Vitelline Vein Research Articles

Expression pattern of Vasohibin during chick development

Vasohibin is an angiogenesis inhibitor that is induced in endothelial cells in an autocrine manner. In this study, we cloned a 500-bp fragment of chick Vasohibin cDNA and analyzed its expression pattern by in situ hybridization during chick development. From HH-stage 3, expression of Vasohibin is observed in the area opaca and it is expressed throughout the primitive streak during later stages. At HH-stage 11, Vasohibin is expressed in head paraxial mesoderm, in the vitelline vein, dorsal neural tube, intermediate and lateral plate mesoderm, Wolffian duct, and blood islands at the caudal part of the embryo. In epithelial somites, expression is seen in the region around the somitocoel, and after somite maturation, expression is observed in the myotome, which becomes stronger with development. Expression is detected in fore and hind brain, also in the retina and lens vesicle of the developing eye. In the early limb bud, expression is initiated in the mesenchyme and becomes stronger during later stages. Expression in the limb mesoderm remains strong at the margins but decreases in the central mesenchyme. At day 7, expression is seen in interdigital grooves of the digits and digit-demarcating regions. During organogenesis, expression is seen in the anlagen of the esophagus, trachea, duodenum, lungs, liver, heart, and gut. Our analysis shows that Vasohibin is expressed in a wide range of tissues and organs suggesting that Vasohibin acts as a physiological regulator of vascular development during chick embryogenesis.

Myocardin‐related transcription factor B is required for normal mouse vascular development and smooth muscle gene expression

Smooth muscle gene expression is required for the proper development and function of multiple organ systems. Expression of smooth muscle genes is critical for contractile function and tissue architectural integrity. One critical transcription factor for smooth muscle gene expression is the Serum Response Factor (SRF). SRF is expressed ubiquitously, but tissue-specific transcriptional regulation is conferred by its binding to cofactors such as myocardin. Myocardin-related transcription factor B (MRTF-B) is a member of a family of genes (Myocardin(Myocd),Myocardin-related transcription factor A(MRTF-A),MRTF-B) that provides tissue-specificity and potentiate SRF-dependent transcription. Unlike myocardin, which is expressed specifically in smooth and cardiac muscle, MRTF-B is expressed in a wide variety of tissues. To examine the function of MRTF-B, we generated mice containing an insertional mutation of MRTF-B. MRTF-B homozygous mutants die in late gestation with vascular defects and liver hemorrhage. At E9.5, MRTF-B is expressed strongly in the septum transversum mesoderm critical for development of the vitelline system that produces the liver sinusoids and portal venous system. MRTF-B deficiency results in defective smooth muscle gene expression in the liver sinusoids, vitelline veins, and yolk sac, which contributes significantly to the lethal phenotype. These data support our hypothesis that MRTF-B has a unique role in regulating smooth muscle genes important for liver, yolk sac, and portal vascular development.

Evidence for an Adaptive Immune Barrier after in Utero Hematopoietic Cell Transplantation.

