Figure 3: Co-localization of AP activity with areas of active and inactive bone matrix formation. Images are taken from cortical bone of a Col3.6GFPcyan reporter mouse. (A) Bone mineral with a calcein green mineralization line on the endocortical surface. (B) Same section now with the Col3.6blue signal derived from the active osteoblasts expressing the reporter. (C) Same section stained for ELF-97 and imaged in the fluorescent channel specific for its fluorescent spectrum. (D) Co-localization of all the fluorescent signals showing that the AP activity of the ELF-97 overlies the osteoblastic cells on the endosteal surface, while the weaker ELF-97 signal on the periosteal side does not have a calcein or Col3.6 reporter signal.