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Biomedical subjects

A Wessels

Publications and source records attributed to A Wessels.

At least 19 recordsLinked to original sources
PubMed2005

Cardiovascular phenotyping of fetal mice by noninvasive high-frequency ultrasound facilitates recovery of ENU-induced mutations causing congenital cardiac and extracardiac defects.

As part of a large-scale noninvasive fetal ultrasound screen to recover ethylnitrosourea (ENU)-induced mutations causing congenital heart defects in mice, we established a high-throughput ultrasound scanning strategy for interrogating fetal mice in utero utilizing three orthogonal imaging planes defined by the fetus' vertebral column and body axes, structures readily seen by ultrasound. This contrasts with the difficulty of acquiring clinical ultrasound imaging planes which are defined by the fetal heart. By use of the three orthogonal imaging planes for two-dimensional (2D) imaging together with color flow, spectral Doppler, and M-mode imaging, all of the major elements of the heart can be evaluated. In this manner, 10,091 ENU-mutagenized mouse fetuses were ultrasound scanned between embryonic days 12.5 and 19.5, with 324 fetuses found to die prenatally and 425 exhibiting cardiovascular defects. Further analysis by necropsy and histology showed heart defects that included conotruncal anomalies, obstructive lesions, and shunt lesions as well as other complex heart diseases. Ultrasound imaging also identified craniofacial/head defects and body wall closure defects, which necropsy revealed as encephalocele, holoprosencephaly, omphalocele, or gastroschisis. Genome scanning mapped one ENU-induced mutation associated with persistence truncus arteriosus and holoprosencephaly to mouse chromosome 2, while another mutation associated with cardiac defects and omphalocele was mapped to mouse chromosome 17. These studies show the efficacy of this novel ultrasound scanning strategy for noninvasive ultrasound phenotyping to facilitate the recovery of ENU-induced mutations causing congenital heart defects and other extracardiac anomalies.

Abnormalities, Multiple↗
PubMed2005

Did Adolf Hitler have syphilis?

The evidence that Adolf Hitler might have suffered from incapacitating syphilis is reviewed. Rumors that he acquired syphilis from a prostitute at the age of 20 years, with possible re-infection during World War I, can no longer be verified. Evidence is that he was sexually rather inactive throughout his life. Suggestions that Hitler's cardiac lesion and complaints such as transitory blindness, tremor of his left arm and leg, recurring abdominal pain and a skin lesion of the leg were of syphilitic aetiology cannot be supported. Hitler's progressive mental and physical deterioration after 1942, his growing paranoia, fits of rage, grandiosity and symptoms of possible dementia would fit in neurosyphilis. There are, however, also other explanations for his terminal syndrome, and evidence that repeated clinical examinations did not show the characteristic signs of dementia paralytica or tabes dorsalis, swings the balance of probability away from tertiary syphilis.

Famous Persons↗
PubMed2004

The epicardium and epicardially derived cells (EPDCs) as cardiac stem cells.

After its initial formation the epicardium forms the outermost cell layer of the heart. As a result of an epithelial-to-mesenchymal transformation (EMT) individual cells delaminate from this primitive epicardial epithelium and migrate into the subepicardial space (Pérez-Pomares et al., Dev Dyn 1997; 210:96-105; Histochem J 1998a;30:627-634). Several studies have demonstrated that these epicardially derived cells (EPDCs) subsequently invade myocardial and valvuloseptal tissues (Mikawa and Fischman, Proc Natl Acad Sci USA 1992;89:9504-9508; Mikawa and Gourdie, Dev Biol 1996;174:221-232; Dettman et al., Dev Biol 1998;193:169-181; Gittenberger de Groot et al., Circ Res 1998;82:1043-1052; Manner, Anat Rec 1999;255:212-226; Pérez-Pomares et al., Dev. Biol. 2002b;247:307-326). A subset of EPDCs continue to differentiate in a variety of different cell types (including coronary endothelium, coronary smooth muscle cells (CoSMCs), interstitial fibroblasts, and atrioventricular cushion mesenchymal cells), whereas other EPDCs remain in a more or less undifferentiated state. Based on its specific characteristics, we consider the EPDC as the ultimate 'cardiac stem cell'. In this review we briefly summarize what is known about events that relate to EPDC development and differentiation while at the same time identifying some of the directions where EPDC-related research might lead us in the near future.

