NEURAL CREST CELLS IN OUTFLOW TRACT SEPTATION OF THE EMBRYONIC CHICKEN HEART - DIFFERENTIATION AND APOPTOSIS

The heart consists of cells deriving from the cardiogenic plate and al so from extracardiac sources. One of the major extracardiac contributi ons is given by the neural crest, The differentiation pathway and fate of the neural crest cells in the outflow tract have been followed ove r a prolonged period during outflow tract septation. We studied the ro le of the neural crest in remodeling the outflow tract by longterm cel l tracing, differentiation markers and apoptosis, The pattern of neura l crest cells migrating to the heart was investigated by heterospecifi c chicken quail chimeras and by retroviral infection of the reporter g ene LacZ to the stemcells. The tagged neural crest cells move to areas that are morphogenetically active, such as the outflow tract, the sem ilunar valves, the wall. of the arteries and the cardiac ganglia, Two differentiated subpopulations are discerned on the basis of immunohist ochemical characterization with antibodies against smooth muscle cells in the arterial vessel wall and against ganglionic cells that were sc attered around the vessels of the arterial pole and the heart, A third subpopulation did not stain with these antibodies, but presented loca lly with the phenomenon of apoptosis as shown with the TUNEL approach. In a developmental series of chicken embryos the populations were fol lowed until stage 40. It was evident that the outflow tract septum in the early phase of development consisted mainly of mesenchymal neural crest cells, In a later phase neural crest cells were still detected a t semilunar valve level, but nearly absent in the outflow tract septum below valve level, The septum at that time had become myocardialized. It is evident that neural crest cells are actually removed from this part of the heart by apoptosis. We are pursuing the hypothesis that an important function of apoptotic cells in heart development might be t o activate the cardiomyocytes to muscularize the outflow tract septum through mobilizing or delivering growth factors at the time and place that septum formation is initiated. Dev. Dyn. 1998;212:373-384, (C) 19 98 Wiley-Liss, Inc.