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Andy Wessels

Publications and source records attributed to Andy Wessels.

At least 19 recordsLinked to original sources
PubMed2026

CD109 exhibits a dynamic expression pattern in coronary endothelium and endocardial-derived valve mesenchyme during heart development with preserved morphogenesis following endothelial-specific deletion.

BACKGROUND: CD109 encodes a GPI-linked glycoprotein that acts as a signaling modulator in the TGF-β pathway. CD109 has emerged in several genome-wide association studies as linked to coronary artery disease, myocardial infarction, and angina pectoris. Heterozygous loss-of-function mutations in CD109 have also been reported in patients with congenital heart defects, suggesting potential developmental relevance, though CD109 has never been investigated in the context of cardiovascular development. We previously identified Cd109 upregulation in murine atrioventricular valves undergoing myxomatous degeneration following a reduction of epicardial-derived cells. Here, we characterize Cd109 expression in the murine cardiovascular system and assess its function during development using in vitro and in vivo approaches. RESULTS: We found that Cd109 is strongly expressed in the endothelium of the coronary vasculature and in endocardial-derived subpopulations in the atrioventricular valves. This expression persists through key stages in cardiovascular development. Western blotting and immunostaining confirm endothelial expression in heart and lung tissues. siRNA-mediated knockdown of CD109 in primary human endothelial cells led to dysregulation of vascular development pathways and decreased tube formation capacity. We generated endothelial-specific Cd109 knockout mice, eliminating Cd109 expression from heart and lung tissues without overt consequences for atrioventricular valve or coronary vascular morphogenesis during heart development. CONCLUSION: CD109 exhibits a highly dynamic spatiotemporal expression pattern during cardiovascular development, with enriched expression in coronary endothelial cells and endocardial-derived subpopulations in the valves. Despite this striking developmental expression pattern, previously reported human genetic associations with cardiovascular diseases, and endothelial-associated phenotypes following siRNA-mediated CD109 knockdown in a primary human endothelial cell line, endothelial/endocardial-lineage deletion of Cd109 did not produce overt abnormalities in atrioventricular valve or coronary vascular morphogenesis during embryonic development. Collectively, these findings identify CD109 as a useful marker of coronary endothelial and endocardial-derived valve cell populations and suggest that CD109 may function in a context-dependent or modulatory manner rather than as an essential regulator of cardiovascular morphogenesis under normal developmental conditions.

CD109↗
PubMed2006

Changes in activation sequence of embryonic chick atria correlate with developing myocardial architecture.

To characterize developmental changes in impulse propagation within atrial musculature, we performed high-speed optical mapping of activation sequence of the developing chick atria using voltage-sensitive dye. The activation maps were correlated with detailed morphological studies using scanning electron microscopy, histology, and whole mount confocal imaging with three-dimensional reconstruction. A preferential pathway appeared during development within the roof of the atria, transmitting the impulse rapidly from the right-sided sinoatrial node to the left atrium. The morphological substrate of this pathway, the bundle of Bachman, apparent from stage 29 onward, was a prominent ridge of pectinate muscles continuous with the terminal crest. Further acceleration of impulse propagation was noted along the ridges formed by the developing pectinate muscles, ramifying from the terminal crest toward the atrioventricular groove. In contrast, when the impulse reached the interatrial septum, slowing was often observed, suggesting that the septum acts as a barrier or sink for electrical current. We conclude that these inhomogeneities in atrial impulse propagation are consistent with existence of a specialized network of fast-conducting tissues. The purpose of these preferential pathways appears to be to assure synchronous atrial activation and contraction rather than rapid impulse conduction between the sinoatrial and atrioventricular nodes.

Animals↗
PubMed2006

BMP and FGF regulate the differentiation of multipotential pericardial mesoderm into the myocardial or epicardial lineage.

