Spheroid migration on collagen I monolayers and invasion in 3D collagen gels.

<p>(A) A549 migration out from the heterospheroids. Six-day-old heterospheroids were seeded on collagen type I-coated coverslips and cultured under conditions as described in Materials and Methods. Migration of the cells from the spheroids was examined under an inverted phase contrast microscope 4 and 24 hours after the spheroids were seeded. Size bars = 100 µm. (B) Fluorescence immunostaining of the spheroids on coverslips after 24 h and migration distance of A549 from the heterospheroids. Spheroids were double stained with antibodies towards human keratin 7 (stained A549 cells, red) and mouse β1 integrin (stained MEFs, green). Six of each type of spheroids were stained. The maximum migration distance (d) of A549 cells were measured on the photographs as indicated in the figure and calculated according to size bar. Size bars = 100 µm. **** p<0.0001. (C) Spheroid invasion in 3D collagen I gel. Six to eight 6-day-old spheroids were embedded in 3D collagen gels (1 mg/ml collagen type I) and invasion of cells was observed and photographed under an inverted phase contrast microscope after 24 h and 48 h. Two representative images are shown. Size bars = 100 µm.