Fig. 2.

Single ECs can form lumenal structures through intracellular vacuole formation and fusion as well as MT1-MMP-dependent lumen expansion in 3D collagen matrices. Real-time video analysis of EC lumen and tube formation was performed examining a single EC (a) versus multiple ECs (b) in 3D collagen matrices over a 24-hour period. Intracellular vacuoles are dynamically formed and through fusion events rapidly create apical membranes necessary for the accelerated events which underlie the EC lumen formation process. Arrowheads indicate intracellular vacuoles, arrows indicate the border of lumen structures, and the open arrow indicates an extended process to facilitate multicellular tube assembly. Scale bars = 25 μm (a) and 50 μm (b).