The development of the cardiac outflow tract in the chick embryo
Date
1993
Authors
Brownlee, Lisa
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Abstract
The development of cellular and extracellular elements of the cardiac outflow tract have been examined using indirect immunofluorescence and tissue culture techniques. In particular the role of fibronectin (FN) in the population of the outflow tract by cardiac neural crest cells has been studied. At stage 10 the truncus arteriosus consists of endothelium and myocardial cuff, separated by a layer of complex extracellular matrix (ECM). By stage 20 there are a few scattered mesenchyme cells in the ECM space. Using HNK-1, an antibody that recognizes neural tube derivatives, the migration of neural crest cells into the truncus was monitored. The neural crest cells begin migration caudally from the aortic arches at about Stage 25. The cells are seen in clusters, within the ECM of the tunica media. As development proceeds they migrate towards the heart down the length of the truncus arteriosus. Almost simultaneously septation of the truncus arteriosus into pulmonary and systemic pathways occurs. The HNK-1 immunoreactive cells become more dense and are organized into a laminar pattern by about stage 33. The cells that will become smooth muscle express the HNK-1 antigen only during their migration, whereas cells that become part of the nervous plexus of the heart continue to express it after differentiation. There is another population of cells in the tunica media that express the HNK-1 antigen early in development (Stage 10), which are not neural crest derived. This limits the utility of HNK-1 as a neural crest cell marker. An anti-FN antibody was used to follow the distributi.on of FN throughout this time. The FN shows up as randomly arrayed fibers before stage 15, that are not abundant at this time being mainly associated with cell surfaces. The fibers increase in abundance as the tract develops and appear to fill up the media as more cells appear. They are localized to the surfaces of the neural crest cells as well as the endothelium and adventitia, but the relative abundance within these layers changes dependent on what stage is examined. By stage 35 the fibers are more abundant around the endothelium. The migrating neural crest cells express β1 integrin at this time, a compontent of FN receptors. Truncus arteriosus ex plants were used to measure the migration of cardiac neural crest cell in vitro. FN and chick ECM substrates promoted migration and an anti-FN antibody inhibited migration. The conclusion is that FN and cardiac neural crest cell s can function together in vitro and may function together in vivo. This study does not directly test the labeled pathway hypothesis of neural crest cell migration, already well established for other populations of neural crest cells however, it does support to the idea that cardiac neural crest cells may use similar cues and mechanisms to guide their migration.