Figure 1.

Mechanical plasticity leads to the persistence of collagen densification and alignment within the tracts induced by cell forces after abolishing cell contractility. (a–d) Collagen densification remained in the tracts formed between adjacent contractile mammary acini after we eliminated cellular forces. (e–h) Fiber alignment persisted in the fibrous tracts formed between adjacent contractile spheroids of fibroblasts. (a) Collagen concentration is given in a system of four interacting acini 4 h after they were seeded, (b) at the onset of inhibiting contractility (10 h after seeding), and (c) 24 h after inhibiting contractility. (d) Estimated collagen concentration in (circles) regions 1, (triangles) 2, (diamonds) 3, and (crosses, background) 4 (marked in (b)) plotted against time after seeding. The acini experiments were repeated four times using distinct collagen gels, and plasticity was observed in all samples. (e) The intensity of collagen fiber alignment was calculated using the intensity of SHG (in blue) between pairs of fibroblast spheroids and cellular autofluorescence (in green) after incubation for 12 h atop a collagen type I gel. The tracts of aligned fibers persisted 24 h after (f) inhibiting cellular contractility using blebbistatin and (g) dissociating the spheroids from the matrix using trypsin. The small white spot in (f) and the blue streak in (g) near the bottom spheroid are imaging artifacts. (h) The SHG intensity of fiber alignment is given, along the region enclosed by the dashed lines versus distance from the axis connecting the midpoints of two cell clusters; SDs are used to plot the pale curves (averaging was performed over 8–12 samples). The fibroblast SHG experiments were repeated using three distinct collagen gels, and plasticity was observed in all samples. To see this figure in color, go online.