PubMed Health⌕ Search

Biomedical subjects

R E Poelmann

Publications and source records attributed to R E Poelmann.

At least 37 records · Page 2Linked to original sources
PubMed1999

Altered hemodynamics in chick embryos after extraembryonic venous obstruction.

OBJECTIVE: To obtain insight into hemodynamics during abnormal cardiac development, a chick model was developed recently in which a spectrum of conotruncal anomalies, in combination with abnormal semilunar valves and/or pharyngeal arch artery malformations, was induced through extraembryonic venous obstruction (venous clip) at stage 17 (70-h incubation). METHODS: In chick embryos of stage 24 and stage 34 control (n = 8; n = 21) and with venous clip (n = 11; n = 18), we simultaneously measured dorsal flow velocities with a 20-MHz pulsed Doppler velocity meter and dorsal aortic (stage 24) and vitelline artery (stage 34) blood pressures with a servo-null system. After the hemodynamic recordings were collected, all 58 embryos were subjected to morphological examination. The hemodynamic data were correlated with the morphology. Statistical comparison was performed between control and experimental values. RESULTS: At stage 24, venous clip embryos showed impaired looping. Physiologically, only a decrease in peak acceleration was found in these embryos (p < 0.05). At stage 34, a spectrum of conotruncal malformations was seen, that consisted of a ventricular septal defect in combination with abnormal semilunar valves and/or pharyngeal arch malformations. A dextroposed aorta in combination with a ventricular septal defect was diagnosed as double-outlet right ventricle. Hemodynamically, peak systolic and mean velocities, peak systolic and mean blood flows and stroke volume were increased while the heart rate was reduced after placement of the venous clip (p < 0.05). In both stages, pressure readings showed no statistically significant differences between control and experimental embryos. CONCLUSION: Our findings suggest that the hemodynamic changes seen in venous clip embryos reflect the presence of a compensatory mechanism.

Animals↗
PubMed1998

Epicardium-derived cells contribute a novel population to the myocardial wall and the atrioventricular cushions.

The epicardium and dorsal mesocardium are known to be the source of structures that form the wall of the coronary vessels. Because mouse knockout studies have shown that proper epicardial formation is also essential for myocardial development, we have studied in detail the migration and differentiation of epicardium-derived cells (EPDCs) within the developing heart. We constructed chicken-quail chimeras by grafting the quail epicardial organ, including a piece of primordial liver, at essentially stages 16 and 17. The embryos were studied at stages 25 to 43. To detect quail-derived EPDCs, an anti-quail nucleus antibody was used in combination with several differentiation markers, eg, for muscle actin, for vascular smooth muscle cells, for procollagen-I, for quail endothelium, and for Purkinje fibers. At stages 25 to 31, EPDCs are encountered in the myocardial wall and the subendocardial region. The latter deposition is spatially facilitated as the endocardium protrudes through transient discontinuities in the myocardium to contact the subepicardial layer. Later on, at stages 32 to 43, EPDCs invaded, by way of the atrioventricular sulcus, the atrioventricular cushion tissue. The localization is apparent at the interface with the myocardium, as well as subendocardially, but never within the endocardial lining. The origin of endothelium, smooth muscle cells, and fibroblasts of the coronary vessel wall from the epicardial graft were confirmed in accordance with already published data. The functional role of the novel EPDCs in the subendocardium, myocardium, and atrioventricular cushions remains to be investigated. A close positional relationship is found with the differentiating Purkinje fibers. Furthermore, a regulatory role is postulated in the process of endocardial-mesenchymal transformation. The ultimate fate of EPDCs seems to be a cardiac fibroblast cell line involved in the formation of the fibrous heart skeleton.

Animals↗
PubMed1998

Neural crest cell contribution to the developing circulatory system: implications for vascular morphology?

