Dental and Cranial Pathologies in Mice Lacking the Cl^-/H⁺-Exchanger ClC-7

ClC-7 is a 2Cl^-/1H⁺-exchanger expressed at late endosomes and lysosomes, as well as the ruffled border of osteoclasts. ClC-7 deficiencies in mice and humans lead to impaired osteoclast function and therefore osteopetrosis. Failure of tooth eruption is also apparent in ClC-7 mutant animals, and this has been attributed to the osteoclast dysfunction and the subsequent defect in alveolar bone resorptive activity surrounding tooth roots. Ameloblasts also express ClC-7, and this study aims to determine the significance of ClC-7 in enamel formation by examining the dentitions of ClC-7 mutant mice. Micro-CT analysis revealed that the molar teeth of 3-week old ClC-7 mutant mice had no roots, and the incisors were smaller than their age-matched controls. Despite these notable developmental differences, the enamel and dentin densities of the mutant mice were comparable to those of the wild-type littermates. Scanning electron microscopy showed normal enamel crystallite and prismatic organization in the ClC-7 mutant mice, although the enamel was thinner (hypoplastic) than in controls. These results suggested that ClC-7 was not critical to enamel and dentin formation, and the observed tooth defects may be related more to a resulting alveolar bone phenotype. Micro-CT analysis also revealed abnormal features in the calvarial bones of the mutant mice. The cranial sutures in ClC-7 mutant mice remained open compared to the closed sutures seen in the control mice at 3 weeks. These data demonstrate that ClC-7 deficiency impacts the development of the dentition and calvaria, but does not significantly disrupt amelogenesis.