virus non-structural protein NS4A restricts eye growth in Drosophila through regulation of JAK/STAT signaling

To gain a comprehensive view of the changes in host gene expression underlying Zika virus (ZIKV) pathogenesis, we performed whole-genome RNA sequencing (RNA-seq) of ZIKV-infected Drosophila adult flies. RNA-seq analysis revealed that ZIKV infection alters several and diverse biological processes, including stress, locomotion, lipid metabolism, imaginal disc morphogenesis and regulation of JAK/STAT signaling. To explore the interaction between ZIKV infection and JAK/STAT signaling regulation, we generated genetic constructs overexpressing ZIKV-specific non-structural proteins NS2A, NS2B, NS4A and NS4B. We found that ectopic expression of non-structural proteins in the developing Drosophila eye significantly restricts growth of the larval and adult eye and correlates with considerable repression of the in vivo JAK/STAT reporter, 10XStat92E-GFP At the cellular level, eye growth defects are associated with reduced rate of proliferation without affecting the overall rate of apoptosis. In addition, ZIKV NS4A genetically interacts with the JAK/STAT signaling components; co-expression of NS4A along with the dominant-negative form of domeless or StatRNAi results in aggravated reduction in eye size, while co-expression of NS4A in HopTuml (also known as hopTum ) mutant background partially rescues the hop-induced eye overgrowth phenotype. The function of ZIKV NS4A in regulating growth is maintained in the wing, where ZIKV NS4A overexpression in the pouch domain results in reduced growth linked with diminished expression of Notch targets, Wingless (Wg) and Cut, and the Notch reporter, NRE-GFP Thus, our study provides evidence that ZIKV infection in Drosophila results in restricted growth of the developing eye and wing, wherein eye phenotype is induced through regulation of JAK/STAT signaling, whereas restricted wing growth is induced through regulation of Notch signaling. The interaction of ZIKV non-structural proteins with the conserved host signaling pathways further advance our understanding of ZIKV-induced pathogenesis.This article has an associated First Person interview with the first author of the paper.

Veins and Arteries Build Hierarchical Branching Patterns Differently: Bottom-Up versus Top-Down

A tree-like hierarchical branching structure is present in many biological systems, such as the kidney, lung, mammary gland, and blood vessels. Most of these organs form through branching morphogenesis, where outward growth results in smaller and smaller branches. However, the blood vasculature is unique in that it exists as two trees (arterial and venous) connected at their tips. Obtaining this organization might therefore require unique developmental mechanisms. As reviewed here, recent data indicate that arterial trees often form in reverse order. Accordingly, initial arterial endothelial cell differentiation occurs outside of arterial vessels. These pre-artery cells then build trees by following a migratory path from smaller into larger arteries, a process guided by the forces imparted by blood flow. Thus, in comparison to other branched organs, arteries can obtain their structure through inward growth and coalescence. Here, new information on the underlying mechanisms is discussed, and how defects can lead to pathologies, such as hypoplastic arteries and arteriovenous malformations.

Zebrafish mutants and TEAD reporters reveal essential functions for Yap and Taz in posterior cardinal vein development

As effectors of the Hippo signaling cascade, YAP1 and TAZ are transcriptional regulators playing important roles in development, tissue homeostasis and cancer. A number of different cues, including mechanotransduction of extracellular stimuli, adhesion molecules, oncogenic signaling and metabolism modulate YAP1/TAZ nucleo-cytoplasmic shuttling. In the nucleus, YAP1/TAZ tether with the DNA binding proteins TEADs, to activate the expression of target genes that regulate proliferation, migration, cell plasticity, and cell fate. Based on responsive elements present in the human and zebrafish promoters of the YAP1/TAZ target gene CTGF, we established zebrafish fluorescent transgenic reporter lines of Yap1/Taz activity. These reporter lines provide an in vivo view of Yap1/Taz activity during development and adulthood at the whole organism level. Transgene expression was detected in many larval tissues including the otic vesicles, heart, pharyngeal arches, muscles and brain and is prominent in endothelial cells. Analysis of vascular development in yap1/taz zebrafish mutants revealed specific defects in posterior cardinal vein (PCV) formation, with altered expression of arterial/venous markers. The overactivation of Yap1/Taz in endothelial cells was sufficient to promote an aberrant vessel sprouting phenotype. Our findings confirm and extend the emerging role of Yap1/Taz in vascular development including angiogenesis.

Wing vein development in the sawfly Athalia rosae is regulated by spatial transcription of Dpp/BMP signaling components

Wing venation among insects serves as an excellent model to address how diversified patterns are produced. Previous studies suggest that evolutionarily conserved Decapentaplegic (Dpp)/Bone Morphogenetic Protein (BMP) signal plays a critical role in wing vein development in the dipteran Drosophila melanogaster and the hymenopteran sawfly Athalia rosae. In sawfly, dpp is ubiquitously expressed in the wing during prepupal stages, but Dpp/BMP signal is localized in the future vein cells. Since localized BMP signaling involves BMP binding protein Crossveinless (Cv), redistribution of BMP ligands appears to be crucial for sawfly wing vein formation. However, how ubiquitously expressed ligands lead to a localized signal remains to be addressed. Here, we found that BMP binding protein short gastrulation (Sog) is highly expressed in the intervein cells. Our data also reveal that BMP type I receptors thickveins (Tkv) and saxophone (Sax) are highly expressed in intervein cells and at lower levels in the vein progenitor cells. RNAi knockdown of Ar-tkv or Ar-sax indicates that both receptors are required for localized BMP signaling in the wing vein progenitor cells. Taken together, our data suggest that spatial transcription of core- and co-factors of the BMP pathway sustain localized BMP signaling during sawfly wing vein development.

Endothelial Snail Regulates Capillary Branching Morphogenesis via Vascular Endothelial Growth Factor Receptor 3 Expression

Vascular branching morphogenesis is activated and maintained by several signaling pathways. Among them, vascular endothelial growth factor receptor 2 (VEGFR2) signaling is largely presented in arteries, and VEGFR3 signaling is in veins and capillaries. Recent reports have documented that Snail, a well-known epithelial-to-mesenchymal transition protein, is expressed in endothelial cells, where it regulates sprouting angiogenesis and embryonic vascular development. Here, we identified Snail as a regulator of VEGFR3 expression during capillary branching morphogenesis. Snail was dramatically upregulated in sprouting vessels in the developing retinal vasculature, including the leading-edged vessels and vertical sprouting vessels for capillary extension toward the deep retina. Results from in vitro functional studies demonstrate that Snail expression colocalized with VEGFR3 and upregulated VEGFR3 mRNA by directly binding to the VEGFR3 promoter via cooperating with early growth response protein-1. Snail knockdown in postnatal mice attenuated the formation of the deep capillary plexus, not only by impairing vertical sprouting vessels but also by downregulating VEGFR3 expression. Collectively, these data suggest that the Snail-VEGFR3 axis controls capillary extension, especially in vessels expressing VEGFR2 at low levels.

