Surgical intervention for patients with some forms of congenital heart diseases (CHD) has increased patient survival to adulthood; however post surgical stress contributes to a high incidence of heart failure, with the right ventricle being more susceptible to ventricular failure. Developing novel therapies for CHDs requires an understanding of the underlying biological mechanisms driving cardiac progenitor cell specification and differentiation. Two distinct progenitor populations, termed the first heart field (FHF) and the second heart field (SHF), have been shown to drive cardiac development . Whereas the FHF contributes to the left ventricle (LV) , the SHF derived cells contribute to the right ventricle (RV), inflow and outflow tracts in the mammalian heart. Unsurprisingly, SHF defects are a major contributor of CHDs. Recently, second heart field progenitors in zebrafish have been shown to give rise to three cardiovascular lineages in the OFT and myocardium in the distal ventricle; thus displaying a multipotent characteristic.
My project focuses on studying the underlying biological mechanisms and the intrinsic competence of cardiac progenitor cells to differentiate into multiple lineages within the heart. There are currently no studies that have assessed the lineage specification of FHF and SHF progenitors in the zebrafish adult heart. This will help us to understand how the two distinct progenitor populations give rise to the adult heart and its structures; thus allowing us to model CHDs in zebrafish. I’m employing a Cre recombinase-mediated lineage-tracing of cells expressing cmlc2 in order to assess the lineage specification of FHF and SHF progenitors in the zebrafish heart. The cmlc2 gene product is found in the sarcomere of cardiomyocytes undergoing differentiation. I am using a tamoxifen-inducible Cre driven by cmlc2 regulatory sequences, Tg(cmlc2:ERCreER).This line, when crossed with Tg(cmlc2:loxP-GFP-STOP-loxP-mCherry) will allow visualization of cardiomyocytes with mCherry fluorescence after tamoxifen induced excision of loxp-flanked STOP sequences . The SHF population begins differentiation later, and adds onto the linear heart tube gradually; expressing the differentiation marker later. Thus, administering tamoxifen to the double transgenic embryos prior to SHF differentiation will lead to the labelling of FHF specific cells with mCherry fluorescence. The late differentiating progenitor population will not undergo excision of the loxp-flanked STOP sequences, and will be marked with GFP fluorescence.