Progressive increase in bone mass and development of odontomas in aging osteopetrotic c-src-deficient mice

The critical role of c-src in osteoclast-mediated bone resorption has been emphasized by gene deletion experiments in mice. However, the long-term effects of the lack of c-src and impaired osteoclast function on the skeleton remain unknown. To further study the physiological role of c-src and to circumvent the early death of src(-/-) mice, due to starvation in the absence of erupted teeth, we maintained mice on a liquid diet. At the age of 2 months the src(-/-) mice presented signs of airway obstruction and all mice died progressively between 2.5 and 6 months of age. Radiography demonstrated severe osteopetrosis of the whole skeleton. Histomorphometrical analysis of the src(-/-) mice confirmed a significant increase in bone mass with age, resulting in complete loss of bone marrow spaces in some bones and explaining the consistent hepatosplenomegaly, due to extraskeletal hematopoesis. Histopathological examination of the skull revealed the presence of odontomas in the region of the unerupted incisors, with a penetrance of 100% in the aging src(-/-) mice. Although odontomas are benign lesions, their progressive growth leads to the obliteration of the nasal airways, progressive suffocation, and death in src(-/-) mice. These results suggest that: (i) in the absence of bone resorption, bone formation continues and leads to progressive accentuation of the osteopetrotic phenotype in src(-/-) mice; (ii) osteoclastic function is required for regular eruption of the incisors and deficient bone resorption is associated with the development of odontomas; and (iii) src(-/-) mice die by suffocation due to airway obliteration as a result of progressive odontoma growth.