Fig 11. Model of early cardiac development.

(A) Cells located in distal regions of the primitive streak contribute first to the left ventricle (mid-streak stage), then to the right ventricle (late-streak stage), and finally to the outflow tract (OB-EB stages). Although the outflow and atria leave the primitive streak at similar stages, they arise from different regions. The outflow tract originates from distal locations in the primitive streak while atrial progenitors are positioned more proximally. The distal primitive streak cells express Foxa2 when they contribute to the ventricles. They stop expressing Foxa2 when they contribute to the outflow tract. (B) Proposed location of the FHF, AHF, and pSHF in comparison to the hypothetical fate of these different cardiac regions at the pre-headfold stage in (A). (C) Lineage tree of the primitive streak. Within the distal end of the primitive streak, independent primitive streak cells contribute to the left ventricle, the right ventricle, the (at the mid-late streak stage) and to the outflow tract (OB-EB stages). A common progenitor between the right ventricle and the outflow tract exists. By contrast, atrial progenitors are located in the proximal primitive streak and a common progenitor between the left ventricle and atrium may exist in the primitive streak. AHF, anterior heart field; aPS, anterior primitive streak; AVC, atrioventricular canal; cranial pxm, cranial paraxial mesoderm; EB, early bud; epi, epicardium; FHF, first heart field; LV, left ventricle; OB, no bud; OFT, outflow tract; Pha, Pharyngeal arches; PS, primitive streak; pSHF, posterior second heart field; RV, right ventricle.