In this study, the distribution patterns of neural crest (NC) cells (NCCs) in the developing vascular system of the chick were thoroughly studied and examined for a correlation with smooth muscle cell differentiation and vascular morphogenesis. For this purpose, we performed long-term lineage tracing using quail-chick chimera techniques and premigratory NCC infection with a replication-incompetent retrovirus containing the LacZ reporter gene in combination with immunohistochemistry. Results indicate that NCC deposition around endothelial tubes is influenced by anteroposterior positional information from the pharyngeal arterial system. NCCs were shown to be among the first cells to differentiate into primary smooth muscle cells of the arch arteries. At later stages, NCCs eventually differentiated into adventitial fibroblasts and smooth muscle cells and nonmuscular cells of the media and intima. NCCs were distributed in the aortic arch and pulmonary arch arteries and in the brachiocephalic and carotid arteries. The coronary and pulmonary arteries and the descending aorta, however, remained devoid of NCCs. A new finding was that the media of part of the anterior cardinal veins was also determined to be NC-derived. NC-derived elastic arteries differed from non-NC elastic vessels in their cellular constitution and elastic fiber organization, and the NC appeared not to be involved in designating a muscular or elastic artery. Boundaries between NC-infested areas and mesodermal vessel structures were mostly very sharp and tended to coincide with marked changes in vascular morphology, with the exception of an intriguing area in the aortic and pulmonary trunks.

Animals↗
PubMed1998

Neural crest cells in outflow tract septation of the embryonic chicken heart: differentiation and apoptosis.

The heart consists of cells deriving from the cardiogenic plate and also from extracardiac sources. One of the major extracardiac contributions is given by the neural crest. The differentiation pathway and fate of the neural crest cells in the outflow tract have been followed over a prolonged period during outflow tract septation. We studied the role of the neural crest in remodeling the outflow tract by long-term cell tracing, differentiation markers and apoptosis. The pattern of neural crest cells migrating to the heart was investigated by heterospecific chicken quail chimeras and by retroviral infection of the reporter gene LacZ to the stem cells. The tagged neural crest cells move to areas that are morphogenetically active, such as the outflow tract, the semilunar valves, the wall of the arteries and the cardiac ganglia. Two differentiated subpopulations are discerned on the basis of immunohistochemical characterization with antibodies against smooth muscle cells in the arterial vessel wall and against ganglionic cells that were scattered around the vessels of the arterial pole and the heart. A third subpopulation did not stain with these antibodies, but presented locally with the phenomenon of apoptosis as shown with the TUNEL approach. In a developmental series of chicken embryos the populations were followed until stage 40. It was evident that the outflow tract septum in the early phase of development consisted mainly of mesenchymal neural crest cells. In a later phase neural crest cells were still detected at semilunar valve level, but nearly absent in the outflow tract septum below valve level. The septum at that time had become myocardialized. It is evident that neural crest cells are actually removed from this part of the heart by apoptosis. We are pursuing the hypothesis that an important function of apoptotic cells in heart development might be to activate the cardiomyocytes to muscularize the outflow tract septum through mobilizing or delivering growth factors at the time and place that septum formation is initiated.

Animals↗
PubMed1998

Patterns of paired-related homeobox genes PRX1 and PRX2 suggest involvement in matrix modulation in the developing chick vascular system.

PRX1 (MHox) and PRX2 (S8) were previously shown to be expressed throughout embryogenesis in complex, mostly mesenchyme-specific patterns. In the developing cardiovascular system both genes were highly expressed in prospective connective tissues, that is, endocardial cushions and valves, the epicardium, and the wall of the great arteries and veins. We further scrutinised expression of PRX1 and PRX2 in the developing vascular system of the chicken embryo and compared patterns with those of established vascular differentiation markers (muscle-actin, procollagen I, and fibrillin-2). PRX1 and PRX2 expression were associated with the primary vessel wall from early stages onward and became increasingly restricted to the adventitial and outer medial cell layers. PRX1 eventually colocalised strikingly with procollagen I and fibrillin-2 expression and generally excluded high smooth muscle actin expression. Furthermore, PRX1 expression preceded the segregation of very distinct nonmuscular cells and smooth muscle cells in the media of the great arteries. PRX2 patterns deviated at later stages from those of PRX1 and showed specific and high transcript levels in the ductus arteriosus from embryonic day 6 onward. Results suggest that PRX genes are not essential in smooth muscle contractile differentiation, but may be involved in matrix modulation in the vascular system and possibly in defining the noncontractile cellular phenotype and in media-adventitia definition.

