Pvr and Pvf2 Are Essential for Valve Cell Differentiation in the Larval <i>Drosophila</i> Heart

The directionality of blood flow is regulated by heart valves, among other things. While the heart valves in vertebrates are multicellular and complex, the valve in the Drosophila heart consists of exactly two highly specialized cells. They arise during early larval development from two cardiomyocytes, those that form the boundary between the aorta and the posterior ventricle. Here, we show that the conserved PDGF signaling pathway is involved in the determination of heart valve cells. RNAi-mediated knockdown of the Pvr receptor and one of its ligands, Pvf2, leads to an inhibition of valve cell differentiation. In contrast, the simultaneous expression of the Pvr and Pvf2 in the entire heart tube leads to the formation of additional heart valve cells in ectopic positions. A single expression of the receptor or the ligand does not lead to heart valve formation.