Development of the venous pole of the heart in the frog Xenopus laevis: a morphological study with special focus on the development of the venoatrial connections.

The heart of lung-breathing vertebrates normally shows an asymmetric arrangement of its venoatrial connections along the left-right (L-R) body axis. The systemic venous tributaries empty into the right atrium while the pulmonary venous tributaries empty into the left atrium. The ways by which this asymmetry evolves from the originally symmetrically arranged embryonic venous heart pole are poorly defined.

Development of the proepicardium in Xenopus laevis.

The proepicardium (PE) is an embryonic progenitor cell population, which provides the epicardium, the majority of the cardiac interstitium, the coronary vasculature and possibly some cardiomyocytes. Recent studies have documented (1) the presence of bilaterally paired PE anlagen in several vertebrates, and (2) species-specific differences in the fate of the left and right PE anlagen. Here, we document PE development in Xenopus laevis (stages 37-46).