Systems biology approach to the dissection of the complexity of regulatory networks in the S. scrofa cardiocirculatory system

Genome-wide experiments are routinely used to increase the understanding of the biological processes involved in the development and maintenance of a variety of pathologies. Although the technical feasibility of this type of experiment has improved in recent years, data analysis remains challenging. In this context, gene set analysis has emerged as a fundamental tool for the interpretation of the results. Here, we review strategies used in the gene set approach, and using datasets for the pig cardiocirculatory system as a case study, we demonstrate how the use of a combination of these strategies can enhance the interpretation of results. Gene set analyses are able to distinguish vessels from the heart and arteries from veins in a manner that is consistent with the different cellular composition of smooth muscle cells. By integrating microRNA elements in the regulatory circuits identified, we find that vessel specificity is maintained through specific miRNAs, such as miR-133a and miR-143, which show anti-correlated expression with their mRNA targets.

[Variants of anatomical structure of lower-limb veins as a possible cause of the development of primary varicosity]

In order to reveal anatomical prerequisites for the development of primary varicose veins we investigated the structure of the venous system on a total of 53 adult human cadaveric lower extremities. Congenital morphological grounds providing the phlebohaemodynemics of the lower limbs are ambiguous in different individual forms. We revealed a total of 18 variants of the structure of deep veins, reflecting various stages of the embryonic development. In 34.1% of cases we saw the forms characteristic of incomplete reduction and unfinished transformation, with 30.2% of cases showing the utmost degree of reduction and transformation. An inadequate outflow along the deep veins conditioned by their anatomical structure is a prerequisite for the development of valvular insufficiency and venous reflux to the superficial veins followed by varicose transformation thereof

Developmental and circulatory profile of the diploic veins

To examine the development of the diploic veins in the calvarium, FITC-dextran was injected into the tail vein. The total area of the diploic veins showed a continuous, age-dependent development. We also measured the red blood cell (RBC) velocities in the diploic veins using an in vivo imaging technique and revealed RBCs with a significantly high velocity and unidirectional characteristics at the entrance route. The route passed from the basal periosteum of the cranial bone via the dura mater and into the diploic veins. Our findings indicate the existence of communications between intra- and extra-cranial circulation.

Phenotypic anchoring of gene expression after developmental exposure to aryl hydrocarbon receptor ligands in zebrafish

The genes mediating developmental aryl hydrocarbon (AhR)-induced cardiovascular deformities remain unclear, with many cytochrome P450 monooxygenase (CYP)-1 isoforms known to be AhR-responsive and now a cyclo-oxygenase (COX) isoform suspected to contribute developmental toxicity. More importantly, no previous study has examined the role of these genes in producing deformities using low enough concentrations of AhR agonists to permit survival beyond early larval stages. Zebrafish (Danio rerio) eggs were aqueously exposed to a variety of agents that had multiple modes of action, but all of which are reported to be AhR ligands; benzo-a-pyrene (BaP) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alone and in combination with resveratrol or alpha-naphthoflavone (ANF). Whole larvae CYP (subtypes 1A, 1B1, 1C1, and 1C2) and COX (subtypes 1, 2a, and 2b) mRNA expression was quantified at 5 and 10 dpf and correlated with developmental phenotype. Both TCDD and BaP caused dose-dependent AhR-associated deformities and mortalities by 10 dpf, while BaP/ANF co-exposure exhibited the highest rate of deformities and mortalities at 5 dpf with all of these larvae having died at the highest rate by 10 dpf. Furthermore, BaP/ANF co-exposure caused the most marked alterations in cardiac and vascular morphology at 10 dpf at the concentrations used, namely decreased ventricular length and chamber width with increased ventricular wall thickness, as well as increased blood vessel luminal diameter. Exposure to TCDD, BaP and ANF alone all significantly increased CYP1A mRNA expression, while only TCDD consistently increased CYP1C1 expression. In contrast, TCDD transiently decreased CYP1C2 expression. BaP alone had no effect on CYP1C1 expression, but decreased COX2b expression when alone or in combination with ANF. In fact, ANF exhibited additive agonistic effects on expression of CYP1A and CYP1C1 with both BaP and TCDD, although additive or potentiating effects of ANF on CYP1C2 and COX2b were observed with only BaP. Correlation analyses revealed that gene expression at 5 dpf, but not 10 dpf, was strongly linked to abnormal cardiac and vascular phenotypes at 10 dpf. Principal components analysis suggests that cardiac deformities and blood vessel dilation were related positively to CYP1A and negatively to COX-2b gene expression. These relationships were separate from the one gene, CYP1C1, that was negatively associated with increased vascular wall thickness. However, further experiments are needed to confirm this difference and to determine whether the relationship is causative or merely associative.

Drosophila Smad2 opposes Mad signaling during wing vein development

In the vertebrates, the BMP/Smad1 and TGF-β/Smad2 signaling pathways execute antagonistic functions in different contexts of development. The differentiation of specific structures results from the balance between these two pathways. For example, the gastrula organizer/node of the vertebrates requires a region of low Smad1 and high Smad2 signaling. In Drosophila, Mad regulates tissue determination and growth in the wing, but the function of dSmad2 in wing patterning is largely unknown. In this study, we used an RNAi loss-of-function approach to investigate dSmad2 signaling during wing development. RNAi-mediated knockdown of dSmad2 caused formation of extra vein tissue, with phenotypes similar to those seen in Dpp/Mad gain-of-function. Clonal analyses revealed that the normal function of dSmad2 is to inhibit the response of wing intervein cells to the extracellular Dpp morphogen gradient that specifies vein formation, as measured by expression of the activated phospho-Mad protein. The effect of dSmad2 depletion in promoting vein differentiation was dependent on Medea, the co-factor shared by Mad and dSmad2. Furthermore, double RNAi experiments showed that Mad is epistatic to dSmad2. In other words, depletion of Smad2 had no effect in Mad-deficient wings. Our results demonstrate a novel role for dSmad2 in opposing Mad-mediated vein formation in the wing. We propose that the main function of dActivin/dSmad2 in Drosophila wing development is to antagonize Dpp/Mad signaling. Possible molecular mechanisms for the opposition between dSmad2 and Mad signaling are discussed.