Animals↗
PubMed2002

Experimental studies on the spatiotemporal expression of WT1 and RALDH2 in the embryonic avian heart: a model for the regulation of myocardial and valvuloseptal development by epicardially derived cells (EPDCs).

Epicardially derived cells (EPDCs) delaminate from the primitive epicardium through an epithelial-to-mesenchymal transformation (EMT). After this transformation, a subpopulation of cells progressively invades myocardial and valvuloseptal tissues. The first aim of the study was to determine the tissue-specific distribution of two molecules that are thought to play a crucial function in the interaction between EPDCs and other cardiac tissues, namely the Wilms' Tumor transcription factor (WT1) and retinaldehyde-dehydrogenase2 (RALDH2). This study was performed in normal avian and in quail-to-chick chimeric embryos. It was found that EPDCs that maintain the expression of WT1 and RALDH2 initially populate the subepicardial space and subsequently invade the ventricular myocardium. As EPDCs differentiate into the smooth muscle and endothelial cell lineage of the coronary vessels, the expression of WT1 and RALDH2 becomes downregulated. This process is accompanied by the upregulation of lineage-specific markers. We also observed EPDCs that continued to express WT1 (but very little RALDH2) which did not contribute to the formation of the coronary system. A subset of these cells eventually migrates into the atrioventricular (AV) cushions, at which point they no longer express WT1. The WT1/RALDH2-negative EPDCs in the AV cushions do, however, express the smooth muscle cell marker caldesmon. The second aim of this study was to determine the impact of abnormal epicardial growth on cardiac development. Experimental delay of epicardial growth distorted normal epicardial development, reduced the number of invasive WT1/RALDH2-positive EPDCs, and provoked anomalies in the coronary vessels, the ventricular myocardium, and the AV cushions. We suggest that the proper development of ventricular myocardium is dependent on the invasion of undifferentiated, WT1-positive, retinoic acid-synthesizing EPDCs. Furthermore, we propose that an interaction between EPDCs and endocardial (derived) cells is imperative for correct development of the AV cushions.

Aldehyde Oxidoreductases↗
PubMed2002

An essential role for connexin43 gap junctions in mouse coronary artery development.

Connexin43 knockout mice die neonatally from conotruncal heart malformation and outflow obstruction. Previous studies have indicated the involvement of neural crest perturbations in these cardiac anomalies. We provide evidence for the involvement of another extracardiac cell population, the proepicardial cells. These cells give rise to the vascular smooth muscle cells of the coronary arteries and cardiac fibroblasts in the heart. We have observed the abnormal presence of fibroblast and vascular smooth muscle cells in the infundibular pouches of the connexin43 knockout mouse heart. In addition, the connexin43 knockout mice exhibit a variety of coronary artery patterning defects previously described for neural crest-ablated chick embryos, such as anomalous origin of the coronary arteries, absent left or right coronary artery, and accessory coronary arteries. However, we show that proepicardial cells also express connexin43 gap junctions abundantly. The proepicardial cells are functionally well coupled, and this coupling is significantly reduced with the loss of connexin43 function. Further analysis revealed an elevation in the speed of cell locomotion and cell proliferation rate in the connexin43-deficient proepicardial cells. A parallel analysis of proepicardial cells in transgenic mice with dominant negative inhibition of connexin43 targeted only to neural crest cells showed none of these coupling, proliferation or migration changes. These mice exhibit outflow obstruction, but no infundibular pouches. Together these findings indicate an important role for connexin43 in coronary artery patterning, a role that probably involves the proepicardial and cardiac neural crest cells. We discuss the potential involvement of connexin43 in human cardiovascular anomalies involving the coronary arteries.

