Hypothesis and Objectives: Based on these findings, we have combined a non invasive in vivo bioluminescence imaging approach with a unique luciferase transgenic murine model to examine the hypothesis that circadian mechanisms regulate transcription driven by the osteocalcin promoter, a bone specific gene. This combined model allows us to monitor the entire skeleton of a single mouse throughout a complete 24hrs cycle.
Materials and Methods: Intact mice of both genders transgenic for the human osteocalcin promoter/luciferase reporter gene were used at ages 1, 3, 5 and 18 months (N=5 for each gender and age). Mice were entrained to a 12hr light: 12 hr dark cycle for a minimum of 2 weeks prior to each study. Bioluminescence was analyzed non-invasively at sequential 6 timepoints throughout a single 24-hour period for each animal. Luminescent signal intensity from multiple fields of osteogenic metabolism (calvaria, tail, teeth, carpals, tarsals) was analyzed quantitatively.
Results: Statistical analyses of luminescent signal intensity from multiple sites of osteogenic activity indicated a periodicity of ~24-hrs in each of the individual skeletal sites tested while the maxillomandibular complex displayed the most robust oscillatory pattern. Neither age nor gender significantly influenced the phase assignment.
Conclusions: These findings might enable better understanding of bone remodeling in the maxillomandibular complex and could have implications for dental treatments in orthodontics and maxillofacial surgery.