Fig. 1.

Invasion assay. (A) Schematic of the cancer cell invasion assay. (B–D) SEM images of MDA-MB-231 breast cancer cells show that the cells adhered on (C) or invaded in 3D collagen matrices (D). (E–G) TEM images show that invasive MDA-MB-231 cells formed filopodia inside 3D collagen matrices. (E) Overview image. (F,G) Magnifications of boxed areas in E. (H,I) Cancer cells that invaded into 3D collagen matrices show a dense cytoskeletal network. (I) Magnification of boxed area in H. Arrows point to the dense cytoskeletal network inside an invasive MDA-MB-231 cell.