Animals↗
PubMed2001

Formation of myocardium after the initial development of the linear heart tube.

Well after formation of the primary linear heart tube, the mesenchymal cardiac septa become largely myocardial, and myocardial sleeves are formed along the caval and pulmonary veins. This second wave of myocardium formation can be envisioned to be the result of recruitment of cardiomyocytes by differentiation from flanking mesenchyme and/or by migration from existing myocardium (myocardialization). As a first step to elucidate the underlying mechanism, we studied in chicken heart development the formation of myocardial cells within intra- and extracardiac mesenchymal structures. We show that the second wave of myocardium formation proceeds in a caudal-to-cranial gradient in vivo. At the venous pole, loosely arranged networks of cardiomyocytes are observed in the dorsal mesocardium from H/H19 onward, in the atrioventricular cushion region from H/H26 onward, and in the proximal outflow tract (conus) from H/H29 onward. The process is completed at H/H stage 43. Subsequently, we determined the potential of the different cardiac compartments to form myocardial networks in a 3D in vitro culture assay. This analysis showed that the competency to form myocardial networks in vitro is a characteristic of the myocardium that is flanked by intra- or extracardiac mesenchyme, i.e., the inflow tract, atrioventricular canal, and outflow tract. These cardiac compartments can be induced to form myocardial networks by a temporally released or secreted signal that is similar throughout the entire heart. Atrial and ventricular compartments are not competent and do not produce the inducer. Moreover, cardiac cushion mesenchyme was found to be able to (trans-)differentiate into cardiomyocytes in the in vitro culture assay. The combined observations suggest that a common mechanism and molecular regulatory pathway underlies the recruitment of mesodermal cells into the cardiogenic lineage during this second wave of myocardium formation through the entire heart.

Animals↗
PubMed2001

Cardiopulmonary malformations in the inv/inv mouse.

The inv/inv mouse carries an insertional mutation in the inversin gene, (inv, for inversion of embryonic turning). Previously it had been reported that almost 100% of the homozygous offspring (inv/inv) were characterized by situs inversus totalis. In this report we identify the spectrum of cardiopulmonary anatomical abnormalities in inv/inv mice surviving to birth to determine whether the abnormalities seen are of the categories classically associated with human situs abnormalities. Stillborn mice, offspring that died unexpectedly (within 48 hr after birth), and neonates with phenotypic characteristics of situs inversus (right-sided stomachs, growth failure or jaundice) were processed for standard histological examination. Of 173 offspring, 34 (20%) neonates (11 stillborn, 9 unexpected deaths, and 14 mice with situs inversus phenotype) were examined, 27 of which were genotyped to be inv/inv. Interestingly, three inv/inv mice (11%) were found to have situs solitus. Twenty-four had situs inversus with normal, mirror-image cardiac anatomy (dextrocardia with atrioventricular concordance, ventriculoarterial concordance and a right aortic arch). The overall incidence of cardiovascular anomalies observed was 10 out of 27 (37%). The most frequent severe malformation, identified in 3 out of 27 animals, was a complex consisting of pulmonary infundibular stenosis/atresia with absence of pulmonary valve tissue and a ventricular septal defect. The pulmonary phenotype in inv/inv mice was situs inversus with occasional minor lobar abnormalities. We conclude that 1) cardiopulmonary malformations in inv/inv mice are not rare (37%), 2) the cardiopulmonary malformations observed in inv/inv specimens are not of the spectrum typically associated with human heterotaxia. In particular, inv/inv mice have a propensity for defects in the development of the right ventricular outflow tract and the interventricular septum, and 3) approximately one out of ten inv/inv mice is born with situs solitus and shows cardiac anomalies that correspond to those observed in inv/inv specimens with situs inversus. Our data therefore suggest that inversin, the product of the inv locus, may have specific roles in cardiac morphogenesis independent of its role in situs determination.