Animals↗
PubMed1998

Disturbed vagal nerve distribution in embryonic chick hearts after treatment with all-trans retinoic acid.

The distribution of the vagal nerve was studied in whole-mount specimens and serial sections of chick embryos after retinoic acid treatment. White Leghorn chick embryos were treated at stage 15 either with 1 microg all-trans retinoic acid (n=11), or with the solvent dimethylsulphoxide (sham-operated embryos, n=8). Eight embryos served as normal controls. At stage 34 all 27 embryos were examined with a dissecting microscope. In order to reveal the vagal patterning, the hearts were removed and whole-mount stained with the HNK-1 antibody. In three hearts of the retinoic acid-treated group a morphologic intracardiac anomaly -- a double outlet right ventricle -- was found. To explore in depth the vagal nerve distribution in the heart, a separate set of hearts of retinoic acid embryos (n=5), sham-operated (n=4) and control embryos (n=5), was devised solely for serial sectioning and staining with the HNK-1 antibody. All hearts of retinoic acid-treated embryos showed a disturbed vagal nerve distribution both over the surface of the heart and within the heart wall. The vagal patterning was not altered in the sham-operated embryos compared to controls. It is concluded that retinoic acid disturbs the development of vagal nerve patterning regardless of the concurrent presence of intracardiac malformations. The mechanism and functional implications remain to be investigated.

Animals↗
PubMed1998

Lineage and development of the parasympathetic nervous system of the embryonic chick heart.

We were interested in the contribution of the cardiac neural crest to the complete anterior and posterior nerve plexus of the chick heart. This includes the pathways by which these cardiac neural crest-derived neuronal precursors enter the heart. As lineage techniques we used the traditional quail-chick chimera in combination with the newly introduced technique of retroviral reporter gene transfer to premigratory cardiac neural crest cells. Retrovirally infected embryos (n=23) and quail-chick chimeras (n=19) between stages HH27 and 40, were immunohistochemically evaluated, using the lineage markers LacZ (retroviral reporter) and QCPN (anti-quail nuclear marker), respectively and the neuronal differentiation markers HNK-1, RMO-270 and DO-170. Between stages HH27 and 33, quail-derived and LacZ positive cells were situated around the arterial cardiac vagal branches at the arterial pole, and vagal branches along the anterior cardinal veins and the sinal vagal branch at the venous pole. From stage HH35 onward, QCPN/LacZ-positive cardiac ganglia were observed throughout the anterior and posterior plexus and were mainly concentrated in the subepicardium near the distal ends of the arterial cardiac vagal branches and the sinal cardiac vagal branch respectively. From stage HH36 both the anterior and posterior plexus contained a population of large cardiac ganglion cells and a population of smaller cells along nerve branches as well as in the cardiac ganglia, which means that differentiation starts in both plexus at the same time. Furthermore only nerve fiber connections between the anterior and posterior plexus were observed. These results show that the cardiac neural crest contributes to the cardiac ganglion cells from both the entire anterior and posterior plexus. Furthermore these results suggest that these precursor cells enter the arterial pole via the arterial cardiac vagal branches and the venous pole via the sinal cardiac vagal branch without intermixing. Finally we show that in addition to the cardiac ganglia, the cardiac neural crest contributes to small myocardial glia or undifferentiated cells along nerve fibers, and some myocardial nerve fibers as well as nerve tissue in the adventitia of the large veins at the venous pole and in the adventitia of the coronary arteries.

Animals↗
PubMed1998

Development of the atrioventricular valve tension apparatus in the human heart.