In utero hematopoietic cell transplantation (IUHCT) is a nonmyeloablative approach that takes advantage of normal immunologic development to achieve donor specific tolerance. Despite the many potential advantages of the fetal recipient, IUHCT across MHC barriers has been limited by low levels of engraftment and the inability to consistently achieve allochimerism.Although the immature immune system of the developing fetus has long been appreciated as a principal advantage of IUHCT, the competence of the fetal immune system to act as a barrier to IUHCT has been a source of debate. Until now, comparisons of allogeneic and congenic engraftment have been inconclusive due to methodologic limitations resulting in minimal and inefficient engraftment. In this study, a new intravascular technique that allows definitive administration of much higher doses of donor cells was employed to directly compare the incidence and levels of engraftment following in utero transplantation of either congenic or allogeneic bone marrow (BM) or enriched hematopoietic stem cells (HSCs). 20E+06 B6 GFP BM cells (H2Kb+, GFP+) or 1E+05 cKit+Sca-1+Lin- B6 GFP cells (H2Kb+, GFP+) were intravenously injected via the vitelline vein into gestational day 14 Balb/c (H2Kd+, allogeneic) or C57Bl/6 (H2Kb+, congenic) fetal mice. The peripheral blood (PB) of recipients was serially analyzed by flow cytometry for GFP+ donor cells at 1, 2, 4 and 6 months of age. A separate group of animals was harvested at 1 week of age (2 weeks after injection) to assess donor chimerism in PB and BM. Our results demonstrate that 100% of surviving recipients of whole BM demonstrate engraftment at 1 week of age, but that 70% of allogeneic recipients lose engraftment by 1 month of age, and 80% ultimately fail to sustain long-term chimerism. In contrast, all congenic recipients maintain engraftment at 6 months of age (Table 1). Chimerism levels in allogeneic recipients drop significantly after 1 month of life while those in congenic recipients remain stable. This results in a significant difference in engraftment levels in allogeneic and congenic recipients beyond 1 month of life (Fig 1). Similar results were seen when enriched HSCs were the donor cell source. 100% (2/2) of congenic recipients of enriched HSCs demonstrated stable low level PB engraftment up to 6 months of life (0.14–0.55% GFP+ donor cells). In contrast, no allogeneic recipients (0/9) of enriched HSCs were chimeric from 1 to 6 months of life. In combination, these results demonstrating a 100% efficiency of long-term engraftment in congenic recipients and loss of engraftment by 1 month of age in the majority of allogeneic recipients strongly implicate an adaptive immune barrier to allogeneic engraftment after IUHCT. Better understanding of the immune mechanisms limiting allogeneic engraftment after IUHCT is required to allow the development of successful strategies for IUHCT.Efficiency of Engraftment after IUHCT in Congenic and Allogeneic Recipients1 week of age (BM)1 week of age (PB)1 month of age (PB)6 months of age (PB)congenic100% (8/8)100% (8/8)100% (25/25)100% (25/25)allogeneic100% (8/8)100% (8/8)29% (9/31)19% (6/31) [Display omitted]

In Utero Transplantation of Transduced Hematopoietic Stem Cells Results in Deletion of Transgene-Specific T Cells.

The developing fetal immune system provides a unique opportunity to manipulate normal immunologic development for therapeutic prenatal and anticipated postnatal interventions. In previous studies we have shown that allogeneic in utero hematopoietic cell transplantation (IUHCT) results in donor specific tolerance that can subsequently facilitate non-myeloablative postnatal cellular or organ transplants. It follows that in utero injection of transduced hematopoietic stem cells (HSC) could potentially induce tolerance to a transgene encoded protein. We hypothesized that expression of a transduced antigenic protein by HSC and their progeny would alter thymic T cell development resulting in deletion of antigen specific T-cells. To test this hypothesis, we used the mammary tumor virus (MTV) superantigen system to evaluate the effect of IUHCT of transduced HSC on T cell development. In this system, expression of different MTV oncogenes by different I-E+ strains of mice results in deletion of T cells expressing the relevant Vβ T cell receptor. Specifically, mice which are Mtv7+ delete T cells expressing the Vβ6 T-cell receptor. In this study, CD150+CD48− enriched Balb/c (I-E+ Mtv7−) HSC were transduced with an HIV-based lentivirus expressing MTV7 under an MND promoter. 1.5E+05 transduced cells were injected intravascularly via the vitelline vein into E14 Balb/c fetuses. Non-injected age matched naive Balb/c mice served as the control group. The peripheral blood (PB) and thymuses of injected fetuses and control mice were harvested at day of life (DOL) 10, 20 and 60 and analyzed by flow cytometry for T lymphocyte Vβ6 expression. Additionally, the T cell composition of the thymus was assessed at DOL10 for CD4 and CD8 single positive (SP) and CD4/CD8 double positive (DP) cells. Thymic flow cytometric analysis at DOL10 revealed that greater than 98% of the T cells were CD4CD8 DP, a stage that has not yet undergone negative selection. No significant difference was noted in the percentage of thymic Vβ6+ DP T-cells at this time point or at DOL20 and DOL60. In contrast, there was a significant decrease in the percentage of Vβ6+ peripheral blood SP cells in those mice injected with MTV7 transduced HSC relative to control mice at DOL10, DOL20 and DOL60 (p<0.05) (Fig 1). The current study supports the ability of enriched transduced HSC to induce deletion of transgene specific T cells after IUHCT. In the future, this strategy may be useful to promote tolerance for pre or postnatal cellular or gene therapy. [Display omitted]