During vertebrate development, arteries exert a morphological control over the venous pattern through physical factors

The adult vasculature is comprised of three distinct compartments: the arteries, which carry blood away from the heart and display a divergent flow pattern; the capillaries, where oxygen and nutrient delivery from blood to tissues, as well as metabolic waste removal, occurs; and the veins, which carry blood back to the heart and are characterized by a convergent flow pattern. These compartments are organized in series as regard to flow, which proceeds from the upstream arteries to the downstream veins through the capillaries. However, the spatial organization is more complex, as veins may often be found paralleling the arteries. The factors that control the morphogenesis of this hierarchically branched vascular network are not well characterized. Here, we explain how arteries exert a morphological control on the venous pattern. Indeed, during vertebrate development, the following transition may be observed in the spatial organization of the vascular system: veins first develop in series with the arteries, the arterial and venous territories being clearly distinct in space (cis-cis configuration). But after some time, new veins grow parallel to the existing arteries, and the arterial and venous territories become overlapped, with extensive and complex intercalation and interdigitation. Using physical arguments, backed up by experimental evidence (biological data from the literature and in situ optical and mechanical measurements of the chick embryo yolk-sac and midbrain developing vasculatures), we explain how such a transition is possible and why it may be expected with generality, as organisms grow. The origin of this transition lies in the remodeling of the capillary tissue in the vicinity of the growing arteries. This remodeling lays down a prepattern for further venous growth, parallel to the existing arterial pattern. Accounting for the influence of tissue growth, we show that this prepatterned path becomes favored as the body extends. As a consequence, a second flow route with veins paralleling the arteries (cis-trans configuration) emerges when the tissue extends. Between the cis-cis and cis-trans configurations, all configurations are in principle possible, and self-organization of the vessels contributes to determining their exact pattern. However, the global aspect depends on the size at which the growth stops and on the growth rate.

Principles and therapeutic implications of angiogenesis, vasculogenesis and arteriogenesis

The vasculature is the first organ to arise during development. Blood vessels run through virtually every organ in the body (except the avascular cornea and the cartilage), assuring metabolic homeostasis by supplying oxygen and nutrients and removing waste products. Not surprisingly therefore, vessels are critical for organ growth in the embryo and for repair of wounded tissue in the adult. Notably, however, an imbalance in angiogenesis (the growth of blood vessels) contributes to the pathogenesis of numerous malignant, inflammatory, ischaemic, infectious and immune disorders. During the last two decades, an explosive interest in angiogenesis research has generated the necessary insights to develop the first clinically approved anti-angiogenic agents for cancer and blindness. This novel treatment is likely to change the face of medicine in the next decade, as over 500 million people worldwide are estimated to benefit from pro- or anti-angiogenesis treatment. In this following chapter, we discuss general key angiogenic mechanisms in health and disease, and highlight recent developments and perspectives of anti-angiogenic therapeutic strategies.

Nipped-A, the Tra1/TRRAP subunit of the Drosophila SAGA and Tip60 complexes, has multiple roles in Notch signaling during wing development

The Notch receptor controls development by activating transcription of specific target genes in response to extracellular signals. The factors that control assembly of the Notch activator complex on target genes and its ability to activate transcription are not fully known. Here we show, through genetic and molecular analysis, that the Drosophila Nipped-A protein is required for activity of Notch and its coactivator protein, mastermind, during wing development. Nipped-A and mastermind also colocalize extensively on salivary gland polytene chromosomes, and reducing Nipped-A activity decreases mastermind binding. Nipped-A is the fly homologue of the yeast Tra1 and human TRRAP proteins and is a key component of both the SAGA and Tip60 (NuA4) chromatin-modifying complexes. We find that, like Nipped-A, the Ada2b component of SAGA and the domino subunit of Tip60 are also required for mastermind function during wing development. Based on these results, we propose that Nipped-A, through the action of the SAGA and Tip60 complexes, facilitates assembly of the Notch activator complex and target gene transcription.

Notch signaling in vascular morphogenesis

PURPOSE OF REVIEW

This review highlights recent developments in the role of the Notch signaling pathway during vascular morphogenesis, angiogenesis, and vessel homeostasis.

RECENT FINDINGS

Studies conducted over the past 4 years have significantly advanced the understanding of the effect of Notch signaling on vascular development. Major breakthroughs have elucidated the role of Notch in arterial versus venular specification and have placed this pathway downstream of vascular endothelial growth factor.

SUMMARY

An emerging hallmark of the Notch signaling pathway is its nearly ubiquitous participation in cell fate decisions that affect several tissues, including epithelial, neuronal, hematopoietic, and muscle. The vascular compartment has been the latest addition to the list of tissues known to be regulated by Notch. Unraveling the contribution of Notch signaling to blood vessel formation has resulted principally from gain-of-function and loss-of-function experiments in mouse and zebrafish. During the past 4 years, these mechanistic studies have revealed that Notch is required for the successful completion of several steps during vascular morphogenesis and differentiation. In addition, the findings that Notch mutations are linked to some late-onset hereditary vascular pathologic conditions suggest the added contribution of this signaling pathway to vascular homeostasis.

Conserved cross-interactions inDrosophilaandXenopusbetween Ras/MAPK signaling and the dual-specificity phosphatase MKP3

The extracellular signal-regulated kinase (ERK) is a key transducer of the epidermal growth factor receptor (EGFR) and fibroblast growth factor receptor (FGFR) signaling pathways, and its function is required in multiple processes during animal development. The activity of ERK depends on the phosphorylation state of conserved threonine and tyrosine residues, and this state is regulated by different kinases and phosphatases. A family of phosphatases with specificity toward both threonine and tyrosine residues in ERK (dual-specificity phosphatases) play a conserved role in its dephosphorylation and consequent inactivation. Here, we characterize the function of the dual-specificity phosphatase MKP3 in Drosophila EGFR and Xenopus FGFR signaling. The function of MKP3 is required during Drosophila wing vein formation and Xenopus anteroposterior neural patterning. We find that the expression of the MKP3 gene is localized in places of high EGFR and FGFR signaling. Furthermore, this restricted expression depends on ERK function both in Drosophila and Xenopus, suggesting that MKP3 constitutes a conserved negative feedback loop on the activity of the Ras/ERK signaling pathway.

Wing venation and Distal-less expression in Heliconius butterfly wing pattern development

Here we show that major color pattern elements of Heliconius butterfly wings develop independently of wing venation. We recovered a hybrid Heliconius displaying a mutant phenotype with a severe vein deficiency. Although this butterfly lacked most of its wing veins, the large, melanic banding patterns typical of the genus were conserved across the entire wing. The only obvious correlation between vein reduction and pigment patterns was a loss of vein-associated melanin stripes near the distal margin of the wings. We examined the expression of the eyespot-associated transcription factor Distal-less in a banded and a spotted species of Heliconius and found no obvious relationship between protein expression and the band or spot patterns typical of the genus. Together, our results suggest that the melanic bands and spots in Heliconius are unlikely to be derived from an eyespot determination system. We propose that major elements of Heliconius wing pattern formation are based primarily on a complex, whole-wing proximodistal axis system.