Using various microscopical techniques we studied the development of the atrioventricular valves in human hearts between 5 and 19 weeks of development. Within the atrioventricular cushions two different layers could be recognized that remained present in all ages studied. The atrial layer, being present at the side of the atrioventricular orifice, was positive for laminin while the ventricular layer, that was connected to the myocardium, was positive for fibronectin and collagen III. Fate-mapping of these two layers, morphometrics, and scanning electron microscopy, supplemented with in vivo labeling of cushion tissue in chicken hearts have lead to new insights in the process of valve development. The cushions became freely movable prevalvular leaflets by delamination of ventricular myocardium underneath the cushion tissue. This myocardium gradually retracted towards annulus and papillary muscles and finally disappeared, resulting in fibrous, non-myocardial valves. The atrial layer of the cushions remained present as a jelly-like surface on the valve leaflets while the ventricular layer of the cushions became the compact fibrous tissue of the leaflets and the chords. Chordal development was first visible at 10 weeks of development when gaps were formed in the ventricular layer of the cushions on top of the papillary muscles. These gaps enlarged into the interchordal spaces while the cushion tissue in between the gaps lengthened to form the chords. We conclude that the leaflets as well as the chords of the atrioventricular valves are derived from atrioventricular cushion tissue. Myocardium is only important for loosening of the leaflets while keeping connection with the developing papillary muscles. Errors in delamination or retraction of myocardium or remodeling of cushion tissue into chords form the basis for various congenital valve anomalies.

Embryonic and Fetal Development↗
PubMed1997

The development of the coronary vessels and their differentiation into arteries and veins in the embryonic quail heart.

Research concerning the embryologic development of the coronary plexus has enriched our understanding of anomalous coronary vessel patterning. However, the differentiation of the coronary vessel plexus into arteries, veins, and a capillary network is still incomplete. Immunohistochemical techniques have been used for whole mounts and serial sections of quail embryo hearts to demonstrate endothelium, vascular smooth muscle cells, and fibroblasts. From HH35 onward, the lumen of the coronary plexus was visualized by injecting India ink into the aorta. In HH17, branches from the sinus venosus plexus expand into the proepicardial organ to reach the dorsal side of the atrioventricular sulcus. From HH25 onward, vessel formation proceeds toward the ventral side and the apex of the heart. After lumenized connections of the coronary vessels with the aorta and right atrium are established, a media composed of smooth muscle cells and an adventitia composed of procollagen-producing fibroblasts are formed around the coronary arteries. In the early stage, bloodflow through the coronary plexus is possible, although connections with the aorta have yet to be established. After the coronary plexus and the aorta and right atrium are interconnected, coronary vessel differentiation proceeds by media and adventitia formation around the proximal coronary arteries. At the same time, the remodeling of the vascular plexus is manifested by disappearance of arteriovenous anastomoses, leaving only capillaries to connect the arterial and venous system.

Animals↗
PubMed1997

Differences in development of coronary arteries and veins.

OBJECTIVE: The differentiation of the coronary vasculature was studied to establish in particular the formation of the coronary venous system. METHODS: Antibody markers were used to demonstrate endothelial, smooth muscle, and fibroblastic cells in serial sections of embryonic quail hearts. The anti-beta myosin heavy chain and the neuronal marker HNK-1 were added to our incubation protocol. RESULTS: In HH32, the coronary vascular network has developed into a circulatory system with connections to the sinus venosus, the aorta and the right atrium. The connections between the aorta and the right atrium allow for direct arteriovenous shunting. Subsequently, differentiation into coronary arteries and veins occurs with an interposed capillary network. The smooth muscle cells of the coronary arterial media derive from the subepicardial layer, whereas the subepicardially located cardiac veins recrute atrial myocardium, as these cells express the beta-myosin heavy chain antigen. Ganglia are located in the subepicardium close to the vessels, while nerve fibres tend to colocalize with the formed vessel channels. CONCLUSIONS: A new finding is presented in which the subepicardial coronary veins have a media that consists of myocardial cells. The close positional relationship of neural tissue and coronary vessels that penetrate the heart wall is explained as inductive for vessel wall differentiation, but not for invasion into the heart.

Animals↗
PubMed1997

Cytokeratin expression in human arteries pertinent to intimal thickening formation in the ductus arteriosus.