Computational Model for Early Cardiac Looping

Looping is a vital event during early cardiac morphogenesis, as the initially straight heart tube bends and twists into a curved tube, laying out the basic pattern of the future four-chambered heart. Despite intensive study for almost a century, the biophysical mechanisms that drive this process are not well understood. To explore a recently proposed hypothesis for looping, we constructed a finite element model for the embryonic chick heart during the first phase of looping, called c-looping. The model includes the main structures of the early heart (heart tube, omphalomesenteric veins, and dorsal mesocardium), and the analysis features realistic three-dimensional geometry, nonlinear passive and active material properties, and anisotropic growth. As per our earlier hypothesis for c-looping, actin-based morpho-genetic processes (active cell shape change, cytoskeletal contraction, and cell migration) are simulated in specific regions of the model. The model correctly predicts the initial gross morphological shape changes of the heart, as well as distributions of morphogenetic stresses and strains measured in embryonic chick hearts. The model was tested further in studies that perturbed normal cardiac morphogenesis. The model, taken together with the new experimental data, supports our hypothesis for the mechanisms that drive early looping.

Computational Model for Early Cardiac Looping

Looping is a vital event during early cardiac morphogenesis, as the initially straight heart tube bends and twists into a curved tube, laying out the basic pattern of the future four-chambered heart. Despite intensive study for almost a century, the biophysical mechanisms that drive this process are not well understood. To explore a recently proposed hypothesis for looping, we constructed a finite element model for the embryonic chick heart during the first phase of looping, called c-looping. The model includes the main structures of the early heart (heart tube, omphalomesenteric veins, and dorsal mesocardium), and the analysis features realistic three-dimensional geometry, nonlinear passive and active material properties, and anisotropic growth. As per our earlier hypothesis for c-looping, actin-based morpho-genetic processes (active cell shape change, cytoskeletal contraction, and cell migration) are simulated in specific regions of the model. The model correctly predicts the initial gross morphological shape changes of the heart, as well as distributions of morphogenetic stresses and strains measured in embryonic chick hearts. The model was tested further in studies that perturbed normal cardiac morphogenesis. The model, taken together with the new experimental data, supports our hypothesis for the mechanisms that drive early looping.

Enlarged Left Vitelline Vein Remnant as a Cause of Cyanosis after the Fontan Procedure: Resolution with an Amplatzer Vascular Plug

A 6-year-old girl with heterotaxy and a functional single ventricle had persistent cyanosis 4 years after a fenestrated Fontan procedure. Cardiac catheterization revealed a large venous fistula from a left-sided hepatic vein to the coronary sinus, resulting in desaturation. The anomalous vein was occluded with an Amplatzer vascular plug.

Circumcaval Ureter: Embryology

Objectives A circumcaval ureter is a rare congenital anomaly usually associated with upper urinary tract stasis and an “S” or “fishhook” deformity of the ureter, in which the ureter itself passes behind the inferior vena cava. Aim of this paper was to debate novel issues concerning the embryologic anomaly of the inferior vena cava which may lead to the ureter obstruction and hydronephrosis. Methods Search of published literature and meeting abstracts. Results A circumcaval ureter results from the posterior cardinal vein persisting as the renal segment of the inferior vena cava during development. Normally, the inferior vena cava develops from the vitelline vein, subcardinal and sacrocardinal veins, which must undergo sequential development, anastomosis and regression to become the inferior vena cava. Normally, the right vitelline vein forms the pre-renal or hepatic segment of the inferior vena cava, the right subcardinal vein forms the renal segment and the right sacrocardinal vein forms the post-renal vena cava. Typically, the circumcaval ureter aetiology is assumed to be abnormal embryologic development of the vena cava as a result of atrophy failure of the right posterior cardinal vein in the lumbar portion. Whether the renal segment of inferior vena cava is formed from the right posterior cardinal vein that lies ventral to the ureter, then the ureter will develop in a “circumcaval” position. Conclusions Although this embryologic anomaly is commonly known to urologists as circumcaval or retrocaval ureter – terms that are anatomically descriptive but misleading in regards to development – it is not the result of an abnormality in ureteral development but rather an anomaly in the development of the inferior vena cava. The term preureteral vena cava may thus emphasize that the circumcaval ureter results from altered vascular, rather than ureteral development.

