chemical staining for alkaline phosphatase (ALP; brown stain) activity was used as a biomarker for osteoblasts and tartrate-resistant ALP (tartrate-resistant acid phosphatase [TRAP]; red stain) activity as a marker for osteoclasts. Little difference was seen between Sam68+/+ (Figure 5A and 5B) and Sam68−/− (Figure 5C and 5D) mice at 4 months of age. ALP- and TRAP-positive cells were reduced in the 12-month-old Sam68+/+ mice (Figure 5E and 5F) and remained unchanged in 12-month-old Sam68−/− mice (Figure 5G and 5H). The reduction in both osteoblast and osteoclast activity in the 12-month-old Sam68+/+ mice argued against bone being lost primarily due to a relative increase in osteoclast over osteoblast activity, as seen in high turnover disease [49].
Figure 5  Histologic Analysis of Undecalcified Bone from Sam68+/+ and Sam68−/− Mice
Sections of tibia fixed in 4% paraformaldehyde and embedded in plastic were stained for ALP (A–C, E–G) activity to identify osteoblasts or for TRAP (B–D, F–H) activity to identify osteoclasts. Staining patterns were similar