Proepicardial cells give rise to epicardium, coronary vasculature and cardiac fibroblasts. The proepicardium is derived from the mesodermal lining of the prospective pericardial cavity that simultaneously contributes myocardium to the venous pole of the elongating primitive heart tube. Using proepicardial explant cultures, we show that proepicardial cells have the potential to differentiate into cardiac muscle cells, reflecting the multipotency of this pericardial mesoderm. The differentiation into the myocardial or epicardial lineage is mediated by the cooperative action of BMP and FGF signaling. BMP2 is expressed in the distal IFT myocardium and stimulates cardiomyocyte formation. FGF2 is expressed in the proepicardium and stimulates differentiation into the epicardial lineage. In the base of the proepicardium, coexpression of BMP2 and FGF2 inhibits both myocardial and epicardial differentiation. We conclude that the epicardial/myocardial lineage decisions are mediated by an extrinsic, inductive mechanism, which is determined by the position of the cells in the pericardial mesoderm.

Animals↗
PubMed2006

Elevated vascular endothelial cell growth factor affects mesocardial morphogenesis and inhibits normal heart bending.

Signaling by means of vascular endothelial cell growth factor (VEGF) and its receptors (VEGFRs) is required for cardiovascular development. To examine how VEGF/VEGFR receptor signaling affects early endocardial cell behavior, embryonic quail hearts were subjected to elevated VEGF165 levels (five- to nine-somite stage). Primitive embryonic hearts microinjected with recombinant human (rh)VEGF165 exhibit several distinct malformations compared with hearts in untreated embryos: the endocardial tube is malformed with tortuous cords and folds surrounded by a diminished cardiac jelly space, and the lumens of affected hearts are conspicuously reduced. Furthermore, the embryonic heart fails to loop properly. Inhibition of bending is accompanied by an apparent failure of the dorsal mesocardium to atrophy--an event thought to be necessary for heart bending. Instead of atrophy, VEGF-treated mesocardia exhibit a marked increased in the number of resident endothelial cells. Collectively, the data suggest that the abnormally robust mesocardia in VEGF-treated hearts impede the mechanical deformation required for normal heart bending. We conclude that the excessive VEGF signaling culminates in a physical or biomechanical mechanism that acts over a wide, tissue-level, length scale to cause a severe developmental defect--failure of heart bending.

Animals↗
PubMed2006

Muscularizing tissues in the endocardial cushions of the avian heart are characterized by the expression of h1-calponin.

Muscularization of mesenchymal tissues in the developing heart is an important event in the morphogenesis of the valvuloseptal complex in four-chambered hearts. Perturbation of muscularization has been implicated in the pathogenesis of cardiac malformations in several animal models for congenital heart disease, including the Trisomy 16 mouse and the TGFbeta2 knockout mouse. Studies to unravel the mechanism of muscularization, as well as studies to determine the extent of the process in frequently used animal-model systems for cardiac development, have, thus far, been hampered by the lack of useful differentiation markers for muscularizing tissues, albeit that it had been demonstrated that, in the mouse, muscularizing cells are characterized by an elevated level of smooth muscle actin expression. In this study, we investigated whether muscularization of endocardial cushions in the avian heart is also accompanied by the expression of smooth muscle cell markers. The results presented in this study demonstrate that, in quail and chick, a specific population of muscularizing cells is recognized by the expression of smooth muscle h1-calponin. Interestingly, other genes typically found in smooth muscle cells (e.g., smooth muscle actin and caldesmon) are not expressed in muscularizing tissues. We conclude that muscularization of cushion-derived mesenchymal tissues is associated with a discrete genetic program reflected by the expression of h1-calponin and predict that h1-calponin will prove an invaluable tool in elucidating the regulation of muscularization and other aspects related to this event.

Amino Acid Sequence↗
PubMed2005

Detection of betaig-H3, a TGFbeta induced gene, during cardiac development and its complementary pattern with periostin.