Mesenchymal cells with leukocyte and lymphendothelial characteristics in murine embryos

The development of lymphatic endothelial cells (LECs) from deep embryonic veins or mesenchymal lymphangioblasts is controversially discussed. Studies employing quail-chick grafting experiments have shown that various mesodermal compartments of the embryo possess lymphangiogenic potential, whereas studies on murine embryos have been in favor of a venous origin of LECs. We have investigated NMRI mice from embryonic day (ED) 9.5 to 13.5 with antibodies against the leukocyte marker CD45, the pan-endothelial marker CD31, and the lymphendothelial markers Prox1 and Lyve-1. Early signs of the development of lymphatics are the Lyve-1- and Prox1-positive segments of the jugular and vitelline veins. Then, lymph sacs, which are found in the jugular region of ED 11.5 mice, express Prox1, Lyve-1, and CD31. Furthermore, scattered cells positive for all of the four markers are present in the mesenchyme of the dermatomes and the mediastinum before lymphatic vessels are present in these regions. Their number increases during development. A gradient of increasing CD31 expression can be seen the closer the cells are located to the lymph sacs. Our studies provide evidence for the existence of scattered mesenchymal cells, which up-regulate lymphendothelial and down-regulate leukocyte characteristics when they integrate into growing murine lymphatics. Such stem cells may also be present in the human and may be the cell of origin in post-transplantation Kaposi sarcoma.

N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase expression during early mouse embryonic development

N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST) is an enzyme which is known to help build up the GlcAbeta1-3GalNAc(4,6-bisSO4) unit of chondroitin sulfate E (CS-E). This enzymatic activity has been reported in squid cartilage and in human serum, but has never been reported as an enzyme required during early mouse development. On the other hand, CS-E has been shown to bind with strong affinity to Midkine (MK). The latter is a heparin-binding growth factor which has been found to play important regulatory roles in differentiation and morphogenesis during mouse embryonic development. We have analyzed the expression pattern of the GalNAc4S-6ST gene during early mouse embryonic development by whole mount in situ hybridization. The results show that GalNAc4S-6ST is differentially expressed in the anterior visceral ectoderm at stage E5.5 and later becomes restricted to the embryonic endoderm, especially in the prospective midgut region. During the turning process, expression of GalNAc4S-6ST gene is detected in the forebrain, branchial arches, across the gut tube (hindgut, midgut and foregut diverticulum), in the vitelline veins and artery and in the splanchnopleure layer. These results open the possibility of a role for GalNAc4S-6ST during early mouse development.

Incompleteness of the Structure of Liver Veins and Tissue Components in Neonatal Animals

Introduction: The formation of the liver structure at mammal embryogenesis is interconnected by drawing up of venous mains. In parallel to the transformation of the main veins, there is a reduction of the blood formation function and the liver transformation from the primary organ of embryogenesis into the secondary one, but the exception is immaturity and underdeveloped maturity mammals (Smirnova, 1967; Mechtiev, 1968; Bresler, 1993). The purpose of research is to establish morphofunctional criteria of the incompleteness in the blood vessels and in tissue components of the liver in neonatal animals.Material and Methods: The afferent and efferent liver veins of calves, piglets and puppies at one day of age were investigated. The complex of morphological, roentgenological, ultrasound and statistic methods was used.Results: It was established that the liver veins in newborn animals portoumbilical (afferent) and caval (efferent) collectors. In 1‐day‐old calves, the afferent collector is connected with caval way of the large vein flow of the main type. Relative weight of the liver in the calves is 2.31–2.85%, hepatocytes form balks and they are not always oriented radially to the central venuels. There are no seats of haemopoesis. Sonography of the liver and its veins proves inconstancy of the sizes depending on acts of breath. In 1‐day‐old piglets, many treelike anastomoses follow with the left hepatic vein. Relative weight of the liver in the piglets is 2.27–4.64%. The parenchyma of the organ is spongy with the seats of haemopoesis (0.04 3.61%). In 1‐day‐old puppies afferent and efferent collectors combine through the venous duct. Additionally, in the abdominal cavity of puppies, there are the vitelline artery (starts from a. mesenterica) and vein (runs to v. porta near the afferent collector), following to the umbilical ring. Relative weight of the liver in the puppies is about 5.18–6.04%. Hepatocytes form the chaotic congestion with haemopoetic points (2.04–7.14%).Conclusion: Thus, incompleteness of morphology of the liver is shown in preservation of provisional vein structures and tissue components of the embryonic type, which is one of the factors complicating diseases of digestive organs in neonatal animals.

