MMP13 knockout decreases Collagen I ordering at E0771 mammary tumor boundaries. WT and MMP13 KO mice were implanted with E0771 mammary tumors as described. Following excision and sectioning of the primary tumor, tumor boundary regions were assessed for Collagen I spatial organization by qualitative (this figure) and quantitative (next figure) analysis of anti-Collagen I immunofluorescence signal. Images of Collagen I signal were taken as described in Figure 2. Note that WT mice (Panel A) exhibited a much more organized and ordered Collagen I structure, characterized in particular by longer and thicker Collagen I fibers oriented more parallel to the tumor boundary, compared to MMP13 KO mice (Panel B) which demonstrated a more diffuse Collagen I pattern with fewer pronounced, rod-like Collagen I fibers.