Regulation of normal cardiac development involves numerous transcription factors, cytoskeletal proteins, signaling molecules, and extracellular matrix proteins. These key molecular components act in concert to induce morphological changes essential for the proper development of a functional four-chambered heart. Growth factors such as BMPs and TGFbeta's play a role in migration, proliferation and differentiation during cardiac development and are important regulators of the extracellular matrix (ECM). Genes responsive to these morphogens are likely to play an equally significant role during cardiac development. Therefore, we sought to clone the chicken TGFbeta induced gene betaig-H3 and evaluate its spatio-temporal expression during heart morphogenesis. Our studies show by Northern analysis, whole mount and section in situ hybridization experiments that betaig-H3 is expressed primarily in the mesenchyme of the atrioventricular and outflow tract cushions and later in the right and left atrioventricular valve leaflets and supporting valve structures. The mRNA expression domains of betaig-H3 show a complementary pattern compared to that of its highly homologous relative, periostin.

Animals↗
PubMed2005

Partial rescue of neonatal lethality of Dhcr7 null mice by a nestin promoter-driven DHCR7 transgene expression.

In humans, genetic disorders affecting post-squalene cholesterol biosynthesis result in a variety of dysmorphology syndromes. One key feature of all of these is the presence of mental retardation and another is the lack of a robust genotype-phenotype correlation. Knockout mice defective in the 3beta hydroxysterol Delta7 reductase (Dhcr7), a model for the most common of such disorders in humans, the Smith-Lemli-Opitz syndrome, all die within 24 h of birth. The cause of this postnatal mortality in these mice has not been fully established. In the present study, we tested the hypothesis that CNS dysfunction was a major cause of this lethality and investigated whether transgenic expression of normal human DHCR7 in neuronal tissues could rescue this neonatal lethality. Transgenic mice, expressing DHCR7 driven by murine nestin promoter, were bred onto Dhcr7 knock-out (Dhcr7(-1-)) background and resulted in a partial rescue of neonatal lethality in 11 of 91 (12%) of transgene-positive Dhcr7(-1-) pups. Despite biochemical analyses that showed continued profound cholesterol deficiency in brain, rescued animals survived between 3 and 17 days. Thus, one important conclusion to be drawn is that defects in CNS in Dhcr7 knockout mice may contribute to the early lethality. Another conclusion is that even small and subtle changes in the brain sterol metabolism were sufficient to enable rescue. These data also provide important clues as to the cause of the variable expressivity seen in SLOS.

Age Factors↗
PubMed2004

ENU induced mutations causing congenital cardiovascular anomalies.

We used non-invasive high frequency ultrasound to screen N-ethyl-N-nitrosourea mutagenized mouse fetuses for congenital cardiovascular anomalies. We ultrasound scanned 7546 mouse fetuses from 262 mutagenized families, and identified 124 families with cardiovascular defects. Represented were most of the major congenital cardiovascular anomalies seen clinically. The ENU-induced mutations in several families were mapped using polymorphic microsatellite DNA markers. One family with forelimb anomalies and ventricular septal defects, phenotypes similar to Holt-Oram syndrome, and one family with transposition of the great arteries and heart situs anomalies were mapped to different regions of mouse chromosome 4. A third mutation causing persistent truncus arteriosus and craniofacial defects, phenotypes reminiscent of DiGeorge syndrome, was mapped to mouse chromosome 2. We note that mouse chromosomes 4 and 2 do not contain Tbx5 or Tbx1, genes previously linked to Holt-Oram and DiGeorge syndromes, respectively. In two other families, the ENU-induced mutation was identified--Sema3CL605P was associated with persistent truncus arteriosus with interrupted aortic arch, and the Gja1W45X connexin43 mutation caused conotruncal malformation and coronary aneurysms. Although our screen was designed as a recessive screen, a number of the mutations showed cardiovascular phenotypes in both heterozygote and homozygote animals. These studies show the efficacy of ENU mutagenesis and high-throughput ultrasound phenotyping in recovering mutations causing a wide spectrum of congenital heart defects. These ENU-induced mutations hold promise in yielding new insights into the genetic basis for human congenital heart disease.