Portal Vein Cavernoma Associated with Goldenhar Syndrome

Portal Vein Cavernoma Associated with Goldenhar Syndrome

Placentação em mocós, Kerodon rupestris Wied, 1820

Placentation studies in fourteen rock cavy females in different gestation phases were developed. The females were pre-anesthetized associating ketamine chloridrate (15mg/kg) and midazolan (1mg/kg). Soon afterwards, they were anesthetized by isoflurane inhalation in association with oxygen at 100% saturation. After the anesthesia, the surgery allowed to exhibit fetal structures and then data collection was performed. Macroscopically, a discoidal placenta, vitelline sack and the amnion of a transparent aspect and avascular, were identified. Microscopically, the umbilical cord presented two arteries, a vein and the allantoid duct, beyond an artery and a vitelline vein. The placenta showed a relationship between the mesometrium and the uterus and was constituted by lobes delimited by interlobular areas and, peripherically, by an area of marginal syncytium containing places with spongiotrophoblast and gigantic trophoblastic cells. The subplacenta was composed by lobules and by a trophoblast of syncytium and cellular nature. The vitelline sack showed a parietal portion sustained by the Reichert s membrane and a well-vascularized visceral portion. The placentation studies in rock cavies indicated the presence of a bicornuate uterus, a chorioallantoid discoidal and labirynthic placenta, with a hemochorial placental barrier of hemomonochorial subtype separating the maternal-fetal countercurrent sanguine flow. Key-words: Rock cavies. Placenta. Microscopy. Placental barrier FICHA CATALOGRAFICA: Oliveira, Moacir Franco Placentacao em mocos, Kerodon rupestris Wied, 1820/ Moacir Franco Oliveira. 208f. : il. Tese (doutorado) Universidade de Sao Paulo. Faculdade de Medicina Veterinaria e Zootecnia. Departamento de Cirurgia, Sao Paulo, 2003. Area de concentracao: Anatomia dos Animais Domesticos e Silvestres Orientador: Prof. Dra. Maria Angelica Miglino. E-MAIL orientador: miglino@usp.br PUBLICACOES RESULTANTES DA TESE: M. A. MIGLINO , A. M. CARTER , C. E. AMBROSIO , M. BONATELLI , M. F. DE OLIVEIRA , R. H. dos SANTOS FERRAZ , R. F. RODRIGUES; T. C. SANTOS Vascular Organization of the Hystricomorph Placenta: a Comparative Study in the Agouti, Capybara, Guinea Pig, Paca and Rock Cavy, Placenta, 25(5):438-448, 2004. www.sciencedirect.com/science/journal/01434004 http://www.biotaneotropica.org.br

Systolic and Diastolic Ventricular Function Assessed by Pressure-Volume Loops in the Stage 21 Venous Clipped Chick Embryo

Cardiac pressure-volume relations enable quantification of intrinsic ventricular diastolic and systolic properties independent of loading conditions. The use of pressure-volume loop analysis in early stages of development could contribute to a better understanding of the relationship between hemodynamics and cardiac morphogenesis. The venous clip model is an intervention model for the chick embryo in which permanent obstruction of the right lateral vitelline vein temporarily reduces the mechanical load on the embryonic myocardium and induces a spectrum of outflow tract anomalies. We used pressure-volume loop analysis of the embryonic chick heart at stage 21 (3.5 d of incubation) to investigate whether the development of ventricular function is affected by venous clipping at stage 17, compared with normal control embryos. Steady state hemodynamic parameters demonstrated no significant differences between the venous clipped and control embryos. However, analysis of pressure-volume relations showed a significantly lower end-systolic elastance in the clipped embryos (slope of the end-systolic pressure-volume relation: 5.68 +/- 0.85 versus 11.76 +/- 2.70 mm Hg/microL, p < 0.05), indicating reduced contractility. Diastolic stiffness tended to be increased in the clipped embryos (slope of end-diastolic pressure-volume relation: 2.74 +/- 0.56 versus 1.67 +/- 0.21, p = 0.103), but the difference did not reach statistical significance. The results of the pressure-volume loop analysis show that 1 d after venous obstruction, development of ventricular function is affected, with reduced contractility. Pressure-volume analysis may be applied in the chick embryo and is a sensitive technique to detect subtle alterations in ventricular function.