Animals↗
PubMed2001

A GATA-6 gene heart-region-specific enhancer provides a novel means to mark and probe a discrete component of the mouse cardiac conduction system.

The transcriptional programs that specify the distinct components of the cardiac conduction system are poorly understood, in part due to a paucity of definitive molecular markers. In the present study we show that a cGATA-6 gene enhancer can be used to selectively express transgenes in the atrioventricular (AV) conduction system as it becomes manifest in the developing multichambered mouse heart. Furthermore, our analysis of staged cGATA-6/lacZ embryos revealed that the activity of this heart-region-specific enhancer can be traced back essentially to the outset of the cardiogenic program. We provide evidence that this enhancer reads medial/lateral and anterior/posterior positional information before the heart tube forms and we show that the activity of this enhancer becomes restricted at the heart looping stage to AV myocardial cells that induce endocardial cushion formation. We infer that a deeply-rooted heart-region-specific transcriptional program serves to coordinate AV valve placement and AV conduction system formation. Lastly, we show that cGATA-6/Cre mice can be used to delete floxed genes in the respective subsets of specialized heart cells.

Animals↗
PubMed2000

Conotruncal anomalies in the trisomy 16 mouse: an immunohistochemical analysis with emphasis on the involvement of the neural crest.

The trisomy 16 (Ts16) mouse is generally considered a model for human Down's syndrome (trisomy 21). However, many of the cardiac defects in the Ts16 mouse do not reflect the heart malformations seen in patients suffering from this chromosomal disorder. In this study we describe the conotruncal malformations in mice with trisomy 16. The development of the outflow tract was immunohistochemically studied in serially sectioned hearts from 34 normal and 26 Ts16 mouse embryos ranging from 8.5 to 14.5 embryonic days. Conotruncal malformations observed in the Ts 16 embryos included double outlet right ventricle, persistent truncus arteriosus, Tetralogy of Fallot, and right-sided aortic arch. This spectrum of malformations is remarkably similar to that seen in humans suffering from DiGeorge syndrome (DGS). As perturbation of neural crest development has been proposed in the pathogenesis of DGS we specifically focussed on the fate of neural crest derived cells during outflow tract development of the Ts16 mouse using an antibody that enabled us to trace these cells during development. Severe perturbation of the neural crest-derived cell population was observed in each trisomic specimen. The abnormalities pertained to: 1) the size of the columns of neural crest-derived cells (or prongs); 2) the spatial orientation of these prongs within the mesenchymal tissues of the outflow tract; and 3) the location in which the neural crest cells interact with the myocardium. The latter abnormality appeared to be responsible for ectopic myocardialization found in trisomic embryos. Our observations strongly suggest that abnormal neural crest cell behavior is involved in the pathogenesis of the conotruncal malformations in the Ts16 mouse.

Animals↗
PubMed2000

Atrial development in the human heart: an immunohistochemical study with emphasis on the role of mesenchymal tissues.

