UCLA

Early stages of cardiac development are well conserved among vertebrates. However, later morphological development results in a more complicated 4 chambered heart in mammals, while fish retain a simple two chambered heart. The onset of these morphological changes coincide with contribution of cells to the heart from the second heart field (SHF). Interestingly, despite the great morphological differences in the structures derived from precursors in the SHF in mammals and zebrafish, the signals regulating SHF development are conserved. Cardiac neural crest cells (CNCCs), which also contribute to later stages of cardiac development are well studied in chick and mouse models, but very little is known about the role of CNCCs in zebrafish heart development. It is possible that as with the SHF the molecular mechanisms of CNCC development is conserved among all vertebrates. In this study I aim to better define the role of CNCCs in zebrafish and determine how well the role for CNCCs is conserved. I show that there are two waves of CNCCs which contribute to the heart in zebrafish. The first invades the developing heart tube between 24 hpf and 30 hpf and gives rise to CNC derived cardiomyocytes. CNCCs with a myocardial fate have an invasive morphology as they enter the heart, and disrupt local adhesion molecules in neighboring cells. The second wave of CNCCs migrates along aortic arch artery 6, onto the ventral aorta by 80 hpf, and ultimately invades the BA. I find that both populations of CNC derived cells persist to adulthood. These two populations are separated not only by developmental time, but also by their response to FGF signaling as they migrate to the heart. The first wave is independent of Tbx1, and FGF signaling, and the second wave relies on FGF signaling for migration to the ventral aorta and BA. Ablation of NC leads to a variety of cardiac defects including reduced heart rate, defects in myocardial maturation, development of the BA and aorta, and defects in SHF contribution to the heart, as well as a dramatic increase of bmp4 expression, and a reduction of tbx1 expression. Many of the cardiac phenotypes I observe in NC ablated embryos are similar to those reported in other species, making zebrafish an ideal model to study signaling which may be important for CNC development in vertebrates.