Required for developmental angiogenesis, but not for vasculogenesis. At 24 hpf, expression almost entirely restricted to the endothelial cells of the developing vasculature, with high levels in the major head and trunk vessels and also in the intersomitic vessels. Morpholino knockdown of the protein causes profound defects in angiogenesis. Although sprouting of the intersomitic vessels occurs, the endothelial cells fail to extend fully across the intersomic region and there is no apparent formation of the dorsal longitudinal anastomosing vessel. No other obvious defect is observed in the developing morphant. Belongs to the formin homology family.