The development of the atrial chambers in the human heart was investigated immunohistochemically using a set of previously described antibodies. This set included the monoclonal antibody 249-9G9, which enabled us to discriminate the endocardial cushion-derived mesenchymal tissues from those derived from extracardiac splanchnic mesoderm, and a monoclonal antibody recognizing the B isoform of creatine kinase, which allowed us to distinguish the right atrial myocardium from the left. The expression patterns obtained with these antibodies, combined with additional histological information derived from the serial sections, permitted us to describe in detail the morphogenetic events involved in the development of the primary atrial septum (septum primum) and the pulmonary vein in human embryos from Carnegie stage 14 onward. The level of expression of creatine kinase B (CK-B) was found to be consistently higher in the left atrial myocardium than in the right, with a sharp boundary between high and low expression located between the primary septum and the left venous valve indicating that the primary septum is part of the left atrial gene-expression domain. This expression pattern of CK-B is reminiscent of that of the homeobox gene Pitx2, which has recently been shown to be important for atrial septation in the mouse. This study also demonstrates a poorly appreciated role of the dorsal mesocardium in cardiac development. From the earliest stage investigated onward, the mesenchyme of the dorsal mesocardium protrudes into the dorsal wall of the primary atrial segment. This dorsal mesenchymal protrusion is continuous with a mesenchymal cap on the leading edge of the primary atrial septum. Neither the mesenchymal tissues of the dorsal protrusion nor the mesenchymal cap on the edge of the primary septum expressed the endocardial tissue antigen recognized by 249-9G9 at any of the stages investigated. The developing pulmonary vein uses the dorsal mesocardium as a conduit to reach the primary atrial segment. Initially, the pulmonary pit, which will becomes the portal of entry for the pulmonary vein, is located along the midline, flanked by two myocardial ridges. As development progresses, tissue remodeling results in the incorporation of the portal of entry of the pulmonary vein in left atrial myocardium, which is recognized because of its high level of creatine. Closure of the primary atrial foramen by the primary atrial septum occurs as a consequence of the fusion of these mesenchymal structures.

Antibodies, Monoclonal↗
PubMed2000

An Nkx-dependent enhancer regulates cGATA-6 gene expression during early stages of heart development.

The evolutionarily conserved GATA-6 transcription factor is an early and persistent marker of heart development in diverse vertebrate species. We previously found evidence for a functionally conserved heart-specific enhancer upstream of the chicken GATA-6 (cGATA-6) gene and in the present study we used transgenic mouse assays to further characterize this regulatory module. We show that this enhancer is activated in committed precursor cells within the cardiac crescent and that it remains active in essentially all cardiogenic cells through the linear heart stage. Although this enhancer can account for cGATA-6 gene expression early in the cardiogenic program, it is not able to maintain expression throughout the heart later in development. In particular, the enhancer is sequentially downregulated along the posterior to anterior axis, with activity becoming confined to outflow tract myocardium. Enhancers with similar properties have been shown to regulate the early heart-restricted expression of the mouse Nkx2.5 transcription factor gene. Whereas these Nkx2.5 enhancers are GATA-dependent, we show that the cGATA-6 enhancer is Nkx-dependent. We speculate that these enhancers are silenced to allow GATA-6 and Nkx2.5 gene expression to be governed by region-specific enhancers in the multichambered heart.

Animals↗
PubMed2000

Modular regulation of cGATA-5 gene expression in the developing heart and gut.

The evolutionarily conserved GATA-5 transcription factor is an early and persistent marker of heart and gut development in diverse vertebrate species. To search for control regions that might regulate the chicken GATA-5 (cGATA-5) gene, we assayed a set of cGATA-5/lacZ constructs in transgenic mice and found evidence for two functionally conserved control regions that regulate different facets of cGATA-5 gene expression. The more distal control region is activated in embryonic endoderm at the head-fold stage, whereas the other control region contains a regulatory module that is activated in a restricted region of endoderm following closure of the gut tube. Remarkably, the latter control region also contains a complex regulatory module that is activated in the cardiac crescent at the head-fold stage and subsequently functions in several mesodermal components of the developing heart, including the outer (epicardial) layer. We discuss these results in terms of possible contributions of epicardial-derived cells to the formation of heart valves, conduction tissue, and compact myocardium. These transgenes thus reveal, and provide a means to further analyze, transcriptional programs for several facets of heart morphogenesis and gut development.

Animals↗
PubMed2000

Loss of function of the Prx1 and Prx2 homeobox genes alters architecture of the great elastic arteries and ductus arteriosus.

