Published online before print August 5, 2004, doi: 10.1161/01.RES.0000141429.13560.cb
© 2004 American Heart Association, Inc.
Integrative Physiology |
Lineage and Morphogenetic Analysis of the Cardiac Valves
From the Experimental and Molecular Cardiology Group (F.J.d.L., A.F.M.M., A.T.S., C.d.G.-d.V., M.J.B.v.d.H., V.M.C.), Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; Cardiac Unit (R.H.A.), Institute of Child Health, University College London, UK; Department of Embryology (J.M.), Center of Anatomy, Georg-August-University Gottingen, Gottingen, Germany; Center for Cardiovascular Development (M.D.S.), Department of Medicine, Molecular and Cellular Biology, and Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Tex; Department of Basic Medical Sciences (S.W.), Anatomy and Developmental Biology, St. George’s Hospital Medical School, Cranmer Terrace, London, UK.
Correspondence to Vincent M. Christoffels, PhD, Department of Anatomy and Embryology, Meibergdreef 15, 1105AZ Amsterdam, The Netherlands. E-mail v.m.christoffels{at}amc.uva.nl
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
We used a genetic lineage-labeling system to establish the material contributions of the progeny of 3 specific cell types to the cardiac valves. Thus, we labeled irreversibly the myocardial (
MHC-Cre+), endocardial (Tie2-Cre+), and neural crest (Wnt1-Cre+) cells during development and assessed their eventual contribution to the definitive valvar complexes. The leaflets and tendinous cords of the mitral and tricuspid valves, the atrioventricular fibrous continuity, and the leaflets of the outflow tract valves were all found to be generated from mesenchyme derived from the endocardium, with no substantial contribution from cells of the myocardial and neural crest lineages. Analysis of chicken-quail chimeras revealed absence of any substantial contribution from proepicardially derived cells. Molecular and morphogenetic analysis revealed several new aspects of atrioventricular valvar formation. Marked similarities are seen during the formation of the mural leaflets of the mitral and tricuspid valves. These leaflets form by protrusion and growth of a sheet of atrioventricular myocardium into the ventricular lumen, with subsequent formation of valvar mesenchyme on its surface rather than by delamination of lateral cushions from the ventricular myocardial wall. The myocardial layer is subsequently removed by the process of apoptosis. In contrast, the aortic leaflet of the mitral valve, the septal leaflet of the tricuspid valve, and the atrioventricular fibrous continuity between these valves develop from the mesenchyme of the inferior and superior atrioventricular cushions. The tricuspid septal leaflet then delaminates from the muscular ventricular septum late in development.
Key Words: lineage analysis • mitral • tricuspid • atrioventricular valve • tendinous chord • valvular • Cre-lox
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The formation of the valvar apparatus at the atrioventricular junction is a complex event, reflected in the high incidence of congenital malformations involving the definitive valves.1 Definitive valves consist of the fibrous annulus, the leaflets, and the supporting tension apparatus, the latter made up of the tendinous cords and the papillary muscles. Studies using immunohistochemistry, scanning electron microscopy, fate-map analyses, and mutagenesis have significantly advanced our understanding of the formation of the valvar apparatus,2–10 showing also that the morphogenetic programs for their formation are conserved in vertebrate evolution.7 The material contributions of the different cell types to the components of the valvar complex, nonetheless, remain controversial. To date, it has been suggested that these components are derived from the subepicardial mesenchyme of the atrioventricular groove,11,12 the myocardium,2,3,7,13 and the atrioventricular endocardial cushions.6–9 Further insight into these lineages is essential if we are to clarify the origin of the components of the valvar apparatus.