Amino Acid Sequence↗
PubMed2004

Late gestational lung hypoplasia in a mouse model of the Smith-Lemli-Opitz syndrome.

BACKGROUND: Normal post-squalene cholesterol biosynthesis is important for mammalian embryonic development. Neonatal mice lacking functional dehydrocholesterol Delta7-reductase (Dhcr7), a model for the human disease of Smith-Lemli-Opitz syndrome, die within 24 hours of birth. Although they have a number of biochemical and structural abnormalities, one cause of death is from apparent respiratory failure due to developmental pulmonary abnormalities. RESULTS: In this study, we characterized further the role of cholesterol deficiency in lung development of these mice. Significant growth retardation, beginning at E14.5 through E16.5, was observed in Dhcr7-/- embryos. Normal lobation but smaller lungs with a significant decrease in lung-to-body weight ratio was noted in Dhcr7-/- embryos, compared to controls. Lung branching morphogenesis was comparable between Dhcr7-/- and controls at early stages, but delayed saccular development was visible in all Dhcr7-/- embryos from E17.5 onwards. Impaired pre-alveolar development of varying severity, inhibited cell proliferation, delayed differentiation of type I alveolar epithelial cells (AECs) and delayed vascular development were all evident in knockout lungs. Differentiation of type II AECs was apparently normal as judged by surfactant protein (SP) mRNAs and SP-C immunostaining. A significant amount of cholesterol was detectable in knockout lungs, implicating some maternal transfer of cholesterol. No significant differences of the spatial-temporal localization of sonic hedgehog (Shh) or its downstream targets by immunohistochemistry were detected between knockout and wild-type lungs and Shh autoprocessing occurred normally in tissues from Dhcr7-/- embryos. CONCLUSION: Our data indicated that cholesterol deficiency caused by Dhcr7 null was associated with a distinct lung saccular hypoplasia, characterized by failure to terminally differentiate alveolar sacs, a delayed differentiation of type I AECs and an immature vascular network at late gestational stages. The molecular mechanism of impaired lung development associated with sterol deficiency by Dhcr7 loss is still unknown, but these results do not support the involvement of dysregulated Shh-Patched-Gli pathway in causing this defect.

Animals↗
PubMed2004

GATA-6 gene enhancer contains nested regulatory modules for primary myocardium and the embedded nascent atrioventricular conduction system.

The cGATA-6 gene is flanked by an enhancer that selectively marks the atrioventricular conduction system (AVCS) in transgenic mice. This enhancer reads anterior/posterior and medial/lateral positional information very early in the cardiogenic program and remains active in progressively more restricted regions of primary myocardium leading up to the emergence of a histologically distinct AVCS. We undertook to parse this enhancer to resolve how the respective AVCS-specific transcription program is regulated at the molecular level. We determined that this AVCS enhancer includes a 102 bp module that is sufficient to restrict expression to primary nonchamber myocardium. This offers a novel tool to analyze the early molecular delineation of primary and chamber myocardium, which subsequently give rise to components of the central and peripheral conduction system, respectively. Furthermore, we show that this 102 bp module in turn contains a nested 47 bp core module that has the potential to direct expression specifically to the AVCS domain of primary myocardium, albeit with low efficiency. Accordingly, we show that a GATA site and a GC-rich site in the 102 bp region bolster the activity of the nested 47 bp AVCS core region even within the context of the parental 1,478 bp enhancer. These are the first functional elements to be reported for a cardiac conduction system-specific control region.

Animals↗
PubMed2004

Identification and detection of the periostin gene in cardiac development.

