Fig. 4. Localization of collagen cleavage and MMP-13 in MT1-MMP-deficient mice. (A-E) Immunolocalization of collagen cleavage in cortical bone. (F-J) Immunolocalization of MMP-13 antigen in cortical bone. Bone sections from MT1-MMP-deficient mice at 30 days (A,F) and 40 days (B-E,G-J). (A) Collagen cleavage is absent from the pericellular area of osteocytes in a 30-day-old MT1-MMP-deficient mouse but is obvious at the endosteal surface (e). (B) 40-day-old MT1-MMP-deficient mouse displaying a complete absence of osteocyte process staining but with collagen cleavage at the periosteal surface (p). (C) Negative control for collagen cleavage. (D) High-power magnification from a 40-day-old MT1-MMP deficient mouse displaying a complete absence of cell process staining but with staining of the periosteal surface (p). (E) High-power magnification of an additional section from the same animal demonstrating in detail the lack of collagen cleavage in osteocyte processes. (F) 30-day-old MT1-MMP-deficient mouse demonstrating MMP-13 reactivity in osteocytes and periosteal (p) and endosteal surfaces (e). Notice the absence of staining associated with osteocyte processes, as seen in wild-type animals (Fig. 3). (G) 40-day-old MT1-MMP-deficient mouse displaying staining of osteocytes for MMP-13 but no staining of cell processes. e, endosteum; p, periosteum. (H) Negative control for MMP-13 antigen. (I,J) High-power magnification from 40-day-old MT1-MMP-deficient mouse demonstrating the absence of cell-process-associated MMP-13 staining. Only osteocyte cell bodies display reactivity for MMP-13. Bars, 30 µm (A-C,F-H), 10 µm (D,E,I,J).