Apoptosis during coronary artery orifice development in the chick embryo

Previous studies regarding the development of proximal segments of the coronary arteries in the chick have demonstrated that these vessels do not develop as angiogenic outgrowths from the aorta. Rather, the proximal segments of the coronary arteries arise from a peritruncal capillary plexus in the epicardium that coalesces around the aortic and pulmonary outflow tracts. Vessels from the peritruncal plexus grow toward and attach to the aorta at about Hamburger and Hamilton (HH) Stage 32 to establish the definitive coronary circulation. Currently, little is known about the process by which patent connections are established between these peritruncal vessels and the aorta. The hypothesis that apoptosis is involved in the formation of the coronary artery orifices was tested in the present study. Aortic and periaortic tissue from HH 29-35 chick embryos was examined using routine light and electron microscopy and TUNEL assays. Apoptotic cells were observed in close spatial and temporal association with the invasion of peritruncal vessels into the aorta (HH 29-31), the initial formation of coronary orifices (HH 32-33), and the further development of the definitive coronary arteries and orifices (HH 34-35). Whereas the origin of these apoptotic cells and the specific factors regulating their death remain unknown, the results of the present study strongly correlate apoptosis with the formation of proximal coronary arteries and their orifices. Our findings suggest avenues for further research and indicate that factors involved in regulating apoptosis should be included in future models of coronary artery development.