ABSTRACT
Figure 2b.1 Heart development in the mouse embryo. The cardiac mesoderm is derived from epiblast cells that move through a distal area of the primitive streak. These progenitor cells migrate to the anterior region of the embryo, where they commit to the cardiovascular lineage by effects of several signaling cues from the anterior visceral endoderm. At E7.75, a cardiac crescent is formed at the anterior and ventral parts of the embryo and then continues to fuse at the midline, forming a beating, linear heart tube composed of a myocardial outer layer and an endocardial inner layer. Then the heart tube is looped to the right, and the venous pole moves cranially and dorsally. Following the balloon-like growth of the looped heart tube, septation of the atria and ventricles and atrioventricular valve formation result in the development of a four-chambered heart. Abbreviations: Ao, aorta; LA, left atrium; LV, left ventricle; PT, pulmonary tract; RA, right atrium; RV, right ventricle. During embryonic development, various signaling cues are required for heart formation [7-11]. For example, cardiac specification is regulated by cues derived from the anterior primitive endoderm. Numerous molecules involving signaling pathways, such as the transforming growth factor beta (TGFβ) superfamily, wingless-type MMTV integration site family (WNT), and fibroblast growth factors (FGFs), are important in heart development, and their effects are highly conserved between species (Table 2b.1). Cardiovascular malformation is often caused by disruption of these signaling ligands, their cognate receptors, or downstream molecules.