To provide these insights, we have used a mouse genetic system based on Cre/lox recombination to label irreversibly14 the myocardium,15 endocardium and endocardially derived mesenchyme of the cushions,16 and the neural crest cells.17,18 We studied chicken-quail chimeras19 to investigate any contribution made by proepicardially derived cells to the formed valves in the chicken. Using these approaches, we have systematically assessed the contributions of the different lineages to the heart and the valvar complexes throughout development. The morphogenetic processes underlying formation of the atrioventricular valvar apparatus in the mouse was studied using a computer-aided 3D reconstruction protocol.20
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Experimental Animals
The
MHC-Cre,15 Tie2-Cre,16 Wnt1-Cre,17 and the R26R transgenic mouse lines14 have been described previously. Embryonic age was determined according to the vaginal plug, with noon of the day on which the plug was first observed being taken as embryonic day 0.5 (E0.5). Embryos and fetuses were dissected in PBS. Amnion or tail biopsy genomic DNA was used for polymerase chain reaction (PCR) assays to detect the Cre- or lacZ transgenes. Proepicardium of HH 16/17 quails was transplanted to stage HH 16/17 chicken embryos according to a protocol established previously.19
ß-Galactosidase Activity Detection, Immunohistochemistry, and RT-PCR
Whole mount 5-bromo-4-chloro-3-indolyl ß-D-galactoside (X-gal) staining of embryos was performed as described.21 For detection of ß-galactosidase activity in 20-µm cryostat sections, embryos were equilibrated in 30% sucrose/PBS and embedded into OCT medium (Sakura, USA). Just before staining, sections of embryos were fixed with a 0.5% glutaraldehyde/PBS solution for 10 minutes at room temperature, followed by X-gal staining. For immunohistochemistry, the following primary antibodies were used: polyclonal antibody against sarco-/endoplasmic reticulum Ca(2+)-ATPase (Serca2a; 1:8000);22 polyclonal antibody against cleaved-caspase 3 (1:100; Cell Signaling Technology); monoclonal antibody against proliferating cell nuclear antigen (PCNA; 1:2000; Santa Cruz Biotechnology); and monoclonal antibody against Desmin (1:50; Monosan Clone D33). Nuclear fast red (Merck) was used to visualize nuclei. Detection of quail cells in 5-µm sections of chicken-quail chimeras was performed as described.19 RNA isolation, RT-PCR, and real-time PCR were performed as described.23
Nonradioactive In Situ Hybridization and 3D Reconstruction
Nonradioactive section in situ hybridization of 10- to 14-µm sections of 4% paraformaldehyde-fixed FVB mouse embryos was performed as described previously.24 Three-dimensional visualization and geometry reconstruction of patterns of gene expression determined by in situ hybridization were performed as described previously.20 Files with reconstructions are available on request.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Tissue-Specific Labeling of Myocardial, Endocardial, and Neural Crest Cells
The developmental onset of recombination of the conditional lacZ allele defines the stage from which the particular lineage can be tracked. The onset of Cre expression in the
MHC-Cre transgene in the FVB background was first detected at E7 (Figure 1A), which should result in onset of recombination shortly thereafter. Indeed, by E9, MHC-Cre/R26R embryos showed ß-galactosidase activity in the hearts, including the myocardium of the atrioventricular canal supporting the developing atrioventricular cushions (Figure 1B). Onset of Cre-mediated recombination in the endocardial cells and cushions of Tie2-Cre/R26R mice is observed at E9.5, concomitant with formation of the cushion mesenchyme.16 Cells from the neural crest in Wnt1-Cre/R26R mice were labeled before they arrived in the heart.18 Together, all 3 lineages are labeled before the beginning of formation of the atrioventricular valvar complexes. Because of this, it is possible to assess the contribution of each lineage to the definitive valves.
|
The MHC-Cre line has been reported to recombine the R26R allele in the myocardium at E11.5.25 To test the specificity of labeling by recombination of the myocardial lineage throughout development, sister sections of MHC/R26R embryos between E11.5 and E15.5 were stained for the presence of Serca2, which is specific for myocardium, and for ß-galactosidase activity on sister sections. Activity of ß-galactosidase was restricted to the myocardium and was never observed in the epicardium or endocardium or in any other nonmyocardial cell in the entire embryo (Figure 1D and 1E). Because the pattern of activity of ß-galactosidase matched completely that of Serca2, we first conclude that the MHC-Cre line does not show ectopic activity, and second, myocardium subsequent to E9 does not transdifferentiate into another cell type. Selectivity of ß-galactosidase activity was similarly tested in Tie2-Cre/R26R mice and found to be restricted to the endocardium and the mesenchyme of the cushions but was never observed in myocardium or epicardium (Figure 1F, 1G, 1J, and 1K). Atrioventricular cushions were stained in their entirety by E12.5 in a pattern coinciding with the gradient in cell density from lumen to myocardium (Figure 1H and 1I). Activity of ß-galactosidase and Serca2 staining were mutually exclusive, showing that mesenchyme derived from the endocardium does not transdifferentiate into myocardium. The endothelial layer of the coronary vessels also expressed ß-galactosidase (see Figure 3D). Furthermore, staining was noted in the ventricular walls (see Figure 3A), revealing endocardial cells that had been trapped during compaction of the myocardial wall. The reported selectivity of recombination of the cells derived from the neural crest in Wnt1-Cre mice,18 including the cardiac neural crest cells, was confirmed (data not shown). Therefore, none of the 3 transgenic lines show evidence of ectopic recombination.