The role of mechanical forces in dextral rotation during cardiac looping in the chick embryo

Cardiac looping is a vital morphogenetic process that transforms the initially straight heart tube into a curved tube normally directed toward the right side of the embryo. While recent work has brought major advances in our understanding of the genetic and molecular pathways involved in looping, the biophysical mechanisms that drive this process have remained poorly understood. This paper examines the role of biomechanical forces in cardiac rotation during the initial stages of looping, when the heart bends and rotates into a c-shaped tube (c-looping). Embryonic chick hearts were subjected to mechanical and chemical perturbations, and tissue stress and strain were studied using dissection and fluorescent labeling, respectively. The results suggest that (1) the heart contains little or no intrinsic ability to rotate, as external forces exerted by the splanchnopleure (SPL) and the omphalomesenteric veins (OVs) drive rotation; (2) unbalanced forces in the omphalomesenteric veins play a role in left–right looping directionality; and (3) in addition to ventral bending and rightward rotation, the heart tube also bends slightly toward the right. The results of this study may help investigators searching for the link between gene expression and the mechanical processes that drive looping.

Endothelial cell interactions initiate dorsal pancreas development by selectively inducing the transcription factor Ptf1a.

Dorsal and ventral pancreatic bud development from the endoderm requires inductive interactions with diverse mesodermal cell types and the action of transcription factors expressed within the endoderm. Presently it is unclear which mesodermal interactions activate which pancreatic transcription factors, and whether such inductions are common for initiating dorsal and ventral pancreas development. Previous studies of Lammert et al. showed that signaling from embryonic blood vessel cells, derived from the mesoderm, promotes pancreatic bud development. Using a combination of mouse Flk1(-/-) embryos lacking endothelial cells and tissue recombination experiments, we discovered that the initial induction of dorsal endoderm cells positive for the pancreatic and duodenal transcription factor Pdx1 does not require aorta or endothelial cell interactions, but dorsal pancreatic bud emergence and the maintenance of Pdx1 expression does. Aortal endothelial cells induce the crucial pancreatic transcription factor Ptf1a in the dorsal pancreatic endoderm; whereas the vitelline veins, which are normally adjacent to the emerging ventral pancreatic bud, are unnecessary for ventral Ptf1a induction or for ventral pancreatic bud initiation. We find that the aorta cells themselves, apart from the blood supply, cause the induction of Ptf1a in dorsal endoderm explants. Thus, endothelial cell interactions specifically promote early dorsal pancreatic development, at least in part, by inducing Ptf1a(+) pancreatic progenitors. Additionally, we find that endothelial cells are necessary for the induction of both the insulin and glucagon genes.

Effects of nitric oxide synthase inhibitors and a substrate, l-arginine, on the cardiac function of juvenile salmonid fish

Control of cardiac function was investigated juvenile brown trout ( Salmo trutta L.) and rainbow trout ( Oncorhynchus mykiss Walbaum) using inhibitors of nitric oxide synthase (NOS), (L -NAME , N G-nitro- l-arginine and L-NMMA, N G-monomethyl- l-arginine) and a substrate of NOS ( l-arginine). Salmonid alevins are excellent models for such studies since they are transparent, the beating heart is easily observed, diffusing distances are small, and they respond within a few seconds to exogenously administered chemicals. The response to inhibitors of NOS ( L-NAME or L-NMMA) was tachycardia interpreted as vasoconstriction through lowered capacity for synthesis of NO. This could be reversed by addition of l-arginine and the subsequent bradycardia was explained as a vasodilation resulting from increased synthesis of NO. Blood flow into the heart is mainly via the vitelline vein and changes of flow resulting from constriction or dilation of this vessel may be probably major determinants of heart rate. The results provide evidence for the presence NOS in juvenile fish and indicate a physiological role for NO in cardiovascular control.

Acutely altered hemodynamics following venous obstruction in the early chick embryo.