Periostin, a member of the fasciclin gene family, acts as a cell adhesion molecule through binding to cell surface integrins. Periostin expression has previously been shown to increase substantially following transforming growth factor beta (TGF-beta) and bone morphogenetic protein stimulation. As these molecules are indispensable for cardiac development, we sought to clone the chicken ortholog of periostin and evaluate its spatiotemporal expression pattern during heart morphogenesis. We show by Northern analysis, whole mount and section in situ hybridization experiments that periostin is predominantly expressed in the developing endothelium of the ventricular trabeculae as well as in the endothelium and mesenchyme of the outflow tract and atrioventricular endocardial cushions. Cardiac expression continues into fetal development where periostin is seen predominantly in the valve leaflets and supporting chordae tendinae.

Amino Acid Sequence↗
PubMed2003

Developmental anatomy of the heart: a tale of mice and man.

Because of the increasing availability of tools for genetic manipulation, the mouse has become the most popular animal model for studying normal and abnormal cardiac development. However, despite the enormous advances in mouse genetics, which have led to the production of numerous mutants with cardiac abnormalities resembling those seen in human congenital heart disease, relatively little comparative work has been published to demonstrate the similarities and differences in the developmental cardiac anatomy in both species. In this review we discuss some aspects of the comparative anatomy, with emphasis on the atrial anatomy, the valvuloseptal complex, and ventricular myocardial development. From the data presented it can be concluded that, apart from the obvious differences in size, the mouse and human heart are anatomically remarkably similar throughout development. The partitioning of the cardiac chambers (septation) follows the same sequence of events, while also the maturation of the cardiac valves and myocardium is quite similar in both species. The major anatomical differences are seen in the venous pole of the heart. We conclude that, taking note of the few anatomical "variations," the use of the mouse as a model system for the human heart is warranted. Thus the analysis of mouse mutants with impaired septation will provide valuable information on cellular mechanisms involved in valvuloseptal morphogenesis (a process often disrupted in congenital heart disease), while the study of embryonic lethal mouse mutants that present with lack of compaction of ventricular trabeculae will ultimately provide clues on the etiology of this abnormality in humans.

Anatomy, Comparative↗
PubMed2003

Hemodynamics is a key epigenetic factor in development of the cardiac conduction system.

The His-Purkinje system (HPS) is a network of conduction cells responsible for coordinating the contraction of the ventricles. Earlier studies using bipolar electrodes indicated that the functional maturation of the HPS in the chick embryo is marked by a topological shift in the sequence of activation of the ventricle. Namely, at around the completion of septation, an immature base-to-apex sequence of ventricular activation was reported to convert to the apex-to-base pattern characteristic of the mature heart. Previously, we have proposed that hemodynamics and/or mechanical conditioning may be key epigenetic factors in development of the HPS. We thus hypothesized that the timing of the topological shift marking maturation of the conduction system is sensitive to variation in hemodynamic load. Spatiotemporal patterns of ventricular activation (as revealed by high-speed imaging of fluorescent voltage-sensitive dye) were mapped in chick hearts over normal development, and following procedures previously characterized as causing increased (conotruncal banding, CTB) or reduced (left atrial ligation, LAL) hemodynamic loading of the embryonic heart. The results revealed that the timing of the shift to mature activation displays striking plasticity. CTB led to precocious emergence of mature HPS function relative to controls whereas LAL was associated with delayed conversion to apical initiation. The results from our study indicate a critical role for biophysical factors in differentiation of specialized cardiac tissues and provide the basis of a new model for studies of the molecular mechanisms involved in induction and patterning of the HPS in vivo.

Animals↗
PubMed2003

Cardiac muscle cell formation after development of the linear heart tube.

After the development of the linear heart tube, additional myocardium is formed leading to the muscular mantle around the caval and pulmonary veins and the muscular septa in the embryonic heart. Here, we report the results of our in vivo and in vitro studies of this late myocardium-generating process in the mouse. By using an immunohistochemical approach, we determined that myocardium formation starts around embryonic day 12 in the dorsal mesocardium. In subsequent stages of development, the process extends downstream into the intracardiac mesenchymal tissues of the atrioventricular canal and outflow tract and upstream into the extracardiac mediastinal mesenchyme embedding the pulmonary and caval veins. Given the spatiotemporal pattern of myocardium formation, we applied a three-dimensional in vitro explant culture assay to investigate the myocardium-generating potential of the different cardiac compartments. We determined that this potential is stage- and mesenchyme-dependent. This latter finding suggests an important role for mesenchyme in myocardium formation after the development of the linear heart tube.