Prx1 (MHox) and Prx2 (S8) are non-clustered homeobox genes that are expressed in a complex, mostly mesenchyme-specific pattern throughout embryogenesis. The expression pattern and gene-targeted mice previously revealed a major role for Prx1 in skeletogenesis. In addition, specific and high expression of both Prx genes was reported in the developing cardiovascular system, predominantly in prospective connective tissues of the heart and in the great arteries and veins. We examined embryos of previously generated gene-targeted mice. Prx2-/- mutants were viable and did not show cardiovascular malformations. Intracardiac morphology of Prxl-/- and Prx1/Prx2-combined null mutants also appeared normal throughout development. However, the Prx1-/- and Prx1/Prx2 double-null mutants showed a vascular abnormality with an abnormal positioning and awkward curvature of the aortic arch in addition to a misdirected and elongated ductus arteriosus, and in two of seven combined mutants, an anomalous retro-oesophageal right subclavian artery. Generally, all great arteries appeared to run somewhat tortuously through the surrounding mesenchyme. The vascular histology and vessel wall thickness were normal in all mutants. Prx1-/- and Prx double-gene-targeted mice revealed similar spectra of vascular anomalies, but double mutants appeared to be more seriously affected. The current findings suggest that other genes may compensate for the loss of Prx in the heart, but, in contrast, our data support a role for Prx in the development of vascular and perivascular matrix.

Animals↗
PubMed2000

Migration of cardiac neural crest cells in Splotch embryos.

Pax3 encodes a transcription factor expressed during mid-gestation in the region of the dorsal neural tube that gives rise to migrating neural crest populations. In the absence of Pax3, both humans and mice develop with neural crest defects. Homozygous Splotch embryos that lack Pax3 die by embryonic day 13.5 with cardiac defects that resemble those induced by neural crest ablation in chick models. This has led to the hypothesis that Pax3 is required for cardiac neural crest migration. However, cardiac derivatives of Pax3-expressing precursor cells have not been previously defined, and Pax3-expressing cells within the heart have not been well demonstrated. Hence, the precise role of Pax3 during cardiac development remains unclear. Here, we use a Cre-lox method to fate map Pax3-expressing neural crest precursors to the cardiac outflow tract. We show that although Pax3 itself is extinguished prior to neural crest populating the heart, derivatives of these precursors contribute to the aorticopulmonary septum. We further show that neural crest cells are found in the outflow tract of Splotch embryos, albeit in reduced numbers. This indicates that contrary to prior reports, Pax3 is not required for cardiac neural crest migration. Using a neural tube explant culture assay, we demonstrate that neural crest cells from Splotch embryos show normal rates of proliferation but altered migratory characteristics. These studies suggest that Pax3 is required for fine tuning the migratory behavior of the cardiac neural crest cells while it is not essential for neural crest migration.

Animals↗
PubMed1999

Distinct spatial and temporal distributions of aggrecan and versican in the embryonic chick heart.

Although chondroitin sulfate proteoglycans (CSPGs) are major components of the embryonic extracellular matrix, little attention has been paid to specific CSPGs in early heart development, in part because appropriate antibodies were not available. Therefore we prepared specific polyclonal antibodies against chicken aggrecan, versican, neurocan, and phosphacan. Western blotting and immunohistochemical studies revealed the presence of aggrecan and versican in stages 12-21 chicken embryo hearts in distinctive spatial and temporal patterns. Because this is the first demonstration of aggrecan in heart tissue, we further used RT-PCR to confirm that aggrecan is expressed in the heart and in situ hybridization to confirm the pattern of expression determined using antibodies. Versican is found in the myocardium and the myocardial basement membrane. In contrast, aggrecan is specifically colocalized with several groups of migrating cells including endocardial cushion tissue cells, epicardial cells, a mesenchymal cell population in the outflow tract that may be of neural crest origin, and a mesenchymal cell population in the inflow tract. The combined observations indicate that versican and aggrecan are expressed in unique patterns and suggest that they play very different roles in development.

Aggrecans↗