|
Contributions of Lineages to Components of Valvar Complexes
Myocardial Lineage
We investigated MHC-Cre/R26R mice to determine the contribution of cells derived from the myocardium to the atrioventricular valves. From E12.5 onward, we observed cells expressing ß-galactosidase in the myocardial layer of the developing valve (Figure 1D and 1E). In contrast, neonatal MHC-Cre/R26R mice and those at E17.5 had no cells expressing ß-galactosidase either in the valvar leaflets or tendinous cords (Figure 2A through 2F). This shows that the myocardium does not contribute materially to the leaflets or cords but disappears. Nonetheless, in some sections of newborn hearts, we did observe solitary ß-galactosidase–positive cells located in leaflets. In sister sections, these cells were also seen to express Serca2, and were therefore myocardial cells and not transdifferentiated fibrous cells (Figure 2C and 2D). Expression of Serca2 and ß-galactosidase at the junction of the papillary muscle and the cords is similar, if not identical, showing that the myocardium does not contribute cells to the cords. Similarly, the atrioventricular fibrous continuity did not express ß-galactosidase (Figure 2G and 2H), demonstrating that it does not receive any contribution from the myocardial lineage. Leaflets of the aortic and pulmonary valves never received any myocardial cells during development (Figure 2I and 2J).
|
Endocardial Lineage
We used the Tie2-Cre/R26R animals to investigate the contribution of the endocardium and endocardially derived mesenchymal cells of the cushions to the valvar leaflets and apparatus. At E17.5, we observed that leaflets of the tricuspid and mitral valves were almost entirely positive for ß-galactosidase expression (Figure 3A through 3C), demonstrating their origin from the endocardium. In addition, the atrioventricular fibrous continuity expressed ß-galactosidase, again revealing their origin from the endocardium (Figure 3B and 3G). The pattern of ß-galactosidase–positive cells in the cords at their junction with the papillary muscles is strictly complementary to the pattern of myocardial-specific expression of Serca2 (Figure 3E and 3F). Therefore, we conclude that the tendinous cords are derived from mesenchyme that is of endocardial origin. Likewise, leaflets of the aortic and pulmonary valves are derived largely from endocardially derived mesenchyme (Figure 3I and 3J).
Neural Crest Lineage
To explore whether or not, during development, cells migrating from the neural crest reside temporarily in the atrioventricular cushions, as they do in the cushions of the outflow tract (OFT),18,26 we analyzed Wnt1-Cre/R26R embryos from E9.5 until E14. At all stages, we observed large numbers of cells expressing ß-galactosidase in the cushions of the OFT (Figure 4A through 4C), consistent with data reported previously.18 We did not observe such blue cells in the atrioventricular cushions. Nonetheless, at E13, we noted nerves from the neural crest invading the heart at its venous pole and extending into the atrioventricular junctional region, but not reaching as far as the atrioventricular cushions (data not shown). After their formation, atrioventricular valves are reported to be free of cells derived from the neural crest.18 Together, we conclude that cells derived from the neural crest never enter the atrioventricular cushions or the valvar primordia.
|
Proepicardial Lineage
Proepicardially derived mesenchymal cells have been shown previously to populate the atrioventricular cushions during development.12,19,27 To investigate any material contribution made by these proepicardially derived cells to the definitive valvar complexes, we made chicken-quail chimeras by grafting the quail proepicardium into the pericardial cavity of HH stage-16 chick embryos.19 We then investigated, at stage 45 (E18), the contribution of the quail proepicardially derived cells to the chicken heart. Whereas the epicardium, the subepicardial connective tissue in the atrioventricular grooves, the coronary vessels, and the intramyocardial fibroblasts were seen to be derived almost exclusively from quail proepicardial cells (Figure 4D), very few such cells were seen in the caudal, or inferior, aspect of the mesenchyme of the tricuspid valvar leaflets (Figure 4E). No quail cells were detected in the cranial, or superior, aspect. Very few quail cells were seen in the mitral valvar leaflets (Figure 4F). Likewise, the leaflets of the aortic and pulmonary valves never received any proepicardial cells during development.19
Formation of the Mitral and Tricuspid Valvar Complexes
Results of the lineage analysis of the distinct components of the valvar apparatus prompted us to analyze the process of valvar formation during its development in the overall plane of the atrioventricular junctions (Figure 5).
|
Mural Leaflets
The first visible event in formation of mural leaflets is the appearance of a small myocardial protrusion from the myocardium of the atrioventricular canal, first detected at E9.5 at the left side and at E10.5 at the right side (Figure 6D and 6E). This protrusion expresses Tbx3 (Figure 6D through 6F), a marker for the myocardium of the atrioventricular canal.28 It does not express Cx40, Cx43 (Figure 6G and 6H), or ANF (data not shown), which are markers of the chamber myocardium.29 Furthermore, compared with adjacent ventricular myocardium, less proliferation is observed in the myocardial cells of the protruding tongue and the atrioventricular canal (Figure 7A through 7C). Therefore, we conclude that the protrusion is an extension from the myocardium of the atrioventricular canal. The protrusion increases in size and forms a circumferential myocardial funnel-like structure originating from the AVC that expresses Tbx3 (Figure 6A through 6C, and 6L). The area resembles, at the right caudal side, the complex in the human embryo that was termed the "tricuspid gully"7 (Figure 6J through 6M). A very similar but less conspicuous complex is also seen at the left atrioventricular junction (Figure 6J through 6M), showing that the process of the formation of the cranial and caudal mural leaflets of the tricuspid valve (Figure 5C) is comparable to that of the mural leaflet of the mitral valve.