2,3,7,8-Tetrachlorodibenzo-p-Dioxin Inhibits Regression of the Common Cardinal Vein in Developing Zebrafish

A role for the aryl hydrocarbon receptor (AHR) pathway in vascular maturation has been implicated by studies in Ahr-null mice. In this study the hypothesis that activation of AHR signaling by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters common cardinal vein (CCV) development in the zebrafish embryo was investigated. The CCV is a paired vessel that grows across the yolk, connecting to the heart. It is extensively remodeled and regresses as the heart migrates dorsally within the pericardium. TCDD significantly reduced CCV growth as early as 44 h post fertilization (hpf), and CCV area was reduced to 63% of control at 62 hpf. This vascular response to TCDD was at least as sensitive as previously defined endpoints of TCDD developmental toxicity in zebrafish. TCDD also blocked regression of the CCV (by 80 hpf), possibly contributing to the "string-like" heart phenotype seen in TCDD-exposed zebrafish larvae. Dependence of the block in CCV regression on zebrafish (zf) AHR2 was investigated using a zfahr2 specific morpholino to knock down expression of AHR2. The zfahr2 morpholino had no effect on CCV regression in the absence of TCDD, but did protect against the TCDD-induced block of CCV regression. This demonstrates that the TCDD-induced block in CCV regression is AHR2 dependent. It is significant that decreased CCV growth occurs before and inhibition of CCV regression occurs concurrent with overt signs of TCDD developmental toxicity. This suggests that alterations of vascular growth and remodeling may play a role in TCDD developmental toxicity in zebrafish.

The fetal circulation

Accumulating data on the human fetal circulation shows the similarity to the experimental animal physiology, but with important differences. The human fetus seems to circulate less blood through the placenta, shunt less through the ductus venosus and foramen ovale, but direct more blood through the lungs than the fetal sheep. However, there are substantial individual variations and the pattern changes with gestational age. The normalised umbilical blood flow decreases with gestational age, and, at 28 to 32 weeks, a new level of development seems to be reached. At this stage, the shunting through the ductus venosus and the foramen ovale reaches a minimum, and the flow through the lungs a maximum. The ductus venosus and foramen ovale are functionally closely related and represent an important distributional unit for the venous return. The left portal branch represents a venous watershed, and, similarly, the isthmus aorta an arterial watershed. Thus, the fetal central circulation is a very flexible and adaptive circulatory system. The responses to increased afterload, hypoxaemia and acidaemia in the human fetus are equivalent to those found in animal studies: increased ductus venosus and foramen ovale shunting, increased impedance in the lungs, reduced impedance in the brain, increasingly reversed flow in the aortic isthmus and a more prominent coronary blood flow.

Hyperlipidemia coincides with reversible growth impairment of cultured human autologous endothelial cells

Patient-related risk factors for the growth of autologous endothelial cells were assessed in a clinical series of 100 consecutive recipients of in vitro endothelialized prosthetic vascular grafts. For all patients, the indication for bypass operation was arteriosclerotic occlusive disease of the distal arteries. Endothelial cells were harvested from a small piece of subdermal vein and cultured in medium containing 20% of autologous serum. Growth was continually monitored. In cultures that failed to grow, the autologous serum supplement to the culture medium was replaced by pooled homologous serum from young healthy donors. The comparison of a multitude of serum parameters between patients whose endothelial cells failed to grow and those showing normal growth revealed a significant difference in serum lipid content: triglycerides: 4.76 +/- 3.36 versus 2.83 +/- 2.28 mmol/L (p = .001); cholesterol: 6.78 +/- 1.69 versus 5.69 +/- 1.32 mmol/L (p = .003); and lipoprotein (a): 35.9 +/- 28.3 versus 22.2 +/- 26.6 mg/dl (p = .04). Following serum exchange with low-lipid pool serum that contained 1.74 mmol/L triglycerides, 4.86 mmol/L cholesterol, 5 mg/dl lipoprotein (a), and 5.79 mmol/L glucose, a remarkable recovery occurred in 85% of these cultures, resulting in fully restored proliferative capacity. As a consequence, population doubling time did not differ between the two groups at any point in time and mass cultures sufficient for confluent graft endothelialization were obtained with hardly any delay. The authors conclude that hyperlipidemia may lead to growth impairment of cultured human endothelial cells. This growth inhibition is reversible if the supplemented autologous serum is replaced by pooled serum with low lipid content.

Vascular development: molecular logic for defining arteries and veins

Vascular development is a complex process. In the past decade, significant advances have been made in the understanding of molecular mechanisms underlying vascular system development. Most recently, a model describing a signaling pathway that governs the differentiation of arteries and veins has emerged. Furthermore, the idea that angiogenesis of arteries and veins are coordinately but also differentially regulated has been proposed based on several pieces of molecular evidence. This article discusses the historical background leading to these most recent discoveries of signaling pathways that dictate arterial-venous formation and proposes a model that describes how arterial and venous systems are specified and established. The article also discusses future perspectives of this exciting area of vascular development in concluding remarks.

Making vascular networks in the adult: branching morphogenesis without a roadmap

The vascular system is unique in that extensive branching morphogenesis may take place in the adult. Developmental neovascularization is guided by precise spatial cues but vessel formation in the adult is not genetically programmed. Here, we review different adult modes for branch patterning, acquiring artery or vein identity and allocating vascular progenitor cells. The endothelium shows a remarkable degree of self-organization into a treelike network and hemodynamic forces are important in rectifying abnormal branching. This discussion is in the context of a contemplated therapy for improving organ perfusion by creating new vascular loops properly integrated within the existing network.

Comparative research on the topography of middle and small cardiac veins in humans and other primates

Many researchers have been interested in cardiac veins, which at present play a very important clinical role in invasive cardiology. In this study the occurrence of middle and small cardiac veins and the topography of their outlet portions were examined. The material consisted of 150 adult human hearts of both sexes of 18 to 85 years of age and 50 adult hearts of representatives of various primates. In the material examined a middle cardiac vein was always observed, whereas the presence of a small cardiac vein was less consistent The outlet portions of the main veins of the heart were characterised by significant variability.

