1. Chapter 1 Molecular Basis of Cardiac Development
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

2. FIGURE 1. 1 An overview of heart development
FIGURE 1.1 An overview of heart development. (A) The heart fields are specified as bilateral fields within the lateral plate mesoderm. The cranial-most aspect (asterisks) will migrate toward the midline first; this seam is depicted by the gray dashed line in B. (B) The heart tube closes ventrally, and cells continue to add from the heart fields. The dorsal aspect of the heart tube will pinch off last. After dorsal closure, additional cells can only be added via the venous (IFT, inflow tract) and arterial (OFT, outflow tract) poles. (C) As additional cells add to the heart tube, the heart tube begins to undergo looping, and the ventral midline becomes the outer curvature of the heart. During looping, the endocardial cushions begin forming in the atrioventricular canal and outflow tract. The atrioventricular canal separates the common atrium (A) from the common ventricle (V). (D) At the end of looping, the atrioventricular cushions are aligned dorsal to the outflow tract cushions, allowing connections between the left atrium and ventricle (LA and LV, respectively) and the right atrium and ventricle (RA and RV, respectively). As the outflow tract is septated, it also undergoes rotation to align the aorta with the left ventricle. Septa form between the ventricles and between the atria. (E) In the mature four-chambered heart, the aorta (Ao) serves as the outlet for the left side of the heart, and the pulmonary artery (PA) serves as the outlet for the right side of the heart.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

3. FIGURE 1. 2 Wnt signaling pathway
FIGURE 1.2 Wnt signaling pathway. In both the canonical and non-canonical (planar cell polarity) pathways, extracellular Wnt ligands bind to the transmembrane receptor Frizzled. In the canonical pathway, Frizzled forms a complex with Dishevelled and additional components, leading to β-catenin stabilization and translocation to the nucleus; β-catenin then promotes Wnt-induced gene expression, such as Nkx2.5 and Islet1. In contrast, in the non-canonical pathway, Frizzled and Dishevelled act on a different set of intracellular signaling molecules (e.g., Rho, Rac) to promote a different set of genes and to inhibit the canonical pathway.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

4. FIGURE 1. 3 Chamber versus non-chamber myocardium
FIGURE 1.3 Chamber versus non-chamber myocardium. Myocardium that is fated to contribute to the chambers is restricted based on interactions between BMP2, a series of Tbx genes, and Hey1 and 2. In the atrioventricular canal and outflow tract, BMP2 induces Tbx2 and 3, which repress chamber myocardium-specific genes. In contrast, chamber-specific Tbx20 expression inhibits BMP signaling, thus eliminating this inhibition and promoting myocardial differentiation. In addition atrial-specific Hey1 and ventricular-specific Hey2 further inhibit BMP2 from interacting with Tbx2 and 3, providing additional feedback to demarcate the chamber myocardium from the developing valves.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

5. FIGURE 1. 4 Chamber septation
FIGURE 1.4 Chamber septation. To form the ventricular septum, the muscular component of ventricular septum elongates toward the atrioventricular canal. From the atrioventricular (AV) canal, a membranous septum forms from the cushion tissue and closes that gap between the atrioventricular canal and the muscular ventricular septum. To form the atrial septum, the septum primum grows from the cranial aspect of the common atrium toward the atrioventricular cushions. Once this septum fuses with the atrioventricular cushions, the cranial aspect detaches. This fenestration is closed by a fold in the dorsal atrial myocardium termed the septum secundum, which forms to the right of the septum primum.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

6. FIGURE 1. 5 Atrioventricular and outflow tract cushions
FIGURE 1.5 Atrioventricular and outflow tract cushions. The outflow tract and atrioventricular cushions are shown after the heart has looped. The major cushions in the atrioventricular canal are the superior and inferior cushions, which are formed by epithelial–mesenchymal transition (EMT). The lateral cushions develop later and are mostly populated by epicardially derived cells.222 In the outflow tract, the proximal left and right cushions are formed through EMT; cardiac neural crest-derived cells migrate from the pharyngeal arches into the outflow tract and form two prongs in the distal left and right outflow tract cushions.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

7. FIGURE 1. 6 Atrioventricular valve formation
FIGURE 1.6 Atrioventricular valve formation. (A) In response to signals from the myocardium (red), a subset of endothelial cells (green) undergoes epithelial–mesenchymal transition (hybrid yellow/green cells) to generate the mesenchymal cells (yellow) that populate the cushions. (B) These mesenchymal cells will undergo proliferation to expand the cushions. (C) After proliferation, these cells will remodel the valve to an elongated shape and secrete extracellular matrix. The mature mitral valve consists of three layers: the atrialis (blue), the spongiosa (yellow) composed of proteoglycans and glycosaminoglycans, and the fibrosa (red) layers. Valve interstitial cells are present in all three layers.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

8. FIGURE 1. 7 Nfat-c1 regulation in the endocardial cushions
FIGURE 1.7 Nfat-c1 regulation in the endocardial cushions. When VEGF is present, VEGF signals via Mek/ERK to promote Nfat-c1-induced proliferation, which is required to populate the endocardial cushions. When VEGF is down-regulated, RANKL acts via the JNK intracellular pathway, which activates Nfat-c1-induced transcription of extracellular matrix remodeling proteins. This switch allows the newly populated cushions to undergo remodeling to form the mature valve leaflets.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

9. FIGURE 1. 7 Nfat-c1 regulation in the endocardial cushions
FIGURE 1.7 Nfat-c1 regulation in the endocardial cushions. When VEGF is present, VEGF signals via Mek/ERK to promote Nfat-c1-induced proliferation, which is required to populate the endocardial cushions. When VEGF is down-regulated, RANKL acts via the JNK intracellular pathway, which activates Nfat-c1-induced transcription of extracellular matrix remodeling proteins. This switch allows the newly populated cushions to undergo remodeling to form the mature valve leaflets.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

10. FIGURE 1. 8 Cardiac neural crest and outflow tract septation
FIGURE 1.8 Cardiac neural crest and outflow tract septation. (A) As cardiac neural crest-derived cells (gray) enter the outflow tract, they form two prongs that spiral into the cushions. At the distal end of the prongs, there is a ‘shelf’ that septates the distal portion of the outflow tract. The proximal portion of the outflow tract is ‘zippered’ shut by the outflow tract cushions. (B) After septation, a plug of cardiac neural crest-derived cells (CNC) can be found between the great arteries, and cardiac neural crest-derived smooth muscle covers the great arteries distal to the semilunar valves.
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease

11. FIGURE 1. 9 Coronary plexus formation. (A) Starting around E11
FIGURE 1.9 Coronary plexus formation. (A) Starting around E11.5, a patchwork of endothelial cells (green) appears on the dorsal aspect of the ventricles, caudal to the sinus venosus. (B,C) This plexus spreads across the ventricles, completely encompassing them by E13.5. (D) After encompassing the ventricles, the plexus remodels to form the mature coronary vasculature. Based on Lavine et al.198 11
© 2014, Elsevier Inc., Willis, et.al., Cellular and Molecular Pathobiology of Cardiovascular Disease