Fig. 4.

Invasion dynamics of human breast cancer cells into collagen gel. RFP-tagged MDA-MB-231 cells were seeded on the top surface of the gel. (A1–A4) The cross-section (xy plane) of the invasion front of every 48 h. The red channel is the fluorescent image of the cells, whereas the green channel is the image of the tracing beads. (B1–B4) The side view (xz plane) of the whole gel at the same time of A1–A4. (C1–C2) When the collagen gel was exposed to glucose rich medium on both sides, there was no invasion by the MDA-MB-231 cells. Here, time 0 is defined as the fifth day after seeding the cells. (D1–D2) Under the same condition, in the presence of glucose gradient, no invasion was observed for MCF-7 cells, cancerous nonmetastatic cells. Here, again, time 0 is defined as the fifth day.