CBX7 deficiency plays a positive role in dentin and alveolar bone development

To clarify the role of CBX7 deficiency in dentin and alveolar bone development, the dental and mandibular phenotypes of homozygous CBX7-knockout (CBX7(-/-)) mice were compared with their wild-type (WT) counterparts at 3 weeks age. In contrast to WT littermates, dental volume and dentin sialoprotein-positive area were significantly increased, whereas the area ratio of predentin to dentin was decreased markedly in CBX7(-/-) mice. Mineral density, cortical thickness, alveolar bone volume, type I collagen and osterix-immunopositive area, osteoblast number and activity, protein expression and mRNA level of Runt-related transcription factor 2 (Runx2), alkaline phosphatase, osteocalcin, osteopontin and bone morphogenetic protein 2 (BMP2) were all remarkably increased, while osteoclast number and activity, and mRNA expression ratio of NF-κB ligand (RANKL) to osteoprotegerin (opg) were all decreased significantly in the alveolar bone of CBX7(-/-) mice compared with their WT counterparts. Moreover, proliferating cell nuclear antigen (PCNA)-positive cells were found more in Hertwig' s epithelial root sheath of CBX7(-/-) mice, and their protein level of cyclin E1, cyclin-dependent kinase 2 (CDK2) were correspondingly increased in contrast to WT mice. Taken together, these results of this study suggest that CBX7 deficiency plays a positive role in dentin and alveolar bone formation.