|
|
The ventricular side of the myocardial funnel forms an irregular trabecular layer that expresses markers of ventricular myocardium but not Tbx3 (Figure 6F through 6I). Therefore, the muscle supporting the leaflets receives contributions from the atrioventricular canal and the ventricle. Behind the funnel, space is generated by proliferation and expansion of the ventricular wall, with holes and trabeculae developing within this area (Figures 6 and 8). This process was not associated with apoptosis. Whereas apoptosis was observed in the cushion mesenchyme at E13.5 and E14.5,30 no evidence of apoptotic activity is found within the myocardium of this area (Figure 7F and 7G). At several sites, the myocardial sheet remains connected to the apical ventricular trabeculae. Formation of the trabeculae at the caudal side of the ventricle shows remarkable directionality, being orientated from the free wall toward the septum at the right side but toward the apex at the left side (Figure 6J through 6M).
|
By E12, the endocardial layer lining the mural parts of the myocardial funnel of the mitral and tricuspid valves has started to thicken at specific sites, most likely by local proliferation, to form the lateral atrioventricular cushions (Figure 5D and 5F). By E14.5, these cushions cover the entire mural parts and have fused with the previously formed inferior and superior atrioventricular cushions (Figure 5H). By this stage, proliferation of the mesenchyme has decreased (Figure 7D and 7E). The atrioventricular canal itself increases significantly in size during this period and accommodates the rapidly expanding primordia of the mural valvar leaflets (Figure 5D, 5F, and 5H). The myocardium below the leaflets and cords starts to disappear at E15 to E16, leaving a connection with the trabecular layer of the myocardium to form the papillary muscles. The disappearance of the myocardium was associated with apoptosis, which was appreciably more abundant from E15.5 onward (Figure 7H through 7N).
Septal and Aortic Leaflets
The septal leaflet of the tricuspid valve and the aortic leaflet of the mitral valve form from the inferior and superior atrioventricular cushions, these already being present at E9.5. The cushions fuse at E11.5 and become draped over the crest of the muscular ventricular septum by E14.5 (Figure 5D through 5I), albeit with considerable parts of both cushions remaining as free structures above the cavity of the left ventricle (Figure 5C, 5H, and 5I). At all sites where the cushions are supported by the septum, the underlying myocardium expresses Tbx3 (Figure 6B, 6C, and 6L). The majority of the mesenchymal cells continue to cycle at E11.5, but cells in the core of the mesenchyme forming the leaflets become quiescent thereafter (Figure 7A through 7E). The right side of the fused cushions transforms into the septal leaflet of the tricuspid valve, along with its supporting tendinous cords, but stays connected to the myocardium until E16.5 to 17.5. Then, the leaflet detaches by delamination of the septal myocardium (Figure 2G and 2H), a process associated with apoptosis of cells at the site of the separation (Figure 7H through 7J, and 7N). In contrast, the aortic leaflet of the mitral valve is never attached to or supported by myocardium during its formation (Figure 5D through 5I), except at its cranial and caudal margins (Figure 5C), with cords connecting to the papillary muscles being formed at these sites.
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
We used a genetic system to label irreversibly the progeny of the myocardium, the endocardium, and the neural crest from embryonic stages onwards, following the fate of these cells into the mature heart. To be valid, Cre-mediated recombination must be specific, with no labeling of unintended lineages. The transgenic lines used here have been reported to be exceptionally specific,16,18,25 and our analysis shows that, throughout cardiac development, Cre-mediated recombination in the heart occurred only in the intended cell types, with no ectopic activity. It has been suggested that myocardium transdifferentiates into fibrous tissues during valvar formation, or mesenchymal cells into myocardium during the "muscularization" of the mesenchymal septal structures.7,13,31 However, the pattern of labeling in the
MHC-Cre/R26R embryos was identical to the pattern of expression of Serca2 and complementary to the pattern of labeling in the Tie2-Cre/R26R embryos. Therefore, we conclude that after the onset of recombination in the heart at E8 to E9, there is no transdifferentiation of either myocardial cells or endocardial cells and their derived mesenchyme.