Animals↗
PubMed2003

Epicardial-like cells on the distal arterial end of the cardiac outflow tract do not derive from the proepicardium but are derivatives of the cephalic pericardium.

A series of recent studies strongly suggests that the myocardium of the cardiac distal outflow tract (d-OFT) does not derive from the original precardiac mesoderm but, instead, differentiates from a so-called anterior heart field. Similar findings were also reported for the endocardium of the d-OFT. However, very little information is available on the origin of the epicardium of the OFT. To address this issue, we have performed a study in which we have combined experimental in vivo and in vitro techniques (construction of proepicardial chimeras, proepicardial ablation, OFT insertion of eggshell membrane pieces, and culture on collagen gels) with molecular characterization techniques to determine this origin and define the properties of d-OFT epicardium compared with proepicardially derived epicardium. Our results demonstrate that the coelomic/pericardial epithelium in the vicinity of the aortic sac (and not the proepicardium) is the origin of d-OFT epicardium. This "pericardially" derived epicardium and the proepicardially derived epicardial tissues differ in their morphologic appearance, gene-expression profile, and in their ability to undergo epithelial-to-mesenchymal transformation. We conclude that the heterogeneity in the epicardial cell population of the OFT could be a factor in the complex developmental remodeling events at the arterial pole of the heart.

Animals↗
PubMed2003

Mouse models for cardiac conduction system development.

The mouse is the animal of choice for the study of molecular mechanisms involved in the regulation of cardiovascular morphogenesis and function. Recently, a series of genetically engineered mouse models have been reported (e.g. cGATA6/lacZ, MinK/lacZ knock-in/knock-out, engrailed2/lacZ, Cardiac troponin I/lacZ) that provide new and exciting information on the development of the atrioventricular conduction system (AVCS). On the basis of these and ongoing studies, concepts for the formation of the AVCS are continuously being adjusted. A proper understanding of the normal developmental mechanisms underlying the cardiac remodelling leading to the formation of the AVCS is imperative for the interpretation of cardiac abnormalities, including conduction disturbances, as observed in some genetically perturbed (knockout) mice. In this paper information on murine AVCS development will be integrated with published and unpublished results from studies in other vertebrates, including human and rabbit. We will illustrate that although many pieces of the puzzle still remain to be gathered, the outline of a very complex and critical event in cardiac morphogenesis is slowly emerging. Specifically, we will re-evaluate the concept of the 'primary ring' in the context of the new insights in the development of the AV junction as provided by the respective mouse models described above.

Animals↗
PubMed2003

Transcriptional regulation in the mouse atrioventricular conduction system.

We identified a GATA6 gene enhancer that selectively marks the developing atrioventricular conduction system (AVCS) in transgenic mice. This enhancer reads anterior/posterior and medial/lateral positional information early in the cardiogenic programme and remains active in progressively more restricted subsets of heart cells leading up to AVCS formation. Additional experiments will be required to determine if the potential to be recruited into the AVCS is similarly restricted to a subset of myocardial cells early in the cardiogenic programme or if this enhancer can also be activated de novo in cells that initially reside outside this field. We are using several strategies to identify factors that regulate this and other AVCS enhancers and hence govern AVCS function. We are also using this enhancer to make transgenic mice that express Cre, or an inducible form of Cre, to track lineages and to delete floxed genes in the developing or mature AVCS. This Cre/lox approach provides a means to deconstruct complex congenital heart phenotypes that involve the conduction system and to test whether genes are required to form the AVCS or to maintain AVCS function. Lastly, we are exploring strategies to isolate and analyse AVCS cells from normal and affected hearts.

Animals↗