CARDIAC NEURAL CREST
The neural crest is a transient population of cells that form from the dorsal ectoderm at the time of neural tube closure (Fig. 1.5). The neural crest population arises through a series of inductive interactions with surrounding tissues around the fourth week of development.
|FIG 1.5 Nervous tissue of embryo at 24 days and 4 weeks.
Once formed, the cells undergo an epithelial-to-mesenchymal transition, migrating ventrally and laterally to contribute to a wide array of tissue types, including the epinephrine-producing cells of the adrenal gland, the parasympathetic neurons, cartilage, bone, connective tissue, and pigment cells. The neural crests themselves are multipotential at the time of their formation; their ultimate fate is a reflection of their relative position along the anterior-to-posterior axis of the embryo. In the cranial portions of the embryo, classic fate mapping studies showed that a subpopulation of neural crest cells enter the arterial pole or the venous pole of the heart to give rise to all of the parasympathetic innervation of the heart, the smooth muscle layer of the great vessels, and portions of the outflow tract. This population is termed the cardiac neural crest. Ablation studies in chicks and genetic studies in mammals demonstrated not only that the cardiac neural crest cells contribute to these regions of the heart but also that they are also essential for the proper formation of each of these structures.