Contributions of Different Tissue to the Valvar Apparatus
Previous studies had suggested important contributions to the atrioventricular valves and cords from either the subepicardial mesenchyme of the atrioventricular grooves or the ventricular myocardium.2,3,7,11–13 Using the recombination system, we have shown for the first time that the myocardial lineage does not contribute materially to the definitive fibrous tissues of the heart, including the valvar leaflets and cords of the tension apparatus. Our data indicate that these components are generated almost entirely from the cells derived from the endocardium, a finding also reported very recently by Lincoln et al,32 although we cannot rule out the possibility that small numbers of cells of nonendocardial origin are present in these components. The septal leaflets and cords of the mature valves themselves are hinged from the layer of atrioventricular fibrous insulation formed on the crest of the muscular ventricular septum. Our analysis shows that the insulating structures are also formed from the endocardially derived mesenchyme of the atrioventricular cushions.
Previous studies have indicated that the proepicardially derived mesenchyme of the atrioventricular groove makes contributions to the atrioventricular cushions,12,19,27 and hence, to the formation of the valves.12 However, our analysis of chicken-quail chimeras at late stages indicates that quail-derived proepicardium provides only a minor material contribution to the leaflets of the formed valves. The fate of those cells derived from the proepicardium that have invaded the cushions remains to be defined. Furthermore, because the expression of ß-galactosidase appears homogenous within the valves of the Tie2-Cre/R26R mice, our analysis indicates that the leaflets and cords are derived almost exclusively from endocardial cells, leaving little room for contributions from the proepicardium. We cannot rule out the possibility of proepicardially derived cells initiating the expression of Tie2-Cre, by which they would become indistinguishable from the cells known to be derived from the endocardial cushions. Generation and analysis of a transgenic line expressing Cre selectively in the proepicardium will settle this issue unambiguously.
It was found previously that cells derived from the neural crest contribute significantly to the cushion mesenchyme within the OFT.18,26 However, the mature leaflets of the OFT valves were also shown to be virtually devoid of neural crest-derived cells.18 Our analysis revealed that these leaflets receive a large contribution from the endocardium (Figure 3), with no material derived from the proepicardium19 or myocardium (Figure 2). These data indicate that endocardially derived mesenchyme replaces neural crest-derived cells during late stages of valve formation. The precise mechanisms underlying this process require further investigation.
Morphogenesis of the Atrioventricular Valvar Apparatus
It is generally held that the valves initially form by delamination or detachment of the atrioventricular cushions from the ventricular myocardial wall.3,7,9 This would result in a freely movable primordial leaflet constituted of mesenchyme and ventricular myocardium. Such a mechanism is responsible for formation of the septal leaflet of the tricuspid valve but cannot account for formation of the aortic and mural leaflets of the mitral valve nor the mural leaflets of the tricuspid valve. Our analysis of these leaflets showed several notable differences from this currently accepted mechanism involving delamination (Figure 8). First, the lateral cushions are formed only after the appearance of a supporting myocardial sheet that is free from the ventricular wall. Second, this myocardial sheet has an atrioventricular rather than a ventricular phenotype. Third, it is growth of this sheet, coupled with expansion and excavation of the underlying ventricular wall rather than delamination or detachment, that generates the mobile valvar leaflets. Previous studies did not explicitly differentiate between the formation of mural as opposed to septal leaflets, which may have contributed to these discrepancies.
Our group has previously assigned an important role for the so-called tricuspid gully in the formation of the tricuspid valve in the human.7 We have now shown that such a gully can also be recognized in the mouse, and appears to be no more than a subdomain of the Tbx3-expressing myocardial funnel that encircles the atrioventricular canal. Previously, the gully was found to be devoid of Gln2 reactivity, considered a marker for the ventricular boundary of the right atrioventricular canal, and hence was presumed to form from ventricular myocardium.7 With the recent emergence of more precise markers that clearly distinguish atrioventricular from ventricular chamber myocardium, we can now show that the entire funnel, including the gully, has an atrioventricular phenotype. However, the atrioventricular muscle within the developing leaflets disappears with continuing development. Therefore, the muscle of the atrioventricular canal that persists after birth is sequestrated on the atrial side of the junction subsequent to formation of the fibrous annulus.8
We have also shown that formation of the mural components of the tricuspid valve is not different intrinsically from formation of the mural leaflet of the mitral valve. Thus, the myocardial sheet supporting the valvar primordia is present throughout the mural margins of the atrioventricular canal but is more prominent at the dorsolateral side of the tricuspid valve. This is because growth of the lateral ventricular wall and excavation of the trabecular layer are more extensive at the right than at the left ventricular side. Furthermore, because of the differences in directionality of formation of the trabeculae in the caudal parts of the ventricles, the tricuspid sheet is initially preserved, whereas the mitral sheet becomes discontinuous (Figure 6J through 6M). The orientation of the trabeculae requires concomitant oriented growth of the myocardial wall. Elegant clonal analyses have already shown differences in the direction of growth of the ventricular chambers, being circumferential at the right side and radial at the left side.33 This is in keeping with our observations concerning the direction of the trabeculae and might explain why the anterior papillary muscle of the tricuspid valve and the septomarginal trabeculation are connected to the ventricular septum, whereas the papillary muscles of the mitral valve are connected to the apex.
