Abstract
ObjectiveThere is no consensus on the embryonic components or morphogenetic processes involved in mature ventricular outflow tract development. Our goal was to use in vivo labelling to investigate the prospective fate of the myocardium of each conal wall. The conal and atrioventricular cushion mesenchyme changes during transformation into mature structures and their role in apoptosis were also investigated.MethodsPlastic labels were placed at the cephalic and caudal conal limits of chicken embryo hearts (stage 22HH) and traced up to stage 36HH. Histological analyses, scanning electron microscopy and apoptotic detection using Lysotracker-Red were performed. The conal longitudinal length and medial displacement were registered. Muscle myosin was identified by immunofluorescence.ResultsLabels positioned in the myocardium of each conal wall moved to the right ventricle (RV), shifting from the arterial subvalvular myocardial zone to the apex. No labels were found in the aortic vestibule. At stage 22HH, the conus was a tubular structure composed of myocardium and endocardium with scarce mesenchyme. The dorso-left conal myocardial wall gradually lost continuity and the free ends separated, while the myocardium was distributed to the RV free wall (24HH-28HH). At stage 22HH, conal crests were not observed, but they were apparent at the dorsal zone of the conus at stage 26HH; towards stage 30HH, they fused to form the supraventricular crest, and the pulmonary infundibulum was evident. The ventro-superior cushion of the AV canal was reorganized into the fibrous and muscular structures lined the aortic vestibule.ConclusionsThe posterior conus is an erroneous concept. The conal myocardium is reorganized in the free wall of the RV. Internally, the conal lumen is transformed into the pulmonary infundibulum. The aortic vestibule is formed from the ventro-superior cushion of the AV canal. Thus, the ventricular outflow tracts have different embryonic origins.
Highlights
It is generally accepted at present that the ventricular outflow tracts of the postnatal tetracavitary heart consist of three well-defined anatomical regions: arterial trunks, arterial valves and subvalvular intracardiac ventricular outflow tracts [1]
Labels positioned in the myocardium of each conal wall moved to the right ventricle (RV), shifting from the arterial subvalvular myocardial zone to the apex
The dorso-left conal myocardial wall gradually lost continuity and the free ends separated, while the myocardium was distributed to the RV free wall (24HH-28HH)
Summary
It is generally accepted at present that the ventricular outflow tracts of the postnatal tetracavitary heart consist of three well-defined anatomical regions: arterial trunks (pulmonary and aortic trunks), arterial valves (valvar leaflets and their supporting annulus) and subvalvular intracardiac ventricular outflow tracts (pulmonary infundibulum and aortic vestibule) [1] In agreement with this idea, it has been pointed out that the embryonic outflow consists of three segments: distal, intermediate and proximal [2]. In 2005 we concluded that the truncus is involved only in the development of the pulmonary and aortic insertion annuls and valves, but it does not form the entire vascular region of the great arteries, which is derived from the aortic sac [17] This statement was supported by at least two findings in the chick embryo heart: 1) The ultrastructural and experimental evidences of myocardial cell differentiation in to connective tissue in the truncus [18]. The boundary between the conus and the truncus was considered the angular junction between the proximal caudocephalic and the distal ventro-dorsal segments of the heart tube (Fig 1A)
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