In the venous clip model specific cardiac malformations are induced in the chick embryo by obstructing the right lateral vitelline vein with a microclip. Clipping alters venous return and intracardiac laminar blood flow patterns, with secondary effects on the mechanical load of the embryonic myocardium. We investigated the instantaneous effects of clipping the right lateral vitelline vein on hemodynamics in the stage-17 chick embryo. 32 chick embryos HH 17 were subdivided into venous clipped (N=16) and matched control embryos (N=16). Dorsal aortic blood flow velocity was measured with a 20 MHz pulsed Doppler meter. A time series of eight successive measurements per embryo was made starting just before clipping and ending 5h after clipping. Heart rate, peak systolic velocity, time-averaged velocity, peak blood flow, mean blood flow, peak acceleration and stroke volume were determined. All hemodynamic parameters decreased acutely after venous clipping and only three out of seven parameters (heart rate, time-averaged velocity and mean blood flow) showed a recovery to baseline values during the 5h study period. We conclude that the experimental alteration of venous return has major acute effects on hemodynamics in the chick embryo. These effects may be responsible for the observed cardiac malformations after clipping.

Adult and embryonic blood and endothelium derive from distinct precursor populations which are differentially programmed by BMP in Xenopus.

Blood and blood vessels develop in close association in vertebrate embryos and loss-of-function mutations suggest common genetic regulation. By the criteria of co-expression of blood and endothelial genes, and lineage tracing of progeny, we locate two distinct populations of progenitors for blood and endothelial cells in developing Xenopus embryos. The first population is located immediately posterior to the cement gland during neurula stages and gives rise to embryonic blood and vitelline veins in the anterior ventral blood island (aVBI), and to the endocardium of the heart. The second population resides in the dorsal lateral plate mesoderm, and contains precursors of adult blood stem cells and the major vessels. Both populations differentiate into endothelial cells in situ but migrate to new locations to differentiate into blood, suggesting that their micro-environments are unsuitable for haematopoietic differentiation. Both require BMP for their formation, even the Spemann organiser-derived aVBI, but individual genes are affected differentially. Thus, in the embryonic population, expression of the blood genes, SCL and GATA2, depend on BMP signalling while expression of the endothelial gene, Xfli1, does not. By contrast, Xfli1 expression in the adult, DLP population does require BMP. These results indicate that both adult and the anterior component of embryonic blood in Xenopus embryos derive from populations of progenitors that also give rise to endothelial cells. However, the two populations give rise to distinct regions of the vasculature and are programmed differentially by BMP.

Development of the intrahepatic biliary tree.

The liver develops from two anlages: the hepatic diverticulum, which buds off the ventral side of the foregut, and the septum transversum, which is the mesenchymal plate that partially separates the embryonic thoracic and abdominal cavities. The endodermal cells of the hepatic diverticulum invade the septum transversum, forming sheets and cords of hepatoblasts arrayed along the sinusoidal vascular channels derived from the vitelline veins emanating from the yolk sac. The vitelline veins fuse to form the portal vein, which ramifies as tributaries within the liver along mesenchymal channels termed portal tracts. Those hepatoblasts immediately adjacent to the mesenchyme of the portal tracts differentiate into a ductal plate, a single circumferential layer of biliary epithelial cells. Mesenchymal cells interpose between the ductal plate and the remaining parenchymal hepatoblasts, which differentiate into hepatocytes. By week 7 the ductal plate begins to reduplicate, forming a double layer of cells around the portal tract. Lumena form between the two cell layers of the ductal plate, forming peripheral biliary tubular structures. These peripheral tubules remodel and, with continued proliferation of the mesenchyme, by the 11th week begin to become more centrally located within portal tracts as terminal bile ducts with a circular cross-section. The remaining ductal plate resorbs, leaving behind only tethers of bile ductules connecting the terminal bile ducts to the parenchyma. Abutting and within the parenchyma are the canals of Hering, ductular structures half-lined by hepatocytes and half-lined by biliary epithelial cells. Maturation of the intrahepatic biliary tree to the mature tubular treelike architecture occurs from the hilum of the liver outward, beginning around the 11th week of gestation and continuing past birth for several months. The architecture of maturation is the same regardless of gestational age or radial location in the liver. Importantly, the immature intrahepatic biliary system maintains patency and continuity with the extrahepatic biliary tree throughout gestation, with no evidence of a solid phase of development. Thus, from the earliest time of hepatocellular bile formation beginning around the 12th week, there is a patent passage to the alimentary canal.