The myocardial layer of the valves disappears only late in development. Our lineage analysis excludes the possibility of transdifferentiation. Others suggested that the myocardium disappears because of differential growth.9 Nonetheless, the disappearance of so many myocardial cells is difficult to reconcile with the moderate 2-fold increase in length of the valve during the period from E15.5 to E17.5 (data not shown). Our finding of apoptotic cells in the myocardial sheet throughout this period strongly indicates that programmed cell death is the underlying mechanism for its disappearance.
|
Acknowledgments |
|---|
We express our gratitude to Drs M. Yanagisawa, A.P. McMahon and F. Wuytack for transgenic mice and antibodies, and to C.R.B. Ramakers, S. Tesink Taekema, and P.A.J. de Boer for their assistance during the study. F.J.d.L., A.F.M.M., M.J.B.v.d.H., and V.M.C. are supported by the Netherlands Heart Foundation grant M96.002. R.H.A. and S.W. are supported by the British Heart Foundation.
|
Footnotes |
|---|
Original received April 2, 2004; revision received July 20, 2004; accepted July 23, 2004.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
- Hoffman JI, Kaplan S. The incidence of congenital heart disease. J Am Coll Cardiol. 2002; 39: 1890–1900.
[Abstract/Free Full Text] - Odgers PNB. The development of the atrioventricular valves in man. J Anat. 1939; 73: 643–657.[Medline] [Order article via Infotrieve]
- van Mierop LHS, Alley RD, Kausel HW, Stranahan A. The anatomy and embryology of endocardial cushion defects. J Thorac Cardiovasc Surg. 1962; 43: 71–83.[Medline] [Order article via Infotrieve]
- Eisenberg LM, Markwald RR. Molecular regulation of atrioventricular valvuloseptal morphogenesis. Circ Res. 1995; 77: 1–6.
[Free Full Text] - De la Cruz MV, Gimenez-Ribotta M, Saravalli O, Cayre R. The contribution of the inferior endocardial cushion of the atrioventricular canal to cardiac septation and to the development of the atrioventricular valves: study in the chick embryo. Am J Anat. 1983; 166: 63–72.[CrossRef][Medline] [Order article via Infotrieve]
- Chin CC, Gandour-Edwards R, Oltjen S, Choy M. Fate of atrioventricular endocardial cushions in the developing chick heart. Pediatr Res. 1992; 32: 390–393.[Medline] [Order article via Infotrieve]
- Lamers WH, Virágh S, Wessels A, Moorman AFM, Anderson RH. Formation of the tricuspid valve in the human heart. Circulation. 1995; 91: 111–121.
[Abstract/Free Full Text] - Wessels A, Markman MWM, Vermeulen JLM, Anderson RH, Moorman AFM, Lamers WH. The development of the atrioventricular junction in the human heart. Circ Res. 1996; 78: 110–117.
[Abstract/Free Full Text] - Oosthoek PW, Wenink ACG, Vrolijk BC, Wisse LJ, de Ruiter MC, Poelmann RE, Gittenberger-de Groot AC. Development of the atrioventricular valve tension apparatus in the human heart. Anat Embryol. 1998; 239: 317–329.
- Gruber PJ, Epstein JA. Development gone awry: congenital heart disease. Circ Res. 2004; 94: 273–283.
[Abstract/Free Full Text] - Wenink ACG, Gittenberger-de Groot AC, Boom AG. Developmental considerations of mitral valve anomalies. Int J Cardiol. 1986; 11: 85–98.[CrossRef][Medline] [Order article via Infotrieve]
- Gittenberger-de Groot AC, Vrancken Peeters MP, Mentink MM, Gourdie RG, Poelmann RE. Epicardium-derived cells contribute a novel population to the myocardial wall and the atrioventricualr cushions. Circ Res. 1998; 82: 1043–1052.
