(A) Quantitative analysis of collagen XII was performed by Western blotting from P4, P10, P30 and P90 Col12a1+/+ and Col12a1−/− mouse FDL tendons. The collagen XII expression was stable during tendon development. (B-E) Collagen XII localization was analyzed by immunofluoresence in P4, P10, P30 and P90 mouse FDLs. Collagen XII reactivity was present throughout the tendon with no change in distribution with age. At P30 and P90 reactivity was less than in the younger tendons, but with same distribution. DAPI, blue for nuclei. Bar = 50 μm.