Angioblasts are TAL1⁺/Flk1⁺cells.

Double immunolabeling demonstrates that endothelial cells of forming vessels (panels A and B, arrowheads) and isolated mesodermal cells (panels C and D) coexpress TAL1 and Flk1. Note the distinctive immunostaining pattern of each protein. Magnification bar: panels A and B = 20 μm, panels C and D = 10 μm.