[Abstract/Free Full Text] - Morse DE, Hamlett WC, Noble CW, Jr. Morphogenesis of chordae tendineae. I: Scanning electron microscopy. Anat Rec. 1984; 210: 629–638.[CrossRef][Medline] [Order article via Infotrieve]
- Soriano P. Generalized lacZ expression with the ROSA26 Cre reporter strain. Nat Genet. 1999; 21: 70–71.[CrossRef][Medline] [Order article via Infotrieve]
- Agah R, Frenkel PA, French BA, Michael LH, Overbeek PA, Schneider MD. Gene recombination in postmitotic cells. Targeted expression of Cre recombinase provokes cardiac-restricted, site-specific rearrangement in adult ventricular muscle in vivo. J Clin Invest. 1997; 100: 169–179.[Medline] [Order article via Infotrieve]
- Kisanuki YY, Hammer RE, Miyazaki J, Williams SC, Richardson JA, Yanagisawa M. Tie2-Cre transgenic mice: a new model for endothelial cell-lineage analysis in vivo. Dev Biol. 2001; 230: 230–242.[CrossRef][Medline] [Order article via Infotrieve]
- Danielian PS, Muccino D, Rowitch DH, Michael SK, McMahon AP. Modification of gene activity in mouse embryos in utero by a tamoxifen-inducible form of Cre recombinase. Curr Biol. 1998; 8: 1323–1326.[CrossRef][Medline] [Order article via Infotrieve]
- Jiang X, Rowitch DH, Soriano P, McMahon AP, Sucov HM. Fate of the mammalian cardiac neural crest. Development. 2000; 127: 1607–1616.[Abstract]
- Manner J. Does the subepicardial mesenchyme contribute myocardioblasts to the myocardium of the chick embryo heart? A quail-chick chimera study tracing the fate of the epicardial primordium. Anat Rec. 1999; 255: 212–226.[CrossRef][Medline] [Order article via Infotrieve]
- Soufan AT, Ruijter JM, van den Hoff MJB, de Boer PAJ, Hagoort J, Moorman AFM. Three-dimensional reconstruction of gene expression patterns during cardiac development. Physiol Genomics. 2003; 13: 187–195.
[Abstract/Free Full Text] - Franco D, de Boer PAJ, de Gier-de Vries C, Lamers WH, Moorman AFM. Methods on in situ hybridization, immunohistochemistry and ß-galactosidase reporter gene detection. Eur J Morphol. 2001; 39: 3–25.[CrossRef][Medline] [Order article via Infotrieve]
- Eggermont JA, Wuytack F, Verbist J, Casteels R. Expression of endoplasmic-reticulum Ca2+-pump isoforms and of phospholamban in pig smooth-muscle tissues. Biochem J. 1990; 271: 649–653.[Medline] [Order article via Infotrieve]
- Fijnvandraat AC, van Ginneken ACG, Schumacher CA, Boheler KR, Lekanne Deprez RH, Christoffels VM, Moorman AFM. Cardiomyocytes purified from differentiated embryonic stem cells exhibit characteristics of early chamber myocardium. J Mol Cell Cardiol. 2003; 35: 1461–1472.[CrossRef][Medline] [Order article via Infotrieve]
- Moorman AFM, Houweling AC, de Boer PAJ, Christoffels VM. Sensitive nonradioactive detection of mRNA in tissue sections: novel application of the whole-mount in situ hybridization protocol. J Histochem Cytochem. 2001; 49: 1–8.
[Abstract/Free Full Text] - Gaussin V, Van de PT, Mishina Y, Hanks MC, Zwijsen A, Huylebroeck D, Behringer RR, Schneider MD. Endocardial cushion and myocardial defects after cardiac myocyte-specific conditional deletion of the bone morphogenetic protein receptor ALK3. Proc Natl Acad Sci U S A. 2002; 99: 2878–2883.
[Abstract/Free Full Text] - Epstein JA, Li J, Lang D, Chen F, Brown CB, Jin F, Lu MM, Thomas M, Liu E, Wessels A, Lo CW. Migration of cardiac neural crest cells in Splotch embryos. Development. 2000; 127: 1869–1878.[Abstract]
- Dettman RW, Denetclaw W, Ordahl CP, Bristow J. Common epicardial origin of coronary vascular smooth muscle, perivascular fibroblasts, and intermyocardial fibroblasts in the avian heart. Dev Biol. 1998; 193: 169–181.[CrossRef][Medline] [Order article via Infotrieve]
- Hoogaars WMH, Tessari A, Moorman AFM, de Boer PAJ, Hagoort J, Soufan AT, Campione M, Christoffels VM. The transcriptional respressor Tbx3 delineates the developing central conduction system of the heart. Cardiovasc Res. 2004; 62: 489–499.
[Abstract/Free Full Text] - Christoffels VM, Habets PEMH, Franco D, Campione M, de Jong F, Lamers WH, Bao ZZ, Palmer S, Biben C, Harvey RP, Moorman AFM. Chamber formation and morphogenesis in the developing mammalian heart. Dev Biol. 2000; 223: 266–278.[CrossRef][Medline] [Order article via Infotrieve]
- Fisher SA, Langille BL, Srivastava D. Apoptosis during cardiovascular development. Circ Res. 2000; 87: 856–864.
