Vegfd can compensate for loss of Vegfc in zebrafish facial lymphatic sprouting.

Lymphangiogenesis is a dynamic process that involves the sprouting of lymphatic endothelial cells (LECs) from veins to form lymphatic vessels. Vegfr3 signalling, through its ligand Vegfc and the extracellular protein Ccbe1, is essential for the sprouting of LECs to form the trunk lymphatic network. In this study we determined whether Vegfr3, Vegfc and Ccbe1 are also required for development of the facial and intestinal lymphatic networks in the zebrafish embryo. Whereas Vegfr3 and Ccbe1 are required for the development of all lymphatic vessels, Vegfc is dispensable for facial lymphatic sprouting but not for the complete development of the facial lymphatic network. We show that zebrafish vegfd is expressed in the head, genetically interacts with ccbe1 and can rescue the lymphatic defects observed following the loss of vegfc. Finally, whereas knockdown of vegfd has no phenotype, double knockdown of both vegfc and vegfd is required to prevent facial lymphatic sprouting, suggesting that Vegfc is not essential for all lymphatic sprouting and that Vegfd can compensate for loss of Vegfc during lymphatic development in the zebrafish head.