Expression of epithelial cytokeratins type 8, 18 and 19 can be used to study smooth muscle cell differentiation during development. We studied the differentiation of smooth muscle cells in the ductus arteriosus before and during intimal thickening and compared the changes occurring in this vessel with the adjoining elastic ascending and descending aorta and the pulmonary trunk. The ductus arteriosus, a vessel connecting the pulmonary trunk and the aorta during fetal life, constricts shorty after birth and eventually closes. Effective closure occurs only in the case of well developed intimal thickening. Cytokeratin expression during fetal development was greatest in the media of the ascending aorta and pulmonary artery, while in the ductus and descending aorta cytokeratin staining was slight. These results suggest that ductus smooth muscle cells and the smooth muscle cells of the descending aorta show a more advanced differentiation as compared to the ascending aorta and pulmonary artery. At neonatal stages cytokeratin expression in the descending aorta, pulmonary artery and the ascending aorta had disappeared as was expected with increased differentiation. In the neonatal ductus arteriosus reexpression of cytokeratins was found in cell clusters in the hyaluronic acid rich environment of the intimal thickening and in the inner media. Reexpression of cytokeratins, especially when organized in clusters, may reflect changes in gene regulation. Therefore the clusters of cytokeratin positive cells in the ductus may be indicative of extensive changes, occurring during closure of this vessel in the neonatal period, in which inner media and intima are especially involved.

Aorta↗
PubMed1997

Embryonic endothelial cells transdifferentiate into mesenchymal cells expressing smooth muscle actins in vivo and in vitro.

All blood vessels are lined by endothelium and, except for the capillaries, surrounded by one or more layers of smooth muscle cells. The origin of the embryonic vascular smooth muscle cell has until now been described from neural crest and locally differentiating mesenchyme. In this study, we have substantial evidence that quail embryonic endothelial cells are competent in the dorsal aorta of the embryo to transdifferentiate into subendothelial mesenchymal cells expressing smooth muscle actins in vivo. At the onset of smooth muscle cell differentiation, QH1-positive endothelial cells were experimentally labeled with a wheat germ agglutinin-colloidal gold marker (WGA-Au). No labeled subendothelial cells were observed at this time. However, 19 hours after the endothelial cells had endocytosed, the WGA-Au-labeled subendothelial mesenchymal cells were observed in the aortic wall. Similarly, during the same time period, subendothelial cells that coexpressed the QH1 endothelial marker and a mesenchymal marker, alpha-smooth muscle actin, were present. In such cells, QH1 expression was reduced to a cell membrane localization. A similar antigen switch was also observed during endocardial-mesenchymal transformation in vitro. Our results are the first direct in vivo evidence that embryonic endothelial cells may transdifferentiate into candidate vascular smooth muscle cells. These data arouse new interpretations of the origin and differentiation of the cells of the vascular wall in normal and diseased vessels.

Actins↗
PubMed1997

Unilateral vitelline vein ligation alters intracardiac blood flow patterns and morphogenesis in the chick embryo.

To study the role of blood flow in normal and abnormal heart development, an embryonic chicken model was developed. The effect of altered venous inflow on normal intracardiac blood flow patterns was studied by visualization of blood flow with India ink. At stage 17, India ink was injected into a capillary or small venule within a specific yolk sac region. After determination of the normal intracardiac flow pattern, the right lateral vitelline vein was ligated, and the new intracardiac flow pattern was studied. Ligation resulted in disturbance of normal intracardiac flow patterns, which was most obvious in the conotruncus. The long-term effect of these abnormal intracardiac flow patterns on the development of the heart and pharyngeal arch arteries was investigated by permanent ligation in ovo with a microclip at stage 17 and subsequent evaluation at stages 34, 37, and 45. These experiments revealed anomalies of the vascular system in 58 of the 91 ligated embryos studied. We observed intracardiac malformations consisting of subaortic ventricular septal defects (n = 52), semilunar valve anomalies (n = 19), atrioventricular anomalies (n = 7), and pharyngeal arch artery malformations (n = 32). It is concluded that abnormal intracardiac blood flow, resulting from hampered venous inflow, may result in serious intracardiac and pharyngeal arch artery malformations comparable to defects observed in embryonic chicken models subjected to neural crest ablation, cervical flexure experiments, and excessive retinoic acid treatment.