[Abstract/Free Full Text] - van den Hoff MJB, Kruithof BPT, Moorman AFM. Making more heart muscle. BioEssays. 2004; 26: 248–261.[CrossRef][Medline] [Order article via Infotrieve]
- Lincoln J, Alfieri CM, Yutzey KE. Development of heart valve leaflets and supporting apparatus in chicken and mouse embryos. Dev Dyn. 2004; 230: 239–250.[CrossRef][Medline] [Order article via Infotrieve]
- Meilhac SM, Esner M, Kerszberg M, Moss JE, Buckingham ME. Oriented clonal cell growth in the developing mouse myocardium underlies cardiac morphogenesis. J Cell Biol. 2004; 164: 97–109.
[Abstract/Free Full Text]
This article has been cited by other articles:
 |
|
 |
|
  K. Niessen and A. Karsan Notch Signaling in Cardiac Development Circ. Res., May 23, 2008; 102(10): 1169 - 1181. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. M. Goddeeris, S. Rho, A. Petiet, C. L. Davenport, G. A. Johnson, E. N. Meyers, and J. Klingensmith Intracardiac septation requires hedgehog-dependent cellular contributions from outside the heart Development, May 15, 2008; 135(10): 1887 - 1895. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. van Wijk, A. F.M. Moorman, and M. J.B. van den Hoff Role of bone morphogenetic proteins in cardiac differentiation Cardiovasc Res, May 1, 2007; 74(2): 244 - 255. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. T.M. Mommersteeg, W. M.H. Hoogaars, O. W.J. Prall, C. de Gier-de Vries, C. Wiese, D. E.W. Clout, V. E. Papaioannou, N. A. Brown, R. P. Harvey, A. F.M. Moorman, et al. Molecular Pathway for the Localized Formation of the Sinoatrial Node Circ. Res., February 16, 2007; 100(3): 354 - 362. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. T.M. Mommersteeg, A. T. Soufan, F. J. de Lange, M. J.B. van den Hoff, R. H. Anderson, V. M. Christoffels, and A. F.M. Moorman Two Distinct Pools of Mesenchyme Contribute to the Development of the Atrial Septum Circ. Res., August 18, 2006; 99(4): 351 - 353. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Nakamura, M. C. Colbert, and J. Robbins Neural Crest Cells Retain Multipotential Characteristics in the Developing Valves and Label the Cardiac Conduction System Circ. Res., June 23, 2006; 98(12): 1547 - 1554. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. M. Christoffels, M. T.M. Mommersteeg, M.-O. Trowe, O. W.J. Prall, C. de Gier-de Vries, A. T. Soufan, M. Bussen, K. Schuster-Gossler, R. P. Harvey, A. F.M. Moorman, et al. Formation of the Venous Pole of the Heart From an Nkx2-5-Negative Precursor Population Requires Tbx18 Circ. Res., June 23, 2006; 98(12): 1555 - 1563. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. B. Hinton Jr, J. Lincoln, G. H. Deutsch, H. Osinska, P. B. Manning, D. W. Benson, and K. E. Yutzey Extracellular Matrix Remodeling and Organization in Developing and Diseased Aortic Valves Circ. Res., June 9, 2006; 98(11): 1431 - 1438. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Liu, F. Liu, A. E. Schneider, T. St. Amand, J. A. Epstein, and D. E. Gutstein Distinct cardiac malformations caused by absence of connexin 43 in the neural crest and in the non-crest neural tube Development, May 15, 2006; 133(10): 2063 - 2073. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. M. Chauvaud, A. C. Hernigou, E. R. Mousseaux, D. Sidi, and J.-L. Hebert Ventricular Volumes in Ebstein's Anomaly: X-Ray Multislice Computed Tomography Before and After Repair Ann. Thorac. Surg., April 1, 2006; 81(4): 1443 - 1449. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. E. Yutzey, M. Colbert, and J. Robbins Ras-Related Signaling Pathways in Valve Development: Ebb and Flow Physiology, December 1, 2005; 20(6): 390 - 397. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. Wilm, A. Ipenberg, N. D. Hastie, J. B. E. Burch, and D. M. Bader The serosal mesothelium is a major source of smooth muscle cells of the gut vasculature Development, December 1, 2005; 132(23): 5317 - 5328. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. A. Stennard and R. P. Harvey T-box transcription factors and their roles in regulatory hierarchies in the developing heart Development, November 15, 2005; 132(22): 4897 - 4910. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Gaussin, G. E. Morley, L. Cox, A. Zwijsen, K. M. Vance, L. Emile, Y. Tian, J. Liu, C. Hong, D. Myers, et al. Alk3/Bmpr1a Receptor Is Required |