Figure 2. EC tip and stalk cells participate in EC lumen and tube formation and both cell types can generate intracellular vacuoles during this angiogenic sprouting process in 3D collagen matrices.
ECs were seeded as confluent monolayers on top of collagen type I matrices containing sphingosine-1-phosphate to induce EC invasive responses. Imaging of the invasive front reveals both tip (black arrows) and stalk (white arrows) cells in these cultures. (A) Both tip and stalk ECs are able to vacuolate (white arrowheads). Intracellular vacuoles are observed particularly in the rear of tip cells and as other cells accumulate behind the tip cell, these cells can also vacuolate and lumenize (schematic illustration). (B) As morphogenesis progresses, vacuole-vacuole fusion and MT1-MMP-dependent lumen expansion events occur concurrently to create lumen spaces (black arrowheads). White arrowhead- intracellular vacuoles, black arrow- EC tip cell. Bars equal 50 µm.