The Drosophila SNR1 (SNF5/INI1) subunit directs essential developmental functions of the Brahma chromatin remodeling complex

The Drosophila melanogaster Brahma (Brm) complex, a counterpart of the Saccharomyces cerevisiae SWI/SNF ATP-dependent chromatin remodeling complex, is important for proper development by maintaining specific gene expression patterns. The SNR1 subunit is strongly conserved with yeast SNF5 and mammalian INI1 and is required for full activity of the Brm complex. We identified a temperature-sensitive allele of snr1 caused by a single amino acid substitution in the conserved repeat 2 region, implicated in a variety of protein-protein interactions. Genetic analyses of snr1(E1) reveal that it functions as an antimorph and that snr1 has critical roles in tissue patterning and growth control. Temperature shifts show that snr1 is continuously required, with essential functions in embryogenesis, pupal stages, and adults. Allele-specific genetic interactions between snr1(E1) and mutations in genes encoding other members of the Brm complex suggest that snr1(E1) mutant phenotypes result from reduced Brm complex function. Consistent with this view, SNR1(E1) is stably associated with other components of the Brm complex at the restrictive temperature. SNR1 can establish direct contacts through the conserved repeat 2 region with the SET domain of the homeotic regulator Trithorax (TRX), and SNR1(E1) is partially defective for functional TRX association. As truncating mutations of INI1 are strongly correlated with aggressive cancers, our results support the view that SNR1, and specifically the repeat 2 region, has a critical role in mediating cell growth control functions of the metazoan SWI/SNF complexes.

Estrogen inhibits development of yolk veins and causes blood clotting in transgenic medaka fish overexpressing estrogen receptor

We established three transgenic medaka fish lines overexpressing the medaka estrogen receptor under the constitutive medaka beta-actin promoter. The transgenic embryos became hypersensitive to estrogens (17 beta-estradiol and 17alpha-ethinylestradiol), and failed to develop yolk veins while blood clots formed in the blood island within 3 days after exposure to the estrogens. The embryos developed normally if exposed to estrogen after an early neurula stage, suggesting that the sensitive stage is before neurulation. The developmental defects were recovered by incubation with an anti-estrogen, tamoxifen. These results indicate that activation of estrogen receptor caused the estrogen-induced developmental defects. Our results show that the transgenic embryos can be used to assay the blood clotting activity of estrogenic compounds in vivo.

Differential effects of vascular growth factors on arterial and venous angiogenesis

OBJECTIVE

Angiogenesis, the development of new blood vessels, has become an area of increased interest for both scientific and clinical application purposes. Proangiogenic agents, such as vascular endothelial growth factor (VEGF) and naltrexone, have been shown to effectively induce new blood vessel growth. Other growth factors, such as the endogenous opioid growth factor (OGF; [Met(5)]-enkephalin) and retinoic acid, are inhibitors of angiogenesis. The differential effects on veins and arteries, however, by any vascular growth factor, have not previously been investigated.

METHODS

The chick chorioallantoic membrane (CAM) assay was used for the in vivo quantitation of angiogenesis. After 3 days of incubation, fertilized chick embryos were explanted, and a 3.2-mm methylcellulose disk containing either the known angiogenic stimulators VEGF (0.2 microg, 1.0 microg) or naltrexone (0.1 microg, 5.0 microg), or the angiogenic inhibitors OGF (1.0 microg, 5.0 microg) or retinoic acid (1.0 microg) was placed onto the CAM surface. An equal volume of distilled water served as a control. After 2 days of growth, the CAM arteries and veins were identified, and images were obtained with a digital camera. Quantitative analysis of angiogenesis was performed on a 100-mm(2) area surrounding the applied disk, and the number and length of the veins and arteries were measured.

RESULTS

The angiogenic stimulators VEGF and naltrexone markedly increased both the total number and length of all blood vessels as compared with control values. The mean length of blood vessels decreased, suggesting the induction of new vessel growth. VEGF and naltrexone proportionately increased vein and arterial angiogenesis, maintaining artery/vein ratios for vessel number and length that were unchanged compared with controls. The angiogenic inhibitors, OGF and retinoic acid, notably decreased the total number and length of blood vessels in the CAM preparations. However, these compounds had a disproportionately greater inhibitory effect on arterial angiogenesis as reflected in decreased artery/vein ratios for vessel number and length.

CONCLUSIONS

The angiogenic stimulators VEGF and naltrexone induce development of veins and arteries in a proportional manner. In contrast, the angiogenic inhibitors OGF and retinoic acid demonstrated a greater inhibitory effect on arterial as compared with venous angiogenesis. Such differential effects on angiogenesis may be important in both defining mechanisms of action and designing therapeutic interventions.

Vascular morphogenesis and remodeling in a human tumor xenograft: blood vessel formation and growth after ovariectomy and tumor implantation

To determine mechanisms of blood vessel formation and growth in solid tumors, we used a model in which LS174T human colon adenocarcinomas are grown in the isolated ovarian pedicle of nude mice. Reconstruction of 3500 histological serial sections demonstrated that a new vascular network composed of venous-venous loops of varying sizes grows inside the tumor from the wall of the adjacent main vein. Loops elongate and remodel to establish complex loop systems. The mechanisms of loop formation and remodeling correspond to intussusceptive microvascular growth (IMG). In the tissue surrounding the tumor segmentation, another mechanism of IMG is prevalent in venous vessels. Comparison to vascular morphogenesis in the ovariectomized pedicle not only confirms the existence of corresponding mechanisms in both systems, but also reveals numerous sprouts that are superimposed onto loop systems and pathological deviations of loop formation, remodeling, and segmentation in the tumor. These pathological mechanisms interfere with vessel patency that likely cause heterogenous perfusion and hypoxia thus perpetuating angiogenesis. Blood vessel formation based on IMG was also detected in a large thrombus that completely occluded a part of an ovarian artery branch.

The vascular anatomy of the developing zebrafish: an atlas of embryonic and early larval development

We have used confocal microangiography to examine and describe the vascular anatomy of the developing zebrafish, Danio rerio. This method and the profound optical clarity of zebrafish embryos make it possible to view the entire developing vasculature with unprecedented resolution. A staged series of three-dimensional images of the vascular system were collected beginning shortly after the onset of circulation at 1 day postfertilization through early- to midlarval stages at approximately 7 days postfertilization. Blood vessels in every region of the animal were imaged at each stage, and detailed "wiring patterns" were derived describing the interconnections between every major vessel. We present an overview of these data here in this paper and in an accompanying Web site "The interactive atlas of zebrafish vascular anatomy" online at (http://eclipse.nichd.nih.gov/nichd/lmg/redirect.html). We find a highly dynamic but also highly stereotypic pattern of vascular connections, with different sets of primitive embryonic vessels severing connections and rewiring in new configurations according to a reproducible plan. We also find that despite variation in the details of the vascular anatomy, the basic vascular plan of the developing zebrafish shows strong similarity to that of other vertebrates. This atlas will provide an invaluable foundation for future genetic and experimental studies of vascular development in the zebrafish.

