Figure 5.

Ballooning chambers by proliferation (1 hour Brdu exposure) and formation of the building plan of the heart. (A) In mouse embryonic day 8, ventral view, the heart is trough-shaped but unlike in human and chicken, local high levels of proliferation are already revealing the future left ventricle. (B) In mouse embryonic day 8.5, ventral view, expression of Nppa and high levels of proliferation identifies the developing left ventricle. (C) By 9.5 days of embryonic mouse development, viewed from the left, the atrium is also expressing Nppa, which again is mirrored in higher levels of proliferation (bottom). In contrast, the atrioventricular canal and the outflow tract maintain a heart-tube-like phenotype. (D) Much of the building plan of the heart is established by embryonic day 11.5 in mouse. (Modified from images in Christoffels et al. 2000 and de Boer et al. 2012, with permission, from Elsevier © 2000.)