Fig. 4. Isl1⁺ progenitor cells during cardiovascular development. β-gal expression was analyzed in Isl1-nlacZ knock-in mouse embryos at the indicated days of development and in the postnatal heart at day 3 (PN 3d) by X-Gal staining. Representative sections at each developmental stage from E8.5-14.5 are shown (left), as are the corresponding heart structures that express Isl1 (middle) and the lineage markers used to identify the different cell types (right). Cranial (Cr)-caudal (Ca), right (R)-left (L), and dorsal (D)-ventral (V) axes are indicated. A, atrial cavity; Ao, aorta; AS, atrial septum; AVN, atrioventricular node; CG, cardiac ganglia; Hcn4, hyperpolarization-activated cyclic nucleotide-gated K⁺ 4; LA, left atrium; LV, left ventricle; MF20, antibody recognizing sarcomeric myosin; OFT, outflow tract; PA, pulmonary artery; RA, right atrium; RV, right ventricle; SAN, sinoatrial node; SM, smooth muscle; sm-actin, smooth muscle actin; V, ventricle cavity. Parts of the figure are reproduced with permission (Sun et al., 2007).