Main tributaries of the coronary sinus in the adult human heart

The coronary sinus collects blood from the heart walls. It is a structure which presently plays a very important clinical role in invasive cardology. In this study, the occurrence of the main tributaries of the coronary sinus was examined as wall as the topography of their outlet portions. Material consistied of 150 adult human hearts of both sexes from aged 18 to 85 years. In the examined material, the graet and middle cardiac veins as well as the posterior vein of the left ventricle were always obserwed. The remaining tributaries of the coronary sinus were less stable. The outlet portions of the main veins of the heart were characterized by significant variability.

rhomboid and Star interact synergistically to promote EGFR/MAPK signaling during Drosophila wing vein development

Genes of the ventrolateral group in Drosophila are dedicated to developmental regulation of Egfr signaling in multiple processes including wing vein development. Among these genes, Egfr encodes the Drosophila EGF-Receptor, spitz (spi) and vein (vn) encode EGF-related ligands, and rhomboid (rho) and Star (S) encode membrane proteins. In this study, we show that rho-mediated hyperactivation of the EGFR/MAPK pathway is required for vein formation throughout late larval and early pupal development. Consistent with this observation, rho activity is necessary and sufficient to activate MAPK in vein primordium during late larval and early pupal stages. Epistasis studies using a dominant negative version of Egfr and a ligand-independent activated form of Egfr suggest that rho acts upstream of the receptor. We show that rho and S function in a common aspect of vein development since loss-of-function clones of rho or S result in nearly identical non-autonomous loss-of-vein phenotypes. Furthermore, mis-expression of rho and S in wild-type and mutant backgrounds reveals that these genes function in a synergistic and co-dependent manner. In contrast, spi does not play an essential role in the wing. These data indicate that rho and S act in concert, but independently of spi, to promote vein development through the EGFR/MAPK signaling pathway.

Positioning and differentiation of veins in the Drosophila wing

Morphogenesis is the process by which structures with characteristic sizes, proportions and patterns of cell differentiation are generated during the development of multicellular organisms. How the elaboration of pattern is related to cell proliferation and growth control is a critical aspect of morphogenesis. The imaginal discs of Drosophila are a suitable model in which this can be investigated at cellular and molecular level, and recent genetic and developmental analysis has identified some of the key genes and mechanisms that participate in the regulation of their growth and patterning. This review will focus on the formation of the venation pattern in the adult wing, particularly on: 1) the subdivision of the wing blade into domains of gene expression that position the veins, and 2) the cell-cell signaling pathways that participate in the final differentiation of veins.

Notch signalling regulates veinlet expression and establishes boundaries between veins and interveins in the Drosophila wing

The veins in the Drosophila wing have a characteristic width, which is regulated by the activity of the Notch pathway. The expression of the Notch-ligand Delta is restricted to the developing veins, and coincides with places where Notch transcription is lower. We find that this asymmetrical distribution of ligand and receptor leads to activation of Notch on both sides of each vein within a territory of Delta-expressing cells, and to the establishment of boundary cells that separate the vein from adjacent interveins. In these cells, the expression of the Enhancer of split gene m beta is activated and the transcription of the vein-promoting gene veinlet is repressed, thus restricting vein differentiation. We propose that the establishment of vein thickness utilises a combination of mechanisms that include: (1) independent regulation of Notch and Delta expression in intervein and vein territories, (2) Notch activation by Delta in cells where Notch and Delta expression overlaps, (3) positive feedback on Notch transcription in cells where Notch has been activated and (4) repression of veinlet transcription by E(spl)m beta and maintenance of Delta expression by veinlet/torpedo activity.

araucan and caupolican provide a link between compartment subdivisions and patterning of sensory organs and veins in the Drosophila wing

The homeo box prepattern genes araucan (ara) and caupolican (caup) are coexpressed near the anterior-posterior (AP) compartment border of the developing Drosophila wing in two symmetrical patches located one at each side of the dorsoventral (DV) compartment border. ara-caup expression at these patches is necessary for the specification of the prospective vein L3 and associated sensory organs through the transcriptional activation, in smaller overlapping domains, of rhomboid/veinlet and the proneural genes achaete and scute. We show that ara-caup expression at those patches is mediated by the Hedgehog signal through its induction of high levels of Cubitus interruptus (Ci) protein in anterior cells near to the AP compartment border. The high levels of Ci activate decapentaplegic (dpp) expression, and, together, Ci and Dpp positively control ara-caup. The posterior border of the patches is apparently defined by repression by engrailed. Wingless accumulation at the DV border sets, also by repression, the gap between the two patches. Thus, ara and caup integrate the inputs of genes effecting the primary subdivisions of the wing disc into compartments to define two smaller territories. These in turn help create the even smaller domains of rhomboid/veinlet and achaete-scute expression.

Postnatal development of the blood vasculature in the rat adrenal gland: a scanning electron microscope study of microcorrosion casts

Postnatal development of the blood vasculature in the rat adrenal gland was examined with scanning electron microscopy (SEM), using a microcorrosion casting method. The cortical vascular bed on postnatal day 1 (P1) was incipient, consisting of an outer capillary layer and an inner sinusoidal vascular layer of the juxtamedullary zone. The vascular bed grew continuously with clearer zonal differentiation as the maturation proceeded. By P7 the outer capillary layer had differentiated into the vasculature of the glomerular and fascicular zone, while the juxtamedullary sinusoidal vascular layer had reduced its thickness to differentiate into the vasculature of the reticular zone. The neonatal adrenal vasculature consisted only of the cortico-medullary system. The medullary arteries and the medullary capillary bed were first observed on P14. The adrenomedulla thus came to receive a twofold blood supply by this time. Before the establishment of the medullary arterial system, the medulla appeared to receive its blood supply partly from the cortical capillaries and partly from the radial sinusoidal vessels passing through the cortical vascular bed. The radial sinusoidal vessels were suggested to differentiate into the cortical capillaries. The medullary arteries may originate from the vessels associated with chromaffin bodies incorporated into the adrenal gland or differentiate from the radial sinusoidal vessels. Histological changes, including cortical cell involution and hemorrhage occurring during the neonatal period, would seem to have crucial relevance to the remodeling of the adrenal vasculature.

Vein is a novel component in the Drosophila epidermal growth factor receptor pathway with similarity to the neuregulins

The activation signal from tyrosine kinase receptors, such as the epidermal growth factor receptor (EGFR), is relayed via a highly conserved intracellular pathway involving Ras, Raf, and MAPK. In Drosophila, the EGFR and components of the intracellular pathway are broadly expressed, yet receptor activation evokes tissue-specific cell responses. Extracellular events that lead to receptor activation are one mechanism by which signaling is modulated. Here we show molecular and genetic evidence that Drosophila vein (vn) encodes a candidate EGFR ligand and that vn expression is spatially restricted. Consequently, vn may promote tissue-specific receptor activation. Unlike two other ligands, Gurken (Grk) and Spitz (Spi), which are transforming growth factor alpha-like proteins, Vn has both an immunoglobulin-like and an EGF-like domain. This combination of domains mirrors those in the vertebrate neuregulins that bind EGFR relatives.