Animals↗
PubMed1996

Differential expression of alpha-6 and other subunits of laminin binding integrins during development of the murine heart.

The development of the heart from a single heart tube to a four chambered organ with two separated unidirectional flows is a highly complex process. Events like looping, septation, tissue remodelling, and development of valves take place in a time period in which the heart already exerts its pump function. Adhesion of cells to each other and to their extracellular matrix as well as the capability to migrate in such a dynamic environment are extremely important. Integrins and extracellular matrix components have already been implicated in this process. In this report, we describe in detail the differential expression of the alpha-6 integrin subunit during late murine heart development, e.g., in the process from looping to the end of septation. We compare mRNA and protein expression patterns with those of beta-1 and other subunits of laminin-binding integrins, alpha-3 and alpha-7. We show a constant and high expression of alpha-6 in the atrial myocardium and a decrease in expression in the ventricular trabecular myocardium. The compact myocardial wall and the ventricular septum do not express alpha-6, except for the myocardium of the distal outflow tract at early stages. Moreover, we describe expression of this integrin subunit in the endocardial cushions that contribute to the development of the atrioventricular and semilunar valves. We propose a role for the alpha-6-beta-1 laminin receptor in the adhesion of cells to their extracellular matrix at sites of high stress due to cardiac contraction or blood flow induced shear stress. Moreover, site specific endothelial expression within the heart and surrounding extracardiac tissue is discussed. This study suggests a distinct role for alpha-6-beta-1 in the heart and provides insight concerning probably important roles of integrins and their extracellular matrix ligands during embryonic development.

Animals↗
PubMed1996

Expression of the beta 4 integrin subunit in the mouse heart during embryonic development: retinoic acid advances beta 4 expression.

Using immunohistochemical techniques as well as in situ hybridization we were able to elicit the expression pattern of the beta 4 integrin subunit in the murine heart during development. We show that beta 4 is not expressed in the heart before E13 and is afterwards restricted to the endocardium of the atrioventricular canal, the outflow tract, and the venous valves in the right atrium. As these are all sites of high shear stress in the heart, we propose a role for alpha 6 beta 4 in the tight adhesion of the endocardial cells to their basement membranes in these segments. Moreover, mouse embryos were treated with all-trans retinoic acid, which was previously shown to induce congenital malformations, among which malformations of the heart. We show an advanced expression without ectopic localization of cardiac beta 4 after the administration of retinoic acid. This advanced appearance of beta 4 was also shown in extracardiac tissue like migrating neural crest cells. Several hypotheses on the mechanism of beta 4 up-regulation and a possible role for alpha 6 beta 4 in the development of heart malformations after the administration of retinoic acid are discussed.

Animals↗
PubMed1996

Onset of elastogenesis and downregulation of smooth muscle actin as distinguishing phenomena in artery differentiation in the chick embryo.

During development, the arterial system is grossly divided into elastic and muscular vessel types. Apart from local environmental factors, it has been suggested that vascular smooth muscle cell origin (mesoderm or neural crest) is involved in this, as yet poorly understood, arterial differentiation. We describe differentiation of the thoracic arterial system in the chick embryo, using immunohistochemical techniques staining for muscle-specific actin, vinculin and desmin and histological staining to visualise elastin. The initial developmental stages of the vessel wall in all arteries appeared to be highly similar, with all arteries showing peri-endothelial actin and vinculin staining. Major alterations did not occur until the start of elastogenesis, which coincided with complete loss of actin staining from the proximal part of the great arteries. Later in development, however, actin was re-expressed in a subpopulation of medial cells, which also expressed vinculin and desmin. Concomitantly another, nonmuscular, cell type became evident in the great arteries. Transient loss of actin expression and segregation of very distinct cell populations occurred only in vessels prone to elastic development and known to receive a neural crest contribution. In contrast, arteries that developed a muscular phenotype never lost the initially acquired peri-endothelial actin expression. We also show a significant difference in the organisation of elastic fibres between elastic vessels that contain neural crest derivatives and those that do not. The ductus arteriosus still presents as an enigma in the sense that it is the only part of the pharyngeal arch complex that develops a muscular phenotype.

Actins↗