The Drosophila secreted protein Argos regulates signal transduction in the Ras/MAPK pathway

The Drosophila argos gene encodes a secreted protein with an EGF motif which acts as an inhibitor of cellular differentiation in multiple developmental processes. To investigate the cellular pathways regulated by Argos, we screened for mutations which could modify the phenotype caused by overexpression of argos. We show that the effects of argos overexpression on the eye and wing vein development are suppressed by gain-of-function mutations of the MAPKK/D-MEK gene (Dsor1/D-mek) and the MAPK/ERK-A gene (rolled) and were enhanced by loss-of-function mutations of Star. Loss-of-function mutations in components of the Ras/MAPK signaling cascade act as dominant suppressors of the phenotype caused by the argos null mutations. A loss-of-function argos mutation enhanced the overproduction of R7 neurons caused by gain-of-function alleles of Son of sevenless and Dsor1. Conversely, overexpression of argos inhibited formation of the extra R7 cells that was caused by high-level MAPK/ERK-A activity. A phenotype of the sev; argos double mutants revealed that sev is epistatic to argos. These results provide evidence that Argos negatively regulates signal transduction events in the Ras/MAPK cascade.

A JAK-STAT pathway regulates wing vein formation in Drosophila

We present evidence that the JAK-STAT signal transduction pathway regulates multiple developmental processes in Drosophila. We screened for second-site mutations that suppress the phenotype of the hyperactive hopTum-1 Jak kinase, and recovered a mutation that meiotically maps to the known chromosomal position of D-Stat, a Drosophila stat gene. This hypomorphic mutation, termed statHJ contains a nucleotide substitution in the first D-Stat intron, resulting in a reduction in the number of correctly processed transcripts. Further, the abnormally processed mRNA encodes a truncated protein that has a dominant negative effect on transcriptional activation by the wild-type cDNA in cell culture. statHJ mutants exhibit patterning defects that include the formation of ectopic wing veins, similar to those seen in mutants of the epidermal growth factor/receptor pathway. Abnormalities in embryonic and adult segmentation and in tracheal development were also observed. The hopTum-1 and statHJ mutations can partially compensate for each other genetically, and Hop overexpression can increase D-Stat transcriptional activity in vitro, indicating that the gene products interact in a common regulatory pathway.

Araucan and caupolican, two members of the novel iroquois complex, encode homeoproteins that control proneural and vein-forming genes

In Drosophila imaginal wing discs, the achaete-scute (ac-sc) proneural genes and rhomboid (veinlet) are expressed in highly resolved patterns that prefigure the positions of sensory organs and wing veins, respectively. It is thought that these patterns are generated by a combination of factors (a prepattern) regulating these genes. We provide evidence for the existence of this prepattern by identifying two of its factors, Araucan and Caupolican. They are members of a novel family of homeoproteins, with homologs in vertebrates. Araucan and Caupolican, present in domains of the imaginal discs larger than those expressing ac-sc and rhomboid, are necessary for expression of these genes in the overlapping domains. Araucan and Caupolican appear to be positive, direct regulators of ac-sc.

Long-term electrical stimulation of rabbit skeletal muscle increases growth of paired arteries and veins

We tested whether chronic stimulation of skeletal muscle can increase the growth of paired arteries and veins in rabbit extensor digitorum longus muscle (EDL). The right EDL of female New Zealand White rabbits was stimulated via the common peroneal nerve at 10 Hz using 300 microseconds square waves at 3-4 V. Two-hour periods of stimulation was alternated with 4-h periods of rest, 7 days/wk for approximately 60 days. The left EDL served as control. The hindlimb vascular system was maximally dilated and perfuse-fixed with 3% glutaraldehyde and 2% paraformaldehyde at arterial and venous pressures of 80-100 and 15-20 mmHg, respectively. Muscles were postfixed in OsO4 and embedded in EPOX 812 resin. One millimeter-thick transverse sections were cut at uniform locations through the entire breadth of the muscle and analyzed using videomicroscopy along with computerized morphometric and stereological techniques. All paired arteries and veins on each full muscle section were analyzed. Chronic muscle stimulation caused the wall volume of paired arteries and veins to increase by an average of approximately twofold and the lumen volume to increase by an average of approximately threefold compared with the contralateral muscles. The wall-to-lumen area ratio of the arteries and veins was not affected. Muscle stimulation also caused the numerical density of arteries having a diameter > 100 microns to increase by approximately fourfold and the density of veins having a perimeter > 500 microns to increase by approximately 10-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein gene product 9.5 in the developing and mature rat vomeronasal organ

Protein gene product 9.5 (PGP 9.5) was immunocytochemically identified in structures of the developing and mature rat vomeronasal organ (VNO). This study started with embryos at 17 days of gestation. By this stage, PGP 9.5 was immunolocalized within both the receptor cells of the neuroepithelium and cells of the receptor-free epithelium, located on the opposite side of the lumenal space. Nerve fibers surrounding the nascent vomeronasal vein also showed PGP 9.5 immunoreactivity. Labeling was retained in the neuroepithelium and nerve fibers around the vein during development and into adulthood. Within the pool of receptor cells of the adult neuroepithelium, labeling was observed within the cytoplasm of the somata and dendrites; some receptor cells also expressed nuclear labeling. The number of immunoreactive cells in the receptor-free epithelium appeared to increase postnatally but by adulthood immunoreactivity virtually was absent. These results suggest a role for PGP 9.5 in development and maturation of the VNO and a continuing role within the steadily renewing receptor cell population found in the mature neuroepithelium. The findings of this study also suggest that PGP 9.5 is localized within the nerve fibers surrounding the vomeronasal vein from early in development through adulthood.

Early postnatal growth of skeletal muscle blood vessels of the rat

The development of blood vessels during the first three postnatal weeks was studied in the ventral stripe of the spinotrapezius muscle of the rat by use of India ink-gelatine injections, and electron microscopy. The number of terminal arterioles and collecting venules remained unchanged postnatally in the observed area. A remarkable proximodistal gradient of vascular development was apparent: while the basic structure of the hilar vessels remained unchanged in the time studied, the intramuscular arteries and veins matured gradually. More peripherally, gradual maturation of terminal and precapillary arterioles was observed. The capillary endothelium and the pericytes showed immature features, and remained unchanged during the time studied. An intense rebuilding activity was found in the endothelial cells of the growing venules, expressed by various forms of gaps, covered by an intact basal lamina and pericytes. Numerous mast cells and macrophages were found along all vessels. Intramuscular lymphatics were not present prior to the first postnatal week.

Trophoblastic invasion and modification of uterine veins during placental development in macaques

Trophoblast cells invade and modify the uterine vasculature to provide circulation of maternal blood through the placenta. Although evidence indicates fundamental differences between trophoblast modification of arteries and veins, interactions between trophoblast cells and uterine veins have not been addressed. In this report we describe the processes by which trophoblast cells invade and restructure uterine veins during placentation in the macaque. Antibodies were used to identify trophoblast, endothelium, and basement membranes. During early gestation, trophoblast migrated from the trophoblastic shell and, by intravasation, replaced portions of the wall and endothelium of veins in the vicinity of the shell; this is in contrast to invasion by extravasation reported for the arteries in this species. These areas had discontinuous endothelial basement membranes and the endothelial cells were variably hypertrophied. Deeper portions of veins were not invaded; this too is in contradistinction to the spiral arteries where trophoblastic modification extends to the myometrial segments. Later in gestation, those portions of veins interacting with trophoblast were contained within the trophoblastic shell or situated such that one side abutted the shell. These regions of the veins were lined by endothelium, but it could not be determined whether this represented re-endothelialization of regions formerly lined by trophoblast or if these endothelial cells were never displaced.

[The development of pre- and post-natal veins]

Superficial and deep veins have different evolutions, structures and functions. Phylogenetically, superficial veins of limbs appear before the deep ones. In mammals other than man, both anatomical and histological abnormalities of superficial and deep veins have been noticed. In phlebology, the date of the first appearance of these veins was examined, from the infantile age to the age of 60 in 2,259 patients. Incomplete truncal varicose veins or an excess of certain perforating veins were found in 13.9% cases among children of school age. In 71.0% cases, these defects had a hereditary origin.

[Anatomical variability of the left gastric artery and vein in newborn infants]

Structural variants of the left gastric artery (LGA) and left gastric vein (LGV) in newborns have been studied on 93 preparations of the stomach with ++extra-organic arteries and on 90 preparations of the stomach with ++extra-organic veins. There is certain correlation between the length of the trunk and character of branching of the LGA. A branch of the LGA, running to the posterior surface of the cardial part in the upper part of the gastric body, which is not described in the literature, has been found. Rather often in newborn children from the iliac trunk instead of the LGA, a left gastro-hepatic trunk has got off. The number of tributaries from the posterior surface of the gastric body to the LGV is found to be significantly greater than the number of tributaries from the anterior surface of the gastric body to this vein.

[Morphology and development of the veins of the uterus in cattle during the fetal and neonatal periods]

A total of 101 specimens were used; they came from 89 fetuses (4th to 40th week of gestation) and 12 neonates (1 to 14 days old). The age of the fetuses was determined according to the method of Kantorova (1960). The uterine veins were filled with latex using an automatic injection apparatus of our own construction. The study showed that blood left the uterus of the examined animals through constantly present veins (Ramus uterinus venae ovaricae, V. uterina and Ramus uterinus venae vaginalis) as well as through a number of inconstant veins to which belonged the Vv. vaginales accessoriae craniales et caudales. The constant uterine veins and their branches differed from their adult counterparts by being morphologically more differentiated, especially by having more branches of which some disappeared with time. The uterine veins developed toward the end of the fetal period. They arose either from the most caudal Vv. mesonephridicae lumbales (V. ovarica and its branches), or from the segmental, visceral veins of the pelvis (V. uterina and Vv. vaginales).

The development of the vasculature of the pelvic fin in the Australian lungfish, Neoceratodus forsteri

The development of the vasculature of the pelvic fin in the Australian lungfish, Neoceratodus forsteri, was studied by the dye-injection method. The primitive iliac artery of the primitive iliocecal artery which originates in the dorsal aorta drains into the posterior cardinal vein. As development proceeds, the primitive iliac artery penetrates the fin anlage, and finally becomes the pelvic fin artery. The chief venous channel in the fin anlage draining into the posterior cardinal vein is the pelvic fin vein. The arterio-venous condition in the pelvic fin anlage in this animal changes successively as follows: 1) one artery and one vein, 2) two arteries and one vein, 3) two arteries and two veins. The postaxial arterial element elongates to be located in the preaxial region, and the postaxial vein is located in the postaxial region from beginning to end.

Maturational changes in the pharmacological characteristics and actomyosin content of canine arterial and venous tissue

The purpose of this study was to compare the pharmacological characteristics and actomyosin content of arterial and venous tissue at different times during development. Rings of arteries (femoral, renal, carotid, pulmonary) and veins (saphenous, pulmonary, jugular) were obtained from 1 wk, 1 month, and adult dogs, mounted at their optimal length for force development and the contractile response to potassium chloride and phenylephrine determined. The strain at optimal length was less at all ages in pulmonary artery and pulmonary and jugular veins than in other vessels. All vessels exhibited an increase in maximum contractile response with development but the increase was greater for phenylephrine. In general, the magnitude of the maximum response of the jugular and pulmonary veins and pulmonary artery was less than other vessels at all ages. The sensitivity (half maximum response) either increased or was unchanged in arteries with development, while in the veins it either decreased or was unchanged. The relaxant effects of verapamil and isoproterenol were determined on potassium chloride contracted vessels. Arterial tissue was minimally responsive to isoproterenol at all ages while venous tissue either increased its responsiveness (saphenous, pulmonary) with development or remained highly responsive (jugular). Verapamil, unlike isoproterenol, was an effective relaxant of all vessels. The actomyosin content (mg/mm) of femoral and renal arteries and saphenous and jugular veins increased with development but this increase was accompanied by a parallel increase in total protein so that the ratio (actomyosin/total protein) was unchanged. In jugular veins from adult dogs this ratio was smaller than in arterial tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal development of the vascular pattern in the rat telencephalic pia-arachnoid. A SEM study

The postnatal changes in arrangement of the vascular system of the pia-arachnoid of rats are described based on scanning electron microscopy of microcorrosion casts and transmission electron microscopy. At birth, the distal arteries and veins are embedded in a dense plexiform network of immature capillaries. Arteries and veins are interconnected by many small capillary anastomoses. The trunks are located above the pial plexus. The underlying plexiform vessels provide the matrix for the formation of additional collateral and precortical segments during further development. During the first postnatal week, the distal pial arteries and veins become visible as separate channels and emerge from the subjacent capillary plexus. The pattern of anastomosing arterial rings is now clearly visible. The pial arterial tree can be subdivided into conductive, collateral, and precortical distributive segments, according to Jokelainen et al. (1982). Subsequently, passive expansion of the vascular system takes place during the period of rapid brain growth. In young adults the majority of the formerly closed arterial rings are interrupted, possibly by regression of single collateral arterial segments (Fig. 6). The dense venous capillary plexus of the pia is maintained during the first eight days in spite of marked brain growth. The process of reduction of this capillary plexus starts at the arterial side and proceeds from proximal to distal segments of the veins during the second and third week. The capillary segments, which provide anastomosis between arterial and venous vessels, disappear at the same time as the regression of the dense venous capillary network.(ABSTRACT TRUNCATED AT 250 WORDS)